SOIL SPECIM EN
PREPARATION FOR
LABORATORY TESTING
A symposium
presented at the
Seventy-eighth Annual Meeting
AMERICAN SOCIETY FOR
TESTING AND MATERIALS
Montreal, Canada, 22-27 June 1975

ASTM SPECIAL TECHNICAL PUBLICATION 599
D. A. Sangrey, symposium co-chairman
R. J. Mitchell, symposium co-chairman
List Price $35.00
04-599000-38

,4N~L
~L~/~AMER~CAN SOCIETY FOR TESTING AND MATERIALS
1916 Race Street, Philadelphia, Pa. 19103

qi]|lY

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(~) BY AMERICAN SOCIETY FOR TESTING AND MATERIALS 1976
Library o f Congress Catalog Card Number; 76-704

NOTE
The society is not responsible, as a body,
for the statements and opinions
advanced in this publication.

Printed in Bahimore, Md.
June 1976

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Foreword
The symposium on Soil Specimen Preparation for Laboratory Testing
was presented at the Seventy-eighth Annual Meeting of the American
Society for Testing and Materials held in Montreal, Canada, 22-27 June
1975. Committee D-18 on Soil and Rock for Engineering Purposes sponsored the symposium. D. A. Sangrey, Cornell University, and R. J.
Mitchell, Queen's University of Kingston, presided as symposium cochairmen.

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Related
ASTM Publications
Performance Monitoring for Geotechnical Construction, STP 584 (1975),
$14.00, 04-584000-38
Field Testing and Instrumentation of Rock, STP 554 (1974), $18.75,

04-554000-38
Analytical Methods Developed for Application to Lunar Sample Analysis,
STP 539 (1973), $15.00, 04-539000-38

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A Note of Appreciation
to Reviewers
This publication is made possible by the authors and, also, the unheralded efforts of the reviewers. This body of technical experts whose
dedication, sacrifice of time and effort, and collective wisdom in reviewing the papers must be acknowledged. The quality level of ASTM publications is a direct function of their respected opinions. On behalf of ASTM
we acknowledge with appreciation their contribution.

A S T M Committee on Publications

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Editorial Staff
Jane B. Wheeler, Managing Editor
Helen M. Hoersch, Associate Editor
Charlotte E. DeFranco, Senior Assistant Editor
Ellen J. McGlinchey, Assistant Editor

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Contents
Introduction
Effect of Water Saturation History on the Strength of
Low-Porosity Rocks--G. BALLIW, B. LADANYI,AND
D. E. GILL
Testing Equipment
Rock Types
Specimen Preparation
Testing Procedures
Experimental Results
Conclusions

4
5
7
8
11
12
19

Four Factors Influencing Observed Rock Properties-P. G. CHAMBERLAIN,E. M. VAN EECKHOUT,AND
E. R. PODNIEKS
Discussion of Critical Factors
Summary

21
22

34

Trimming Device for Obtaining Direct Shear Specimens from
Samples of Stiff Fissured Clay Shale--G. N. DURHAM
Residual Shear Test Procedures
Waterways Experiment Station Residual Shear Testing
WES Direct Shear Trimming Device
Specimen Preparation
Discussion

37
38
38
39
40
42

Effects of Specimen Type on the Residual Strength of Clays and
Clay Shales--F. C. TOWNSENDAND P. A. GILBERT
Previous Investigations
Materials and Equipment
Specimen Preparation
Test Results and Analyses
Conclusions

43
44
45
47
49

63

Effects of Storage and Extrusion on Sample Properties-ARA ARMANAND S. L. MCMANIS
Literature Survey
Sampling and Field Testing
Laboratory Tests and Results
Selection of Representative Specimens
General Conclusions

66
67
68
69
80
85

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Transportation, Preparation, and Storage of Frozen Soil Samples
for Laboratory Testing--T. H. W. BAKER
Factors Affecting Laboratory Tests on Frozen Soils
Frozen Soil Samples
Machining and Preparation of Specimens for Testing
Rough Cutting Methods
Finishing Methods
Storage and Protection During Laboratory Testing
Conclusions


