【作者】 刘鸿；

【导师】 周德培；

【作者基本信息】 西南交通大学 ， 岩土工程， 2012， 博士

【摘要】 岩土锚固技术在实际工程中有广泛的应用,特别是20世纪90年代以来,压力分散型锚索才开始在我国的一些工程中得到了应用和发展,对锚固机理的研究虽然做了一些工作,但还未获得公认的成果,影响了这种锚索的进一步推广应用。结合工程界目前广泛关注的热点和难点问题,通过理论分析、地质力学模型试验和数值模拟计算,研究了压力分散型锚索的锚固机理,并在此基础上开展了设计计算方法的研究。取得的主要成果如下：(1)揭示了锚索体系的受力和变形特征。压力分散型锚索通过承压板将锚索的张拉力转换成作用在各单元锚索注浆体上的压力后,锚索体系表现出三种受力和变形特征：其一,注浆体承受压力作用后会发生径向膨胀变形,浆体周围的岩土体会对这种变形施加约束从而给浆体施加了径向压力,由此在孔壁即浆-岩界面产生的摩阻力是提高锚固力的重要原因；其二,若浆-岩界面的抗剪强度不足或锚固段长度较短,各锚索单元张拉荷载较大时,各单元锚索上的压力在传递过程中会相互影响,发生应力叠加现象；其三,在单元锚索的连接处即承压板处会出现拉应力,该处拉压变形不协调会造成此处注浆体开裂。(2)研制了新的模型试验设备。压力分散型锚索将张拉力以压力的形式分散作用在各单元锚索的注浆体上,各单元锚索的受力和变形特性及其相互影响,是锚固机理研究的重要内容。为此研制了一套新的地质力学模型试验设备和相应试验方法,可对压力分散型锚索的各单元锚索进行分级循环张拉,研究各单元锚索的受力特征和传力机制。(3)提出了基于注浆体径向膨胀变形的锚固力提高值的计算公式。根据受压注浆体的径向膨胀变形特性得到了单元锚索轴向应力和剪应力按负指数函数变化的分布规律,单元锚索承载体处的轴向应力和剪应力为其最大值,以后随注浆体长度的增加而逐渐减小。压力分散型锚索较拉力型锚索锚固力提高的原因在于注浆体径向膨胀变形会受到径向约束压力作用,并同时产生了摩阻力,锚固力提高值τa可按照公式τa=Pm tanφ／(3S)计算。(4)提出了单元锚固段长度的计算公式。坚硬岩体对注浆体径向膨胀变形的约束较大,各锚索单元上的压力在传递过程中不会相互影响,也不会发生应力叠加现象。软弱岩土体对注浆体径向膨胀变形的约束较小,各锚索单元间的应力会相互影响,容易发生应力叠加现象。根据剪应力提高值L和浆-岩界面固有粘结力C值,提出了不发生应力叠加现象条件下单元锚固段长度的计算公式,即lsa=P/πD(τa+C)](5)提出了注浆体压缩变形的验算方法。各单元锚索的承载体连接了前后两个单元锚索,张拉荷载通过承压板给本级单元锚索注浆体施加压力的同时,也给与之相连的孔底或单元锚索注浆体施加了拉力。在此连接处的拉压变形不协调时会造成该处出现裂纹而影响锚固效果。基于连接处的拉压变形特性,提出了以注浆体压缩位移来验算注浆体的变形程度,并给出了验算方法和公式:σ0/βE≤[S0],为控制注浆体变形和开裂提供了理论参考。(6)对现有设计方法提出了改进建议。本文在压力分散型锚索锚固机理、锚固力提高的原因、各锚索单元间的压力传递以及承载体处注浆体的受力与变形等方面取得了较好成果,现有设计方法在这些方面存在不足。在详细分析现有设计方法的基础上,提出了补充和改进建议。更多还原

