【作者】 许烨霜；

【导师】 沈水龙；

【作者基本信息】 上海交通大学 ， 岩土工程， 2010， 博士

【摘要】 本研究应用室内试验与数值分析相结合的方法研究地下构筑物对多层含水层的渗流阻挡效应及其对城市地面沉降的影响机理;室内试验还用于验证数值分析中的计算参数。将上述构筑物的挡水作用机理的分析方法与试验确定的参数,用于分析上海市近年来的地面沉降加速现象。本研究的主要内容与成果如下:1)上海市自20世纪90年代以来出现的沉降加剧现象的主要原因仍然是地下水位的持续下降作用。通过对上海市地面沉降量、地下水开采量以及地下水位三者实测数据的相关性分析发现,目前的沉降量与地下水开采量之间相关性较差;但沉降量与地下水位之间仍具有密切的相关性。2)上海市中心区近年的地面沉降与工程建设密切相关。引起沉降的与工程建设相关的因素包括建筑物的附加荷载、工程施工以及地下水位下降。本研究的目的是分析工程建设中引起地下水位下降的因素——地下构筑物的长期挡水作用对上海市中心区地面沉降的影响。3)应用室内试验确定单层含水层中地下构筑物在含水层中的插入深度与宽度对地下水渗流的阻挡作用机理。试验结果表明,构筑物下游侧的地下水位变化随构筑物埋深的增加而增大,构筑物最优插入深度比(构筑物对水位下降作用最大的插入深度与所插入土层的厚度之比)约为70%;随着构筑物宽度的增加,下游侧测点水位变化呈增长趋势,上游侧水位变化呈减小趋势。4)应用数值模拟确定多层含水层中地下构筑物对多层含水层地下水的阻挡作用以及含水层之间的越流变化规律。数值模拟结果表明,地下构筑物的存在对地下水位、地下水渗流方向、含水层之间的越流变化以及地面沉降量等有较大的影响;相关因素包括构筑物的埋深范围、挡水宽(长)度、以及构筑物与开采井之间的相对位置等。构筑物插入第II含水层的最优插入深度比约为56%。5)应用数值模拟的方法分析上海市多层含水层-隔水层交互堆积地层中地下构筑物的存在对上海市特别是中心区的含水层地下水渗流与地面沉降的作用规律。以上海市含水层与隔水层交互堆积的地层为对象,建立三维地下水渗流及一维土体固结相结合的地面沉降计算模型分析构筑物的挡水效应。为了简化问题,计算中考虑了两种极端的情况:①构筑物分布式配置,②构筑物集中式配置;真实情况可能介于两者之间。计算成果如下:①构筑物分布式配置,即材质等效法:将中心城区内含水层内大量的地下构筑物的作用简化为渗透系数和压缩系数降低了的新材料,即等效渗透系数与等效压缩系数。该方法用来模拟大范围地下构筑物对地面沉降的影响。模拟结果表明,第II含水层中的构筑物对上海中心城区的沉降量影响最大,外环内第II含水层中构筑物含量每增加10%,中心城区年均沉降量大约增长32%;而第I含水层及微承压中的构筑物对沉降的影响程度较小,各含水层构筑物含量每增加10%时,中心城区年均沉降量大约增长3%左右。②构筑物集中式配置,即含水层局部挡水法:将局部含水层单元的材质直接替换为构筑物材质,而其它地方仍使用天然地层的材质,即考虑含水层局部挡水效应。该方法用来考虑局部环形构筑物对中心城区的地面沉降作用效应。计算结果表明,如果集中配置区域内构筑物的含量超出某临界值,其所围区域内将产生构筑物挡水引起的附加沉降。构筑物含量的临界值对微承压含水层为65%,第I含水层为62%,第II含水层为58%。更多还原

【Abstract】 This study was undertaken to evaluate the impact behaviour on groundwater seepage and land subsidence when infrastructures such as deep buiding foundations, underground structures, subway tunnels, underground path structures, were constructed in the multi-aquifer-aquitard system (MAAS) such as in Shanghai. In order to investigate the mechanism of these impacts, laboratory element tests and numerical simulations based on groundwater seepage model were conducted to analysis cutoff behavior on groundwater seepage of infrastructures. Laboratory element tests were also conducted to determine the parameters in numerical simulation. The obtained mechanism based on the laboratory tests and numerical simulation was employed to investigate the patterns of land subsidence in Shanghai via considering the impact of infrastructure in MAAS of Shanghai. Based on the research results, countermeasures of future construction plan of infrastructures in MAAS were proposed. The gist and primary new findings of this dissertation includes:1) Land subsidence in Shanghai since 1990 was still related to drawdown of groundwater level. A serious of regression analyses was carried out to investigate the relationship among subsidence, groundwater level of each aquifer, and volume of groundwater withdrawal. The results show that subsidence since 1990 is not correlated with the volume of groundwater withdrawal; however, it is still correlated with the drawdown of groundwater level.2) Land subsidence in Shanghai is also correlated with activities of urban construction. Factors resulting in land subsidence during activities of urban construction include additional load during and after structural construction and drawdown of groundwater level, e.g. groundwater pumping during excavation, leaking of underground sturctures. The existence of infrastructure in aquifers in the urban region is a significant reason, which results in the drawdown of groundwater level.3) A series of laboratory investigation on the cutoff behavior of an impervious wall in a phreatic aquifer was conducted. Test results show that drawdown of groundwater level at the lower side of the wall increases with the increase of the inserted depth of the wall in soil and increases with the increase of the width the wall. The optimal insertion depth ratio of the wall (ratio of the depth over the thickness of soil layer) is about 70%.4) A series of numerical analyses was conducted to investigate the obstruction behaviour of underground structures in MAAS. The analytical results show that the existence of underground structures changes the groundwater level, groundwater flow direction, and the rate of subsidence and causes leakage of groundwater among aquifers through aquitards. Influential factors include depth of infrastucture penetrated into the aquifers, the width of underground structures, and the relative position between infrastructure and groundwater discharge or recharge well. The optimal ratio of penetration depth of infrastructure in aquifer II is about 56%.5) A series of numerical analyses was conducted to analyze behavior of seepage and land subsidence via considering the impact of understructures in MAAS of Shanghai. Since it is difficult to make sure the distribution of understructures and it is also difficult to allocate each understructure in numerical model, following two extreme situations are assumed in this study.i) Distributed underground structure: In this situation, the whole aquifer with underground structures is assumed as a uniform material with so-called effective hydraulic conductivity and effective compressibility. This method changes the aquifer with underground structures into another material with lower coefficient of hydraulic conductivity and compressibility. The results revealed that the rate of subsidence in the urban area increased via considering existence of underground structures. When the volume ratio of underground structures in aquifer II increases 10%, subsidence increases about 32%. However, if the volume ratio of underground structures in aquifer I and low-pressure aquifer increases 10%, subsidence increases only about 3%.ii) The second assumed situation is so-called concentrated allocation of underground structure in aquifer, which embowels the heavily urbanized area. In this situation, part of soil material in aquifer is directly replaced by structure material to investigate the impact of concentrated infrastructures on the emboweled urban area. Results showed that additional subsidence within the emboweled urban area increases with the increase of volume ratio of underground structure (VROUS). However, when VROUS is controlled within a critical value, additional subsidence in the emboweled urban area can be controlled within the allowable value. The critical value of VROUS for low-pressure aquifer is 65%, for aquifer I it is abot 62%, and for aquifer II it is about 58%.更多还原