【作者】 彭柏兴；

【导师】 王星华；

【作者基本信息】 中南大学 ， 岩土工程， 2009， 博士

【摘要】 湘浏盆地属地洼盆地。盆地内的长、株、潭地区广泛分布着白垩系砾岩、泥质粉砂岩、粉砂质泥岩、泥岩等软质岩石,具有成岩差,易风化、崩解等特殊性质。近年来,红层嵌岩桩被广泛应用于大型桥梁和高层、超高层建筑中,但完整的试桩资料和实测成果不多,制约了人们对其承载机理的全面认识。深入了解红层的工程特性是有效利用红层的先决条件,加强对湘浏盆地红层工程特性及其桩基承载性状研究对长株潭城市一体化的规划、建设有着重要意义。本文在分析和参考大量国内外文献基础上,对湘浏盆地的地质形成条件及研究现状进行了归纳总结;通过一系列物理力学性能试验,对红层物理力学性质进行了系统分析;采用现场试验和数值模拟相结合方法,对红层嵌岩桩的若干问题进行了研究。取得如下成果:(1)从地质环境演化、分布范围、地层和岩类划分等角度出发,对红层软岩的发育特征及其时空变化规律进行了系统研究,发现红层工程性质主要受盆地构造部位、岩性特征、岩相特征、沉积介质的物理化学条件及构造作用等因素影响,建立了红层演化模型。(2)通过X-衍射、热物理分析、膨胀试验、崩解试验、压水试验、动力参数测试、单轴抗压试验、剪切试验、载荷试验和高压旁压试验等手段,对红层的风化分带、抗压强度、承载力取值及路基填料等系列问题进行了研究。经过多参数的综合分析,建立了红层动、静参数之间的相关方程,为红层风化程度与岩体强度分析提供了有效途径。(3)通过对4根人工挖孔灌注桩进行单桩静力载荷试验,分别采用滑动测微计和应变计测试桩身轴力的变化,研究了红层嵌岩桩的承载性能、桩身轴力传递规律、桩侧阻力和端阻力的发挥性状。结果表明,红层嵌岩桩表现为端承摩擦桩特性,Q-s曲线呈缓变型;桩身轴力传递规律和桩侧阻力的发挥与覆盖层厚度、桩长、桩周土性质密切相关。由于红层具有较强的结构性,发挥极限侧阻所需位移仅为2～6mm,测试得到的极限侧阻力远高于规范值,表现出强化效应,端阻力和侧阻力并非同步发挥。(4)综合分析了嵌岩段侧阻力的研究成果、侧阻力的激发机理。应用剪切试验、基岩内桩侧摩阻力试验和高压旁压试验及桩身应力测试对湘浏盆地内泥质粉砂岩的嵌岩段桩侧阻力的研究,分析了不同方法确定结果的差异根源。结果表明,按《建筑桩基技术规范》(JGJ94-94)确定的侧阻力偏低,提出了以单轴天然抗压强度标准值为基础,按0.15～0.30系数折减计算嵌岩段极限侧阻力的取值标准,对类似地区桩基设计有一定的参考价值。(5)根据相关岩石破坏理论,研究了嵌岩桩端阻力的工作机理。对当前嵌岩段端阻力的确定方法进行了比较分析,对不同方法确定的嵌岩桩端阻差异进行了研究。通过对原位测试成果的整理、分析,认为目前规范中关于嵌岩桩端阻力计算公式不适用于红层软岩嵌岩桩,并采用拟合方法得到了红层极限端阻力的荷载传递函数及计算公式。(6)总结了国内外嵌岩桩承载力计算的研究现状,分析了现行不同规范在嵌岩桩设计取值上的差异,给出了符合当地实际的红层嵌岩段总阻力的修正公式。利用统计学中的正交试验设计方法和敏感性分析,综合考虑桩长、桩径、岩基强度,结合工程实例对红层嵌岩桩进行设计优化,以达到经济合理的目的。(7)以原型桩为基础,运用有限单元法对红层大直径桩的桩-土-岩相互作用进行模拟。对桩径、桩身模量、桩端持力层性质及嵌岩深度对嵌岩桩承载性状的影响进行了分析,其结果可用于指导工程实践和理论研究。更多还原

