A Study of ock Stresses and 

Engineering Geol gy in Quarri s 

of the Barre Granite of Vermo· 

A Study of Rock Stresses and 

Engineering Geology in Quarries 

of the Barre Granite of Vermont 

By Thomas C. Nichols, Jr. 

U.S. GEOLOGICAL SURVEY BULLETIN 1593 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas l. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1986 

For sale by the Branch of Distribution 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging in Publication Data 

Nichols, Jr., Thomas C. 

A study of rock stresses and engineering geology in quarries of the Barre granite of Vermont. 

(U.S. Geological Survey bulletin ; 1593) 

Bibliography: p. 

Supt. of Docs. No.: I 19.3:1593 

l. Rock mechanics-Vermont-Barre Region. 2. Engineering geology-Vermont-Barre Region. 3. Granite 

industry and trade-Vermont-Barre Region. 

I. Title. II. Series. 

QE75.B9 no. 1593 557.3 s 85--600205 

[TA706.5] [624.1'51'097434] 
CONTENTS 

Abstract 1 

Introduction 1 

Acknowledgments 1 

In situ stress investigations, Barre, Vermont 1 

Objectives and methods 1 

Geologic setting 2 

Geology of the Barre Granite 3 

Origin and age 3 

Structure 3 

Modal composition and petrofabrics 6 

Site selection 8 

Deformation, stress, and temperature measurements 8 

Type of measurement and locations 9 

Results of temperature measurements 10 

Prequarrying stresses 12 

Overcore measurements 13 

Measured prequarry stresses compared to predicted gravity stresses 17 

Stress changes and surface deformations caused by quarrying 17 

Time-dependent deformation of cores 19 

Elastic modulus determinations 21 

Discussion of results 23 

Measurements indicative of inelastic-rock response stress 24 

Local distribution of determined vertical and horizontal stress 24 

Influence of geologic features on determined stress distribution 25 

Fractures and faults 26 

Evidence for influence of geologic history 26 

Fabric 27 

Mechanical behavior characteristics-results of quarrying 28 

Relief characteristics 28 

Modulus 28 

Significance of Barre data to quarrying and engineering practice 29 

Conclusions 30 

References 30 

FIGURES 

I. Map showing location of report area adjacent to Barre, Vt. 2 

2. Photographs of working area in Wetmore and Morse quarry, Barre, Vt. 2 

3. Map showing area of outcropping Barre Granite southeast of Barre, Vt. 3 

4. Topographic map of the upper and lower quarry areas showing shear zones 

along granite-metamorphic boundary 4 

5. Equal-area diagrams of poles to natural fractures mapped in the lower and 

upper quarry areas at Barre, Vt. 5 

6-10. Photographs showing: 

6. Tendency of sheeting fractures developed in upper quarry area to terminate at boundaries of older fractures 6 

7. Very extensive but widely spaced northwest-trending fractures found 

in the upper quarry area 7 

8. Well-developed northeast-trending shear zones found in the interior portion of the pluton, lower quarry area 7 

Contents Ill 
9. Well-developed northeast-trending fracture and shear zones terminate 

abruptly at massive unfractured granite of upper quarry area 8 

10. Open and healed microcracks in quartz crystals, Barre Granite 9 

11. Perspective view of lOX 10X5.7-m block of Barre Granite and adjacent 

quarry area, Wetmore and Morse quarry, showing locations of boreholes and 

sheeting fractures 10 

12. Isometric view of lOX 10X5.7-m block of Barre Granite showing borehole, 

overcore, and hydro fracture locations and section views of the same block 

showing locations of prequarry and postquarry measurements 11 

13. Schematic diagram showing locations of displacement deformation nets 1, 

2, 2E, 3, and 4, Wetmore and Morse quarry 12 

14. Graph showing measured temperature versus time in lOX 10X5.7-m block 

and adjacent rock 13 

15. Plot of secondary maximum principal stress magnitudes measured on the 

block versus maximum distance of stress measurement location from known 

fractures 15 

16. Equal-area diagrams showing orientations of principal stresses determined 

within lOX 10X5.7-m block of Barre Granite 16 

17. Gravity stresses determined by a plane-strain finite-element calculation in the 

vertical plane AB 18 

18. Graphs showing displacements versus time for nets 1, 2, 2E, and 3 after 

the lOX 10X5.7-m block of Barre Granite was quarried 19 

19. Photograph showing disking of 5. 7 -em-diameter cores retrieved from hole 

5 drilled after the 10 x 10 X 5. 7 -m block was quarried 21 

20-24. Graphs showing: 

20. Extensional strains measured through time on exterior of overcore annuli after extraction from borehole 21 

21 . Strains occurring through time on a 5-cm core after extraction from 

drill hole Ia in lOX 10X5.7-m block 22 

22. Variation of static Young's modulus in the horizontal plane, unquarried 

block of Barre Granite 23 

23. Variation of static Young's modulus in vertical planes striking N. 50° 

W. and N. 40° E., unquarried block of Barre Granite 24 

24. Variation of static Young's modulus in the horizontal plane, large quarried Barre Granite block 25 

25. Vertical section through hole 2H showing locations of overcores and a natural 

fracture 26 

26. Photographs showing fractures at edges of partially freed granite blocks (A), 

and in bottom of quarry (B), Barre, Vt. 29 

TABLES 

1. Determinations of stresses made on Barre Granite adjacent to and within the 

lOX 10X5.7-m block prior to and after quarrying, Wetmore and Morse quarry 14 

2. Measured and gravity stresses in the x, y, and z directions in Barre Granite 17 

3. Internal radial borehole displacements for typical overcore samples through 

specified time intervals, Barre Granite 21 

4. Young's moduli determined on cores of Barre Granite by sonic-pulse methods 26 

IV Contents 
A Study of Rock Stresses and Engineering Geology 

in Quarries of the Barre Granite of Vermont 

By Thomas C. Nichols, Jr. 

Abstract 

In situ stress studies in granite quarries of the Rock 

of Ages Corporation near Barre, Vermont, have revealed 

that: 

1. Apparent local in situ stress distribution is strongly 

affected by geologic structure and rock outcrop 

geometry. 

2. Geologic history and paleostress fields may in part 

be responsible for the determined local stress distributions and rock anisotropies. 

3. Measured stress changes caused by rock quarrying 

are nearly equivalent to the stresses measured 

prior to quarrying; that is, quarrying relieves virtually all stress. 

4. Extensional failures, detrimental to efficient rock extraction, that occurred as a result of quarrying and 

coring are difficult to explain by commonly used 

failure criteria. 

5. Rebound deformations observed in the quarries that 

are detrimental to the quarrying occur as both 

rapid and time-dependent deformations. Nearly instantaneous deformations measured on surface 

grids are in good agreement with the measured 

stress relief caused by quarrying. Additional shortterm, time-dependent deformations were nearly 

the same as the initial deformations. However, 

there is reason to doubt that the initial rapid deformations used for the interpretation of stresses 

are elastic. If they are a result of inelastic microfracture opening, the stress interpretations may be 

in considerable doubt. 

For engineering purposes, these studies 

demonstrate that the levels and distribution of 

local in situ stress and the rock response resulting 

from engineering excavation may be difficult to 

adequately assess without making sufficient and 

meaningful in situ geotechnical measurements. 

INTRODUCTION 

The experiment described herein was an attempt to 

evaluate the state of stress and mechanical rock behavior 

caused by excavation at shallow depths in an outcropping 

crystalline quarry rock, the Barre Granite of Vermont. In 

addition, it was hoped that the information obtained would 

aid the quarry operation in developing more efficient quarrying procedures in locations where unloading failures 

damage good quarry rock. The distribution of elastic properties, stress magnitudes, and orientations was compared 

to geologic structures, quarry procedures, outcrop 

geometry, and quarry history in an effort to determine 

their relationship. Finally, an attempt was made to 

evaluate the relief behavior of the granite by observing 

deformations and associated stress changes caused by 

quarrying a large block in the area of the investigation. 

Acknowledgments 

I wish to thank John F. Abel, Jr., of the Colorado 

School of Mines for his timely and helpful discussion concerning the technical aspects covered in this report. In 

addition, I wish to thank the Rock of Ages Corp. of Vermont for their generous cooperation and for letting us use 

their facilities for conducting the field experiments. 

IN SITU STRESS INVESTIGATIONS, BARRE, 

VERMONT 

Objectives and Methods 

At Barre, Vt. (fig. 1), the U.S. Geological Survey 

(USGS) conducted a field experiment in the Barre Granite, a pluton of Devonian age, to determine the nature 

and variation of the stress and strain fields within a large 

(lOX 10X5.7-m) granite block prior to and as a result of 

quarrying (Nichols and others, 1977). The objectives were 

to ( 1) locally determine and map geologic and other physical features that may influence the local stress field, (2) 

determine the prequarrying and postquarrying stress fields, 

and (3) on cored samples, conduct laboratory physicalproperties tests necessary to interpret field tests. 

Conventional deformation measurements, undercoring, overcoring, and hydrofracturing techniques were used 

In Situ Stress Investigations, Barre, Vermont 1 
QUEBEC 

CANADA ----------

UNITED STATES 

• Montpelier 

~[ Barre 

VERMONT 

• Rutland 

White River 

Junction 

NEW HAMPSHIRE 

.concord 

Brattleboro 

25 50 KILOMETERS 

I 

I 

\ 

I 

1 MAINE 

\ 

I 

I 

\ 

\ 

l 

' ' 

Figure 1. Location of report area (shaded) adjacent to 

Barre, Vt. 

to investigate the stress and strain response of the block 

and the surrounding rock that occurred as a result of quarrying operations. The block investigated was in the Wetmore and Morse quarry, owned by the Rock of Ages 

Corp., and exposed at a depth of 67 m below the original 

ground surface (fig. 2). The investigations included mapping the block and surrounding rock to record the geologic 

and geometric features. Locally, these were mainly sheet 

joints, other natural and quarry-associated fracture systems, fabric anisotropies herein called the "rift, grain or 

lift, and hardway planes," and the configuration of the 

quarry. The "rift" is the plane of easiest rock splitting, 

the "grain or lift" is the second easiest plane of splitting, 

and the "hardway" is the most difficult plane of splitting. 

According to the quarry operator, in the vicinity of our 

measurements, the rift is nearly vertical and strikes N. 

40° E., the lift is horizontal, and the hard way is vertical, 

striking N. 50° W. 

Geologic Setting 

The geology of the area and detailed investigations 

of the Vermont granites have been described by various 

workers. Dale (1909) published a comprehensive report 

on the structural and physical aspects of commercial granites in New England, which included the Barre Granite. 

2 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

Figure 2. Working area in Wetmore and Morse quarry, 

Barre, Vt.· A, View to the north. Large arrow designates 

10x10xs)-m Barre Granite block prior to quarrying. 

Sheet fractures dip southeast (small arrows). 8, Closeup 

of block showing sheet (large arrows) and other fractures 

(small arrows). 
Balk ( 1937) made a detailed study of structural relations 

in the Barre Granite and other granitic plutons. White and 

Jahns ( 1950) published a description of structural relations 

in central Vermont. Stratigraphic studies have been made 

in the area by Currier and Jahns (1941 ), Doll (1943), 

and Cady (1960). Petrographic studies of the Barre Granite have been conducted by Finlay ( 1902) and Chayes 

(1952). A report by Murthy (1957), in which he mapped 

and described the bedrock geology of the East Barre, Vt., 

quadrangle, is used as the geologic basis for this report. 

The term Barre Granite as used here refers to a 

granite body that crops out in a bifurcated, somewhat elliptical shape (fig. 3) about 2 km southeast of Barre , Vt. 

The outcropping body is about 7. 1 km long, and 3. 0 km 

wide, with the long axis trending about N. 28° E. Most 

of the Barre Granite is bounded by the Silurian Westmore 

Formation (Doll, 1951); a small portion of the northeast 

boundary is in contact with the younger Waits River Formation, also of Silurian age. 

44 

1 0' 

EXPLANATION 

iOOf Town 

~Road 

Barre Granite 

1 KILOMETER 

Figure 3. Area of outcropping Barre Granite southeast 

of Barre, Vt. 

The Westmore Formation consists primarily of various interbedded micaceous and quartzose schists with individual beds from 8 to 30 em thick. The total thickness 

of the formation varies from 0.9 to 1.2 km. The mica 

schists in the westernmost outcrops become progressively 

more quartzose to the east. Local porphyroblasts of garnet 

and biotite occur in the mica schists, and garnet porphyroblasts are quite common in the micaceous beds interbedded with more quartzose lithologies. 

The Waits River Formation consists primarily of 

calcareous rocks with interbedded mica schists and is estimated to have a thickness of about 1.5-2.0 km. 

Geology of the Barre Granite 

Origin and Age 

The Barre Granite is thought to be an intrusive body 

concordant ona regional scale but discordant at local contacts. The mode of emplacement probably consisted of 

both passive intrusion along zones of structural weakness 

and forcible intrusion accompanied by the stoping process. 

