Study On Capillary Water Rising Process In Undercutting Area Of Earthen Ruin In Arid Region

As one of the most common and typical developmental diseases of soil sites in arid areas,bottom excavation has a vital impact on the overall stability and instability mode of soil sites.The capillary process in the erosion area is the only way to cause salinization degradation in the erosion area at the bottom of the soil site in arid area,and it is also an important prerequisite for the occurrence of wind erosion loss effect.Through the analysis of real-time monitoring data of water content change of foundation and excavation area in three typical rammed earth sites during four seasons,rainfall and snowfall,it is found that capillary process caused by rainfall(snow)weather is the working condition of capillary process in excavation area.Combined with indoor capillary simulation experiments,it is shown that the plastic limit of foundation soil is the critical condition for capillary process in excavation area.Then,based on the results of sampling and investigation in 10 excavation areas of soil sites in arid areas,and taking fully into account the capillary process characteristics of soil sites in arid areas,the Heisen formula is modified by introducing the influence coefficient k,and a calculation model of the height of excavation areas is proposed.According to the model,the height of excavation area is calculated for three typical monitoring sites,and the height calculation model of excavation area is verified and analyzed.The results show that the model has positive reference significance for the determination of the height of excavation area of soil sites in arid regions.The results are as follows:(1)Through monitoring the water content of the excavation area and foundation in four seasons(spring equinox,summer equinox,autumn equinox,cold),rainfall and snowfall,it is found that only under the condition of precipitation,and the precipitation grade makes the foundation soil meet the specific water-bearing state,the capillary water will rise in the excavation area.(2)Through the limit water content test of the foundation soil of the monitoring site and the analysis of the change trend of the water content of the foundation and the soil in the excavation area under the condition of precipitation,it is found that the critical condition for the capillary process in the excavation area is that the water content of the foundation exceeds its plastic limit value,i.e.the free water available for capillary action in the foundation soil.(3)Based on the research results of the capillary process conditions and critical conditions in the excavation area,combined with the monitoring and analysis of the water content and temperature in the excavation area and foundation in the precipitation monitoring,the characteristics of the capillary process in the excavation area are proposed.It is also found that in the process of precipitation,precipitation and evaporation can control the capillary rising process of the erosion zone by interfering with the capillary water in the foundation,and ultimately affect the development of the height of the erosion zone.(4)Through the grey correlation analysis,it is found that the annual average precipitation is the most important factor affecting the height development of the excavation area,followed by the compacted soil void ratio e,potential evaporation and effective particle size d₁₀.(5)By quantifying the influence of precipitation and evaporation on the capillary rising process in the excavation area,the Heisen formula is modified by introducing the influence coefficient k,and the mathematical model of the excavation area height of the soil sites in arid area is established.The height of excavation area of three typical monitoring sites was verified and calculated,and the error rate was less than 5%.