【Abstract】 Xiang-Liou basin is a DiWa basin, large areas of which is covered with Red beds soft rock composed of argillaceous gravellystone, silty mudstone and mudstone with the features of weak diagenetic process and susceptiable to weathering and easily be disingtegrated. This rock is widespread during Cretaceous in Changsha-Zhuzhou-Xiangtan area. In recent years, rock-socket piles are widely used for bridges and high-rise buildings and skyscraper in Red beds, but there are few integrated test reports on it, which restrain people’s full understanding to rock-socket piles’ bearing mechanism. To know deeply the engineering property of Red beds is precondition of using it effectively,So researching on the engineering characteristics and bearing behavior of piles socketed in Red beds are of great significance for the planing and construction of Chang-Zhu-tan economic integration.Based on analyzing and referring literatures from home and abroad, this thesis conludes the geological condition and study actuality of Red beds in Xiang-Liou basin;Theoretical analysis and study to its physical and mechanical property had been made with a series of trials;Problems such as bearing behavior and mechanism of piles socketed in Red beds had been studied by employing field test with numerical simulation too.Some conclusions have been corned to as follows:(1) The development characteristics and spatial-temproal variability characters of Cretaceous red layer in Xiang-Liou basin have been researched focus on the distribution, the period stratum and rock type classification, the progress of geological environment. It has presented that the Red bed’s project intensity mainly influenced by follow geology environmental condition-basin structure, lithology characteristics, stratum features, water medium physical-chemistry condition, geologic structure, the improving methods are put forward too.(2) Problems such as determinating the wreathing belt, the bearing capacity, the compressive strength and evaluating the properties for construcation meterials have been researched with a series of tests including X-ray technique, permeability test, expansion test, disintegration test, thermal conductivity test, compression test, direct shear test, wave velocity measurement, load test, high pressure pressurement test(PMT). On the basis of laboratory and in-situ test data, the correlation equations are established for characteristic parameters of dynamic and static properties of Red beds with synthetical analysis of multi-parameter, much efficient information about rock werthering and strength is achieved in this paper.(3) The vertical static load test is adopted to investigate 4 large-diameter rock-socket pile in Red layer, in which the variation of axis force in piles is measured by sliding micrometer and strain gauges. Hence, the bearing capacity behavior, load transfer mechanism, the lateral friction and end bearing are researched in this paper. According to the test results, the load transfer performance of rock-socket pile is similar to that of end-bearing friction pile, the Q-s curves are slowly varying. The pile length, covering and soil around pile are all important to the load transfer mechanism and action of lateral friction. For the natural structure of red layer, the critical displacements of piles are 2～6mm and the tested result is much higher than those recommended by the Specifications, which indicates that the shaft resistance is strengthened, while lateral friction and end bearing can not display simultaneously.(4) The developments about side resistance of socketed pile in weak rock and responsing mechanism of side resistance are presented in detail. Testing study is made on the lateral resistance of socketed pile in argillaceous siltstone, which includes straight shear test, side resistance test in rock, high pressure pressurement test (PMT) and stress detector. Through testing and analysis, it is found that the side resistance of red beds evaluated with Technical Code for Building Pile Foundation (JGJ94-94) is quite lower. And then the difference and influence factors for test results have been discussed also. An improved parameter formula is given to calculate the lateral resistance of embedded section with uniaxial compressive strength standard value under natural moisture, and it’s reduced coefficient is 0.15 to 0.30. The results is deserved to be applied to practical problems such as those on soft rocks. (5)The mechanism of bearing at the tip of rock-socket pile is researched with theories of destroying relation to rock. The available methods of calculationin specification are compared and the difference between the end resistances determined by different mithods are studied. The limitation of the way recommanded by the current Code in measuring the end capacity of rock-socketed piles in Red beds are demonstrated firstly, and then on the basis of analysis to all kinds of influential factors and summarization to the testing data, the load transfer function and a new formulae to estimate end capacity are put forward by means of linear fiting.(6)A review on the research of the bearing behavior of rock-socketed pile is taken, and a brief introduction is made about theories and design mothods. An improved formula is given to calculate the total resistence of embedded section, which is comparatively agree with the practice and is instructive for design and deep study. With considering diameter, length and strength of rock at the same time, orthogonal experimental design and sensitivity analysis are used in the design of socketed pile in Red beds to make it both reliable and economical.(7)Based on the static load test of practical engineerimg, the pile-soil-rock interaction of rock-socket pile in Red bed were simulated by using finite element method. The influence factors of the ultimate capacityof rock-socketded pile such as the diameter of pile, the modenm of pile, the property of superstratum soils and rock in base, the length of rock socketed are analyzed, the results of analysis can be used in the design and theory resarch.更多还原