The intrusion of Barre-type granite plutons is thought to 

have occurred 377-383X 106 years ago (Naylor, 1971), 

postdating the regional metamorphism of the Devonian 

Acadian orogeny. Zartman and others ( 1970) suggest that 

the plutons may have cooled slowly as a result of continued burial by upper Paleozoic sediments. This may explain the younger K-Ar ages of 340--349X 106 years determined for granites obtained in the Rock of Ages quarry 

near Barre and the Adamant quarry to the northwest (Faul 

and others, 1963). High-grade thermal metamorphism 

(Murthy, 1957) was superposed on the previously 

metamorphosed Westmore and Waits River Formations at 

the contact with the Barre Granite, indicating that these 

rocks must have been altered at temperatures of at least 

400°-500°C and probably were under moderately deep to 

shallow overburden. The depth of burial was estimated 

to be about 10 km (Nichols, 1980). 

Structure 

Dale ( 1923) described in detail the major fracture 

sets that exist in the active quarries on the Barre Granite 

pluton. He noted that in 26 quarries the most frequent 

joints strike N. 30°-40° E. and N. 75°-90° E., th,e next 

rpost frequent strike N. 60°-70° E., N. 30°-40° W., and 

N. 10°-25° W. Dale also noted that the rift plane was 

reported to be vertical but varied in strike from N. 30° 

E. to N. 75° E., and that the grain plane was horizontal 

in most areas. Murthy ( 1957) observed that the most conspicuous joint set trends approximately N. 20° E. and dips 

between 45° and 80° to the southwest. He asserts that 

In Situ Stress Investigations, Barre, Vermont 3 
Base from U.S. Geological Survey 

East Barre 15' quadrangle, 1944-57, 

original scale 1 :62,500 1 KILOMETERS 

Figure 4. Topographic map of the upper and lower quarry areas showing shear zones along 

granite-metamorphic boundary. Dashed Jines define approximate location of lower (LQ) and 

upper (UQ) quarry areas in the granite. Hachures outline the Upper Smith and Weston 

(5) and the Wetmore and Morse (W) quarries. 

4 Rock Stresses and Engineering Geology, Barre Granite, Vermont 
these fractures are parallel to the rift direction and trend 

of the flow lines. 

Fractures were mapped by the author in both active 

and abandoned quarries to determine if fractures described 

by Dale may vary areally in any systematic way. The 

fracture pattern and density in the south and east sections 

of the pluton differ significantly from those in the westcentral section. The south and east sections of the pluton 

are topographically lower than the west-central section by 

at least 30 m; hence, quarries in the high areas are referred to as the upper quarries (UQ, fig. 4) and those 

in the low areas as the lower quarries (LQ, fig. 4). Figure 

5 shows comparative orientations of fracture systems in 

these two areas. 

The west-central part of the pluton, in which the 

Upper Smith and Weston and the Wetmore and Morse 

quarries (fig. 4) are located, has two strong sets of fractures that appear to be almost nonexistent to the south 

and east in the lower quarries. These are the near-surface, 

well-developed, low-angle sheeting fractures (cluster a, 

fig. 5A, and fig. 6) and the very extensive northwesttrending nearly vertical fractures (cluster b, fig . 5A). 

Nearly closed sheeting fractures with spacings commonly 

<0.3 mare thought to be nontectonic in origin and probably occur as a result of vertical stress relief caused by 

denudation. The northwest-trending fractures, probably of 

tectonic origin, are usually single fractures <0.5 em thick 

and are widely spaced, but may extend laterally hundreds 

of meters (fig. 7). These fractures have vertical slickensides superposed on hydrothermal alteration products, in 

some locations mostly illite. Although the displacement 

on the fractures is very small, the sense of movement 

as evidenced by feather fractures is that of high-angle reverse faulting. Toward the surface of the pluton, the vertical fractures tend to bifurcate and curve into a horizontal 

direction. The deepest sheeting fractures tend to interfinger and intersect the bifurcated fractures and in many 

places have a similar dip; thus, the two sets can easily 

be confused. 

The lower quarries (fig. 4) contain a pervasive set 

of well-developed, steeply dipping, northeast-trending 

fractures (fig. 5B). These are strongly developed fractures 

that are subparallel to the long axis of the pluton and 

the regional trend of the surrounding country rocks. They 

grade into broad, well-developed shear zones (figs. 8, 9), 

found along the granite-metamorphic contacts interior to 

both of the pluton's southern segments (fig. 4), and terminate abruptly as they extend northward into the upper 

quarries (figs. 4, 9). The northeast-trending fracture set 

tends to extend into and through the upper quarry area 

only immediately adjacent to the contact with the 

metamorphic rocks, and here the set is not nearly as well 

developed as in the lower quarries. These fractures also 

are intruded by basic and felsic dikes and are filled with 

hydrothermal alteration products. Murthy (I 957) conA. Upper,quarry 

(125 mapped 

fractures} 

0 

B. Lower quarry 

(11 0 mapped 

fractures) 

N 

a 

N 

0 

Figure 5. Equal-area diagrams (lower hemisphere) of 

poles to natural fractures mapped in the lower and 

upper quarry areas at Barre, Vt. Contours are at 2, 4, 

8, 12, and 16 percent per 1 percent area. Orientation 

of major fracture sets shown by a-f: a is concentration 

of sheeting fractures; b, northwest fractures; c, d, e, and 

f are strongly developed northeast-trending conjugate 

fracture sets. 

eluded that the dikes are primary features and therefore 

the fractures must have originated during or shortly after 

the forceful emplacement of the pluton. Continued uplift 

after the pluton solidified caused intense fracturing along 

and adjacent to the southern interior contact zones. The 

In Situ Stress Investigations, Barre, Vermont 5 
Figure 6. Tendency of sheeting fractures developed in upper quarry area to terminate at boundaries of older fractures. Widely spaced horizontal parallel lines toward bottom of photograph are boundaries of old quarry lift planes. 

View is to the west. 

northeast-trending fracture sets c and d (fig. 5B) with 

high-angle northwest, southeast dips imply a conjugate 

set, whose major principal stresses, a 1 and a 3 , at the 

time of fracturing were respectively vertical and to the 

southeast-northwest. Two more fracture sets, e and f (fig. 

5B), striking respectively east-northeast and north-northeast with steep northwesterly dips, imply a possible second conjugate set of fractures. At the time of fracture, 

the major principal stresses, a 1 and a 3 , were nearly horizontal, bearing to the northeast and southeast, respectively, and a2 was nearly vertical. In either case the minimum principal stress (a3) was nearly horizontal, had a 

bearing southeast-northwest and may have coincided with 

regional tectonic relaxation subsequent to the Acadian 

orogeny. 

6 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

Modal Composition and Petrofabrics 

The composition of the Barre Granite has been 

statistically determined by Chayes ( 1952) to be very uniform, at least in five of the presently active quarries. 

Murthy (1957) checked Chayes' results, and found no significant differences. The results indicated that the granite 

contains about 26 percent quartz, 35 percent plagioclase, 

19 percent potassium feldspar, 18 percent mica (both biotite and muscovite), and less than 2 percent accessory 

minerals. 

Petrofabric analyses have been performed by Willard and McWilliams (1969), Thill and others (1973), and 

Engelder and others ( 1977). These investigators report 

strong preferred orientations of open and healed micro-
Figure 7. Very extensive but widely spaced northwesttrending fractures (arrows) found in the upper quarry 

area. View is to the northwest. 

fractures nearly parallel to the rift plane. Thill's data show 

a second strong set of microfractures, parallel to the grain 

plane. These planes are respectively oriented vertical, 

striking to the northeast, and horizontal. The first two 

reports infer that a great number of the microfractures 

occur in the quartz grains. In addition, the Thill investigation reveals that there is little preferred orientation of the 

quartz, plagioclase, and mica grains but that there is a 

suggestion of orientation of twins within microcline grains 

in the rift plane. My petrographic examination of samples 

taken from the Wetmore and Morse quarry shows a similar strong orientation of two sets of microfractures (fig. 

1 0), both open and healed, subparallel to the rift (N. 40° 

E., vertical) and lift planes (horizontal). The healed 

microfractures are seen here as bubble planes, according 

to an interpretation by Simmons and Richter (1976). This 

is supported by Shelton and Orville (1980), who formed 

synthetic fluid inclusions in fractured natural quartz by 

annealling samples at 600°C and 2 Kbar pressure in the 

presence of water. Most of the micro fractures are within 

the quartz grains and end abruptly at the quartz boundaries 

(fig. I 0). In addition, strong undulatory extinction and 

subgrain development are associated with deformation of 

quartz grains, and according to Tullis and Yund (1977) 

these effects can occur at strain rates of I 0-6 sec- 1 within 

confining stress fields greater than 150 MPa at temperatures above 300°C. 1. Tullis (written commun., 1979) also 

has examined some Barre Granite thin sections and states, 

"Judging from my experience with experimentally and 

naturally deformed quartzites, I would estimate that the 

microstructures shown by the quartz grains in this granite 

were produced at a temperature of close to 300°C (for 

a standard, slow natural strain rate of about 1 o- 14/s)." 

The petrographic evidence thus supports the idea 

that since the solidification of the magma, the granite has 

been subjected to temperatures greater than 300°C and 

burial depths greater than 7 km. The annealed microfractures also indicate strong dislocation activity occurring 

after an initial brittle deformation period. This suggests 

a reheating of the rock mass to over 300°C and the possibility of a superposed thermal event as mentioned by 

Zartman and others (1970) and Naylor (1971). 

Figure 8. Well-developed northeast-trending shear 

zones found adjacent to granitic-metamorphic boundaries in the interior portion of the pluton, lower quarry 

area. 

In Situ Stress Investigations, Barre, Vermont 7 
Figure 9. Well-developed northeast-trending fracture and shear zones seen in lower half of picture (arrows) 

terminate abruptly at massive unfractured granite of upper quarry area. 

Site Selection 

The site for our experiment in the Wetmore and 

Morse Quarry near Barre was selected on the basis of 

the following criteria: 

I . The rock type present at the quarry. The Barre 

Granite is a very uniform hard rock with n~ obvious structural anisotropies other than fractures and microcrack fabric which have been extensively studied and documented. 

On the rock chosen for quarrying, two very fine sheeting 

fractures were discemable and easily mapped. 

2. The geometry of the quarry and the 

lOX 10X5.7-m block to be quarried, although not ideal, 

that was amenable to an elastic numerical analyses. 

3. Previous observations of quarry deformations 

and failures that indicated deformations in response to 

quarrying of the chosen block would be easily measurable. 

4. The many laboratory studies of the physical and 

mechanical properties of the Barre Granite that have been 

conducted. 

8 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

5. The operator's plan for quarrying that allowed 

sufficient time and operating room to adequately investigate the prequarry and postquarry conditions of the 

lOX 10X5.7-m block. 

Deformation, Stress, and Temperature 

Measurements 

Prequarrying measurements of the stress and strain 

fields in the lOX 10X5.7-m granite block and surrounding 

rocks were made for a period of 15 months prior to quarrying of the block. The block was quarried by bumcutting side channels with oxygen-kerosene torches and 

then splitting on the bottom horizontal plane with dynamite charges. After the block was quarried, it was left 

in place and postquarry measurements were made to determine the response of the block and adjacent rocks to removal. 

Various deformation and temperature measurements 

were made on external surfaces and within the block and 
2 mm 

Figure 10. Examples of open and healed microcracks in 

quartz crystals, Barre Granite. Healed microcracks are 

seen as bubble planes. A, Plane of view is horizontal 

and direction (arrow) is N. 40° E. 8, Plane of view is vertical and direction (arrow) is N. 50° W. 

adjacent rocks during the field investigations, and on 

cores removed from the block before and after quarrying. 

Type of Measurement and Locations 

Rock-temperature measurements were monitored 

periodically with resistance type thermometers, in vertical 

holes drilled in the granite block and auxiliary holes just 

northwest of the block. The USGS three-dimensional 

probe installations (figs. 11, 12) in the block provided 

rock-temperature data for each installation. 

Stress determinations within the granite were made 

using the overcoring techniques in vertical and horizontal 

core holes to depths of 8 m. The U.S . Bureau of Mines 

(USBM) and USGS measuring devices were used at 

equivalent depths. 

An attempt was made to select several rock -stress 

measurement techniques in order to obtain independent 

data checks. Methods chosen were the commonly used 

overcoring and hydrofracturing techniques. The overcoring technique basically depends on measuring relief displacements that occur in the rock as it is cored and converting these to rock-stress values through measured elastic-rock constants. The hydrofracturing technique essentially depends on measuring fluid pressures required to 

balance rock pressures as fluids are injected into fractures. 

For the overcoring procedure, three types of instrumentation were chosen: ( 1) the USBM three-axis 

borehole deformation gage (Hooker and Bickel, 1974), 

(2) the USGS three-dimensional borehole probe (Lee and 

others, 1976), and (3) metal-foil resistance strain gages 

(Swolfs, 1976). 

The USBM gage was chosen because of its extensive successful use for measurements of this kind. The 

instrument is well designed and rugged, and can be used 

repeatedly. It was designed upon a sound theoretical basis 

for use in interpreting stresses in an elastic media. The 

instrument is a "soft modulus" device, meaning that it 

measures displacements, while offering little or no resistance to rock deformation . The disadvantage of using this 

device is that for any single measurement it can only be 

used to determine stresses in a single plane. 