88
89
89
97
98
98
104
111

Temperature-Controlled Humid Storage Room-MICItAEL BOZOZUK
Design
Closed Flow Conditioning System
Handling and Preparation of Samples for Storage
Effect of Storage Time on Test Results
Summary

113
115
119
122
122
125

Effect of Storage and Reconsolidation on the Properties of
Champlain Clays--P. LA ROCHELLE, J. SARRAILH,AND
F. A. TAVENAS
Characteristics of the Cemented Clays
Water Migration Following Sampling
Influence of Reconsolidation

Influence of Storage Time
Conclusion

126
128
130
137
140
144

Pore Water Extraction and the Effect of Sample Storage on the
Pore Water Chemistry of Leda Ciay--J. K. TORRANCE
Soil Material
Storage Procedures
Pore Water Extraction
Results and Discussions
Conclusions and Recommendations

147
149
149
150
151
155

Variation in Atterberg Limits of Soils Due to Hydration
History and Specimen PreparationmD. A. SANGREY,D. K.
NOONAN, AND G. S. WEBB
Test Program
Conclusions


158
160
167

Effect of Specimen Preparation Method on Grain Arrangement
and Compressibility in SandmARsHUD MAHMOOD,J. K.
MITCHELL, AND ULF LINDBLOM

Soil Fabric
One-Dimensional Compressibility

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169
170
171


Experimental Investigation
Fabric Results
Compression Test Results
Conclusions

171
178
180
190


A Technique for the Preparation of Specimens of Loose
Layered Silts--V. A. NACCIAND R. A. D'ANDR~A
Soil Description
Specimen Preparation
Typical Testing Procedure and Result
Conclusions

193
195
195
198
200

Shrinkage of Soil Specimens During Preparation for
Porosimetry Tests--T. F. ZIMMIEAND L. J. ALMALEH
Equipment
Experimental Work
Conclusions

202
204
211
214

Compaction and Preparation of Soil Specimens for
Oedometer Testing--A. R. BOOTH
Choice of Compaction Method
Construction of Mold
Method of Compaction

Adjustment of the Degree of Saturation
Comparison of Specimens
Effect on Results
Conclusions

216
217
218
219
221
223
224
225

Laboratory Preparation of Specimens for Simulating Field
Moisture Conditions of Partially Saturated Soils--T. Y.
CHH AND S. N. CHEN
Review of Current Methods for Pretesting Treatment
Development of Equipment and Procedures for Pretesting
Treatment
Test Results and Discussion
General Conclusion

232
236
243

Scalping and Replacement Effects on the Compaction
Characteristics of Earth-Rock MixturesmR. T. DONAGHE
AND F. C. TOWNSEND

Procedure
Test Results and Discussion
Conclusions

248
249
257
274

Study of Irregular Compaction Curves--P. Y. LEE
Laboratory Investigation

278
281

229
230

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Discussion of Test Results
Conclusions

Importance of Specimen Preparation in Microscopy-J. E. GILLOTT
Microscopic Methods
Specimen Preparation for Fabric Analysis
Specimen Preparation for Analysis of Particle Size

and Shape
Ion Bombardment
Replication, Shadowing, and Coating
Discussion
Conclusions

282
287

289
291
293
299
300
302
304
305

Use of Ultrasonic Energy for Disaggregation of Soil
SamplesmA. I. JOHNSONAND R. P. MOSTON
Ultrasonic Equipment
Testing Methods
Summary

308
308
311
312

Soil Drying by Microwave Oven--P. V. LADEAND

H. NEJADI-BABADAI
Heating with Microwaves
Effects of Heating Clay Mineral Systems
Preliminary Investigations
Determination of Water Content
Effects of Microwave Heating on Soil Characteristics
Summary and Conclusions
Discussion

