岩溶地区地基处理关键技术研究

发布时间：2018-06-29 13:01

本文选题：刚性桩复合地基 + 群桩　；参考：《华南理工大学》2013年博士论文

【摘要】：广东粤北地区的韶关、清远、肇庆等地，作为岩溶相当发育的地区，存在较多的工程隐患，因此，迫切要求找到合适的基础形式和地基处理方式。在华南理工大学亚热带建筑科学国家重点实验室重点项目的资助下，就这一问题，华南理工大学土木与交通学院对岩溶地区地基处理关键技术进行了深入的研究，并在粤北地区进行了一系列的试验、测试和观测。采用单桩压板试验确定复合地基承载力，忽视了群桩对复合地基受力性能的影响，无法合理确定桩土承载能力的发挥情况。在进行考虑上下部相互作用的结构分析时，由于计算机的限制往往难以进行，提出符合工程实际的、便于计算分析的方法显得尤为重要。而且，在对筏基的实测中发现，筏板钢筋的应力测量值明显小于计算值，说明原有计算模型存在不足且偏于保守，所以要求设计方法应能更真实地反映筏板中钢筋的实际受力情况。同时，随着复合地基在抗震地区的广泛应用，对结构与复合地基之间动力相互作用的研究也十分迫切。本文采用理论分析与试验研究相结合的方法，以实际工程为背景，围绕刚性桩复合地基-筏基-上部结构体系进行了深入的研究，主要研究内容及创新性工作有以下几个方面： 1）进行了24个复杂岩溶地质条件下的单桩复合地基载荷试验。结果表明，桩间土的承载能力发挥较早，在特征值荷载时桩土很难达到各自的设计值；无垫层，当土层承载力较高时，只要基础与垫层接触紧密，土体仍可发挥一定的承载力；砂石垫层厚100mm，特征值荷载下的桩间土平均应力为0.31MPa，桩-土应力比约19，土承担荷载比为46.5%，桩、土承载力发挥系数分别约为0.72、1.78。砂石垫层厚300mm，特征值荷载下桩间土平均应力约为0.38Mpa，桩-土应力比14.6，土承担荷载比为61%。分析表明该种处理方案可行。 2）通过与单桩复合地基压板试验对比，验证了所采用的土体弹塑性模型、接触关系和所选参数的正确性，可以较为准确地分析刚性桩复合地基的受力、变形性能。在此基础上，，研究了群桩复合地基载荷板的尺寸效应，得到了大尺寸压板的最终沉降估算公式，垫层厚度为100mm，基础边长为30m、40m、50m的最终沉降为16.7mm、17.5mm、18.1mm，垫层厚度为300mm，基础边长为30m、40m、50m的最终沉降为32.4mm、34.5mm、36.1mm，与实测值吻合。分析了群桩复合地基的宏观本构关系，结果表明，随着桩数的增多压板沉降增大，土体承载能力发挥度减小。垫层厚为100mm、200mm、300mm，特征值荷载作用下，49桩复合地基的平均沉降约是单桩复合地基平均沉降的1.6、2.18、2.2倍，此时，土应力分别为单桩复合地基土应力的46%、65%、78%；加载初期，单、多桩的刺入相差不大，随荷载增加群桩的刺入量比单桩大，垫层厚度为100mm、200mm、300mm，特征值荷载下单桩的刺入量分别为3.9mm、6.8mm、8.4mm，49桩的刺入量分别为6.8mm、18.7mm、19.2mm。群桩在达到49个，以及垫层达到300mm后，桩土应力、基础沉降、刚性桩的刺入等变化很少，褥垫层的调节作用趋于稳定。 3）根据试验和群桩有限元分析，结合工程经验，提出了针对该类复合地基的二折线弹簧宏观本构模型，特征值荷载对应的沉降为12mm，极限荷载对应的沉降为40mm。借助SAP2000可以利用该模型进行考虑上部结构与复合地基相互作用的基础受力分析，特征值荷载对应的基础沉降从4mm到20mm进行变化，除个别地方的筏板弯矩变化幅值接近9%，其它地方变化都很小。结果表明，该方法既可以考虑上部结构刚度对基础的影响，又可以反应土体一定程度的非线性特性和基础的整体沉降。 4）建立地基的实体单元模型，考虑筏板与垫层之间的摩擦，借助ABAQUS进行考虑上部结构与复合地基相互作用的弹塑性分析。结果表明，在弹塑性计算中荷载设计值下，截面应力分布较均匀，截面最大拉应力约为1.63Mpa，钢筋最大应力约80Mpa；荷载标准值下钢筋最大应力为48Mpa，计算结果与实测值吻合较好，验证了本文分析方法的正确性。通过计算分析，与常用方法的计算结果比较表明，地基反力模式、筏板与垫层之间的摩擦是影响筏板内力计算结果的主要因素。地基反力在筏板边缘剧增，最大值达到平均值的3.5倍，极易造成地基局部区域的提前破坏。最后，分析了地基土变形模量、褥垫层厚度、褥垫层模量、筏板厚度等参数对筏板内力及变形的影响。结果表明，地基反力和筏板应力与筏板同地基相对刚度有关。 5）采用有限元与无限元耦合的方法，建立动力相互作用三维整体模型，进行了动力弹塑性时程分析。通过与普通桩筏基础的时程分析结果对比，研究了刚性桩复合地基-上部结构体系的抗震性能。结果表明，7度小震时，复合地基没有减震作用；7度大震时，桩基中桩体弯矩、剪力最大值是刚性桩复合地基中桩体弯矩、剪力最大值的1.8倍，褥垫层产生了较大的塑性变形和相对基底的滑移，具有一定的耗能减震作用，并且复合地基中筏基及上部结构的动力响应约是桩基体系中对应量的90%，减震系数在0.8-0.9之间。本论文的研究成果已应用于广东粤北地区的碧湖苑、时代美居、翠湖花园等工程项目建设中，取得良好效果。
[Abstract]:Shaoguan, Qingyuan, Zhaoqing and other places in the north of Guangdong Province, as a relatively developed area of karst, there are many hidden dangers of engineering. Therefore, it is urgent to find the appropriate basic forms and foundation treatment methods. Under the support of the key project of the National Key Laboratory of subtropical architecture science of South China University of Technology, South China Science and technology The Institute of civil engineering and transportation has conducted an in-depth study of key technologies for foundation treatment in karst areas, and conducted a series of tests, tests and observations in northern Guangdong.
