Test on Mechanical Properties of Cemented Soils Using Secondary Development Data Acquisition Test System
A secondary development of computer aided data acquisition test system is performed in order to improve the disadvantages of original system. In this way, the qualified influences of cement content and curing time on yield strength and stiffness of soil can be automatic acquisition in consolidated undrained triaxial tests. The data collected from the system show that the deviatoric stress of soil increases with increasing axial strain initially followed by a relatively smooth decline after yield point. Yield strength increases with increasing cement content and curing time at the same strain. A well-defined linear relationship between yield strength and cement content are observed and also the relationship between yield strength and curing time. Finally, a linear function is defined to express the linear relationship between yield strength and those two factors and corresponding linear coefficients are obtained through a multiple regression analysis of test data. Stiffness of specimens shows an initial sharp degradation followed by smooth attenuation with increasing axial strain. The addition of cement and long curing time can effectively improve the stiffness of specimens especially at low strain areas.
A new approach for evaluating the ductility, volumetric stiffness and permeability of cut-off wall backfill materials
The behaviour of soil–cement and plastic concrete cut-off walls in dams is critically affected by ductility and volumetric stiffness. Post-construction deformation of cut-off walls is common due to the differences in strength and stiffness of the wall and the surrounding embankment material and changes in loading due to changes in the seepage regime. Conventional concrete barriers crack as they deform creating regions of high permeability and concentrated flow in the cracked region. Ductile barriers such as soil–bentonite walls will deform without cracking, but lack structural integrity. The behaviour of intermediate materials, such as soil–cement and plastic concrete, is currently not well understood. A laboratory testing procedure has been developed to quantify the ductility of soil–cement and plastic concrete relative to changes in permeability (hydraulic conductivity) with strain. Tests were performed on a number of soil–cement specimens having varying cement and bentonite contents. The test results show that this method is effective in illustrating and quantifying the differences in behaviour of the soil–cement specimens and effectively measuring low-permeability materials (10−6–10−8 cm s−1). This procedure can be instrumental for defining and quantifying the properties of soil–cement mixtures and plastic concrete used for cut-off wall backfill materials.
Yielding–compressibility–strength relationship for an artificially cemented soil cured under stress
Previous work by Rotta et al on the effects of the cemented matrix formation on the stiffness and yielding characteristics of soil elements situated at different depths in a natural soil deposit (weathered sandstone) was reanalysed. In the original research the isotropic compressive response of an artificially cemented soil was evaluated in terms of the variation of the yield stresses as a function of the void ratio existing during bond formation, the stress history and the cement content. New unconfined compression tests were conducted on the same artificially cemented soil to determine the effects of isotropic compression on soil. The yielding-compressibility-strengh relationship was examined. Similar patterns were found in the variations of incremental yield stress in isotropic compression, the unconfined compressive stress, and the initial bulk modulus with curing void ratio and cement content.