城市地下结构施工对邻近构筑物影响的研究
发布时间：2018-09-02 05:50
【摘要】：在日益发展的城市化进程中，密集的高层与超高层建筑和发达的地下交通网络已成为城市必不可少的重要组成部分。基坑工程常处于密集的既有建(构)筑物附近，基坑施工受到了更加严格的环境制约。预测基坑施工引起的变形及其对周边环境的影响，对于城市中心地区深基坑的设计与施工具有重要指导意义，为了更好跟有效地保护邻近建筑物的安全，在深基坑工程中，对开挖卸荷力学效应的研究变得更加意义重大。 在众多对基坑工程变形与稳定研究中起到重要作用的因素中，土体抗剪强度和本构模型是最为关键的，而它们的准确性与土体应力路径有着密切的关系。本文结合广州中心城区深基坑工程实践，采用试验研究、理论分析、数值模拟等方法，对城市地下结构施工对周边环境的影响进行了研究,取得了以下创新性研究成果。 1.对广州市的地质分区进行调研，给出广州市各岩土环境分区对地下工程适应性的评价，确定了中心城区典型土体为研究对象，结合广州市岗顶酒店基坑工程，采用SLB-1型应力应变控制式三轴剪切渗透试验仪，对基坑开挖影响范围内的淤泥质土、粉质粘土层进行了常规三轴试验和考虑应力路径的k0固结卸荷试验，对土体的抗剪强度指标与应力应变关系的差异在不同固结压力和应力路径条件下进行对比分析了。试验结果表明：前期固结压力对土体强度的影响比较大，k0固结后土体的强度比等压固结的强度高，在土样同属于压缩剪切破坏的情况下，加载条件与卸载条件下土样的破坏强度相差不大。土体孔隙水压力的随轴向应变的变化规律与土体的平均固结压力、土质以及应力路径有关，对于常规三轴试验、k0固结加载试验以及侧向卸载试验，孔隙水压力的随轴向应变的变化趋势可以用指数衰减性的函数曲线来拟合，而轴向卸载试验中孔隙水压力的随轴向应变的变化趋势可以用两段二次抛物线的函数曲线来拟合，总的来说，土体的平均固结压力越大、塑性指数越高孔隙水压力上升得越快，临界孔隙水压力越大。 2.基于不同应力路径下土体试验的结果，验证了k0固结条件土体在不同应力路径下关系曲线存在很好的线性关系，说明k12K m10固结条件下卸荷状态下的曲线能够用双曲线来拟合，以此为基础，把土体在不同应力路径下非线性弹性模型的切线模量表达式推导出来，给出了土体卸荷非线性弹性本构模型参数的确定方法。通过对（13）—曲线的分析，得到：初始切线模量与应力路径、土质以及平均固结压力有关，土体的平均固结压力越大随之塑性指数越低初始切线模量也越大；轴向卸载的初始切线模量值最大、侧向卸载的初始切线模量次之、轴向加载的初始切线模量最小；轴向加载的初始切线模量与围压的关系可以用幂函数来表示，而侧向卸载、轴向卸载的初始切线模量与围压成线性关系。 3.基于MIDAS/GTS有限元分析软件，采用土体卸荷非线性弹性本构模型，从基坑开挖施工全过程、基坑开挖的空间作用、盾构隧道等效刚度折算系数大小、隧道所处土层弹性模量大小等来研究基坑开挖对下方盾构隧道变形的影响，并结合岗顶酒店基坑工程实例进行分析。分析表明，随着基坑开挖，下方隧道竖向位移的增量比水平位移的增量要大，总体来说，深基坑开挖引起隧道的变形以竖向变形为主。盾构隧道变形主要受其上方基坑开挖的影响，隧道上方的基坑开挖，对隧道变形的影响程度较小。 4.通过引入盾构管片的等效纵向刚度、等效横向刚度，来简化盾构管片的计算模型。基于MIDAS/GTS有限元分析软件，采用土体卸荷非线性弹性本构模型，从邻近隧道的空间相对位置、盾构隧道等效刚度折算系数大小、隧道所处土层弹性模量大小等来研究隧道施工对下邻近隧道的影响。分析表明，在盾构隧道下方，沿着盾构隧道方向修建隧道(0°)时，上方盾构的变形也是沿着全长范围的，，受新建隧道的影响最大。当盾构隧道和新建隧道夹角45°和90°时，上方盾构隧道管片变形分布具有明显的对称性，沿着盾构隧道向两边延伸，新建隧道对其的影响逐渐减弱。两隧道夹角45°~90°之间，交叠处影响效果很接近；45°时的情况下两隧道交叠范围较大，因此其影响范围也相对较大，所以沿着盾构隧道两个方向上，盾构管片变形减小的速率要小。 5.结合岗顶酒店基坑工程实例，引入遗传算法对传统的BP神经网络进行改进，通过遗传算法搜索，确定了该样本参数下最优的隐含层节点数及最大循环次数，通过自学习与训练确定了最优的神经网络权值参数，提出了深基坑开挖沉降及水平位移预测的基于遗传BP网络建模方法，实现了降低岩体力学参数的变异性所对模型造成的误差，仅在一定范围内取值计算，其预测结果的精度得到保证，通过实例预测可以看出，四组预测值与实测值中最大的绝对水平位移误差为0.25mm，最大的沉绝对沉降位移误差为0.09mm；最大的相对水平位移误差为1.7%，最大的相对沉降位移误差为1.57%。
[Abstract]:In the process of urbanization, dense high-rise and super-high-rise buildings and developed underground transportation network have become an indispensable part of the city. Foundation pit engineering is often located near dense existing buildings. Foundation pit construction is subject to more stringent environmental constraints. The influence of surrounding environment has important guiding significance for the design and construction of deep foundation pit in urban center area. In order to better and effectively protect the safety of adjacent buildings, the study of mechanical effect of excavation unloading becomes more significant in deep foundation pit engineering.
Among the factors that play an important role in the study of deformation and stability of foundation pit engineering, the shear strength and constitutive model of soil are the most important, and their accuracy is closely related to the stress path of soil. The influence of urban underground structure construction on surrounding environment is studied and the following innovative research results are obtained.