320
321
322
323
324
330
333
335

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S T P 5 9 9 - E B/J u n. 1976

Introduction

A laboratory test run on an inappropriate specimen is often worse
than no test at all. Certainly there are tests for which the preparation
does not significantly change the measured soil property; but the far

more common situation is to have a real or potential variation in the
measured soil property as a result of alternative specimen preparation
techniques. The objective of this symposium was to collect and exchange
information on this problem. Hopefully this will lead to improvements
in our specimen preparation methods or at least a better understanding
of the influence of our preparation methods on final test results.
The entire question of adverse effects on test results through specimen
preparation needs to be examined in the context of the use being made
of the test results. In some cases, accepted practice or a certain design
method are based on a test result involving a particular specimen
preparation technique. If newer, and clearly better, specimen preparation methods are proposed for this test, there will often be reluctance
on the part of users to change, simply because they are accustomed to
the older methods and have a strong empirical experience to account
for the poorer specimen preparation. Another common situation is
that there are some test parameters which can be used in different design methods. For some of these design methods, the specimen preparation is very important, while for others it is much less important.
What general principles, if any, can be applied to the preparation of
soil specimens for laboratory testing? In general, laboratory soil testing
should be done on specimens as nearly identical to field deposits as
possible. For natural soils, this means a minimum of disturbance, contamination, and alteration. For artificially prepared, Or reconstructed,
soils, the objective is to duplicate the in situ structure and state of the
soil, at least in those ways that would influence test results. An overall
objective should be to define methods of specimen preparation and
testing which achieve the smallest variability in the end result. Some
methods are inherently less variable than others, and these will produce
more accurate and more predictable end results.
An objective of the ASTM symposium is to provide a forum for the
exchange of information on a topic of interest or concern. The morning
session of this symposium was separated into two major topic areas.
The first group of papers was concerned with rock as an engineering
material, with stress-strain and strength behavior being the main subjects.

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2

SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING

From the interest shown for this session it is clear that geotechnical
engineers are becoming increasingly sensitive to the problems of rock
engineering and the role of geotechnical engineering methods in solving
rock mechanics problems.
Storage, extrusion, and predrying effects were covered during the
second part of the morning session. The overall conclusion to be drawn
from this group of papers is that there exists a great potential for
change in soil and rock specimens and their measured properties if
samples are handled poorly and stored for long periods of time. Results
from this group of papers have a direct bearing on present ASTM
standard methods and, in some cases, clearly indicate a need for reconsideration of existing specifications.
Three major topic areas were included in the afternoon session.
Methods for preparing reconstructed loose cohesionless soil specimens
in the laboratory were discussed in the first group of papers. These
specimens were intended for studies of liquefaction potential and similar
large deformation response. This very current subject was of particular
interest to a large part of the symposium audience.
Preparation of compacted soil specimens was a second topic area

dealing with reconstructing soil specimens in the laboratory. Papers in
this part of the symposium were primarily concerned with the problems
of preparing a laboratory specimen which represented the field situation.
As in the case of the second half of the morning session, there were
some direct implications for present ASTM standard methods indicated
in these papers.
The final session of the symposium was appropriately concerned with
recent techniques applied to laboratory preparation of soil specimens.
All of the papers described new equipment or new techniques for
preparing and testing soil specimens. None of the methods described
are presently covered by ASTM standard methods, but it is reasonable
to expect a need for standards in the near future if there is more widespread use of these new techniques.
A number of present ASTM standard methods were included in the
studies reported in this special technical publication. In several cases,
the results of these research studies indicated a need to reconsider the
present specification, or at least some of its details. Whether it is
appropriate to change an existing standard method or add a method is
an important decision which cannot be based on a single research
study; however, users of specifications should be aware of potential
problems even if the specification is not changed. The listing in Table 1
summarizes the papers included in this special technical publication
and the ASTM standard methods to which they apply. Only the major
associations are noted and there are numerous minor specification references which have not been included.
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INTRODUCTION


