| Tunnel in sandy soil possesses the characteristics of low cohesion and granular mixtures. The collapse of tunnel in sandy soil abrupt, unremitting and sensitive to disturbance. There is an obviously shortage of continuous medium assumption for the study of tunnel in sandy soil, therefore, it is necessary to conduct the research by micro analysis to get an extensive knowledge of its stability, based on which the macro structure and its safety are assessed further.Firstly, a micro structure model of soil particle is established by the micro analysis. Then quantitative relation is put forward between sand parameter in microscopic dimension and structure strength in macroscopic dimension. A failure criterion of sand mass is proposed from the view of micro analysis. Secondly, based on the contact mechanics of sand particles, the mechanics and scope of disturbed zone are elaborated. Then the paper presents its application method and sensitivity analysis in detail. Thirdly, the paper lucubrates the macro structure stability of sandy tunnel and initiate the concept of composite-arch structure. As to the concept, the paper specified its evolution law, stability criterion and influence factors. Finally, the paper obtained the reinforce rule of tunnel in sandy soil, focusing on grouting, feet-lock bolt and self-adjust support. The main conclusions are listed as follow.(1)There is a close relation between macro collapse and micro structure of surround sandy soil. The concept of bearing factor of shear stress is put forward through the research of sand particle. The significance of the factor is that it links the parameters of micro structure and macro structure. Two models,"wedge-roll" and "wedge-plastic hinge", are proposed based on the concept. The micro model reveals that the shear failure of sandy soil is the result of stress redistribution and particle rearrangement. During this process, the friction angle decreases and the interior stress becomes averaged, and the bearing force of shear surface increases at beginning and then decreases.(2)Except shear failure of soil, which is common in tunnel structure, the soil mass can get damaged due to local instability of soil particles. In the case that the cohesion is low, the local instability of particles even common than shear failure. The scope and shape of disturbed zone is mainly determined by the following four factors:cohesion force, internal friction angle, factor of lateral pressure and external load. The shape of disturbed zone is sensitive to the factor of lateral pressure, and the scope is determined by the other three parameters mainly.(3)The characteristics of sandy soil surrounding tunnel can be described by composite arch. The evolutionary law of composite arch corresponds to the three damage mode:1) the upper soil collapses and the arch moves upward;2) arch springing get instable and the arch get wider;3) the lower soil slipped and the arch get higher and wider. The paper designed a search algorithm based on the theory chain reaction. The algorithm can find the potential slip zone below tunnel. The algorithm can be controlled by the number of divergent points, divergent direction and spread distance, which guarantees the efficiency of the algorithm.(4)The failure characteristics of sandy soil surrounding tunnel has much to do with its micro structure. Hence, the reinforce measure to stabilize soil should take the character into consideration. Among the various reinforce measure, grouting,feet-lock bolt and self-adjust support are considered quite effective. The paper designed a self-adjust support. This support possesses self-adjust ability and is insensitive to the installation time, therefore, the support obtained a higher preliminary stiffness and a stable tunnel structure later. |
PDF Full Text Request