基础托换在砖石古建筑保护中的应用研究
发布时间：2018-08-26 15:34
【摘要】：砖石结构古建筑一般不专门设置整体性好的基础，而是直接坐落在夯土地基上，故砖石结构古建筑普遍存在不均匀沉降的病害。而解决该病害的有效方法之一是采用基础托换技术。 本文以古建筑整体顶升保护工程为背景，对整体顶升工程中涉及的一些关键问题进行了研究，主要的研究工作如下： (1)在基础托换工程中采用了顶管托换方法，对顶管施工对上部墙体沉降影响进行了分析。将上部墙体考虑为深梁模型，在Burland研究的基础上，考虑了弹性模量与剪切模量比值的变化与中性轴位置的变化，推导出了将沉降比和应变结合起来的安全沉降公式，可用来分析不同结构形式墙体的允许安全沉降。采用有限元方法对砌体墙在给定沉降下墙体应变的变化情况进行了模拟，将砌体墙进行匀质化，采用等效体积单元来模拟砌体的连续性和各向异性特点，分析了墙体厚度、墙体开洞率和上部荷载对墙体应变的影响。 (2)在基础托换工程中采用了开口钢管桩，将沉桩过程分为土塞闭合前后两个阶段，考虑了土体灵敏度和土塞的影响，结合工程实测数据，对小直径开口钢管桩的沉桩阻力进行了分析，提出了相应的沉桩阻力计算公式，得到不同土层的拟合系数。分析了时间效应对桩基承载力的影响。结合现有资料，对现有考虑时间效应的承载力公式进行了改进，提出了考虑桩基长径比和桩土界面摩擦角变化的考虑时间效应的承载力计算公式。所得公式满足工程精度要求，简单易用，可用于预估钢管桩考虑时间效应的承载力。 (3)对桩基的稳定性进行了分析。 考虑了桩侧土抗力的影响，基于能量法，对桩的计算长度进行了分析，得到了均匀地基和层状地基中桩身计算长度公式。采用有限元方法分析了垫块对桩稳定性的影响。将桩身与垫块、垫块与垫块之间的作用采用接触单元模拟，分析了桩的线性和非线性屈曲荷载。考虑了垫块的错动，分析了不同计算长度时径向位移和屈曲荷载的变化。结果指出，不考虑上部垫块时桩的临界屈曲荷载大于考虑垫块影响时桩的临界屈曲荷载；当桩长较小时，上部垫块对桩的屈曲稳定的影响可以忽略，当长度较大时，，上部垫块对静压桩的屈曲稳定的影响有随桩长增加而减小的趋势。 (4)对不排水情况下砂土的液化特性进行了研究，分析了单调荷载作用下砂土的强度值，在弹性地基中桩基沉降解析解的基础上提出了考虑桩侧土体液化造成的桩土部分滑移的的部分液化模型。在液化深度以上，分析时应考虑桩侧土体液化而导致的强度降低；在液化深度以下，分析时可仍按弹性方法考虑。得到了液化部分土体深度计算公式，在此基础上分析了液化深度对桩基稳定性的影响。 本文的创新点如下： 1．分析了顶管托换对上部墙体的影响，将上部墙体考虑为深梁模型，考虑了弹性模量与剪切模量比值的变化与中性轴位置的变化，推导出了将沉降比和应变结合起来的允许沉降公式，可用来分析不同结构形式墙体的允许安全沉降。 2．分析了沉桩阻力的影响因素，将沉桩过程分为土塞闭合前后两个阶段，考虑了土体灵敏度和土塞的影响，结合工程实测数据，对小直径开口钢管桩的沉桩阻力进行了分析，提出了相应的沉桩阻力计算公式，得到不同土层的拟合系数。并对现有考虑时间效应的承载力公式进行了改进，提出了考虑桩基长径比和桩土界面摩擦角变化的考虑时间效应的承载力计算公式。 3．考虑了桩侧土抗力的影响，基于能量法，对桩的计算长度进行了分析，得到了均匀地基和层状地基中桩身计算长度公式。在弹性地基中桩基沉降解析解的基础上提出了考虑桩侧土体液化造成的桩土部分滑移的部分液化模型。得到了液化部分土体深度计算公式，在此基础上分析了液化深度对桩基稳定性的影响，修正了桩基的临界荷载。
[Abstract]:In general, the ancient masonry structures do not specially set a good foundation, but directly located on the Rammed Soil foundation, so there is a widespread uneven settlement of the ancient masonry structures. One of the effective ways to solve this problem is to use the foundation underpinning technology.
