砂卵石地层基坑预应力锚索复合土钉支护技术研究

发布时间：2018-03-24 04:10

本文选题：预应力锚索复合土钉支护　切入点：砂卵石地层　出处：《中国地质大学（北京）》2014年博士论文

【摘要】：基于土钉支护技术而发展起来的预应力锚索复合土钉支护技术充分结合了土钉支护技术和预应力锚索支护技术的优点，已在基坑支护工程中得到广泛应用。但是目前该技术多应用于粉土、粘土等粘性土地层，而在砂卵石地层中的应用和研究则相对较少，理论明显滞后于工程实践。为此，论文针对这一问题进行了较为深入的研究，所开展的主要工作及研究成果如下：（1）在对典型工程实例进行分析的基础上，采用理论分析、现场试验和监测及数值模拟等多种方法对砂卵石地层中的预应力锚索复合土钉支护技术设计理论及方法进行了全面而深入的研究。认为在砂卵石地层中进行基坑预应力锚索复合土钉支护设计时应对砂卵石地层取非零的粘聚力（或结构力），这样不但可以大大减小支护工程量，而且亦能保证施工安全。（2）基于莫尔-库仑强度理论讨论了砂卵石地层的抗剪强度，认为对于砂卵石地层，其固有的结构力（咬合力）及摩阻角是描述其抗剪强度的重要参数，应该且必须在设计中予以考虑。同时通过现场直剪试验，对砂卵石地层强度参数进行了原位测试，认为砂卵石地层的粘聚力与其在天然状态下的密实度、结构性等密切相关，建议取为3~10kPa。（3）基于土钉支护设计中的土体准粘聚力理论，认为由于土钉支护而形成的复合土体，其粘聚力较原位土体将会有所增加，并推导了相应的准粘聚力计算公式。（4）采用FLAC3D数值方法对砂卵石地层中预应力锚索复合土钉支护机理进行了研究，，认为砂卵石地层的粘聚力对基坑边坡位移有重要影响，随着砂卵石地层粘聚力的增加，基坑边坡土体位移迅速减小。预应力锚索的施加可以明显改善土钉受力，减小基坑边坡位移。（5）通过对砂卵石地层基坑工程中的土钉、锚索内力的现场监测结果表明：土钉及锚索受力都出现沿其长度先增大后减小的趋势，且随着基坑开挖深度的增加，其受力亦出现先增大而后减小的现象。同时对比分析了砂卵石地层粘聚力取零与非零两种情况下的设计与计算结果，表明当取粘聚力为非零值时，实际监测结果与计算结果更为接近，从而说明了在砂卵石地层中粘聚力取非零值的合理性。（6）以实际基坑工程为背景，采用数值试验的方法讨论了砂卵石地层粘聚力取值大小对基坑边坡土体位移、锚索及土钉受力和土体塑性区的影响。结果表明随着砂卵石地层粘聚力的增加，基坑边坡土体位移及支护结构受力明显减小，但其减小幅度随粘聚力的增加而逐渐变缓。
[Abstract]:Based on the soil nailing technology, the prestressed anchor cable composite soil nailing support technology combines the advantages of soil nailing support technology and prestressed anchor cable support technology. It has been widely used in foundation pit support engineering. But at present, the technology is mostly used in clay and silt layer, but the application and research in sandy pebble stratum is relatively few, and the theory is obviously lagging behind the engineering practice. The thesis has carried on the thorough research to this question, has carried on the main work and the research result as follows:. 1) based on the analysis of typical engineering examples, theoretical analysis is adopted. The design theory and method of prestressed anchor cable composite soil nailing supporting technology in sandy pebble stratum are studied comprehensively and deeply by field test, monitoring and numerical simulation. It is considered that foundation pit is carried out in sand pebble stratum. In the design of composite soil nailing with prestressed anchor cable, the cohesive force (or structural force) of sand pebble stratum should be taken as non-zero, which not only can greatly reduce the amount of support engineering, And can also ensure construction safety. (2) based on Mohr-Coulomb strength theory, the shear strength of sand pebble formation is discussed. It is considered that the inherent structural force (bite force) and friction angle are important parameters to describe the shear strength of sand pebble formation. It should and must be taken into account in the design. At the same time, the in-situ testing of the strength parameters of the sand pebble formation is carried out through direct shear tests in the field. It is considered that the cohesion of the sand gravel formation is closely related to its density and structure in the natural state. It is suggested to be 3 / 10 KPA. 3) based on the theory of quasi-cohesive force of soil in soil nailing design, it is considered that the cohesive force of composite soil formed by soil nailing support will be increased compared with that of in-situ soil, and the corresponding formula for calculating quasi-cohesive force is derived. The FLAC3D numerical method is used to study the mechanism of prestressed anchor cable composite soil nailing support in sand pebble strata. It is considered that the cohesive force of sand gravel stratum has an important effect on the displacement of foundation pit slope, and with the increase of cohesion force of sand pebble stratum, the soil nailing support mechanism of prestressed Anchorage cable in sand pebble formation is studied. The soil displacement of excavation slope decreases rapidly, and the application of prestressed anchor cable can obviously improve the stress of soil nailing and reduce the displacement of slope of foundation pit. The field monitoring results of the internal force of anchor cable in sand pebble foundation pit show that the stress of soil nailing and anchor cable increases first and then decreases along with the length of soil nailing, and increases with the increase of excavation depth of foundation pit. At the same time, the design and calculation results of the cohesive force of sand and pebble strata with zero and non-zero are compared and analyzed. It is shown that when the cohesive force is taken as non-zero, The actual monitoring results are closer to the calculated results, which shows the rationality of the non-zero cohesive force in the sandy pebble formation. (6) based on the actual foundation pit engineering, the numerical test method is used to discuss the influence of the cohesion of sand and pebble stratum on the displacement of the soil mass of the foundation pit slope. The results show that the displacement of soil mass and the force of supporting structure decrease obviously with the increase of cohesive force of sand pebble stratum, but the decrease range of soil displacement decreases gradually with the increase of cohesive force.
【学位授予单位】：中国地质大学（北京）
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU753

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