Study On Mechanical Properties Of Back Filling Layer And Its Influence On The Loads Of Shield Tunnel With Large Cover Depth

With the construction of transportation infrastructure such as highway,railway and urban rail transit in China gradually advancing from shallow to large depth,shield tunnel is gradually constructed in large cover depth more and more.However,due to the few engineering cases at present,few studies on the mechanical properties of the backfill layer and the loading characteristics of the segments of the shield tunnel under the condition of large cover depth are available for reference.Therefore,this study has important theoretical significance and engineering value.Based on the Donghuan Tunnel of Guangzhou-Foshan Loop Line,direct shear test of backfill layer,mechanical properties test of surrounding rock,theoretical analysis and numerical simulation are carried out,the mechanical properties of different back fill layers for large cover depth shield tunnel is investigated.The main work and research results are as follows:(1)Through on-site sampling and indoor sample preparation,direct shear tests are carried out to investigate the compression and shear properties of bean gravel grouting layer under two compactness,two particle sizes and four bean gravel contents;(2)Based on the compression and shear characteristics of bean gravel,the numerical model of bean gravel backfill layer is established by using the discrete element method,and the effects of compactness and particle size on the macroscopic mechanical parameters such as elastic modulus,poisson’s ratio and internal friction angle are analyzed;(3)Based on the compression and shear characteristics of bean gravel grouting layer and the theory of cellular automata,the finite difference model of bean gravel grouting backfill layer is established through the self-written conversion interface program,and the effects of bean gravel content on the macroscopic mechanical parameters such as elastic modulus,poisson’s ratio and internal friction angle of the backfill layer are analyzed;(4)Based on the physical and mechanical parameters of surrounding rock and the macro mechanical parameters of the backfill layer obtained from indoor test and numerical simulation,the numerical model of the whole process awalys is on segment linings is established against construction and operation period,the effects of the type,compactness,particle size,content of bean gravel and thickness of backfill layer on the mechanical performance of segment structure for shield tunnel with large cover depth are analyzed,and the stress and deformation characteristics of segment structure under uneven bean gravel filling and grouting defects are proved.