Based on the integral jacking protection project of ancient buildings, this paper studies some key problems involved in the integral jacking project. The main research work is as follows:
(1) Pipe jacking underpinning method is adopted in foundation underpinning project to analyze the influence of pipe jacking on the settlement of upper wall. The upper wall is considered as a deep beam model. On the basis of Burland's research, the change of elastic modulus to shear modulus ratio and the change of neutral axis position are considered, and the combination of settlement ratio and strain is deduced. The formula of safe settlement can be used to analyze the allowable safe settlement of wall in different structure forms.The finite element method is used to simulate the variation of wall strain under given settlement.The masonry wall is homogenized and the equivalent volume element is used to simulate the continuity and anisotropy of the masonry. Influence of thickness, wall opening rate and upper load on wall strain.
(2) Open-ended steel pipe piles are used in foundation underpinning project, and the pile driving process is divided into two stages before and after the closure of soil plug. Considering the influence of soil sensitivity and soil plug, the pile driving resistance of small-diameter open-ended steel pipe piles is analyzed based on the measured data, and the corresponding calculation formula of pile driving resistance is put forward, and the simulation of different soil layers is obtained. The influence of time effect on the bearing capacity of pile foundation is analyzed.Based on the existing data,the bearing capacity formula considering time effect is improved,and the bearing capacity formula considering time effect considering the variation of the length-diameter ratio of pile foundation and the friction angle between pile and soil interface is put forward.The formula meets the requirement of Engineering precision,is simple and easy to use. It is used to estimate the bearing capacity of steel pipe pile considering time effect.
(3) the stability of pile foundation is analyzed.
Based on the energy method, the effective length of piles is analyzed, and the formula of effective length of piles in uniform and layered foundation is obtained. The influence of cushion on the stability of piles is analyzed by finite element method. Linear and nonlinear buckling loads. Considering the displacement of cushion blocks, the changes of radial displacement and buckling load under different effective lengths are analyzed. The effect of upper cushion on the buckling stability of jacked piles decreases with the increase of pile length.
(4) The liquefaction characteristics of sandy soil under undrained condition are studied, and the strength of sandy soil under monotonic loading is analyzed. Based on the analytical solution of pile settlement in elastic foundation, a partial liquefaction model considering the partial slip of pile-soil caused by liquefaction of pile-side soil is proposed. Under the liquefaction depth, the calculation formula of the depth of the liquefied part of the soil is obtained, and the influence of the liquefaction depth on the stability of the pile foundation is analyzed.
The innovation of this paper is as follows:
1. The influence of pipe jacking underpinning on the upper wall is analyzed. The upper wall is considered as a deep beam model. The variation of the ratio of elastic modulus to shear modulus and the position of neutral axis are considered. The allowable settlement formula which combines the settlement ratio and strain is deduced. It can be used to analyze the allowable safe settlement of walls with different structural forms.
2. The influencing factors of pile-sinking resistance are analyzed, and the process of pile-sinking is divided into two stages before and after the closure of soil plug. Considering the influence of soil sensitivity and soil plug, the pile-sinking resistance of small diameter open-ended steel pipe pile is analyzed with the engineering measured data. The corresponding calculation formula of pile-sinking resistance is put forward, and the fitting coefficients of different soil layers are obtained. The existing bearing capacity formula considering time effect is improved, and the bearing capacity formula considering time effect considering the variation of length-diameter ratio of pile foundation and friction angle between pile and soil interface is proposed.
3. Considering the influence of soil resistance on pile side, the effective length of pile is analyzed based on energy method, and the formula of effective length of pile body in uniform foundation and layered foundation is obtained. Based on the formula for calculating the depth of liquefied soil, the influence of liquefied depth on the stability of pile foundation is analyzed, and the critical load of pile foundation is corrected.
