工程降水引起基坑及土体变形机理、规律及控制策略研究
发布时间：2018-08-26 14:47
【摘要】：已有大量文献报道了基坑施工过程中引起的支护结构及土体变形问题,基坑承压水降水引起的地面沉降问题也得到了大量关注。但少有文献对潜水降水单独作用时基坑支护结构变形的问题开展研究,承压水降水引起的土体空间分布形式也少有学者探讨。本研究报道了6个现场降水试验,揭示了潜水降水引起支护结构的变形及承压水降水引起土体变形的空间分布形式;基于降水试验分别建立了潜水、承压水降水的三维精细化数值模型,通过降水试验实测资料从地下水渗流和基坑及土体变形两个方面对模型进行了验证;利用上述模型分别研究了潜水、承压水降水引起基坑及土体变形的机理,探讨了在常见工程降水条件下基坑及土体变形的规律;进一步的,通过现场试验和数值模型分别研究了控制潜水、承压水降水引起基坑及土体变形的策略。本文的工程实测和数值计算研究得到了以下成果:(1)基坑开挖前的潜水降水可引起支护结构发生显著的指向坑内的悬臂侧移,最大能达到所报道工程允许最大侧移的37.6%-47.6%。而土体渗透系数越大,渗透性各项异性越明显,基坑宽度越大,一次性降水深度越大,潜水降水引起的墙体侧移也越大。研究表明,降水井旁渗流力及墙土相互作用使得坑内土体发生指向坑内的水平位移、开挖侧约1/2倍最大降水深度范围内墙土总压力减小、墙体两侧负摩擦的不对称为潜水降水引起支护结构变形的根本原因。而先撑后降、分段降水、分层降水策略则能很好的控制这部分支护结构的变形。(2)承压层短期降水将引起土体变形呈“三段式”的空间分布,承压层上侧土体变形“上小下大”,地表沉降最小;承压层土体变形“上大下小”;承压层下侧土体发生隆起。而不论承压层降水时间长短、竖向补给条件如何,其上、下弱透水层渗透性如何,承压水降水引起的最大土体变形位置均在承压层上有水位降深的土层顶板处。研究表明,承压水降水使得其上土体出现主应力拱、附加拉应力,最终导致“上小下大”变形的出现;承压层土体则在土体附加压力作用下出现从下至上叠加的压缩变形并形成“上大下小”的规律;承压层下侧弱透水层中有较大向上的渗流力,使得土体隆起。而地下水回灌策略可以很好控制承压水降水引起的土体变形,双回灌井组合回灌策略则适用于对沉降要求更严格的工程,总的来说,同灌同扬方案效果最好,先灌后扬次之,先扬后灌应避免采用。
[Abstract]:A large number of literatures have reported the problems of supporting structure and soil deformation caused by foundation pit construction, and the problem of ground subsidence caused by dewatering of confined water in foundation pit has also been paid much attention. However, there are few literatures to study the deformation of foundation pit supporting structure under the action of submersible precipitation alone, and the spatial distribution of soil caused by confined water dewatering is also seldom discussed by scholars. In this paper, six field dewatering experiments are reported, which reveal the spatial distribution of the deformation of support structure caused by submersible dewatering and the deformation of soil caused by confined water dewatering. The three dimensional fine numerical model of confined water dewatering is verified from groundwater seepage, foundation pit and soil deformation by the measured data of dewatering test. The mechanism of deformation of foundation pit and soil caused by dewatering of confined water is discussed, and the law of deformation of foundation pit and soil under the condition of common engineering dewatering is discussed. Dewatering of confined water causes deformation of foundation pit and soil. In this paper, the following results have been obtained: (1) the submersible dewatering before excavation of foundation pit can cause the support structure to move significantly towards the cantilever in the pit, and the maximum value can reach 37.6- 47.6of the maximum allowable lateral displacement of the reported project. The larger the soil permeability coefficient, the more obvious the heterogeneity of permeability, the wider the foundation pit width, the greater the depth of one-time precipitation, and the greater the lateral displacement of the wall caused by diving precipitation. The results show that the seepage force and the interaction between wall and soil make the soil in the pit move horizontally towards the pit, and the total pressure of the wall soil decreases in the range of about 1 / 2 times the maximum depth of precipitation at the excavation side. The asymmetry of negative friction on both sides of the wall is the fundamental cause of deformation of support structure caused by submersible dewatering. However, the deformation of this support structure can be well controlled by supporting first and then falling, section precipitation and stratified precipitation strategy. (2) Short-term precipitation in confined layer will cause the soil deformation to be "three-segment" spatial distribution, and the deformation of the upper side of the confined layer will be "small, small and large". The surface settlement is the smallest, the deformation of the confined layer is "large and small", and the soil of the lower side of the confined layer is uplifted. However, regardless of the time of dewatering, the vertical recharge condition, the permeability of the upper and lower weak permeable layers, the maximum deformation of soil caused by the dewatering of confined water is located at the roof of the deep soil layer with the water level falling on the confined layer. The research shows that the dewatering of confined water causes the main stress arch and the additional tensile stress on the upper soil, resulting in the appearance of "upper small and lower big" deformation. Under the action of additional pressure, the compressional deformation of the soil in the confined layer is superimposed from the top to the bottom, and the law of "big up and small down" is formed, and there is a large upward seepage force in the weak permeable layer at the bottom of the confined layer, which makes the soil uplift. The groundwater recharge strategy can well control the soil deformation caused by confined water dewatering. The combined recharge strategy of double recharge well is suitable for the engineering with more strict settlement requirements. In general, the effect of the same irrigation scheme is the best, followed by the irrigation first and then the uplift. Use should be avoided after irrigation.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU753
