【作者】 胡贺松；

【导师】 彭振斌； 唐孟雄；

【作者基本信息】 中南大学 ， 地质工程， 2009， 博士

【摘要】 桩锚支护结构是20世纪80年代开始应用及发展起来的一种新型抗滑结构,在深基坑治理、滑坡整治中已获得了广泛应用。目前国内外学者对于桩锚支护结构的耦合力学特性、数值实现方法以及稳定性影响因素相关方面的研究尚显不足。论文采用收集前人资料、理论分析、现场试验、数值仿真技术及工程监测等技术方法,对基坑桩锚支护效应、桩锚结构与土体的相互作用、桩锚结构参数对基坑稳定性的影响、基坑稳定性计算的数值方法以及桩锚结构之间的相互作用机理方面进行了相应研究,为理论应用和工程实践提供科学指导。通过桩土、土锚相互作用机理的理论分析,得到了桩锚联合支护结构与土体的相互作用模型及其变形协调条件和破坏模式。根据桩锚与土体相互作用特性,建立了桩锚数值计算单元,为进一步的数值计算奠定基础。通过锚杆拉拔试验和数值模拟试验,建立了锚杆极限锚固力和围压之间的拟合模型以及锚杆极限锚固力和锚杆长度之间的拟合模型,从而实现了锚固力同围压以及锚杆长度之间的定量分析,表明随着拉拔荷载的增大,锚杆的位移呈非线性增长;拉拔力较小时,荷载主要由界面胶结力和摩擦力承担;随着滑移增大,界面胶结力丧失很快,摩擦阻力也因颗粒磨细而衰减;锚杆轴力分布均为锚头处最大,沿着锚杆体逐渐减小。拉拔位移的增大导致锚杆发挥的锚固力逐渐增大;而围压的增大导致锚杆的破坏荷载逐渐增大,二者符合指数关系。通过对比极限平衡法和强度折减法分析基坑稳定性的异同,说明了极限平衡法分析基坑稳定性的机理和其局限性及强度折减法研究基坑稳定性的优点,验证了强度折减法的有效性。利用基于强度折减的FLAC3D数值模拟方法对基坑滑动面的分布情况及其影响因素进行了分析,表明随着粘结力的增大,滑动面逐渐从浅层滑动面转换为深层滑动面,滑动面上缘逐渐远离基坑项部;随着内摩擦角的增大,滑动破坏模式从深层破坏转变为浅层破坏,滑动面上缘逐渐靠近基坑顶部。利用桩单元和锚杆单元的特性,采用节点删除,重新建立连接的方法,在FLAC3D中实现了二者相互作用的数值模拟;通过桩锚支护结构参数的影响分析,建立了不同锚杆倾角下锚杆长度与安全系数之间的拟合模型,实现锚杆参数对稳定性影响的定量研究,表明基坑的安全系数和锚杆长度之间的关系呈高度线性相关;随着锚杆长度的增加,基坑滑动面逐渐从浅层滑动面转化为深层滑动面。桩锚支护过程中,桩单元和锚杆单元之间的相互作用的耦合特性及其应力和变形的传递特征表明:支护桩主要承受压力作用,压力的分布沿桩身呈现先增大后减小的趋势;随着锚杆长度的增加,支护桩所承受的压力逐渐减小;开挖过程中支护桩的轴力沿桩深方向分布不均匀,开挖初期支护桩主要承受拉力;随着开挖的进行,支护桩受力形式逐渐由受拉转换受压形式。通过一典型工程实例的现场监测和数值计算结果的对比分析,说明了本文数值方法的可靠性以及数值计算结果的有效性。更多还原

【Abstract】 The pile-anchor reinforcement structure is a new type of slip resisting structure and was applied developed from 80s, 20 century, which is widely used in the reinforcement of deep foundation and slope. But in recently, the studies on the couple mechanical characteristic of pile-anchor reinforcement structure, its numerical realization method and foundation stability influential factors are still not enough.According to the former material, theoretical analysis, insitu test, numerical simulation technique and engineering monitoring, the reinforcement effect of pile-anchor for foundation, the interaction between pile-anchor structure and soil, the effect of pile-anchor reinforcement parameters to the foundation stability, the numerical method of foundation stability calculation and the interaction between pile structure and anchor structure are studied in the present paper, which will give guidance for the theoretical application and real engineering.The interaction mechanism of the pile-soil and cable-soil is analyzed, the interaction model of pile-anchor structure and soil is founded to study the deformation condition and failure modes. The pile-anchor numerical calculation element is built according to the interaction between pile-anchor and soil, which will give the foundation for the further numerical calculation.According to insitu monitoring, the fitting models for limit anchoring force with surrounding pressure, and the anchoring force with the cable length are built, then the relationship between the ancoring force with surrounding pressure and cable length can be quantitilized analyzed, which shows that, with the increase of loading, displacement of cable increases gradually in the nonlinear way; when the loading is small, the load is mainly resisted by the cohesion and friction of the interface; with the slip of cable increases, the cohesion of the interface decreases rapidly, while the friction decreases as well for the grain been milled; the distribution of the cable axial force shows the maximum magnitude at the cable and decreases along the cable shaft; with the increase of the tensile displacement, the anchoring force of the cable becoming gradually large; with the increase of the surrounding stress, the failure load of the cable increases gradually, whose relationship meets the exponential equation.The differences between limit equilibrium method and shear strength reduction method are compared, in which the mechanism and limitation of the limit equilibrium method are analyzed, while the characteristic and implementation procedure of the shear strength reduction method is studied, which validates the strength reduction method.The FLAC3D numerical simulation method based on thhe strength reduction method is used to study the distribution of foundation slip plane and their influential factors, which show that with the increase of the cohesion, the slip plane moves from shallow part of foundation to the inter part of foundation; the upper part of the slip plane moves farther to the vertex of foundation; with the increase of internal friction angle, the failure mode of the foundation changes from deep slippage to shallow slippage, the upper part of the slip plane moves closer to the vertex of the foundation.According to the characteristic of pile element and cable element, the join nodes of the two elements are deleted, then the new connection between them is built, the interaction between them in the FLAC3D is numerical realized; the influencing factors for pile-anchor structure are analyze, and fitting model for the cable length and safety factor with different cable inclination is studied, which shows that the relationship between foundation safety factor F and cable length can be described by linear equation with high coefficient; with the increase of cable length, the slip plane of foundation changes from shallow slip plane to the deep slip plane;The interaction effect of pile and cable is analyzed as well as their stress and deformation transformation characteristic, which show that, the reinforcement pile mainly resists the compression in the axial direction; the distribution of the compression shows the trend of first increases then decreases along the pile shaft; with the increase of cable length, the compression along the pile shaft decreases gradually; during the excavation procedure, the mode for the axial force of reinforcement pile changes from tensile to compressive.According to the monitoring and numerical calculation results for a typical engineering, the validations for the numerical method and numerical calculation results are proved.更多还原