3

TABLE 1--ASTM standards and relevant papers.
ASTM Designation
D 421
D 422
D 423
D 698
D 1140
D 1557
D 1587

D 2049
D 2216
D 2217
D
D
D
D

2664
2936
2938
3080

RelevantPapers from This Symposium

Sangrey, Noonan, and Webb
Johnson and Moston
Johnson and Moston

Sangrey, Noonan, and Webb
Chu and Chen
Donaghe and Townsend
Lee
Johnson and Moston
Chu and Chen
Donaghe and Townsend
Lee
Arman and McManis
Bozozuk
LaRochelle, Sarrailh, Roy, and Tavenas
Torrance
Mahmood,Mitchell, and Lindblom
Lade and Nejadi-Babadai
Sangrey, Noonan, and Webb
Johnson and Moston
Ballivy, Ladanyi, and Gill
Chamberlain,Van Eeckhout, and
Podnieks
Durham
Townsend and Gilbert

This ASTM special technical publication contains a group o f symposium papers addressing a broad range of materials and testing methods.
It is clearly shown that in most cases the methods of specimen preparation have a pronounced influence on the subsequent test results. In a
few cases, the opposite conclusion is drawn, for example, in the paper
by Townsend and Gilbert, but it is equally important to know about
minor effects as it is major ones. Several o f the papers present results
and conclusions which have a direct bearing on present ASTM standard
methods. Collecting such information is a major reason for having a
symposium and special technical publication supported by ASTM. The

responsibility for critically reviewing these research studies and, where
appropriate, making modifications to existing standards rests with the
A S T M committee structure.

D. A . S a n g r e y
Cornell University, Ithaca, N.Y.;
symposium co-chairman.

R . J. M i t c h e l l
Queen's University at Kingston, Ontario,
Canada; symposium co-chairman.

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G. Ballivy, ~ B. Ladanyi, 2 a n d D. E. Gill 2

Effect of Water Saturation History
on the Strength of
Low-Porosity Rocks

REFERENCE: Ballivy, G., Ladanyi, B., and Gill, D. E., "Effect of Water Saturation
History on the Strength of Low-Porosity Rocks," Soil Specimen Preparation for Laboratory Testing, ASTM STP 599, American Society for Testing and Materials, 1976, pp.
4--20.
ABSTRACT: The purpose of the tests described in this paper was to investigate how
the mechanical properties of rock observed in the tests are influenced by the whole saturation history of the specimen prior to testing. Three aspects of the saturation history were
studied in this paper: the effect of drying and resaturating the specimen prior to testing,
the effect of resaturation method, and the effect of the chemical nature of the resaturating

fluid. Three rock types were used in the tests: a gneiss, a cemented sandstone, and a fine
grained limestone. All three rocks had apparent porosities below 2 percent.
Results of triaxial and splitting tests are reported in the paper. One series of specimens
was brought from the site in its natural saturated state and tested without drying while
the others were either air or oven dried and then resaturated prior to testing. The resaturation was performed either by immersing the specimen in water under vacuum, or by
injecting the saturation fluid, under pressure, through a thin channel drilled along the
specimen axis. Either distilled or seawater were used as the resaturating fluid.
The results show that the inclusion of a drying and wetting cycle prior to testing has a
clear overconsolidation effect on the rock behavior, that is, it increases its apparent
strength. On the other hand, the channel saturation technique gives a better saturation
of the specimen and results in a strength decrease. Finally, the results show that the chemical composition of the saturation fluid has also a significant effect on the measured rock
strength.
The practical conclusion to be drawn from this study is that representative rock
samples, taken in connection with a given project, should, from the moment of coring
until they are tested, be held under environmental conditions that are as close as possible
to those which will prevail after the completion of the project. This implies that no drying
and wetting cycles should be included if they are not expected to occur in practice. If this
condition cannot be met, specimens should be saturated using a natural saturation fluid
and using an efficient saturation technique such as the described axial channel saturation method.
KEY WORDS: soils, rock mechanics, rock sampling, splitting tests, triaxial tests, saturation methods, pore pressure
~Geotechnical engineer, Lalonde, Girouard, Letendre and Associates, Montreal, P.Q.,
Canada.
ZProfessor and associate professor, respectively, Department of Mineral Engineering,
Ecol6 Polytechnique, Montreal, P.Q. Canada.
4
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BALLIVY ET AL ON LOW-POROSITY ROCKS

