Stability Analysis And Numerical Simulation Methods Research Of Prestressed Anchor Composite Soil Nailing Support

In recent years, with the great development of the urban constructions, municipal engineerings are being built, and the scale of the underground space is expanding constantly too. The deep foundation pit of the skyscraper is increasing greatly. Because of the dense of the urban building, the places that the deep foundation pit of the skyscraper can be made used of is becoming narrower and narrower, as a result the cost spent on construction and support technology are increasing year by year. In this case, a kind of economic and efficient support method is required in deep foundation pit bracing engineering.The composite soil nailing system not only takes over many advantages of soil nailing system, such as construction speed and low engineering cost, but also remedies a number of defects, for example the deformation of the foundation and so on. In many complex forms, pre-stress anchor composite soil nailing support for its economy and practical way in deep foundation pit, the surrounding environment and the geological condition, more complex cases have a unique advantage. At present, mechanism of force bearing situation of the composite system, principals of the failure mode are still not very clear. The actual design of the system is mainly based on the experience and checking, the phenomenon that the theory lags behind the engineering practice is obvious.The main programs studied in this thesis can be listed as follows.(1) The support characteristics of the pre-stress anchor composite soil nailing, the present applied situation and the common design method was summarized;(2) The model test method was used to simulate excavation support and loading damage, and some measuring element s were used to record the displacement of foundation pit wall, soil nail (anchor) internal force, and to observe the position and development foundation pit crack state;(3) FLAC3D software was applied to simulate excavation support and loading destruction numerical mode of the foundation pit. From the aspects of the mechanical characteristics of soil nail, excavation deformation characteristics and loading failure mode, mechanical properties and stability models of the prestressed anchor composite soil nailing support were discussed;(4) Results of the model test and numerical simulation of operation were summaried, draw the mechanical mechanism of the pre-stress anchor composite soil nailing support, and then the reasonable design method of the pre-stress anchor composite soil nailing support was given.The main research conclusion of this paper are summarized as follows.(1) Prestressed anchor composite soil nailing support can effectively control the pit wall displacement, has greatly improved the foundation pit "drum belly" phenomenon;(2) Prestressed effective control of the soil displacement is realized mainly by the transmission through the surface, the influenced scope produced by which is limited;(3) In the support way of prestressed anchor composite soil nailing, the axial force close to the anchor of soil nailing when compared to common soil nailing support evidently decreased, by the contrast, the axial force away from the soil nailing is increased;(4) Exerting influence on the anchor can be influenced the potential location of slide surface, the upper portion of the soil nailing support in the soil there may exist two potential sliding surface;(5) The location of the failure mode of the prestressed anchor composite soil nailing support is different from that of common soil nailing support, the former’s failure mode is located the upper part of soil nailing support;(6) Pre-stress anchor can produce compressive zone in the soil, which can effectively control plastic zone scope of soil body, when the foundation pit destroyed the plastic zone did not reach the breakthrough;(7) The safety coefficient of the prestressed anchor composite soil nailing support is higher than ordinary soil nailing support;(8) When making the design of the pre-stress anchor composite soil nailing support, the two potential existing slide surfaces in the upper part of soil nailing soil supported by the anchor should be considered seriously.(9) The stability analysis method of pre-stress anchor composite soil nailing support based on the experiment and simulation data is reasonable and reliable.