Section 5 Laboratory tests on soil and rock
5.13 Swelling testing of rock material
5.13.1 General
(1)This standard deals with the following tests for determination of swelling potential exposed to wetting and drying or unloading in an aqueous environment:
− the swelling pressure index under conditions of zero volume change;
− the swelling strain index for radially-confined specimens with axial surcharge;
− the swelling strain developed in unconfined rock specimens.
NOTE Some rock materials, notably those with high clay content, are prone to swelling, weakening and disintegration when exposed to wetting and drying or unloading in an aqueous environment. The index tests provide an indication to estimate swelling properties under well-controlled conditions. The tests are usually done on softer rock materials like claystone and shale. The tests can be used for the characterization of harder rocks subjected to weathering.
(2) Rocks that disintegrate during the tests should be further classified using relevant soil classification tests such as the shrinkage, liquid and plastic limits, particle size distribution and the type and content of clay minerals.
NOTE Annex V provides more details on each of the swelling tests and their interpretation as well as some guidelines.
5.13.2 General requirements
(1) The specimens should conform closely to the practice recommended for right cylinders or for rectangular prisms. The sample size should allow for preparation of test specimens by re-coring and/or machining in a lathe, with the axis for one direction of the swell measurement
perpendicular to a bedding or foliation.
NOTE For recommendations for right cylinders and rectangular prisms, see X.4.8.
(2)P The following shall be specified:
− the selection of test samples;
− the test specimen preparation, orientation and dimensions;
− the numbers of test per formation required;
− the test method, equipment and calibrations;
− the water to be used (natural or distilled water, water chemistry);
− the recording period;
− the need for curves of swell pressure or displacement as a function of time elapsed since flooding;
− the selection of required additional parameters;
− the reporting requirements.
5.13.3 Evaluation of test results
(1)P The results shall be reviewed in the light of the description, and classification parameters shall be established.
(2) The value used in design derived from laboratory tests should be compared with field experience with comparable rock types under similar climatic, loading and wetting conditions.
(3) The short and especially long term weathering processes of swelling, weakening or disintegration due to wetting and drying may only be partly mirrored by the laboratory tests, even for similar conditions of loading and water content, because of the influence of among others natural fissuring, stress, drainage and pore water chemistry.
5.13.4 Swelling pressure index under zero volume change 5.13.4.1 Objective and requirements
(1) The test is intended to measure the pressure necessary to constrain an undisturbed rock specimen at constant volume when immersed in water.
(2) The test may be used to estimate the swell pressure in-situ by comparison of documented experience for the rock stratum.
(3)P The test specimen shall be cored using Category A sampling methods.
NOTE The test can be carried out following the recommendation given in V.2.
5.13.4.2 Evaluation of test results
(1)P The applied force to maintain the condition of zero volume change shall be corrected for the deformation in the test cell system itself (ball bearings and bedding of filter stones towards the end platens).
(2) The maximum swell pressure under zero volume change should be used as an upper limit of swell pressure under the specified laboratory conditions.
(3) Before the laboratory-determined maximum swell pressure is used in design, field evidence should be taken into consideration related to short and especially long term weathering processes of swelling, weakening or disintegration due to wetting and drying, loading conditions, water content and pore water chemistry.
5.13.5 Swelling strain index for radially-confined specimens with axial surcharge 5.13.5.1 Objective and requirements
(1) The test is intended to measure the axial swelling strain developed against a constant axial surcharge, when a radially confined, undisturbed rock specimen is immersed in water.
(2)P The test specimen shall be cored using Category A sampling methods.
NOTE The test can be carried out following the recommendation given in V.3.
5.13.5.2 Evaluation of test results
(1)P The measured strain under the applied force during the test stages shall be corrected for the deformation in the test cell system itself (ball bearings and bedding of filter stones towards the end platens).
(2) The axial swelling strain under constant axial surcharge should be used to estimate the swell potential in-situ taking into account the documented experience for the rock stratum.
(3) Depending on the applied vertical stress, the test provides background for the evaluation of the vertical heave or the lateral deformation of a rock/structure interface.
5.13.6 Swelling strain developed in unconfined rock specimen 5.13.6.1 Objective and requirements
(1) The test is intended to measure the swelling strain developed when an unconfined undisturbed rock specimen is immersed in water.
(2)P The test shall only be applied to specimens prepared from at least category B sampling methods that do not change their geometry appreciably during testing.
(3) It is advised that slaking, less durable, rocks should be tested using a confined swelling test.
NOTE The test may be carried out following the recommendation given in V.4.
(4)P The report shall clearly indicate that the specimen was not radially confined during the swelling test.
5.13.6.2 Evaluation of test results
(1) The test may be used to estimate the swell potential in-situ by comparison to documented experience for the rock stratum.
(2) Unconfined swelling strains and their directions with respect to bedding or foliation should be used only as an estimate of in-situ swelling potential.