The bearing capacity of composite foundation is determined by single pile pressure plate test, and the effect of pile group on the bearing capacity of composite foundation is ignored. It is not reasonable to determine the bearing capacity of the pile and soil. In the analysis of the interaction of the upper and lower parts, the computer restrictions are often difficult to carry out in the consideration of the interaction of the upper and lower parts. The analysis method is particularly important. Moreover, in the measurement of raft foundation, it is found that the stress measurement value of the raft steel bar is obviously less than the calculated value, which indicates that the original calculation model is insufficient and conservative. Therefore, the design method should be able to reflect the actual stress situation of the reinforcement in the raft more truthfully. At the same time, with the composite foundation in the earthquake resistant area The study of dynamic interaction between structure and composite foundation is very urgent. This paper combines theoretical analysis and experimental research, and takes practical engineering as the background to study the rigid pile composite foundation raft foundation superstructure system. The main research content and innovative work are as follows On the other hand:
1) the load test of single pile composite foundation under 24 complex karst geological conditions has been carried out. The results show that the bearing capacity of the soil between piles is early, and the pile and soil are difficult to reach their respective design values when the characteristic load is loaded; when the bearing capacity of the soil layer is high, the soil can still play a certain bearing capacity as long as the foundation is closely contacted with the cushion. The gravel cushion is 100mm, the average stress of the soil under the characteristic load is 0.31MPa, the pile to soil stress ratio is about 19, the soil bearing load ratio is 46.5%, the bearing capacity of pile and soil is about 300mm, the average stress of the soil under the characteristic load is about 0.38Mpa, the pile soil stress ratio is 14.6, the soil bearing load ratio is 61%. analysis. It shows that the treatment scheme is feasible.
