LANDSLIDES OF THE CINCINNATI, OHIO, AREA

Landslides in 

Colluvium

U.S. GEOLOGICAL SURVEY BULLETIN 2059-B

Landslides in Colluvium

By ROBERT W. FLEMING and ARVID M. JOHNSON

LANDSLIDES OF THE CINCINNATI, OHIO, AREA

U.S. GEOLOGICAL SURVEY BULLETIN 2059-B

The behavior ofcolluvial 

landslides is strongly affected 

by differences in thickness

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Robert M. Hirsch, Acting Director

For sale by

U.S. Geological Survey, Map Distribution

Box 25286, MS 306, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government.

Library of Congress Cataloging-in-Publication Data

Reming, Robert W.

Landslides in colluvium; the behavior of colluvial landslides is strongly affected by 

differences in thickness / by Robert W. Reming and Arvid M. Johnson.

p. cm. (U.S. Geological Survey bulletin ; 2059) 

(Landslides of the Cincinnati, Ohio, area; ch. B)

Includes bibliographical references.

Supt. of Docs, no.: 119.3:2059

1. Landslides Ohio Cincinnati Region. 2. Colluvium Ohio 

Cincinnati Region. I. Johnson, Arvid M. II. Title. III. Series. 

IV. Series: Landslides of the Cincinnati, Ohio, area ; ch. B. 

QE75.B9 no. 2059 

[QE599.U5]

557.3 s dc20 93-15779 

[551.3'07] CIP
CONTENTS

Abstract................................................................................................................................. Bl

Introduction.......................................................................................................................... 2

Acknowledgments ..................................................................................................... 2

Geology and Physiographic Setting ..................................................................................... 2

Delhi Pike Landslide Area ................................................................................................... 3

Delhi Pike Study Area ......................................................................................................... 5

Thick Landslides ........................................................................................................ 5

Sequence of Movement ....................................................................................... 7

Deformation Caused by Thick Landslides .......................................................... 10

Subsurface Water in Thick Landslides ................................................................ 12

Summary of Thick Landslides ............................................................................. 13

Thin Landslides ......................................................................................................... 15

The Thin Landslide at Delhi Pike ........................................................................ 16

Trenches and the Failure Surfaces ....................................................................... 19

Properties of the Colluvium ................................................................................................. 20

Stability Analyses ................................................................................................................ 22

Concluding Remarks ........................................................................................................... 23

References Cited .................................................................................................................. 24

PLATE

[Plate is in pocket]

1. Profiles of trenches and map of landslide features, borings, and trenches in the Delhi Pike study area near 

Cincinnati, Ohio.

FIGURES

1. Map showing location of the Delhi Pike study area and important geographic features ......................................... B3

2. Geologic map of the Delhi Pike study area .............................................................................................................. 4

3. Photographs showing emergent toes of deep-seated landslides near intersection of

Hillside Avenue and Darby Road ............................................................................................................................. 6

4. Photograph of landslide scarp for thick slide that heads on Delhi Pike .................................................................... 7

5. Sketch map of positions of tilted pine trees, walls, and landslide toes on the property

at 5434 Hillside Avenue ........................................................................................................................................... 8

6. Photographs of two pine trees tilted by landslide movement at 5434 Hillside Avenue ........................................... 9

7. Graph showing thickness of growth rings in the "west tree" of figure 6, plotted as a

function of time ......................................................................................................................................................... 10

8. Graph showing thickness of growth rings in the "east tree" of figure 6, plotted as a

function of time ......................................................................................................................................................... 11

9. Photograph of bulge produced by landslide toe in asphalt parking area at Anderson

Ferry Road and River Road....................................................................................................................................... 12

10. Photograph of landslide toe in Mount Adams section of Cincinnati ........................................................................ 13

11. Photograph of near-vertical bump in landslide toe ................................................................................................... 13

12. Water-level record of 1 year for an open-tube piezometer in a limestone layer in

bedrock .........................................._^ 14

m
IV CONTENTS

13. Photograph looking uphill along Delhi Pike from the location of trench 2 .............................................................. B15

14. Photographs of thin landslide along Columbia Parkway, east of downtown Cincinnati.......................................... 17

15. Water-level and precipitation record for an open-tube piezometer placed at contact between colluvium and

	bedrock..................................................................................................................................................................... 18

16. Scanning-electron micrographs of portions of the failure surface ............................................................................ 20

17. Photograph of kinked roots on an exposed failure surface ....................................................................................... 20

18. Graph of hypothetical force-ratio-displacement models for thin and thick landslides ............................................. 23

TABLES

1. Summary of selected physical properties of Eden and Pate Soil Series ................................................................... B21

2. Summary of physical properties of colluvium and shale from the Delhi Pike study area......................................... 21

3. Residual strength of colluvium from the Delhi Pike study area ............................................................................... 22

CONVERSION FACTORS

For the convenience of readers, the metric units used in this report may be converted to inch-pound units by using the following 

factors:

Multiply metric units By To obtain inch-pound units

micrometers (um) 3.937xlO~5 inches

millimeters (mm) 0.03937 inches

centimeters (cm) 0.3937 inches

meters (m) 3.281 feet

kilopascals (kPa) 0.145 pounds per square inch
LANDSLIDES IN COLLUVIUM

i f 

By Robert W. Fleming and Arvid M. Johnson

ABSTRACT

The most common and destructive landslides in the 

Cincinnati, Ohio, area are formed in colluvium. Colluvium is 

formed from bedrock units by weathering and slaking of 

shales. The principal colluviurn-producing bedrock unit is 

the Kope Formation, which occupies the lower 60-70 m of 

hillslopes between the level of the Ohio River and an upland 

some 150 m above the river level. This formation, which 

contains about 80 percent shale and 20 percent limestone, 

slakes readily to produce a stony, silty clay colluvium. Overlying formations contain smaller amounts of shale, typically 

produce smaller amounts of a more stone-rich colluvium, 

and support steeper slopes. The colluvium forms a wedgeshaped mass ranging up to about 15 m in thickness. In the 

upper parts of the slopes, grades are steeper and the colluvium is thinner.

We recognize a significant difference in landslide 

behavior in slopes underlain by thick and thin colluvium. 

Landslides in thick colluvium that is, more than 2 m 

thick typically occur in the spring but can occur at any time 

of the year in response to a disturbance, such as grading. 

During a movement episode, the landslides typically move 

only a few centimeters to perhaps a meter. In form, these 

thick landslides consist of a single zone of overlapping 

scarps at the head and multiple toe bulges downslope. The 

flanks of movement are indistinct; shear displacement is evidently distributed over a broad zone. Analysis of a 37-yr 

record of movement, as revealed in disturbance to trees at 

our Delhi Pike study site, showed a small amount of movement nearly every year. During the 37-yr interval, there were 

two episodes of abrupt movement of several centimeters, 

both during years of above-average precipitation. For the 

most part, however, movements occurred during years of 

normal precipitation, when water levels were below the failure surface except at the most downslope toe of movement.

'U.S. Geological Survey, Box 25046, MS 966, Denver, CO 80225. 

'lDept. of Earth and Atmospheric Sciences, Purdue University, West 

Lafayette, IN 47907.

Landslides in thin colluvium that is, less than about 2 

m thick typically occur in the spring after the ground has 

thawed and before the vegetation has fully blossomed. Their 

movements are associated with rainfall, but precise timing 

has not been measured. Measurements of water levels in thin 

colluvium reveal that, during most springtimes, the colluvium is saturated to the ground surface for brief intervals. 

The thin landslides take the form of multiple scarps and a 

single toe of movement. For most thin landslides, the flanks 

are well-defined, simple boundaries. The multiple scarps are 

evidence for stretching or extension being the dominant form 

of kinematic behavior. Indeed, thin landslides are characterized by stick-slip behavior in which the landslides may 

accelerate after initial failure and slide completely out of 

their scars. During movement, they commonly pull themselves apart, leaving deposits that consist of separated hummocks or slabs of colluvium.

Four trenches were dug into the colluvium to examine 

the failure surfaces and to obtain samples for laboratory testing. The failure surfaces are paper thin, highly polished, and 

striated. At all scales of observation, roughness is evident in 

the surfaces. At a scale of a few micrometers, the surfaces 

have small steps between shiny surfaces that appear to be 

analogous to chatter marks on rocks in fault zones. At a 

larger scale, the surfaces are scratched by fossil fragments 

and sand-size grains in the colluvium. At a still larger scale, 

the surfaces bifurcate around rock fragments, and multiple 

surfaces occur where the shape of the failure surface is 

changing.

Residual shear tests were conducted on samples from 

near the failure surfaces. Strength parameters varied depending on the way the sample was prepared and tested. Minimum values were obtained in a ringshear device on samples 

that had the coarse fractions removed. A reasonable estimate 

of the residual strength parameters is an angle of internal 

friction of 16 degrees with a small cohesion intercept of 10 

kPa. Other typical properties of the colluvium are LL=45, 

PI=22, sand =10 percent, silt = 30 percent, and clay = 60 percent. The clay minerals are predominantly illite and mixedlayer clay. Stability analyses conducted by back-calculation 

gave expectable results for the thick landslides. At equilibrium, our measured values of residual strength are adequate

Bl
B2 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

to support the slope for the geometry and water conditions 

observed. For the thin landslides, the measured strength 

appears insufficient to support the slope. Additional strength 

provided by tree roots, roughness of the failure surface, or 

small residual cohesion could account for the discrepancy 

between apparent strength and stability.

