| Residual soils cover nearly two-thirds of the land area in Xiamen and construction of earth structures involves the use of them. Under natural or imposed changes in environmental conditions, drying processes (evaporation or drainage), wetting processes (infiltration or capillary), and alternate wetting and drying processes caused by seasonal variation or groundwater level fluctuation are normally occurs for residual soil. The residual soil deposits might undergo severe change in volume, strength, seepage and consolidation behaviors in response to these processes. Among them, the shear strength of an unsaturated soil plays an important role in many geotechnical problems such as soil slope stability, bearing capacity and lateral earth pressures. Furthermore, the soil-water characteristic curve (SWCC) is a relationship between suction and water content or degree saturation and it can assist in the understanding of the influence of water content on the unsaturated soil strength. Therefore, matric suction, unconfined compression strength(UCS) and direct shear strength tests under different initial dry density, water content, vertical stress and drying and wetting cycles have been done. Based on the tests results, SWCC model, UCS model and shear strength model of two residual soils (i.e. sandy clayey and clay) are established. The main research work on SWCCs and strength of unsaturated residual soil are presented as follows:(1) Matric suction was conducted by filter paper method and the influences of initial dry density and initial water content, soil structure, the stress and drying and wetting, upon the desorption and adsorption soil-water characteristics of sandy clayey and clay residual soil in Xiamen are examined and discussed. The SWCC of the sandy clayey specimens are different from that of the clay specimens. The sandy clayey specimens have low air-entry value and high rate of desorption and the opposite of the clay specimens.(2) Removing a parameter of the residual degree of saturation, six modified SWCC models are gained based on the published SWCC models which were selected for evaluation and model scores are calculated according to the fitting precision of experimental data. The weights of SWCC models are put forward by considering the number of model fitting parameters. Then, the recalculated model scores, taking the model weight into account, show that the modified Gardner model gets the highest score for residual soil in Xiamen among all of the modified SWCC models. Furthermore, the equations for determining of parameters of SWCC such as air-entry value, slope at the inflection point, residual suction and residual degree of saturation are deduced. These equations can be used for computational analyses to replace the conventional graphical method in providing consistent results.(3) Experimental programs of considering the influence of the initial dry density and initial water content on the UCS of the sandy clayey and clay were designed and two UCS models are proposed respectively which can be used to predict the UCS of residual soil in Xiamen. At the same time, the effects of the level, path and times of drying and wetting cycle processes on the UCS of two kinds of residual soil are investigated.(4) A scries of unsaturated direct shear tests were conducted on the residual sandy clayey and clay soil, the matric suction of specimens with different water content were also measured. The experimental results show cohesion, friction angle and shear strength of two kinds of residual soil change behavior due to changes of water content and soil suction. Two different total shear strength equations are established by the test results, Then, the comparison shear strength tests were done to examine the validity of the proposed equations. The errors between the tested shear strength and the predicted shear strength are small and the proposed equations are shown to provide the good predictions on shear strength. The shear strength tests under different level, path and times of drying and wetting cycles on two kinds of residual soil were also conducted and the strength behavior is concluded on the changes of the level, path and times of drying and wetting cycles... |
PDF Full Text Request