The USGS probe was chosen because it can be used 

to determine the 3-dimensional stress condition at the 

measurement location. Also, the instrument is a borehole 

inclusion, much stiffer than the USBM gage, and primarily monitors deformations and temperature changes. The 

theoretical basis for the gage is more complex than that 

of the USBM gage and also requires that the response 

of the rock be elastic. The instrument, although less expensive than the USBM gage, can only be used once. 

Strain gages were chosen for very near surface measurements because they are the least expensive and can 

be easily applied to accessible rock surfaces. The theory 

used for stress interpretation is simple and requires that 

the monitored strains be those of the elastic response of 

the rock. Stresses can only be determined for the plane 

on which the gages are mounted. 

Deformation, Stress, and Temperature Measurements 9 
A disadvantage of all three gages is that they cannot 

differentiate strains of thermal origin from those of stress 

changes. Compensation for or interpretation of thermal 

strains is required in each case. The first two instruments 

were installed in boreholes at various depths (figs. 11, 

12) and overcored, whereas the strain gages were installed 

on prepared rock surfaces on the block prior to overcoring. 

All of the data obtained from the overcore measurements are reported herein as stresses, using the assumption that the rock response during the overcore measurement was elastic. The data show evidence that the response was not entirely elastic and that the data perhaps 

more properly should be presented as displacement or 

strains. However, as there is doubt, and because the data 

are more simply reduced to stresses by the existing programs for each instrument, the data are left in terms of 

stresses and the arguments for elastic versus inelastic response will be presented in the discussion. The reader, 

therefore, is cautioned to view the stress data critically 

and to consider that the expression of these data may be 

more appropriate in terms of strain rather than stress. The 

principal directions of strain and the ratio of principal 

strain magnitudes would remain the same as for the stress 

values because the stresses have been calculated using an 

average elastic modulus and Poisson's ratio in all directions. 

In addition, hydrofracturing tests were used to 

measure stresses at depths of 3.5 and 5.5 m in the block 

(fig. 12), but are not discussed further because the data 

were incomplete (Nichols, 1980). 

To determine surface displacements, five displacement nets were established: two on the top surface, two 

on a vertical face of the block to be quarried, and one 

on a horizontal surface adjacent to the top of the block 

(fig. 13). The nets were each composed of three arms 

and covered most of the exposed surface of the quarried 

block. Each arm had measuring points at both ends that 

consisted of steel bolts that were mechanically wedged 

into drill holes. The bolts on nets 1 and 2 were spaced 

6.05 m apart; on net 3, 1.89 m apart; on net 2E, 1.52 

m apart; and on net 4, 4.15 m apart. The angles between 

arms were 60° on nets 1 , 3, and 4; 45° and 90° on net 

2. The nets were measured periodically with precision 

steel tapes that were calibrated for temperature change. 

Additional strain and displacement measurements 

were made on cores that were removed from the large 

block both before and after quarrying. Strain gages were 

applied to external surfaces of solid cores and overcore 

annuli several hours after coring to continue monitoring 

strain relief with time. Continued measurements were 

made also across the central boreholes within overcore 

annuli. These latter measurements were made with the 

USBM borehole deformation gage. 

10 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

A 

SECTION AB 

Vertical wall 

Figure 11. Perspective view of 10X10X5.7-m block of 

Barre Granite and adjacent quarry area, Wetmore and 

Morse quarry, Barre, Vt., showing locations of boreholes 

and sheeting fractures. The coordinate system (x, y, z) 

and the cross section (AB) were used in the finite-element calculation of gravity stresses. Horizontal instrument holes are designated by 1H, 2H, and 3H. The group 

of vertical instrument holes is shown in detail on 

Figure 12. 

Results of Temperature Measurements 

Figure 14 shows the average daily temperatures 

measured in the auxiliary holes at depths of 1.52, 2.74, 

4. 27, and 7. 0 1 m during the periods of field investigation 

in July, October, and November 1975, and October and 

November 1976. In addition, the rock temperatures at all 

of the USGS 3-D probe installations to the time of overcoring are shown. Two of these probes were used to monitor temperature changes over a year's time at depths of 

4.58 and 4.61 m in holes 1 and 1a on the block (fig. 

12). The maximum spread of measured temperatures during the periods of field investigation was 2. 78°C for all 

measurements except those at 1.5 m, but generally was 

much less than this, whereas at 1.5 m depth the temperature spread was much larger at 11.1 °C. The 1.5 m temperatures ranged from 6. 7°C warmer than temperatures below 

3 m during the July 1975 investigations to 3. 9°C cooler 

during the November 1976 investigations. The temperature variations on both USGS probes at the 4.6 m depth 

showed nearly identical responses with a maximum seasonal variation of 5. 8°C. 
11 0 

Q) 

(,) 

~ EB 

-m 

·:;;: 

<( 

EXPLANATION 

Hole number and location 

Overcore location prior to quarrying z N. 50cw. 

Overcore location after quarrying 

Section I 

Hydrofracture location prior 

to quarrying 

Number and location of 

surface overcore 

Sheeting fractures 

/ 

/ 

/ 

/ 

/ 

/ 

/ Section III 

xJ ___ _ 10 meters--------------.j 

Holes 

10 meters X 

z 

Holes 

3a 

Prequarry measurements Postquarry measurements 

EXPLANATION 

o Locations of measurements using USBM borehole gage 

Locations of measurements using USGS borehole gage 

Trace of sheeting fracture intercept in holes 

0 <v· ~0 

~· 

A 

l fl) 

Qi 

a; 

E 

B 

y 

Figure 12. A, Isometric view of the 10x 10x5.7-m block of Barre Granite showing borehole locations, overcore 

and hydrofracture locations, sheeting fractures, and coordinate axes x, y, and z, Wetmore and Morse quarry, Barre, 

Vt. Sections I, II, and Ill are separated by sheeting fractures. B, Section views of the same block showing locations 

of prequarry and postquarry overcoring stress measurements. Viewed normal to x axis. Dashed lines indicate location 

of sheeting planes in boreholes. 

Because there were insufficient data on the thermal 

rock properties and thermal gradients within the block at 

the time of investigations, it is impossible to determine 

the induced thermal stresses. The block in its unquarried 

position is essentially unbounded on the top and one side, 

thus not perfectly confined. However, based on thermal 

Deformation, Stress, and Temperature Measurements 11 
Leg number'\. 

2 3 

Net 1 

Quarried block 

1---------10 meters-----+~ 

Plan view 

Vertical wall 

Elevation view 

Figure 13. locations of displacement nets 1, 2, 2E, 3, and 4, Wetmore and Morse quarry. Nets 1, 2, 

and 2E are on the top horizontal surface, where net 2E is an extension of legs 1 and 2 on net 2, and 

nets 3 and 4 are on the existing side vertical surface. Nets 2, 2E, 3, and 4 are on the unquarried 10X10x5.7-

m block of Barre Granite. 

stress data, Hooker and Duvall (1971) determined athermal stress of approximately 0. 305 MPa per oc for the 

Mount Airy Granite of North Carolina, assumed to be 

an elastic half space. Because the elastic constants of the 

Mount Airy Granite are very similar to those of the Barre 

Granite, this figure may be reasonable for thermal stresses 

at Barre. Therefore, thermal stresses, based on the temperature differences measured (0.85 MPa for 2. 78°C difference), appear to be small enough to be neglected for 

the scope of this paper. 

12 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

Prequarrying Stresses 

Prequarry stress data and sign convention are given 

in table 1. The magnitudes and orientations of the 

maximum, intermediate, and minimum principal stresses 

ITJ. IT2 , and IT3 and the maximum and minimum secondary 

principal stresses P and Q in the horizontal and designated 

vertical planes are shown according to their borehole location and depth of overburden. Stresses obtained by overcoring the USBM borehole gage were determined using 
EXPLANATION 

1.42 Depth of reading, in meters 

20 o Temperature measurements made from stress probes 

over the period of time each remained in the 

rock prior to overcoring 

--1.52 

G-0 1.42 • Temperature measurements at time of overcoring 

~ 15 

u.i 

a: 

Average temperatures measured with resistance 

type thermometers during the time of each field 

investigation 

:::::> 

1-

<( 

a: 

w 

a.. 

~ 10 1-

5 

4.27 and 7.01-

~1.52 

4.27 ==e----3.12 3.01 G-e 

7.01 

7.01--

1.52--

1.52-

OL_ ______ ~ ________ _J ________ ~ ________ _L ________ _L ________ J_ ________ ~--------~--------L-----~ 

5 7 9 11 3 5 7 9 11 

1975 1976 

MONTH AND YEAR 

Figure 14. Measured temperature versus time in 10x1Qx5.7-m block and adjacent rock. 

plane-strain analyses and lie in planes normal to borehole 

axes. For comparison, stresses determined by overcoring 

the USGS 3-D borehole probe were rotated into planes 

normal to borehole axes. 

Overcore Measurements 

The measurements made in the block were located 

in sections I, II, or III bounded by sheeting fractures (fig. 

12A). These were made in vertical holes 1, 1a, 2, 6, 

7, 7a, 8, and horizontal hole 1H. Therefore, all of the 

stress determinations made with the USBM gage except 

those made for hole 1 H were in the horizontal plane. In 

that the top of the block was more fractured than the 

lower portions, the measurement locations near the top 

were closer to fracture surfaces. Effects of fracture proximity on stress distribution within sections I, II, and III 

can be seen on figure 15, which shows a plot of the 

maximum secondary principal stress magnitudes (P) versus the approximate distance of the stress measurement 

location from known fractures. Also, figure 15 shows a 

lower hemisphere plot of the stress orientations for these 

measurements. The distance of the measurement from a 

fracture appears to be a significant factor in determining 

the stress magnitude, much more so than the depth of 

measurement. The principal stress orientations on the 

other hand seem to be more a function of the section 

location. The measurements made at the greatest distances 

from fractures have the greatest stress magnitudes apparently independent of the section location, whereas the 

stress orientations in sections I and II, independent of the 

proximity to fractures, are very similar and those in section III are consistently rotated more than 90° clockwise. 

The directions of minimum secondary principal stresses (Q) determined from the surface measurements are 

from N. 40° E. to N. 48° E., demonstrating that near or 

on the surface, Q is parallel to the rift plane (N. 40° E.). 

The findings of Swolfs ( 1976) and of Engelder and others 

( 1977), who both made strain relaxation measurements on 

surface rocks of the Barre quarries, also led them to conclude that minimum strains are parallel and maximum strains are normal to the rift plane. They inferred that the 

mechanism of strain relaxation in the Barre Granite was 

the opening of microcracks in the rift plane. This appears 

to be true only near the surface of section I. 

Horizontal hole 1H in section III is under 3.85 m 

of overburden. The stress components measured at three 

locations in this hole are in vertical planes that strike N. 

50° W. The magnitude and plunge of P and Q for each 

measurement are very consistent, and P agrees well with 

the measurement made in horizontal planes, the maximum 

being 8.43 MPa, plunging 25° to the southeast. This 

value, like the other values of P in section III, does not 

appear to be affected by the sheeting fractures. 

Deformation, Stress, and Temperature Measurements 13 
... 

~ 

~ ~ 

~ 

; 

m 

Ill 

c. = 

m 

OQ = 

:r 

m 

:r 

CJQ 

C) 

2 

~ Ill = .. 

; 

C) 

~ 

2. 

