Study On Application Of Composite Soil Nailing Wall In Deep Foundation

Composite soil nailing support to support different site conditions and geological conditions to local conditions, supporting the flexible combination of structure, which is economically viable, safe and reliable,so at home and abroad in the digging project has been more and more applications. And the national norms and procedures do not have the corresponding design and provisions of the composite soil nailing support, the current theoretical research technology is far behind the development of engineering practice, large model test and test data less, there are many problems worthy of study, design theory to further improve. Based on the example of the deep foundation pit support in Lu' an City,this paper uses the composite soil nailing technology combined with prestressed anchor and soil nail, and uses the three-dimensional fast Lagrangian difference method (FLAC3D) to consider the three-dimensional dynamic excavation support Process calculation model, deep foundation pit excavation support the whole process of numerical simulation analysis.Composite soil nail structure of the internal force and deformation of a detailed study of the performance. The main work and conclusions of this paper are as follows:(1) The formation and development of composite soil nailing support, the research status and the theoretical research results are discussed in a more comprehensive way. This paper summarizes the types of composite soil nailing and the advantages and disadvantages of various types and applicability.(2) The mechanism of composite soil nail is introduced, and the fixing mechanism of soil nail for prestressed anchor cable composite soil nail is analyzed. Based on the theory of classical earth pressure and uniform strength, the lateral earth pressure calculation model is used to calculate the trapezoidal distribution of large and small soil nailing walls. The computational model is a better way to describe the lateral earth pressure distribution in soil nailing walls. On this basis, the design and calculation of soil nails and anchor cables were carried out.(3) The internal force and displacement of soil nails and anchors were studied by field test and FLAC3D numerical analysis in combination with the composite soil nail support of foundation pit of Lu' an No. 3 foundation. The results show that:?the axial force of the soil nail changes with the excavation process of the foundation pit, which is distributed in the middle and two small branches. ?The axial force of the prestressed anchor is different in the free cross section and the anchorage section. After the prestressing tension is completed,there is a certain prestress loss, and then the distribution of the axial force along the length of the anchor is greatly reduced and gradually stabilized. ?The maximum horizontal displacement of the foundation pit of the prestressed anchor composite soil nail structure occurs at the side wall position of the foundation pit.?Compared with the potential fracture surface of the traditional soil nail, the potential fracture surface of the composite soil nail structure will move a certain distance. ?The results of FLAC3D simulation and the monitoring results of pit displacement are close, indicating that the model is established and the selection of parameters is reasonable in addition to the calculation method. The calculation results can reflect the deformation of deep foundation pit. Therefore, the field test and FLAC3D numerical calculation combined, can well reflect the deformation of the excavation process.The conclusion is that it has important theoretical and practical value for the design of the retaining structure of the foundation pit, the choice of the construction scheme and the determination of the deformation monitoring scheme of the foundation pit.