ASTM D4394-84(1998)
(Test Method)Standard Test Method for Determining the In Situ Modulus of Deformation of Rock Mass Using the Rigid Plate Loading Method
Standard Test Method for Determining the In Situ Modulus of Deformation of Rock Mass Using the Rigid Plate Loading Method
SCOPE
1.1 This test method covers the preparation, equipment, test procedure, and data reduction for determining in situ modulus of deformation of a rock mass using the rigid plate loading method.
1.2 This test method is designed to be conducted in an adit or small underground chamber; however, with suitable modifications it could be conducted at the surface.
1.3 This test method is usually conducted parallel or perpendicular to the anticipated axis of thrust, as dictated by the design load.
1.4 Time dependent tests can be performed but are to be reported in another standard.
1.5 The values stated in inch-pound units are to be regarded as the standard.
1.6 The references appended to this standard contain further information on this test method.
1.7 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of 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. For specific precaution statements, see Section 8.
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Designation: D 4394 – 84 (Reapproved 1998)
Standard Test Method for
Determining the In Situ Modulus of Deformation of Rock
Mass Using the Rigid Plate Loading Method
This standard is issued under the fixed designation D 4394; 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 3.1.2 load—total force acting on the rock face.
3.1.3 peak-to-peak modulus of deformation—the slope of
1.1 This test method covers the preparation, equipment, test
the stress - strain curve line connecting the peaks of the curves
procedure, and data reduction for determining in situ modulus
obtained from successive pressure cycles (see Fig. 1).
of deformation of a rock mass using the rigid plate loading
3.1.4 recovery modulus of deformation—the tangent modu-
method.
lus of the unloading stress - strain curve. This modulus is
1.2 This test method is designed to be conducted in an adit
usually higher than the other moduli and is used in calculations
or small underground chamber; however, with suitable modi-
where unloading conditions exist. The difference between the
fications it could be conducted at the surface.
tangent and recovery moduli indicates that material’s capacity
1.3 This test method is usually conducted parallel or per-
of hysteresis or energy dissipation capabilities (see Fig. 2).
pendicular to the anticipated axis of thrust, as dictated by the
3.1.5 rigid plate—plate with deflection of less than 0.0001
design load.
in. (0.0025 mm) from center to edge of plate, when maximum
1.4 Time dependent tests can be performed but are to be
load is applied.
reported in another standard.
3.1.6 secant modulus of deformation—the slope of the
1.5 The values stated in inch-pound units are to be regarded
stress-strain curve between zero stress and any specified stress.
as the standard.
This modulus should be used for complete load steps from zero
1.6 The references appended to this standard contain further
to the desired load (see Fig. 2).
information on this test method.
3.1.7 tangent modulus of deformation—the slope of the
1.7 This standard does not purport to address all of the
stress - strain curve obtained over the segment of the loading
safety concerns, if any, associated with its use. It is the
curve judged by the investigator as the most representative of
responsibility of the user of this standard to establish appro-
elastic response. It neglects the end effects of the curve and is
priate safety and health practices and determine the applica-
better suited to small stress changes. The ratio between the
bility of regulatory limitations prior to use. For specific
secant modulus and the tangent modulus can be used as a
precaution statements, see Section 8.
means of measuring the stress damage of the material (see Fig.
2. Referenced Documents 2).
2.1 ASTM Standards:
4. Summary of Test Method
D 4395 Test Method for Determining the In Situ Modulus
4.1 Areas on two opposing parallel faces of a test adit are
of Deformation of Rock Mass Using the Flexible Plate
flattened and smoothed.
Loading Method
2 4.2 A mortar pad and rigid metal plate are installed against
D 4403 Practice for Extensometers Used in Rock
each face and a hydraulic loading system is placed between the
3. Terminology rigid plates.
4.3 If deflection is to be measured within the rock mass,
3.1 Definitions of Terms Specific to This Standard:
extensometer instruments should be installed in the rock in
3.1.1 deflection—movement of the rigid plate, mortar pad,
accordance with Practice D 4403.
or rock in response to and in the same direction as the applied
4.4 The two faces are loaded and unloaded incrementally
load.
and the deformations of the rock mass at the surfaces and, if
desired, within the rock, are measured after each increment.
This test method is under the jurisdiction of ASTM Committee D-18 on Soil
The modulus of deformation is then calculated.
and Rock and is the direct responsibility of Subcommittee D18.12 on Rock
Mechanics.
Current edition approved Nov. 12, 1984. Published January 1985.