$ 

~ 

~ a 

Table 1. Determinations of stresses (MPa) made on Barre Granite adjacent to and within the 10x10X5.7-m block prior to and after quarrying, Wetmore 

and Morse quarry, Vermont 

[<r,, s2, and <r3 , are principal stresses. P and Q are secondary principal stresses that are determined in a horizontal plane and a vertical plane with the strike the same as the 

bearing. Positive stresses are compressional and negative stresses are tensile. Maximum principal stresses P and <r1 are the most compressive. leaders(--) indicate no data] 

Hole 

No. 

la 

la 

Overburden 

depth 

(m) 

1.42 

3.12 

3.01 

4.58 

4.61 

2 1 .53 

2 3.05 

2 5.34 

2 5.80 

1H 3.87 

1H 3.84 

1H 3.81 

2H 67 

2H 67 

2H 67 

6 

7 

8 

7a 

3H 40 

3a 

3 

3 

3a 

3 

4.61 

3.25 

2.10 

4.42 

2.53 

7.02 

Distance' Section 2 

(m) 

1.42 

3.12 

3.01 

4.58 

4. 61 

1.53 

3.05 

5.34 

5.80 

1.64 

3.28 

4.92 

1.64 

3.28 

4.92 

0 

0 

0 

0 

0 

4.61 

3.25 

2.10 

4.42 

2.53 

7.02 

I 

II 

III-II 

III 

III 

I 

II 

III 

III 

III 

III 

III 

I 

I 

I 

I 

III 

II 

II 

III 

II 

(") 

p 

-0.35 

6.34 

1.50 

6.29 

6.44 

.57 

5.70 

8.78 

9.58 

7.22 

8.43 

8.17 

17.99 

12.4 

6.21 

8.28 

2.32 

0 

3.89 

9.1 

-.99 

. 11 

.28 

-.09 

.42 

9.63 

Q 

-0.92 

. 31 

.16 

3.58 

3.74 

.29 

1.27 

4.63 

5.28 

.97 

1.98 

1.66 

2.26 

6.13 

1.95 

2.07 

.58 

0 

1.90 

6.62 

-2.32 

-.27 

-.18 

-.65 

-.44 

4.92 

1 Distance of measurement from surface. 2 See figure 12A. 

Attitude of P 

(degrees) 

Bearing Plunge 

01 02 

Prequarrying measurements 

N. 11 W. 

N. 3 W. 

N. 15 W. 

N. 88 W. 

Overcore, USGS 3-D probe 

0 

0 

0 

0 

0.09 

9.63 

1.60 

6.29 

-0.36 

3.07 

.21 

4.89 

Block lift, USGS 3-D probe 3 

03 

-0.95 

.28 

-. 73 

2.16 

a, 

Bearing 

N. 68 W. 

N. 0 W. 

S. 13 E. 

S. 87 E. 

N. 86 E. 0 6.80 4.41 3.28 N. 82 E. 

N. 22 W. 

N. 26 W. 

N. 88 W. 

N. 89 W. 

S. 50 E. 

S. 50 E. 

S. 50 E. 

N. 40 E. 

N. 40 E. 

N. 40 E. 

Overcore, USBM 3-axis probe 

0 

0 

0 

0 

20 

24 

25 

60 

57 

10 

Overcore, metal-foil strain gage 

N. 42 W. 

N. 46 W. 

N. 50 W. 

N. 50 W. 

N. 28 E. 

N. 34 E. 

N. 45 W. 

N. 87 W. 

N. 49 W. 

N. 82 W. 

0 

0 

0 

6 

Postquarrying measurements 

Overcore, USGS 3-D probe 

0 0.9 -1.04 -2.35 

0 .82 .11 -.45 

Overcore, USBM 3-axis probe 

0 

0 

0 

0 

N. 51 E. 

N. 60 W. 

Plunge 

79 

45 

12 

2 

21 

79 

68 

Attitudes, in degrees 

02 03 

Bearing Plunge Bearing 

S. 9 E. 

S. 9 E • 

s. 80 w. 

s. 4 w. 

N. 31 W. 

s. 26 w. 

N. 32 E • 

6 

45 

12 

44 

45 

10 

N. 80 E. 

s. 85 w. 

N. 34 E. 

N. 1 E. 

s. 9 w. 

N. 63 W. 

S. 57 E. 

3 Stresses were determined by changes caused by quarrying of block. 

" Measured in unquarried rock below section III after the overlying block was quarried. 

Plunge 

9 

5 

73 

46 

37 

4 

22 
(ij 

u 

Ul 

Ill 

a.. 

Ill 

Cl 

Q) 

:::::! 

~ 

(/) 

(/) 

w 

a: 

~ 

(/) 

....I 

<( 

a.. 

10 

8 

6 

u 4 z 

a: 

a.. 

>-

a: 

<( 

0 

z 

0 

u 

~ 2 

0 

.& 3.01 

• 1.53 

•0 

• 1.42 

<0.5m 

A 

• 4.61 .& 3.12 

• 4.58 

.& 3.05 

.o 

.o 

0.5-1.5m 

• 7.02 

• 5.80 

• 5.34 

• 0 

7.02 

• 

.& 

• 

>1.5m 

MAXIMUM DISTANCE FROM NEAREST NATURAL FRACTURE 

B 

N 

•• 

•• 

EXPI.ANA TION 

Depth of measurement, 

in meters 

Location in Section I 

Location in Section II 

Location in Section Ill 

Figure 15. A, Plot of maximum secondary principal stress magnitudes (P) measured on the block versus maximum 

distance of stress measurement location from known fractures. 8, Equal area diagram (lower hemisphere) showing 

orientations of the secondary maximum principal stresses (P). 

The orientations of the three-dimensional principal 

stresses (rrh rr2, rr3) are plotted on a Schmidt equal area 

net on figure 16. Figure 16A shows rr1, rr2, and rr3 for 

the stresses remaining in the block after relief caused by 

natural fractures or by quarrying the block. The stresses 

measured in sections I, II, and III in hole 1 at 1.42 m 

(1-1.42) and in hole 1a at 3.01 m (la-3.01) are prequarry 

stresses that remain after relief by the sheeting fractures. 

Also shown for comparison are the postquarry stress 

orientations determined in sections II and III in hole 1 

at 4.61 m (1-4.61) and hole 3a at 3.25 m (3a-3.25) that 

remain after relief by the quarrying operation. The directions of the free block sides, N. 40° E. and N. 50° W., 

and the orientation of the sheeting fractures are also 

shown. The fracture-relieved stress orientations at 1-1.42 

and 1a-3.01 are subparallel and subperpendicular to the 

fracture orientation and appear to be influenced by the 

geometry of fracture development, and possibly by the 

nonrelieved principal stresses of block section III (at locations 1-3.12, 1-4.61, and 1a-4.58) seen on figure 16B, 

which bear in similar directions. The postquarry stress 

orientations, however, at 1-4.61 and 3a-3.25 (fig.' 16A), 

as would be expected, are nearly parallel and perpendicular to the quarried block sides, and thus, seem to be controlled by the block geometry. 

Other prequarrying stress measurements were made 

in horizontal boreholes 2H and 3H drilled into the vertical 

walls to the southwest and northwest of the large block 

Deformation, Stress, and Temperature Measurements 15 
4 (1) 4.61 

0 (1a) 3.01 

N 

A 

(3a) 3.25 

N. 50° W. N. 40" E. \ 

sn (1 a) 3.01 

(3a) 3.25 • 

(1) 1.42 

(1) 4.61 

(1)4.61 / o ------ (1 a) 3.01 . 

s 

\ 

(1) 1.42 ... 

I 

J 

I 

(3a) 3.25 ... 

N 

(1) 3.12 .... (1) 4.61 0 (1a) 4.58 

sn 

... (1) 3.12 

(1 a) 4.580 0 {1) 3.12 

s 

B 

\ 

N. 40° E. I 

(1) 4.61 • 

I 

(1a) 4.58 

I 

I 

sf 

EXPLANATION 

(1) 4.61 

. 0"1 , hole number in parentheses and depth 

of measurement location in meters 

0 

... 

sn 

sf 

The normal to the sheeting fractures 

Orientation of sheeting fractures 

Figure 16. Equal area diagrams (lower hemisphere) showing orientations of principal stresses determined within 

10X10x5.7-m block of Barre Granite. A, stress orientations measured at locations relieved either by quarrying of 

block or by natural fractures. B, stress orientations unrelieved, prior to quarrying of block. 

(fig. 11). Hole 2H is under 67 m of overburden (fig. 

2). The three stress determinations made in this hole at 

distances of 1.64, 3.28, and 4.92 m from the vertical 

wall (fig. 11) demonstrated horizontal stresses to be very 

similar to the unrelieved stresses measured in the same 

direction in the unquarried block (table 2). The vertical 

stresses (table 2), however, from the first two measurements were several times greater than the vertical stress 

in the block, whereas the vertical stress of the third measurement was slightly less than nearly all of the unrelieved 

vertical stresses determined in the block. The third measurement, although 4.92 m into the granite face, was less 

than 0. 5 m from an iron-stained fracture dipping to the 

southeast at about 45°. The measurement location was in 

the footwall side of the fracture underlying at least 67 

m of overburden. Hole 3H is under about 40 m of overburden. One stress determination was made at this location on the surface of the vertical wall that strikes N. 

50° W. This was done by overcoring strain gages mounted 

on a prepared vertical surface (Swolfs, 1976), and the 

determined horizontal stress was slightly higher than those 

unrelieved horizontal stresses measured in the N. 50° W. 

16 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

direction in the block. The vertical stress was more than 

double the vertical stress in the block but less than half 

of the vertical stress in hole 2H near the face of the other 

high wall. 

From the prequarry stress measurements made in 

the vicinity of the block, several distinctive characteristics 

were revealed. 

1. The determined stress magnitudes and orientations are strongly influenced by relief within 0.5 m of 

fractures and free surfaces. Stresses normal to planes 

parallel to these surfaces are the most severely affected. 

2. The principal stress orientations away from 

fractures in the unquarried block appear to be related more 

to spatial locations and geometry than to fracture orientations. The near-surface stress orientations may be related 

to a microfabric feature, the rift plane, whereas for deeper 

measurements, this relation is not apparent and directions 

appear to be controlled by the section location. 

3. The determined horizontal stress magnitudes do 

not appear to change much as a function of depth of overburden, whereas the vertical magnitudes increase considerably at depth. 
Table 2. Measured and gravity stresses (MPa) in the x, 

y, and z directions in Barre Granite adjacent to and within the 10X10X5.7-m block prior to quarrying 

[<rx, <ry, and <Tz are normal stresses in the N. 40° E., N. 50° W., 

and vertical directions. Measured and calculated gravity stresses 

are indicated by m and g. Positive stresses are compressional 

and negative stresses are tensile. Calculated stresses are based 

on a plane-strain finite-element calculation using the overburden load and Poisson's ratio of 0.25. Leaders (--) indicate no 

data] 

OverHole burden ox cry crz 

No. depth (m) (g) (m) (m) (g) (m) (g) 

Overcore, USGS 3-D probe 

1. 42 -0.69 0.27 -0.58 0.07 -0.06 0.10 

3.12 3.05 .48 3.60 . 13 6.33 .26 

Block lift, USGS 3-D probe 1 

4.61 5.05 .50 5.14 . 19 4.33 .42 

Overcore, USGS 3-D probe 

1a 3.01 .61 .48 1 .05 . 13 .59 .26 

1a 4.58 5.25 .50 4.62 . 19 3.47 .42 

Overcore, USBM 3-axis probe 

2 1.53 .36 .27 .50 .07 

2 3.05 2.06 .48 4.91 . 13 

2 5.34 6.14 .48 7.28 .23 

2 5.80 6.91 .45 7.95 . 27 

1H 3.87 6.49 .9 1. 70 0.29 

1H 3.84 7.37 .13 3.05 0. 28 

1H 3.81 7.01 .17 2.83 0.36 

2H 67 6.19 .80 1 4.06 2.80 

2H 67 7.99 . 70 10.54 2.10 

2H 67 6.08 .66 2.08 1 . 90 

Overcore, metal-foil strain gage 

6 0 2.19 0 8. 16 0 

7 0 .58 0 2.32 0 

8 0 .00 0 0 0 

7a 0 1.90 0 3.89 0 

3H 40 9.10 1 .00 6.62 

1 Stresses were determined by changes caused by quarrying 

of block. 

Measured Prequarry Stresses Compared to Predicted 

Gravity Stresses 

Table 2 shows normal stress components in the x, 

y, and z directions (fig. 11) calculated from prequarry 

measurements. These directions, respectively, N. 40° E. , 

N. 50° W. , and vertical, bound the unquarried rectangular 

block and lie within and normal to the section AB (fig. 

11). Gravity stresses in the AB plane for the x, y, and 

z directions were determined by a plane-strain finite-element calculation (Nichols and others, 1977) using the assumption that the confinement in the y direction is sufficient to allow little or no strain. The closest free surface 

from plane AB in the y direction is the small vertical 

surface at the upper southeast side of the block. Its distance from the AB plane is sufficiently far that by St. 

Venant' s principle it is assumed not to have a large effect 

(Sokolnikoff, 1956) on the confinement of the unquarried 

block. The stresses are contoured on figure 17 and reported for each measurement site in table 2. The measured 

horizontal stresses in most cases are at least five times 

greater than the calculated horizontal gravity stresses. 

Most of the measured vertical stresses are from 5 to 20 

times the calculated vertical gravity stresses. The measured horizontal stresses under 6m and 67 m of overburden are approximately the same, whereas the measured 

vertical stresses at 67 m are much greater than at 6 m 

and are at least five times the calculated vertical gravity 

stresses in most locations. There are a few measurements 

that do not conform to this trend, those at I.42 m in 

borehole I, 3.0I min borehole Ia, and 4.98 in borehole 

2H. These measurements are all very close to sheeting 

fractures which probably relieved much of the stress. The 

majority of measurements at this location therefore indicate that unless relieved by fracturing the horizontal 

stresses remain approximately the same to a depth of 67 

m, whereas the vertical stresses increase with depth and 

have a 5: I ratio to the calculated gravity stresses. 

Thus, the prequarry state of stress in the block and 

surrounding rock mass, as determined by overcore measurements and assuming an elastic rock response, appears 

to be different from one caused by gravity loading alone. 

Both the measured horizontal and vertical stresses are 

much greater (by at least a factor of 5) than those predicted by the gravity model. The measured stresses also 

differ from the gravity model in that both the horizontal 

and vertical stress components of the gravity model increase with depth, whereas only the vertical component 

of the measured stresses appears to increase significantly 

with depth. Also, the measured vertical component increases with depth at a much greater rate than does the 

vertical gravity component. 

Stress Changes and Surface Deformations Caused by 

Quarrying 

Stress determinations made in the lOX IOX5.7-m 

block after quarrying (table I) were used to determine 

changes in the block caused by quarrying. The determined 

prequarry stress magnitudes seemed to be a function of 

distance away from natural fractures, and within 0.5 m 

of natural fractures these stresses were greatly relieved. 