【学位授予单位】：西安建筑科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU-87;TU753
本文编号：2205338
[Abstract]:In general, the ancient masonry structures do not specially set a good foundation, but directly located on the Rammed Soil foundation, so there is a widespread uneven settlement of the ancient masonry structures. One of the effective ways to solve this problem is to use the foundation underpinning technology.
Based on the integral jacking protection project of ancient buildings, this paper studies some key problems involved in the integral jacking project. The main research work is as follows:
(1) Pipe jacking underpinning method is adopted in foundation underpinning project to analyze the influence of pipe jacking on the settlement of upper wall. The upper wall is considered as a deep beam model. On the basis of Burland's research, the change of elastic modulus to shear modulus ratio and the change of neutral axis position are considered, and the combination of settlement ratio and strain is deduced. The formula of safe settlement can be used to analyze the allowable safe settlement of wall in different structure forms.The finite element method is used to simulate the variation of wall strain under given settlement.The masonry wall is homogenized and the equivalent volume element is used to simulate the continuity and anisotropy of the masonry. Influence of thickness, wall opening rate and upper load on wall strain.
(2) Open-ended steel pipe piles are used in foundation underpinning project, and the pile driving process is divided into two stages before and after the closure of soil plug. Considering the influence of soil sensitivity and soil plug, the pile driving resistance of small-diameter open-ended steel pipe piles is analyzed based on the measured data, and the corresponding calculation formula of pile driving resistance is put forward, and the simulation of different soil layers is obtained. The influence of time effect on the bearing capacity of pile foundation is analyzed.Based on the existing data,the bearing capacity formula considering time effect is improved,and the bearing capacity formula considering time effect considering the variation of the length-diameter ratio of pile foundation and the friction angle between pile and soil interface is put forward.The formula meets the requirement of Engineering precision,is simple and easy to use. It is used to estimate the bearing capacity of steel pipe pile considering time effect.
(3) the stability of pile foundation is analyzed.
Based on the energy method, the effective length of piles is analyzed, and the formula of effective length of piles in uniform and layered foundation is obtained. The influence of cushion on the stability of piles is analyzed by finite element method. Linear and nonlinear buckling loads. Considering the displacement of cushion blocks, the changes of radial displacement and buckling load under different effective lengths are analyzed. The effect of upper cushion on the buckling stability of jacked piles decreases with the increase of pile length.
(4) The liquefaction characteristics of sandy soil under undrained condition are studied, and the strength of sandy soil under monotonic loading is analyzed. Based on the analytical solution of pile settlement in elastic foundation, a partial liquefaction model considering the partial slip of pile-soil caused by liquefaction of pile-side soil is proposed. Under the liquefaction depth, the calculation formula of the depth of the liquefied part of the soil is obtained, and the influence of the liquefaction depth on the stability of the pile foundation is analyzed.
The innovation of this paper is as follows:
1. The influence of pipe jacking underpinning on the upper wall is analyzed. The upper wall is considered as a deep beam model. The variation of the ratio of elastic modulus to shear modulus and the position of neutral axis are considered. The allowable settlement formula which combines the settlement ratio and strain is deduced. It can be used to analyze the allowable safe settlement of walls with different structural forms.
2. The influencing factors of pile-sinking resistance are analyzed, and the process of pile-sinking is divided into two stages before and after the closure of soil plug. Considering the influence of soil sensitivity and soil plug, the pile-sinking resistance of small diameter open-ended steel pipe pile is analyzed with the engineering measured data. The corresponding calculation formula of pile-sinking resistance is put forward, and the fitting coefficients of different soil layers are obtained. The existing bearing capacity formula considering time effect is improved, and the bearing capacity formula considering time effect considering the variation of length-diameter ratio of pile foundation and friction angle between pile and soil interface is proposed.
3. Considering the influence of soil resistance on pile side, the effective length of pile is analyzed based on energy method, and the formula of effective length of pile body in uniform foundation and layered foundation is obtained. Based on the formula for calculating the depth of liquefied soil, the influence of liquefied depth on the stability of pile foundation is analyzed, and the critical load of pile foundation is corrected.
【学位授予单位】：西安建筑科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU-87;TU753
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