【作者】 谢玖琪；

【导师】 林涛；

【作者基本信息】 南京林业大学 ， 岩土工程， 2012， 硕士

【摘要】 随着软土地区城市建设的迅速发展，基坑工程常处于密集的既有建(构)筑物附近，基坑施工受到更加严格的环境制约。预测基坑施工支护结构的变形及其对周围地表沉降的影响，对于软土地区深基坑的设计与施工具有重要指导意义。本文结合南京地铁十号线深基坑工程实践，采用理论分析、实测分析和数值模拟等方法，对深基坑开挖引起的支护结构变形对周围地表沉降的影响进行了研究，主要工作和成果如下：(1)将围护结构地下连续墙数值模拟计算结果和现场监测结果进行了对比分析，墙身最大水平位移、地表沉降、连续墙及地表沉降曲线等模拟结果和实测基本一致，说明模拟结果是可行的。(2)通过墙体水平位移面积Aq和墙后周围地表沉降面积Ad的关系研究，发现Ad/Aq因工况不同，其比值也不同，并且随着开挖深度的增加，比值是减小的，说明Ad的增速是小于Aq的，同时也反映周围地表沉降具有滞后性；通过各工况定量分析，Ad/Aq大致位于0.4到0.6之间。(3)基坑开挖对墙后地表沉降的的影响范围主要分布在距基坑边沿的1.5倍最终开挖深度，主要影响区在d/H为0~1.0之间，次要影响区在d/H为1.0~1.5之间；沉降最大值出现在d/H比值为0.5区域。(4)从设计因子、施工因子和土的物理性质因子三个角度研究了影响支护结构变形的各因子对周围地表沉降的敏感性。①设计因子：周围地表垂直沉降随着地下连续墙刚度的增加，沉降值逐渐减小，但当墙体刚度增加到一定程度时，再通过增加墙体刚度来减小地表沉降作用不明显；随着围护结构地下连续墙入土深度的增加，地表沉降减小，但在满足嵌固深度达到基坑稳定的要求下，再增加入土深度对减少周围地表沉降不是很明显。水平支撑的刚度和间距或者数量对抑制地下连续墙变形，减小周围地表沉降有较大影响；钢支撑施加设计预加轴力的100%和75%效果差不多，地表沉降只减小了4.8%。②施工因子：基坑开挖后支撑时间或者暴露时间对周围地表沉降影响较大，2天后支撑比立即支撑地表沉降最大值大1.5mm，5天后支撑比立即支撑大3.9mm，并且是一个加速沉降的态势。在基坑“先撑后挖”和“先挖后撑”的施工方法对比中，前者相比后者，沉降最大值减小约7.1%。地面超载对墙后周围地表沉降是直接和较为敏感的，墙后地表沉降随地面超载值的加大而增大，沉降曲线凹形逐渐加深，地表沉降最大值逐渐增大。③土的物理性质因子：土体的弹性模量对墙后周围地表沉降的影响是显著的，增加土体的模量，可以有效减小地表沉降，控制基坑的变形。当土体的内摩擦角和粘聚力增大时，墙后地表沉降都是减小的，且内摩擦角对地表沉降的影响相比粘聚力稍微大一点。更多还原

【Abstract】 Deep excavations with complicated environment conditions have sprung up during urbanunderground space developing process；these deep excavations are usually surrounded bybuildings and utilities. More severe restrictions are required for these deep excavations. Toensure safety of those adjacent structures and the influence of the ground surface settlementaround of deformation of the supporting structure are needed to be predicted in advance.This isvery important guiding significance about deep foundation pit design and construction in soft soilarea.This thesis carried out researches on the influence of the ground surface settlement aroundof deformation of the supporting structure about deep foundation pit engineering of metro lineNo.10in Nanjing,by means of theoretical analysis,measurement analysis and numericalsimulation.The main work and achievements are as following:(1)According to a contrast and analysis,the simulation results are in accord with measuredresults about the maximum horizontal displacement of wall body,surface subsidence,diaphramwall,and the ground surface settlement curve.Thus the simulation results is feasible.(2)Through the relation research between the horizontal displacement area of wall body ofAqand the ground surface settlement area of Ad, the ratio of Ad/Aqwas different with differentworking conditions.With the increase of excavation depth,the ratio became smaller.At the sametime,it also reflected the surface settlement around with a time lag.The ratio of Ad/Aqlocated at0.4to0.6roughly by quantitative analysis of the conditions.(3) The influence scope of the surface subsidence mainly distributed in the edge of1.5timeseventually excavation depth.The ratio of d/H between0~1.0was the main effect area；The ratioof d/H between1.0~1.5was secondary influence area.About the ratio of0.5of the d/Happeared the maximum settlement.(4)The affection factors of the deformation of the supporting structure were supplied to thesensitivity of surface subsidence around,including factors of design,construction and soilphysical properties.1)Design factors: With the increasing stiffness of underground continuous wall, thesedimentation value of the vertical surface subsidence around was decreasing, but when the wallrigidity increased to certain degree, increasing wall rigidity to reduce the surface settlement didnot play a significant role.As the buried depth of underground continuous wall increased, theground surface settlement reduced, but meeting the stability of foundation pit request in theembedded depth of solid, adding depth to reduce the ground surface settlement was not obvious.The stiffness and spacing or quantity of the level of support had a great influence on controlingthe deformation of underground continuous wall and reducing the surface settlement around. Compared with the effect of100%and75%design axial force of steel support, the groundsurface settlement was only reduced by4.8%.2)Construction factors: The support time or exposure time after the foundation pitexcavation had a great influence on the ground surface settlement.Compared with immediatesupport,the maximum ground surface settlement of the2days later support inceeased1.5mm,5days later,increasing3.9mm, then it was a trend to speed up.Between the two constructionmethods of“no excavation without support” and “no support without excavation”,themaximum ground surface settlement of the former reduced about7.1%.Overloading effected theground surface settlement directlyand sensitively.with increasing overloading value,themaximum surface subsidence also increased gradually.3)Physical properties of soil factors: The modulus of elasticity of soil to effect of surfacesubsidence was very significant.Increasing the soil modulus could effectively reduce the surfacesettlement and control the deformation of foundation pit.When the internal friction angle of soiland the cohesion increased, the surface subsidence reduced.And compared to the cohesion, theinternal friction angle had more effection on the ground surface settlement.更多还原