【作者】 涂兵雄；

【导师】 贾金青；

【作者基本信息】 大连理工大学 ， 结构工程， 2013， 博士

【摘要】 预应力锚杆柔性支护法是一种新的深及超深基坑支护技术,目前采用该技术支护的大连远洋大厦深基坑深度为25.6m,大连国际金融中心超深基坑已经达到30.0m。预应力锚杆柔性支护技术主要由预应力锚杆、锚下承载结构以及喷射混凝土面层组成,具有造价低、工期短、施工占地小、施工便捷、安全可靠等优点,并广泛适用于风化岩层和中等强度及以上的岩土层,应用十分普遍。本文主要针对预应力锚杆柔性支护法技术,重点以压力型锚杆锚固机理、喷射混凝土面层上的土压力、锚下承载结构的承载力以及基坑的力学行为作为研究对象,利用理论分析、解析计算、试验对比和数值模拟等多种研究手段,得到了一些可直接应用于工程或供理论参考的研究成果。主要研究内容如下：(1)综合考虑锚固体弹性模量和泊松比,岩土体粘聚力、内摩擦角、弹性模量、泊松比,以及锚固体与岩土体界面上的粘结力以及外摩擦角,并引入锚固体与岩土体界面粘结力工作条件系数,推导了压力型锚杆锚固体与岩土体界面剪应力和锚固体轴力的计算公式并进行了参数影响分析。结果表明：压力型锚杆锚固段上剪应力和轴力均呈指数分布,且随到承载体处距离的增加而逐渐衰减。考虑锚固体与岩土体界面粘结力影响后,得到的锚固体界面上的剪应力比不考虑界面粘结力得到的剪应力要小,而轴力要大。在此基础上,分析了压力型单孔复合锚的锚固机理,推导了其锚固体上的剪应力和轴力计算公式,其荷载传递规律及参数影响研究结果表明：岩土体相对越坚硬,即岩土体弹性模量越大、泊松比越小、粘聚力越大、内摩擦角越大,则剪应力分布越不均匀,且剪应力和轴力衰减越快。压力型单孔复合锚由于在锚杆钻孔内同时设置多个承载体,形成多级锚固单元共同受力,各承载体单元受到的荷载大大降低,界面上的剪应力也大大降低,各单元锚固段上的侧摩阻力都得到较好的发挥,受力更加均匀合理。(2)采用解析的方法,对压力型锚杆在受拉荷载及锚固体系极限承载力时的最大锚固长度进行了研究,得出了相应的锚固长度的计算方法,并分析了不同参数对锚固长度的影响,结果表明：岩土体弹性模量越大,泊松比越小,粘聚力越大,内摩擦角越大,则荷载在锚固段上传递的长度越小；泊松比对荷载传递长度的影响很小,几乎可以忽略不计。通过与压力型锚杆的室内模型试验结果对比,理论计算的荷载传递长度与模型试验测试结果吻合较好。另外,本文得出的压力型锚杆的锚固长度计算方法计算的结果与规范值比较吻合,由于规范假定侧摩阻力均匀分布,当实际锚固长度大于规范值或大于本文方法的计算值时,有可能会因为超出部分锚固段上的侧阻力得不到发挥而导致锚杆的锚固力达不到设计要求。本文得出的锚固长度计算方法,简单实用,可以较好地指导指导实际工程设计与施工。(3)基于土拱效应,建立了预应力锚杆柔性支护法喷射混凝土面层土压力的分析模型,推导得出了作用在喷射混凝土面层上的土压力计算公式,并与简仓法和规程法进行了对比分析,结果表明：基于主动土压力的土钉规程法计算面层土压力明显偏高；本文法计算结果与简仓法比较吻合,但是简仓法由于没有考虑面层与岩土体间的外摩擦角以及岩土体的粘聚力影响,计算结果相对比较粗糙。通过进一步研究分析,提出了预应力锚杆柔性支护法喷射混凝土面层上土压力的简化计算公式。并将土拱效应应用于粘性填土的平动刚性挡土墙,推导了考虑土拱效应的挡土墙上主动土压力解析式,在不同情况下该解的简化解与现有经典解析结果及前人推导结果完全吻合,计算结果表明：土拱效应使挡土墙的主动土压力呈非线性分布,考虑土拱效应后,挡土墙中上部的土压力要大于经典土压力计算结果,而在中下部尤其是底部,得到的主动土压力偏小(4)采用三维有限元分析软件,对预应力锚杆柔性支护法的锚下承载结构进行了数值试验分析,研究了不同型号槽钢组合形式下锚下承载结构的承载力,结果表明：厚垫板和竖向肋筋在一定程度上可以适当提高锚下承载结构的承载力；喷射混凝土约束可以有效控制锚下承载结构的侧向变形,增强结构的稳定性；且喷射混凝土全约束时,约束混凝土和槽钢形成复合承载结构,锚下承载结构的承载力得到较大提高,而喷射混凝土半约束时基本不提高结构的承载力；在槽钢上翼缘指定位置设置水平连接筋能有效控制结构的侧向变形,且设置水平连接筋后,喷射混凝土约束对控制槽钢侧向变形的效果大幅削弱。工程应用结果表明,通过数值试验得到的锚下承载结构承载力能很好地满足工程需要。本文得到的数值试验结果可为预应力锚杆柔性支护设计和施工提供科学依据和技术指导。(5)结合预应力锚杆柔性支护深基坑工程案例,通过锚杆的拉拔试验,分析了锚杆在风化岩层中的抗拔力及锚固段侧模阻力分布规律,结果表明：锚杆的侧摩阻力呈非线性分布,锚杆的抗拔力并不随锚杆长度的增加而线性增加,仅仅采用增加锚杆锚固段长度的方法来提高锚杆的抗拔力是不合理的。采用FLAC软件对预应力锚杆柔性支护基坑进行了数值模拟,模拟得到的水平位移与实际工程监测值吻合较好。并重点分析了锚杆预应力对基坑变形及滑移场的影响,结果表明：锚杆预应力能有效控制基坑变形并改善基坑的滑移场,在一定范围内,预应力越大效果越明显,但是当锚杆预应力超过一定范围后,继续增大预应力几乎不起作用,反而在一定程度上延长工期。相关研究结论对预应力锚杆柔性支护基坑的合理设计与优化施工都具有一定的参考作用。更多还原

【Abstract】 Prestressed anchor flexible supporting system is a new technology for retaining of deep and ultra-deep excavation. Currently, the depth of excavation of Dalian Yuan-yang Building using this technology is25.6meter, and the depth of ultra-deep excavation of Dalian International Finance Centre Building is near30meter. Prestressed anchor flexible supporting system mainly consists of shotcret, prestressed anchor, bearing structure under anchor head. For the advantage of low cost, short construction period, small covered area, construction convenient, safe and reliable, and so on, the system is wildly used in engineering, especially with construction sites contain weathered rock, medium intensity and stiff soil. According to the prestressed anchor flexible supporting system, some studies, which are focused on the anchorage mechanism of pressure-anchor, earth pressure on the shotcret, bearing capacity of bearing structure under anchor head and the mechanical behavior of foundation pit, are inverstigated by theoretical analysis, analytic calculations, comparison between experimental results and theoretical results, and numerical test. The main contents