Dry-shrinkage Characteristics And Crack Evolution Law Of Red Soil Of Hipparion

A red stratum,Hipparion red soil,is widely distributed at the bottom of the loess in northwestern China.Studies have shown that the Hipparion soil has good water-tight conditions.Under the action of extreme rainstorm,drought or reciprocating uplift of the groundwater level,the soil is easy to form a weak zone between the layers,and the strength attenuation and creep deformation occur,which induces some large-scale landslide slid along the top of the Hipparion clay.In addition,because the Hipparion red clay is rich in clay minerals such as montmorillonite,illite and kaolinite,it has the characteristics of water swelling and water shrinkage.Engineering geological activities such as road,railway,water conservancy,construction and coal resource development in northwest China inevitably cross the Hipparion red soil layer.After excavation,the Hipparion red soil is exposed to the air,and the water content is gradually reduced,resulting in dehydration and shrinkage cracking,which affects the stability and safety of tunnels,slopes and large structures.Therefore,this paper takes the Hipparion red soil as the research object,carries out the dehumidification test of the Hipparion red soil samples under different initial water content,different dry density and different environmental temperature,and studies the water shrinkage shrinkage law and crack in the process of drying,which is of great significance to the engineering construction involving the Hipparion red clay and other cohesive soils.The specific work and conclusions are as follows:(1)Hipparion red soil dehumidification test.It is concluded that the dehydration curve shows three distinct stages:rapid dehydration period,deceleration dehydration period and residual dehydration period.The water loss curve of the sample is significantly affected by the initial water content,dry density and ambient temperature.The larger the initial water content,the smaller the dry density and the higher the ambient temperature,the faster the water loss rate of the sample and the more severe the water loss process.(2)Hipparion red clay shrinkage test.It is concluded that the contraction curves show four distinct stages:the rapid contraction phase,the deceleration contraction phase,the residual contraction phase,and the zero contraction phase.The shrinkage curve of the sample is significantly affected by the initial water content,dry density and ambient temperature.The larger the initial water content,the smaller the dry density and the higher the ambient temperature,the more severe the shrinkage process.After the shrinkage,the shrinkage strain is correspondingly larger.And the initial shrinkage strain increases by about 0.2 times for the initial water content of the three-toed horse red clay sample;the final shrinkage strain increases by about 0.10 for every 0.05g.cm~-33 of dry density;the temperature rises every 10°C,the final shrinkage strain of the sample increased by about 0.21 times;the final shrinkage strain of the sample showed a good linear relationship with the initial water content,dry density and temperature.(3)Quantitative analysis test of crack evolution of the Hipparion red clay.Through the design of the indoor test monitoring device,the dry dehumidification test was carried out on the remodeling of the Hipparion red soil,and the dynamic quantitative data of the drying shrinkage crack evolution was obtained by digital image quantitative processing technology.The crack evolution law is different from the traditional law(The crack area and average width always increase during the drying process,eventually tend to be stable.)The difference is that the crack of the sample shrinks in the middle of the dry period,showing the"self-healing"of the crack.Then the"crack"theory was put forward to analyze the mechanism of this phenomenon.Finally,the concept of healing degree was introduced,and the healing effect of cracks under different initial water content was studied.The conclusions were as follows:The initial water content has a significant influence on the crack healing degree of the sample,and the initial water content is lower.The earlier the crack of the sample heals and the greater the final healing degree.