lithological, Geotechnical Properties Analysis, 

and Geophysical log Interpretation of 

U.S. Geological Survey Drill Holes 

1C-79, 2C-80, CW 81-2, and CE 82-1, 

Tyonek Formation, 

Upper Cook Inlet Region, Alaska 

Prepared in cooperation with the State of Alaska 

Department of Natural Resources 

Lithological, Geotechnical Properties Analysis, 

and Geophysical Log Interpretation of 

U.S. Geological Survey Drill Holes 

1 C-79, 2C-80, CW 81-2, and CE 82-1, 

Tyonek Formation, 

Upper Cook Inlet Region, Alaska 

By JACK K. ODUM, LYNN A. YEHLE, HENRY R. SCHMOLL, 

CYNTHIA A. GARDNER, and LARRY L. DEARBORN 

Prepared in cooperation with the 

State of Alaska Department of Natural Resources 

U.S. GEOLOGICAL SURVEY BULLETIN 1835 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1988 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center 

Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Lithological, geotechnical properties analysis, and geophysical log interpretation 

of U.S. Geological Survey drill holes IC-79, 2C-80, CW 81-2, and CE 82-1, 

Tyonek Formation, Upper Cook Inlet region, Alaska. 

(U.S. Geological Survey bulletin; 1835) 

"Prepared in cooperation with the State of Alaska Department of Natural 

Resources." 

Bibliography: p. 

1. Geology, Stratigraphic-Miocene. 2. Geology, StratigraphicOligocene. 3. Geology-Alaska-Cook Inlet Region. 4. Borings-AlaskaCook Inlet Region. 5. Tyonek Formation (Alaska) I. Odum, Jack K. 

II. Alaska. Dept. of Natural Resources. Ill. Series. 

QE694.L58 1988 551.7'85'097983 87-600451 
CONTENTS 

Abstract 1 

Introduction 1 

Acknowledgments 2 

Drill hole location 2 

Field and laboratory procedures 3 

Geologic setting 3 

Physiography and surficial geology 3 

Tertiary bedrock 4 

Lithologic description of cored strata of the Tyonek Formation 4 

Depositional environment model 4 

Lithologic distribution 6 

Geotechnical results and interpretation 6 

Durability 6 

Slake-durability-index test 7 

Sandstone units 8 

Strength 10 

Point-load-strength test 10 

Laboratory unconfined compressive strength 12 

Grain, natural bulk, and dry bulk density 15 

Grain-size distribution, Atterberg limits, and activity index 15 

Clay mineralogy 16 

Geochemical analysis 16 

Ultrasonic compressional- and shear-wave velocity 17 

Compressional-wave velocity 20 

Shear-wave velocity 20 

Dynamic Poisson's ratio and elastic moduli 21 

Geophysical logging and ground water 22 

Capps coal field 22 

Drill hole USGS 1 C-79 22 

Drill hole USGS 2C-80 23 

Chuitna coal field 23 

Drill hole USGS CW 81-2 23 

Drill hole USGS CE 82-1 24 

Conclusions 25 

References cited 25 

Contents Ill 
FIGURES 

1. Index map showing the location of four U.S. Geological Survey drill holes 

in the Capps and Chuitna coal fields 2 

2. Generalized surficial geologic map of Beluga plateau and vicinity 5 

3. Depositional environment model of the Tyonek Formation 6 

4. Photograph of Susitna River mouth and lower Susitna Flats area of the upper Cook Inlet region 7 

5. Generalized stratigraphic columns for drill holes USGS 1C-79, 2C-80, CW 

81-2, and CE 82-1 9 

6. Histograms showing the overall trend of lithologic character of Capps and 

Chuitna coal fields 10 

7. Graph comparing the distribution of slake-durability-index values, by 

lithology, of the Capps and Chuitna coal fields 11 

8. Point-load-strength-index values of specific lithologies, arranged by descending stratigraphic order 13 

9. Comparison of the range and mean values of point-load-strength index by 

lithology 14 

10. Lithologic comparison of laboratory-derived unconfined-compressivestrength values 15 

11. Range of "qualitative hardness terms" associated with lithologies of the 

Tyonek Formation 17 

12. Distribution of ultrasonic compressional- and shear-wave velocity values for 

Chuitna coal field core samples 20 

13. Compressional-wave velocities and estimated dozing, ripping, and blasting 

capabilities of various rock types 22 

TABLES 

1. Strata characteristics by lithology for each drill hole 8 

2. Ranges and means of slake-durability-index values 11 

3. Ranges and means of approximate unconfined-compressive strength derived 

from axial and diametral point-load tests without respect to coal field 14 

4. Ranges and means of laboratory unconfined-compressive-strength test data 

based on a composite of all samples from the Capps and Chuitna coal 

fields 16 

5. Relative abundance of clay-mineral groups for all four drill holes 18 

6. Ranges and means of compressional- and shear-wave velocity for specific 

lithologies from drill holes in the Chuitna coal field 21 

7. Average ultrasonic velocities, bulk densities, and calculated Poisson's ratio 

and dynamic elastic moduli for the Tyonek Formation 23 

IV Contents 
CONVERSION FACTORS 

For readers who wish to convert measurements from the metric system of units to U.S. customary 

units, the conversion factors are listed below. 

millimeter (mm) 

centimeter (em) 

meter (m) 

kilometer (km) 

Metric unit 

square centimeter (cm2

) 

gram (g) 

meganewton per square meter (MN/m2). 

megapascal (MPa) 

Multiply by 

0.03937 

0.3937 

3.281 

0.6214 

0.1550 

0.035 

145 

145 

To obtain U.S. customary unit 

inch (in.) 

inch (in.) 

foot (ft) 

mile (mi) 

square inch (in. 2

) 

ounce (oz) 

pounds per square inch (psi) 

pounds per square inch (psi) 

Contents V 

Lithological, Geotechnical Properties Analysis, 

and Geophysical Log Interpretation of 

U.S. Geological Survey Drill Holes 

1C-79, 2C-80, CW 81-2, and CE 82-1, 

Tyonek Formation, 

Upper Cook Inlet Region, Alaska 

By Jack K. Odum, Lynn A. Yehle, Henry R. Schmoll, 

Cynthia A. Gardner, and Larry L. Dearborn 1 

Abstract 

The Tyonek Formation of early Oligocene through middle Miocene age is composed of nonmarine sequences of sandstone, siltstone, claystone, carbonaceous claystone, and 

subbituminous coal and lignite, all probably deposited in a 

poorly drained alluvial basin environment. Four continuously 

cored drill holes penetrated this coal-bearing formation to obtain lithologic, geotechnical, and geophysical information that 

would be useful in evaluating the stability of natural and manmade slopes, ground response to seismic activity, blasting effects, equipment selection for excavation, ground-water 

conditions, and erosion and weathering potential of both spoil 

piles and in-situ geologic materials. Drill holes USGS 1 C-79 

(121 m deep) and USGS 2C-80 (61 m deep) were drilled in 

the Capps coal field, approximately 100 km west northwest of 

Anchorage, Alaska. Drill holes CW 81-2 (1 02 m deep) and CE 

82-1 (115 m deep) were drilled in the Chuitna coal field, approximately 80 km west of Anchorage. Analyses of lithologic 

abundances and stratigraphic unit characteristics indicate that 

the Capps coal field strata are probably representative of a basin 

margin setting, whereas the Chuitna coal field strata were 

deposited in a more midbasin position, that is, in an environment of finer grained sediments. 

Test-result ranges of slake-durability index, point-loadstrength index, laboratory unconfined compressive strength, 

and ultrasonic velocities differ widely for specific lithologies. 

However, on the basis of computed means, lithologies within 

a drill hole or coal field area can be arranged in the following 

order of increasing strength and durability: noncemented and 

weakly lithified sandstone, siltstone, claystone, carbonaceous 

claystone, and coal. An arrangement of lithologies into three 

groups is probably more realistic. The noncemented and weakly lithified sandstone, in most cases, can be considered to 

1

State of Alaska Department of Natural Resources. 

have almost zero unconfined compressive strength and 

durability. Siltstone, claystone, and carbonaceous claystone all 

have low-to-moderate strength and durability depending on 

clay-particle content and size, orientation, and quantity of 

micaceous and carbonaceous lamina and stringers. Coal units 

have unconfined strengths of at least twice those of the other, 

fine-grained lithologies. Local carbonate-cemented sandstone 

lenses have unconfined compressive strengths much higher 

than coal . However, these lenses are rare in occurrence and 

are not generally included in comparison discussions of the 

other major lithologies. Overall, the strength classification in 

terms of hardness for the majority of the lithologies of the 

Tyonek Formation is from stiff soil to soft rock. 

INTRODUCTION 

This report summarizes the results of field and 

laboratory measurements on core from drill holes USGS 

1C-79, 2C-80, CW 81-2, and CE 82-1, located in the 

upper Cook Inlet region of south-central Alaska (fig. 1). 

The general objective of the Energy Lands Program in 

Alaska, of which this study is a part, is to provide information that would lead to a better understanding of the 

nature and extent of the engineering and environmental 

geology concerns in areas of potential coal and other 

development in the Beluga resource area of the upper 

Cook Inlet region, Alaska. This report contains 

lithologic, geotechnical, and geophysical information that 

is needed to evaluate and predict the response of the coalbearing Tyonek Formation to large-scale mining and 

related development in the Capps and Chuitna coal fields. 

Specifically, the information may be used to evaluate the 

stability of natural and manmade cut slopes, ground 

response to seismic activity, blasting effects, equipment 

Introduction 
EXPLANATION 

Margin of mountains and hills underlain 

hy pre-Tertiary metamorphic and 

igneous rocks (patterned areal 

-.--. Margin of plateau underlain by sedimentary rocks 

of Tertiary age-licks on side of plateau 

E Snow and ice field 

• U.S. Geological Survey drill hole 

Figure 1. Index map showing the location of the four U.S. Geological Survey drill holes in the Capps and Chuitna coal fields, 

in the upper Cook Inlet region, Alaska. 

selection for excavation, ground-water conditions, and 

erosion and weathering potential of spoil piles and insitu geologic materials. 

Acknowledgments 

Thanks are given to the many individuals and 

organizations that provided help toward our efforts to 

gather data on the geologic units of the Tyonek Formation. Drilling and sample recovery was accomplished by 

Exploration Supply and Equipment Co., Anchorage, 

Alaska. Beluga Coal Co. of Placer U.S., Inc., San Francisco, Calif., and Diamond (Shamrock) Alaska Coal Co., 

Anchorage, provided geologic field data. Field assistance 

and sample analysis and testing were provided by the U.S. 

Geological Survey, Denver, Colo. Special thanks are 

given to A.D. Pasch, Anchorage Community College, 

Anchorage, and B.A. Carpenter, formerly of the Alaska 

Division of Geological and Geophysical Surveys, Anchorage, for well-timed geologic help in the field. 

