ASTM D4554-90(1995)
(Test Method)Standard Test Method for In Situ Determination of Direct Shear Strength of Rock Discontinuities
Standard Test Method for In Situ Determination of Direct Shear Strength of Rock Discontinuities
SCOPE
1.1 This test method covers the measurement of peak and residual direct shear strength of in situ rock discontinuities as a function of stress normal to the sheared plane. This sheared plane is usually a significant discontinuity which may or may not be filled with gouge or soil-like material.
1.2 The measured shear properties are affected by scale factors. The severity of the effect of these factors must be assessed and applied to the specific problems on an individual basis.
1.3 The values stated in SI units are to be regarded as the standard.
1.4 This standard does not purport to address the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D 4554 – 90 (Reapproved 1995)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
In Situ Determination of Direct Shear Strength of Rock
Discontinuities
This standard is issued under the fixed designation D 4554; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope the tangent to the failure curve at a normal stress that is
relevant to design.
1.1 This test method covers the measurement of peak and
2.1.5.1 Discussion—Different values of c and f relate to
residual direct shear strength of in situ rock discontinuities as
different stages of a test (for example, c8, c 8, fa, and fb,of
r
a function of stress normal to the sheared plane. This sheared
Fig. 2).
plane is usually a significant discontinuity which may or may
not be filled with gouge or soil-like material.
3. Summary of Test Method
1.2 The measured shear properties are affected by scale
3.1 This test method is performed on rectangular-shaped
factors. The severity of the effect of these factors must be
blocks of rock that are isolated on all surfaces, except for the
assessed and applied to the specific problems on an individual
shear plane surface.
basis.
3.2 The blocks are not to be disturbed during preparation
1.3 The values stated in SI units are to be regarded as the
operations. The base of the block coincides with the plane to be
standard.
sheared.
1.4 This standard does not purport to address all of the
3.3 A normal load is applied perpendicular to the shear
safety concerns, if any, associated with its use. It is the
plane and then a side load is applied to induce shear along the
responsibility of the user of this standard to establish appro-
plane and discontinuity (see Fig. 3).
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
4. Significance and Use
2. Terminology 4.1 Because of scale effects, there is no simple method of
predicting the in situ shear strength of a rock discontinuity
2.1 Definitions of Terms Specific to This Standard:
from the results of laboratory tests on small specimens; in situ
2.1.1 discontinuities—this includes joints, schistosity,
tests on large specimens are the most reliable means.
faults, bedding planes, cleavage, and zones of weakness, along
4.2 Results can be employed in stability analysis of rock
with any filling material.
engineering problems, for example, in studies of slopes,
2.1.2 peak shear strength—the maximum shear stress in the
underground openings, and dam foundations. In applying the
complete curve of stress versus displacement obtained for a
test results, the pore water pressure conditions and the possi-
specified constant normal stress.
bility of progressive failure must be assessed for the design
2.1.3 residual shear strength—the shear stress at which
case, as they may differ from the test conditions.
nominally no further rise or fall in shear strength is observed
4.3 Tests on intact rock (free from planes of weakness) are
with increasing shear displacement and constant normal stress
usually accomplished using laboratory triaxial testing. Intact
(Fig. 1). A true residual strength may only be reached after
rock can, however, be tested in situ in direct shear if the rock
considerably greater shear displacement than can be achieved
is weak and if the specimen block encapsulation is sufficiently
in testing. The test value should be regarded as approximate
strong.
and should be assessed in relation to the complete shear stress
- displacement curve.
5. Apparatus
2.1.4 shear strength parameter, c (see Fig. 2)—the projected
5.1 Equipment for Cutting and Encapsulating the Test
intercept on the shear stress axis of the plot of shear stress
Block—This includes rock saws, drills, hammer and chisels,
versus normal stress (see Note).
formwork of appropriate dimensions and rigidity, expanded
2.1.5 shear strength parameter, f (see Fig. 2)—the angle of
polystyrene sheeting or weak filler, and materials for reinforced
concrete encapsulation.
This test method is under the jurisdiction of ASTM Committee D-18 on Soil
5.2 Equipment for Applying the Normal Load (see Fig.
and Rock and is the direct responsibility of Subcommittee D18.12 on Rock
3)—This includes flat jacks, hydraulic rams, or dead load of
Mechanics.
sufficient capacity to apply the required normal loads.