Therefore, the relief that occurred within the block as a 

result of quarrying was a function of distance away from 

natural fractures. After quarrying, stress determinations in 

sections II and III of the block show the secondary principal stress magnitudes (P and Q in table 1) to be between 

0.42 and -2.32 MPa with a mean value of (P+Q) of -0.41 

MPa. The mean maximum principal stress (P) after quarrying is -0.05 MPa; therefore, it appears that on relief, 

the net state of stress in the block is one of slight tension 

Deformation, Stress, and Temperature Measurements 17 
A 

Contour interval 0.2 MPa 

10 METERS 

Vertical stress fT2 

8 

Contour interval 0.2 MPa 

10 METERS 

Horizontal stress O"x parallel to the N. 40° E. plane 

c 

Contour interval 0.1 MPa 

10 METERS 

Horizontal stress (Tv parallel to the N. 50° W. direction 

but normal to plane AB 

Figure 17. Gravity stresses determined by a plane-strain finite-element calculation in the vertical plane AB (fig. 11), 

striking N. 40° E., cutting the quarry wall and the unquarried 

block of Barre Granite, Wetmore and Morse quarry. For this 

calculation, Young's modulus was 31 GPa, Poisson's ratio was 

0.25, and the density was taken to be 2.7 g/cm3. 

18 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

possibly as a result of thermal stresses. By comparing 

the values of the prequarry and postquarry maximum principal stresses (P, table 1) in sections II and III, the stress 

reduction has been determined to be on the order of 1.6 

to 9.6 MPa. If section I relieved in a similar manner, 

determined stress drops as large as 8. 3 MPa are probable. 

Data from a USGS 3-D stress probe situated in section 

III (hole la, 4.58 m), during the final separation of the 

block on the lift plane, showed an initial maximum stress 

decrease of 6.5 MPa, which is consistent with stress measurements at this depth (table 1) before and after quarrying. 

After the block was quarried, initial rapid surface 

deformations, measured on the surface nets, were followed by slower time-dependent deformation. The surface-displacement nets were measured just before and for 

I 0 days after the block was quarried. 

The changes on each leg could be measured to the 

nearest 25 J.Lm, which, over a gage length of approximately 6 m, is a strain of 4.2x 10--{). Considering that 

the stress release caused by quarrying may have been as 

large as 9.6 MPa, the resulting extensional strains are on 

the order of 350 X I 0--{). The displacement measurements, 

therefore, are considered to be sufficiently sensitive to 

monitor the displacements caused by stress release. Figure 

I8 shows the data for these readings on nets I, 2, 2E, 

and 3. The displacements on nets I and 2 were converted 

to strains from which strain ellipses were calculated to 

determine principal strain directions. From the first-day 

strain ellipse determined for net 2, plane stress changes 

were determined which are also shown on figure I8. The 

1-day interval is based on the assumption of a nearly 

linear elastic response. 

Net 1, on the unquarried adjacent horizontal surface, showed mostly initial rapid contractions 1 day after 

quarrying, which were followed by slower and much 

larger contractions for 10 days. The lengths of legs 1, 

2, and 3 were respectively 5.94, 5.94, and 5.85 m. After 

1 day, legs 1 and 2 showed contractions of 559 and 356 

J.Lm, respectively, and leg 3 showed expansion of 76 J.Lm. 

Contractions for the 10-day period were 2.03, 0.94, and 

1.32 mm, respectively. The calculated strain ellipses show 

the maximum strain after the 1st day to be 110 x 1 0--{) 

bearing N. 20° W., and after the 1Oth day to be 354 X 1 0--{) 

bearing N. 70° W. 

Nets 2 and 2E responded in overall expansion rather 

than contraction. The lengths of legs 1, 2, and 3 of net 

2 were 5.85, 6.04, and 6.04 m, respectively. The expansions on these legs the 1st day after quarrying were respectively 0.25, 1.17, and 0.69 mm and the lOth day 

after quarrying were 0.53, 1.91, and 1.55 mm. The 

maximum calculated extensional strain for the 1st day was 

-193 x 10--{) bearing N. 37° E. which, if elastic, is equivalent to a maximum stress relief of 6. 7 MPa in the same 

direction. For I 0 days, the maximum strain was 
z 

0 

U5 

(/) 

w 

c:c 

0.. 

:::!!: 

0 (J)U 

c:c 

w 

.... 

w 

:::!!: 

::J 

-1 

~ z 

0 

U5 

z 

w 

.... 

X 

w 

z 

0 

U5 

(/) 

w 

c:c 

0.. 

:::!!: (J)0 

c:cu 

w 

.... 

w 

:::!!: 

::J 

-1 

~ z 

0 

U5 

z 

w 

.... 

X 

w 

2.0 

1.0 

c:: 

I 

0 --L--

-1.0 BLOCK QUARRIED 

2.0 

1.0 

0 -...,--

-1.0 

1:::"-~ I 

I 

I 

I 

l......_ 

I Leg 2A-2 

~ BLOCK QUARRIED 

Net 1 

Net 2£ 

-2.0 L.__ __ ___L ___ __j__ ___ l.__ __ __..L ___ __j 

0 2 4 6 8 10 

TIME, IN DAYS 

N 

, FIRST DAY ~ 

v.; ,cr 

+,. ~~+ ~ /' 

Principal Strain Changes 

(Extension) 

0 --,__ 

I 

I 

ffi ~ U5 ~j :::!!: ~ -1 .0 

::J .... -1 X ~ w 

z 

0 

U5 

(/) 

w 

a: 

0.. 

:::!!: 

0 (/) u a: 

w 

.... 

w 

:::!!: 

::J 

::::! 

:::!!: z 

0 

U5 

z 

w 

.... 

X 

w 

2 4 6 

BLOCK QUARRIED 

TIME, IN DAYS 

s 10 

Figure 18. Graphs showing displacements versus time for nets 1, 2, 2E, and 3 after the 10X10X5.7-m block of 

Barre Granite was quarried. Principal strain changes for the initial first-day response for net 2 are shown. 

-327 x 10-6 bearing N. 52° E. The initial expansions the 

1st day after the block was quarried had about the same 

orientation and a little more than half the magnitude of 

those measured after 1 0 days. 

Net 3, on the vertical southwest face of the quarried 

block, demonstrated initial compressive displacements 

after 1 day and subsequent comparable time-dependent 

displacements after 10 days. 

Net 4 was located across both sheeting fractures. 

These fractures apparently sustained movement that made 

the deformation ellipse calculations of the net unrealistic; 

therefore, the calculations are not reported here. 

Important points to note: (1) After quarrying, the 

lOX 10X5.7-m block of granite appears to be almost totally stress relieved. The final average state of stress appears to be slightly in tension. (2) The stress reduction 

is a maximum of 9.6 MPa. (3) In most cases the time-dependent surface deformations were of the same sense and 

comparable in magnitude to the initial deformations. (4) 

The magnitudes of initial horizontal stress releases calculated for surface net 2 (fig. 19) are comparable to the 

stresses measured in the block before quarrying (table 1). 

These magnitudes of released stresses on the surface are 

also comparable to the stress changes measured by stress 

instrumentation in the interior of the block (section II) 

during quarrying (table 1). 

Time-Dependent Deformation of Cores 

The cores retrieved from boreholes continued to deform with time, much in the same manner as the time-dependent deformations observed on a larger scale on the 

surface-deformation nets. In addition, 5. 7 -em-diameter 

cores retrieved from instrument hole 5, drilled after the 

block was quarried, demonstrated considerable disking 

(fig. 19). The disking occurred in cores taken from depths 

as much as 2 m prior to removal from the core b~el. 

Cores further dissected in the laboratory also demonstrated 

additional release of time-dependent strains. Previous tests 

performed in the laboratory on a cube of Barre Granite 

(Nichols, 1976) demonstrated the same phenomenon. 

Conceivably, extensional fractures, both natural 

sheeting fractures and quarry-induced fractures may occur 

as a result of inelastic unloading strains. Measured and 

Deformation, Stress, and Temperature Measurements 19 
Figure 19. Disking (regularly spaced tensile 

failures) of 5.7-cm-diameter cores retrieved 

from hole 5 drilled after the 10x10x5.7-m 

block was quarried . Disking occurred in 

cores taken to a depth of 2 m in Wetmore 

and Morse quarry, Barre, Vt. 

inferred strains of this nature are further discussed here 

as possible causes of failure. 

Disking, described as extensional failure normal to 

core axes that occurs as a result of coring, has been interpreted to require large radial compressive stresses (Durelli 

and others, 1968) applied at the bottom of the rock cut 

surface (kerf). In the quarried granite block, however, 

there were no externally applied forces; therefore, the observed disking (fig. 19) must have resulted from extensional strains resulting from coring. At any rate, the fractures occurred after the rock was cored from the quarried 

block and were accompanied by time-dependent extensional axial strains sufficiently large to cause failure. 

The overcore annuli extracted from the 

lOX 10X5.7-m block during the overcoring process also 

continued to creep, as did the surface of the block. Within 

6 hours after each overcore extraction, the annulus was 

removed and a second USBM deformation instrument, not 

being used for field operations, was placed in the central 

3. 8-cm-diameter borehole, and displacements were then 

monitored under conditions of small temperature variations and ambient humidity. Maximum and minimum displacements, U 1 and U2 , that occurred with time in addition to those of the initial overcore are listed in table 

20 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

3. These values were calculated using a 60° rosette analysis to determine displacement ellipses. The data show that 

the absolute value of the time-dependent displacements 

occurring as a result of cutting new rock surfaces within 

an intact rock mass can be as large as or larger than those 

of the initial displacements. Figure 20 shows the magnitudes of principal strain changes that were monitored 

by 45° strain-gage rosettes applied to the external core 

surfaces within 3-4 hours after each core was cut. The 

90° gage elements were oriented to measure axial and circumferential strains. All of the external strains on the overcore annuli were extensional, whereas the internal 

borehole showed both extensional and shortening displacements. 

Some of the core samples were returned to our constant-temperature and humidity laboratory in Denver for 

further monitoring and creep studies. Curve A on figure 

21 shows the continuous creep behavior of a 5-cm core 

from the time of its removal in the field. Curves B and 

C show the plots of gages that were mounted on the same 

core, 200 and 530 hours after it was cored. The gages 

were read within 3 hours after installation and were 

periodically monitored in a constant-temperature and 

humidity room. Very little change was observed over a 

period of approximately 3 months. Superposed on the 

creep curve is a theoretical model of viscoelastic response 

derived by Savage (Nichols and Savage, 1976) for the 

Barre Granite, suggesting that the actual measured response may fit such a model. 

Most core-drilling procedures carried out in crystalline rocks require the use of water to carry away cuttings 

-700 

~ 

=- -600 z 

<( 

a: -500 1-

(/) 

...J 

<( I -400 z 

0 

u; 

z 

w -300 1-

X 

w 

...J -200 <( 

Q.. 

u 

z -100 

a: 

Q.. 

(A) 1.53 

TIME, IN DAYS 

EXPLANATION 

Hole number in parentheses and depth to 

center of overcore in meters 

No data 

Figure 20. Extensional strains measured through time on 

exterior of overcore annuli after extraction from borehole. 

Overcore holes A and H were drilled in surfaces adjacent 

to the quarry and are not shown on figure 11. 
Table 3. Internal radial borehole displacements (f.1m) for 

typical overcore samples through specified time intervals, Barre Granite 

[U1 and U2 are maximum and minimum displacements, positive 

being contraction and negative being extension] 

Internal borehole displacement 

Hole Depth principal directions Time 

interval 

No. (m) u1 u2 (hrs) 

3 7.02 2817 607 0 

-45 -130 21 

99 62 47 

1.53 124 -163 0 

1247 -419 20 

1699 -592 40 

1834 -805 65 

2065 -920 90 

2101 -968 112 

2217 -950 135 

3a 2.53 74 -79 0 

119 13 7 

2456 -2916 11 

2423 -3132 13 

13 -69 0 

2383 -1803 18 

1overcore holes A and H were drilled in surfaces adjacent 

to the quarry and are not shown on figure 11. 

and to cool the bits. The creation of new fracture surfaces 

and the introduction of water to these surfaces have temporary and permanent effects on strains measured on the 

new surface (Savage, 1979). Several laboratory experiments were conducted to determine these effects and to 

determine the amount of permanent strain that may be 

released as a result of further dissecting the rock specimens. 

The results of these experiments, too lengthy to discuss here, led to the following conclusion: Further cutting 

and wetting of new surfaces on granite cores, that had 

been stored for over a year after being removed from the 

intact bedrock, produced large temporary strains 

( 500 X 1 0-6) that recovered upon drying the surfaces. Permanent strains greater than 5 x 10-6 were not detected over 

the 18-month period following the cutting of the cores. 

The temporary strains were primarily a function of the 

available moisture and relative age of the new surface. 

