【作者】 吴保全；

【导师】 李天斌；

【作者基本信息】 成都理工大学 ， 地质工程， 2008， 博士

【摘要】 高层和超高层建筑的不断发展,要求地基土承担越来越高的荷载且变形也有更严格的限制。我国大部分城市内的地基土具备二元结构,其由表层土和下部硬土层组成。表层土因为力学性质较差大部分不能直接作为高层建筑的地基。传统的设计方法往往忽略表层土有侧限状态下强度和变形破坏机理的有利因素,而是直接采用经济造价高的桩基础穿越表层土,通过高强度桩身、高承载力持力层（硬土层）等实现荷载的传递和地基变形的控制。因此,高层建筑物地基基础埋深越来越大,不符合社会经济和土力学发展的方向和要求。随着地基土研究的深入和经济发展的需要,解决高层建筑的地基基础埋深大和利用表层土时没有合适地基类型等问题就越加突出和迫切。本文通过研究,提出有侧限结构复合地基设计原理从理论上解决了上述问题。为了使研究成果具有现实意义和客观性,选择二元结构特征明显的郑州地区表层粉土为研究对象并设计新的地基类型对其验证。采用大型的破坏性静载荷试验、室内外测试、原型桩试验和理论分析等手段,对表层粉土的变形破坏方式、格栅结构和土共同作用的机理等进行了系统性深入研究。在此基础上,结合一维固结理论、复合理论、均化理论、系统观点并采用大量的地基工程设计资料、原位测试数据、以及国内外已有的试验研究成果,建立了格栅结构复合地基的设计计算方法、施工工艺及质量控制体系。经过数年的努力,取得的主要成果如下。（1）通过工程勘察、室内外试验及测试、实例调查、理论分析等,对郑州市地基土的岩性组合类型、结构类型、地基土强度、变形破坏机理等进行了深入研究,得出集中大荷载作用下的粉土破坏并非沿着传统理论假设的剪切滑动面移动,也非地基土的冲剪破坏,而是粉土在基础下首先发生挤密和鼓胀侧扩,随着荷载增加产生隆起破坏,破坏土分布在基础底板周边很小的宽度内,归纳出粉土的变形破坏方式为“挤扩—隆起”。（2）粉土地基的整体失稳方式是通过地基中不同深度层次的局部化破坏而累积形成的整体变形破坏。这些局部化破坏的过程中包括渗流和挤扩——隆起等破坏。在无侧限条件下,局部化破坏过程没有限制因素,表层土中地下水渗流途径短、渗流压力较大,表层土侧向变形破坏经常发生,从而造成表层地基土中多发生局部化破坏。按照一定的方向、顺序分层压缩并分层挤扩隆起破坏就构成表层粉土地基的整体变形破坏。（3）根据复合地基中人工结构对地基土的侧限作用、地基土的变形破坏机理、室内外侧限试验的结果,首次将高层建筑地基分为有侧限结构地基和无侧限结构地基两大类型。无侧限结构地基中地基土的变形处在K₀状态（静止土压力）下,可发生无明显人工结构约束的侧向变形破坏。有侧限结构地基中由于人工结构对地基土构成侧限和垂直向的强度增强,强制表层土地基以垂直变形为主,控制侧向变形趋于零。根据一维固结理论和有侧限试验,建立了有侧限结构复合地基设计原理并对其中一种地基类型—水泥搅拌桩格栅结构复合地基进行研究。发现此类型地基对表层土的挤扩—隆起和渗流破坏、地基土强度提高的有效性和对高层建筑基础浅埋与表层土利用的适宜性。（4）通过对水泥土搅拌桩和格栅结构工程—力学性质的研究,首次提出格栅结构复合地基中采用单桩弱强度、垂向变强度和群桩整体高刚度的理念。在完善了设计方法和施工工艺后,通过桩在地基土中受力状况的分析,结合桩身应力应变测试数据和结论,推导出桩身变强度的具体计算公式为:q_u=（q-p_s）/ηA_P。该式表明桩任意深度处的截面强度q_u随着桩承担荷载p与桩身摩阻力q的差值减少而减少。满足这一计算公式的桩身强度即可实现地基中的附加应力的有效传递。（5）通过研究,指出桩与土、格栅结构、复合地基等变形模量涵义的区别性,以及搅拌桩格栅结构复合地基的变形模量与桩尺寸、桩端土模量E₂、桩周土模量E_s、格栅结构模量E_P等具有相关性,通过应力状态分析,以弹性理论为基础推导出地基模量计算公式为:E=mKK₁E₂+（1-m）E_s,K₁=p/（p-q）,K=E_p/（E_p+E₂）。其相关性通过桩置换率m、桩端部土模量折减系数K、桩土间荷载折减系数K₁等表达。（6）推导出格栅结构复合地基的承载力f_spk、承载力折减系数β等指标的计算公式为:f_spk=β（1-m）f_sk+mR_α/A_P、β=1/（1+e）。消除了β取经验值的不确定性,并建立与地基土原始孔隙比之间的关系。（7）数栋高层建筑物的格栅结构复合地基运行符合各种规范规定,验证其原理和方法的正确性,据此,编写了一套适宜郑州地区高层建筑格栅结构复合地基的设计、施工、监理、检测的技术指南,为此地基类型设计、计算提供了依据。更多还原