DRILL HOLE LOCATION 

Two principal coal fields are present west of Anchorage, Alaska (fig. 1): The Capps field is approximately 100 km to the west-northwest of Anchorage, and the 

Chuitna field is 80 km to the west. In the Capps field, 

two holes were drilled. Drill hole USGS 1 C-79, which 

is 121 m deep, is situated on a relatively flat upland surface (fig. 1). The site, located at NEY4 sec. 23, T. 14 N., 

R. 14 W., Tyonek B-5 quadrangle, Alaska, is approximately 100 km west of Anchorage and 38 km northwest 

of Cook Inlet (fig.1). Drill hole USGS 2C-80, which is 

61 m deep, is located at NEY4 sec. 26, T. 14 N., R. 14 

W., Tyonek B-5 quadrangle, Alaska, approximately 

1.3 km southwest of drill hole USGS 1C-79. Stratigraphic 

correlation of the Waterfall coal bed between both drill 

holes indicates that the lower two-thirds of drill hole 

USGS 2C-80 lies stratigraphically below the bottom of 

hole USGS 1 C-79. Core from both holes is believed to 

be representative of the lower part of the Tyonek Formation of early Oligocene through middle Miocene age 

2 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
(Wolfe and Tanai, 1980). Preliminary lithologic observations, field-test data, and geophysical log interpretation for these two drill holes were reported by Chleborad 

and others (1980, 1982). Detailed litl:wlogic logs and the 

results of field and laboratory geotel:hnical te~ts for these 

two drill holes were reported by Odum (1986). 

Two holes were also drilled in the Chuitna coal 

field. Drill hole USGS CW 81-2, which is 102m deep, 

is situated on the edge of a smal1, gently sloping basin 

that drains northwestward into the Chuitna River. The 

site is located on the west side of the Chuitna River at 

SEV4NWV4 sec. 33, T. 13 N., R. 13 W., Tyonek A-5 

quadrangle, Alaska, approximately 90 km west of 

Anchorage. Drill hole USGS CE 82-1, which is 115 m 

deep, is situated on a north-trending interfluve between 

branches of a tributary to Chuit Creek, about 5.6 km 

north of its confluence with the Chuitna River. The site, 

located at SWV4SWV4 sec. 24, T. 13 N., R. 13 W., 

Tyonek A-5 quadrangle, Alaska, is approximately 

104 km west of Anchorage and 29.7 km northwest of 

Tyonek, a native village on the northwest side of Cook 

Inlet (fig. 1). Strata from these two holes are believed to 

be representative of probably the middle to upper part 

of the Tyonek Formation. However, because of local 

faulting, folding, and limited surface exposures in the 

area, the exact stratigraphic relationship between the two 

holes is not certain. The Chuitna coal bed of Barnes 

(1966), which crops out for 13.7 km along the Chuitna 

River canyon, is correlated with the stratigraphically 

highest coal bed in the Pan American well (Calderwood 

and Fackler, 1972; fig. 1) and is also considered to correspond with the named brown coal bed in the Chuitna 

coal field, east of the Chuitna River, in the terminology 

of Ramsey (1981). Five other coal beds have been 

recognized beneath the brown coal bed, and in stratigraphically descending order, they are: the yellow, green, 

blue, orange, and red coal beds (Ramsey, 1981). This 

report refers to the two major coal beds in drill hole 

USGS CE 82-1, as the upper and lower beds, which may 

correlate (B.J.G. Patch, Placer U.S., Inc., San Francisco, 

Calif., written commun., 1981) with the green and blue 

coal beds, respectively, of Ramsey (1981). Coal bed terminology ("M", "0", and "Q") used in stratigraphy 

in drill hole USGS CW 81-2 (fig. 5C) is adapted from 

B.J.G. Patch, Placer U.S., Inc., San Francisco, Calif. 

(written commun., 1981). Preliminary field-test data and 

geophysical log interpretation for drill holes USGS CW 

81-2 and USGS CE 82-1 were reported by Odum and 

others (1983, 1986). Detailed lithologic logs and the 

results of field and laboratory geotechnical tests for these 

two drill holes were reported by Odum (1986). 

FIELD AND LABORATORY PROCEDURES 

All four drill holes were continuously cored using 

an HQ-sized rotary-wireline core system (6.35-cm-core 

diameter). The core was retrieved, logged, and preserved 

as follows: Core contained in the split-barrel samplers was 

transferred at the drill rig to the logging team. Drilling 

information, such as drilling rate, depths of core intervals, percent of recovery, nature of drilling fluids, and 

hydrologic conditions, was recorded. 

The core was photographed on color film using 

both instantaneous-development and 35-mm single-lens 

reflex cameras. Included in each photograph was a card 

identifying the core-run number, depth interval, and an 

appropriate page from the rock-color chart of Goddard 

and others (1970) for color comparison and identification. Information on discontinuities, color, laminations, 

hardness, and degree of weathering was recorded. 

Point-load-strength-index and moisture-content 

measurements were performed on selected samples to provide a base of field data to compare with subsequent 

laboratory tests. To test "soft" samples having unconfined compressive strengths of less than 0.44 MPa, a 

pocket-penetrometer strength tester (Soiltest, Inc., 1978) 

was used. For material of greater strength, a point-load 

tester was used following the procedures described by 

Brock and Franklin (1972) and the ISRM (1972a). The 

presence of carbonate cement was determined by applying diluted (15 percent) hydrochloric acid to the core at 

selected intervals. 

Untested core was wrapped in cheesecloth, labeled, 

coated with polycrystalline wax, and placed in cardboard 

boxes that were padded with split styrene inserts to 

minimize disturbance during transport to the U.S. 

Geological Survey Engineering Geology laboratory, 

Golden, Colo. To avoid hydrocarbon contamination, 

core samples containing coal strata were not waxed, but 

sealed in plastic sleeves. 

Soon after the completion of drilling, continuous 

natural gamma radiation, gamma-gamma radiation, 

neutron radiation, hole diameter, spontaneous potential, 

single-point resistance, and temperature measurements 

were obtained. Logging procedures followed the techniques described by Keys and MacCary (1971). 

Upon arrival at the U.S. Geological Survey laboratory, the core samples were stored in a controlled highhumidity environment. Samples selected for geotechnical 

and physical properties testing were prepared and tested 

according to the American Standards for Testing and 

Materials (ASTM) procedures. Index tests were performed according to the procedures developed by the 

originating authors. Previously published field pointload-strength-index and moisture-content values, along 

with new laboratory data, are presented in the various 

figures and tables in this report. 

GEOLOGIC SETTING 

Physiography and Surficial Geology 

The Capps and Chuitna coal fields are situated on 

the Beluga plateau (Schmoll and Yehle, 1978; fig. 1), 

Geologic Setting 3 
which is one of the higher lying physiographic subdivisions of upper Cook Inlet basin and is characterized by 

a relatively thin cover of Quaternary deposits. The 

Quaternary deposits are mainly glacial in origin and 

Pleistocene in age and overlie Tertiary bedrock (Schmoll 

and others, 1984). The eastern and southwestern borders 

of the plateau are marked by prominent escarpments that 

descend to the Susitna lowland and the ChakachatnaMcArthur embayment, respectively; in these low-lying 

areas the Tertiary rocks are buried more deeply by 

Pleistocene and Holocene deposits that are mainly of 

, estuarine origin. The Beluga plateau rises gently in elevation from 50-m-high coastal bluffs that border Cook Inlet along its southern margin to elevations of about 

1 ,000 m to the northwest at the margin of the Tordrillo 

Mountains which rise abruptly to peaks as high as 4,000 

m. Lower hills and mountains, including Mount Susitna 

and Beluga Mountain, interrupt the continuity of the 

plateau and rise to elevations of about 500 m. 

The glacial deposits that cover the Beluga plateau 

have been mapped by Yehle, Schmoll, and Chleborad 

(1983a, b), Yehle, Schmoll, and Gardner (1983), and 

Schmoll and Yehle (1987). Deposits have been subdivided 

mainly on the basis of a series of prominent end and 

lateral moraines that were deposited in a complex, interwoven pattern by glaciers of different ages and sources 

(Schmoll and Yehle, 1986). The positions of these moraines, as well as major areas of other surficial deposits, 

are shown with respect to the locations of the four drill 

holes on figure 2. The end and lateral moraines are characterized by variably hummocky terrain and generally 

thicker deposits of glacial diamicton (till), whereas the 

areas of ground moraine are more gently rolling to nearly flat and have thinner glacial diamicton. Outwash channels and plains, which are commonly covered by gravel 

that may be only a thin veneer and are generally too small 

to show at the scale of figure 2, are found within and adjacent to the margins of most of the moraines. 

Numerous landslide deposits occur within and on 

the escarpments that border the plateau, but only the largest of these deposits are shown on figure 2. Other surficial deposits include a variety of volcaniclastic debris 

flows. 

The plateau is drained principally by the Beluga and 

Chuitna Rivers and their tributaries, which are incised 

15-75 m beneath the plateau surface and flow in narrow, 

steep-walled valleys. Most of the valley walls are thinly 

veneered by colluvium that conceals the Tertiary bedrock 

in many places, but exposures of bedrock are common 

along the major river-valley walls and are present locally 

in the valley bottoms where Holocene alluvium on low 

terraces is generally thin. 

Tertiary Bedrock 

The Tertiary sedimentary rocks of the upper 

Cook Inlet basin are continental in origin and comprise 

forearc-basin deposits of both early and late Cenozoic 

tectonic cycles (Fisher and Magoon, 1978). Surface exposures in the Beluga area were described in detail by 

Barnes (1966), whose work emphasized the coal deposits. 

The Tertiary rocks throughout the basin had been collectively called the Kenai Formation, primarily on the 

basis of subsurface data that were compiled during exploration for oil and gas. The Kenai Formation was later 

raised to group rank and divided into five formations 

(Calderwood and Fackler, 1972). In ascending order, 

these formations are the West Foreland, Hemlock, 

Tyonek, Beluga, and Sterling. Subsequently, the West 

Foreland Formation was excluded from the Kenai Group 

by Magoon and others (1976). 

The Tyonek Formation underlies the area of the 

Capps coal field, as well as most of the Beluga area to 

the southeast. It is early Oligocene through middle 

Miocene in age; outcrops near Capps Glacier and along 

the Chuitna River serve as the type section for the Seldovian Stage (Wolfe and others, 1966; Wolfe, 1977). The 

type section of the formation, in a well south of Tyonek 

village, is 2,331 m thick and includes at least 15 thick coal 

bed sequences (Calderwood and Fackler, 1972). Only a 

small part of the formation is exposed, including two 

principle coal beds, and the stratigraphic thickness of 

these exposed beds is not well known (Schmoll and others, 

1981). Strata exposed in the Chuitna River area are believed to belong to the upper part of the Tyonek Formation; this interpretation is supported by a published 

radiometric age of about 15.8 Ma from a volcanic ash 

that was taken from one of the coal beds along the 

Chuitna River (Turner and others, 1980, p. 95). 

LITHOLOGIC DESCRIPTION OF CORED STRATA 

OF THE TYONEK FORMATION 

Depositional Environment Model 

The Tyonek Formation is composed of nonmarine 

units of sandstone, siltstone, claystone, carbonaceous 

claystone, and subbituminous coal and lignite, all probably deposited in a poorly drained, alluvial-basin environment. Hite's (1976) depositional model (fig. 3) depicts 

a basin ward merging of coarse-grained alluvial fans that 

were situated along tectonically active basin margins, with 

finer grained alluvial and flood-plain deposits near the 

center of the basin. Excellent settings for peat accumulation are found in flood plains: sag ponds along faults, 

sloughs and abandoned channels, and poorly drained 

regions between coalescing fans (Hite, 1976). 

The Capps coal field is situated near the margin of 

what Hackett (1977) termed the Beluga basin, whereas 

the Chuitna coal field is located in what is thought to be 

a more midbasin position, that is, in an environment of 

finer grained sediments. Figure 4, a photograph of the 

4 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
!:': 

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s. 

l""l 

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s. 