5

It is well known [1-5] 3 that the strength of rock depends, in large
measure, on the degree of saturation of specimens at the monent of
testing. In fact, it has been stated, in ASTM Test for Triaxial Compressive Strength of Undrained Rock Core Specimens Without Pore Pressure
(D 2664-67) "that the field moisture condition of the specimen should
be preserved until time of test . . . or should be tailored to the problem
at hand."
The wetting of specimens prior to testing has a strength reduction
effect which is generally very large for all kinds of rocks. This effect
results essentially from a reduction of the free surface energy of the
material [3]. This phenomenon is well known, but its physical and
thermodynamic aspects have not been completely clarified to date [6].
The intent of the present study is to illustrate more specifically the
effect of water saturation history on the strength of low apparent
porosity rocks. Three types of rocks have been tested, namely, a
cemented cambrian sandstone, a lithographic ordovician limestone, and
a charnokite (archaean granito-gneiss).
As it is not usual to preserve the field moisture conditions of the
specimen until laboratory testing, this paper also examines the effects
of various resaturation processes on rock strength. Study of these
processes included development of new resaturation equipment, special
specimen preparation, and the use of two different pore fluids.

Testing Equipment

The rock cutting was performed with a circular watercooled diamond
saw blade. Whenever required, the ends of the specimens were ground
flat on a lathe. The specimens were weighed on electronic balances,
and calipers were used to measure their final dimensions.
The oven used for drying the specimens was built in such a way that
the air, heated to 40.5~ as it entered the oven, was forced to circulate
throughout it; the total volume of air in the oven was renewed every
minute.
Resaturation by fluid injection was done with the apparatus shown
schematically in Fig. 1. It consists essentially of a pressure vessel (A),
through the cover of which eight specially prepared specimens can be
connected to eight tubes; these tubes are all connected to a second
pressure vessel (B) which acts as a saturation fluid reservoir. A nitrogen
gas bottle (C) pressurizes, through a regulator, the saturation fluid contained in the vessel (B); this pressurized fluid is injected, by means of
the tubes, through a channel drilled along the axis of each of the
specimens. A second nitrogen gas bottle (D) applies a pressure, also
3 The italic numbers in brackets refer to the list o f references appended to this paper.

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6

SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING

FIG. l--Apparatus for saturation of rock specimens by radial divergentflow from a central
channel; (a) view of the apparatus; (b) scheme of the saturation system.
through a regulator, on the saturation fluid contained in the vessel (A),

thus providing a constant fluid pressure at the outside surface of the
specimens.
The saturation fluid pressure gradient results from the difference between the pressures produced by the nitrogen gas bottles C and D. This
gradient produces radial divergent flow within the specimens. The
apparatus was constructed in such a way that all steel surfaces coming
into contact with the saturation fluid were lined with plastic material.
For the tests results reported in this paper, the pressure in C was 300
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BALLIVY ET AL ON LOW-POROSITY ROCKS

