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Title: Consolidated-undrained direct-simple shear tests on saturated clays : Research in earth physics, phase report no. 16
Authors: Ladd, Charles C. (Charles Cushing)
Edgers, Lewis
Keywords: Clays
Clay soils
Consolidated soils
Direct shear tests
R tests (Soils)
Saturated soils
Soil mechanics
Shear strength
Publisher: U.S. Army Engineer Waterways Experiment Station.
Series/Report no.: WES Contract Report;No. 3-101 Phase Report No. 16
Abstract: Abstract: The results of consolidated-undrained direct-simple shear tests are presented on seven normally consolidated clays of widely varying composition and plasticity. The effect of overconsolidation ratio is studied with six of these clays. The tests were performed with the Geonor device, which uses a 8.0 cm dia. sample enclosed in a wire-reinforced rubber membrane. The vertical load is varied to maintain constant volume during undrained shear. Consolidated undrained direct-simple shear tests are easier to perform than Kₒ - consolidated triaxial tests with pore pressure measurements. The test also yields data during consolidation similar to that obtained from conventional oedometer tests. Analysis of the stresses in undrained direct-simple shear tests show that: (1.) the assumption that the applied stress system is one of pure shear is only valid at low strains; (2.) the peak value of the horizontal shear stress τ𝚑 probably lies between the maximum shear stress in the sample and the shear stress on the plane of maximum obliquity; (3.) the test does not yield meaningful effective stress strength envelopes at the peak τ𝚑. Direct-simple shear test results are compared to undrained data from triaxial compression and extension and plane strain active and passive tests for several clays. Based on these data and several case studies, it is concluded that consolidated-undrained direct-simple shear tests will: (1.) underestimate the undrained modulus of lean clays, but yield reasonable data with plastic clays; (2.) yield very good to slightly conservative factors of safety for circular arc undrained stability analyses involving Kₒ - consolidated non-stratified soft clays.
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