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EXPLANATION 

MORAINAL DEPOSITS 

8 Younger moraines 

~ Chichantna moraines 

D Denslow Lake moraines 

B Seven-thirty lake moraines 

~ ~ Eight-ten lake moraines 

tm Nikolai moraines 

~ Nikolai kame field 

B Fou rteen-o-live lake moraines 

Q Threemile Creek moraines 

• Blueberry Hill moraines 

~ Upper Chuitna moraines LW.±J 

a Pre-(?) upper Chuitna moraines 

B Older moraines, undifferentiated 

5 0 5 10 Kilometers 

Figure 2. Generalized surficial geologic map of the Beluga plateau and vicinity, upper Cook Inlet region, Alaska. 

ALLUVIAL DEPOSITS 

L2IJ 

Younger alluvium 

(Holocene) 

Older alluvium 

(Pleistocene) 

ESTUARINE DEPOSITS 

-

II 

Younger estuarine deposits 

(Holocene) 

Older estuarine deposits 

(Pleistocene) 

COLLUVIAL DEPOSITS 

~ Colluvium, undifferentiated 

~ Major landslides 

OTHER DEPOSITS 

[2] Bedrock 

-

LJ Volcaniclastic deposits 

~~ Glaciers and snow fields 

DRILL HOLE LOCATION 

0 USGS 1 C-79 

® USGS 2C-80 

0 USGS CW 81-2 

0 USGS CE 82-1 
~~ 

~~ 

~ 

LEGEND 

PLAN VIEW 

~Fan 

..,, 

t"'\ Swamp 

.:t.. Poorly drained alluvial plain 

CROSS-SECTION VIEW 

~~ Fan deposit 

~ Alluvial channel deposit 

..., Coal 

Figure 3. Depositional environment model of the Tyonek Formation showing a poorly drained alluvial basin (Hite, 1976). 

Susitna River mouth and lower Susitna Flats area of the 

upper Cook Inlet region, shows a modern example of 

such an environment with modern and older Susitna 

alluvium and intertidal areas. 

Lithologic Distribution 

Detailed lithologic logs of each drill hole, along with 

physical properties and geotechnical data, were presented 

by Odum (1986). Thin accumulations of organic material 

and volcanic ashbeds that total less than one meter in 

thickness are directly beneath the ground surface. 

Underlying these surficial deposits are diamictons 

(presumably of glacial origin and of Quaternary age), 

which in turn, overlie the Tyonek Formation. 

Figures SA-D are generalized stratigraphic columns 

of USGS drill holes: Capps coal field, (A) 1C-79 and (B) 

2C-80; and Chuitna coal field, (C) CW 81-2 and (D) CE 

82-1. Histograms that accompany the generalized 

lithologic logs of figures SA-D indicate the abundance, 

expressed as a percentage of the total cored-hole depth, 

of each major lithology within the drill hole. Table 1 lists 

the lithologic unit characteristics (thinnest, thickest, 

average thickness, and relative abundance for major 

lithologies) for the four drill holes. 

Figure 6 summarizes information on the abundance 

of each major lithology that was cored in the the two coal 

fields. Arrows on the right side of the figure indicate 

whether the abundance of a lithology is greater in the 

Capps field (arrow pointing downward) or in the Chuitna 

field (arrow pointing upward). Table 1 also indicates that 

the maximum thicknesses of the finer grained lithologies 

are greater in the Chuitna area than in the Capps area. 

These differences in lithologic abundance between the two 

areas probably reflect the more basin ward location of the 

Chuitna area with respect to the basin-margin location 

of the Capps area. It may also reflect a basin-wide change 

in depositional energy, such as a slowing of margin uplift 

and (or) basin subsidence during early and middle 

Miocene time (Kirschner and Lyon, 1973). 

GEOTECHNICAL RESULTS 

AND INTERPRETATION 

Durability 

Durability, with respect to geologic materials, is 

defined as the resistance of material to weathering and 

disintegration over time. The slake-durability-index test 

provides a means of estimating the deterioration potential of a geologic material to climatic wetting and drying 

(Franklin and Chandra, 1972). These index tests are used 

6 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
Figure 4. Photograph of Susitna River mouth and lower Susitna Flats area of the upper Cook Inlet region, showing a modern example of a poorly drained alluvial-basin environment. 

here to compare lithologies in different localities as well 

as to determine engineering weatherability. 

Slake-Durability-Index Test 

In this paper, slake-durability-index test results are 

reported in percent of the total sample weight that remains after two cycles of testing. A test cycle consists of: 

(1) Drying and weighing ten roughly spherical specimens 

with initial individual sample weights between 40 and 

60 g, (2) tumbling the specimens in a mesh cage with 

2-mm openings while partially submerged in a water tank 

for ten minutes, and (3) drying and reweighing the 

specimen material that remains in the cage. The index is 

calculated by dividing the weight of the remaining 

material by the original sample weight times 100 (ISRM, 

1972b). A high slake-durability-index percentage indicates 

that the material has a relatively high resistance to 

disintegration due to climatic wetting and drying. 

Slake-durability-index tests were performed 

Geotechnical Results and Interpretation 7 · 
Table 1. Strata characteristics by lithology for each drill hole 

[ --- indicates information not available; n.a. indicates not applicable] 

Lithology Thickest 

unit 

(m) 

Thinnest 

unit 

(m) 

CAPPS COAL FIELD: USGS 1C-79 

Diamicton •••••• 

Sandstone •••••• 

Siltstone •••••• 

Claystone •••••• 

Carbonaceous ••• 

claystone. 

Coal ••••••••••• 

9.5 

55.2 

1.6 

8.5 

1.4 

7.6 

0.1 

0.1 

0.2 

0.1 

0.2 

CAPPS COAL FIELD: USGS 2C-80 

Diamicton •••••• 

Sandstone •••••• 

Siltstone •••••• 

Claystone •••••• 

Carbonaceous ••• 

claystone. 

Coal ••••••••••• 

1. 8 

11.8 

14.0 

0.8 

2.3 

4.3 

0.4 

0.2 

0.2 

0.1 

0.1 

CHUITNA COAL FIELD: USGS CW 81-2 

Diamicton •••••• 

Sandstone •••••• 

Siltstone •••••• 

Claystone •••••• 

Carbonaceous ••• 

claystone. 

Coal ••••••••••• 

1. 8 

11.8 

14.0 

0.8 

2.3 

4.3 

0.4 

0.2 

0.2 

o. 1 

0.1 

CHUITNA COAL FIELD: USGS CE 82-1 

Diamicton •••••• 

Sandstone •••••• 

Siltstone •••••• 

Claystone •••••• 

Carbonaceous ••• 

claystone. 

Coal . ..•.••.... 

3. 1 

16.1 

10.7 

1.6 

2.5 

10.8 

0.5 

0.1 

0.1 

0.2 

o. 1 

primarily on clay-bearing lithologies (siltstone, claystone, 

and carbonaceous claystone). In addition, tests were run 

on seven intact pieces of very fine grained, weakly lithified 

sandstone and a few pieces of sub bituminous coal. Figure 

7 compares the distribution of durability-test results by 

specific lithologies, for samples collected from the two 

coal fields. Pre~ented in table 2, in order of increasing 

durability of the lithologies, are the range and mean 

Average 

thickness 

(m) 

o.s 

1. 0 

0.5 

2.3 

4.3 

0.4 

0.6 

0.9 

5.4 

4.6 

2.5 

1. 3 

3.3 

5.8 

2.0 

1. 0 

0.9 

2.7 

Sandstone 

core loss 

(percent) 

n.a. 

72.4 

n.a. 

n. a. 

n.a. 

n.a. 

n.a. 

76.0 

n.a. 

n.a. 

n.a. 

n.a. 

n.a. 

70.6 

n.a. 

n.a. 

n.a. 

n.a. 

n.a. 

62.5 

n.a. 

n.a. 

n.a. 

n.a. 

Total core 

(percent) 

7.9 

55.1 

6.7 

10.5 

4. 6 

15.2 

3.0 

28.8 

34.2 

2.3 

9.4 

22.3 

3.7 

20.3 

20.0 

9.8 

17.6 

28.8 

2. 7 

28.3 

32.5 

8.8 

10.2 

17.5 

values that were calculated from a composite of all tests 

shown in figure 7, regardless of their coal field 

association. 

Sandstone Units 

In each drill hole, an individual sandstone unit was 

found to be the thickest continuous lithologic unit. A 

8 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
0 

10 

20 

30 

CJ) 40 

a: 

w 

~ 50 

w 

~ 

:::c 70 

~ 

a.. 

w 80 

Cl 

90 

0 

10 

20 

CJ) 30 

a: 

w 

~ 

w 40 

~ 

:::c 50 

~ 

a.. 

w 60 Cl 

70 

80 

90 

100 

A 

c 

CAPPS COAL FIELD 

DRILL HOLE USGS 1C-79 

(Chleborad and Others, 1980) 

Capps bed 

Waterfall bed 

UJ 

cr: 

0 

u 

....J 

<l: 

f0 

f0 

fz 

UJ 

u 

cr: 

UJ 

0... 

60 

50 

40 

30 

20 

CHUITNA COAL FIELD 

DRILL HOLE USGS CW 81-2 

(Odum and Others, 1983) 

M bed 

50 

calcareous .~#.!~®·_...... sandstone 

UJ 

cr: 

0 

u 

....J 

<l: 

f0 

f40 

0 beds 

Q bed 

u.. 

0 

fz 

UJ 

u 

cr: 

UJ 

0... 

30 

CJ) 

a: 

w 

~ 

10 

20 

w 30 

~ 

CJ) 

a: 

w 

~ 

w 

~ 

:::c 

~ 

a.. 

w 

Cl 

50 

8 

D 

CAPPS COAL FIELD 

DRILL HOLE USGS 2C-80 

(Chleborad and Others, 1982) 

Waterfall bed UJ 

cr: 

0 

u 

....J 

g 

fu.. 

0 

fz 

UJ 

u 

cr: 

UJ 

0... 

CHUITNA COAL FIELD 

DRJLL HOLE USGS CE 82-1 

(Odum and Others, 1986) 

Upper bed 

(Green bed ?) 

Lower bed 

(Blue bed ?) 

UJ 50 cr: 

0 

u 40 ....J 

~ 0 

fu.. 

0 

fz 

UJ 

u 

cr: 

UJ 

0... 

30 

20 

10 

Figure 5. Generalized stratigraphic columns for U.S. Geological Survey drill holes. Histograms accompanying figures indicate 

the percentage of a specific lithology present within that drill hole with respect to the total cored thickness. The number in 

the sandstone column indicates the percentage of encountered sandstone that was not recoverable. 

Geotechnical Results and Interpretation 9 
Capps Coal Field 

lower part of 

Tyonek Formation 

Chuitna Coal Field 

upper (?) part of 

Tyonek Formation 

(nearer basin margin) 

50 

(nearer center of basin) 

w40 

wa: 

(!)Q 

<uao 1--...J 2< 

~b20 wla..LL 

010 

0 

z 

0 

..... 

(.) 

:i 

<t 

-

c 

ww IIJ . zzz ..... 

