【作者】 熊宗喜；

【导师】 王成彪； 刘红岩；

【作者基本信息】 中国地质大学（北京） ， 岩土工程， 2014， 博士

【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。更多还原

【Abstract】 The prestressed anchor cable composite soil nailing supporting technology is developedfrom the soil nailing supporting technology fully combines the advantages of the soil nailingsupporting technology and the prestressed anchor cable supporting technology, which is widelyused in foundation pit supporting engineering. But now it is often used in cohesion strata such assilt and clay, and its application in sand and gravel strata is rather little, in which the theoryevidently lags behind the practice. Therefore, further study is fouced on this subject, and themain works undertoken and the research results are as follows.(1) On basis of analyzing the typical engineering examples, the overall and further researchon the design theory and method of the prestressed anchor cable composite soil nailingsupporting technology in sand and graval strata is done by means of theoretical analysis, fieldtest and monitoring and numerical simulation. It is concluded that the non-zero cohesion orstructure force should be given to the sand graval strata in foundation pit prestressed anchorcable composite soil nailing supporting design, which can not only greatly reduce the supportingquantities, but also ensure the security of the construction.(2) The shear strength of the sand and graval strata is discussed based on Mohr-Coulombstrength theory, and it is regarded that the inherent structure force (interlocking force) andfriction angle are the important parameters in describing its shear strength to the sand and gravalstrata, which should be considered in the design. The strength parameters of the sand and gravalstrata is tested in situ through the direct shear test. It is regarded that the cohesion of the sand andgraval strata is much related to the its density and structure characteristic, and it is suggested tobe3~10kPa.(3) Based on the quasi-cohesion theory in the soil nailing supporting design, it is regardedthat the cohesion of the composite soil formed by the soil nailing supporting will increase, andthe calculation formula of the quasi-cohesion is deduced.(4) The prestressed anchor cable composite soil nailing supporting mechanism is studied bya numerical code——FLAC3D. It is concluded that the cohesion of the sand and graval strata hasmuch effect on the displacement of the foundation pit slope. With increase in its cohesion, thedisplacement of the foundation pit slope rapidly decreases. The existence of the prestressedanchor cable can evidently improve the soil nailing’s force, reduce the displacement of thefoundation pit slope.(5) Through the field monitoring of the force of the nails and anchor cables of thefoundation pit in sand and graval strata, the results show that the force of the nails and anchorcables firstly increase and then decrease along with its length, and the same phenomenon also occurs with the excavation of the foundation pit. By comparing the design and calculation resultsof these two conditions with the cohesion of the sand and graval being zero and non-zero, itshows that the actual monitoring results is in more agreement with the calculation result whenthe cohesion is non-zero. It shows the rationality of the non-zero cohesion of the sand and graval.(6) Taking the actual foundation pit engineering as an example, the effect of cohesion of thesand and graval on the displacement of the foundation pit slope, the force of the anchor cablesand soil nailings and the soil plastic zone is discussed by numerical method. The results showthat the displacement of the foundation pit slope and the force of the supporting structureevidently decreases with the increase in cohesion of the sand and graval strata, while its decreaseextent gradually becomes flat.更多还原