，
本文编号：2205200
[Abstract]:A large number of literatures have reported the problems of supporting structure and soil deformation caused by foundation pit construction, and the problem of ground subsidence caused by dewatering of confined water in foundation pit has also been paid much attention. However, there are few literatures to study the deformation of foundation pit supporting structure under the action of submersible precipitation alone, and the spatial distribution of soil caused by confined water dewatering is also seldom discussed by scholars. In this paper, six field dewatering experiments are reported, which reveal the spatial distribution of the deformation of support structure caused by submersible dewatering and the deformation of soil caused by confined water dewatering. The three dimensional fine numerical model of confined water dewatering is verified from groundwater seepage, foundation pit and soil deformation by the measured data of dewatering test. The mechanism of deformation of foundation pit and soil caused by dewatering of confined water is discussed, and the law of deformation of foundation pit and soil under the condition of common engineering dewatering is discussed. Dewatering of confined water causes deformation of foundation pit and soil. In this paper, the following results have been obtained: (1) the submersible dewatering before excavation of foundation pit can cause the support structure to move significantly towards the cantilever in the pit, and the maximum value can reach 37.6- 47.6of the maximum allowable lateral displacement of the reported project. The larger the soil permeability coefficient, the more obvious the heterogeneity of permeability, the wider the foundation pit width, the greater the depth of one-time precipitation, and the greater the lateral displacement of the wall caused by diving precipitation. The results show that the seepage force and the interaction between wall and soil make the soil in the pit move horizontally towards the pit, and the total pressure of the wall soil decreases in the range of about 1 / 2 times the maximum depth of precipitation at the excavation side. The asymmetry of negative friction on both sides of the wall is the fundamental cause of deformation of support structure caused by submersible dewatering. However, the deformation of this support structure can be well controlled by supporting first and then falling, section precipitation and stratified precipitation strategy. (2) Short-term precipitation in confined layer will cause the soil deformation to be "three-segment" spatial distribution, and the deformation of the upper side of the confined layer will be "small, small and large". The surface settlement is the smallest, the deformation of the confined layer is "large and small", and the soil of the lower side of the confined layer is uplifted. However, regardless of the time of dewatering, the vertical recharge condition, the permeability of the upper and lower weak permeable layers, the maximum deformation of soil caused by the dewatering of confined water is located at the roof of the deep soil layer with the water level falling on the confined layer. The research shows that the dewatering of confined water causes the main stress arch and the additional tensile stress on the upper soil, resulting in the appearance of "upper small and lower big" deformation. Under the action of additional pressure, the compressional deformation of the soil in the confined layer is superimposed from the top to the bottom, and the law of "big up and small down" is formed, and there is a large upward seepage force in the weak permeable layer at the bottom of the confined layer, which makes the soil uplift. The groundwater recharge strategy can well control the soil deformation caused by confined water dewatering. The combined recharge strategy of double recharge well is suitable for the engineering with more strict settlement requirements. In general, the effect of the same irrigation scheme is the best, followed by the irrigation first and then the uplift. Use should be avoided after irrigation.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU753
，
本文编号：2205200
本文链接：https://www.wllwen.com/guanlilunwen/chengjian/2205200.html