INTRODUCTION

Annual per capita costs of damage due to landsliding in 

Hamilton County, Ohio (Cincinnati and vicinity), are among 

the highest of anywhere in the United States. Annual per 

capita costs for the period 1973-78 were $5.80, unadjusted 

for inflation; total costs of damage were nearly $31 million 

for the same 6-year period. Not included in this total was 

nearly $30 million expended after 1978 for a single landslide 

that occurred in 1974 in the Mt. Adams section of Cincinnati 

(fig. 1) (Fleming and Taylor, 1980).

A separate study of costs of landslide repair, done by 

students and faculty from the University of Cincinnati, found 

that the annual direct cost of emergency repairs to local 

streets in the City of Cincinnati is about $0.5 million. 

Deferred repairs of landslide damage to Cincinnati streets 

amounted to about $18.5 million in 1987 (Earth Surface Process Group, 1987).

The most common and destructive landslides are in 

slopes underlain by colluvium. The colluvium is derived by 

weathering of subjacent bedrock and accumulates on slopes 

as a wedge-shaped mass of stony clay.

Two distinct types of landslides occur in the colluvium. 

The two types have different morphologies and kinematic 

behavior, and they appear to be triggered by different stimuli. The most striking difference between the two types of 

landslides is in thickness. Thin landslides, less than 2 m 

thick, occupy the upper parts of hillslopes where the colluvium is thin. Thick landslides, more than 2 m thick, occupy 

the lower parts of the slopes.

In this chapter, we describe the Delhi Pike area, which 

is an area of landsliding we believe to be representative of 

landslides in colluvium throughout the Cincinnati metropolitan area. The area has been the focus of several detailed 

studies reported in other chapters in this bulletin. The purpose of this chapter is to describe the physical setting and 

movement styles of the landslides and, thus, to provide a 

context for the more narrowly focused chapters that follow.

ACKNOWLEDGMENTS

Onder Gokce, University of Cincinnati, helped map the 

landslides, logged borings and trenches, and read inclinometers and piezometers. He incorporated many of those data in 

his Ph.D. dissertation. Sherry Agard, U.S. Geological Survey, Denver, analyzed the tree cores. Roger Nichols, U.S. 

Geological Survey, Denver, conducted the drilling and

testing program. The base map was prepared from aerial 

photographs by James Derrick. Property owners Dale 

Schmale, Edgar Alien, and the College of Mount St. Joseph 

granted access for the study. To all these people and to the 

college, we express our sincere appreciation.

GEOLOGY AND 

PHYSIOGRAPHIC SETTING

The landscape in the Cincinnati area consists of a dissected upland surface, hillslopes along the Ohio River and 

principal tributaries, and flood plains and terraces. Maximum relief is about 150 m. The uplands are mantled mainly 

by glacial deposits, mostly of Illinoian age. Sedimentary 

bedrock underlies the till at various depths. Bedrock is typically exposed in the upper parts of hillslopes as ledges of 

limestone and in the floors of some of the smaller postglacial 

valleys. The Ohio River and its tributaries (Mill Creek, Licking River, Little Miami River, Miami River, and Whitewater 

River; fig. 1) have been strongly imprinted by their glacial 

history and have flood plains and terraces of varying widths. 

Materials in the terraces and flood plains vary from sand and 

gravel to laminated silts and clays.

The bedrock geology of the Cincinnati area consists of 

very gently dipping (1-2 m/km) shale and limestone of Late 

Ordovician age. The shale beds in the bedrock sequence are 

poorly cemented and slake to their constituent grains in 

response to moisture and temperature changes. Three of the 

bedrock units contain significant amounts of shale and produce colluvium. These are, from the oldest, the Kope Formation, the Fairview Formation, and the Miamitown Shale. The 

Kope Formation occurs near the level of the Ohio River and 

occupies the lower 60-70 m of hillslopes along the Ohio 

River and its tributaries. The overlying 30-m-thick Fairview 

Formation and undifferentiated bedrock as much as about 50 

m thick occupy the remaining slope between the river and an 

upland area, which is typically mantled by loess or glacial 

deposits.

In general, the amount of shale decreases upsection. 

The lower part of the Kope Formation contains about 80 percent shale. Shale content diminishes to about 70 percent in 

the upper 12m of the Kope Formation, and the Fairview Formation and overlying undifferentiated bedrock contain less 

than 50 percent shale (Osborne, 1974; Ford, 1974; Luft, 

1971,1972; and Gibbons, 1972). The changing shale content 

commonly is expressed as a slight break in slope at the contact between the Kope and overlying formations; slopes 

formed on the Kope Formation are a few degrees flatter than 

slopes on overlying bedrock.

The colluvium varies in thickness depending on its 

position on the slope. In the lower part of the slope, colluvium is as thick as about 15 m. Colluvium thickness 

diminishes to a meter or less near the top of the Fairview Formation in the upper part of the slope.
LANDSLIDES IN COLLUVIUM

84°30'

B3

39°15' 

39°00

0 5 10 MILES

0 5 10 KILOMETERS

Figure 1. Location of the Delhi Pike study area and important geographic features in the Cincinnati, Ohio, area.

DELHI PIKE LANDSLIDE AREA

The Delhi Pike landslide area is about 12 km west of 

downtown Cincinnati in unincorporated Hamilton County, 

Ohio (fig. 1). The Delhi Pike landslides are just a few of the 

many landslides that occur within a narrow stretch of the 

Ohio River Valley extending from Mill Creek to the Miami 

River about 22 km farther west. This stretch of the valley 

was created when glacial ice of Illinoian age blocked a more 

northern channel, creating a lake. Silts and clays deposited in 

the lake have been involved in major landslides in other parts 

of the metropolitan area. The spilling of the lake eroded the 

modem channel of the Ohio River (Durrell, 1961a, 1961b).

The total width of this narrow section of the valley, as 

measured between the uplands of Ohio and Kentucky, is 

about 1.5 km, compared to a width of 2.5 km upstream and 

4.0 km downstream. The narrow part of the valley lacks a 

continuous flood plain or terraces and essentially consists of 

slopes of colluvium from the level of the Ohio River to 

ledges of limestone outcrop near the top. Landslides have 

occurred along these slopes on both sides of the Ohio River. 

In 1973, extensive landsliding resulted in temporary closure 

of a 5-km stretch of State Route 8 west of Bromley, Ky. (fig. 

1), and in the destruction of several homes. At the same time, 

in Ohio, landslides were destroying homes and sections of 

several roads. As part of this widespread landslide disaster,
B4 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

multiple landslides caused the permanent closure of Delhi 

Pike in our study area (The [Delhi Township] News, April 

11,1973, p. 1, "Sister's Hill too hazardous; closed by County 

Engineer").

Many of the streets, buildings, and railroads in the 

Delhi Pike area were constructed before the turn of the century. A topographic map of Cincinnati published in 1912 

shows the same street and railroad alignments in the area that 

exist today. Transportation routes are parallel to the Ohio 

River and trend along the hillslopes roughly parallel to topographic contours. From the level of the Ohio River, at progressively higher elevations, are railroad tracks (12 m), 

River Road (about 20 m), and Hillside Avenue (about 40 m 

upslope from the river) (fig. 2). Delhi Pike was an old road 

that provided a connection between Hillside Avenue at elevation 170 m and Delhi Township at elevation 260 m in the 

uplands. A few homes were built on the downslope side of 

the lower part of Delhi Pike, but the upslope side was apparently too steep for development.

The colluvial slope has an overall concave-upward profile. Slope inclination increases from about 8° or less near 

the Ohio River to about 10°-12° along the section between 

River Road and Hillside Avenue. On the upslope side of 

Delhi Pike, the inclination is 18°-25°. The initial character

of the lower, more gently sloping portions of the slope has 

been obscured by development. In undeveloped areas in 

other parts of the county, slopes at this level have a smooth 

but lobate texture; the lobes, typically 1 or 2 m high and 

10-20 m across, appear to represent the distal ends of landslides or earthflows.

Only a few landslides have been active in historic time 

in the gentle slopes along River Road. Two notable slides 

occurred at North Bend, about 10 km downstream from 

Delhi Pike, and near Riverside-Harrison School, about 8.7 

km upstream. The landslide at North Bend, near the William 

Henry Harrison Monument, occurred during the 1970's 

above the outside of a bend in the river, where the slope was 

locally oversteepened by river erosion and loaded with a 

small amount of fill. The other landslide, near the RiversideHarrison School, occurred in response to an excavation for a 

railroad roundhouse in 1927 and ultimately destroyed about 

40 homes (Von Schlichten, 1935). Both examples demonstrate that the thick colluvium near the level of the Ohio 

River will fail by landsliding if the hillslope is adversely 

disturbed.

Within the Delhi Pike study area, the slopes have failed 

extensively (fig. 2). Hillside Avenue is deformed along 

much of its length, and numerous empty lots containing

Figure 2 (above and facing page). Geologic map of the Delhi Pike study area. See figure 1 for location. Contact between the Kope (Ok) 

and Fairview (Of) Formations is exposed in cut slope in western part of the map area. Contact was projected through map area using apparent 

dip angle from published geologic maps of areas directly across the Ohio River in Kentucky (Gibbons, 1972). The Fairview Formation was 

assumed to be 30 m thick.
LANDSLIDES IN COLLUVIUM B5

house foundations and overgrown remnants of driveways 

and walls attest to a long history of slope movements. Still 

farther upslope are scarps, scars, and lobes produced by failure of a thinner mantle of colluvium.

DELHI PIKE STUDY AREA

Within the area of extensive landslides shown in figure 2, a smaller area containing both thick and thin landslides was selected for detailed study (pi. 1). The trace of 

Delhi Pike extends east-west across the middle of the area 

and divides shallow landslides uphill from deep-seated 

landslides downhill. Subsurface conditions were investigated with borings and trenches. Instrumentation was 

installed in both shallow and deep slides to determine the 

geometry and water conditions and to obtain samples for 

laboratory testing.