Annual Book of ASTM Standards, Vol 04.08.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 4394
tend to be heavily influenced by the deformational character-
istics of the rock mass at that location and may give results that
are unrepresentative of the rock mass. The use of the average
plate deflection will mitigate this problem.
6.3 Measurement of the deflection within the rock mass can
utilize a finite gage length to reflect the average rock mass
deformation properties between the measuring points. This
approach entails three drawbacks, however. First, the rock
mass is tested at very low stress levels unless the measurement
points are very close to the rock surface, and because of this,
the same problems as with surface measurements occur. Tests
at low stress levels may give unrealistically low modulus
values because microfractures, joints, and other discontinuities
in the rock are open. Secondly, the disturbance caused by
implanting the deflection transducer in the rock mass is difficult
to evaluate. The techniques in this test method are designed to
produce minimal disturbance. Thirdly, in rocks with very high
modulus, the accuracy of the instruments may be insufficient to
provide reliable results.
6.4 Time-rate of loading has negligible influence on the
modulus.
FIG. 1 Rock Surface Deformation as a Function of Bearing
6.5 Calculations neglect the stress history of the rock.
Pressure
6.6 This test method is insensitive to Poisson’s ratio, which
must be assumed or obtained from laboratory testing.
7. Apparatus
7.1 Equipment necessary for accomplishing this test method
includes items for: preparing the test site, drilling and logging
the instrumentation holes, measuring the rock deformation,
applying and restraining test loads, recording test data, and
transporting various components to the test site.
7.2 Test Site Preparation Equipment— This should include
an assortment of excavation tools, such as drills and chipping
FIG. 2 Relationship Between Tangent, Secant and Recovery
hammers. Blasting shall not be allowed during final prepara-
Moduli
tion of the test site. The drill for the instrumentation holes
should, if possible, have the capability of retrieving cores from
5. Significance and Use
depths of at least 30 ft (10 m).
5.1 Results of this type of test method are used to predict 7.3 Borehole Viewing Device—Some type of device is
displacements in rock mass caused by loads from a structure or desirable for examination of the instrumentation holes to
from underground construction. It is one of several tests that compare and verify geologic features observed in the core if
should be performed. The resulting in situ modulus is com- core recovery is poor or if it is not feasible to retrieve oriented
monly less than the elastic modulus determined in the labora- cores.
tory. 7.4 Deformation Measuring Instruments— Instruments for
5.2 The modulus is determined using an elastic solution for measuring deformations should include a reliable multiple-
a uniformly distributed load (uniform stress) over a circular position borehole extensometer (MPBX) for each instrumen-
area acting on a semi-infinite elastic medium. tation hole and a tunnel diameter gage. For surface measure-
ments, dial gages or linear variable differential transformers
5.3 This test method is normally performed at ambient
temperature, but equipment can be modified or substituted for (LVDTs) are generally used. An accuracy of at least 60.0001
operations at other temperatures. in. (0.0025 mm), including the error of the readout equipment,
and a sensitivity of at least 0.00005 in. (0.0013 mm) is
6. Interferences
recommended. Errors in excess of 0.0004 in. (0.01 mm) can
6.1 A completely inflexible plate used to load the rock face invalidate test results when the modulus of rock mass exceeds
6 4
is difficult to construct. However, if the plate is constructed as 5 3 10 psi (3.5 3 10 MPa).
rigid as possible, the rock face is smoothed, and a thin, 7.5 Loading Equipment—The loading equipment includes
high-modulus material is used for the pad, the error is minimal. the device for applying the load and the reaction members
6.2 The rock under the loaded area is generally not homo- (usually thick-walled aluminum or steel pipes) which transmit
geneous, as assumed in theory. Rock will respond to the load the load. Hydraulic rams or flatjacks are usually used to apply
according to its local deformational characteristics. Therefore, the load hydraulically with sufficient capability and volume to
deflection measurements at discrete points on the rock surface apply and maintain desired pressures to within 3 %. If flatjacks
D 4394
are used they should have sufficient range to allow for 7.8 Bearing Plates—The bearing plates should approximate
deflection of the rock and should be constructed so that the two a rigid die as closely as practical. A bearing plate that has been
main plates move apart in a parallel manner over the usable found satisfactory is shown on Fig. 3. Although the exact
portion of the loading range. A spherical bearing of suitable design and materials may differ, the stiffness of the bearing
capacity should be coupled to one of the bearing plates. plate should at least be the minimum stiffness necessary to
7.6 Load Cells and Transducers—A load cell is recom- produce no measurable deflection of the plate under maximum
mended to measure the load on the bearing plate. An accuracy load.
