Macro- and micromechanical evaluation of cyclic simple shear test by discrete element method

Direct simple shear tests are considered to be simple laboratory tests that are capable of imposing a cyclic loading that is analogous to that induced by earthquakes. A realistic evaluation of the test results demands a profound micromechanical investigation of specimens. Three-dimensional discrete element method models of a stacked-ring simple shear test were constructed, in which monotonic and cyclic loadings were applied under constant-volume conditions, and good agreement between the monotonic and cyclic macromechanical behaviors was noted. Micromechanical properties of specimens that were subjected to a cyclic loading are discussed in terms of lateral and intermediate principal stress development, fabric anisotropy, and principal stress rotation. The stress and strain states inside the specimen were investigated and it was shown that despite the uniform stress distribution inside the specimen, the volumetric strain distributes non-uniformly during loading and the non-uniformity grows with cycling, which leads to localized zones of dilative and contractive behavior.

Design and verification of portable direct shear tester with application to remolded colluvium geomaterials

The mechanical properties of colluvium strongly govern the stability of colluvial slopes, and they arc essential for the related analysis and design. Nevertheless, their measurement is not easy on account of heterogeneity in property and difficulty of sampling. This study attempted to evaluate the shear strength of remolded colluvium by means of a simple direct shear test in the field. A portable direct shear tester was designed to overcome the inconvenience and expensiveness of the conventional large-scale in-situ direct shear test. It can be easily assembled and applied for the silnplc field direct shear test. For calibration, the results of the portable direct shear tester were compared with the results of the laboratory direct shear tester for four different types of soil samples, i.e. standard sand, slate debris, arenaceous shale debris and mixture of gravel and sand. Correlation formulas were established based on the calibration, enabling the portable direct shear tester to measure and estimate the shear strength of remoldcd colluvium in field. This study primarily focuses on the colluvium in Central Taiwan, including the lateritic Dadu Terrace and the arcnaceous shale of Taiping-Wufcng mounts. The portable direct shear tester was applied to sites selected in these areas, and the results were furthcr analyzed and discussed.

Behavior of compacted clay-concrete interface

Tests of interface between compacted clay and concrete were conducted systematically using interface simple shear test apparatus.The samples,having same dry density with different water content ratio,were prepared.Two types of concrete with different surface roughness,i.e.,relatively smooth and relatively rough surface roughness,were also prepared.The main objectives of this paper are to show the effect of water content,normal stress and rough surface on the shear stress-shear displacement relationship of clay-concrete interface.The following were concluded in this study:1)the interface shear sliding dominates the interface shear displacement behavior for both cases of relatively rough and smooth concrete surface except when the clay water content is greater than 16%for the case of rough concrete surface where the shear failure occurs in the body of the clay sample;2)the results of interface shear strength obtained by direct shear test were different from that of simple shear test for the case of rough concrete surface;3)two types of interface failure mechanism may change each other with different water content ratio;4)the interface shear strength increases with increasing water content ratio especially for the case of clay-rough concrete surface interface.

An examination of the mechanical interaction of drilling slurries at the soil-concrete contact

Evidence gained from previous field tests conducted on drilled shaft foundation shows that using drilling slurries to stabilize a borehole during the construction may influence the interfacial shear strength.This paper deals with an exhaustive study of the effects of drilling slurries at the contact between soil and concrete.This study involved adapting a simple shear apparatus and performing approximately 100 experimental tests on the interaction between two types of soils;clay and sandy clay and five specimens of concrete with different surface shapes.It also involved using bentonite and polymer slurries as an interface layer between soil and concrete.Results showed that an interface layer of bentonite slurry between clay and concrete decreases the interfacial shear strength by 23% and as an interface layer between sandy clay and concrete,bentonite increases interfacial shear strength by 10%.Using polymer slurry as an interface layer between clay and concrete decreases the interfacial shear strength by 17% while using it as an interface layer between sandy clay and concrete increases the interfacial shear strength by 10%.Furthermore,the data show that using bentonite and polymer slurry as an interface layer between clay and concrete decreases the sliding ratio by 50% to 60%,while increasing the sliding ratio by 44% to 56% when these are used as an interface layer between sandy clay and concrete.

Nonlinear elastic model for compacted clay concrete interface

In this paper,a nonlinear elastic model was developed to simulate the behavior of compacted clay concrete interface(CCCI)based on the principle of transition mechanism failure(TMF).A number of simple shear tests were conducted on CCCI to demonstrate different failure mechanisms;i.e.,sliding failure and deformation failure.The clay soil used in the test was collected from the"Shuang Jang Kou"earth rockfill dam project.It was found that the behavior of the interface depends on the critical water contents by which two failure mechanisms can be recognized.Mathematical relations were proposed between the shear at failure and water content in addition to the transition mechanism indicator.The mathematical relations were then incorporated into the interface model.The performance of the model is verified with the experimental results.The verification shows that the proposed model is capable of predicting the interface shear stress versus the total shear displacement very well.