THICK LANDSLIDES

The heads of the thick landslides are in the fill on the 

downhill edge of Delhi Pike. The fill contains overlapping 

low scarps and tension cracks (pi. 1) extending to the break 

in slope at the shoulder of the road. These cracks, which indicate stretching or extension of the landslide material, are 

confined to the fill area. All indications of landsliding farther 

downslope are of shortening or compression. The compressional features are difficult to recognize in natural slopes but

are well expressed where they intersect a wall, road, or walkway. Figure 3 consists of two photographs of toes of deepseated landslides; locations are shown on the map of the 

Delhi Pike landslide complex (pi. 1).

The lowermost toe (fig. 3A) is a broad bulge in Hillside 

Avenue, where the vertical component of displacement is 

larger than the horizontal component. The edge of the road 

showed no visible offset even though the bump grew perceptibly over the 5-yr period of observation. Farther uphill, displacement on another toe of movement (fig. 3B) is almost 

entirely horizontal.

The deep-seated landslide did not displace inclinometer 

casings enough during our monitoring period of 1979-80 to 

allow us to accurately determine the positions of failure surfaces. Based on borings, the maximum depth to the failure 

surface was about 4 m at the head of the slide (including the 

thickness of side-hill fill), 2.3 m near the stone walls (boring 

Wl), about 6 m near boring 9, and about 3.5 m at boring 20 

(locations shown in pi. 1).

The shape of the failure surfaces can be inferred from 

the mappable features at the ground surface. The head of 

the landslide consists of a narrow zone, as much as 4-5 m 

wide, of extensional faults and cracks. The faults and 

cracks are vertical to steeply dipping downslope. The horizontal offset of Delhi Pike is smaller than the vertical separation of blocks of displaced road (fig. 4). Bulges and other 

indications of shortening are evident at the first break in 

slope downslope from the head. These bulges apparently

200 400 600 800

100 200 

CONTOUR INTERVAL 25 FT (7.6 M)

1000 FEET

V 

300 METERS

Undifferentiated

Fairview Formation

Kope Formation

Upper 

Ordovician

EXPLANATION

 Bedrock contact Dashed where approximate 

Landslide scarp Dashed where approximate 

Landslide toe Dashed where approximate 

Strike-slip fault Showing direction of movement
B6 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

Figure 3. Emergent toes of deep-seated landslides near intersection of Hillside Avenue and Darby Road. See map on plate 1 for locations. 

A, View west toward the intersection. The broad bump in the middle of view is a toe for a thick landslide that extends 60 m upslope. Note 

the tilted utility pole at the left of the view and damage to the stone wall on the right. The asphalt paving over the bump has recently been 

replaced. The dark-colored marks in the eastbound (oncoming) lane are produced by vehicles scraping on the road surface after bouncing 

over the bump. The road has not been significantly displaced laterally; the principal movement direction is vertical. B, Stairway, about 18 

m farther upslope, displaced a few centimeters to the right (south). Principal movement direction is horizontal.
LANDSLIDES INCOLLUVIUM B7

Figure 4. View to northeast of landslide scarp for thick slide that 

heads on Delhi Pike.

reflect predominantly horizontal displacement; a cistern 

that was originally about 3 m from the stone wall (Mr. Dale 

Schmale, oral commun., 1980) near boring 14 is now only 

2 m away, and the wall has not been perceptibly displaced 

vertically.

The next series of bulges and thrusts occurs just downhill from a break in slope above Hillside Avenue (pi. 1, fig. 

3). The displacement of the stone and concrete work on the 

slope is nearly horizontal. Still farther downslope, at Hillside Avenue, the displacement direction is predominantly 

upward. This toe of movement appears to be the downslope 

limit of active sliding. In plan view, the toes are lobate and 

have local relief of a few centimeters to about 2 m.

Trench 1 was placed through one of the landslide 

lobes on the east side of the study area. Here, the colluvium 

consists of two separable units, a brown pedologic soil 

overlying yellowish-gray colluvium (pi. 1). One slickensided failure surface was found in the trench wall. Toward 

the upslope end of the trench, the surface was within the 

yellowish-gray colluvium; toward the downslope end of the 

lobe, the yellow-gray colluvium had overridden part of the 

brown pedologic soil. The failure surface was essentially 

horizontal at a depth of about 2 m. Boring 11 is about 4 m 

west of trench 1 and contains an inclinometer casing. The 

casing, originally 6.6 m long, has been constricted at a 

depth of 3.6 m (measured May 10, 1990). Thus, at this lobe 

of the landslide complex, at least two failure surfaces exist, 

one at a depth of about 2 m and the other at 3.6 m. The failure surface at 2 m apparently created the lobe containing 

trench 1 and boring 11 (pi. 1). The failure surface at 3.6 m 

may reach the surface at the 560-ft (171-m) contour. If so, 

the deeper failure surface slopes about 7° downhill toward 

Hillside Avenue. We do not know whether movement has 

occurred on the shallower surface since our study began, 

but if it has, the amount was insufficient to constrict the 

inclinometer casing at that depth.

SEQUENCE OF MOVEMENT

A sketchy history of the overall movement of the thick 

landslide can be inferred from deformation of features on the 

landslide and from an interview with the property owner, 

Mr. Dale Schmale (oral commun., 1981). Prior to abrupt 

movement of the landslide in the spring of 1973, the property 

identified as 5434 Hillside Avenue contained four structures a house, a barn, a garage, and a shed. The house was 

at least 100 yr old and was situated on the flat area near borings 9, 10, and 14 (pi. 1). The garage, barn, and shed were 

east of the house near trench 1. Mr. Schmale purchased the 

property in 1972 and was involved in remodeling the house 

when it was destroyed by movement. The first indication of 

trouble was when a 400-yr-old tree, located at a toe of movement just east of boring Wl, toppled onto the house 

(Schmale, oral commun., 1981). At that time, there were 

cracks in Delhi Pike, but Mr. Schmale had noticed no evidence for sliding on his property. Within a few days after the 

tree toppled, the house and other structures were deformed 

beyond repair. The entire episode of movement occurred in 

a 3-week period of April 1973.

As recently as 1990, the overall appearance of the property remained as it was in 1973. Small amounts of movement 

had occurred that were sufficient to squeeze the borings 

closed and to reestablish the bulge in Hillside Avenue, in 

spite of repeated repairs. However, there had been no episodes of abrupt movement similar to the episode in 1973.

Additional inferences can be made about movement of 

the thick landslides from disturbance to trees. Trees on 

undisturbed hillslopes tend to grow vertically from the tip of 

the stem and to form concentric growth rings (Kozlowski, 

1971). When a tree is tilted, it responds to the change both 

internally and externally. New growth from the stem tip continues to grow vertically, producing a bend or curve in the 

stem. Eccentric growth in the trunk creates asymmetric tree 

rings and reaction wood. In conifers, the growth rings are 

wider and reaction wood forms on the downslope side 

(Agard, 1979). In general, reaction wood can be distinguished visually from normal wood in that it is darker, has a 

denser, smoother appearance, and has little contrast between 

early wood and late wood in a growth ring (Agard, 1979).

Tree cores were used to examine the growth behavior of 

two pine trees on the thick landslide at Delhi Pike. The pine 

trees were planted in the early 1940's in an open area along 

the driveway to the house at 5434 Hillside Avenue. Both 

trees have been tilted and deformed in response to landslide 

movements. The positions of the trees relative to nearby 

landslide features are shown in figure 5.

Figure 6A is a photograph of the two pine trees viewed 

northwest from near the site of the house at 5434 Hillside 

Avenue. The tree on the left is termed the "west tree" and 

the tree on the right the "east tree." The bulge in the foreground is a toe bulge that, from right to left, trends through 

dry grass and crosses the ivy-covered stone wall about in line 

with the west tree. The bulge passes just to the right of the
B8 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

Photo point 

fig. 6B

N 

(Approx.)

20 METERS

+ + +

W-2

EXPLANATION

Topographic contour Contour interval 2 ft (0 6 m)

Landslide toe 

 Core number and direction

Figure 5. Sketch map of positions of tilted pine trees, walls, and landslide toes on the property at 5434 Hillside Avenue.

west tree, and landslide movement has pushed the tree 

toward the left or downslope. In response, the tree has 

grown straight for about 5 m and then is continuously curved 

except for one small, more abrupt bend about halfway to the 

top. The continuously curved portion of the tree appears to 

be a response to small annual increments of landslide 

movement, and the single, abrupt bend could be a response 

to one event of more than normal movement of the landslide.

The east tree is about midway between two toe bulges 

(fig. 5). The same toe bulge that is pushing the west tree 

forward is about 3 m downslope from the east tree. Another 

toe bulge is about 3 m upslope from the east tree. The trunk 

of the east tree is straight in the lower 5 m and has a gentle 

bend over the next 5 m to an abrupt bend about 10 m from 

the base (fig. 6B). The abrupt bend is apparently a response 

to a dramatic uphill tilt to the tree. In the year following the 

abrupt tilting, the east tree put out a large branch on its uphill 

side (fig. 6fi). From the abrupt bend to the top of the tree, the 

trunk is somewhat, but not systematically, contorted. Counting sets of branches from the tops of both trees down to the 

abrupt bends shows that both bends were created about the 

same time, a little more than 20 yr before the 1980 growing 

season.

Cores were taken from the trees at heights of 30-50 cm 

above the ground. The core numbers and directions of coring

are shown on figure 5. The cores were examined microscopically and the rings were counted and measured by Sherry 

Agard (U.S. Geological Survey, Denver, Colo.).

