Standard Test Method for Determining the Internal and Interface Shear Strength of Geosynthetic Clay Liner by the Direct Shear Method
5.1 The procedure described in this test method for determination of the shear resistance for the GCL or the GCL interface is intended as a performance test to provide the user with a set of design values for the test conditions examined. The test specimens and conditions, including normal stresses, are generally selected by the user.
5.2 This test method may be used for acceptance testing of commercial shipments of GCLs, but caution is advised as outlined in 5.2.1.
5.2.1 The shear resistance can be expressed only in terms of actual test conditions (see Notes 2 and 3). The determined value may be a function of the applied normal stress, material characteristics (for example, of the geosynthetic), soil properties, size of sample, moisture content, drainage conditions, displacement rate, magnitude of displacement, and other parameters.
Note 2: In the case of acceptance testing requiring the use of soil, the user must furnish the soil sample, soil parameters, and direct shear test parameters. The method of test data interpretation for purposes of acceptance should be mutually agreed to by the users of this standard.
Note 3: Testing under this test method should be performed by laboratories qualified in the direct shear testing of soils and meeting the requirements of Practice D3740, especially since the test results may depend on site-specific and test conditions.
5.2.2 This test method measures the total resistance to shear within a GCL or between a GCL and adjacent material. The total shear resistance may be a combination of sliding, rolling, and interlocking of material components.
5.2.3 This test method does not distinguish between individual mechanisms, which may be a function of the soil and GCL used, method of material placement and hydration, normal and shear stresses applied, means used to hold the GCL in place, rate of horizontal displacement, and other factors. Every effort should be made to identify, as closely as is practicable, the sheared area and failure mode of the specimen. Care should be taken, including close visual inspection of the specimen after testing, to ensure that the testing conditions are representative of those being investigated.
5.2.4 Information on precision between laboratories is incomplete. In cases of dispute, comparative tests to determine whether a statistical bias exists between laboratories may be advisable.
5.3 The test results can be used in the design of GCL applications, including but not limited to, the design of liners and caps for landfills, cutoffs for dams, and other hydraulic barriers.
5.4 The displacement at which peak strength and post-peak strength occur and the shape of the shear stress versus shear displacement curve may differ considerably from one test device to another due to differences in specimen mounting, gripping surfaces, and material preparation. The user of results from this standard is cautioned that results at a specified displacement may not be reproducible across laboratories and that the relative horizontal displacement measured in this test at peak strength may not match relative shear displacement at peak strength in a field condition.
1.1 This test method covers a procedure for determining the internal shear resistance of a geosynthetic clay liner (GCL) or the interface shear resistance between the GCL and an adjacent material under a constant rate of deformation.
1.2 This test method is intended to indicate the performance of the selected specimen by attempting to model certain field conditions.
1.3 This test method is applicable to all GCLs. Remolded or undisturbed soil samples can be used in the test device. See Test Method D5321/D5321M for interface shear testing of non-GCL geosynthetics. See Guide D7702/D7702M for a summary of available information related to the evaluation of direct shear results obtained using this test method.
1.4 This test method is not suited for the development of exact stress-strain relationships within the test specimen due to the nonuniform distribution of shearing forces and displacement.
1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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