U) ooo > 1-t-1- <t 0U)0 .... Ct-> (.) Z...l<t c:e-...1 m m 0 o a: 

<t 

0 

50 

W40 wa: 

(!)0 

< 0 ao 1--..J 

~<( 

ul--20 a:O 

~Iu. 10 

0 

0 zw 

oz 

..... 0 

Ot-

-~n :ic 

~z 

..1 

<t 

0 

0 

Q <t 

U) 

Chuitna, relative 

to Capps 

' SANDSTONE 

(Chuitna less) 

SILTSTONE 

(Chuitna more) ~ 

CLAYSTONE 

(Chuitna more) ~ w w ..... .... z z U) <( 

~ 0 0 > 0 ..... ..... CARB. CLAYST. <( (.) 

U) U) .... (Chuitna more) ..... > (.) 

= 

<( 

~ U) .... ai COAL (.) £r (Chuitna more) <( 

(.) 

Figure 6. Histograms showing the overall trend from a coarser grained to a finer grained lithologic character between the Capps 

coal field (basin-margin locality) and the Chuitna coal field (more basinward locality). Arrows indicate an increase (upward pointing arrow) or decrease (downward pointing arrow) in rock type between the two areas. The number in the sandstone column 

indicates the percentage of encountered sandstone that was not recoverable. 

single sandstone unit in drill hole USGS 1 C-79 measured 

approximately 55 m in thickness, and in the other three 

drill holes the maximum thickness of a single sandstone 

unit ranged from 12 to 16 m (table 1). The majority of 

the sandstone units encountered in all four drill holes, 

however, were generally so weakly lithified that they were 

nonrecoverable (table 1, sandstone percent loss column). 

These nonrecoverable sandstone units must be considered 

to have no durability for engineering purposes and could 

best be described as loose, very fine to coarse grained 

sands with an occassional gravel lens, rather than 

sandstone. 

The slake-durability-index mean, for recoverable 

sandstone core, of 19.8 percent (table 2), is derived from 

seven test samples that were collected from all four drill 

holes. These samples were typically very fine to fine 

grained and contained appreciable amounts of silt- and 

clay-sized particles. Some samples contained thin but 

recognizable lamina of siltstone, claystone, and carbonaceous materials. The presence of carbonate cementing material, detectable by diluted (15 percent) 

hydrochloric acid, in the sandstones and other lithologies 

was for all practical purposes nonexistent in the Capps 

coal field core and occurred rarely in the Chuitna coal 

field core. X-ray powder diffraction analysis identified 

the carbonate cementing material as calcite (M.E. 

Brownfield, oral commun., 1986). The most notable occurrence of cementing appeared in drill hole USGS CW 

81-2, where a 1.1-m-thick unit of coarse sand and gravel 

was cored within a thick section of otherwise nonrecoverable, loose, fine- to medium-grained sand. In addition, 

near the bottom of drill hole USGS CE 82-1, a thin 

0.3-m-thick carbonate-cemented unit was also encountered. A few other occurrences of cementing were 

found in some siltstone units that were cored from the 

Chuitna coal field. 

Strength 

Point-Load-Strength Test 

The point-load-strength test is an inexpensive and 

rapid field-orientated means of approximating unconfined compressive strength from measured tensile 

10 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
CAPPS COAL FIELD CHUITNA COAL FIELD 

DRILL HOLES DRILL HOLES 

USGS 1 C-79 .and 2C-80 USGS CW 81-2 and CE 82-1 

100- 100-

(J) .. .. >< w w ..J • 

Q () 80- so- ~ > z () • • X 

C\1 I X • 

> I . - • t- ~ • • ex _. z • I 

z 60- 60-

m oC( • 

.I < ~ • a: w - X - a: .. 

:::» w Q ~ • I • 

I < 40- X. 40-

w .... I .a X 

z ~ w .. 

I ~ 

< () - • - a: I _. w .. ex 

UJ a.. • .. X 

20- • 20- ex 

I • - •• - ~ 

• • 0 Q) 

0 -- ~ - Q) Q) 

c )( c c • -)( Q) 

- - - c 0 0 0 0 - ..: Cii - - ..: ...; fl) fl) fl) fl) fl) fl) -fl) 

~ >- >- "0 >- >- "0 «S «S c «S «S c (J) () «S (J) 0 «S () (J) () (J) 

.ci .ci ... ... «S «S () () 

Figure 7. Graph comparing the distribution of slake-durability-index values, by lithology, of the Capps and Chuitna 

coal fields. 

Table 2. Ranges and means of slake-durability-index values 

[Results grouped by lithology, without respect to drill hole origin, and arranged in order 

of increasing durability] 

Lithology Ntnnber Range Mean 

of test (percent) (percent) 

specimens 

Sandstone ••••••• 7 0-30 19.8 

Siltstone ••••••• 40 14-86 40.3 

Carbonaceous •••• 13 12-82 46.3 

claystone. 

Claystone ••••••• 13 15-75 49.1 

Geotechnical Results and Interpretation 11 
strength. The point-load strength (IJ is defined as P/D2, 

where D is the diameter between the loading points of 

the testing apparatus and P is the load applied. As 

prescribed by the International Society of Rock 

Mechanics (ISRM, 1972a), the point-load strength value 

is "normalized" to a reference diameter of 50 mm using 

the chart developed by Brock and Franklin (1972). The 

resultant value, Is(50), is then referred to as the pointload strength index. Bieniawski (1975) has recommended 

that the reference diameter be changed to 54 mm, which 

is the standard core size for the Rock Quality Determination (RQD) system (Deere, 1968) and also the standard 

core size for unconfined-compressive strength tests 

(American Society for Testing of Materials (ASTM) 1971; 

ISRM, 1972b; Abeyesekera and Lovell, 1981). Hassani 

and others (1980) presented a different "normalization" 

chart and accompaning diameter-correction equations, 

as an alternative to the Brock and Franklin (1972) chart 

currently being used by ISRM. 

In this study, the point-load strength values for the 

diametral test (load applied approximately parallel to the 

bedding planes and normal to the core axis) were 

"normalized" to the ISRM prescribed diameter of 

50 mm, using Brock and Franklin's (1972) chart. In the 

literature (Dunrud and Osterwald, 1980), there is more 

than one empirically determined coefficient (ranging from 

22 to 35) by which the point-load strength index is 

multiplied to obtain an approximation of unconfined 

compressive strength. For consistency with previously 

published field-test data, all the approximate unconfinedcompressive strength values are computed by multiplying the resultant value (ls(50)) by Brock and Franklin's 

empirical coefficient of 24. 

The point-load-strength-test method is optimally 

applied to core having horizontal to low-angle bedding 

so that diametral tests are parallel to the bedding planes, 

and axial tests are perpendicular to bedding planes. Both 

drill holes (IC-79 and 2C-80) in the Capps coal field encountered strata that show essentially horizontal bedding. 

Drill holes USGS CW 81-2 and CE 82-1 in the Chuitna 

coal field encountered zones of strata with dips of 5-20° 

and 25-35 °, respectively. However, diametral tests on the 

Chuitna cores still failed along recognizable bedding 

planes. For a few axial tests, however, the degree of dip 

made it difficult to obtain through-breaks; part of the 

failure occurred along bedding planes. Test results that 

were known to be related to improper failure were not 

used in the subsequent numerical analysis. 

Figure 8 displays the approximate unconfinedcompressive strength values in terms of loading orientation for each drill hole. Also displayed is the ratio of 

strength-perpendicular-to-bedding to strength-parallel-tobedding; this ratio is termed strength anisotropy. The 

results are grouped by lithology and graphed in descending stratigraphic order. These figures indicate little 

evidence for an increase in approximate unconfined compressive strength with increasing depth for any individual 

lithology over the relatively shallow depths that were 

penetrated. Figure 9 compares and summarizes the range 

and mean values of both axial and diametral tests performed on the Capps and Chuitna coal field cores. The 

horizontal bars in each column indicate the mean value 

of tests for that lithology. 

Figure 9 shows that ranges and means of strength 

test results for the finer grained lithologies (siltstone, 

claystone, and carbonaceous claystone) for the Capps 

coal field cores are very similar regardless of loading 

orientation. The testable sandstone samples, however, are 

typically very fine to fine grained and (or) silty to clayey, 

and they show a small range of strengths and a very low 

mean strength. Both sandstone and siltstone from the 

Chuitna coal field cores show ranges and means similar 

to the corresponding lithologies in the Capps field. 

Chuitna field claystone and carbonaceous claystone, 

however, show wider ranges for diametral tests and narrower ranges for axial tests when compared to similar 

lithologies in the Capps field. The lower mean for axial 

tests on the Chuitna claystone, as well as the differences 

in the ranges, may be a reflection of the 5-20 ° beddingplane dips that occur in some samples. Overall, however, 

the claystone mean values are not appreciably different 

from those determined for the Capps field cores. The subbituminous coals have strength values notably higher than 

those of the other common lithologies and overall mean 

values are approximately the same between the two fields. 

Not shown on figure 9 are two diametral tests that 

were performed on carbonate-cemented lenses, or 

nodules, that are located within weakly lithified sandstone 

units from drill hole USGS CW 81-2 (fig. 5C). A weakly 

cemented sample from a depth of 39.9 m measured 

6.4 MN/m2, while a sample from the extremely well 

cemented, 1.1-m-thick, pebbly to coarse-grained sandstone unit at 50.1 m had a very high measured strength 

of 55.2 MN/m2 • 

Table 3 lists the range, mean, and anisotropy values 

for all tests, by lithology and orientation, without respect 

to coal field. There appears to be a rough correlation between increasing strength and decreasing grain size similar 

to that observed in the ordering of the slake-durabilityindex results. Anisotropy values reflect the increasing 

fissile character of the rocks due to the overall increase 

in clay-mineral and carbonaceous content with decreasing grain size. The uncemented sandstone units have little 

to no strength. 

Laboratory Unconfined Compressive Strength 

Selected core samples from the four drill holes were 

prepared and tested according to ASTM ( 1971) methods 

(D 2938-71a). Specimens had a length-to-diameter ratio 

12 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
POINT-LOAD-STRENGTH-INDEX VALUES 

(Approximate unconfined compressive strength} 

By lithology and descending stratigraphic order 

Diametral (II) Anisotropy (l.)/(11) 

Siltstone 

Cia 

Cia 

(II) load parallel to bedding (.!.) load perpendicular to bedding 

CAPPS COAL FIELD 

USGS DRILL HOLE 1 C-79 

Axial (J.} MN/m2 

123456 

Diametral (II) MNJm2 

123456 

(II) load parallel to bedding (.1.) load perpendicular to bedding 

Anisotropy (J.)/(11) 

1 2 3 

CHUITNA COAL FIELD 

USGS DRILL HOLE CW 81-2 

Axial (J.} Diametral (II} Anisotropy MN/m2 MN/m2 (.1.)/(11) 

S ;ltstone 5 • ! 

Sandstone ~1 

(II) load parallel to bedding U.l load perpendicular to bedding 

Siltstone 

CAPPS COAL FIELD 

USGS DRILL HOLE 2C-80 

Diametral (II) 

MN/m2 

1 2 3 

Sandstone bl 

(II) load parallel to bedding U.l load perpendicular to bedding 

CHUITNA COAL FIELD 

USGS DRILL HOLE CE 82-1 

Anisotropy (.1.)/(11) 

Figure 8. Point-load-strength-index values of specific lithologies are arranged by descending stratigraphic order. Values have been 

"normalized" to a reference diameter of 50 mm and multiplied by Brock and Franklin's (1972) empirical coefficient of 24 to obtain 

approximate unconfined-compressive strength values. 

of 2.0-2.5, and core-cylinder end surfaces were within 

0.024 mm (0.001 in.) of perpendicularity with the core axis. 