The results for the west tree are in figure 7. Shown are 

the thicknesses of the growth rings for the downhill (W3), 

uphill (Wl), and the lateral (W2 and W4) sides of the tree. 

Also plotted is the percent eccentricity of the growth rings on 

opposite sides of the tree. Both W2 and W4 penetrated the 

center of the tree and established that the tree was a 40-cmhigh sapling in 1943.

For W2 and W4, the growth rings are almost exactly the 

same size through 1947, when the east side of the tree (W4) 

began producing consistently thicker rings. This pattern 

continued through 1980 with exceptions only in 1962-63 

and 1970. For cores W3 and Wl, the downhill portion of the 

growth ring, which is the direction of tilt, was consistently 

thicker than the uphill portion. Exceptions occurred only 

during 1963-65 and 1969.

The data for the east tree are plotted on figure 8. Cores 

E3 and El are the downhill and uphill sides of the tree, 

respectively, and E4 and E2 are the left and right sides of the 

tree as viewed looking uphill. E6 is a core taken from a point 

just above the abrupt bend about 10m above the ground surface. The E6 core passed through the center of the trunk and 

continued through the tree.
LANDSLIDES IN COLLUVIUM B9

Figure 6. Two pine trees tilted by landslide movement at 5434 

Hillside Avenue. A, Both trees as seen from the southeast. "West 

tree" is on left and "east tree" is on right. B, "East tree" as seen from 

the northwest

The east tree is strongly tilted upslope, and the El 

growth rings (uphill side) are consistently thicker than those 

on the downhill side. Exceptions are in 1949-50, 1955, 

1962-63, and 1968. The trend of the eccentricity shows 

increasing thickness of the uphill side of the ring relative to 

the downhill side. The core for E6 dates the year of strong 

tilting as 1958 or 1959.

For both the east and west trees, the year 1959 is a year 

of markedly suppressed growth. The east tree also experienced suppressed growth in 1958. Growth was somewhat 

suppressed in both trees in 1965, but we have found no other 

evidence of landslide movements that year.

The combined observations of external changes to the 

trees (curved trunks and abrupt bends) and the tree-ring data 

lead to the following conclusions. There were active slope 

movements at the site as early as the mid-1940's, but the 

tree-ring data cannot be extended back in time beyond those 

years. The most dramatic movement apparently occurred in 

1958, following near-record precipitation in calendar year 

1957. Abrupt tilting and suppressed growth affected both 

trees during the 1959 growing season.
BIO LANDSLIDES OF THE CINCINNATI, OHIO, AREA

£10

t

Ring Widths

Wl &W3

ws ; i

060 

b=40

W2&W4

1940

Wl +W3

Eccentricity

A A

W4

W2 + W4

1940 1950 1960 

YEAR

1970 1980

Figure 7. Thickness of growth rings in the "west tree" of figure 6, plotted as a function of time. Cores are from the uphill (W1), downhill 

(W3), and lateral (W2 and W4) sides of the tree. Also plotted is the percent eccentricity of rings on opposite sides of the tree.

We were able to measure a small amount of movement 

in an inclinometer casing in boring 8 and with an extensometer (for locations, see pi. 1) during 1979-80. The inclinometer casing was deformed slightly by movement during the 

winter of 1979-80. Extensometer 2 extended through a 

storm drain that crossed under Delhi Pike about 25 m east of 

the pine trees. The upslope end of the extensometer was 

attached to a box culvert in nonmoving ground between the 

thin landslides uphill and the cracks in Delhi Pike downhill. 

Movement was measured from December 1979 to June 

1980. The extensometer automatically recorded elongation 

in increments of 1.73 mm by punching a paper tape; movement was sampled every 15 min. The first indication of 

movement was on January 30,1980, when 5.2 mm was measured over an 8-hr period. Additional movement of at least 7 

mm was distributed over the next 4 months; the recorder was 

inoperable for 2!/2 weeks in April. Overall, 12.1 mm was 

measured during the 6-month interval.

Although our measurements clearly showed movement 

during 1979 and 1980, the tree rings formed in those years 

had no irregularities in growth-ring thicknesses (figs. 7 and 

8). We suspect that a small amount of movement occurs during most years, but large, abrupt movements of the thick 

slides at Delhi Pike apparently occurred only during 

1958-59 and 1973.

The current owner of the property, Mr. Schmale, can 

testify that the perception of small movements is difficult 

without a good reference feature for measurement. Even 

though the pine trees along his driveway at 5434 Hillside 

Avenue had been strongly tilted by 1972, there was no evidence of distress in his house standing less than 10 m downslope from the lower toe bulge shown in figure 5 (Mr. Dale 

Schmale, oral commun., March 17, 1981). Active landsliding had already damaged property several hundred meters

east of Mr. Schmale's property. However, it was Mr. 

Schmale's impression that the ditch and shoulder of Delhi 

Pike were intact and free from cracks in 1972. Abrupt movement in the early spring of 1973 revealed several layers of 

patching in Delhi Pike, which would have covered preexisting cracks but proves the existence of pre-1972 movement 

uphill from Schmale's house. Because the 100-yr-old house 

was virtually free of structural distress at the time of abrupt 

landsliding in 1973, it is unlikely that displacement had 

occurred on throughgoing landslide failure surfaces then. 

The displacement occurring in the Delhi Pike apparently 

extended to a toe only 10-15 m downhill and did not involve 

the house. At the time of our study (1979-81), we were able 

to identify two additional landslide toes downslope from the 

house, and movement on those failure surfaces responsible 

for the landslide toes was measured in inclinometer casings 

in borings 9 and 20.

We interpret these observations to mean that the slope 

was failing progressively, perhaps beginning with the construction of Delhi Pike in the 1800's. The failure process 

consisted of creating multiple failure surfaces, which produced several toes of movement at increasing distances 

downslope, beginning from a single scarp in Delhi Pike. The 

100-yr-old farm house was not destroyed until progressive 

failure produced a failure surface that emerged farther down 

the slope. The single scarp on Delhi Pike is now the upper 

part of a landslide that contains at least four toes and, presumably, four separate failure surfaces that emanate from the 

single failure surface near the scarp.

DEFORMATION CAUSED BY THICK LANDSLIDES

One of the more interesting aspects of the deeper seated 

landsliding along Hillside Avenue is that so much evidence
LANDSLIDES IN COLLUVIUM fill

£10 

tn

F.10

£10

fc

E1 &E3

Ring Widths

E2&E4

E6Top

Downslope

1959 

pith

1940 1950 1960 

YEAR

1970 1980

!40

060

140

1940

E3

Eccentricity

E1 +E3

E4

E2 + E4

Downslope 

Up + Downslope

1950 1960 

YEAR

1970 1980

Figure 8. Thickness of growth rings in the "east tree" of figure 6, plotted as a function of time. Cores are from the uphill (El), downhill 

(E3), and lateral (E2 and E4) sides of the tree. E6 is the tree core from just above the sharp bend shown in figure 6B. The bend probably 

formed in 1958. Also plotted is the percent eccentricity of rings on opposite sides of the tree.

of past development remains in place. We counted nearly 30 

foundations along Hillside Avenue between Anderson Ferry 

Road and Delhi Pike for houses that apparently have been 

destroyed by landsliding. The landslides have been 

damaging structures in this area for more than a century. 

Homes involved in movement episodes typically are distressed to the point that they must be razed. Yet, the cumulative movement of all these events has not markedly deflected 

the alignment of Hillside Avenue, and foundations of 

destroyed structures are recognizable and persist. Evidently, 

the deep-seated landslides undergo significant internal 

deformation relative to the amount of sliding displacement.

The deformation that is typical in landslide toes is illustrated in figure 9. The view is of a landslide toe encroaching 

on asphalt pavement along a break in slope at Anderson 

Ferry Road and River Road (fig. 1). This photograph, taken 

in August 1982, documents deformation that occurred over 

a period of about 9 years.

The bulge in the asphalt was about 26 m wide at the 

uphill edge and encroached 6.1 m into the blacktopped area. 

At the uphill edge, the blacktop was elevated 1.5 m, while it 

was displaced horizontally a maximum of 1 m in the middle. 

The horizontal displacement diminished to zero at the edges 

of the bulge. The distal edge of the bulging blacktop is not

thrust over adjacent, unfailed blacktop but merely elevated 

vertically. Thus, the direction of displacement at the leading 

and flanking edges of the deformed blacktop in the toe 

appears to be nearly vertical upward. Six meters back from 

the leading edge, motion is 1.5 vertical to 1.0 horizontal.

Figure 10 shows another example of deformation produced by movement of a landslide toe. In this case, at a landslide in the Mt. Adams area of Cincinnati, the curb of the 

street has not been displaced, but two slabs of concrete sidewalk have been lifted and displaced over the curb. For the 

larger slab on the right, horizontal displacement is 0.60 m, 

and the uphill edge of the slab is elevated 0.82 m.

The early stages of formation of a landslide toe were 

expressed along a driveway from Hillside Avenue just west 

of Delhi Pike. A slope underlain by colluvium was cut to 

provide access for construction of new apartments. Shortly 

after the cut was made, cracks formed in the colluvial slope 

about 25 m uphill from the edge of the road. A small bulge 

formed along the edge of the road, involving as much as 2 m 

of the paved surface. A photograph taken in 1982 (fig. 11) 

shows a bulged patch on the blacktop surface and a bulge 

along the edge of the driveway. In the foreground along this 

bulge on the edge of the driveway, several near-vertical 

shear surfaces are exposed. Tabular limestone fragments
B12 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

Figure 9. Bulge produced by landslide toe in asphalt parking area at Anderson Ferry Road and River Road. Vertical displacement in the 

toe greatly exceeds horizontal displacement.

