【摘要】：已有大量文獻報道了基坑施工過程中引起的支護結(jié)構(gòu)及土體變形問題,基坑承壓水降水引起的地面沉降問題也得到了大量關(guān)注。但少有文獻對潛水降水單獨作用時基坑支護結(jié)構(gòu)變形的問題開展研究,承壓水降水引起的土體空間分布形式也少有學(xué)者探討。本研究報道了6個現(xiàn)場降水試驗,揭示了潛水降水引起支護結(jié)構(gòu)的變形及承壓水降水引起土體變形的空間分布形式;基于降水試驗分別建立了潛水、承壓水降水的三維精細(xì)化數(shù)值模型,通過降水試驗實測資料從地下水滲流和基坑及土體變形兩個方面對模型進行了驗證;利用上述模型分別研究了潛水、承壓水降水引起基坑及土體變形的機理,探討了在常見工程降水條件下基坑及土體變形的規(guī)律;進一步的,通過現(xiàn)場試驗和數(shù)值模型分別研究了控制潛水、承壓水降水引起基坑及土體變形的策略。本文的工程實測和數(shù)值計算研究得到了以下成果:(1)基坑開挖前的潛水降水可引起支護結(jié)構(gòu)發(fā)生顯著的指向坑內(nèi)的懸臂側(cè)移,最大能達到所報道工程允許最大側(cè)移的37.6%-47.6%。而土體滲透系數(shù)越大,滲透性各項異性越明顯,基坑寬度越大,一次性降水深度越大,潛水降水引起的墻體側(cè)移也越大。研究表明,降水井旁滲流力及墻土相互作用使得坑內(nèi)土體發(fā)生指向坑內(nèi)的水平位移、開挖側(cè)約1/2倍最大降水深度范圍內(nèi)墻土總壓力減小、墻體兩側(cè)負(fù)摩擦的不對稱為潛水降水引起支護結(jié)構(gòu)變形的根本原因。而先撐后降、分段降水、分層降水策略則能很好的控制這部分支護結(jié)構(gòu)的變形。(2)承壓層短期降水將引起土體變形呈“三段式”的空間分布,承壓層上側(cè)土體變形“上小下大”,地表沉降最小;承壓層土體變形“上大下小”;承壓層下側(cè)土體發(fā)生隆起。而不論承壓層降水時間長短、豎向補給條件如何,其上、下弱透水層滲透性如何,承壓水降水引起的最大土體變形位置均在承壓層上有水位降深的土層頂板處。研究表明,承壓水降水使得其上土體出現(xiàn)主應(yīng)力拱、附加拉應(yīng)力,最終導(dǎo)致“上小下大”變形的出現(xiàn);承壓層土體則在土體附加壓力作用下出現(xiàn)從下至上疊加的壓縮變形并形成“上大下小”的規(guī)律;承壓層下側(cè)弱透水層中有較大向上的滲流力,使得土體隆起。而地下水回灌策略可以很好控制承壓水降水引起的土體變形,雙回灌井組合回灌策略則適用于對沉降要求更嚴(yán)格的工程,總的來說,同灌同揚方案效果最好,先灌后揚次之,先揚后灌應(yīng)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.
【學(xué)位授予單位】：天津大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TU753
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本文編號：2205200