Consolidated-drained Tests Research Articles

Stress-dependent behavior of marine clay admixed with fly-ash-blended cement

To investigate the stress-dependent behavior of fly-ash blended cement (FAC)-admixed marine clay, isotropic consolidated drained (CID) triaxial tests were performed in the confining pressure range of 50–350 kPa. Stress dilatancy was observed when the confining pressure was in the lowest range of 50–100 kPa. The peak strength increased linearly with increasing confining pressure; this linear relationship was described by the following equation: pp = 1.7σ3 + 581 kPa, wherein pp is the peak strength and σ3 is the confining pressure. In the CID tests, failure modes of specimens were similar under different confining pressures. From the Mohr circles, it was found that the angle of shearing resistance was 52.8° and the cohesion intercept was 230.5 kPa. When the confining pressure was lower than the primary yield stress, some variation in the secant modulus were observed. However, the secant modulus tends to increase when the confining pressure exceeds the primary yield stress.

Consolidated-undrained triaxial testing of Opalinus Clay: Results and method validation

Specific equipment and procedures developed for geomechanical testing of hydrocarbon caprocks were adopted to conduct truly undrained triaxial tests with Opalinus Clay. The amount of pore pressure development during consolidation, and the resulting effective stress, is managed by equilibrating the samples in vacuum desiccators of different relative humidities (vapor equilibration technique) prior to assembling into the test apparatus. A drained consolidation test was first conducted to determine the appropriate strain rate for consolidated-undrained (CU) triaxial testing. Opalinus Clay samples were then consolidated in the triaxial rig to mean effective stresses in the range from 3 to 52 MPa and eventually sheared. Within the explored stress range elastic and pore pressure coupling parameters were found to be stress dependent. The different stress paths to peak indicate a transition from overconsolidated to rather normally consolidated state, yet failure was in all tests dilatant, i.e. associated with a drop in pore pressure and strain-softening (more so at low effective stress). Accurate pore pressure monitoring enabled the discrimination of different deformation stages during deviatoric loading. In terms of Mohr–Coulomb strength parameters, transition from peak to post-peak strength is manifested by a reduction in the effective cohesion whereas the effective friction angle remains nearly constant. The robustness of the CU testing methodology is demonstrated by (i) diagnostic analyses, (ii) inconsistency of CU tests with two CU tests deliberately loaded faster to explore the effect of strain rate, and (iii) consistency of CU tests with two consolidated-drained tests. Finally, test results of two caprock shales are also shown for comparison. The caprocks are of similar basic properties as the Opalinus Clay and stem from a large data base of tests conducted using the same methodology.

Influence Factor on Dilatancy of Coarse-Grained Soil Based on Large-Scale Triaxial Test

Abstract：Using large-scale shearing device, K0 consolidated-drained triaxial test and isotropiclly consolidated-drained triaxial test under different confining pressures are performed for overburden material of ShuangJiangKou earth dam which relative density is 0.9. And meanwhile, isotropically consolidated-drained triaxial test under different confining pressures are also performed for overburden material of ShuangJiangKou earth dam which relative density is 0.8. The difference of strength and deformation between under under K0-consolidation condition and isotropic consolidation condition and between under different relative density, and the influence of confining pressure, relative density and consolidation condition on the dilatancy of coarse-grained are analyzed. The results show that the strength of K0 consolidated-drained triaxial shear test is slight greater than that obtained by isotropically consolidated-drained test. The strength of coarse-grained soil increases with increase of relative density.The volume strain value of isotropically consolidated-drained triaxial shear test is bigger than that of K00 consolidated-drained test, and the volume strain value decreases with the decreases of relative density. The dilatancy of coarse-grained soil decreases with the increase of confining pressure, and increases with the increase of static lateral pressure coefficient.

Anisotropic shear strength of a residual soil of sandstone

This paper discusses results of laboratory tests carried out with a residual soil originated from the weathering of eolian sandstone from southern Brazil. Parent rock features, like microfabric and particle bonding, are remarkably well preserved within this residual soil. Stiffness and shear strength properties were evaluated with consolidated drained (CID) and consolidated undrained (CIU) triaxial compression tests. Undisturbed specimens were tested with two different orientations between the specimen axis and bedding surfaces (i.e., parallel (δ = 0°) or perpendicular (δ = 90°)) to investigate the effect of anisotropy. When CID triaxial tests were performed with δ = 0°, the yield surface associated with the structure was much larger than when tests were performed with δ = 90°. Coincidently, CIU tests with δ = 0° showed peak shear strengths much greater than for δ = 90° at comparable test conditions. Once the peak shear strength was surpassed, CIU tests followed collapse-type effective stress paths not shown by corresponding tests with remolded specimens. A near coincidence was observed between the yield surface determined with CID tests and the envelope of collapse-type effective stress paths for δ = 0° and δ = 90°.