岩溶地区高层建筑刚性桩复合地基—筏板基础体系的受力性能研究

发布时间：2018-01-17 14:10

本文关键词：岩溶地区高层建筑刚性桩复合地基—筏板基础体系的受力性能研究　出处：《华南理工大学》2015年博士论文　论文类型：学位论文

【摘要】：岩溶地质占我国面积的35%,多集中在广东、广西、湖南、四川等人口密集省份。高层建筑可有效满足人口密集地区的住房需求,但对地基基础安全性要求高。岩溶地质构造十分复杂,隐伏土洞、溶洞广泛存在,给工程建设带来许多难题。因此,如何保证岩溶地区高层建筑地基基础安全稳定,是十分重要的课题。刚性桩复合地基-筏板基础具有承载力高、施工方便、成本较低等优点,经过工程实践证明,十分适用于岩溶地区高层建筑。本文通过大量试验及理论研究,解决了刚性桩复合地基荷载分配和沉降计算问题,揭示了褥垫层作为散体材料的特殊性质及其对上部结构抗震性能的影响,得到了筏板受力变形规律,解释了正常使用状态下筏板钢筋应力较小的真正原因,从而形成了完整的桩-土-垫层-筏板-上部结构力学性能体系。总结起来,本文对以下内容进行了深入研究和探讨:(1)针对粤北5个典型岩溶场地高层建筑项目进行了54根刚性桩单桩复合地基现场静载试验。5个工程涵盖了常见的地质条件和复合地基方案,包括:1)浅层6m淤泥质土+CM桩复合地基;2)10m厚卵石层+长螺旋桩复合地基;3)浅层高承载力粉质粘土+PHC管桩复合地基;4)浅层低承载力中砂+PHC管桩复合地基;5)埋深浅且倾角大基岩+载体桩复合地基。测量得到刚性桩复合地基受荷沉降及浅层桩间土应力的变化规律,统计得到沉降、土应力、桩土应力比、土承担荷载比例等关键指标的变化范围。(2)假设桩、土受荷沉降符合“双曲线”模型,利用褥垫层中的力平衡和位移协调条件,推导出刚性桩复合地基沉降、土应力、桩对垫层刺入量等的解析计算方法。利用它对桩、土、垫层、复合地基受荷沉降进行了参数分析,得到了规律性结论。(3)应用离散元(DEM)方法模拟褥垫层颗粒,实现了有限差分-离散元(FDMDEM)耦合计算方法。首先进行3种常用褥垫层材料的物理力学性质试验,得到密度、空隙率、压缩模量等宏观指标。利用PFC2D程序进行自然堆积和侧限压缩数值试验,标定颗粒细观参数的取值。使用FISH语言编制命令流,在PFC2D和FLAC之间传递变量,实现耦合计算,从细观尺度揭示褥垫层颗粒的受荷运动规律。以褥垫层材料、厚度hc,桩径d、桩距D,桩间土变形模量E和桩端土变形模量Eb作为因素,进行耦合模型数值正交试验,通过级差和方差分析得到各因素对承载力极限值fspu、桩刺入量Δ、桩土应力比N、桩承担荷载百分比Rp的影响规律,给出它们的区间估值以及选用原则。(4)对不同厚度、不同材料褥垫层进行单调及循环加载下的剪切试验。单调加载下得到水平力峰值归一化系数μn和滑动位移umax;循环加载下得到褥垫层受剪的“三折线”骨架曲线,以及其中弹性段、塑性段、滑移段关键指标的计算公式。采用“三折线”骨架曲线模拟褥垫层滞回性能,针对不同高度、不同型式有无褥垫层结构进行罕遇地震下弹塑性时程分析。对比两种情况下结构的宏观指标,得到褥垫层对上部结构抗震性能影响的定量结论。(5)针对一实际高层建筑进行筏板钢筋应力、浅层地基土应力、整体沉降长期监测,发现:1)上部结构完成3~5层之前,筏板钢筋应力增长很快,之后基本不变;2)结构封顶时,钢筋应力仅有5~20MPa,从浇筑筏板到结构封顶,钢筋应力变化在50MPa以内,远低于其强度设计值。(6)采用数值模拟方法,分析了地基模型、上部结构刚度、筏板底摩擦力以及受拉区混凝土对规则受力筏板计算弯矩和变形的影响规律。建立实测项目的刚性桩复合地基-筏板-上部结构整体模型,进行施工模拟。对比实测结果,统计受拉区混凝土应力,分析施工过程中筏板温度、刚度的变化规律,证明了筏板钢筋应力由“急剧增长”到“缓慢变化”的原因是:1)上部结构完成3~5层之前,筏板刚度较小,以整体弯曲为主,弯矩增长快;2)筏板混凝土水化过程中与钢筋的粘结没有完全形成,弯矩主要由钢筋承担。钢筋应力较小的原因是:1)混凝土收缩对钢筋产生了-40~-20MPa的初始压应力;2)结构封顶时,筏板受拉区混凝土并未开裂,承担了很大一部分弯矩,但这部分安全储备不可缺少。
[Abstract]:Karst in China accounts for 35% of the area, mostly concentrated in Guangdong, Guangxi, Hunan, Sichuan and other densely populated provinces. High-rise buildings can effectively meet the housing needs in densely populated areas, but the safty of the foundation requirements. Karst geological structure is very complicated, concealed soil cave, karst caves exist many difficulties the construction of the project. Therefore, how to ensure the high-rise building foundation in karst area safety and stability, is a very important subject. The rigid pile composite foundation raft foundation with high bearing capacity, convenient construction, low cost, through the engineering practice, very suitable for high-rise buildings in karst area. Through a lot of experiments and theoretical research. To solve the problem of load distribution of rigid pile composite foundation and the settlement calculation, reveals the cushion as special properties of granular material and the upper structure seismic performance, the raft The force and deformation, explains the reinforced raft under normal state should be the real reason smaller force, thus forming a complete system of upper structure mechanical properties of pile soil cushion and raft. To sum up, this paper discusses and studies the following contents: (1) according to the 5 typical North Guangdong karst area high-rise building project of 54 rigid pile composite foundation static load test on site.5 Engineering covers the common geological conditions and composite foundation scheme, including: 1) 6m shallow silty soil +CM pile composite foundation; 2) 10m thick gravel + long spiral pile composite foundation; 3) shallow high bearing capacity of silty clay +PHC pile composite foundation; 4) shallow low bearing sand +PHC pile composite ground force; 5) the shallow depth and steep bedrock + carrier pile composite foundation. The measured variation of load and settlement of shallow soil stress between piles under rigid pile composite foundation, statistics The settlement, soil stress, pile-soil stress ratio, the variation range of soil load bearing proportion and other key indicators. (2) assume that pile and