are as follows:(1) The computational formula of axial force of anchorage body and shear stress on the interface between anchorage body and soil mass are derived. Analysis of parameters, such as elastic modulus and Poisson’s ratio of anchorage body, cohesion, internal friction angle, elastic modulus and Poisson’s ratio of soil mass, adhesion and external friction angle of interface between anchorage body and soil mass, and the conditional coefficient of adhesion, is also carried out. The results show that the distributions of shear stress and axial force on the anchorage body of comparison anchor are exponential, and decrease as the distance to the bearing body. When considering the influence of adhesion on the interface between anchorage body and soil mass, the shear stress becomes small and axial force becomes large. The anchorage mechanism of the single bore multiple comparison anchor is analyzed, and the computational formula of shear stress on the interface and axial force of anchorage body are derived. Analysis results of the rule of load transferring and parameters influence show that distribution of shear stress becomes uneven and the shear stress and axial force decrease quickly when the soil mass is stiff (that is to say the values of soil mass modulus, cohesion and internal friction angle are large, and the value of Poisson’s ratio is small). Because the multiple bearing bodies bear the load together in the single bore multiple comparison anchor, the load on each bearing body reduces greatly, as well as the shear stress on the interface. Lateral friction and force on each anchorage body are developed sufficiently and the distributions are more uniform.(2) The anchorage lengths of comparison anchor under load and ultimate bearing capacity of the anchorage system are studied analytically, and the appropriate method for calculating the anchorage length is derived. Analysis results of the influence of parameters on the anchorage length show that the load transferring length is small for the condition with great modulus, small Poisson’s ratio, great cohesion and internal friction angle of soil mass. The influence of Poisson’s ration on the load transferring length is too little and can be neglected. Comparison between the theoretical calculated load transferring length and that from monitoring in the model experiment shows great agreement, as well as the comparison between the calculated anchorage length in this paper and that specified in the code. If the actual calculated length is large than specified values in the code or calculated values, the pull-out force may be less than the designed value because of the insufficient development of the lateral friction of the excessed anchorage length, duing to the assumption of uniform distribution of lateral friction. The calculated formulation, which is simple and practical, of anchorage length can provide better guidance for engineering design and construction.