Current edition approved May 25, 1990. Published July 1990. Originally
published as D 4554 – 85. Last previous edition D 4554 – 85.
D 4554
FIG. 1 Shear Stress – Displacement Graphs
NOTE 1—If a dead load is used for normal loading, precautions are
center of the base of the shear plane at an angle approximately
required to ensure accurate centering and stability. If two or more
15° to the shear plane with an angular tolerance of6 5°. The
hydraulic rams are used for loading, care is needed to ensure that their
exact angle should be measured to 61°.
operating characteristics are identically matched and they are in exact
parallel alignment.
NOTE 2—Tests where both shear and normal forces are provided by a
single set of jacks inclined at greater angles to the shear plane are not
5.2.1 Each ram should be provided with a spherical seat.
recommended, as it is then impractical to control shear and normal
The travel of rams, and particularly of flat jacks, should be
stresses independently.
sufficient to accommodate the full anticipated specimen dis-
5.4 Equipment for Measuring the Applied Force—This
placement. The normal displacement may be estimated from
includes one system for measuring normal force and another
the content and thickness of the filling and roughness of the
for measuring applied shearing force with an accuracy better
shear surfaces. The upper limits would be the filling thickness.
than 62 % of the maximum forces reached in the test. Load
5.2.2 Hydraulic System—A hydraulic system, if used,
cells (dynamometers) or flat jack pressure measurements may
should be capable of maintaining a normal load to within 2 %
be used. Recent calibration data applicable to the range of
of a selected value throughout the test.
testing should be appended to the test report. If possible, the
5.2.3 Reaction System—A reaction system to transfer nor-
gages should be calibrated both before and after testing.
mal loads uniformly to the test block includes rollers or a
5.5 Equipment for Measuring Shear, Normal, and Lateral
similar low friction device to ensure that at any given normal
Displacement—Displacement should be measured (for ex-
load, the resistance to shear displacement is less than 1 % of
ample, using micrometer dial gages) at eight locations on the
the maximum shear force applied in the test. Rock anchors,
specimen block or encapsulating material, as shown in Fig. 4
wire ties, and turnbuckles are usually required to install and
(Note 3). The shear displacement measuring system should
secure the equipment.
have a travel of at least 100 mm and an accuracy better than 0.1
5.3 Equipment for Applying the Shear Force (see Fig. 3):
mm. The normal and lateral displacement measuring systems
5.3.1 One or More Hydraulic Rams, of adequate total
should have a travel of at least 20 mm and an accuracy better
capacity with at least 150-mm travel.
than 0.05 mm. The measuring reference system (beams,
5.3.2 Hydraulic Pump, to pressurize the shear force system.
anchors, and clamps) should, when assembled, be sufficiently
5.3.3 Reaction System—A reaction system to transmit the
rigid to meet these requirements. Resetting of gages during the
shear force to the test block. The shear force should be
test should be avoided, if possible.
distributed uniformly along one face of the specimen. The
resultant line of applied shear forces should pass through the NOTE 3—The surface of encapsulating material is usually insufficiently
D 4554
NOTE 1—In this case, intercept c on shear axis is zero.
r
f 5 residual friction angle,
r
f 5 apparent friction angle below stress s ; point A is a break in the peak shear strength curve resulting from the shearing off of major irregularities on the
a a
shear surface. Between points O and A, f will vary somewhat; measure at stress level of interest. Note also that f 5f + i where:
a a u
f 5 friction angle obtained for smooth surfaces of rock on rock, and
u
i 5 inclination angle of surface asperities.
f 5 apparent friction angle above stress level s (Point A); note that f will usually be equal to or slightly greater than f and will vary somewhat with
b a a r
stress level; measure at the stress level of interest, r.
c8 5 cohesion intercept of peak shear strength curve; it may be zero.
c 5 apparent cohesion at a stress level corresponding to f , and
b
c 5 cohesion intercept of residual shear strength which is usually negligible.
r
FIG. 2 Shear Strength – Effective Normal Stress Graph
smooth and flat to provide adequate reference for displacement gages;
otherwise specified, be retained as close as possible to its
glass plates may be cemented to the specimen block for this purpose.
natural in situ conditions during preparation and testing.