Figure 10. Landslide toe formed in Mount Adams section of Cincinnati. Ratio of vertical to horizontal displacement is 1.4:1.

within the colluvium are preferentially oriented with their 

minimum dimension normal to the shear surfaces. At other 

places, limestone fragments in colluvium do not show a 

strong preferential orientation. Here, the fragments have 

been reoriented by pervasive shearing such that the crosssectional area exposed to shear is a minimum.

SUBSURFACE WATER IN THICK LANDSLIDES

The abrupt movement of thick landslides in April 1973, 

which destroyed several homes, occurred during a period of 

excessive precipitation. However, over a period of years, 

movement of the thick landslides appears to have been
LANDSLIDES IN COLLUVIUM B13

Figure 11. Near-vertical bump formed in landslide toe. Limestone clasts have been preferentially oriented with their minimum dimension 

at right angles to the direction of pervasive shearing. The bump has formed without appreciable horizontal offset.

caused as much by construction activity as by excess precipitation.

Our drilling and trenching failed to find saturated conditions anywhere within the thick colluvium except in boring 

20 at the toe. Saturated conditions must exist at other places 

in the colluvium, for we noted a line of springs near boring 

12 (pi. 1) and an ephemeral spring near boring 14. Boring 12 

was flooded with surface water from the springs and provided no worthwhile data, but colluvium in borings 9,10,13, 

and 14 was unsaturated.

The typical subsurface water condition was illustrated 

by measurements in boring 13. There, the colluvium was not 

saturated. Free water was first encountered in the first limestone bed under the colluvium that was penetrated by drilling. This water was under artesian pressure and responded to 

an annual cycle of maximum pressure in the late spring and 

minimum pressure in the early fall (fig. 12). In those parts of 

the landslide that extend nearly to the contact between bedrock and colluvium (that is, the head region), the artesian 

pressures could significantly reduce stability. Most of the 

toes of the thick landslides are entirely within the colluvium 

and significantly removed from the bedrock containing 

artesian water. The effect of the artesian pressure is

dissipated a short distance from the contact between bedrock 

and colluvium (R.L. Baum, U.S. Geological Survey, oral 

commun., 1985).

Probably during exceptional periods of precipitation, 

saturation and elevated pore-water pressures in the thick colluvium are more extensive than we found. However, inasmuch as we measured movement of the thick landslide 

during a period of below-average precipitation and during a 

period when water levels were generally below the various 

failure surfaces, saturation of the colluvium is not necessary 

for renewed movement on the existing failure surfaces.

SUMMARY OF THICK LANDSLIDES

The thick landslides occur in colluvium that is thicker 

than about 2 m. Morphologically, they consist of a simple 

head, a complex of toes, and poorly expressed flanks. The 

heads occupy a narrow zone containing a few scarps and 

open cracks; the horizontal component of displacement in 

the heads is smaller than the vertical component. The toes of 

movement typically emerge at several places downslope. If 

the toe emerges at a sharp break in slope, such as a roadcut, 

the vertical component of displacement is much larger than
B14 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

Boring 13

Colluvium

_ Bedrock 

(shale)

 ^ Bentonite seal

Open-tube 

piezometer

(Limestone)

Zone of 

Uplift Pressure

9

1979

11 1 

TIME (MONTHS)

Figure 12. Water-level record of one year for an open-tube piezometer (No. 13, pi. 1) sealed in a limestone layer in bedrock. Depth to 

layer was 3.4 m, and water level varied from 3.3 m during September 1979 to 1.8 m about May 1, 1980. The line of intersection of the 

limestone layer with the base of the colluvium is a zone of artesian pressure that develops a head as great as 1.5 m during the spring. (See 

inset figure.) (From Fleming and others, 1981.)

the horizontal component. If the toe emerges at a smooth or 

flat part of the slope, displacement is virtually all horizontal, 

and the lobe of moving ground may override the preexisting 

ground surface. The flanks of the landslide lobes are poorly 

expressed and could not be located in the field. Shear displacement on the landslide flanks is evidently distributed 

over too broad an area to produce cracking or faulting. However, the distributed shear may contribute to the extensive 

structural damage to homes that seems to take place when 

only small amounts of displacement have occurred.

The presence of a single head and multiple toes implies 

a single failure surface under the upper part of the landslide 

that splays into multiple failure surfaces farther downslope. 

The failure surface(s) appear to be contained within the 

colluvium rather than at the contact between colluvium and 

bedrock.

Eccentric growth rings and reaction wood in tree cores 

and multiple generations of asphalt patching on Delhi Pike 

are evidence that the thick landslide began to form at the

head and enlarged progressively. The position of the uppermost cracks in the head roughly coincides with the boundary 

between cut and fill in the roadbed. The abrupt movement 

that occurred in 1958-59 apparently extended only a few 

meters downslope from the cracks in the road to a complex 

of toes. The house and other structures on the property were 

destroyed by another episode of abrupt movement in 1973. 

Presumably, new failure surfaces formed that successively 

emerged farther down the slope in 1973 and later. Movement appeared to be continuing in 1990 on at least the deepest of these surfaces, which emerged as a bump in new 

asphalt on Hillside Avenue.

Abnormally large amounts of annual precipitation coincided with the abrupt movement episodes in 1958 and 1973. 

The association between excessive precipitation and landsliding has been so thoroughly documented for landslides 

around the world that it is unnecessary to do so here. We 

measured about 12 mm of movement of the thick Delhi Pike 

landslide during our only period of monitoring in 1979-81.
LANDSLIDES IN COLLUVIUM B15

Precipitation during the entire period of our study was average to below average, and water levels in open piezometers 

were generally below the level of the failure surface(s).

Our measurements in open-tube piezometers failed to 

document saturated conditions within the colluvial body of 

the landslide, although we did find water under artesian pressure in the limestone layers in the underlying bedrock. The 

pressures varied on an annual cycle, producing minimum 

values during the fall and maximum values in late spring. 

Most of the failure surfaces are well above the contact 

between bedrock and colluvium and, thus, subsurface water 

pressure in the bedrock is not a major control on the reactivated movement of these thick landslides.

THIN LANDSLIDES

The thin landslides occur on the uphill side of Delhi 

Pike (fig. 2) where slopes are significantly steeper than in the 

area of thick slides. Slope inclinations range from about 18° 

to 25°. An open woods of maple and ash trees, typically 

spaced about 3 m apart and lacking any appreciable understory, occupies the upper part of the slope. Farther downslope, near Delhi Pike, the hillslope supports a dense 

understory of various shrubs and vines and a canopy of small 

locust and elm trees. The change in vegetation occurs a short 

distance from the contact between the Kope and Fairview 

Formations.

For the most part, the slope is devoid of obvious scarps, 

flanks, or landslide toes. Rather, the hillslope has a very gentle undulatory surface superimposed on a series of irregularly spaced topographic benches. Slopes that have not failed 

within historical time may lack the well-defined scarps and 

flanks that are commonly observed in landslide deposits. 

More recent slope failures show all the classic features of 

landslides and, even though they quickly reestablish a vegetative cover, they remain recognizable topographic forms. 

Our experience with excavations and landslides throughout 

the metropolitan area is that virtually all these colluvial 

slopes have failed at some time in the past, and a trench anywhere through the colluvium would reveal a continuous failure surface near the colluvium-bedrock contact.

The typical form of the area underlain by thin landslides 

is best expressed toward the western edge of the area shown 

in figure 2, uphill from Hillside Avenue. Uppermost scarps 

of the slides extend into and beyond areas underlain by Fairview Formation and form a crudely scalloped upper boundary within the colluvium. The upslope ends of the landslides 

are broad amphitheaters with generally smooth slopes. Over 

most of the area, the scarps are expressed as a slight but continuous break in slope. The portion of the landslide on the 

Fairview Formation contains widely scattered benches and 

ramps that are subparallel to the topographic contours. These 

benches appear to be remnants of slide blocks that have 

detached from the scarp and been smoothed over time.

Downslope, on the Kope Formation, the benches and 

ramps are more consistently parallel to the topographic contours. The amphitheaters that produce the scalloped upper 

limit to sliding exist upslope from the Kope Formation; 

downslope, on the Kope Formation, slopes become straight 

without significant bulges or swales parallel to the contours. 

The benches on these straight slopes are 15-30 m long and 

consist of a stretch of slope about 2 m wide that is flatter than 

the overall slope and a similar width that is steeper.

Such benches are common on slopes formed on the 

upper part of the Kope Formation throughout the Cincinnati 

metropolitan area. We initially believed that these features 

were toes or lobes of thin landslides (Fleming and others, 

1981, fig. 6). Later trenching of several of these benches 

revealed that they overlie a limestone layer in the bedrock. 

The benches invariably contain a small-displacement listric 

fault in the colluvium that connects with the failure surface 

at the base of the landslide. Thus, the more or less continuous 

benches are not lobes or toes of movement. The listric fault 

is evidence of stretching and arching of the colluvium over a 

buried limestone layer.

The toe of thin-landslide movement (fig. 2) is at Delhi 

Pike where colluvium has spilled onto the uphill side of the 

road. Figure 13, a photograph of Delhi Pike from about the 

location of trench 2 (for location, see pi. 1), gives the impression that the road is very crooked. The road, however, contains only a gentle curve toward the left in the middle of the 

view and a curve to the right in the distance; otherwise it is 

straight. The uphill side of the road is covered in varying 

amounts by lobes of thin slide debris that have accumulated 

since the road was closed in 1973. The downhill edge of the 

road has been displaced by scarps of the thick landslides, but 

the uphill side of Delhi Pike has not moved.