7

psi (2.07 MPa), and in D, 50 psi (0.34 MPa). The photograph in Fig. 1
shows the apparatus just described.
Both a standard testing machine and, more often, a programmable
universal testing machine (Tinius Olsen) were used for loading the specimens to failure. Diametral splitting tests were conducted between rigid
plattens. Triaxial tests were performed in a modified Hock cell, in which
the confining pressure was supplied by a pump (Structural Behavior
Engineering Laboratories, Model 100 LP + 100 P). To test the specimens
which had been resatured by fluid injection, the plattens were modified as
shown in Fig. 2b. As far as the pore pressure is concerned, a nitrogen gas
bottle, combined with a pore fluid reservoir, was used whenever the back
pressure to be maintained during testing was less than 500 psi (3.45 MPa);
otherwise, the back pressure was provided by the pump. Figure 2a is a
photograph of the Hoek cell with modified plattens. Specimen deformations were measured with electromechanical extensometers, in which
sensors were linear potentiometers. The longitudinal deformation of the

triaxially tested specimens was measured outside the cell; the signal output
by the measuring devices was recorded against the load applied by the
testing machine on a standard X - Y recorder. In the case of the splitting
tests, the changes in both the vertical and the horizontal diameter were
measured and recorded, as for the triaxial tests.

Rock Types
The tests were performed on three types of rocks from various locations
in the province of Quebec.

Cambrian Cemented Sandstone (Potsdam Group)
It is predominantly a white to off-white orthoquartzite with dolomitic
cement; the apparent porosity of this bed is less than 2 percent.

Ordovician Sublithographic Limestone (Trenton Group, Tdtreauville
Formation)
It consists of beds of dense bluish-black limestone up to 6 in. in thickness, separated by shale partings; it has a lithographic stone appearance
[7]. The total porosity of this rock is low (1.2 to 1.9 percent) [8], and its
apparent porosity is less than 1 percent.

Charnokite
This is an Archaean granito-gneiss from the Quebec City area.
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8

SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING


FIG. 2--Hoek's cell with modified plattens; (a) view of the cell and the plattens; (b) modified bottom platten.

Specimen Preparation
General

All the specimens were prepared from NX (diameter: 2~ in. or 5.38 cm)
core samples. The present study involved two types of samples which
have been cored below the water table.
Saturated Samples--Samples selected were kept immersed in water at
the drilling site and delivered to the laboratory, where they were submitted
to various procedures, including drying and resaturation.
Air-Dried Samples--In the other cases, the samples selected at the
drilling site were kept under ambient conditions and delivered to the
laboratory where they were submitted to various procedures.
In all cases, the core specimens were cut to the desired lengths a short
time after delivery, and the effect of wetting caused by the cooling water
during the cutting was considered insignificant as far as mechanical properties are concerned.
The control of specimen saturation was made by a periodical weighing.
Usually, a specimen was considered to have reached a given saturation
degree when periodical weighings showed constant weight for at least
three consecutive days.
Specimens f o r Tensile Splitting (diametral compression) Tests

As a rule, specimen disks submitted to splitting tests were about 90 of
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BALLIVY ET AL ON LOW-POROSITY ROCKS

9

an in. (1.90 cm) thick. The following groups of specimens were prepared
from the two previously described types of samples (see Table 1).
TABLE l--Groups of specimens prepared by different methods

and number of tests in each group.

Group

Tension Splitting Tests

Triaxial
Compression Tests

Air-Dried Specimens
A
AO
AS
AOS
AOSC
AOC

42
9
19
17


50
97
80
8

Saturated Specimens
S
SO
SOS

57
23
42

From saturated samples (S):
Group S--The specimens of this group, prepared from saturated samples,
were obtained by cutting specimens of core into disks which had been
temporarily removed from their water bath. The specimens were then
measured, weighed, and tested.
Group SO--The specimens of this group were the same as in group S,
except that they were oven dried before testing.
Group SOS--This group is the same as group S, except that the specimens, after being measured, were oven dried and resaturated by immersion
before testing.
From air-dried samples (A):
Group A--The specimens of core, selected from air-dried sample lots,
were cut into disks. The specimens were measured, weighed, and tested.
Group AO--The specimens of this group were prepared as were those
in group A, except that they were oven dried before testing.
Group AS--These specimens were prepared as those in group A, except
that they were resaturated by immersion prior to testing.