The moisture content of the samples was maintained as 

close to natural conditions as possible by rapid waxing 

in the field and subsequent storage in a controlled highhumidity room at the receiving laboratory. Due to the 

naturally weak nature of many of the lithologies of the 

Tyonek Formation that was previously demonstrated by 

the results of slake-durability and point-load-strengthindex testing and by the additional sample loss incurred 

during specimen preparation (paralleling of cylinder ends), 

test results must be considered somewhat biased toward 

the more competent samples of a specific lithology. 

Figure 10 shows the distribution of test results with 

respect to specific lithologies and allows a comparison 

of similar lithologies between the two coal fields. Table 

4 presents the range and mean values for a composite of 

all tests. The ordering of lithologies with respect to mean 

increasing strength is similar to that determined from tests 

of the axial point-load strength index in that siltstone is 

slightly stronger than claystone. 

The wide range of strength values that were measured for the four samples from the 1-m-thick carbonatecemented, pebbly to coarse-grained sandstone unit 

(fig. 10) from drill hole USGS CW 81-2 (fig. 5C), probably reflects varying degrees of cementation and grain 

Geotechnical Results and Interpretation 13 
e c ........ wZ 

2~ 

ii' 

0 Z:c 

<( 01-U(!) 

0 Zz 

.....1 ::J w 

a: 

I- w 1-

1-Ul 

Z <tw 

~> o xcn ~ OUl 

a::W 

a_ a: 

a_O.. 

<{~ 

0 

u 

CAPPS COAL 

FIELD 

0. 0 ....._......._......._""--""--..L......I..-L......J 

.1 II .1 II .1 II .1 II 

CHUITNA COAL 

FIELD 

.1 II .1 II .1 II .1 II 

30 

25 

20 

15 

10 

5 

(/)0 

~.....I 

~w 

~u: 

.1 II 

-c::::::a 

(II) 

(.1) 

Siltstone 

Claystone 

Carb. Clayst. 

Sandstone 

Coal 

Mean value 

Diametral test 

load parallel 

to bedding 

Axial test load 

perpindicular 

to bedding 

Figure 9. Comparison of the range and mean values of point-load-strength indexes by lithology. Values are graphed in terms 

of approximate unconfined compressive strength and loading orientation. 

Table 3. Ranges and means of approximate unconfined-compressive strength derived from axial and diametral pointload tests without respect to coal field 

[Results are grouped by lithology and loading orientation and arranged in order of increasing anisotropy. (A), axial loading (perpendicular to bedding); (D), diametralloading (parallel to bedding); --- indicates value cannot be calculated] 

Lithology Number of Range Mean Anisotropy 

samples tested (MN/m2) (MN/m2 ) (A/D) 

Sandstone ••••••• (A) 13 0.6-2.6 1.5 

(D) 15 0.9-1.9 1.4 1.07 

Siltstone ••••••• (A) 77 o.5-7.2 3.2 

(D) 86 0.9-6.9 3.1 1. 13 

Claystone ••••••• (A) 29 0.4-7.2 2.8 

(D) 33 0.8-7.0 3.7 1.30 

Carbonaceous •••• (A) 16 1.2-7.2 3.7 

claystone. (D) 22 0.8-9.2 4.0 1.56 

Coal •••••••••••• (A) 24 4.6-23.4 11.9 

(D) 19 5.5-26.4 11. 9 1.83 

Calcareous •• .., ••• (D) 2 6.2-55.2 30.8 

sandstone. 

size. These specimens had the visual appearance of and 

tested very much li~e concrete. 

Figure 11 is a·chart relating "Qualitative Hardness 

Terminology" to laboratory-determined unconfinedcompressive-strength values (Jennings and Robertson, 

1968). The horizontal bars, to which specific hardness 

terms have been applied, represent the range of 

unconfined-compressive strengths that were compiled 

from literature by Jennings and Robertson (1968). The 

pattern-shaded areas represent the range of terms that 

could be applied to the laboratory test results on rocks 

from the 'JYonek Formation. Except for the sub bituminous 

14 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
N 

E 

I 

I 

I 

I 

I 

I 

CAPPS COAL FIELD 

1. 32.2 

:· 25.0 I. 22.6 I 

CHUITNA COAL FIELD 

I I I I I I :£ 116.81 I 

lA 51.7: I I. 35.2 I • 18.2 I .......... 

z 

I I 

10.0-1-----

I I I 

1o.o~-- ___ '" __ --L~ -~·-~~ --

I. 19.0 

I 1e 17.2 : ----·--- - ~ . - X -.- -

>- a: 

0 

~ a: 

0 

m 

<( 

....J 

.. ::I: 

t-

(.!) 

z 

w 

a: 

ten 

w 

> 

CJ) 

CJ) 

w 

a: 

a.. 

~ 

0 

u 

0 

w 

z 

u:: 

z 

0 

u 

z 

::::> 

9.0...: 

. 8.0_ . 

. 

7.0_ . 

. 6.0...: 

. 

5.0..: 

- 4.0~ . 

. 

3.0_ . 

. 2.0_ . 

- 1.0;... 

• • 

•• 

• 

• • • 

I 

X 

• 

f 

• 

• • • 

• • 

9.0..: . 

. 

. s.o..: . 

. 

. 7.0_ . 

-. 6.0.: -

-. 5.0.: -

. 4.0-= 

-. 3.0..: -

-

: 2.0--

-

- 1.o..: -

-

-

• • 

• • I 

•• i 

i 

I 

• 

X 

XX 

X 

X 

X 

ex 

X 

X 

• •• 

• 

• 

• 

• 

• 0.0 ....L...--.L-.----1----'-----' 0.0 ....J-1....---.L---....L--·-_.... __ _. 

Q) 

c: 

0 

t) 

~ 

U5 

- .(J)2$ 

::J Q) 

0 c: 

Q)c: Q)(.) 0 

1;)> .s ~ co (J) 0 u >..c co .... - co uu 

Q) 

c: 

0 

t) 

"C 

c: 

co 

CJ) 

co 

0 

u .(J)~. ~ ::J Q) 

0 c: Q) (J) Q) 

Q) Q) o c: ::Jo c c: (.) ...... 0 0 co (J) 0 1i) ...... c: > t) ~"C 

~.8 J2 "C co c: 

co .... u c: (.) -~ - co co co (/) uu cnu 

co 

0 

u 

Figure 10. Lithologic comparison of laboratory-derived unconfined-compressive-strength values. 

coal and the small samples of carbonate-cemented pebbly sandstone, the cored lithologies of the Tyonek Formation are characterized as having hardnesses that range 

from very soft soil to soft rock. 

Grain, Natural Bulk, and Dry Bulk Density 

All values fall within the normal range of values 

associated with similar sedimentary lithologies. Average 

natural-bulk-density values, along with average ultrasonic 

compressional- and shear-wave velocities, were used to 

calculate the representative dynamic Poisson's ratio and 

elastic moduli for the Chuitna coal field cores. 

Grain-Size Distribution, Atterberg Limits, 

and Activity Index 

Core samples were disaggregated and tested for 

grain-size distribution and Atterberg limits. This information was used to refine descriptions of fine-grained 

lithologies (Odum, 1986). Atterberg limits reflect the 

quantity of water that is attracted to the particle surfaces. 

As grain size decreases, surface area increases and water 

content will be increasingly influenced by the amount of 

clay in a material. The activity index, defined by 

Skempton (1953) as the ratio of the plasticity index to 

percent-by-weight of particles finer than 0.002 mm, is an 

indication of clay mineralogy and swelling potential. The 

Geotechnical Results and Interpretation 15 
range and mean clay-activity index values for the various 

clay-bearing lithologies in the Tyonek Formation are 

listed below. 

Clay Activity Index 

Lithology Range Mean 

Claystone . . . . . . . . . . . . . . . . . . . . . . . . . . 0.47-1.00 0.60 

Carbonaceous . . . . . . . . . . . . . . . . . . . . . . . 0.27-1.33 0.63 

claystone. 

Siltstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.30-1.35 0.85 

Based on Skempton's (1953) classification, these 

lithologies have "low to normal" activity, are likely to 

contain kaolinite- and illite-group clay minerals, and have 

"medium" swelling potential. 

Clay Mineralogy 

Clay mineralogy was determined by X-ray analysis 

according to procedures presented by Schultz (1964). 

Analytical results are listed in table 5 in terms of claymineral group (kaolinite, illite, mixed layer, montmorillonite, and chlorite) abundance. Kaolinite and illite 

groups are generally the most abundant and, in many 

instances, make up 40-60 percent of the samples' clay 

fraction. Only three samples, all from drill hole USGS 

CW 81-2, show montmorillonite abundance greater than 

10 percent; no sample exceeded 20 percent. Abundances 

of the mixed-layer clay group were very similar to the 

abundances calculated for the montmorillonite group. 

Of mineralogical note is the presence of the 

strontium-rich hydrated-aluminophosphate mineral 

goyazite (P.D. Blackman, written commun., 1981). This 

mineral is present in a 3-cm-thick volcanic tuff(?) at a 

depth of 52.4 m, which is 2.1 m above the base of the 

Capps coal bed in drill hole USGS 1C-79. 

Geochemical Analysis 

Whole-rock chemical composition and traceelement analysis of the non-coal lithologies from the 

Capps coal field was reported by Hinkley and others 

(1982). Similar analysis for the Chuitna coal field cores 

is currently being prepared by J .R. McNeal and others, 

U.S. Geological Survey. Chemical and trace-element 

analysis of Quaternary soils in the vicinity of the Capps 

drill sites has been reported by Gough and Severson 

(1983) and Severson and Gough (1983). 

Affolter and Stricker (1985) performed proximate 

and ultimate analyses and heat-of-combustion and formsof-sulfur measurements and determined the abundance 

of 40 major, minor, and trace elements. These data, along 

with an evaluation of low-temperature-ash mineralogy, 

were compiled from the analysis of 43 samples that were 

taken from eight coal beds: the Capps and Waterfall 

(from the Capps field), and theM, 0, Q, and three unnamed beds (from the Chuitna field). Affolter and 

Stricker (1985) summarized as follows: 

"Analyses show an apparant rank that ranges from subbituminous B to subbituminous C, with a variable ash content of 4.7-46.5 percent and one ofthe lowest sulfur ranges 

reported for any United States coal of 0.08-0.33 percent. 

Nearly half the elements analyzed (Si, AI, K, Ti, Be, Cr, 

Cu, F, Ga, La, Li, Sc, Th, U, V, Y, Yb, and Zr) show a variation in concentration that is directly related to the ash content of the coal (linear correlation coefficients >0.8). 

Mineral composition of the low-temperature ash is 

predominantly kaolinite and mica-type clays with varying 

amounts of quartz. These data suggest that many of the 

Table 4. Ranges and means of laboratory unconfined-compressive-strength test data 

based on a composite of all samples from the Capps and Chuitna coal fields 

[Arranged in order of increasing strength] 

Lithology Number of Range Mean 

samples tested (MN/m2) (MN/m2) 

Sandstone ••••••••••••• 6 0.2-1. 7 1. 0 

Claystone ••••••••••••• 12 0.6-4.4 2.6 

Siltstone ••••••••••••• 33 0.5-5.1 3.0 

Carbonaceous •••••••••• 15 2.2-9.7 5.8 

claystone. 

