| The composite soil nailing systems, which can bear excavating loads, keep existing stress state of subsoil and prevent seepage of underground water, are composed of some structure measurements. This technique, characterized by being of many kinds of structure and having clear reinforcing aim, has been made widely application in excavation retaining engineering. It takes over many advantages of soil nailing system and remedies a number of defects and application restrictions of soil nailing system. Although some studies have been carried out, which provides a few of theoretical bases for applying the technique, knowledge of force bearing situation of the composite system is still not very clear, design of the system is short of necessary analysis methods and the theoretical system is imperfect. Improvements on theoretical analysis and study by experiment or field test may accelerate much more wide application of the technique, therefore, a great amount of project investment will be saved and both social and economic benefits will be achieved substantially.The main program of study aimed at several respects as follows.To begin with, structure types, constructing methods and using conditions for composite soil nailing were summed up and its working mechanism was analyzed.Secondly, a study of one kind of composite soil nailing, that is, a combination of soil nails with waterproof cement-soil mixing pile wall, was carried out by laboratory model test, the retaining structures were modeled according to a similarity rule that geometric length of the structure is in inverse proportion to deformation duration of the structure and the staged excavation and retaining was carried out during experiment to simulate actual construction procedures in situ. Ground subsidence, rebound deformation and horizontal deflection were measured, displacements inside the excavated slope were monitored and ground cracks and failure modes caused by extra excavation were investigated. Working mechanism of the composite system was described much more fully by means of analyzing of test data.Thirdly, Study on one kind of composite soil nailing, that is, a combination ofsoil nails with waterproof cement-soil mixing pile wall, were carried out by the theory of elastic foundation beam. The infinite-length elastic foundation beam model of the facing were analyzed in horizontal and vertical modeling. In order to calculate simplified, a new method , which internal forces of cross sections of the facing in vertical were studied by kinematical displacement, was proposed and the calculate formula of facing were derived from different situation and strength of the cross sections were designed and checked. The calculation indicate: the internal forces of facing in vertical model will be a control factor of design, the cross section tensile strength of cement-soil wall will govern strength of the facing and it is feasible that the proposed kinematical limit analysis method are used to analyze internal forces of the facing;Finally, general principles, requirements and main construction technique measurements were summarized by examining several typical cases of the composite system.The principal conclusions include:(a) the composite system is composed of both active-bearing structural members and inactive-bearing ones, being of a character of combination of rigid retaining structures with flexible ones, so its working mechanism will be behaved as sharing loadings, waterproof and impermeability, loading transfer, local reinforcement and pre-reinforcement;(b) the experimental results show that much more subsoil will participate in retaining action, soil stresses of internal slope will be shared uniformly and deflections caused by excavation will be reduced notably because of cooperation of nails and cement-soil mixing pile wall;and (c) the internal forces of facing in vertical model will be a control factor of design and the cross section tensile strength of cement-soil wall will govern strength of the...
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