A True Triaxial Apparatus for Soil Testing with Mixed Boundary Conditions

Abstract

The mechanical description of a new true triaxial apparatus for soil testing is presented. The design took into consideration flexibility in accommodating different specimen sizes, easy assembly procedure, and well-controlled boundary conditions. The apparatus can perform stress-controlled and strain controlled experiments. It is well instrumented with load, displacement, and pressure sensors and has the capabilities to capture strain localization and shear band development. Verification experiments were conducted on F-75 Ottawa sand to study the influence of b-value (b = (σ2 − σ3)/(σ1 − σ3)) on stress-strain and volumetric behavior of sand. The results show that the specimen stiffness increases, and the amount of post-peak softening increases as b-value increases. The peak and critical state friction angles and the rate of dilation increase as b-value increases from 0 to 0.25, followed by a smaller increase in the friction angles and no change in the rate of dilation as b-value increases. Specimens failure is characterized by nonuniform deformations that initiate during the hardening regime before the peak stress; however, shear bands become visible on the specimen surface during the post peak softening at which specimens' volumetric strain changes from dilative behavior to the constant volume condition.

Development of a prototype for modelling soil–pipe interaction and its application for predicting uplift resistance to buried pipe movements in sand

“…As expected, the peak friction angle ( ds,p ) increases as the normal stress decreases, with the rate of increase depending on the initial density of the sample. Other researchers that measured the constant-volume friction angle of sands (e.g., Wang and Lade 2001;Alshibli and Williams 2005) concluded that cv and its direct shear test counterpart residual friction angle, res , are material parameters that are independent of both the initial sand density and the level of confining stress. Results presented in Fig.…”

The Generalized Mohr-Coulomb Failure Criterion

“…For geomaterials, there have been some failure criteria that consider the effect of σ 2 on shear strength [22]. In this section, we collect some test data of true triaxial tests from Reades and Green [35], Alshibli and Williams [36], Lade and Wang [37], Hu et al [38], Jiang et al [39], Mogi [40], Takahashi and Koide [41], Haimson and Chang [42], Sutherland and Mesdary [45], Shi et al [46], Ma and Haimson [47], Chang and Haimson [48], and Liu [49]. Comparisons are made from the prediction capacity of both shear strength and deformation among the four failure criteria of the M-C, L-D, SMP, and the GMC.…”

“…Figure5displays the shear strength τ f evaluated by GMC-L according to some true triaxial tests from the literature[35][36][37][38][39][40][41][42], which suggests that for each fixed σ 3 , τ f increases as b increases.…”

Landslide and Land Subsidence Hazards to Pipelines

“…More sophisticated stress-controlled tests can simulate earthquake loading or other field situations (Sassa and others, 2004). Research has also continued to develop true triaxial test systems in which stresses on all three principal axes differ independently (Alshibli and Williams, 2005;AnhDan and others, 2006), unlike traditional triaxial systems in which only the lateral confining stress and axial stress can differ.…”