Coal •••••••••••••••••• 9 8.6-32.2 18.4 

Calcareous •••••••••••• 4 32.1-116.8 59.0 

sandstone. 

16 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
VERY SOFT SOIL 

tn 

:1 

m: SOFT SOIL 

w 

1- FIRM SOIL 

tn 

tn 

w STIFF SOIL 

z 

Q VERY STIFF SOIL m: 

c( 

:::c VERY SOFT ROCK 

w 

> 

- SOFT ROCK 

1-

c( 

1- HARD ROCK 

..1 

c( VERY HARD ROCK :;:) 

0 VERY VERY HARD ROCK 

0.01 

claystone 

sandstone 

' ' / siltstone 

0.1 1 10 

carbonaceous 

claystone 

calcareous sandstone 

100 1000 

UNCONFINED COMPRESSIVE STRENGTH, MN/m2 

Figure 11. Range of "qualitative hardness terms" associated with the lithologies of the Tyonek Formation, based on the range 

of laboratory-derived unconfined compressive strengths. Horizontal bar indicates range of strengths determined by various workers. 

elements that vary with ash content may also be associated 

with the clay minerals. The M bed, in the Chuitna field, 

has the lowest ash content and the lowest concentration 

of ash-correlated elements, whereas the Capps bed has 

the highest ash content, and therefore, the highest concentration of these elements. The variability of content is 

probably a direct result of the proximity of the original peat 

swamp to nearby tectonically active highlands. The peat 

is thought to have accumulated in non-marine swamps as 

indicated by the low-average forms of sulfur for all eight 

coal beds (0.13 percent organic sulfur, 0.02 percent sulfate 

sulfur, and only 0.01 percent pyritic sulfur). Trace elements 

that normally show positive correlation with sulfur in lower 

United States coals, such as As, Cd, Co, Fe, Mo, Ni, Pb, 

and Zn, are low in concentration for tested coal from the 

Tyonek Formation." 

Ultrasonic Compressional- and 

Shear-Wave Velocity 

Ultrasonic testing uses high-frequency (generally in 

excess of 20 kilocycles per second) mechanical vibrations 

to characterize the physical properties of an elastic 

material, for example, soil and rock. The equipment 

system used in this study was constructed by David R. 

Cunningham (U.S. Geological Survey) according to 

specifications outlined by Dr. Richard W. Stephenson, 

University of Missouri-Rolla. The system consists of: (1) 

A pulse generator capable of delivering a variable-voltage 

direct-current pulse with pulse widths of 1-100 

microseconds and pulse intervals of 1-99 milliseconds, 

2) an oscilloscope, 3) a sample support device, and 4) two 

ultrasonic probes (one transmitter and one receiver). The 

coupling medium used for bonding of the ultrasonic 

probes to the rock specimen was silicon grease for 

compressional-wave transmission and phenalsilicitate for 

shear-wave transmission. Test specimens, in general, had 

a length-to-diameter ratio of at least 2: 1. 

Intact, weakly lithified, and noncarbonatecemented-sandstone specimens suitable for testing could 

be obtained only from drill hole USGS CE 82-1. All 

carbonate-cemented sandstone specimens came from 

small units scattered throughout the 15-m-thick, loose 

to weakly lithified sandstone unit that was penetrated by 

drill hole USGS CW 81-2. The four coal specimens that 

were selected for testing from drill hole USGS CE 82-1 

broke along high-angle fractures during the sample 

preparation. 

Geotechnical Results and Interpretation 17 
Table 5. Relative abundance of clay-mineral groups for all four drill holes ... [Abundance ranges: 1 = 40-60 percent, 2 = 20-40 percent, 3 = 10-20 percent, 4 = less than 10 percent] 

= 

5" Depth of Clay-mineral groups 

1i sample (m) Chlorite Kaolinite Illite Montmorillonite Mixed layer Lithology 'C 

i 

~ 

s· USGS IC-79 ::I 11.9 ••••••..••. 3 2 1 4 4 Claystone. a. 

~ 15. 4 •••.••••••. 3 2 2 4 3 Carbonaceous claystone. 

1 7. 6 ••••••••••• 3 2 2 4 4 Silty claystone. 

:I: 18. 6 .•••••.•... 4 1 2 4 4 Clayey siltstone. 0 

rD 

~ 23.5 ••••••••••• 3 2 2 4 3 Sandy siltstone. -1 28. 9 ....••.•.•. 3 2 2 4 3 Siltstone. -< 0 32. 6 ....••.•... 3 2 2 4 4 Carbonaceous claystone. ::I 

I'D 

'1J:" 

.,., 

0 

3 3 9. 2 .•••••••••• 3 2 2 4 4 Claystone. ~ 42.4 ••••••••••• 3 2 2 4 3 Carbonaceous claystone. s· 

,':l 4 5. 6 ••••••••••• 2 2 2 4 4 do. 

c: 46.1 ••••••••••• 2 1 2 4 4 Siltstone. 'C 

'C 

~ 115.3 •••••.•..•. 2 1 3 4 4 Carbonaceous claystone. ~ 115.5 ••••.•.••.• 3 1 3 4 4 do. 0 

0 

'1J:" 15. 8 •••••••••.. 2 1 3 4 4 do. 

5" 

i 

jiiC USGS 2C-80 ~ 1. 9 •••.••••.•. 2 1 3 4 4 Sandy siltstone. s· 

,':l 3. 4 .•...••.... 2 2 2 4 4 Clayey siltstone. 

> 

~ 4. 7 ....•••.... 2 1 2 4 4 do. <I> 5. 2 ........••• 3 1 3 4 4 do. :II('" 

Ql 

7. 2 ........... 2 1 3 4 4 do. 

9. 2 ........••. 2 1 2 4 4 do. 

11.9 •••••••••.. 2 2 2 4 4 do. 

16. 2 ••••••••••• 2 1 2 4 4 Claystone. 

17. 7 ••••.•••••• 2 1 2 4 4 Carbonaceous claystone. 

23.6 ..•••••.•.. 2 1 2 4 4 do. 

2 9. 6 ••••••••••• 2 1 2 4 4 do. 

33. 3 ...•..••••• 2 1 3 4 4 Carbonaceous siltstone. 

35. 7 •••.••.•••• 2 1 3 4 4 do. 

40. 2 .•...•....• 2 1 3 4 4 Siltstone. 

44. 8 ..•.......• 2 1 3 4 3 Carbonaceous claystone. 
Table 5. Relative abundance of clay-mineral groups for all four drill holes-Continued 

[Abundance ranges: 1 = 40-60 percent, 2 = 20-40 percent, 3 = 10-20 percent, 4 = less than 10 percent] 

Depth of Clay-mineral groups 

sample ( m) Chlorite Kaolinite Illite Montmorillonite Mixed layer Lithology 

--

USGS CW 81-2 

11. 2 .•.....•••• 3 2 2 3 4 Carbonaceous siltstone. 

16. 6 ...••..•.•• 4 1 1 4 4 Clayey siltstone. 

35.1 ........... 4 4 1 4 4 Carbonaceous claystone. 

40. 7 •••.•••.... 4 1 2 4 3 Sandstone. 

57. 2 .•...•••••• 3 1 2 4 4 Carbonaceous claystone. 

64. 7 ....••..... 4 1 2 4 4 Carbonaceous claystone. 

6 7. 7 ••..•.••... 3 2 1 4 4 do. 

73.9 ••••••••••• 2 3 3 4 4 Claystone. 

7 4. ~ ••••••••.•. 4 1 1 4 4 do. 

7 7. 4 ••••.....•• 4 1 3 4 4 Clayey siltstone. 

81.6 ••••••••••• 3 1 2 4 4 Carbonaceous claystone. 

84. 7 ..•......•• 2 1 2 3 4 Clayey siltstone. 

88. 6 .•........• 3 1 4 3 2 do. 

90.1 ........... 4 1 2 3 4 Claystone. 

~ 101.6 ••..••••••• 3 1 2 4 3 Carbonaceous siltstone. ~ 

0 

;;- USGS CE 82-1 l"l 

::r 

::I 

;:;· 2 3. 6 ••••••••••• 4 1 2 4 4 Siltstone. r:w 

- 24.8 .......•... 3 2 1 4 4 Claystone. ;:IC 

~ 3 7. 6 ••...•••••. 3 2 1 4 4 Siltstone. 

~ 44. 7 .......•... 4 4 1 4 4 do. r:w 57. 2 .......••.• 3 4 4 Carbonaceous claystone. ::I 1 2 c.. 

::I 

~ 6 7. 7 ••••••••••• 4 2 1 4 4 Clayey siltstone. " ;:;; -:8.7 ••••••••••• 3 1 2 4 4 Carbonaceous claystone. ~ o· 9 5. 2 ••••••••••• 3 1 2 4 4 Claystone. ::I 98. 0 •••........ 3 2 2 4 2 Carbonaceous claystone. 

... 99. 3 ..••••••••• 3 2 1 4 4 do. ~ 
Figure 12 displays the distribution of compressionaland shear-wave velocities for specific lithology samples 

from the two Chuitna coal field holes, and table 6 presents the velocity range and mean values for the same 

samples. In general, compressional- and shear-wave velocity range and mean values for individual lithologies are 

highest for USGS CW 81-2 core. Siltstone is the one exception to this pattern, because siltstone samples from 

USGS CE 82-1 have a slightly higher mean velocity. For 

compressional-wave velocities, there is an ordering of lithologies similar to that seen for other index and laboratory 

tests. Sandstone has the lowest velocity; siltstone, claystone, and carbonaceous claystone show a respective slight 

increase in velocity, yet can be generally grouped; coal has 

the highest velocity of the common lithologies. The 

velocities of the carbonate-cemented pebbly sandstone are 

substantially higher than any other material tested. A 

similar ordering based on shear-wave velocities exists except for the low velocities recorded for carbonaceous 

claystone. These lower shear-wave velocities are undoubtedly the result of the irregularly oriented positioning of 

coal lamina and stringers, which slow the propagation of 

the shear waves through the sample. 

Compressional-Wave Velocity 

Because of weathering, cementation, saturation, 

and expansion due to the removal of confining stresses 

during drilling, laboratory-derived velocities are often 

highly variable for near-surface earth materials. However, 

correlations and approximations between velocities and 

earth materials do exist and are useful if the physical conditions of the samples and their non-in-situ testing status 

are considered. 

There is an empirical relationship between 

compressional-wave velocity and the quality or relative 

strength of most rocks and soil that was stated by Darracott (1976): "the greater the velocity the greater is their 

relative strength". He also infers that although rules of 

thumb may be misleading, one used for foundation 

studies in South Africa is: ''Allowable bearing capacity 

= 300 kN/m2 per 1,000 m/s of compressional velocity". 

Another comparison has been made between the economical dozing, ripping, and blasting characteristics (modified 

from the Caterpillar Tractor Co., 1972, by Miller, 1979) 

of rocks and seismic compressional-wave velocities (fig. 

13). The bars shown on figure 13 correspond to the range 

of lithologic velocities of tested core samples of the Tyonek 

Formation. Velocities around 2,100 m/s are generally 

assumed to be the upper limit of economical ripping due 

to equipment wear and the necessity of additional 

crushing of large ripped blocks before removal. 