of at least 61000 lbf (64.4 kN), including errors introduced by
8. Safety Hazards
the readout system, and a sensitivity of at least 500 lbf (2.2 kN)
are recommended. Alternatively, a pressure gage or transducer 8.1 All personnel involved in performing the test should be
may be used to monitor hydraulic pressure for calculation of formally prequalified under the quality assurance procedures
load, provided the device can measure the load to the same listed in Annex A1.
specifications as the load cell. An accuracy should be at least 8.2 Verify the compliance of all equipment and apparatus
620 psi (60.14 MPa), including error introduced by readout with the performance specifications in Section 7. If no require-
equipment, and a sensitivity of at least 10 psi (0.069 MPa). If ments are stated, the manufacturer’s specifications for the
a hydraulic ram is used, the effects of ram friction shall be equipment may be appropriate as a guide, however, care must
determined. If flatjacks are used, care shall be taken that the be taken for sufficient performance. Performance verification is
jacks do not operate at the upper end of their range. generally done by calibrating the equipment and measurement
7.7 Bearing Pads—The bearing pads should have a modu- system. Accomplish calibration and documentation in accor-
6 4
lus of elasticity of at least 4 3 10 psi (3 3 10 MPa) and dance with the quality assurance procedures.
should be capable of conforming to the rock surface and 8.3 Enforce safety by applicable safety standards. Pressure
bearing plate. High-early strength grout or molten sulfur lines must be bled of air to preclude violent failure of the
bearing pads are recommended. pressure system. Total deformation should not exceed the
FIG. 3 Rigid Bearing Plate for 12 in. Diameter Test
D 4394
expansion capabilities of the flatjacks; normally this is approxi- tests on typically excavated surfaces are adequate. If the
mately 3 % of the diameter of a metal jack. undisturbed in-situ modulus is desired, larger diameter plates
and higher loads may be used, although practical consider-
9. In-Situ Conditions
ations often limit the size of the equipment. Alternatively,
careful excavation procedures, such as presplitting or other
NOTE 1—The guidelines presented in this section are the domain of the
types of smooth-wall blasting, may be employed in the test
agency or organization requesting the testing and are intended to facilitate
definition of the scope and development of site-specific requirements for area to limit damage to the rock and the resulting need for large
the testing program as a whole.
plates and loads.
9.5 Cores, if any, should be logged and tested for rock
9.1 Test each structurally distinctive zone of rock mass
quality designation (RQD), fracture spacing and orientation,
selecting areas that are geologically representative of the mass.
condition of joint surfaces, strength, and deformation.
Test those portions of the rock mass with features such as
9.6 Site conditions may dictate that site preparation and pad
faults, fracture zones, cavities, inclusions, and the like to
construction be performed immediately after excavation.
evaluate their effects. Design the testing program so that effects
of local geology can be clearly distinguished.
10. Procedure
9.2 The size of the plate will be determined by local
geology, pressures to be applied, and the size of the adit to be 10.1 A schematic of an optimum test setup is shown in Fig.
tested. These parameters should be considered prior to exca- 4. A properly located wooden platform (not shown) allows for
vation of the adit. Optimum adit dimensions are approximately alignment of all test components.
six times the plate diameter; recommended plate diameter is 10.2 Conduct the test across a “diameter” or chord of the
1 1
commonly 1 ⁄2 to 3 ⁄4 ft (0.5 to 1 m). Other sizes are used adit with the two test surfaces nearly parallel and in planes
depending upon site specifics. oriented perpendicular to the thrust of the loading assembly.
9.3 The affects of anisotropy should be investigated by 10.3 Surface Preparation:
appropriately oriented tests: for example, parallel and perpen- 10.3.1 Method—Prepare the surface by a method that will
dicular to the bedding of a sedimentary sequence, or parallel cause minimal damage to the finished rock surface. Drilling
and perpendicular to the long axes of columns in a basalt flow. may be required to reach uniform depth. Residual rock
9.4 Tests shall be performed at a site not affected by between the drill holes may be removed by burnishing or
structural changes resulting from excavations of the adit. The moving the bit back and forth until a smooth face is achieved.
zone of rock that contributes to the measured deflection during Alternatively, in hard, competent rock, controlled blasting with
the plate loading test depends on the diameter of the plate and very sma
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