Experimental Study on Viscoplastic Property of Unsaturated Reticulate Red Clay Used as an Engineered Barrier

In this study, to explore the feasibility of a compacted red clay as an engineered barrier in landfills, the viscoplastic property of remodeled unsaturated reticulate red clay was studied through a series of triaxial tests. According to the deviatoric stress–axial strain curves obtained through loading tests with varying strain rates and under different conditions, the viscoplastic parameter β of remodeled reticulate red clay was obtained. The effects of different matric suctions and net confining pressures on the viscoplasticity of unsaturated reticulate clay were analyzed. The test results showed that remodeled reticulate red clays with different degrees of saturation have similar viscoplastic properties, and their stress–strain curves are all isotach. The stiffness of unsaturated reticulate red clay increased with increasing confining pressure and matric suction. The relationship between β and the net confining pressure can be described using a linear equation. The β value of the specimens increased with increasing matric suction under a constant net confining pressure. A similar linear relationship was observed between β and the matric suction. These relationships are explained considering the loading rate effect mechanism.

Behavior of Cemented Reticulate Red Clay

Mechanical properties of cemented reticulate red clay were studied in present research. Test results show that: (1) shear strength of cemented reticulate red clay increase exponentially as the increasing of cement content; (2) shear strength of cemented reticulate red clay decrease polynomially as the increasing of water content; (3) mechanical properties of cemented reticulate red clay affected significantly by curing time and curing confined pressure. In order to study viscous properties of cemented reticulate red clay, cemented reticulate red clay specimens were compressed in triaxial chamber at different shear rate. Results of the compression tests show that it is obvious that the axial strain-deviator stress relationship of cemented reticulate red clay affects by the strain rate.

Creep Property of Reticulate Red Clay under Stepped-Load Creep Tests

Stepped-load creep tests of undisturbed and remodeled specimens of reticulate red clay was performed in the present study. Test results and analyses of the results show that: (1) Both undisturbed and remodeled specimens showed significant creep deformation in primary loading, unloading and reloading stage, and the creep deformation of remodeled specimen is much bigger than that of undisturbed one in primary loading and reloading stage; (2) The effect of a previous loading stage on the deformation induced at a succeeding stage is significant in primary loading and reloading stage; (3) The amount of the creep deformation can be calculated accurately by an empirical formula.

Simulation on Triaxial Compression Creep Deformation of Reticulate Red Clay

Triaxial compression creep tests were performed on the undisturbed specimens of reticulate red clay from Dongting Lake area (China) under different confined stress. By analyzing the laboratory test results, following conclusions were drawn: (1) creep deformation occurred in all compression tests; (2) creep deformation increases as the increasing of the creep stress (compress stress) slightly; (3) the creep deformation occurred in the triaxial compression creep tests can be well simulated with Singh-Mitchell model.

Study on Shear Rate Effects of Reticulate Red Clay

Direct shear tests were performed to study the shear rate effects of reticulate red clay around Dongting Lake. In the direct shear tests, four sets of undisturbed specimen of reticulate red clay were sheared under the different vertical pressure of 50kPa, 100kPa, 200kPa and 300kPa. Specimens were sheared with six different shear rates of 0.04mm/s, 0.02mm/s, 0.01mm/s, 0.007mm/s, 0.004mm/s and 0.003mm/s under each vertical pressure. Test results show that: (1) shear strength of reticulate red clay increases along with the vertical pressure; (2) shear rate effects of reticulate red clay are affected by vertical pressure significantly; (3) due to its reticulate structure of reticulate red clay, it shows some differences in shear rate effects comparing with other clay.