Shear-Wave Velocity 

In engineering studies, shear-wave velocity tends to 

I 

: D 4930 

1 

w I ~ 0 3640 > 

cC 

~ 

I I I 

2750 ·----- ----- ~ .!6.lQ... 

.... 2500 

0Q 

..... z a: 0 2250 

ceCJ 

W W2000 

:c0 

0 ;;;1750 

ca:: 

z ~ 1500 

cew 

~ ::& 1250 

..I~ 1000 

cez (..) 7 so ~g 

U) w 500 tn> 

w 

a: 

G. 

::& 

0 

(..) 

250 

• 

al 

.. 

• 

• • 

i 

Ill 

c 

0 

~ ·; 

n 

XXX ·' X 

xl 

xe 

! 

41 

c 

2 

Ill 

:0. 

111 

u 

0 

D 

• 

D 

• 

ex • 

X • 

• X 

• 

• 

~ :! § Ill ; c Ill :0. 0 '1:1 Ill Ill c u '1:1 Ill 

c Ill 

-e Ill 

Ill u Ill iii u u 

• 3370 

-----

I 

• 

• 

J 

iii 

0 

u 

Figure 12. Distribution of ultrasonic compressional- and shearwave velocity values for Chuitna coal field (USGS CW 81-2 

and CE 82-1) core samples. 

have more potential applications than compressionalwave velocity but is considerably more difficult to 

measure. Shear-wave velocities are thought to be better 

indicators of lithology because shear-wave propagation 

is primarily controlled by the structural strength of the 

matrix and the size and strength of the grains, rather than 

by the degree of saturation (Whitely, 1983). While most 

classification schemes indicate that the dividing line between shear-wave velocity for soil (overburden) and that 

for firm compact soil is 600 mls, the dividing line between firm soil and rock ranges from 765 to 1,800 mls 

(Ohto and Shima, 1967, in Mooney, 1974; Murphy and 

others, 1979). The mean shear-wave velocities listed in 

table 5 for siltstone, claystone, carbonaceous claystone, 

and sub bituminous coal fall within the above-cited transitional (soil to compact rock) velocity range. Thus, mean 

shear-wave velocities, as well as laboratory unconfinedcompressive-strength means, characterize the majority of 

the unconfined lithologies of the Tyonek Formation as 

firm soil to soft rock. 

Shearing strength is defined by the Coulomb equation (Terzaghi and Peck, 1967, p. 103) as shear strength 

at failure. For small structures on cohesive soils that are 

not drained when tested, shearing strength is proportional 

to about one-half of the unconfined compressive strength. 

Imai and Yoshimura (1975) have empirically related 

20 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
Table 6. Ranges and means of compressional- and shear-wave velocity for specific lithologies from drill holes in the Chuitna 

coal field 

[Arranged in order of increasing compressional-wave velocity. * indicates that samples were only available from drill hole CE 82-1; ** 

indicates that samples were only available from drill hole CW 81-2] 

Lithology Compressional Velocity (m/s) Shear velocity (m/s) 

Range Number of Mean Range Number of Mean 

samples tested samples tested 

DRILL HOLE CW 81-2 

Siltstone •••••••• 1681-2091 10 1875 685-975 5 821 

Carbonaceous ••••• 1872-2232 7 2074 685-940 4 837 

claystone. 

Claystone •••••••• 2014-2262 4 2154 916-989 4 958 

Coal ••••••••••••• 2299-2350 3 2327 965-1050 2 1011 

Calcareous ••••••• 2480-4827 4 3643 1678-2131 2 1905 

sandstone. 

DRILL HOLE CE 82-1 

Sandstone •••••••• 1474-1932 2 1703 435-945 2 690 

Claystone •••••••• 1744-1880 3 1810 850-888 3 867 

Carbonaceous ••••• 1762-1909 3 1822 705-736 3 724 

claystone. 

Siltstone •••••••• 1659-2233 15 1927 654-975 13 845 

Coal ••••••••••••• All samples failed during compressional velocity testing. 

DRILL HOLES CW 81-2 AND CE 82-1 COMBINED 

Sandstone* ••••••• 1474-1932 2 1703 435-945 2 690 

Siltstone •••••••• 1659-2233 25 1908 654-975 18 838 

Claystone •••••••• 1744-2262 7 2008 850-989 7 922 

Carbonaceous ••••• 1762-2232 10 2123 685-940 8 794 

claystone. 

Coal**••••••••••• 2299-2350 

Calcareous ••••••• 2480-4827 

sandstone.* 

3 

4 

shear-wave velocity for soil and relatively weak rocks to 

unconfined compressive strength. They have also reported 

relatively good correlations of in-situ shear-wave 

velocities in modern alluvial deposits and Tertiary strata 

with standard penetration "N" value (a measure of 

penetration resistance to a cylinder blade edge driven by 

a 61-kg hammer falling 76 em). 

Dynamic Poisson's Ratio and Elastic Moduli 

If the compressional- and shear-wave-velocity ratio 

is measured, then Poisson's Ratio can be computed; if the 

bulk density is measured, then elastic moduli can also be 

computed. Neither soil nor rock are perfectly elastic and 

their strength characteristics can be quite different under 

static and dynamic loads. The dynamic load nearly always 

2327 

3643 

965-1050 

1678-2131 

2 1011 

2 1905 

produces higher apparent strengths than does the static 

load. Both Coon and Merritt (1970) and Miller (1979) have 

compared laboratory (ultrasonic) dynamic measurements 

on intact core with in-situ dynamic measurements. They 

have reported a bias (in many cases, forced by core quality) for laboratory measurements toward selecting intact 

samples, whereas the in-situ measurements will include 

discontinuities and weak zones. Larkin and Taylor (1979) 

have also compared shear moduli obtained from their 

downhole measurements on relatively low strength rocks 

to those obtained from laboratory measurements on the 

same rocks. They found that the inhole shear moduli were 

linear only for strain less than about I0-5 em/em. They 

also found that the laboratory-derived moduli agreed approximately with the inhale moduli in the range of relative 

low strain but that the laboratory moduli decreased considerably as the strain was increased. 

Geotechnical Results and Interpretation 21 
SUB BITUMINOUS 

COAL 

NONWELDED TO 

WELDED TUFF 

SHALE, CLAYSTONE 

AND MUDSTONE 

NONINDURATED 

SANDSTONE 

> 

!:: 

0 

<C 

D. 

<C 

0 

C) 

z 

N 

0 

c 

> 

C) !:: 

z 0 BLASTING CAPACITY 

0: <( 

D. D. <( 

a: 0 

TRACTOR 

w~O 

,._COOl 

c cc 

-· '-'coal 

~ I";: ---'SII~stone 

__, claystone ~ ~arbonaceous claystone 

-· r----" sandstone 

INDURATED -,- --- SANDSTONE calcareous sandstone 

CARBONATE ROCKS ---- INTRUSIVE IGNEOUS I ---r- ROCKS O 2 3 4 5 6 7 

VELOCITY, IN MIS {X 103

} 

---Weathered bedrock 

~ Unweathered bedrock 

Range of laboratory 

compr es & ion a 1-w ave 

velocities 

__[_ J 

8 

Figure 13. Compressional-wave velocities and estimated dozing, ripping, and blasting capabilities of various rock types. Data 

are taken from surface measurements in the Powder River 

basin, Wyoming (literature and estimates). The rippability chart 

was modified from the Caterpillar Tractor Co. (1972) by Miller 

(1979). 

Table 7 presents average values for Poisson's ratio 

and the dynamic elastic moduli (shear, Young's, and 

bulk) for the lithologies that were found in the core of 

the Tyonek Formation. The dynamic elastic moduli that 

are presented in table 7 were computed from mean 

compressional- and shear-wave velocity data (table 6) and 

mean bulk density values from the selected core samples 

that were tested on laboratory ultrasonic equipment that 

generated high loading rates at low-strain levels. These 

dynamic elastic moduli are undoubtedly higher than insitu measured moduli would be. 

GEOPHYSICAL LOGGING 

AND GROUND WATER 

Continuous natural gamma radiation, gammagamma radiation, neutron radiation, hole diameter, spontaneous potential, single-point resistance, and temperature measurements were obtained by logging the four 

holes soon after the completion of drilling. Single-point 

resistance and spontaneous potential logs were not obtained in drill hole USGS CE 82-1 due to hole collapse 

following casing removal (Odum and others, 1986).- A 

Well Reconnaissance Geologger2 with single-conductor 

cable was used following the techniques described by Keys 

and MacCary ( 1971). 

The geophysical-log responses document most major lithologic contacts. In general, interpretations of the 

suite of logs reinforce the subtle differences noted on the 

lithologic logs (Odum, 1986). This summary consists of 

excerpts of the more noteworthy observations and interpretations that were previously published in reports on 

each individual drill hole (Chleborad and others, 1980, 

1982; Odum and others, 1983, 1986). 

Capps Coal Field 

Drill Hole USGS lC-79 

The temperature log, which was run iHside the drill 

stem after the hole was allowed to stabilize for 20 hr, 

indicated a temperature gradient of approximately 

1.6 °C/100 m for the measured interval of 40.8-118 m. 

In that interval, the temperature ranged from 4.1 °C at 

40.8 m to 5.1 °C at 118 m. The gradient is low relative 

to typical gradients of 1.8-2.4 °C/100 m seen outside the 

Cook Inlet area but is similar to that measured in an unsuccessful oil well near Anchorage (Keys and Mac Cary, 

1971), where the low-temperature gradients were attributed to significant ground-water circulation. 

The anomalous rise in temperature at 118.7 m 

occurs near the top of the Waterfall coal bed. The heat 

source is possibly an exothermic reaction in the coal 

caused by frictional forces generated in the drilling 

process. High drilling pressure was applied at that depth 

(119m) in an effort to core the coal, with what was later 

determined to be a badly worn bit. Some of the retrieved 

sample was badly broken and smelled like creosote and 

hydrogen sulfide. The temperature probe was raised and 

lowered several times to check the validity of the local 

heat source and then left stationary at the 118.7-m level 

(the bottom of the hole) for about 2 hr. A maximum 

temperature of 10.7 °C was recorded at the end of the 

2-hr period (Chleborad and others, 1980). 

The following descriptions of the hydrologic conditions are based on information obtained from a 76-mdeep test hole 30 m south of drill hole 1C-79 (G.L. 

Nelson, written commun., 1979). The materials were unsaturated to the total depth except for a few thin perchedwater-table zones. Only the perched-water-table zone at 

9.1 m yielded any measurable water (about 2 L/min). A 

little seepage was detected between 40.8 and 41.4 m, but 

the zone between 60.9 and 76.2 m is quite permeable. The 

2 Any use of trade names in this report is for descriptive purposes 

only and does not imply endorsement by the U.S. Geological Survey. 

22 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
Table 7. Average ultrasonic velocities, bulk densities, and calculated Poisson's ratio and dynamic elastic moduli for the Tyonek 

Formation 

Lithology 

Sandstone 2.13 1703 690 

Siltstone 2.01 1908 838 

Claystone 1.96 2008 922 

Carb. Clayst. 2.07 2123 794 

Coal 1.15 2327 1008 

Calc. Sandst. 2.55 3643 1904 

perched-water-table zone at 9.1 m corresponds to the 

contact between the surficial diamicton and the underlying claystone, which indicates that the claystone is an 

aquiclude that inhibits the downward migration of water. 