1. By investigating the geological zoning of Guangzhou City, the adaptability of each geotechnical environment zoning to underground engineering in Guangzhou City is evaluated, and the typical soil body in the central city is selected as the research object. Combined with the foundation pit engineering of Guangzhou Gangding Hotel, the SLB-1 triaxial shear permeability tester with stress-strain control is adopted to test the influence of foundation pit excavation. Conventional triaxial tests and k_0 consolidation and unloading tests with stress paths in silty soil and silty clay layers were carried out. The differences between shear strength index and stress-strain relationship were compared and analyzed under different consolidation pressures and stress paths. The strength of soil after K 0 consolidation is higher than that of isobaric consolidation. The failure strength of soil samples under loading and unloading conditions is similar to that under compression and shear failure. The variation of pore water pressure with axial strain is related to the average consolidation pressure, soil quality and stress path of the soil. For the conventional 3. In axial test, K 0 consolidation loading test and lateral unloading test, the variation trend of pore water pressure with axial strain can be fitted by exponential decay function curve, while the variation trend of pore water pressure with axial strain in axial unloading test can be fitted by two quadratic parabola function curve. Generally speaking, soil mass The higher the average consolidation pressure, the higher the plastic index, the faster the increase of pore water pressure and the greater the critical pore water pressure.
2. Based on the results of soil tests under different stress paths, it is verified that there is a good linear relationship between the curves of soil under different stress paths under k_0 consolidation conditions. It is shown that the curves under unloading conditions under k_12K_m10 consolidation can be fitted by hyperbola. On this basis, the nonlinear elastic model of soil under different stress paths is established. The formula of tangent modulus is deduced and the method to determine the parameters of the nonlinear elastic constitutive model for unloading soils is given. Through the analysis of (13) - curve, it is found that the initial tangent modulus is related to stress path, soil quality and average consolidation pressure, and the greater the average consolidation pressure, the lower the initial tangent modulus is with the plastic index. The initial tangent modulus of axial unloading is the largest, the initial tangent modulus of lateral unloading is the second, and the initial tangent modulus of axial loading is the smallest; the relationship between the initial tangent modulus of axial loading and confining pressure can be expressed by power function, while the initial tangent modulus of axial unloading is linear with confining pressure.
