Study Of Mechanical Response On Adjacent Tunnel In Processes Of Foundation Excavation

With the ever-increasing of comprehensive development and utilization of groundand underground space, more and more deep excavations are adjacent to the existingtunnels. The conflict between the foundation pit engineering and the underground tunnelbecomes more and more serious, which has become the focus problem of cityconstruction. The adjacent excavation will no doubt induce the deformation of soil layer,then result in the internal forces and displacement of the tunnel, and threaten greatly thesafety of tunnel. Therefore, how to correctly evaluate the impacts of excavation offoundation pit on the inner force and deformation of existing tunnel is an importantsubject which needs to be solved quickly in this complex environment condition. Basedon the plan of Changjiang Scholar and Innovative Groups for the geotechnicalengineering of mountainous area（NO. IRT1045）), this paper has been analyzed bytheoretical analysis, numerical simulation and model test. The main contents of thispaper as following:①The statistics cases have been collected in which the foundation pits areadjacent to the existing tunnel. By using data statistical method, the influential factorsare classified, such as the overview of foundation pit engineering, relative distancebetween the foundation pit and tunnel, supporting structure, reinforcement, space-timeeffect, underground water, etc. Then, according to the statistics chart and data, thedeformation characteristics of the nearby tunnel caused by excavation of deepfoundation pit can be analyzed and summarized systematically.②The displacement effect due to the surrounding wall soil unloading of adjacentexcavation is not considered by the theoretical analysis method. Based on the principleof equivalent stiffness of continuous model, the horizontal and vertical additional stressis calculated by the Mindlin solutions. Furthermore, the tunnel structure is considered asthe beam with infinite length. The additional stress is imposed on the Winkler modeland the governing equation is built up on the adjacent tunnel structure. So the influenceof foundation pit excavation of subway tunnel will be estimated.③Through the indoor model test, the relative horizontal and vertical distancesbetween the foundation pit and adjacent tunnel are adjusted. The impact of excavationof foundation pit on the bending moment, soil pressure and internal diameter of exitingtunnel is analyzed, and change rules of inner force and deformation of adjacent tunnel during the excavation of foundation pit are studied.④According to the lagrange finite difference method, the incremental and iterativecalculation format of the hardening soil model is derived in detail. The update stressalgorithm of shear yield surface is given. Based on the secondary development programprovided by FLAC^3D, VC++programming language is used to realize the calculationprocess and compile into dynamic-link library files which is loaded and invoked. Finally,the model calculation results are compared with soil measured test results to prove thecorrectness and reasonableness of the secondary development program.⑤By adopting the developed HS model and on the basis of the model tests of theimpact on the existing tunnel by excavation of foundation pit, the numerical calculationmodel is established. Compared the value with the test result, the impact of thefoundation pit excavation on the existing tunnel is analyzed. According to the deepexcavation adjacent to the tunnel with soil combination, and the developed HS model isadopted to simulate the excavation. The difference between tunnel and no tunnelcondition is compared. So the affected degree of the deformation of the foundation pitand the underground tunnel structure is comprehensively realized. And the internal forceand deformation of existing underground tunnel affected by deep foundation pit areanalyzed.