| In recent years,the space for human activities has been expanding,and the foundation pit engineering has also developed in the direction of depth and shape diversity,and it is particularly important to put forward stricter requirements in the stability of foundation pit excavation.At present,when studying the deformation stability coefficient of excavation of arc foundation pit and designing the internal support structure and envelope structure,the size of the arc curvature of the enclosure wall and the number of center angles of the arc foundation pit are rarely considered.The existing literature still has limited research on the systematic study of arc foundation pits.Taking the arc foundation pit engineering of a subway station as the research background,this paper conducts an in-depth study on the excavation deformation stability and enclosure structure optimization of the arc foundation pit through theoretical analysis,numerical simulation and on-site measurement,and the conclusions are as follows:(1)Through the analysis of the force deformation of the soil of the arc foundation pit,considering the effect of the ring earth pressure on the arc foundation pit envelope,the calculation formula of the ring earth pressure is proposed,and the ring bending influence coefficient is introduced,when designing the arc foundation pit,the influence of the circular bending influence coefficient of the arc foundation pit on the deformation of the envelope structure should be considered,when the central angle of the arc foundation pit exceeds 60°,it will cause an error of about 5% of the anti-slip stability coefficient of the arc foundation pit.(2)According to the ABAQUS calculation results and on-site measurement results,the vertical displacement of the soil mass,the horizontal displacement of the wall and the vertical displacement deformation characteristics of the top of the wall are not exactly the same on both sides of the arc foundation pit during the excavation process,the vertical displacement characteristics of the soil on the east side of the arc foundation pit are "check type",according to its stable vertical displacement average fitting curve is close to the fourth polynomial,the vertical displacement characteristics of the soil on the west side of the arc foundation pit are close to the "check type",and its characteristics are weaker than those on the east side.According to its average value of the vertical displacement after stabilization,the fitted curve is close to a cubic polynomial.The overall feature of horizontal displacement of the wall is "fish belly" type,and with the increase of excavation depth,the "fish belly" type feature gradually becomes obvious,close to the excavation surface of the foundation pit.The vertical displacement of the wall top on both sides of the arc foundation pit is in line with the trend of "settlement→ rising → settlement".(3)With the increase of excavation depth,the axial force of the first layer of concrete support showed an upward trend,and finally slowly tended to a stable state;The change trend of the axial force of the second layer of steel can be divided into two stages,the maximum supporting axial force of the first stage is about 1000 k N,and the second stage reaches the maximum when the foundation pit is the deepest,the maximum value is about 2000 k N,and then slowly stabilizes;The change trend of the axial force of the third layer of steel support is relatively stable.Compared with the maximum value of the simulation results,the error of the first layer compared with the simulated value was 128.2 k N,accounting for 12.83% of the measured value.The error of the second layer compared with the analog value is 68.6 k N,accounting for 6.48% of the measured value.The error of the third layer compared with the analog value is 158.2 k N,accounting for 14.70% of the measured value.In general,the error between the simulated value and the measured value is within the acceptable range,which indicates that it is reasonable and correct to use the model to predict the deformation of the arc foundation pit wall.(4)The simulated value of vertical displacement of soil mass,displacement of enclosure wall and supporting axial force under different working conditions are more consistent with the measured value deformation trend,on the whole,the measured value is slightly greater than the simulated value,and comprehensively compare the data analysis such as vertical displacement of soil mass,horizontal displacement of wall depth,vertical displacement of wall top,etc.,and there is still room for optimization in the design of the envelope structure.(5)The design optimization of the arc foundation pit enclosure structure based on the control of the displacement variable of the foundation pit,by adjusting the number of corners of the foundation pit center(i.e.radius of curvature)and appropriately changing the embedding depth of the enclosure wall and the second support type,the vertical displacement of the soil,the horizontal displacement of the wall and the vertical displacement of the wall top are reduced compared with the original scheme as a whole,and the optimization scheme of the arc foundation pit enclosure structure can reduce the deformation of the arc foundation pit to a certain extent,which shows that By adjusting the number of center angles of the enclosure wall and appropriately changing the design combination of the embedding depth of the enclosure wall and the second support type,the stability of the arc excavation can be increased.Under the premise of meeting the safety of the foundation pit,it can reasonably reduce the economic indicators,provide technical approaches and guidance suggestions for the deformation prediction of other arc-shaped foundation pits,and achieve the development concept of "green and energy saving". |
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