Researchon Surrounding Rock Large Deformation Characteristics And Chamber Enlargement Support In TBM Block Tunnel Section In "Yindajihuang" Project In Qinghai Province

Surrounding rock mass deformation is a common type geological disastersoftunnels and underground works,which likely to cause construction difficulties,damageto equipment, delay the construction period, the increase in projectinvestment.Yindaji-huang water supply project constructed by hard rock double shieldTBM.Across the southern margin fault zone of Dabanshan, there was a serious bigwall rock deformation, resulting in boring interrupt and block at the Stake numberCH16+775.Combinedwithconstruction it’s necessary and urgent to carry outsystematicrock mass large deformation investigation,testing analysis andexperimental research.On this basis,from the aspect of themechanisms、types andsupport to carry out a thorough and systematic study on the comprehensive preventionand control of large deformationis very import for repair and start TBM In addition,the study of great significance for ensuring construction quality and safety, shorten theconstruction period, design optimization, and can gain experience in thecomprehensive prevention and control of the big deformation and provide a referencefor other similar projects.This paper describes the geological conditions of the yindajihuang water supplyproject tunnel in dabanshan south margin fault zone,on the basis of Summarying ofthe surrounding rock failure mode characteristics,combined with the rock massengineering propertiesthe test results we identified the large deformation mechanism.The rock mechanics of linear elastic and elastic-plastic theory is being useto analyze and predict deformation of surrounding rock,surrounding rockdisplacement field of the stress field and plastic zone distribution simulated by thenumerical method,based on the above two points,this paper evaluated the supportprogram on surrounding rock large deformation. then developed the monitoringmeasurement and feedback program on problems that may occur.Mainly thefollowing results:1.TBM block tunnel section in yindajihuang water supply project is located in thesouthern margin fault zone in dabanshan,construcion reveal the nature of rock mass ispoor, laboratory tests show the TBM block section surrounding rock in addition to thelow strength and high content of clay minerals in its mineral composition. high freeexpansion show high expansion potential.2. Southern margin fault zone in dabanshansurrounding rock deformation andfailure mode are the plastic flow of soft rock, plastic wedge extrusion, collapse anddebris flow like mud and water mixture;Large deformation and its development arerelated to high field stress, swelling, rock structure, groundwater etc.According tothese analysics,it was considered that TBM block section large deformationmechanism are high field stress,soft rock plasticitythe flow,soft rock expansiondeformation and plastic wedge shear slip;or the composite of these three ways.3. By verifying the parameters of surrounding rock by the elasto-plastic analysistheory, we can conclude that the calculation results and actual conditions is close inconsideration of the simplified calculation model, so it is reasonable to select thesurrounding rock parameters.4.Using the numerical simulation method to simulate the stress and deformationof the burrowed segment, The calculated results is broadly in line with the actualsituation. Based on the results,we simulate spread-dig construction，Calculated resultsshow that The deformation values can reach1.39m and the thickness of the destroyedareas is about9.7-12.5m in the condition of the surrounding rock stress release fully.Ifthe surrounding rock can’t be shored up timely,it will happen very seriousdeformation and failures.5. The large deformation surrounding rock Support is on the basis of mechanicalmechanism analysis in order to control plastic circle of generation, to constantlyimprove and optimize supporting design by connecting the whole procedure, such as supporting design, construction and monitoring feedback. Monitoring measurementplays an important role in the process of surrounding rock mass deformation support.6.the support design of spread-dig construction use self-feeding anchor rod,steelgrid and thick layer of sprayed concrete as the main stress structure.throngh make useof grouting, advance pipe lodgepole and drainage pipe to improve broken degree ofsurrounding rock to achieve the timbering beforehand methods.at the sametime,install deformation groove to release the stress of surrounding rock to Reduce thestress of the support structure.In the practice,some problems may be arise,such as thelarge deformation of surrounding rock, Insufficient stiffness of the support structure,tosolve the problems,we install convergence meter, Bolt stress transducer steel-stringtransducer, strain gauge to monitor measuration and feedback for analysis to ensurethe security and stability of the project construction and operation.