Study On Application Of Chemical Improvement Technique In Preventive Maintenance Of Expansive Soil Slope

A large amount of expansive soil slopes are distributed on Shiyan-Tianshui Expressway(Shi-Tian highway),the slope operating in a few years showed different degree of deformation and slip phenomenon,difficult to maintenance work.It is imperative to carry out preventive maintenance of expansive soil slope during operation period.Depending on expansive soil slope conservation project in West Section of Shi-Tian highway in southern Shaanxi,through field investigation,laboratory test,field test,theoretical analysis and field monitoring method,carrying out chemical modification techniques of expansive soil slope research on application preventative maintenance.The main tasks are:(1)The deformation of expansive soil slope in West Section of Shi-Tian highway has the following form:surface creep or slip deformation of non supported slope,bulging and slip surface of supported slope,deformation and failure of retaining structures of supported slopes,deformation and failure of drainage system of expansive soil slope.The cause of deformation and failure of operating expansive soil slope is analyzed.(2)Through wet and dry cycle test of indoor expansive soil,discussing the mechanism of deformation and failure of expansive soil slope:in the humidification process,expansion force begins to produce,expansive soil volume expands,,the soil crack rate increases,the more rain water into the cracks,the damage of expansive soil slope structure is further increased.At the same time,the deformation of the skeleton increases,which leads to the probability of deformation and failure of the expansive soil slope.During drying and wetting cycles of the expansive soil,the strength of soil decreases,cracks gradually increased,the slope appear bulging,cracking phenomenon.(3)Carrying out indoor chemical modified mixture test with expansive soil in West Section of Shi-Tian highway,the experiment showed that the ratio of polyvinyl alcohol:active lime:water =2%:5%:93%was the best.(4)The chemical modified expansion test found that physical and mechanical properties of soil improved,expansion rate decreased by 27%-37%,Swelling force decreased by 10-15kPa,the strength has been increased by 17-45%,particle size distribution and water physical properties are improved,the control range of the moisture content increases with water content,the dry density fluctuates little with the change of water content,the test proves that the improved soil is superior to the original soil and it is suitable for the operation and maintenance of expansive soil slopes in rainy areas such as Hanzhoung.(5)Selecting the test section in the Xixiang service area and K437+600,through theoretical analysis,field monitoring and numerical simulation,the expansive soil slope before and after improvement is evaluated,using Bishop circle method to calculate the stability of expansive soil slope before and after improvement,the water content and soil pressure at different depths of the slope are detected and the relative displacement of the pier is monitored by displacement monitoring,numerical simulation software is used to simulate the actual situation of the expansive soil slope before and after improvement.The results of analysis by three methods can be seen,The chemical improvement scheme has played a positive role in the preventive maintenance of expansive soil slope to some extent.