| Weiyuan--Wudu Expressway Muzailing Tunnel field area has extremely developed folds and faults,and the tunnel passes through 11 fault fracture zones.The surrounding rock in the fault fracture zone is weak and broken,with poor self-stability,high ground stress and other adverse geological conditions.In order to effectively control t-he surrounding rock deformation of the tunnel in the fault fracture zone,ensure the s-afety of the construction personnel,reduce project investment,and accelerate the prog-ress to ensure the completion on time,this paper combined with the field displacement monitoring data and applied the methods of numerical simulation and comparative a-nalysis to carry out the following studies:(1)Study on the controlling factors and evolution mechanism of large deformation in fault fracture zone,conclusion:(1)Large deformation is controlled by rock mass p-roperties,rock mass structure,tectonic stress environment and groundwater seepage;(2)The evolution mechanism of large deformation of surrounding rock is mainly the pl-astic flow of soft rock,the flexure of thin layered surrounding rock,the structural rheology,and the capacity enlargement.(2)Based on the geological survey and engineering design data of muzhailing tunnel,MIDAS/GTS software was used to carry out the simulation calculation of four excavation methods,including the annular excavation with core soil retaining method,the three-step method,the middle partition method and the double-sidewall excavation method.Different excavation methods are used to analyze the variation of the settleme-nt of the arch roof and the horizontal convergence of the side wall with the construc-tion step.Conclusion:(1)The end face deformation degree is greater than the target palm face;(2)Arch settlement palm surface first displacement accounted for the proporti-on of the total deformation of the ring excavation retaining core soil method of abou-t 35%,three steps method of about 26%,the middle wall method of about 13%,the double side wall guide pit method of about 6.8%;The proportion of the leading disp-lacement of the convergent palm surface of the boundary wall to the total deformatio-n is 16% for the annular excavation method,25% for the three-step method,19% for the middle partition method,and 12% for the double-side wall guide pit method.(3)Comparative analysis of different excavation methods target palm surface extrusion displacement value and distribution.Comparison of values: the core soil method for ring excavation is the largest,and the double-sidewall excavation method is the smallest.The position where the maximum value of the palm surface appears: the circular excavation retaining core soil method is located in the upper left corner of the lower rightstep,the three-step method is located in the core area of the middle step,the middle partition method is located in the upper edge of the lower step of the left guide pit,and the double-side wall guide pit method is located in the core area of the upper mi-ddle step.(3)The main stress of the initial support in the fault fracture zone in the high i-nsitu stress environment is large after the tunnel is completed,and the supporting tim-ing and parameters of the initial support need to be optimized.(4)The four excavation methods in the equivalent plastic strain area all have th-e form of smaller arch and side wall and larger tunnel bottom.The plastic zone of t-he method is small and the expansion rate is slow.(5)Based on the calculation of excavation method,the single-layer advanced sm-all pipe grouting model with different length,different ring grouting range and differe-nt pipe diameter parameters was established,and the control effect of single-layer adv-anced small pipe with different parameters on the vault settlement and the extrusion displacement of palm surface was analyzed.When the Angle of extrapolation is 10°、5 m in length,grouting range 150 °,42 mm diameter phi advance ductule control effect is good,by 20.06%,compared with no forepole vault subsidence displacement c-onstraints extrusion by 51.64%. |
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