Analysis Of Settlement Effect Of Water Level Rise And Drop On Red Clay Subgrade Model

The red clay,as region-special clay soil,is distributed in more than ten provinces in China.The monsoon climate in China is distinct.Therefore,the seasonal precipitation leads to the constant variation of groundwater level,then the settlement causing the cracking and settlement of red clay roadbed,and finally the damage of the road.In this paper,a roadbed model box and a groundwater level control system were independently developed based on the red clay in Lingui.Furthermore,a half model of the roadbed of the expressway with a scale of 1:10 was also established.An experimental investigation of red clay characteristics was conducted using direct shear tests and wet disintegration tests with different cycles of drying and watering.The main outcomes are as follows,(1)The physical property tests of red clay were conducted.The influence of the seasonal groundwater on the settlement of the roadbed model and the strength and humidification characteristics of red clay soil is also analysed.(2)The indoor model tests were conducted to simulate the variation process of the seasonal groundwater level.The changing pattern of internal water and overall settlement of red clay roadbed is analysed.It is found that the settlement curve after post-construction is approximately logarithmic,that the internal settlement of subgrade soil is smaller than the surface settlement and that the subgrade resettles due to the lifting and of groundwater.Also,the infiltration of groundwater humidified the roadbed soil,where the soil peels off causing the settlement of the roadbed.(3)It was found by the direct shear test that the shear strength of the red clay gradually decreased when the samples continuously passed through the drying and watering cycles.The shear strength of red clay samples after the first drying and watering cycle is the most significant.The shear strength decreases with the increasing number of times of the drying and watering cycles on the soil samples.The cohesive force shows a decreasing trend with the increasing number of times,while the internal friction angle shows an overall increasing trend.(4)It is found through the wet disintegration test that the wet disintegration of red clay is mainly divided into three stages: wet balance,disintegration,moisture absorption and weight gain.The required time for the wet disintegration is gradually reduced with the increasing number of times of the drying and watering cycles on the red clay samples,while the disintegration rate is first decreased and then increased,the residual mass of the soil sample is diminished,and the non-disintegration rate is decreased,and the wet disintegration produced an increasing number of large cracks in the residual soil.The rate of disintegration shows a trend of increasing first and then decreasing.