(3) Based on soil arching effect, the analysis model for calculating earth pressure on the shotcrete in prestressed anchor flexible supporting system is established and the relevant formula are derived. Comparative analysis of calculating results with those from silos method and code method shows that the calculated earth pressure on the shotcrete from code method, which is based on the active earth pressure, is large apparently. Calculated results from the derive formula are agreement with those from silos method. However, the values calculated from silos method are relatively imprecise because of the ignorance of soil cohesion and external friction angle. By further analysis, the simplified formula for calculating the earth pressure on the shotcrete is proposed. While considering the soil arching effect in the backfill of rigid retaining wall with a horizontal translating, the formulation for calculating the active earth pressure acting on the rigid retaining wall is derived, which show fully agreement with those from the classical analytical formula and those derived by earlier researchers. Analytical results show that the distribution of active earth pressure on the wall is non-linear because of the arching effect, and the earth pressure are larger than that from classical formula in the upper zone while smaller in the lower zone.(4) Numerical tests about the bearing structure under anchor head are carried out for prestressed anchor flexible supporting system by using three-dimensional finite element analysis software. The analysis results of bearing capacity of structure under anchor head for different types of channel steel show that thick plate and vertical ribs can increase the capacity of structure to a certain extent. Confined shotcrete can effectively control the lateral deformation and enhance the stability of the structure. Because fully confined shotcrete and channel steel can form a composite bearing structure, the capacity of the structure can be improved greatly. But half confined shotcrete can not improve the capacity of structure. Horizontal connecting rebar in the proper location can effectively control the lateral deformation of structure. The influence of confined shotcrete on the lateral deformation reduces greatly when the horizontal connecting rebar is installed. Engineering application results show that, capacities of bearing structure obtained by numerical tests can meet the project well. Results from numerical tests can provide scientific and technical guidance for the design and construction of prestressed anchor flexible supporting system.(5) Based on the actual engineering with prestressed anchor flexible supporting system, the pulling resistance of anchor and the distribution of lateral friction on the interface between anchorage body and soil mass are analyzed through pull-out tests of anchor. Results show that the distribution of lateral friction is non-linear and the pulling resistance of anchorage does not increase linearly with the anchorage length. So it may be unreasonable to improve the anchor pullout resistance just by increasing the anchorage length. An actual project with prestressed anchor flexible supporting system is simulated using FLAC software and the horizontal displacement is in great agreement with that from monitoring. The prestress influence is analyzied emphasizly on the displacement and slip field of the foundation pit in this paper. The results show that prestress of anchor can control the displacement and improve slip field of the foundation pit. However, when the prestress exceeds a certain range, the continued prestress has nearly no effect but extend schedule. Related results can provide a certain reference value for rational design and optimized construction for prestressed anchor flexible supporting system.更多还原