The general form of the thin landslides, then, is multiple 

scarps and a simple, single toe. This general form is

Figure 13. View uphill along Delhi Pike from the location of 

trench 2. Landslides affect both sides of road. Despite appearances, 

the road is not crooked; thin landslides from upslope have spilled 

onto the left side and scarps of thick landslides have broken the 

right side of the road.
B16 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

expressed even more definitively at other thin landslides in 

the Cincinnati metropolitan area. Two examples are 

described below:

In 1980, a thin landslide on a slope near the Delhi Pike 

landslide complex literally pulled itself apart by stretching 

movement. The landslide, described by Riestenberg and 

Sovonick-Dunford (1983), was broken into numerous separate blocks. Some blocks slid completely out of the landslide 

scar, and others were connected to each other only by tree 

roots. A careful analysis of striations on the exposed failure 

surface and a match of trees and roots allowed Riestenberg 

and Sovonick-Dunford (1983) to reconstruct the sequence of 

failure. The landslide apparently failed from the top down; 

two elements at the extreme upper scarp were the first to fail. 

Twelve individual blocks could be traced from their initial to 

final positions. At the conclusion of movement, several 

blocks from upslope overrode blocks that were farther 

downslope.

This style of failure (that is, landslide debris being 

pulled apart into separate blocks, some of which slide completely out of the landslide scar) is evidence for a large 

reduction in resistance to sliding following the initial movement. Riestenberg and Sovonick-Dunford (1983) attributed 

the large initial strength to tree roots. Failure of the roots that 

extended through the potential failure surface could have 

resulted in a dramatic loss in strength. Riestenberg and 

Sovonick-Dunford (1983) calculated that the roots could 

have increased the factor of safety against sliding ninefold.

Another example of extreme extension of thin landslides is shown in figure 14. This landslide, which occurred 

in 1973 a few kilometers east of downtown Cincinnati along 

Columbia Parkway, is typical of many thin landslides. The 

landslide slid completely out of its site of failure, moved 

about 20 m over the ground surface, and spilled over a retaining wall onto Columbia Parkway. In figure 144, part of the 

landslide path is indicated by the light-colored material in 

the middle of the view. The initial failure occurred at the 

uphill end of the light-colored area. Individual landslide 

blocks that have separated during movement but remain on 

the slope are on the right side of the light-colored area. 

Unfailed material is on the left. At the extreme upper end of 

the scar, bedrock was exposed (not visible in the photograph) 

at the sole of the landslide. The lower part of the landslide 

scar contains four discontinuous benches or undulations. At 

least two of these benches continue to the left into the 

unfailed colluvium and are probably expressions of buried 

limestone layers in the bedrock underlying the colluvium.

The benches that are visible in the light-colored area in 

figure 14A are formed within the colluvium. Here, the colluvium has not failed to the level of the bedrock as part of the 

initial landslide but, rather, has been overridden by landslide 

debris from the deeper scar upslope. The landslide apparently pushed away a layer of the upper part of the slope 

including the vegetation, the pedologic A horizon, and 

underlying colluvium to a depth that contained most of the

tree roots. Figure 145 shows a portion of the landslide debris 

that has spilled over the retaining wall onto Columbia Parkway. The retaining wall was not damaged by the shallow 

landslide, which, by the time it reached the wall, was moving 

over unfailed colluvium. Note the colluvium piled against 

the uphill side of the tree on the far left side of figures 14A 

and B. This movement history also is suggestive of a large 

drop in strength following initial failure of the landslide.

THE THIN LANDSLIDE AT DELHI PIKE

We studied one of the thin landslides uphill from Delhi 

Pike that appeared to be actively moving. Borings, trenches, 

open-tube piezometers, and movement indicators were 

placed as shown in plate 1. Seven shallow, open-tube 

piezometers were installed at the bedrock-colluvium interface. One inclinometer was placed in the 6.5-m-deep boring 

7. A recording extensometer was installed across the two 

scarps near the head of the slides. Trenches 2, 3, and 4 were 

excavated through the colluvium into the bedrock to expose 

the failure surface. Trench 4 was excavated after a 1-yr 

period of monitoring.

This apparently active landslide has well-defined features (pi. 1). It is about 65 m long and 30 m wide in its upper 

part. The width is indeterminate in the lower part because the 

flanks are indistinct. In the upper part of the landslide, the 

ground surface is very irregular and bumpy; the bumps there 

correspond to individual landslide blocks that have pulled 

apart. Depressions separating these blocks are marked by 

distinct scarps on their upslope sides. Large flagstones of 

limestone (as large as 1.0x0.5x0.15 m) are scattered over the 

ground surface, and chips of weathered shale are present in 

the depressions between blocks. Topographically, the landslide surface is depressed as much as 0.5 m within the flanks 

in the upper 40 m. Farther downslope, the flanks are level 

with adjacent materials, and the surface contains benches 

that are similar to those farther west.

The uppermost scarp, at an approximate elevation of 

220 m (720 ft) is about 1 m high and devoid of vegetation. 

There are several other scarps in the upper half of the landslide. Along some of these scarps, the separation between 

landslide blocks is wider at the flanks (2-3 m) than in the 

interior of the landslide (<1 m). This pattern of opening 

gives the curious impression that displacement was larger at 

the flanks than in the interior of the landslide.

In three places uphill and downhill from boring P-5 

and uphill from boring P-7 the wavy pattern on the map

Figure 14 (on facing page). Thin landslide along Columbia Parkway, east of downtown Cincinnati. A, Slide path was created when 

landslide from upslope slid completely out of its original position 

and pushed the colluvium and vegetation, including roots, off the 

remainder of the underlying colluvium. Undulations in the lightcolored colluvium in the path of movement are benches reflecting 

limestone layers in underlying bedrock. B, Landslide debris has 

spilled over retaining wall onto Columbia Parkway.
LANDSLIDES IN COLLUVIUM B17
B18 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

in plate 1 depicts areas where displacement has separated 

the blocks all the way to the failure surface at the colluvium-bedrock contact.

An old, abandoned road that crossed the slide a few 

meters downhill from extensometer 1 has been offset about 

7 m. Farther downhill, an additional 2-3 m of displacement is revealed by the size of scarps. Thus, the maximum 

displacement of the landslide was apparently about 10m.

There is no evidence at the toe for 10 m of displacement, and there are no indications of shortening in the landslide uphill from the mapped toe at Delhi Pike. Thus, we 

suspect that this landslide occurred before the abrupt movement in 1973 that caused closure of Delhi Pike. If so, as 

much as 600 m3 of landslide debris may have been hauled 

away from the road surface. If not, there is a very large discrepancy between the amount of displacement evident in the 

area of stretching and the amount observable at the toe.

No movement was recorded by the extensometer and 

the inclinometer during the year of monitoring in 1979-80.

In 1990, the landslide appeared superficially to be 

unchanged since the end of our monitoring in 1981; clearly, 

it had made no large, abrupt movements in that time. However, the inclinometer in boring 7 was found to be squeezed 

closed at a depth of 2 m. Thus, the thin landslides do displace 

colluvium with small creeplike movements as well as the 

abrupt stretching failures observed in other places.

The time of activity of thin landslides throughout the 

metropolitan area is restricted to the interval between the 

spring thaw and the leafing of vegetation. Episodes of movement of thin landslides usually occur during major storms in 

the period of mid-March to early May. During the remainder 

of the year, either the vegetation is serving as an effective 

agent for dewatering the thin colluvium or the ground is frozen. Open-tube piezometers were dry except during the 

spring, when water levels responded almost immediately to 

rainfall (fig. 15). The behavior of subsurface water in the thin 

colluvium has been described by Gokce (1989) and by 

Haneberg and Gokce (in press).

Colluvium

Highest 

water

Lowest 

water level-si;_

'Bentonite 

plug

0.5

Open-tube

piezometer

(in sand) 1.0

Weathered 

Bedrock (shale)

12 

3/31/80

TIME (ONE-HOUR UNITS)

Figure 15. Water-level and precipitation record for an open-tube piezometer (P-5, pi. 1) placed at contact between colluvium and bedrock. 

This piezometer was dry for most of the year but, during the spring, water levels changed dramatically in response to rainfall. This particular 

record shows water-level response to a 1.7-cm rainfall on March 30-31,1980. Sketch to the left of the water record shows location of piezometer relative to colluvium and weathered bedrock. (From Fleming and others, 1981.)
LANDSLIDES IN COLLUVIUM B19

TRENCHES AND THE FAILURE SURFACES

All three trenches into the thin landslides (trenches 2,3, 

and 4 on pi. 1) extended through the colluvium and into bedrock. There was no evidence that sliding extended into the 

bedrock, but virtually all the colluvium overlying the bedrock has failed. In all the trenches, one or more failure surfaces were present in the colluvium and (or) in the thin 

transitional zone to bedrock. Trenches 2 and 3 were short 

trenches into the toes of the thin landslides. Trench 4 

extended nearly 60 m from a topographic bench near boring 

P-5 to Delhi Pike.

The colluvium is separable into two units on the basis 

of color. At the surface, the colluvium is a brown to darkbrown, stony, silty clay. The dark clay overlies a yellowbrown silty clay. The underlying bedrock is a mottled 

olive-gray shale with a few scattered beds of limestone in 

the shale. The thin transitional zone between the colluvium 

and bedrock contains abundant small chips of shale in a 

clayey matrix.

A few open tension cracks were found in the colluvium. 

Some of these cracks occurred at the edges of benches, 

where arching of the colluvium over the edges would produce stretching.

