Study On Soil Desiccation Cracking Process Based On Electrical Resistivity Tomography

In recent years,long duration,wide scope and high strength of extreme drought climate frequently occurred under the influence of the global climate change.Under the influence of extreme drought climate,the engineering soil loses water,desiccation cracking occurs,which affects the engineering properties of the soil and leads to many engineering geological problems and disasters.However,the existing research methods are not enough to completely solve the problems of soil evaporation and desiccation cracking.Therefore,this paper took the ERT technique as the research method,the quartz sand and the Xiashu Soil as the objects of study,carried out a series of laboratory tests,systematically studied the relationship between the apparent resistivity and moisture content/desiccation cracking in the drying process and provided effective research means for further analysis on the evaporation process of soil water in the breakout of distribution characteristics and migration patterns.The paper has mainly obtained the following achievements:(1)The ERT technique was applied to the soil pan evaporation experiment.The relationship between the soil apparent resistivity and soil moisture content was established preliminarily.The lower the moisture content of the sample,the higher the soil apparent resistivity.The curve of the sample average apparent resistivity and soil moisture content agreed with the index relationship formula.Through the relationship formula,the change rules of sample moisture field in the drying process can be gained.(2)The ERT technique was applied to the soil column evaporation experiment.The relationship between moisture content of the soil column profile and the measured resistance was calibrated.The measured resistance of the soil column in the drying process was monitored in order to gain the water field evolution rules for soil column.The results showed that the soil evaporation process can be divided into three stages:constant evaporation rate,reduction evaporation rate and residual phase;The change in temperature can lead to the change of soil resistance.The higher the temperature,the lower soil resistance.During the evaporation,the frontal edge of evaporation moved down gradually from the surface of the soil column.The resistivity cloud of soil column can reflect the movement of the evaporation front in the evaporation process.The space-time water field evolution rules of soil column can be gained by adopted the ERT technique.(3)The ERT technique was applied to the evaporation model of soil.The TDR measuring equipment was also adopted to verify the reliability of the ERT technique.The profile apparent resistivity of soil model was monitored and the space-time water field evolution rules of soil column were gained.The research results showed that the apparent resistivity of soil model was more sensitive to the change of moisture content,which changed much earlier than TDR soil humidity sensor.By contrast,the ERT technique is more efficient and practical.(4)The rules of soil desiccation cracking in drying process were investigated.The one-dimensional and two-dimensional desiccation cracking tests were conducted by using the ERT technique.The clayey soil resistivity was monitored and compared with the crack image data.The research results showed that in the initial stage of evaporation,soil resistivity decreased slowly with increasing time,which is mainly due to the enhancement of the clayey soil electric double layer conductivity induce by the hydration film thinning and the increment of the contact area between soil particles.As evaporation proceeded,more and more gas entered into the soil,and the top layer of soil transformed from saturated to unsaturated state.The soil resistivity transformed from the slowly decreasing trend to the slowly increasing trend.Once the micro cracks formed in the soil,the soil resistivity increased sharply,while the soil without cracks kept the slowly increasing trend.Combining the apparent resistivity cloud and crack image data,it can be found that there was a very good consistency between them and the apparent resistivity cloud can effectively reflect the development situation of desiccation cracking.(5)The research results show that the ERT technique can effectively gain the space-time evolution characteristics of the soil moisture field and the evolution rules of desiccation cracking during drying process.It can provide the ideal technical means for the study of extreme drought climate under the action of soil engineering properties response.