2) by comparing with the single pile composite foundation pressure plate test, the elastoplastic model of soil, the contact relationship and the correctness of the selected parameters are verified, and the stress and deformation performance of the rigid pile composite foundation can be more accurately analyzed. On this basis, the size effect of the composite foundation load plate is studied, and the large size pressure plate is obtained. The final settlement estimation formula, the thickness of the cushion is 100mm, the base length is 30m, the final settlement of the 40m, 50m is 16.7mm, 17.5mm, 18.1mm, the thickness of the cushion is 300mm, the base length is 30m, the 40m, 50m is finally settled by the 32.4mm, it is consistent with the measured value. The macroscopic constitutive relation of the pile composite foundation is analyzed, the result shows that with the increase of pile number, the number of piles is increased. Under the action of 100mm, 200mm, 300mm, the average settlement of the 49 pile composite foundation is about 1.6,2.18,2.2 times of the average settlement of the single pile composite foundation, and the soil stress is 46%, 65%, 78% of the soil stress of the single pile composite foundation, respectively. The prickling amount of the pile group is larger than that of single pile with the increase of load. The thickness of the cushion is 100mm, 200mm, 300mm. The prickling amount of single pile under the characteristic load is 3.9mm, 6.8mm, 8.4mm, the 49 piles are respectively 6.8mm, 18.7mm, 19.2mm. group pile in 49, and after the cushion reaches 300mm, the pile soil stress, foundation settlement, rigid pile stab entry and so on Rarely, the adjustment of the mattress layer tends to be stable.
3) according to the test and the group pile finite element analysis, combined with the engineering experience, a macroscopic constitutive model of two fold spring for this kind of composite foundation is proposed. The corresponding settlement of the eigenvalue load is 12mm. The settlement of the corresponding limit load is 40mm. with the aid of SAP2000, the model can be used to consider the foundation of the interaction between the superstructure and the composite foundation. According to the force analysis, the foundation settlement corresponding to the eigenvalue load changes from 4mm to 20mm. The amplitude of the raft bending moment change in some places is close to 9%, and the changes in other places are very small. The results show that the method can not only consider the influence of the superstructure stiffness on the foundation, but also reflect the nonlinear characteristics of the soil body and the whole subsidence of the foundation. Drop.
4) establishing the solid element model of the foundation, considering the friction between the raft and the cushion, and considering the elastoplastic analysis of the interaction between the superstructure and the composite foundation with the help of ABAQUS. The results show that under the load design value, the stress distribution of the section is more uniform, the maximum tensile stress of the section is about 1.63Mpa, and the maximum stress of the steel bar is about 80Mpa The maximum stress of the steel bar under the load standard is 48Mpa, and the calculation results are in good agreement with the measured values. The correctness of the analysis method is verified. The calculation analysis shows that the friction between the foundation and the cushion is the main factor affecting the calculation results of the internal force of the raft. On the edge of the raft, the maximum value reached 3.5 times the average value, which could easily cause early damage to the local area of the foundation. Finally, the influence of the deformation modulus of the foundation soil, the thickness of the cushion, the cushion modulus and the thickness of the raft plate on the internal force and deformation of the raft was analyzed. The results showed that the relative stiffness of the foundation and raft plate was relative to the raft foundation. Of
5) the dynamic elastoplastic time history analysis is carried out by using the coupling method of finite element and infinite element, and the dynamic elastoplastic time history analysis is carried out. By comparing with the time history analysis of ordinary pile raft foundation, the seismic performance of the rigid pile composite foundation superstructure system is studied. The results show that the composite foundation has no shock absorption when the 7 degree small earthquake. When the 7 degree earthquake, the bending moment of the pile in the pile foundation is the maximum value of the pile bending moment in the rigid pile composite foundation and the maximum value of the shear force of 1.8 times. The cushion layer produces a large plastic deformation and relative base slip, which has a certain energy dissipation and damping effect, and the dynamic response of the raft foundation and the superstructure in the composite foundation is about the pile foundation system. 90% of the corresponding amount, the damping coefficient is between 0.8-0.9.
The research results of this paper have been applied to the construction of the Bi Hu Yuan in the north of Guangdong, the beauty of the times, and the construction of the green lake garden.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU472

【参考文献】