In summary the field data and results of the laboratory experiments reveal time-dependent deformation as 

great as 3200 f.Lm and strains as great as 700 x 10-6 were 

measured on freshly extracted cores from the Barre Granite. Nonrecoverable strains measured after coring were on 

the order of 500 X 10-6. It is concluded that much of the 

nonrecoverable strain measured on these cores is due to 

rebound and some is due to capillary absorption of moisture. Contrasting recoverable strains measured in the laboratory on specimens cut from cores after at least a year 

of storage are almost entirely caused by capillary absorption and drying. The magnitude of the strains is a function 

of the relative humidity and the age of the new cut surface. Savage ( 1979) constructed a theoretical model that 

agreed very well with measured laboratory strains. Thus, 

the nonrecoverable time-dependent strains attributed to rebound seem to be short term, whereas recoverable strains 

of capillary absorption vary in time with relative humidity 

and age of surface. Longer term rebound strains are too 

small to be measured with the technique used here for 

periods of time less than a year. 

Elastic Modulus Determinations 

Directional Young's modulus determinations were 

made on specimens from or near overcore locations by 

sonic pulse methods and static loading methods. The sonic 

data presented in table 4 consist of dynamic moduli determined in three orthogonal directions: (1) perpendicular to 

the rift plane, (2) parallel to the rift plane and horizontal, 

and (3) parallel to the rift plane and vertical. Specimens 

used for sonic testing were taken from holes 1, 2, 1H, 

and 2H at or near overcore locations. Swolfs (1976) determined sonic moduli on a specimen from hole 8 (also 

shown in table 4). The sonic data can be compared to 

figures 22, 23, and 24, which show plots of static moduli 

determined in horizontal and vertical planes on overcore 

specimens taken from boreholes IH, 2, 2H, 3, 3H, 3a, 

and 3s. The vertical borehole 3s, not previously mentioned, is located on an unquarried surface approximately 

30 m northwest of the 67-m-high vertical quarry wall in 

which hole 2H is located. Determinations were made 

every 15° in a plane normal to the core axis. This was 

done by pressurizing the external surface of each annulus 

with a known hydrostatic pressure and monitoring displacements across the internal borehole every 15°. The 

USBM deformeter was used to monitor the borehole displacements. From the displacements and known applied 

pressures, directional moduli can be calculated in the 

plane of measurement. Thus, overcore annuli taken from 

vertical boreholes will yield moduli every 15° in the horizontal plane, and those taken from horizontal boreholes 

will yield moduli in a vertical plane. 

Several significant patterns of modulus distributions 

can be seen. The data on all figures show that the granite 

has definite modulus anisotropies that vary in magnitude 

and direction. The anisotropies appear at each location 

to have orthorhombic symmetry. The maximum, minimum, and intermediate planar values appear to be nearly 

orthogonal. 

The sonic-moduli values were approximately 25 

percent greater than the static-moduli values and were 

very consistent in the common directions of measurement. 

Both sets of measurements showed_ the moduli in the N. 

Deformation, Stress, and Temperature Measurements 21 
z 

< a: 

1-

C/) 

(X1o-6) 

700 

600 

500 

400 

A 

VISCOELASTIC STRAIN 

RELIEF MODEL 

(X10-6) B 

Gage 2(Axial) 

20~ Gage 5(Axial) 

300 45 ~ : -2: =: ======~===G=ag=e=6=(4=5::::) 

z 

0 

Ci.i 

z 

w 

1-

200 

100 

r;s 0 

0 

(X10-6) c 

200 400 600 

Gage 1 O(Axial) 

Gage 12(Horizontal) 

800 1000 1200 1400 1600 1800 2000 

+ FIELD ELAPSED TIME (HOURS) 

CORING 

EVENT 

Figure 21. Strains occurring through time on a 5-cm core after extraction from drill hole 1a. Dashed line is implied 

from other sample measurements. Superposed curve is a theoretical viscoelastic model of strain relief based on 

the creep properties of the granite. Curves A, B, and C show response of strain gages mounted 4, 200, and 530 

hours, respectively, after coring. Gages mounted on side of core taken from 3-m depth in drill hole. 

40° E. direction to be greater than those in the N. 50° 

W. direction, and the vertical moduli to be intermediate. 

The modulus values and distribution are important 

data needed for the interpretation of in situ stress mea1iurements. In as much as Hooker and Johnson (1969) demonstrated that the effect of modulus anisotropy is small, an 

average value of the measured moduli is used herein for 

the interpretation of deformation measurements made with 

both the USBM and USGS borehole devices. 

The following conclusions can be drawn from the 

moduli data. 

1. On the block prior to quarrying in the active 

quarry area, the direction of horizontal maximum modulus 

does not generally coincide with the N. 40° E. direction 

of the rift plane (fig. 22). Only near the surface of the 

block did these directions tend to be parallel. 

2. The maximum and minimum magnitudes of 

horizontal moduli, always approximately 90° apart, appear 

to be nearly the same at all locations in the unquarried 

22 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

block. At equivalent depths, the orientations are similar 

but tend to change in a clockwise direction with depth. 

The measured vertical-moduli magnitudes were approximately equal on all cores from nearly the same depth in 

a horizontal hole. These were intermediate to the 

maximum and minimum horizontal magnitudes, thus imparting an apparent orthorhombic symmetry at these locations. Variations of vertical moduli with depth in the unquarried block were not determined. 

3. The directions of maximum and minimum moduli on the block prior to quarrying do not always coincide 

with the respective principal stress directions. Only on 

the surface of the block and at 5. 8-m depth do the horizontal secondary principal stress directions (table 2) coincide with the directions of maximum and minimum moduli. On the surface, the secondary major principal stress 

P is parallel to the minimum modulus (Swolfs, 1976), 

but at 5.8 m it is parallel to the maximum modulus. At 

3.1-m depth, Pis nearly parallel to the maximum modulus 
Direction of rift plane 

::::r 

~ 

u 

(/) 

~ 

a.. 

~ 

~ 

~ 30 (/) 

::::> 

.....J 

::::> 

Cl 

0 

~ 

(/) 

0 

z 

::::> 

0 

~ 

N. 70° E. N. 40° E. N. 10° E. N. 20° W. N. 50° W. N. 80° W. N. 70° E. N. 40° E. 

DIRECTION OF HORIZONTAL MEASUREMENT 

(CORE AXES VERTICAL) 

Figure 22. Variation of static Young's modulus in the horizontal plane in cores from unquarried block of Barre 

Granite. Curve numbers indicate borehole number in parentheses and depth in meters of cored sample used 

for determination. 

direction. At the surface, the principal strains probably 

are the result of opening of microfractures in the rift plane 

(Swolfs, 1976; Engelder and others, 1977) where the 

maximum modulus is parallel to the rift plane. Below the 

surface, maximum strains, however, do not appear to 

occur primarily as the result of opening of microfractures 

in the rift plane. 

4. The data obtained indicate that the depth of 

burial and degree of confinement affect the rock modulus. 

The modulus values of unweathered rock still under 67 

m of overburden (fig. 23) are from 14 to 22 percent greater than modulus values measured in the same directions 

within the large quarried block (also unweathered) with 

only 5.7 m of overburden. On the other hand, the modulus values of rock at 1.49-m depth in the unquarried 

weathered rock surface (fig. 22) are 25 percent lower than 

those in the quarried block. The largest modulus values 

in the rock under 67 m overburden were in the direction 

of the greatest distance to a free rock surface (N. 40° 

E.), which was horizontal and parallel to the vertical 67-m 

highwall (fig. 23). The lowest values (table 4) were in 

a direction of the shortest distance to a free rock surface 

(N. 50° W .) or normal to the 67-m high wall. Instantaneous changes of moduli were not observed as a result of 

rock quarrying; therefore, if changes do occur with removal of overburden they may be time dependent. 

DISCUSSION OF RESULTS 

The results have demonstrated that with the number 

and diversity of measurements, progress was made toward 

accomplishing the objectives of the study, but many unanswered questions remain. In retrospect, there were 

many problems in the logistics of the experiment; that 

is, the quarry geometry was less than ideal, yet the best 

obtainable; the geologic structure was not optimally located or oriented for an ideal experiment; and finally, not 

enough measurments were made to determine the distribution of data obtained. Despite these shortcomings and any 

possible undetermined experimental and instrument errors, 

Discussion of Results 23 
:::::J 

<{ 

u 

(/) 

<{ 

Cl. 

<{ 

(.!) 

(.!) 

(/) 

::J 

...J 

::J 

Cl 

0 

:2: 

~ 

(.!) 

z 

::J 

0 

>-

20 

Intersection of rift plane 

90 60 30 0 -30 -60 -so 

ANGLE OF INCLINATION 

(CORE AXES HORIZONTAL) 

Figure 23. Variation of static Young's modulus in vertical planes striking N. 50° W. and N. 40° E. in core from 

unquarried block of Barre Granite. Angles are positive clockwise measured from horizontal. Curve numbers 

indicate borehole number in parentheses and distance in meters from surface of cored sample used for determination. 

sufficient evidence exists in the data to indicate that the 

rock response may be in part inelastic and inappropriately 

used for elastic stress analyses, thereby introducing a fundamental error in interpretation. 

Measurements Indicative of Inelastic-Rock 

Response Stress 

The basic but perhaps unfounded assumption used 

in determining rock stresses from overcore measurements 

is that the recorded initial unloading rock deformations 

are elastic and recoverable upon reloading. Using this assumption, it is relatively easy to determine the elastic-rock 

constants necessary for stress calculations, merely by 

loading extracted overcore annuli and monitoring the elastic deformations. However, from the data obtained at 

Barre, there are indications that the initial unloading rock 

deformations measured in this process may not be dominantly elastic and therefore, may lead to stress determina24 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

tions with a significant error. The best evidence of nonrecoverable unloading response includes the short-term 

time-dependent unloading rock response measured in the 

field, the disking failures observed in unloaded cores, the 

in situ strain relaxation close to natural fractures, and the 

unreasonable vertical to horizontal stress distribution that 

is indicated in an elastic analysis of the overcore measurements. 

Local Distribution of Determined Vertical and 

Horizontal Stress 

As demonstrated, the measured strains at the Barre 

Granite investigation site are greatly affected less than a 

meter away from fractures and free surfaces. Therefore, 

to approximate the in situ stress distribution at our site, 

vertical and average horizontal stresses were determined 

from measurements made over 1.5 m away from such 

influences. The determined vertical stress components rap-
(/) 

~ 

..J 

~ 

0 

0 

~ 

(/) 

(!) 

z 

~ 

0 

>-

40 

20 

N. 70° E. 

Direction of rift plane 

(3)2.1 0 and 4.42 

N. 40° E. N. 10° E. N. 50° W. N. 80° W. N. 70° E. N. 40° E. 

DIRECTION OF HORIZONTAL MEASUREMENT 

(CORE AXES VERTICAL) 

Figure 24. Variation of static Young's modulus in the horizontal plane of large quarried Barre Granite block. Curve 

numbers indicate borehole number and depth in meters of cored sample used for determination. 

idly increase and become much greater than the gravity 

stress at depth, whereas the average horizontal stresses, 

though much larger than gravity stresses, appear to change 

very little at depth. Less than 6 m from the surface of 

the unquarried block the ratio of measured vertical stresses 

to the calculated vertical gravity stress ~ is greater than 

5. At 67·-m depth in the highwall the a average ~ =5.0. g 

The ratio of measured average horizontal stresses (a h) to 

measured vertical stresses (<Tv). herein called K, is greater 

than 1 but less than 2 in the unquarried block. At 67 -m 

depth in the highwall, K is less than 1.0 but greater than 

0.4. 

In this very local situation, however, it should be 

noted that there are insufficient measurements to establish 

the interpreted stress distribution with any degree of confidence, especially as it appears to be somewhat anomalous. 

Many more data points are needed to determine the extent 

and reality of the measured stress distribution. If the distribution is real and not a result of inelastic deformations, 

then the impact to engineering practice and locally to 

quarrying becomes very significant. 

Influence of Geologic Features On Determined 

Stress Distribution 

For many years the influence of geology on in situ 

stress fields has been considered to be important. Mechanical behavior of geologic materials has been investigated 

thoroughly in the laboratory. The mechanical effects of 

anisotropy, discontinuities, material contrasts, environmental factors, fabric, and rheologic characteristics of 

geologic materials have been extensively studied (Handin 

and others, 1963; Donath, 1971; and Heard, 1968). However, very few attempts have been made to design field 

tests that demonstrate the applicability of laboratory conclusions. Notable tests are those by Swolfs and others 

(1974), and Lee and others (1976). The data from the 

Barre, Vt., experiments provide information as to how 

Discussion of Results 25 
Table 4. Young's moduli determined on cores of Barre 

Granite by sonic- pulse methods 

[leaders (--) indicate no data] 

Location of core 

Depth of 

Hole over- No. burden 

1 

1 

1 

1 

1 

1 

1 

1 

1 

2 

2 

2 

2 

2 

2 

2 

2 

2 

1H 

1H 

1H 

2H 

2H 

2H 

8 

8 

(m) 

0.55 

.55 

.55 

• 72 

.72 

• 72 

1.29 

1.29 

1.29 

1.53 

1.53 

1.53 

3.05 

3.05 

3.05 

5.34 

5.34 

5.34 

3.84 

3.84 

3.84 

67 

67 

67 

0 

0 

Core 

distance 

in hole 

(m) 

0.55 

• 55 

.55 

• 72 

.72 

• 72 

1.29 

1.29 

1.29 

1.53 

1.53 

1.53 

3.05 

3.05 

3.05 

5.34 

5.34 

5.34 

1.48 

1.48 

1.48 

1.53 

1.53 

1. 53 

Orientation of 

measurement 

Bearing Plunge 

N. 40° E. 

N. 50° W • 

N. 40° E. 

N. 50° W •

N. 40° E. 

N. 50° W. 

N. 40° E. 

N. 50° W. 

N. 40° E. 

N. 50° W. 

N. 40° E. 

N. 50° W. 

N. 40° E. 

N. 50° W. 

N. 40° E. 

N. 50° W. 

N. 40° E. 

N. 50° W. 

Young's 

modulus 

(X106 

psi) (GPa) 

5.16 

4.13 

4.62 

6.36 

3.70 

5.34 

3.79 

4.62 

35.6 

28.5 

31.9 

43.9 

25.5 

36.8 

26.1 

31.9 

6.96 48.0 

4.41 30.4 

5.53 38.1 

5.29 36.5 

4.38 30.2 

4.46 30.8 

5.08 35.0 

4.62 31.9 

5.25 36.2 

5.17 35.7 

4.51 31.1 

7.07 48.8 

3.86 26.6 

5.57 38.4 

6.79 46.8 

4.50 31.0 

geologic features can affect the measured in situ stress 

field. 

