Research On Seepage Control Measure Of Expansive Soil Slope Based On Unsaturated Seepage Theory

Middle Route of South-to-North Diversion Project is a strategic project to optimize water allocation. Total length of the project is about 1421 km with 340 km in expansive soil area. The crack,expansibility and over-consolidation of expansive soil influence the stability of the expansive soil slope. The cracks produced by wet-dry cycle make it easier for water infiltration which bring challenge to Middle Route of South-to-North Diversion Project.The protective cover layers in middle route South-to-North Diversion is to make the expansive soil slope stable. The Protective design of expansive soil canal above canal water level is commonly used unexpansive clay and modified expansive soil to replace expansive soil above canal water level. We worry about the long-term effectiveness of the canal slope above canal water level. So, based on state "twelfth five-year" scientific and technological support project “technology of Seepage and drainage in expansive soil canal slope”. Protection scheme of double-layer which is based on unsaturated seepage theory is proposed, through using the dye tracer method and measuring negative pressure in soil layer and the drainage process at the side and bottom of the model to monitor the change of soil water content and drainage process in the course of rainfall.the main conclusions are listed as follows:(1) The model test of double-layer structure indicate that the protective layers can store some water while the rainfall which permeate into coarse layer will drain along the slope out of the slope. Under the protection of double-layer structure, the drainage will not be formed at the bottom of the model. This illustrates that the double-layer structure can control the change of water content effectively.(2) The protective effect comparison of double-layer structure on canal slope under different initial water content indicates that lateral drainage in higher initial water content soil is better than the lower case.(3) The tests of coarse particle monolayer structure under rainfall conditions indicate that the control effect of coarse particle monolayer structure on soil water content is poor.