Research On Variation Characteristics And Influencing Factors Of Water Content In Shallow Layer Of Expansive Soil Slope

Expansive soil is a kind of regional special soil rich in minerals such as kaolinite,montmorillonite and illite,which has strong water sensitivity and swell-shrink characteristic,and is very sensitive to the changes of humidity and heat in the environment.The change of soil moisture content of expansive soil slope will cause the phenomena of soil potential of expansion and contraction and soil softening,resulting in the instability of slope with a very gentle slope,under the influence of natural climate.The above phenomena are ultimately related to the change of soil moisture content.Therefore,it is of great significance to study the variation of water content in the shallow layer of the expansive soil slope in a certain region and its influencing factors for the construction of the local expansive soil slope engineering.In this paper,model test and numerical simulation are used to study the influence characteristics of different factors on the variation of water content in the shallow layer of expansive soil slope in nanning area.Firstly,the influence rules of different slopes and initial water content on the water content in the shallow layer of expansive soil slope are explored.Secondly,the influence of different overburden(vegetation,overburden material,overburden thickness)on water content in shallow layer of expansive soil slope was studied.The influence rules of various influencing factors on water content in shallow layer of expansive soil slope are summarized.The main research contents and results are as follows:(1)A multi-slope combination model was used to carry out the model test of the influence of slope on the seepage characteristics of expansive soil slope,and the distribution relationship between runoff and seepage under rainfall conditions of slopes with different slopes,as well as the variation law of water content of slope soil over time were analyzed.The results show that in the expansive soil slope rainfall infiltration,the smaller the slope,the longer the time of runoff,and the more obvious the infiltration of rainwater on the slope,supplemented by surface runoff;With the increase of slope,the change of soil water content decreases.When the slope reaches a certain grade,continuous slope elevation can increase slope runoff and prevent slope infiltration,but the effect becomes smaller gradually.The higher the initial water content of slope,the slower the change rate of soil water content and the smaller the change value.(2)The influence of different overburden on the change of water content in the shallow slope of expansive soil was studied.The change characteristics of water content in the shallow slope under the green slope of expansive soil were analyzed in the exposed slope,green slope of planting,green slope of overburden clay and green slope of planting in overburden sand layer,under long-term climate environment.The results show that when the slope surface is exposed,the soil mass is significantly affected by the natural climate,in which the penetration crack appears at the top of the slope,the soil mass in the middle of the slope has obvious shallow sliding and traction sliding,and the slope surface is greatly affected.The overlying vegetation not only weakens the scouring effect of rainwater on the expansive soil slope surface,but also reduces the seasonal influence of natural climate on the shallow water content of expansive soil.On the green slope and the green slope with the overlying sand layer,the soil water content is weakly affected by the atmosphere,mainly by the vegetation layer or the overlying layer,and the shallow water content of the slope increases slowly with the increase of time.When the overlying clay planting green slope is carried out on the expansive soil slope,the shallow water content of the slope is weakened by the influence of natural climate,and the soil in the slope is relatively stable.(3)The influence of slope shallow water content under rainfall infiltration and the long-term response of slope shallow water content under overburden were simulated.The results show that the lower the rainfall intensity and the longer the duration,the greater the infiltration of the shallow soil and the greater the change of the shallow water content of the expansive soil slope.The cumulative infiltration per unit area decreases with the increase of slope,but the decreasing range of infiltration decreases with the increase of slope.When the expansive soil is exposed to the slope surface,the moisture content of the slope soil is strongly influenced by the atmospheric dry and wet cycle.The influence of atmosphere on the shallow water content of the expansive soil slope overlaid with clay green is weakened,and with the increase of overburden thickness,the shallow water content of the expansive soil slope is more stable.