【摘要】：磚石結(jié)構(gòu)古建筑一般不專門設(shè)置整體性好的基礎(chǔ)，而是直接坐落在夯土地基上，故磚石結(jié)構(gòu)古建筑普遍存在不均勻沉降的病害。而解決該病害的有效方法之一是采用基礎(chǔ)托換技術(shù)。 本文以古建筑整體頂升保護(hù)工程為背景，對(duì)整體頂升工程中涉及的一些關(guān)鍵問(wèn)題進(jìn)行了研究，主要的研究工作如下： (1)在基礎(chǔ)托換工程中采用了頂管托換方法，對(duì)頂管施工對(duì)上部墻體沉降影響進(jìn)行了分析。將上部墻體考慮為深梁模型，在Burland研究的基礎(chǔ)上，考慮了彈性模量與剪切模量比值的變化與中性軸位置的變化，推導(dǎo)出了將沉降比和應(yīng)變結(jié)合起來(lái)的安全沉降公式，可用來(lái)分析不同結(jié)構(gòu)形式墻體的允許安全沉降。采用有限元方法對(duì)砌體墻在給定沉降下墻體應(yīng)變的變化情況進(jìn)行了模擬，將砌體墻進(jìn)行勻質(zhì)化，采用等效體積單元來(lái)模擬砌體的連續(xù)性和各向異性特點(diǎn)，分析了墻體厚度、墻體開(kāi)洞率和上部荷載對(duì)墻體應(yīng)變的影響。 (2)在基礎(chǔ)托換工程中采用了開(kāi)口鋼管樁，將沉樁過(guò)程分為土塞閉合前后兩個(gè)階段，考慮了土體靈敏度和土塞的影響，結(jié)合工程實(shí)測(cè)數(shù)據(jù)，對(duì)小直徑開(kāi)口鋼管樁的沉樁阻力進(jìn)行了分析，提出了相應(yīng)的沉樁阻力計(jì)算公式，得到不同土層的擬合系數(shù)。分析了時(shí)間效應(yīng)對(duì)樁基承載力的影響。結(jié)合現(xiàn)有資料，對(duì)現(xiàn)有考慮時(shí)間效應(yīng)的承載力公式進(jìn)行了改進(jìn)，提出了考慮樁基長(zhǎng)徑比和樁土界面摩擦角變化的考慮時(shí)間效應(yīng)的承載力計(jì)算公式。所得公式滿足工程精度要求，簡(jiǎn)單易用，可用于預(yù)估鋼管樁考慮時(shí)間效應(yīng)的承載力。 (3)對(duì)樁基的穩(wěn)定性進(jìn)行了分析。 考慮了樁側(cè)土抗力的影響，基于能量法，對(duì)樁的計(jì)算長(zhǎng)度進(jìn)行了分析，得到了均勻地基和層狀地基中樁身計(jì)算長(zhǎng)度公式。采用有限元方法分析了墊塊對(duì)樁穩(wěn)定性的影響。將樁身與墊塊、墊塊與墊塊之間的作用采用接觸單元模擬，分析了樁的線性和非線性屈曲荷載�？紤]了墊塊的錯(cuò)動(dòng)，分析了不同計(jì)算長(zhǎng)度時(shí)徑向位移和屈曲荷載的變化。結(jié)果指出，不考慮上部墊塊時(shí)樁的臨界屈曲荷載大于考慮墊塊影響時(shí)樁的臨界屈曲荷載；當(dāng)樁長(zhǎng)較小時(shí)，上部墊塊對(duì)樁的屈曲穩(wěn)定的影響可以忽略，當(dāng)長(zhǎng)度較大時(shí)，，上部墊塊對(duì)靜壓樁的屈曲穩(wěn)定的影響有隨樁長(zhǎng)增加而減小的趨勢(shì)。 (4)對(duì)不排水情況下砂土的液化特性進(jìn)行了研究，分析了單調(diào)荷載作用下砂土的強(qiáng)度值，在彈性地基中樁基沉降解析解的基礎(chǔ)上提出了考慮樁側(cè)土體液化造成的樁土部分滑移的的部分液化模型。在液化深度以上，分析時(shí)應(yīng)考慮樁側(cè)土體液化而導(dǎo)致的強(qiáng)度降低；在液化深度以下，分析時(shí)可仍按彈性方法考慮。得到了液化部分土體深度計(jì)算公式，在此基礎(chǔ)上分析了液化深度對(duì)樁基穩(wěn)定性的影響。 本文的創(chuàng)新點(diǎn)如下： 1．分析了頂管托換對(duì)上部墻體的影響，將上部墻體考慮為深梁模型，考慮了彈性模量與剪切模量比值的變化與中性軸位置的變化，推導(dǎo)出了將沉降比和應(yīng)變結(jié)合起來(lái)的允許沉降公式，可用來(lái)分析不同結(jié)構(gòu)形式墻體的允許安全沉降。 2．分析了沉樁阻力的影響因素，將沉樁過(guò)程分為土塞閉合前后兩個(gè)階段，考慮了土體靈敏度和土塞的影響，結(jié)合工程實(shí)測(cè)數(shù)據(jù)，對(duì)小直徑開(kāi)口鋼管樁的沉樁阻力進(jìn)行了分析，提出了相應(yīng)的沉樁阻力計(jì)算公式，得到不同土層的擬合系數(shù)。并對(duì)現(xiàn)有考慮時(shí)間效應(yīng)的承載力公式進(jìn)行了改進(jìn)，提出了考慮樁基長(zhǎng)徑比和樁土界面摩擦角變化的考慮時(shí)間效應(yīng)的承載力計(jì)算公式。 3．考慮了樁側(cè)土抗力的影響，基于能量法，對(duì)樁的計(jì)算長(zhǎng)度進(jìn)行了分析，得到了均勻地基和層狀地基中樁身計(jì)算長(zhǎng)度公式。在彈性地基中樁基沉降解析解的基礎(chǔ)上提出了考慮樁側(cè)土體液化造成的樁土部分滑移的部分液化模型。得到了液化部分土體深度計(jì)算公式，在此基礎(chǔ)上分析了液化深度對(duì)樁基穩(wěn)定性的影響，修正了樁基的臨界荷載。
[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.
【學(xué)位授予單位】：西安建筑科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TU-87;TU753

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