Fractures and Faults 

In the Barre Granite, fractures locally modify both 

measured stress magnitudes and orientations. The Wetmore and Morse quarry in which the USGS experiment 

was performed is dominated by low-angle sheeting fractures with some widely spaced tectonic fractures that have 

rotated into a nearly horizontal position in the vicinity 

of four measurements. Our measurements demonstrated 

that both sets affect the determined local stress field within and adjacent to the large lOX 10X5.7-m block. 

Most measurements affected by fractures were made 

near the dominant sub horizontal sheeting fractures. The 

effect of these fractures was to significantly relieve the 

vertical stress component and, to a lesser extent, to relieve 

the horizontal components. An excellent example of such 

relief is demonstrated by the stress determinations made 

under 67 m of overburden in horizontal hole 2H. Figure 

25 depicts the locations of these measurements with re26 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

spect to the logged low-angle fracture. The measured 

components of vertical stresses and the calculated gravity 

stresses are shown for each location. The vertical stress 

component close to the fracture has been greatly relieved 

and nearly equals the calculated gravity stress. The horizontal stress magnitudes in the direction of maximum confinement (N. 40° E.) show no relief at any of the three 

locations and remain nearly the same as those in the unquarried block (table 2) under only 3-5 m of overburden. 

Further, if a portion of the granite is totally separated on all sides, such as the quarried block, then nearly 

95-percent stress relief occurs in all directions. Most of 

this relief occurs almost instantaneously, but there are 

continued time-dependent deformations for several days. 

Evidence for Influence of Geologic History 

Possibly, the geologic history of a crystalline rock 

mass may contribute significantly to the present-day stress 

field in microscopic and macroscopic domains, especially 

those measured stress distributions that are difficult to explain by present-day applied tectonic or gravity forces. 

The measured vertical-stress components (if real), the 

IRON-STAINED 

FRACTURE 

J-._2.9 2.0 

g 

2.1 

14.1 

m 

10.5 

m 

Figure 25. Vertical section through hole 2H showing locations of overcores and a natural fracture. Vectors at 

each location show measured vertical stresses (m) and 

calculated gravity stresses (g) from table 2. Values are 

Megapascals. 
time-dependent response, the stress relief near fractures, 

and the release of strain perpendicular to the rift plane 

may be a response to stress fields created by past geological processes. There is fabric- and mechanical-behavior 

evidence that changes in elastic properties also may be 

caused by long-term relief of paleostress fields. 

The crystalline rocks listed herein have all undergone thermal changes as a result of burial, denudation, 

and tectonic forces. The Barre Granite has undergone significant brittle and ductile deformation as a result of intrusion and cooling, which is reflected in the rock fabric. 

Fabric 

As pointed out previously, the Barre Granite has 

a dominant microscopic fabric that includes strongly developed open microfractures within quartz grains in a 

nearly vertical planar trend striking about N. 30°-70° E. 

Strong macroscopic fabrics can be seen in the well developed but apparently different fracture systems of the 

upper and lower quarry areas (fig. 5). 

The microfracture fabric that pervades the Barre 

Granite in quarried areas may have been formed as a result of one or possibly two cooling stages within a deviatoric stress field that existed during the time of fracturing. Nur and Simmons (1970) attributed the development 

of microcracks to large shear stresses at grain boundaries 

caused by differential thermal strains upon the cooling of 

rock masses. Savage ( 1978) demonstrated that under a 

hydrostatic state of stress, tensile stresses on the order 

of 480 MPa are developed and stored in quartz grains 

(compared to compressive stresses of about 159 MPa in 

the feldspar grains) within an idealized granite by cooling 

the granite through 300°C. If stresses of this magnitude 

existed on a grain to grain basis within the Barre pluton, 

they are certainly sufficient to cause tensile failure and 

some relaxation in the quartz crystals. If a stress field, 

such as that required to create the northeast-trending fracture system (p. 12), is superposed on Savage's idealized 

hydrostatic cooling model, the tensile fractures in the 

quartz grains would have a strong preferred orientation. 

For instance, suppose that the pluton was still buried to 

a depth of 10 km and had cooled from about 500° to 

200°C, but was under an external stress field where a3 

was horizontal and approximately 75 MPa. The melting 

temperature of a water-saturated granite at a depth of 10 

km is about 700°C (Verhoogen and others, 1970, p. 278, 

658), and the Precambrian shield geotherm at the same 

depth is less than 200°C; therefore, the chosen cooling 

temperatures seem reasonable. In addition, the cooling 

time (Verhoogen and others, 1970, p. 588) for the size 

of the pluton ( 4-km diameter) appears to be less than 1 

million years, which also seems reasonable. At this depth, 

a 3 acting in the horizontal plane may be estimated to be 

that caused by the weight of overburden, 75 MPa, if the 

rock is considered to be elastic. The estimated a3 is calculated using the equation ah=( I~v) av, from elastic 

theory, letting Poisson's ratio v = 0. 25 and the vertical 

stress, av=225 MPa. Under these conditions the largest 

tensile stress component in the quartz resulting from the 

superposition of the cooling stresses would be about 405 

MPa, and microcracks could develop normal to this direction. If the rock adjusted through creep to a lithostatic 

stress condition prior to cooling and rr3 approached the 

vertical stress of 225 MPa, the resulting tensile stress 

component in the quartz would be 255 MPa, which is 

still sufficient for tensile failure. Effective stresses, based 

on hydrostatic pore pressures would allow even more tensile stress in the quartz. In support of this argument, 

quartz grains in thin sections are seen to have open tensile 

microcracks with a preferred orientation of approximately 

N. 40° E. (fig. 10). Bubble planes in quartz grains, evidence of healed microfractures oriented about N. 70° E., 

can be seen in the thin sections, indicating a possible rotation of the minimum principal paleostress axes of about 

30° in the horizontal plane. The bubble planes indicate 

that the granite has gone through at least one reheating 

event in which the oldest microfractures have been healed 

or annealed. The microscopic fabric of the Barre Granite 

is evidence that supports Savage's microscopic model as 

a viable one, allowing large thermally induced stresses 

to be stored on the very local grain-to-grain basis. 

On a much larger scale, macrofabric such as the 

vertical tectonic fractures in the upper quarries and the 

well-developed shear zones that dominate the lower quarries also illustrate the influence of past tectonic history. 

As previously discussed, a paleotectonic stress field with 

sufficiently large magnitude shear stresses to create these 

features probably was transmitted across the pluton during 

the cooling stages of the granite. In addition, a thermoelastic stress field caused by the cooling of the pluton 

was probably superposed and stored in the pluton. On 

this larger scale Savage (1978) also demonstrated that radial stresses may be stored uniformly across an ideal 

spherical pluton when cooled in a hydrostatic stress field. 

The magnitude of stresses he calculated for a pluton similar in composition to the Barre Granite, surrounded by 

metamorphic rocks, was 23.2 MPa in compression, which 

is somewhat larger than those measured in this experiment. 

Relief of the pluton through uplift and erosion has 

occurred only on the top surface which represents ~ very 

small fraction of the nearly totally confined volume of 

granite extending below the surface. Therefore, because 

of this limited relief, it is reasonable to believe that if 

cooling stresses of the magnitude calculated by Savage 

existed in the Barre Granite, the present-day measured 

stress field may be attributed to this phenomenon and the 

superposed present-day gravity stress field. 

Discussion of Results 27 
Mechanical Behavior Characteristics-Results of Quarrying 

Relief Characteristics 

The distribution of measured deformations away 

from fractures and free surfaces illustrates the manner in 

which stress in the Barre Granite becomes relieved at fracture surfaces. Note again that all of the vertical-stress determinations made less than 0.5 m from a sheet fracture 

agree with the calculated gravity stress curve, indicating 

that only the weight of the overlying rocks was measured. 

For those data taken more than 1 m from a sheet fracture, 

the interpreted vertical stresses increase at depth, becoming much greater than the calculated gravity stresses and 

somewhat greater than the horizontal stresses. If these 

stresses are not a result of erroneous interpretation resulting from inelastic deformations, it is possible that the 

stress field resulting from the cooling of the granite left 

its imprint. The fact that observed vertical deformations 

appear to increase significantly with depth and distance 

away from sheeting fractures, whereas horizontal deformations increase only slightly with depth and diminish only 

when very close to sheeting fractures, may be a function 

of vertical unloading of the combined thermoelastic and 

gravity stress field by erosion. The degree of horizontal 

unloading by erosional processes is considerably less than 

vertical unloading; thus, horizontal stresses have a much 

smaller gradient with depth. The smaller horizontal gradient is consistent with gravity loading in a rock mass 

that is laterally perfectly constrained, where the increase 

of horizontal gravity stress ( rrh) can be approximately related to the vertical gravity stress ( rr v by the relationship 

<Th =( I~v)rrv. If a uniform thermoelastic cooling stress 

(rrt) of unknown magnitude and gradient is superposed 

upon the gravity stress, then the relationship becomes 

rrh+rrth=( I~v)rrv+<Tth where <Tth is the horizontal component of the thermoelastic stress. The total horizontal stress 

becomes <Tii=C~v)rrv+<Tth and in the same manner the 

total vertical stress becomes rrv=rrv+<Ttv· Using calculated 

values of rrh and <Tv, estimated values of <Tth and <Ttv based 

on our data, and v=0.25 in the above relationship gives 

1. At 3-rn depth: crv=0.06 MPa, crh=0.02 MPa, O"tv=l.6 MPa, 

O"th=6.5 MPa. crh=6.52 MPa, crv=l.66 MPa 

2. At 67-m depth: crv= 1.5 MPa, crh=0.5 MPa, O"tv=crth=9.0 MPa, 

crh=9.5 MPa, crv=10.5 MPa 

These figures are close enough to the measured values to demonstrate that a large-volume thermoelastic stress 

field, relieved only near the surface and superposed on 

a gravity stress field, may be a reasonable explanation 

of the total stress field. 

In addition, stresses in the large block at Barre appeared to be completely relieved after quarrying, except 

for time-dependent deformations that continued over a 

period of 10 days after quarrying. Thus, the volume of 

28 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

the block is smaller than the rock volume subjected to 

the applied stress field indicating the existence of a largevolume viscoelastic paleostress field. 

The relief characteristics to a depth of 67 m suggest 

the possibility that a gravity stress field is superposed on 

a large-volume thermoelastic stress field. This superposition results in a vertical stress component much larger 

than gravity that increases significantly to 67 m compared 

to a horizontal component that may show only a small 

increase to this depth. At 67-m depth, the vertical component is larger than the horizontal component. A stress field 

of this nature may be supported by the geologic thermoelastic history of the pluton. 

Modulus 

Elastic theory predicts that in ideal materials stress 

is directly related to strain through the modulus. As discussed above, in the Barre Granite there are significant 

variations of modulus with depth and fabric anisotropy 

that can only be related to the measured stress levels in 

a general way. 

Young's modulus values have been computed from 

measurements made on various cores retrieved from core 

holes. Though no field measurements were made that 

could be used to adequately determine the in situ Young's 

modulus, the laboratory data obtained demonstrated that 

the rock moduli increased with sample depth and decreased with elapsed time since removal of the overburden. A decrease of rock modulus occurs as a result of 

erosion or excavation of the overburden and likely is a 

result of inelastic creep deformation caused by the opening of fractures and further enhanced by chemical weathering processes. 

