Model Test And Numerical Simulation Study Of Transparent Soil On Influence Of Tunnel Excavation And Soil Loss Rate On Pile Foundation Of Adjacent Buildings

With the development of the city,people’s demand for underground projects is increasing,and underground projects often need to excavate tunnels.If no protective measures are taken,tunnel excavation may pose a threat to the service performance and limit state requirements of nearby structures.Due to the lack of detailed understanding of the impact of tunnel excavation on the structure,expensive protection measures are usually required.At present,most of the researches on pile-soil-tunnel interaction at home and abroad focus on the excavation process of the tunnel,but pay limited attention to the loss rate of the soil itself.Moreover,due to the nature of the natural soil,the visualization degree is low in the model test research,and the complete and accurate deformation field cannot be obtained.In this study,artificial transparent soil material and particle image processing technology are combined and applied to pile-soil-tunnel model test.A 3D test measurement system including optical platform,model box,drainage pipe system,sheet light source laser,industrial CCD camera,etc.is designed by ourselves to measure the 3D displacement field of surrounding soil in the process of tunnel excavation without insertion.The sensitivity analysis of important parameters of artificial transparent soil model test was carried out by finite element analysis software Plaxis 3D.The results show that:1)The vertical and horizontal displacement modes are the result of the ability of soil to form/maintain arching mechanism.2)The change of soil loss rate has a significant impact on the shape of settling tank.3)Soil volume loss is related to tunnel volume loss as a function of normalized depth.The results show that the changes are significant.4)Under the condition that the tunnel cover diameter ratio C/D is constant,the greater the soil loss rate,the greater Vs,and the greater the maximum displacement Xmax,which is approximately linearly and positively correlated.5)The maximum settlement of tunnel centerline increases with the increase of soil loss rate.6)The width of settlement field of shallow tunnel generally increases with the increase of C/D ratio and decreases with the increase of soil loss rate.7)For sand with large pile length,when the volume loss is large,the soil arching is obvious,which reduces the trend of tunnel volume loss spreading to the surface.In the case of short piles and no piles,the soil does not form a closed arch,and there is a nearly vertical ear-shaped shear band at the tunnel shoulder.The soil above the tunnel moves downward as a near rigid body(there is no shear strain near the tunnel centerline).Under the condition of short piles and green land,the soil cannot form arch.The settlement field of short piles is qualitatively different from that of piles.8)The minimum pressure occurs at different volume loss rates,depending on C/D.The greater the C/D,the higher the soil loss rate corresponding to the minimum pressure turning point.