Group AOS--The specimens in this group were prepared as were those
of group A, except that they were oven dried and subsequently resaturated
by immersion prior to testing.

Specimensfor Triaxial Compression Tests
Specimens submitted to triaxial compression tests were about 4 88
long (10.80 cm) cylinders. They were all prepared from the samples of

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10

SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING

Type A, that is, the air-dried samples, and they fall into one of the
following groups:
Group AO--This group is the same as AO, described for specimens
for tensile splitting.
Group AOS--This group is the same as AOS, described for specimens
for tensile splitting.
Group AOSC--The specimens in this group were prepared as were
those in the splitting tests, except that a 89
hole was drilled along each
of their axes for about 80 percent of their length [11]. No cooling fluid
was used during this operation.
Figure 3 shows a specimen into which a hole has been drilled, as


FIG. 3--Specimens with central channel; (a) radially saturated sandstone specimens with
cut fitting, ready for testing; (b) section of a specimen with complete fitting.

described previously. This figure shows also the brass fitting that was
cemented to the collar of the channel, in order to enable the specimen to
be mounted on the resaturation apparatus described previously. This fitting
covers the hole wall for a length equal to about 30 percent the specimen
length, leaving an unlined cylindrical channel in the central portion of
the specimen; the length of this cavity is then about 60 percent of that of
the rock specimen. Figure 3a is a photograph of such a specimen. Note
that the threaded part of the fitting was cut away before testing.
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BALLIVY ET AL ON LOW-POROSITY ROCKS

11

Group AOC--The specimens in this group were as in group AOSC,
except that they were not submitted to resaturation, although they were
provided with a central channel.
A review o f the groups and the tests made in each group is presented in
Table 1.

Testing Procedures
Splitting Tests
Specimens were mounted on the testing machine in such a way that the
loading could be performed along two diametrically opposite lines on the

lateral surface o f the disks. The electromechanical extensometers were
then mounted and set to zero. The loading proceeded at such a speed
that the minor principal stress increased at a rate o f 100 psi/s. Tensile
strengths were calculated from the usual formula
2P
To

-

nDL

(1)

where

To = tensile strength,
P = maximum load applied,
D = diameter of the specimen, and
L = thickness o f the specimen.
Only the tests in which failure started at the center o f the cross section
o f the specimen, and in which failure plane coincided with the loaded
diametrical plane, were considered to be valid.

Triaxial Compression Tests
Jacketed specimens were mounted in the triaxial cell with proper spherically seated plattens. The cell was placed subsequently into the testing
machine, and the extensometer was installed. The loads were applied at
such a speed t h a t the major principal stress within the specimens increased
at a rate of 100 psi/s. Prior to the test, the confining pressure was applied
to the specimen by increasing simultaneously the axial and the cell pressure.
Whenever required, back pressure was raised to the desired level (200 psi

= 1.38 MPa with limestone specimens, 300 psi = 2.07 M P a with charnokite specimens, and up to 5000 psi = 34.5 MPa with sandstone specimens).
Pore pressure was applied from the bottom plattens, and the testing was
started only when the same pore pressure could be read at the top plattens. Similar procedures have been reported in the literature already [8].
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12

SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING

The extensometer was then set to zero, and the specimens were brought
to failure by increasing the axial stress.

Experimental Results
Check o f Pore Pressure Distribution in Triaxial Specimens
Before starting the study of the effect of specimen preparation history
on its strength, a check of the system of pore pressure application in the
triaxial cell was made by a series of triaxiai tests on cemented Potsdam
sandstone. All the specimens in these tests were of the AOSC group, that
is, they had a central hole and were resaturated by immersion after being
air and oven dried. The triaxial tests were conducted according to the
Heck's procedure [9], but the pore pressure u was kept constant during
the tests.
Such a system, if working well, that is, if resulting in a uniform distribution of the applied pore pressure (back pressure) throughout the
specimen at failure, should result in essentially drained test conditions.
According to the concept of effective stress, failure strengths of such a
series of tests, plotted against the effective confining pressure, should fall
on a single failure line [10].

