Mechanical Response And Its Control Of Overlying Existing Underground Structure With Shallow Tunnel Construction

ABSTRACT:With the increase of rapid urbanization, urban underground space development, dominated by urban railway construction, has gone into climax. In the construction of urban underground engineering, a series of factors-complexity of the urban environment, closely-located line networks and the sequence of construction time makes the undercrossing between tunnels inevitable. The engineering safety problems mainly manifested in two aspects:the safety of engineering structure itself and the safety of surrounding environment. Relatively, environment security problem is more outstanding, which becomes the core content of crossing engineering. Therefore, focusing on the effect and its control of existing underground structure with crossing shallow buried covered excavation has great realistic significance.Base on the data of No.4,5,9,10and the airport subway line and more than ten closely-located municipal pipelines in Beijing, the deformation rule and the interactive mechanism is investigated by the method of statistics, theoretical analysis, numerical simulation and. The paper achieved the following results(1) Analysis the deformation rule of existing underground structure through field measurement in Beijing:On the whole, the deformation of existing structure presents a flexible feature and can be described by Peck formula. Nevertheless, from the deformation the pipes between movement joints, rigid motion characteristics dominate, where the forms mainly include whole settlement, rotation and deflection.A pipeline connected by several underground pipes presents a "chained" feature, which is similar to natural strata deformation.(2) The analytical solution of strata displacement in a shallow buried circular tunnel is deduced by the image method and equivalent modulus layer method. Compared with the deformation of natural strata, existing underground structure’s vertical and horizontal deformation is smaller, but impact area is greater. The research results show that the stiffness of existing underground structure has impeditive and impeditive effect for ground deformation. Thus, the interaction relationship between new tunnel, rocks and existing underground structure is elaborated.(3) Based on the two phase method, the shape of deformed underground structure mainly falls into three categories-V, U and W. Among the three, the displacement of mode-V is large, the stress and the crack of that is the small, which just stand the opposite side of mode-U. As to mode W, the deformation, stress and crack are the smallest. The paper studied the contributing factors to the deformation and stress, including excavation area, spacing between tunnels, rigidity of existing underground structure and crossing angel.(4) The response mechanism and its evolution rule is revealed by the numerical method and the interaction theory of soil and structure, mainly from the following three aspects:the ground deformation makes the rock pressure reduced and frictional resistance force increased, then let the existing underground structure has the vertical and horizontal unbalanced forces, so the settlement, tilt, flexure and twist appeared in structure with lateral and longitudinal direction; the downward frictional resistance is an important part of unbalanced force, which not be neglected; because of time and space features of stratum deformation, the unbalanced force is evolutive, so the vertical and horizontal deformation of existing undergrong structure is dynamic change.(5) By adopting the combination of the measured data analysis and numerical simulation method, discusses the new tunnel construction methods, auxiliary construction methods, a new tunnel with both with the buried depth of underground structure, double hole spacing, underground structure stiffness, the newly built tunnel deformation crack position on the Peck formula experience parameters, the influence of the experience parameter correction formula is given. Combining empirical parameter correction formula and Peck formula, for both affected by wear under construction of underground structure deformation provides a simple and fast prediction method, and the effectiveness of the prediction method is verified by engineering examples.(6) On the basis of the above research results, the safety control technology is supplemented. The system of refined control in-process is established, which gained a successful application in actual engineering.