【Abstract】 The continuously developing high building or ultra high building request for foundation soil that can undertake more and more high load and whose deformation is much less. The foundation soil in most cities of our country has the binary medium model, which composes with the topsoil and the underneath soil. Because of the weaker strength and higher deformation of topsoil, it can’t directly be the foundation of the high building or ultra high building. The traditional design method usually neglects the beneficial factors that the topsoil have a strength at the lateral confinement and the mechanism for deformation of the topsoil, but and directly adopts the expensive pile foundation that cuts through the topsoil, it delivers load and controls deformation to pass the high strength pile and the high bearing capacity soil. Therefore, it doesn’t adapt with development direction and request of the social economy and soil mechanics that the foundation depth of the high and higher buildings is more and more deep.Accompany with the extensive development of research about the foundation soil and the demand of economic development, the problems that the foundation depth of the high building or ultra high building is deeper and there is not suitable foundation type using of topsoil are more and more obvious and urgent. In this paper, it was been proposed that the design principle of composite foundation with the lateral confinement structure, and the above-mentioned problem had been resolved. That the research has realistic meaning and objectivity is emphasized, the silt at Zhengzhou that has the typical characteristic of binary medium model is made use of and verified by new foundation type. By many means, such as the large-scale destructive static load experiment, indoor and on-site testing, prototype pile experiment and theories analytical, the interaction mechanism of the grid structure and the soil have been studied thoroughly and systematically.Basing on these results, the design calculation method of grid structure composite foundation and the construction technology and quality control system of foundation had been established through theory of one dimension of solid, theory of compound, theory of average, system standpoint and the design data, In-situ testing data, a great deal of foundation engineering, the international experiment research results. Through author pays more than effort for few years, the main results are as follows:（1）Through engineering Investigation, the indoor and on-site experiment and test, case investigation, theories analysis etc, the thorough research on foundation at Zhengzhou had been conducted in the combinations types of rock and soil, structure types, strength of foundation soil, mechanism of deformation and failure etc. The conclusion had been drawn that the silt failure under the concentrated load carry is not along the suppose shear face of traditional theories to slide, but the silt take place compression firstly and expanded with the center bulge and the side, and swelled up for break soil as follow increasing load, and break soil is outer circle in the foundation, and the way of the silt to be breached is called "compression-expansion-swelled up" .（2）The instability of the silt in foundation is one accumulate deformation and failure that constituted from the different depth local failure. Its process includes the seepage and compression-expansion-swelled up. When there is not lateral confinement, the process of local failure doesn’t have limitless factor that the seepage path of the groundwater is shorter and pressure of the groundwater is higher, therefore, the lateral deformation take place usually at the topsoil, and the partial failure at the topsoil takes place. The failure of compression-expansion-swelled up that is according to the certain direction and the order layering constitutes the deformation and failure in the topsoil foundation.（3）According to the lateral confinement effect of the artificial structure on the foundation soil in the composite foundation, the deformation failure mechanism of the foundation soil, and the result of the indoor and outdoor lateral confinement experiment, the foundation of high-rise building is divided to two types including lateral confinement structure foundation and non-lateral confinement structure foundation firstly. In the non-lateral confinement structure foundation, when the foundation soil deformation is in the condition of K₀ （stationary soil pressure）, the lateral deformation failure with obscure artificial structure constraint will happen. In the lateral confinement structure foundation, because the effect of artificial structure on the foundation soil, the lateral confinement of the foundation soil is formed and the strength in the vertical direction is enhanced, imperatively makes the vertical deformation of the superficial foundation soil the majority and controls the lateral deformation of which to zero gradually. Based on the one-dimension consolidation theory and the lateral confinement experiment, the design principle of the lateral confinement structure composite foundation is established, and the study on the cement agitation pile grid structure composite foundation, one type of the lateral confinement structure composite foundation, is carried out. It’s indicated that the lateral confinement structure composite foundation has the availability in the compression -expansion- swelled up and seepage failure of topsoil and practicability in the shallow bury of high-rise building foundation and the utility of the topsoil.（4）According to the research of the engineering—mechanics property of the cement-soil churning pile and grid structure, the concept was put forward firstly, such as that a single pile is weak strength and is change strength and the foundation is high strength in the composite foundation. After perfected design method and construction craft, based to the analysis of stress and strain dint of the pile in the foundation soil and the test data and the conclusion of stress and strain of the pile, the deduced calculation formula of change strength of cement-soil churning pile is: rily depth noodles strength q_u that is decreased because the difference of the undertaken load p and resistance q of the pile is reduced. The pile strength that satisfies this calculation formula can immediately carry out the affixture stress in the foundation to deliver effectively.（5） Through the research, pointing out the differences between the pile and soil, grid structure, modulus of deformation implication of composite foundation and so on, and which has the relevance between the deformation modulus of grid structure composite foundation and the pile size,pile model measures E₂, the pile week earthen model measures Es,grill structure module E_p and so on. Through the stress condition analysis, inferring the subgrade modulus formula by taking thetheory of elasticity as the foundation is: E = mKK₁E₂ + （1- m）E_s, K₁= p /（p - q）,K =E_p/（E_p+E₂）. Its relevance through pile rate of displacement m, reductioncoefficient K in pile nose soil modulus, load reduction coefficient K₁ between pile earth expressions and so on.（6）Inferring the grid structure composite foundation bearing capacity f_spk, the bearing capacity reduction coefficientβand so on. The target formulas is: f_spk=β（1-m）f_sk+mR_a/A_p ,β= 1/（1+e） , which eliminatedβhas taken theempirical value the uncertainty, and has established the foundation soil primitive void ratio relations.（7） Through some high building of grid structure composite foundation movement which conforms to each standard, that has confirmed its principle and the method accuracy, according to this, compiled a set to be suitable the Zhengzhou area high-rise construction grid structure composite foundation design, the construction, overseeing, the examination technical guide, and which provided the basis for this foundation type design, the computation.更多还原