3. Based on the MIDAS/GTS finite element analysis software, the influence of excavation on the deformation of shield tunnel is studied by using the nonlinear elastic constitutive model of soil unloading, including the whole process of excavation, the spatial effect of excavation, the equivalent stiffness conversion coefficient of shield tunnel and the elastic modulus of soil layer. The analysis of a hotel foundation pit project shows that the increment of the vertical displacement of the tunnel below is larger than that of the horizontal displacement with the excavation of the foundation pit. Generally speaking, the deformation of the tunnel caused by the excavation of the deep foundation pit is mainly vertical deformation. The influence of deformation is less.
4. The calculation model of shield segment is simplified by introducing the equivalent longitudinal stiffness and transverse stiffness of shield segment. Based on the MIDAS/GTS finite element analysis software, the nonlinear elastic constitutive model of unloading soil is adopted to calculate the equivalent stiffness of shield tunnel from the relative position of adjacent tunnel, the equivalent stiffness conversion coefficient of shield tunnel, and the elastic modulus of soil layer. The analysis shows that under the shield tunnel, the deformation of the upper shield is along the whole length of the tunnel when the tunnel is constructed along the direction of the shield tunnel (0 degree), and the influence of the new tunnel is the greatest. When the angle between the shield tunnel and the new tunnel is 45 degree and 90 degree, the segment of the upper shield tunnel is deformed. The distribution is obviously symmetrical, and the influence of the new tunnel is gradually weakened along the shield tunnel extending to both sides. The effect of the overlap between the two tunnels is very close when the angle of the tunnel is between 45 degrees and 90 degrees. The overlap area of the two tunnels is larger when the angle is between 45 degrees and 90 degrees, so the influence scope of the two tunnels is relatively large. The rate of deformation decreases.
5. Combining with the engineering example of the foundation pit of Gangding Hotel, genetic algorithm is introduced to improve the traditional BP neural network. The optimal number of hidden layer nodes and the maximum number of cycles under the sample parameters are determined by genetic algorithm search. The optimal neural network weight parameters are determined by self-learning and training, and the settlement of deep foundation pit excavation and the maximum number of cycles are proposed. Horizontal displacement prediction based on genetic BP network modeling method can reduce the errors caused by the variability of mechanical parameters of rock mass. The accuracy of prediction results can be guaranteed only by calculating values within a certain range. The maximum absolute settlement displacement error is 0.09 mm, the maximum relative horizontal displacement error is 1.7%, and the maximum relative settlement displacement error is 1.57%.
【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU94
[Abstract]:In the process of urbanization, dense high-rise and super-high-rise buildings and developed underground transportation network have become an indispensable part of the city. Foundation pit engineering is often located near dense existing buildings. Foundation pit construction is subject to more stringent environmental constraints. The influence of surrounding environment has important guiding significance for the design and construction of deep foundation pit in urban center area. In order to better and effectively protect the safety of adjacent buildings, the study of mechanical effect of excavation unloading becomes more significant in deep foundation pit engineering.
Among the factors that play an important role in the study of deformation and stability of foundation pit engineering, the shear strength and constitutive model of soil are the most important, and their accuracy is closely related to the stress path of soil. The influence of urban underground structure construction on surrounding environment is studied and the following innovative research results are obtained.