【Abstract】 Rock or soil anchoring technology has extensive application in practical engineering, especially since the ninties of the20century, dispersed pressure anchor cable began its application and development in some engineerings of China. Although some study work on anchorage mechanism has been done, the recognized results have not yet obtained, which affected the further application of the anchor cable. Combined with the extensive attention the hot and difficult issues of the engineering profession, the anchorage mechanism of the pressure dispersed anchor cable has been studied by theoretical analysis, geomechanical model test and numerical simulation, the design calculation method has been studied and developed on the anchorage mechanism basis. The main achievements are as follows:(1) The features of mechanics and deformation of the cable system have been revealed.The pressure dispersed anchor cable transformes the tension load into the pressure of grouting body of the anchor cable unit through the bearing body, anchor cable system exhibits three stress characteristics:one, the radial expansion deformation of the grouting body will occur after the grouting body under pressure, and the hole wall of rock and soil will constrain the radial deformation to exert radial pressure on the grouting body, the radial constraint effect producing the friction resistance along the pulp-rock interface is the very important reason of the anchoring force improved; secondly, if the shear strength of the pulp-rock interface is insufficient or the anchoring segment length is shorter, and the load of each anchor cable unit is very bigger, the pressure on each anchor cable unit will influence each other in the transmission process, the stress superposition phenomenon will occur between the anchor units; thirdly, the tensile stress near the bearing body appears, when the tension and compression deformation of the grouting body deformation of the near units does not coordinate with each other, the grouting body will crack.(2) A set of new model test equipment has been studied and developed.The dispersed pressure anchor cable apply the tension load on the grouting body of each anchor cable unit in the form of pressure, the characteristics of the mechanics and deformation of each anchorage unit and the influence on each other are the important content of mechanism of anchorage. A set of new geomechanical model test apparatus and test method have been studied and developed, and the tension test can adopt the grading cyclic loading method in each bearing unit of the dispersed pressure anchor cable to study the mechanical characteristics of each anchorage unit and load transfer mechanism.(3) The calculation formula of the increased value of the anchoring force based on the radial expansion deformation of the grouting body has been studied and developed.According to the radial expansion deformation characteristics of the grouting body under pressure, the distribution laws of negative exponential function changes of the axial stress and shear stress of the anchor cable have been put forward, the maximum value of the axial stress or shear stress bearing is located at the bearing body, and reduced gradually with the grouting body length increased. Compared with tensile type anchor cable, the anchorage force of the dispersed pressure anchor cable increased because of the radial expansion deformation of the grouting body can be affected by radial confinement pressure while frictional resistance produced, the increased value of shear stress in accordance with the calculation formula τa-Pmtanφl(3S).(4) The length of anchorage segment of anchor cable unit has been studied and developed.The constraint on the radial expansion deformation of grouting body by the hard rock is very larger, the pressure of each anchor cable unit would not be affected in the transmission process, and the stress superposition phenomenon won’t produce also, the constraint on the radial expansion deformation of grouting body by the Soft rock is smaller, the stress between the anchor unit will influence each other, which is prone to stress superposition phenomenon. According the increased value φa of the shear intensity of grouting-rock interface and the inherent cohesion C between the grouting body and rock soil, these two part resistance of the cable unit all play out, and consider the structure of the safety coefficient Fs, under the condition of the stress superposition phenomenon eliminated,the calculation formula of the length of anchoring segment of unit la can be replaced by the following formula la=FsP/πD(τa+c).(5) The calculation method of grouting body based on compression deformation has been put forward.When the bearing body of the anchor cable element connects two elements which are before and after the bearing body, as applying the tension load on the bearing body of the anchor cable element through the bearing body, a pulling force is also applied on the the bottom of the hole or the anchor cable unit.when the grouting body deformation of the near units does not coordinate with each other, the grouting body which is contact with the bearing body will cause tensile crack and affect the the anchorage effect. Based on the feature of the tensile and compressive deformation, the deformation degree of the grouting body calculated by the grouting compressive displacement to has been put forward, the formula for the calculation is s0=S0=σ0la/3e≤[S0], and the theory reference to control the deformation and cracking of the grouting body has been provided.(6) The improvement suggestions about the existing design method have been proposed.This dissertation achieved good results about the anchorage mechanism of the pressure dispersed anchor cable, the reason of the anchorage force improvement, the transmission of the pressure of the anchor cable units, the stress and the deformation of the grouting body at the bearing body etc. The existing design methods have deficiencies in these aspects. On the basis of detailed analysis of the existing design methods in the foundation, the suggestions of improvement and supplement has been proposed.更多还原