The positions and shapes of the failure surfaces are 

simple where the landslide geometry is simple and complex 

where large stones or bedrock ledges interfere with the sliding. Where the slope is smooth (for example, between 25 

and 35 m on the trench 4 profile on pi. 1), the failure surface is a simple planar surface at the contact with weathered bedrock. A bumpy or hummocky ground surface 

typically coincides with more complex failure surfaces. A 

bench in the bedrock abruptly steepens the slope of the failure surface at the colluvium-bedrock contact. One to two 

meters downslope from the bedrock bench, one or more listric faults intersect the basal shear surface (as seen, for 

example, at 44 and 47 m on the trench 4 profile). The listric 

faults, in part, accommodate the change in slope of the 

basal failure surface, where it passes over the ledge, and 

also allow stretching of the landslide.

These landslides apparently undergo a significant 

amount of internal deformation as they move. The flagstones of limestone are haphazardly oriented near the 

ground surface. With increasing depth, the large dimensions of the stones become parallel to the failure surface. 

Voids are under or upslope from some of the stones and, in 

a few places, we noted that a layer of soft clay had been 

deposited in the void space.

The failure surfaces are typically paper thin, glossy, and 

abundantly striated. At all scales of observation, the surfaces 

show roughness. Roughness was produced by small stones 

or fossil fragments projecting into the surface. Small steps, 

2-3 mm high, are common where the colluvium breaks from 

one shiny surface to another. These steps have the same 

appearance as chatter marks on fault surfaces in rock.

At a slightly larger scale, the failure surfaces commonly 

bifurcate around rock fragments. Also, multiple surfaces 

occur where the slope of the failure surface is changing over 

a short distance. Still larger undulations in the failure surface occur where a limestone layer produces a bench on the 

top of the bedrock. When multiple failure surfaces are 

present, as in trench 3 (pi. 1), the material between the surfaces is softer and more moist than that outside the failed 

zone.

Figure 16 shows two scanning electron micrographs of 

fragments of the failure surface. Figure 16A, magnified at 

16x, is a view normal to a major failure surface. Direction 

of sliding was from right to left. For the most part, the surface is streamlined in the direction of sliding and contains 

discontinuous ridges and furrows parallel to the direction of 

sliding.

The light-gray circular spots on the failure surface that 

are about 0.2 mm in diameter are aggregates of calcium sulfate crystals. We observed clear water on the surfaces of soil 

peds from the pedologic B horizon but did not directly 

observe water along the failure surface. The crystal aggregates are indirect evidence that free water exists seasonally 

along the surface of sliding. The crystal aggregates were not 

found in the interiors of the blocks or on smaller, subordinate 

shiny surfaces such as the one shown in figure 16B.

Figure 16B is an oblique view, at about 40x magnification, of a short slickensided surface in a sample containing 

several slickensided surfaces. The left and right sides of the 

sample (out of view in this image) are both slickensided surfaces. The flat, slickensided surface in the middle of the view 

does not visibly extend through the sample, which is only 

about 1 cm thick. The edge of another smooth surface, subparallel to the first, is exposed about 150 |im to the left of it. 

None of these surfaces appear to be parallel to the others, but 

neither are they grossly out of alignment with each other, as 

might be expected if they were conjugate shear fractures. 

Our supposition is that the complex fracture zones occur 

where the failure surface is changing shape either by passing 

over an asperity or emerging to the ground surface. These 

particular samples are from near the downslope end of trench 

4, where shortening deformation was occurring and material 

was pushed onto Delhi Pike.

The continuous, well-developed failure surface traceable in trench 4 (pi. 1, profile) indicates that the strength is at 

a residual value (Skempton, 1964, 1985). However, three 

other observations suggest that the strength mobilized in the 

field might be larger than the laboratory-measured residual 

strength. One observation, already mentioned, is roughness 

on the failure surfaces that could contribute to increased 

strength. The roughness was observed over a scale of about 

six orders of magnitude, from micrometers to meters. We 

also noted that sliding is accompanied by deformation of the 

colluvium over a zone that extends to about a half meter 

above the failure surface. Large limestone clasts within this 

zone are preferentially oriented parallel to the failure
B20 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

Figure 16. Scanning-electron micrographs of portions of the failure surface. A, View normal to a slickensided surface. B, View oblique 

to several subparallel slickensided surfaces.

surface, whereas clasts outside this zone appear to be haphazardly oriented. The deformation that creates parallel 

clasts is work done by the landslide in the process of sliding 

and contributes to resistance to sliding. And, finally, the 

presence of multiple failure surfaces is evidence that the failure geometry is less than optimum for sliding. Presumably, 

multiple slip surfaces are also an indication of internal deformation of landslide material.

We do not know if the internal remolding of material 

and the creation of multiple slickensided surfaces occur 

simultaneously during landslide movement. If they do, the 

residual strength of the soil, as back-calculated from field 

conditions, might be significantly larger than the strength 

measured on a single failure surface in the laboratory.

There is evidence that landslide movement may be limited to only one of the slickensided surfaces during a movement episode. The roots that extended into bedrock near the 

downslope end of trench 4 were kinked at only one level 

even though they penetrated at least two slickensided surfaces (fig. 17). Perhaps multiple failure surfaces are created 

during the first-time failure of the slope and subsequent 

movement involves a more simple geometry.

PROPERTIES OF THE COLLUVIUM

The colluvium is a stony, silty clay containing variable 

amounts of sand to boulder-size fragments of limestone. 

Within the colluvium, soil scientists recognize two soil 

series whose distributions roughly correspond to areas

Figure 17. Kinked roots on an exposed failure surface. The 

abrupt kinks in the roots formed at the position of the failure surface. There were at least two failure surfaces at this position near 

the toe of the landslide, but the roots were deformed only along the 

surface exposed in the photographs. (Photograph by Mary Riestenberg, College of Mount St. Joseph.)

containing thin and thick landslides (Lerch and others, 

1982). These soils are named the Pate Series, representative 

of thick colluvium, and the Eden Series, representative of 

thin colluvium. In general, the colluvium consists of darkbrown silty clay (10YR4/3) overlying yellow-brown silty
LANDSLIDES IN COLLUVIUM 

Table 1. Summary of selected physical properties of Eden and Pate Soil Series

B21

Data from Soil Conservation Service (1978)

Soil 

series

Eden

Pate

Soil 

series

Pate

Depth 

(cm)

0-15

15-61

0-15

15-91

91-183

Depth 

(cm)

0-30

30-95

95-144

Soil T . . . 

, . Liquid hon- ,. .. limit 

zon

A 35-65

B 45-75

A 25-35

Bt 40-60

B3 40-60

Soil 

horizon

A

Bt 1

B3

Plasticity 

index

12-25

20-45

8-20

15-30

20-35

Data

Permeability 

(um/s) j

0.4-4

0.4-1

1 -4

0.4

0.4

1

1

1

1

1

from Norton

Moist 

bulk ( 

density 

(g/cm3)

.35-1.65

.45-1.65

.35-1.60

.50-1.70

.60-1.80

(1979)

Gradation (percent)

Coarse (>76 um)

Gravel

0-40

10-45

0-10

0-10

15-50

Sand

0-25

0-35

0-20

0-20

0-30

Composition of clay minerals in clay-size fraction (percent)

Vermiculite

9

30

34

Micas and illite

77

47

48

Kaolinite

15

23

17

Fine (< 76 um)

Silt

0-30

5-35

5-35

5-30

10-35

Clay

27-60

40-60

20-40

35-55

35-55

Clay fraction 

(percent)

23

31

20

1 The Bt horizons contain 2-5 percent montmorillonite. Other horizons contain only trace amounts of 

montmorillonite.

clay (10YR4/4). Within a given soil profile, the thicknesses 

of both the dark and yellow-brown coliuvium are highly 

variable. And, although the dark coliuvium in most places 

occurs near the ground surface, it occurs locally as wedges 

or layers within the yellow-brown coliuvium. The burial of 

surficial layers may be due in some cases to root throw from 

overturning of trees (Hack and Goodlett, 1960) and in other 

cases to the overriding of surficial materials by landslides. 

We noted overridden soil in trench 1 (pi. 1). The pedologic 

B horizon contains translocated clay and has a prismatic 

blocky structure. Free water was observed on the surfaces of 

soil peds in the B horizon shortly after rain storms.

Other than small variations in color and texture, the 

physical properties are the same for both soil series. The 

routine engineering properties of the coliuvium are reported 

in tables 1 and 2. Data in table 1 are from the Soil Conservation Service (SCS) (1977, 1978) and Norton (1979) for 

the entire range of the Pate and Eden Soil Series and thus 

are representative of the coliuvium over a wide geographical area.

The principal difference in properties between the Pate 

and Eden Series is in the amount of coarse fraction. Eden 

soils, which occur on the higher, steeper reaches of the 

slopes, contain more rock fragments than the Pate soils. The 

amount of increase is illustrated by the increase in rock fragments larger than about 10 cm exposed in the walls of the

Table 2. Summary of physical properties of coliuvium and shale 

from the Delhi Pike study area

[All tests performed according to American Society for Testing and Materials standards]

Physical property Average Range

Atterburg limits (20 tests):

Liquid limit ....................... 45 36-52

Plastic limit ....................... 23 19-26

Plasticity index .................. 22 15-27

Gradation (20 tests; percent):

Sand .................................. 10 4-18

Silt .................................... 32 22-44

Clay................................... 59 47-68

Permeability (8 tests; cm/s)* ..... 1.4xlO~3 4xlO~3- 

Field density (9 tests; g/cm3) .... 2.01 1.74-2.13 

Specific gravity of solids (1 test) 2.79

*Nine samples tested, undisturbed in the trench; data from one 

sample (SxlO"6) not included in range or average.

trenches. In trench 1, the most downhill trench, rock fragments occupied just 1.4 percent of the exposed trench wall. 

