Stability Of Large-Span Tunnel Construction In Loess Ground

ABSTRACT:For the problem on stability of surrounding rocks of large-span loess tunnel, summarized past studies on stability of tunnel surrounding rocks:Surrounding rock’s instability causes, failure modes and failure criteria. Compared with theoretical analysis, numerical simulation and on-site monitoring method for the study of surrounding rock stability of loess and stability under the condition of considering the reinforcement, through the comparison and analysis, the main research results are shown below:(1) Summarized the influence factors of the stability of surrounding rock, failure mode and failure criteria systematically, especially the summary and analysis of instability of surrounding rock damage cases under the condition of containing groundwater. It is concluded that the stability of surrounding rock and the water content, factors such as the depth of the relationship.(2) By analysis of the ground reaction curve in loess tunnel, by collecting the data fitting loess absorption curve, to deduce the deformation solution in theory and to fix the model parameters; then consider the effects of the ground reaction curve and the longitudinal deformation profile under the condition of different water content and different depth; combination of the ground reaction curve and the longitudinal deformation profile, made a representation of loess tunnel surrounding rock deformation time-space effect.(3) In view of the large-span loess tunnel support, according to the calculation method of shell mechanics, the mechanics model of the early composite supporting structure made up of sprayed concrete and steel frame in the circular cross section tunnel is deduced, through the numerical calculation of ABAQUS to verify the accuracy of the models. For a variety of factors that affect the effect of early are analyzed; and the local effect model of steel frame is established, raised in the case of equivalent stiffness of steel frame at the beginning of sphere of influence.(4) According to the on-site monitoring data, obtained early stress and deformation law of large-span loess tunnel, illustrates the rheological properties of loess tunnel with a clear; The stress of the supporting structure in space is not uniform, it can be seen similar with the actual engineering through the comparison of numerical simulation and should be considered in the design of the tunnel.