The seepage detected between 40.8 and 41.4 m corresponds to the upper part of the Capps coal bed and 

the base of the carbonaceous claystone above. The 

permeable zone between 60.9 and 76.2 m corresponds to 

what is mostly a nonrecovery zone believed to be composed of friable sandstone. The only direct indication of 

hydrologic conditions between 76.2 and 121 m comes 

from drill hole 1 C-79 where circulation of drilling fluid 

was never attained, which indicates downward continuation of the unsaturated permeable material. 

Drill Hole USGS 2C-80 

All coal beds within the logged interval, except for 

a very thin bed at 40.2 m, caused conspicuous deflections 

on the radiation logs. These responses were the result of 

a very low natural-gamma radiation level, a low backscatter level on the neutron log because of the abundance of 

hydrogen molecules, and relatively low density indicated 

by a marked increase in the gamma-gamma count rate. 

The suite of geophysical logs, especially the 

0.402 7 .4x 108 2.1 X 109 5.2x 109 

.381 1.4x 109 3.9x 109 5.4x 109 

.363 1. 7 X 109 4.6x 109 5.6x 109 

.419 1.3x 109 3.7x109 7 .6x 109 

.384 1.2x109 3.3x 109 4.7x109 

.312 9.3x 109 10 

2.4x 10 2.2x 1010 

natural-gamma and electric logs, strongly indicate that 

beds below 47.2 m, for which no core was retrieved, are 

probably composed of relatively clean granular 

material-most likely medium- or coarse-grained sandstones. The highly sensitive and finely calibrated 

thermistor-type probe detected a rapid temperature increase of over 0.5 °C below 49.7 m. A warmer, nearly 

constant temperature of 3.3 °C occurred below 50.3 m. 

Chuitna Coal Field 

Drill Hole USGS CW 81-2 

The suite of seven geophysical logs were run under 

flowing artesian conditions of 15-19 L/min, and the only 

casing in the hole was an 11-cm (inside diameter) steel 

casing that extended to 7.6 m below the ground surface. 

The initial depth of geophysical logging, 98.5 m, was 

about 3.5 m less than the final depth of drilling, 102m, 

due to accumulations of caved material. During the logging process, the hole continued to fill slowly with debris 

from the walls. 

Two conspicious lithologic units are evident on 

the log suite: a very competent, dense, low-porosity, 

Geophysical logging and Ground Water 23 
carbonate-cemented pebbly sandstone bed from 50.0 to 

51.1 m; and a hard tuffaceous(?) bed from 85.9 to 

86.1 m. The dense nature of the carbonate-cemented bed 

was strongly reflected on all logs except the spontaneous 

potential and temperature logs. The fact that this bed 

withstood significant hole caving, both above and below 

itself as shown by the caliper log, is evidence of its competence. Although cemented sandstones are commonly 

not thought of as aquicludes, this bed, if it has much 

lateral continuity, may severely restrict vertical groundwater movement. 

The tuffaceous(?) bed caused significant responses 

on three logs as follows: (1) Low natural-gamma spike, 

(2) high electrical-resistance spike, and (3) high densitygamma-gamma spike. The lack of diagnostic character 

on the neutron log is probably due to the relatively large 

sphere of radiation influence with respect to the thinness 

of the bed, whereas the smaller sphere of influence of 

the other radiation logs allowed detection of this bed. 

The two thickest intervals (43.1-50.0 m and 

51.1-55.5 m), for which no core was recovered, have 

similar geophysical log responses. This suggests that these 

two intervals are composed of moderately well sorted, 

weakly lithified sandstone. The caliper log clearly shows 

that the material is highly susceptible to caving. Therefore, it seems logical to conclude that the porosity, and 

probably the permeability, of these beds is substantially 

greater than that of the carbonate-cemented sandstone 

bed that was cored at 50 m. 

The drill-hole-fluid temperature log is the most 

valuable log of the suite for the delineation of the groundwater system. Ground water moving through porous or 

fractured rocks within about 100 m of the surface may 

be expected to keep those permeable beds (aquifers) 

cooler than impermeable beds (aquicludes). This 

phenomenon is thought to occur because the average annual temperature of recharging water is less than that of 

subsurface rocks that are not subjected to ground-water 

circulation. The aquiclude, instead, retains more geothermal heat. The interface between relatively permeable and 

relatively nonpermeable beds is, therefore, commonly a 

zone of significant temperature change. This change takes 

the form of an increase of temperature as the probe's 

sensor is lowered past the bottom of an aquifer and into 

an aquiclude. The magnitude of decrease on the temperature log, when it is in an aquifer, is commonly proportional to the volume of water that enters the hole at that 

point. 

The temperature log shows three depths where 

temperatures in the drill hole rise significantly. A 0.4 °C 

increase occurs within the top half of the upper coal bed 

at approximately 19.8 m, a similar more abrupt rise 

within the same coal bed is at about 26 m, and a rise of 

1.3 °C occurs at 73.6 mat the bottom of the middle coal 

sequence. 

Drill Hole USGS CE 82-1 

A suite of five borehole geophysical logs was 

recorded for this drill hole, starting 15 hr after drilling 

ended. Following five logging runs, the casing was pulled 

upward in an attempt to expose more of the upper section for electric logging. However, the loose, sandy unit 

above 15 m, identified from the gamma-gamma and 

lithologic log (fig. 5D), collapsed into the hole. Even during the 8 hr of logging, material caving from below the 

casing reduced the hole depth by approximately 4 m. This 

rate of filling by natural caving was greater than that 

which occurred in the other three core holes. 

The neutron log normally reflects the variation of 

"total porosity" of the saturated earth materials. This 

log indicates that the sandstone unit between 44.8 and 

57.2 m has the least saturated porosity of the geologic 

units in this hole, although log interpretations are complicated by hole enlargement. This interpretation agrees 

with logging observations for other holes in the area 

(Chleborad and others, 1980, 1982; Odun{ and others, 

1983, 1986). 

The gravelly zone between 52.9 and 55.8 m is characterized as being a moderately firm, cemented sandy 

gravel, and higher density and lower prorsity is indicated 

by the radiation logs. The gamma-gamma response 

indicates that material in this zone has the highest bulk 

density found in this hole. 

A bowing in the temperature profile is observable 

opposite the upper coal bed, followed downhole by a 

gentle decline in borehole temperature in the underlying 

sandstones and siltstones. Because the area's groundwater flow system has not been defined, any explanation 

of the bowing phenomenon is speculative. An alternative 

to a hydrothermal cause is that enough oxygen-rich drilling water may have been lost to the coal to produce 

detectable heat from slight oxidation. Two sharp spikes 

of about 0.22 °C were recorded at 75.3 and 108.2 m. The 

sudden increase in temperature at 75.3 m seemingly 

correlates with the most pronounced hole enlargement recorded on the caliper log. Although perhaps 

coincidental, the geotechnical log mentions slickensides 

at 75.9 m in a moderately thick, firm to very firm 

siltstone. Ground water, slightly warmer than its surrounding environment, is believed to be entering the 

borehole from a thin, presumably fractured zone. This 

inflow and temperature anomaly could result from a 

depressed water level in the borehole after drilling 

ceased that had not risen to stabilization (static level) at 

the time of logging. 

The temperature spike at 108.2 m could not be explained by observing the other logs. The radiation and 

caliper logs do not indicate a zone of weakness here. If 

the temperature "blip" is real, fractures too narrow for 

the probes to detect must be present. 

24 Interpretation of Drill Holes, Tyonek Formation, Upper Cook Inlet Region, Alaska 
CONCLUSIONS 

The Tyonek Formation of early Oligocene through 

middle Miocene age is a nonmarine sequence of sandstone, siltstone, claystone, carbonace<;ms claystone, coal, 

and lignite, all deposited in a poorly drained alluvial 

basin. Distribution histograms showing the relative abundance of various lithologies indicate that drill holes in the 

Chuitna coal field have a higher percentage of finegrained rock units than the drill holes in the Capps coal 

field. This difference in lithologic character may reflect 

a higher energy basin-margin environment for the Capps 

field location as opposed to a lower energy, more basinward setting of the Chuitna field, or it may reflect a basinwide change in depositional energy in response to a 

slowing of basin margin uplift and (or) a slowing of basin 

subsidence during early and middle Miocene time. 

A suite of geophysical logs that were run in each 

drill hole proved to be invaluable in interpreting the 

lithology of unrecoverable intervals, which were mainly 

composed of weakly lithified sandstone. The log suites 

also provided independent confirmation of the existence 

of practically all major lithologic contacts. Based on this 

experience, geophysical logging could be substituted for 

continuous coring in some areas, with little loss in 

reliability of identifying significant geologic units. 

The geophysical log suites provided useful information on ground-water conditions. Drill-hole fluidtemperature profiles were especially interesting because 

they delineated specific depth intervals where ground 

water was either entering or exiting the drill hole. 

However, the typical 20 hr that were allowed for thermal equilibration after the completion of drilling may 

have been insufficient for temperature logging of normal 

ground-water flow in holes USGS 1 C-79 and 2C-80, 

especially if an exothermic reaction in the coal was 

generated by excessive bit friction. Regardless of the 

origin, thermal anomalies recorded on the temperature 

logs identified zones of fractured coal or poorly lithified 

sandstone that were substantially more permeable. 

In general, the range and mean values derived from 

the field and laboratory tests, along with distinctive 

similarities in drill hole geophysical logs, indicate that 

there is little difference in the physical character of 

specific lithologies between the two coal field areas. The 

hardness classification of most of the lithologies of the 

Tyonek Formation ranges from stiff soil to soft rock. 

Test-result ranges of slake-durability index, point-load 

strength index, unconfined compressive strength, and 

ultrasonic velocities vary widely for a specific lithology. 

However, on the basis of computed means of the above 

properties, the lithologies within a given drill hole or coal 

field area can be arranged in the following order of increasing strength and durability: weakly lithified sandstone, siltstone, claystone, carbonaceous claysrone, and 

coal. From this order, there appears to be a rough correlation between a decrease in overall grain-size content 

and an relative increase in physical strength and durability. This relationship suggests that the clay particles are 

acting as a weak cementing agent when other agents such 

as carbonate, oxides, and silica, are, for all practical purposes, absent. 

The inherently nonhomogeneous nature of many 

of these lithologies of the Tyonek Formation causes difficulty in testing, interpreting individual test results, and 

ultimately, characterizing a lithologic unit within the formation. Thin laminae of micaceous minerals cause zones 

of weakness that may produce significantly diverse test 

results for samples that are similar in appearance. 

Because the majority of the sandstone units of the 

Tyonek Formation were essentially nonrecoverable due 

to their nonlithified character, an arrangement of the 

lithologies into three groups may be more realistic. For 

most purposes, sandstone can be considered to have zero 

unconfined strength and durability, and therefore may 

present some slope stability problems during construction. Siltstone, claystone, and carbonaceous claystone all 

have low to moderate strength and durability depending 

on clay-particle content, size, and orientation and on 

quantity of micaceous and carbonaceous inclusions. The 

coal units have unconfined strengths at least twice those 

of the finer grained lithologies. The rare carbonatecemented pebbly sandstone unit has a strength and 

durability anomalously higher than all other lithologies. 

If, during construction, these carbonate-cemented units 

were found to be thicker, to occur in larger quantity, and 

(or) to have relatively large lateral extent, they definitely 

would be of engineering significance. 

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