In trenches 2 and 3, just uphill from Delhi Pike, rock fragments compose 3.5 and 2.6 percent, respectively, of the 

trench walls. In trench 4,6-12 m farther uphill than trenches
B22 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

2 and 3, rock fragments compose 4.6 percent of the trench 

wall. And, at the upper end of trench 4, rock fragments 

compose 9 percent of the trench wall. While these amounts 

of coarse fraction might influence the physical properties of 

the colluvium somewhat, nowhere is the coarse fraction 

large enough to dominate the behavior of the soil. The 

mechanical behavior of the soil is dominated by the properties of the fine fraction.

We tested 20 samples from the borings and trenches 

including dark-brown colluvium, yellow-brown colluvium, 

and weathered shale for Atterberg limits, gradation, permeability, field density, and specific gravity of the solids. 

Results are summarized in table 2. We did not quantify the 

composition of clay minerals in the clay-size fraction, but 

they are predominantly illite and mixed-layer clays and have 

subordinate amounts of kaolinite.

The only significant difference between our data in 

table 2 (which are specifically for the Delhi Pike site) and the 

SCS data in table 1 (which represent a large geographic area) 

is in the values of permeability. We consistently obtained 

values more than 10 times larger than those in the SCS data. 

These discrepancies are probably due more to differences in 

the test methods than to differences in the materials. Our 

tested samples were trimmed from block samples obtained 

from the trench walls using the falling-head method (Lambe 

and Whitman, 1969), whereas the SCS measurements were 

based on percolation tests in the field.

The most important physical property of the soil, with 

respect to slope stability, is its strength. Among the several 

methods used to measure the strength of a soil, engineering 

practice has demonstrated that the relevant measure of resistance to sliding is the residual strength (Skempton, 1964). 

Residual strength is commonly measured in a direct- or ringshear device that accumulates large displacements on a welldeveloped failure surface. The residual strength is the minimum strength measured under fully drained conditions for at 

least three different normal loads.

We conducted five separate tests of residual strength on 

samples collected from the trench walls. Three of the tests 

were by repeated direct shear and two by ring shear. One of 

the direct-shear tests was on a remolded total sample that 

contained coarse sand and fossil fragments. The other two 

direct-shear tests and both of the ring-shear tests had various 

coarse fractions removed: the +230 mesh (>63 |im) fraction 

was removed for one test of each type, and the +30 mesh 

(>600 urn) fraction was removed for the other test of each 

type. All the tests were conducted under three different normal loads equivalent to burial at depths of 1,2, and 4 m. The 

results of the tests are in table 3.

Residual strength parameters, expressed as the slope of 

the best-fit line through the three data points, are angles of 

internal friction ranging between 12° and 24°. The largest 

value was obtained for the sample that did not have the 

coarse fraction removed. Smallest values, 12°-17°, were 

consistently obtained with the ring-shear device on samples

Table 3. Residual strength of colluvium from the Delhi Pike 

study area

[All tests performed according to American Society for Testing and Materials standards]

Strength parameters

Test conditions Residual 

friction 

(degrees)

Residual 

cohesion 

(kPa)

Direct-shear test

Total sample:

Cohesion assumed zero .

"Best fit" ......................

+30-mesh fraction removed:

Cohesion assumed zero .

"Best fit" ......................

Minimal friction ...........

+230-mesh fraction removed:

Cohesion assumed zero .

"Best fit" ......................

Minimal friction ...........

24

21

21

18.5

12

21

20

11

0

3

0

8

16

0

5

16

Ring-shear test

+30-mesh fraction removed:

Cohesion assumed zero .

"Best fit" ......................

+230-mesh fraction removed:

Cohesion assumed zero .

"Best fit" ......................

17.5

12

16

12.5

0

5.5

0

3

that had the coarse fraction removed. Whether the fraction 

removed was +30 mesh or +230 mesh made only a slight difference in the strength parameters.

The best-fit straight line through the data points for 

each test had a small cohesion intercept that ranged from 3 

to 16 kPa. There has been much discussion in the literature 

about whether a sample at residual strength can have a small 

cohesion intercept as part of its total strength parameters. 

The data obtained here are not relevant to that issue, and 

interested readers are referred to Skempton (1985) and to the 

references that he cites relative to residual strength.

Shannon and Wilson, Inc. (oral commun., 1980) studied a large landslide in colluvium in the Mt. Adams section 

of Cincinnati (fig. 1). Their laboratory measurements 

showed that the colluvium had residual friction angles of 15° 

and zero cohesion. Back-calculation of strength parameters 

for the landslide produced a residual friction angle of 13° and 

a cohesion of 96 kPa.

STABILITY ANALYSES

We performed stability analyses for both thin and thick 

landslides at the Delhi Pike site. For the thin landslides, we 

used the geometry revealed by trench 4 (pi. 1) and averages
LANDSLIDES IN COLLUVIUM B23

of measured properties. Figure 15 shows the response for 

water levels in thin slides to even a moderate-size spring 

rainstorm. Storms large enough to raise the unconfmed water 

surface as high as the ground surface are likely even in years 

of average precipitation. We back-calculated strength 

parameters for the above conditions using the method of 

Janbu (1973). At equilibrium, a frictional resistance of 39° is 

necessary to support the slope. This value is much larger 

than the strength we would expect to find along the welldeveloped failure surfaces exposed in trench 4.

Skempton (1964,1985) reports measurements of residual strength on clays of similar physical properties in the 

range of 13° to 15°. Results of our measurements of residual 

friction angles of the colluvium varied from about 24° to 12° 

for different types of tests and methods of sample preparation (table 3). The largest values were obtained from 

untreated but remolded samples tested in a direct-shear 

machine. The smallest values were obtained on samples that 

had the coarse fraction (>30 and >230 mesh) removed and 

were tested in a ring-shear device. After the tests, we 

inspected the failure surfaces developed during shearing. 

Samples having larger residual strength invariably contained 

sand-size particles along the planes of failure.

Even assuming the maximum value of residual strength 

that we measured, the colluvium is only marginally strong 

enough to resist failure by thin iandsliding. Therefore, some 

additional factor(s) must have enhanced the resistance to 

sliding. Possible factors mentioned earlier include tree roots, 

roughness of the failure surface, and (or) small residual 

cohesion.

The factor of safety of slopes underlain by thick landslides is apparently consistent with laboratory measurements 

of strength. We back-calculated the stability of the slope that 

we studied on the downhill side of Delhi Pike, using the 

same properties as for the thin slides. The computed effective residual friction angles necessary for equilibrium range 

from 23° for a slope saturated to the ground surface to 12° 

for a slope with the water level below the failure surface. 

Both extreme values appear to be unrealistic. We measured 

saturated conditions to a level of 1 m above the failure surface at the toe and noted the presence of springs locally 

within the failed mass. On the other hand, near the middle 

of the landslide, we did not find saturated conditions in the 

colluvium anywhere above the bedrock; the failure surface 

in the colluvium was at least 2 m above the bedrock-colluvium contact. Thus, an estimated average residual friction in 

the range of 16° to 20° would be consistent with field and 

laboratory data.

CONCLUDING REMARKS

In summary, slopes in thin colluvium appear to be more 

stable than we would predict from laboratory measurements 

of residual strength of the colluvium. The puzzling question

06

0.5

0.2

x-~Thin landslides

Residual strength

Thick landslides

INCREASING DISPLACEMENT -

Figure 18. Hypothetical force-ratio-displacement models for thin 

and thick landslides. Back-calculation of stability of thin colluvium 

reveals that the residual strength is insufficient to support the slope. 

Field behavior indicates that some form of stick-slip behavior produces large initial strength that is lost after a small amount of displacement The back-calculation of stability of thick colluvium 

reveals that failure is consistent with the measured value of residual 

strength.

about thin landslides, then, is not why some slopes have 

failed, but rather why failure is not more extensive. Observations of episodes of movement of typical thin landslides (fig. 

18) suggest that a type of stick-slip phenomenon may contribute to iarger-than-measured initial strength. We 

observed that a small displacement causes a large loss of 

resistance, and a thin landslide commonly accelerates out of 

the slide scar. The situation, shown schematically in figure 

18, may be equivalent to the abrupt loss of strength in firsttime failures of slopes compared to reactivation of previously failed slopes. For thin colluvium, however, the slope 

has previously failed and yet retains greater resistance to 

sliding than predicted by laboratory measurements.

The landslides in the thick colluvium behave more or 

less as we would predict from laboratory measurements of 

residual strength of the colluvium. We know of no examples 

in which thick landslides have moved more than a few 

meters during any given episode of movement. More commonly, the total displacement during a movement episode is 

only a few centimeters. A force-displacement diagram for 

the thick landslides (fig. 18) illustrates the concept that the
B24 LANDSLIDES OF THE CINCINNATI, OHIO, AREA

maximum mobilized resistance to sliding is residual friction. 

The cause of the difference in behavior between the two 

landslide types could be due to a small amount of residual 

cohesion and/or roughness of the failure surface and perhaps 

tree roots.

The presence of multiple failure surfaces is an interesting aspect of the thick landslides. The history of failure at the 

Schmale residence indicated that the failure surfaces formed 

progressively from a common headscarp along Delhi Pike. 

Our stability analysis is relevant only to the deepest of the 

failure surfaces. The tree rings and constricted inclinometer 

casings are evidence that movement continues to occur on 

the more shallow failure surfaces.

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Manuscript approved for publication March 30,1993. 

Published in the Central Region, Denver, Colorado. 

Photocomposition by Shelly A. Fields. 

Graphics by Gayle M. Dumonceaux. 

Edited by Peter L. Martin.

Cover design by Arthur L. Isom, based on an original drawing by 

K.A. Richards, University of Cinicinnati.

.S. GOVERNMENT PRINTING OFFICE: 1993-573-038/86010