Study On Geotechnical Engineering Problems Of Large Section Underground Excavation In Combination Of Soil And Rock Formation

Based on the engineering background of the underground excavation section of Xuzhou Metro Line 1 and Line 2 super-large transfer station-Pengcheng Square Station,combined with relevant geotechnical engineering problems,such as the weakening of surrounding rock stability by vibration wave in mining method,the geological hazards that may be induced by the excavation of group caves,the collapse and roof fall problems easily caused by the construction of soil-rock interface,this paper summarized the construction schemes on site.Applying numerical simulation and field measurement to evaluate the rationality of the scheme,analyze the stability of surrounding rock under dynamic and static loads,and guide engineering practice.The main results and conclusions of this paper are as follows:(1)The hydrogeological conditions and surrounding environment of the underground excavation project was summarized by investigating the field datas,which indicates the key and difficult points of the geotechnical engineering problems in the underground excavation construction.(2)Vibration velocity of ground particle caused by blasting vibration wave was obtained by three-dimensional numerical calculation and field measurement,as the same time,sadovski formula was modified by regression analysis.The attenuation law of particle vibration velocity at soil-rock interface was summarized,and the reasons for the difference of vibration velocity waveforms of different particle were analyzed.The dynamic response of support structure under dynamic load is obtained by tracking the change process of pressure stress circle and tension stress circle of initial support structure after initiation,which reveals the rationality of blasting parameters and puts forward suggestions for vibration reduction.(3)Through summarizing the excavation schemes of group caves,considering the constraints of construction sequences and assuming two other construction schemes,using numerical simulation method to analyze the ground settlement and convergence of tunnel inner perimeter caused by the three schemes,it was found that the first scheme is more reasonable.Among the construction stages,the construction of the right line tunnel contributes most to the ground settlement,and some support suggestions were put forward for the construction of the underground excavation in this stage.In this paper,through monitoring the displacement values of surface observation points in representative sections by field measurement,the three stages of ground settlement are summarized,and the settlement laws and corresponding supporting measures in each stage are summarized.The stress variation of rock mass under the construction of scheme 1 was analyzed,and the maximum stress concentration area was obtained.(4)Using numerical simulation and field measurement methods to analyze the surface settlement,clearance convergence and vault settlement under pre-support conditions,it was founded that advanced tune shed and leading conduit technology can improve the characteristics of surrounding rock and reduce the engineering risk caused by undermining construction at weak joint.Through the analysis of temporal curve,the law of stratum subsidence under this geological condition is obtained,and the poor selfstabilization ability of surrounding rock is revealed,which can guide engineering practice.