These plates should be of adequate size to accommodate movement of the
NOTE 4—A test block size of 700 by 700 by 350 mm is suggested as
specimen. Alternatively, a temperature calibrated tensioned wire and
standard for in situ testing. Smaller blocks are permissible, if, for example,
pulley system with gages remote from the specimen may be used. The
the surface to be tested is relatively smooth; larger blocks may be needed
system, as a whole, must be reliable and must conform with specified
when testing very irregular surfaces. For convenience, the size and shape
accuracy requirements. Particular care is needed in this respect when
of the test block may be adjusted so that the faces of the block coincide
employing electric transducers or automatic recording equipment.
with joints or fissures. This adjustment minimizes block disturbance
6. Procedure during preparation. Irregularities that would limit the thickness or em-
placement of encapsulation material or reinforcement should be removed.
6.1 Preparation of Test Specimen:
6.1.1 Outline a test block such that the base of the block 6.1.2 Apply a layer of weak material at least 20 mm thick
coincides with the plane to be sheared. The direction of (for example, foamed polystyrene) around the base of the test
shearing should correspond, if possible, to the direction of block, and then encapsulate the remainder of the block in
anticipated shearing in the full-scale structure to be analyzed concrete or similar material of sufficient strength and rigidity to
using the test results. To inhibit relaxation and swelling and to
prevent collapse or significant distortion during testing. Design
prevent premature sliding, it is necessary to apply a normal the encapsulation formwork to ensure that the load bearing
load to the upper face of the test specimen as soon as possible
faces are flat (tolerance 63 mm) and at the correct inclination
after excavation of the opening and prior to sawing the sides. to the shear plane (tolerance 62°).
The load, approximately equal to the overburden pressure, 6.1.3 Carefully position and align reaction pads, anchors,
may, for example, be provided by screw props or a system of etc., if required to carry the thrust from normal and shear load
rock bolts and crossbeams. Maintain the load until the test systems to adjacent sound rock. Allow all concrete time to gain
equipment is in position. Saw the test block to the required adequate strength prior to testing.
dimensions (usually 700 by 700 by 350 mm) using methods 6.2 Consolidation of Test Specimen:
that avoid disturbance or loosening of the block. Saw a channel 6.2.1 The consolidation stage of testing is necessary in order
approximately 200 mm deep by 80 mm wide around the base to allow pore water pressures, in the rock and especially in any
of the block to allow freedom of displacements during testing. filling material adjacent to the shear plane, to dissipate under
The block and particularly the shear plane should, unless full normal stress before shearing. Behavior of the specimen
D 4554
FIG. 3 Typical Arrangement of Equipment for In Situ Direct Shear Test
during consolidation may also impose a limit on permissible Corrections to the applied normal load may be required to hold
rate of shearing (see 6.3.3). the normal stress constant (see 7.5). A shear determination
6.2.2 Check all displacement gages for rigidity, adequate should preferably be comprised of at least five tests per block,
travel, and freedom of movement, and record a preliminary set tested at different but constant normal stress. If conditions
of load and displacement readings. warrant, test more than one block for each shear plane.
6.2.3 Raise normal load to the full value specified for the 6.3.2 Apply the shear force either incrementally or continu-
test, recording any consequent normal displacements (consoli- ously.
dation) of the test block as a function of time and applied loads 6.3.3 Take approximately 10 sets of readings before reach-
(Fig. 5 and Fig. 6). ing peak strength (Fig. 1 and Fig. 3). The rate of shear
6.2.4 If consolidation occurs, it may be considered complete displacement should be less than 0.1 mm/min in the 10-min
when the rate of change in normal displacement recorded at period before taking a set of readings. This rate may be
each of the four gages is less than 0.005 mm/min for at least 10 increased to not more than 0.5 mm/min between sets of
min. Shear loading may then be applied. readings, provided that the peak strength itself is adequately
6.3 Shear Testing: recorded. For a “drained” test, particularly when testing
6.3.1 The purpose of shearing is to establish values for the clayfilled discontinuities, the total time to reach peak strength
peak and residual direct shear strengths of the test plane. should exceed 6t , as determined from the consolidation
curve (see 7.1 and Fig. 6). If necessary, the rate of shear should
be reduced and the application of later shear force increments
delayed to meet this requirement.
NOTE 5—The requirement that the total time to reach peak strength
should exceed 6t is derived from a conventional soil mechanics
consolidation theory assuming a requirement of 90 % pore water pressure
dissipation. This requirement is most import
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