1. By investigating the geological zoning of Guangzhou City, the adaptability of each geotechnical environment zoning to underground engineering in Guangzhou City is evaluated, and the typical soil body in the central city is selected as the research object. Combined with the foundation pit engineering of Guangzhou Gangding Hotel, the SLB-1 triaxial shear permeability tester with stress-strain control is adopted to test the influence of foundation pit excavation. Conventional triaxial tests and k_0 consolidation and unloading tests with stress paths in silty soil and silty clay layers were carried out. The differences between shear strength index and stress-strain relationship were compared and analyzed under different consolidation pressures and stress paths. The strength of soil after K 0 consolidation is higher than that of isobaric consolidation. The failure strength of soil samples under loading and unloading conditions is similar to that under compression and shear failure. The variation of pore water pressure with axial strain is related to the average consolidation pressure, soil quality and stress path of the soil. For the conventional 3. In axial test, K 0 consolidation loading test and lateral unloading test, the variation trend of pore water pressure with axial strain can be fitted by exponential decay function curve, while the variation trend of pore water pressure with axial strain in axial unloading test can be fitted by two quadratic parabola function curve. Generally speaking, soil mass The higher the average consolidation pressure, the higher the plastic index, the faster the increase of pore water pressure and the greater the critical pore water pressure.
2. Based on the results of soil tests under different stress paths, it is verified that there is a good linear relationship between the curves of soil under different stress paths under k_0 consolidation conditions. It is shown that the curves under unloading conditions under k_12K_m10 consolidation can be fitted by hyperbola. On this basis, the nonlinear elastic model of soil under different stress paths is established. The formula of tangent modulus is deduced and the method to determine the parameters of the nonlinear elastic constitutive model for unloading soils is given. Through the analysis of (13) - curve, it is found that the initial tangent modulus is related to stress path, soil quality and average consolidation pressure, and the greater the average consolidation pressure, the lower the initial tangent modulus is with the plastic index. The initial tangent modulus of axial unloading is the largest, the initial tangent modulus of lateral unloading is the second, and the initial tangent modulus of axial loading is the smallest; the relationship between the initial tangent modulus of axial loading and confining pressure can be expressed by power function, while the initial tangent modulus of axial unloading is linear with confining pressure.
3. Based on the MIDAS/GTS finite element analysis software, the influence of excavation on the deformation of shield tunnel is studied by using the nonlinear elastic constitutive model of soil unloading, including the whole process of excavation, the spatial effect of excavation, the equivalent stiffness conversion coefficient of shield tunnel and the elastic modulus of soil layer. The analysis of a hotel foundation pit project shows that the increment of the vertical displacement of the tunnel below is larger than that of the horizontal displacement with the excavation of the foundation pit. Generally speaking, the deformation of the tunnel caused by the excavation of the deep foundation pit is mainly vertical deformation. The influence of deformation is less.
4. The calculation model of shield segment is simplified by introducing the equivalent longitudinal stiffness and transverse stiffness of shield segment. Based on the MIDAS/GTS finite element analysis software, the nonlinear elastic constitutive model of unloading soil is adopted to calculate the equivalent stiffness of shield tunnel from the relative position of adjacent tunnel, the equivalent stiffness conversion coefficient of shield tunnel, and the elastic modulus of soil layer. The analysis shows that under the shield tunnel, the deformation of the upper shield is along the whole length of the tunnel when the tunnel is constructed along the direction of the shield tunnel (0 degree), and the influence of the new tunnel is the greatest. When the angle between the shield tunnel and the new tunnel is 45 degree and 90 degree, the segment of the upper shield tunnel is deformed. The distribution is obviously symmetrical, and the influence of the new tunnel is gradually weakened along the shield tunnel extending to both sides. The effect of the overlap between the two tunnels is very close when the angle of the tunnel is between 45 degrees and 90 degrees. The overlap area of the two tunnels is larger when the angle is between 45 degrees and 90 degrees, so the influence scope of the two tunnels is relatively large. The rate of deformation decreases.
5. Combining with the engineering example of the foundation pit of Gangding Hotel, genetic algorithm is introduced to improve the traditional BP neural network. The optimal number of hidden layer nodes and the maximum number of cycles under the sample parameters are determined by genetic algorithm search. The optimal neural network weight parameters are determined by self-learning and training, and the settlement of deep foundation pit excavation and the maximum number of cycles are proposed. Horizontal displacement prediction based on genetic BP network modeling method can reduce the errors caused by the variability of mechanical parameters of rock mass. The accuracy of prediction results can be guaranteed only by calculating values within a certain range. The maximum absolute settlement displacement error is 0.09 mm, the maximum relative horizontal displacement error is 1.7%, and the maximum relative settlement displacement error is 1.57%.
【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU94
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