Figure 4 shows that, with the usual scatter of results, this assumption
was found to be valid in the tests with the Potsdam sandstone. These
results illustrate that the pore pressure application system used in the tests
was quite effective, even for rocks of such a low porosity.

Effect o f Specimen Preparation History on the Results o f Tension
Splitting Tests
Figures 5 and 6 show the results of a large series of tension splitting
tests carried out on specimens of Trenton limestone, prepared according
to various procedures. The results show clearly that tensile strength is
affected very much by the specimen preparation history. In fact, three
different groups of results can be seen in Figs. 5 and 6. The lowest strengths
were found for specimens saturated without over drying (groups S and
AS), the highest, for those that were air and oven dried (group AO), while
the strengths of those tested air or oven dry (A and SO), as well as those
tested after having been saturated following air or oven drying (AOS and
SOS), were located between the two extremes.
These results lead to the conclusion that an oven drying, or a severe air
drying, produces a clear overconsolidation effect on the strength of rock,
and that the effect is irreversible, that is, it cannot be eliminated by subsequent resaturation of specimens. On the other hand, Fig. 5 shows that

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BALLIVY ET AL ON LOW-POROSITY ROCKS

ksi


' MPo

13

/

~,o
-

4O0

/

I-z
w

40.

~35~(
LEGEND:

t,~176
,o] , L,o

Test with opplied
e pressure
u= 8 0 0 psi
Specimen:Cemented sondstone~
group AOSC


20
3

MPo
ksi

EFFECTIVE CONFINING PRESSURE O''5

FIG. 4--Results of triaxial compression tests with Potsdam sandstone.

the overconsolidation effect seems to affect much less the modulus of
elasticity of rock, because the peak strength points, shown in Fig. 5, are
distributed around a mean straight line without any systematic trend.

Effect of Specimen Preparation History on the Results of Triaxial Tests
Figure 7 shows, in terms of principal stresses at failure, a summary of
all triaxial test results obtained with specimens of Trenton limestone and
charnokite prepared by various described methods. In addition, the median
failure line for AOSC specimens of Potsdam sandstone is shown also in
the figure for comparison. The tests with Trenton limestone were made
at different confining pressures varying from 500 to 5000 psi, while those
with charnokite were all at an effective confining pressure of 1000 psi
(6.9 MPa). Some results for the latter are summarized also in Table 2,
together with the corresponding water contents after immersion in the
distilled and the seawater, respectively.
The test results lead to a number of interesting conclusions concerning
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14

SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING

psi

MPa

1500

/

I0

/

A0
bJ
Ico
I000,

'AOS,

-6
w

I

-4


/

500-

-2

/
0

/

LEGEND

IM P a [ ~ e d l o n

/

vol~e
of To ond F~v

0.5%
19 ~ ' ~ - s t a n d o r d

deviotion

number of tests

0'5


Ii0
VERTICAL

STRAIN

1',5
210
8v = A.~I

,

25

, II,
per cent

I

5--Effect of mode o f saturation on splitting tensile strength and failure strain of
Trenton limestone. For the definition o f symbols, see Table 1.
FIG.

the effect of preparation history on the failure behavior of rocks under
triaxial test conditions. The results show clearly that:
1. The strength of dry specimens is from 20 to 30 percent higher than
that of comparable specimens when tested saturated, at any confining
pressure.
2. The presence of a central hole in the specimen improves and accelerates
considerably the resaturation of the specimen. This is seen clearly in the
results obtained for the charnokite. This method, however, could not

have been applied to the specimens of Trenton limestone, which had a
tendency to fracture along bedding planes during pressure saturation. The
limestone, therefore, was soaked in water, and a back pressure of 200 psi
was applied through the central channel. This saturation method was
clearly less effective, which explains the much smaller difference between
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