The Theory Of Composite Soil Nailing Technology In Deep Excavation Project And Its Application

With the development of urban construction, skyscrapers are coming forth and under-ground spaces are exploring continuously, more and more deep excavation projects appear and the problems of engineering technology become complicated accordingly. As a in-situ reinforced technelogy, soil nailing support technology has advantages of short-time construction cycle, easy operating, high adaptability and safety and low-price and so on. However, the prestressed rock bolting has advantapes of resisting fall-down, controlling deformation and preventing earth-shear and so on. Both of them are combined and compensated with each other, the safety and economy aim of deep excavation support projects will come true. Therefore, composite soil nailing support technology contained prestressed rock bolting and soil nailing is analyzed.Firstly, the work mechanism and effect of prestressed rock bolting and soil nailing are analyzed deeply, then the analysis of their effect is obtained on the basis of connection with the factors which inclued ground water level, rock quality, length of soil nailing, distances between soil nalings, angle of nailing, shotcrete layer, pressure grouting of rock bolting and forms of rock bolting and so on. The designing and calculating method of deep excavation support projects with composite soil nailing support technology supported is put forward.Secondly, in order to search the most dangerous slip surface of the deep excavation supported by prestressed composite soil nailing, based on the traditional exhaustive searching method and combined with engineering practical condition and utilization of plane geometric knowledge, geometric parameter controlling method is put forward and the solving formula for the location of the most dangerous slip surface is obtained. A new calculation method for determination of the most dangerous slip surface is established.Besides, according to the demands of feedback design and construction with deformation monitoring in the deep excavation support, the deformation prediction method of composite soil nailing wall on the basis of Verhulst prediction model is put forward and applied to the deformation prediction of some pretressed composite soil nailing supporting project. The results show that the calculation value agrees well with the measured one and the correctness and rationality of prediction model in the paper are verified.Lastly, based on considerarion of factors which include the characteristic of soil including non-elasticity, anisotropy, high variability along with the environment and time and so on and uncertainty of exterior load and environment change and deficiency of the design theory itself, the concept of dynamic design of the support scheme in the composite soil nailing support design according to the results of field monitoring and test is put forward, and combined the engineering practice, the method of field monitoring and test is discussed.