Experimental Study On Rheological Characteristics For Nanning Unsaturated Expansive Soil

Basing on present studies on rheological characteristics of soil at home and abroad, and together with comprehensive analysis, this dissertation carries out relevant studies on rheology behaviors of expansive soils, which is supported by the National Natural Science Project Fund and Hunan Province Natural Science Fund. By means of tests in-doors, theoretical analysis and numerical analysis, the research work has been accomplished with the following achievements:1) The soil sample is Nanning unsaturated expansive soils, which underwent different load tests in terms of separate-loading, step-loading and preloading-unloading-secondary loading. The results show the following compression creep characteristics:â‘ Decay creep curves are found in separate-loading tests for the soil sample without consideration of swelling deformation, while in step-loading tests, the non-decay creep could only be presented for the soil with low water contents and high compression pressures.â‘¡The relation between instantaneous strains and loads follows conic law in the separate-loading tests. With the same loads, the instantaneous strains of the soil in separate-loading tests are greater than those in step-loading tests, while the accumulative deformation is reverse, with bigger values in step-loading tests comparing to the separate-loading tests.â‘¢Non-decay creep characteristics are presented in preloading-unloading-secondary loading tests for the soil with low water contents and high compression pressures. Moreover, the bigger the pre-loads, the more obvious the accelerating non-decay creep would be.â‘£The ultimate strains of the soil reduce with the increase of the preloading pressure, and increases with the increase of the water contents.2) The shear creep characteristics and long-term strength of Nanning unsatured expansive soil under the action of different vertical pressures have been studied, which obtains:â‘ For the shear loads less than 42.5kPa, the decay creep curves of soil were presented, while for the loads more than 42.5 kPa, the non-decay creep curves of the soil were showed.â‘¡Under the vertical loads of 50kPa and 100kPa respectively, the soil samples failed at 60min and 360min respectively during the shearing when the shear load was up to 161.5kPa.â‘¢Under the vertical loads of 200kPa and 300kPa respectively, obviously accelerating creep phases of the soil are found with the shear load achieving to 170 kPa.â‘£The long-term strengths of the soil are about 72.9% of the short-term strengths when water content is 16%.3) The stresses relaxation of the Nanning unsaturated expansive soil has been studied regarding to different water contents, showing that:â‘ The stress relaxation curves fall into a non-completed decay type. The stresses gradually decrease and tend to a stable value as time elapses. The relaxation curves can be divided into three stages clearly:an accelerating relaxation stage, a uniform speeding relaxation stage and a stable relaxation stage.â‘¡The curves of stress-strain are shown in a linear relationship when water content is 16%, while the curves of stress-strain are shown in a non-linear relationship when the water contents are up to 20.5% and 22.4% respectively.â‘¢The K-H constitutive function well agreed with the observed data, which is able to reflect stress relaxation characteristics of Nanning unsaturated expansive soil.4) A series of contrast tests between the Nanning unsaturated expansive soil and Zhuzhou red clay have been done under the same conditions. The results display that:â‘ Under the conditions of low water contents and high compression pressures, the creep curves of expansive soil showed non-decay developments while the red clay showed decay developments. So the accelerating creeping phenomenon of Nanning expansive soil is more obvious than that of the Zhuzhou red clay.â‘¡The ultimate strains of expansive soil were bigger than those of the red clay under the same water contents. Under the condition of low water contents and low pressures, the resilience values of expansive soil are bigger than those of the red clay.