soil under loading settlement accords with hyperbolic model, using the cushion of force equilibrium and displacement compatibility conditions of rigid pile composite foundation is deduced, the soil stress. Analytical calculation on the cushion pile penetration method. The use of it on the pile, soil and cushion composite foundation load settlement parameters were analyzed, obtained the conclusions. (3) the application of discrete element method (DEM) simulation of cushion particles, the finite difference discrete element (FDMDEM) coupling the first 3 kinds of calculation methods. The physical and mechanical properties of cushion layer materials commonly used test, obtained density, void ratio, compression modulus and other macroeconomic indicators. The natural accumulation and unconfined compression numerical tests using the PFC2D program, the calibration value of micro parameters of particles. The programmed with FISH command stream in PFC2D And FLAC transfer between variables, coupling calculation, from the meso scale reveal cushion particles bearing movement. With the cushion material, thickness HC, pile diameter D, pile spacing D, pile-soil deformation modulus of pile end soil deformation modulus of E and Eb as factors, the orthogonal numerical coupling model test. Through the analysis of variance and differential fspu of various factors on the ultimate bearing capacity of pile penetration value, Delta, pile-soil stress ratio N, influence of pile bearing load percentage of Rp, given their interval estimation and selection principle. (4) of different thickness, shear test and monotonic under cyclic loading with different materials the cushion under monotonic loading. The peak stress level obtained normalized coefficient n and sliding displacement Umax; cyclic loading under cushion shear "three line" and the skeleton curve, wherein the elastic section, plastic section, calculation formula of slip segment key indicators. The "three line "The skeleton curve simulation of cushion hysteretic behavior, according to different height, different types have no cushion structure under rare earthquake elastic-plastic time history analysis. A comparison of two case of macro index structure, quantitative conclusions effect of cushion on the upper structure seismic performance. (5) for a high-rise building for the raft reinforcement stress, shallow soil stress, the overall settlement of long-term monitoring, it is found that: 1) before the completion of the upper structure of the 3~5 layer, the raft reinforcement stress increases quickly, after basically unchanged; 2) cap structure, the steel stress is only 5~20MPa, from pouring raft to the cap structure, reinforced the stress changes within 50MPa, its strength is far lower than the design value. (6) using the method of numerical simulation analysis of foundation model, stiffness of superstructure, raft bottom friction force and bending moment calculation and the deformation of the raft concrete tensile force on the rules established. The overall model test project for rigid pile composite foundation raft superstructure, construction simulation. Comparing the measured results, statistical concrete tensile stress analysis of raft temperature in the construction process, variation of stiffness, stress that the raft reinforced by the "rapid growth" to "slow change" the upper structure is: 1) before completion of 3~5 layer, smaller raft rigidity, overall bending moment, rapid growth; 2) bonded concrete hydration process in the raft board and reinforced the not fully formed, moment is mainly borne by the steel reinforced stress. The smaller is: 1) produced -40~-20MPa the initial stress of reinforced concrete shrinkage; 2) cap structure, raft concrete in tension zone did not crack, assume a large part of the moment, but this part of safety is indispensable.

【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU470

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