Study On Dynamic Interaction Of Newly-built Underground Structure Dynamic Loads To Existing Subway Shield Tunnels

The current rapid development of urban rail transit,subway as an important part of its superiority embodied in time,space,economy and many other aspects.While vigorously developing underground space,new underground facilities had to cross adjacent existing tunnels,causing overlapping of multiple tunnels.On the one hand,the difficulty in construction is extremely high.On the other hand,the dynamic load of the train during operation will also have an adverse effect on the structure of the adjacent tunnel,the foundation soil and the ground facilities.At present,there are few studies on the dynamic response of the tunnel under vibration loads and its effect on close-distance overlapping tunnels.This paper uses theoretical analysis,on-site and laboratory tests,and numerical simulation methods to make close contact with vibration loads.The dynamic response of the tunnel structure was studied in depth.At the same time,the long-term settlement of the tunnel under dynamic load of subway and automobile was analyzed.The main tasks are as follows:(1)The dynamic responses of tunnels and subways with domestic and international dynamic loads,the long-term settlement of tunnel structures under cyclic loading are reviewed and summarized,and the main problems existing in existing studies are summarized and analyzed.(2)Summing up the dynamic characteristics of the main engineering of Suzhou foundation soil,the soil dynamic parameters such as shear wave velocity,dynamic shear modulus and damping ratio of the engineering site were obtained through wave velocity test,resonance column test and indoor dynamic triaxial test..(3)By using theoretical analysis and numerical simulation methods,the dynamic response analysis of the tunnel structure under close dynamic load is studied.Studies have shown that: 1 For the tunnel with dynamic load,the acceleration response amplitude is arching> arching> vault,and the adjacent tunnel affected by vibration transmission,the acceleration value is one order of magnitude smaller than that of the dynamic load;The acceleration response law in the tunnel axis direction reflects the vibration from near and far,and the energy decays gradually;3 The key to the tunnel structure is still the initial stress under the action of the gravity field.The additional stress increment after the dynamic load is applied is tiny.,less than 10% of the initial stress;4 due to the integrity of the tunnel structure,dynamic load after the deformation of the tunnel section of the measurement point is basically the same;5 for orthogonal or parallel up and down close tunnel,when the upper and lower trains pass at the same time,Because the time,frequency and amplitude of the two actions are similar,they will cancel each other when the waves are transmitted towards each other,resulting in a decrease in stress increment and acceleration at each measurement point.(4)Based on the engineering geological conditions of the project,a finite element model of the dynamics of the subway train under cyclic loading was established,and the long-term settlement deformation of the tunnel structure was analyzed.For the cyclic load of subway,the cumulative settlement rate in the first 15 days is extremely fast.In the operating time of nearly one year,the cumulative settlement of the tunnel has reached 80% of the final steady state.Therefore,in the actual monitoring,special attention should be paid to the Deformation in the first year of settlement.