As previously stated, the moduli increased with 

depth; also the orientations of maximum stiffness, parallel 

to the rift plane only at the surface, tended to change 

in a counterclockwise direction with depth. For stress 

measurements made below 3 m, the determined secondary 

major stress direction P was nearly parallel to the 

maximum modulus direction, whereas at the surface P 

was perpendicular to this direction. Geologic controls for 

the variation of maximum stiffness orientations with depth 

are not known, but should be investigated. It is possible 

that the directions and magnitudes of stiffness may vary 

merely as a function of changing preferential directions 

of microcrack opening as overburden loads are removed 

by erosion. This phenomenon was alluded to by Farrow 

(1973) when he demonstrated that a laboratory specimen 

of Mount Airy Granite, when repeatedly hydrostatically 

loaded to 34.5 MPa, changed the elastic principal strain 

orientations ~EJ, and aez, by approximately 90°, thereby 

implying an identical recoverable change in the stiffness 

directions. He interpreted these changes to be a result of 

differential micro fracture closure. 
Thus, the quarrying operations as well as natural 

erosional processes may have considerable effect on the 

stiffness variations within the rock mass at this location 

and therefore affect the measured state of stress. The dominant observed microcrack fabric appears to be a controlling factor only near the surface , where the removal of 

confinement has allowed the opening of these cracks. The 

unloading history of the granite then appears to be significant to the orientation as well as magnitude of the in 

situ stress field. 

SIGNIFICANCE OF BARRE DATA TO 

QUARRYING AND ENGINEERING PRACTICE 

In the Barre quarries, the quarrying conditions are 

less than ideal. In the vicinity of our experiment, commercial-grade rock is commonly lost, because it fails prior 

to or because of extraction (fig . 26). The incidence of 

failures increases with the depth of quarrying. 

The data from Barre contribute only in a general 

way to the understanding of these fa ilures and raise additional questions that remain unanswered. If the vertical 

stress gradient does increase with depth relative to the 

horizontal as the data indicate , then quarrying at increased 

depths would tend to greatly enhance vertical displacements on the quarry floor that give rise to sheet fractures. 

However, the fractures do not always develop instantaneously as overburden is stripped away, so the displacements causing failure often are time dependent, indicating 

a viscoelastic response or a time-dependent readjustment 

of the stress field . Disking of cores taken from the quarried lOX 10X5.7-m block, described on p. 38, is a fai lure 

of this nature. 

The other tensile failures on the corners and edges 

of partially quarried blocks also were time dependent and 

within a locally relieved portion of the rock. Deformation 

measurements were not made on these boundaries to determine displacements leading to failure, but other measured displacements on the side of the quarried block and 

on extracted core samples show comparatively large extensional strains for days after being relieved, indicating 

a viscoelastic response sufficient to cause tensile failure. 

The failures described here no doubt are affected 

by the quarry geometry. If the depth to width ratio (DIW) 

is relatively large and becomes increasingly large with 

depth of quarrying, the unusually high measured verticaldeformation gradient may continue to increase and cause 

significant damage to the quarry floor. Whereas, if D/W 

is kept relatively low , the vertical gradient could be partially relieved. This would mean the quarrying would have 

to be broadened as well as deepened. 

For engineering practice, the results presented herein may be of consequence to the design practices for large 

excavations. Useful design criteria to allow enhanced excavation stability and integrity of quarried blocks depend 

on obtaining reliable information of stress distribution, 

time-dependent rebound of the excavated rock, and rock 

temperature variations, as well as observations of failure 

modes. In addition, the data observed at Barre indicate 

the possibility of rock strength decreasing with time . Depending on the design life of the excavation, this factor 

may be important and should also be studied. 

Figure 26. Fractures at edges of partially freed granite 

blocks (A), and in bottom of quarry (8), Ba rre, Vt. 

Significance of Barre Data to Quarrying and Engineering Practice 29 
Finally, the deformation measurements may be most 

useful without attempting to determine the associated 

stress field. The interpreted stress magnitudes stated herein are questionable, whereas the deformation measurements used for the interpretation are judged to be of good 

quality. In order to make more reliable stress determinations, additional work must be done in evaluation of the 

degree of elastic versus inelastic response of rock masses 

when the in situ constraints are removed. 

CONCLUSIONS 

Shallow stress measurements in the Barre Granite 

of Vermont demonstrate that locally the determined stress 

distribution cannot be explained wholly by gravity or present-day tectonic loading. Tectonic forces may explain the 

horizontal loads, but past thermoelastic loads caused by 

cooling of rocks may possibly explain both the horizontal 

and excess vertical loads. The geologic history and associated thermoelastic stresses may explain the magnitudes and directions of stresses in geologic terranes such 

as the Barre Granite . Work done in the unloading of such 

a stress field by the removal of external loads results in 

viscoelastic recovery and the subsequent development of 

fractures resulting from extensional strains. On the other 

hand, it is quite possible that the interpreted stresses are 

in error because a significant component of the measured 

deformations are inelastic rather than elastic. In either 

case, unloading by natural erosional processes results in 

the formation of sheeting fractures, whereas unloading by 

quarrying results in the formation of extensional fractures 

on edges and free surfaces of the partially quarried granite 

outcrops. 

The viscoelastic responses can be critical to good 

quarrying procedure and to the stability of engineering 

excavations and installations, especially those that are designed for long-term use. Thus, it is very important to 

analyze in situ stress or strain fields and deformations resulting from the removal of rock masses in the crystalline 

terranes, in order to develop constitutive relations and failure criteria that can be used for design purposes. 

REFERENCES 

Balk, Robert, 1937, Structural ·behavior of igneous rocks: 

Geological Society of America Memoir 5, 177 p. 

Cady, W. M., 1960, Stratigraphic and geotechnic relationships 

in northern Vermont and southern Quebec: Geological Society of America Bulletin, v. 71, no . 5, p. 531-576. 

Chayes, Felix, 1952, The finer grained calc-alkaline granites of 

New England: Journal of Geology, v. 60, p. 207- 254. 

Currier, L. W., and Jahns, R. H., 1941 , Ordovician stratigraphy 

of central Vermont: Geological Society of America Bulletin , 

V . 52, p. 1487-1512. 

30 Rock Stresses and Engineering Geology, Barre Granite, Vermont 

Dale, T . N., 1909, The granites of Vermont: U.S . Geological 

Survey Bulletin 404 , 135 p. 

---1923, Commercial granites of New England: U.S . 

Geological Survey Bulletin 738, 488 p. 

Doll, C. G ., 1943, A Paleozoic revision in Vermont: American 

Journal of Science , v. 241, p . 57-64. 

---1951 , Geology of the Memphremagog quadrangle and 

the southeastern portion of the Irasburg quadrangle, Vermont: Vermont Geological Survey Bulletin 3, 113 p. 

Donath, F. A. , Faill, R. T. , and Tobin, D. G., 1971, Deformational mode fields in experimentally deformed rocks: 

Geological Society of America Bulletin, v. 82, no. 6, p. 

1441-1462. 

Durelli, A. J. , Obert, Leonard, and Parks, V. J., 1968, Stress 

required to initiate core discing: Society of Mining Engineers Transactions, v. 241 , p. 269-271 . 

Engelder, Terry, Sbar, M. L., and Kranz , Robert, 1977, A 

mechanism for strain relaxation of Barre Granite--Dpening 

of microfractures: Pure and Applied Geophysics, v. 115, 

p. 27---40. 

Farrow, R. A., 1973 , A new method for the determination of 

three-dimensional deformation anisotropy in rock specimens: 

U.S. Geological Survey Bulletin 1258-E, 12 p. 

Faul , Henry, Stern , T . W., Thomas, H. H., and Elmore, P. 

L. D., 1963 , Ages of intrusion and metamorphism in the 

northern Appalachians: American Journal of Science, v. 

261' p. l-19. 

Finlay, G. 1. , 1902, The granite area of Barre, Vermont: Vermont State Geologist, 3d Report, p. 46-59. 

Handin, John, Hager, R. V., Jr., Friedman, Melvin, and 

Feather, J. N. , 1963, Experimental deformation of sedimentary rocks under confining pressure-Pore pressure tests: 

American Association of Petroleum Geologists Bulletin, v. 

47 , no. 5, p. 717- 755. 

Heard, H. C., 1968, Experimental deformation of rocks and 

the problem of extrapolation to nature, in Riecker, R. E., 

NSF Advanced Seminar in Rock Mechanics: Boston College, v . 2, p. 439- 508. 

Hooker, V. E., and Bickel, D. L., 1974, Overcoring equipment 

and techniques: U.S . Bureau of Mines Progress Report 

DMRC 10002, 29 p. 

Hooker, V. E. , Bickel, D. L. , and Aggson, J. R., 1972, In 

situ determination of stresses in mountainous topography: 

U.S. Bureau of Mines Report of Investigations 7654, 19 

p. 

Hooker, V. E., and Duvall, W. 1., 1971, In situ rock temperature stress investigations in rock quarries: U.S. Bureau of 

Mines Report of Investigations 7589, 12 p. 

Hooker, V. E., and Johnson , C. F. , 1969, Near-surface horizontal stresses including the effects of rock anisotropy: U.S. 

Bureau of Mines Report of Investigations 7224, 29 p . 

Lee, F. T., Abel , J. F., Jr., and Nichols, T . C. , Jr., 1976, 

Stress changes caused by excavation, Idaho Springs, Colorado: U.S. Geological Survey Professional Paper 965, 4 7 

p. 

Murthy, V. R., 1957 , Bedrock geology of the East Barre area, 

Vermont: Vermont Geological Survey Bulletin 10, 121 p. 

Naylor, R. S., 1971 , Acadian orogeny- an abrupt and brief 

event: Science, v. 172, no . 3983, p. 558-560. 
Nichols, T. C., Jr., 1975, Deformations associated with relaxation of residual stresses in a sample of Barre Granite from 

Vermont: U.S. Geological Survey Professional Paper 875, 

32 p. 

---1980, The state of stress in the Barre Granite of Vermont, and other near-surface rocks of North AmericaPaleo and present-day stress fields and the significance to 

engineering practice: Boulder, Colorado, University of Colorado, Ph . D. thesis, 196 p. 

Nichols, T. C., Jr., and Savage, W. Z. , 1976, Rock strain recovery; factor in foundation design: in Rock engineering for 

foundations and slopes; Proceedings of a specialty conference, American Society of Civil Engineers, New York, N. 

Y., v. I (Anonymous), p. 34-50. 

Nichols, T. C., Jr., Savage, W. Z., and Brethauer, G. E., 1977 , 

Deformations and stress changes that result from quarrying 

the Barre Granite of Vermont, in Energy and mineral resource recovery, ANS Topical Meeting , Golden, Colorado, 

1977: U.S. Department of Energy , p. 791 - 803 . 

Nur, Amos, and Simmons, Gene, 1970, The origin of small 

cracks in igneous rocks: International Journal of Rock 

Mechanics and Mining Sciences, v. 7, no . 3, p. 307-315 . 

Savage, W . Z. , 1978, The development of residual stress in 

cooling rock bodies: Geophysical Research Letters, v. 5, 

no. 8, p. 633-636. 

---1979, A model of the strain response of Barre Granite 

to wetting and drying: U.S. Geological Survey Open-File 

Report 79-768 , 17 p . 

Shelton, K. L., and Orville, P.M ., 1980, Formation of synthetic fluid inclusions in natural quartz: American Mineralogist, 

v. 65, nos. 11 and 12, p. 1233- 1236. 

Simmons, Gene , and Richter, Dorothy , 1976, Microcracks in 

rocks, in Strens, R. G . J. , The physics and chemistry of 

minerals and rocks: New York, Wiley-Interscience, p. 105-

137 . 

Sokolnikoff, I. S., 1956, Mathematical theory of elasticity: New 

York, McGraw-Hill, 476 p. 

Swolfs, H. S., 1976, Field investigation of strain relaxation and 

sonic velocities in Barre Granite, Barre, Vermont: Terratek 

Final Report TR 76-13 , 13 p. 

Swolfs, H. S ., Handin , J., and Pratt, H. R., 1974, Field measurements of residual strain in granitic rock masses: International Society of Rock Mechanics Congress, 3d, Denver, 

Colorado, Proceedings, v. 2, pt. A, p. 563-568 . 

Thill , R. E., Bur, T. R., and Steckley, R. C., 1973, Velocity 

anisotropy in dry and saturated rock spheres and its relation 

to rock fabric: International Journal of Rock Mechanics and 

Mining Sciences, v. 10, no . 6, p. 535-558 . 

Tullis, Jan , and Yund, R. A. , 1977, Deformation behavior of 

quartz and feldspar in experimentally deformed granite: 

Journal of Geophysical Research , v. 28, p. 5705-5718. 

Verhoogen, John , Turner, F. J., Weiss, L. E., and Wahrhaftig, 

Clyde, 1970, The earth, an introduction to physical geology: 

San Francisco, Holt, Rinehart, and Winston, 748 p. 

White, W . S., and Jahns, R. H., 1950, Structure of central 

and east-central Vermont: Journal of Geology, v. 58, no . 

3,p. 179- 220 . 

Willard, R. J., and McWilliams, J. R., 1969, Microstructural 

techniques in the study of physical properties of rock: International Journal of Rock Mechanics and Mining Sciences, 

V. 6, p. J-J2. 

Zartman, R. E., Hurley, P. M., Krueger, H. W., and Giletti, 

B. J. , 1970, A Permian disturbance of K-Ar radiometric 

ages in New England- its occurrence and cause: Geological 

Society of America Bulletin, v. 81, no . II, p. 3359-3374. 

t? u .S. GOVERNMENT PRINTING OFF ICE:1986-676-047/26029 

References 31