Study On Reinforcing Technique For Shield Tunneling Passing Alongside Weak Buildings

Due to the particularity of its passenger transport function,the urban subway must go through the urban centres during the process of site selection.However,there are usually a large number of old buildings(structures)in the urban centres,which have poor ability to bear further deformation and uneven settlement.Nowadays shield method is the main method of tunnel construction of subway.Although shield method has the characteristics of strong construction adaptability,there are still potential safety hazards in the construction when shield passes alongside weak structure buildings.If the construction is carried out in the adverse geological conditions,the risk will further increase.Therefore,reliable reinforcing measures must be applied to ensure the safety of buildings(structures).In the case of limited construction conditions,the traditional vertical isolation piles can not meet the requirements of construction,so reasonable and effective reinforcing methods are required.Based on the engineering of shield machines passing alongside the family building of the bus company in the Niuzhan West Lane of Taiyuan Metro Line 2,this paper puts forward the reinforcing measures for the shield passing alongside weak structure with a short distance when the site of construction is limited in the complex geological condition by the method that combines the numerical simulation with the field measurement,then makes a comparative study of the reinforcing effect,and expounds the mechanism of reinforcement.The main contents of this paper are as follows:(1)Calculate the settlement of the ground and buildings in the complex geological conditions by the finite element software,the laws of settlement during the tunnel excavation are obtained,and the main reasons affecting the settlement of the buildings are found.Aimming at the construction difficulties of the tunnel passing alongside the buildings in short distance and the reasons for the settlement of the buildings caused by shield construction,the reinforcing measures of micro anchor piles and radial active grouting are proposed.(2)In order to explore the reinforcing effect and mechanism of anchor piles,this paper studies the restraining effect of anchor piles arranged at different angles with the ground and at different horizontal distances frombuildings and tunnels for the settlement of buildings,the displacement laws of deep soil under different construction conditions as well as the settlement and side inclination of buildings are obtained by numerical simulation,the settlement after using the reinforcing measures of anchor piles are summarized and the best way of construction is selected.(3)In order to study the influence of setting time of grouting material,the weight of slurry and grouting range for construction when research the reinforcing effect of active grouting,the numerical simulation schemes of different setting time and grouting range of slurry are compared without considering the pressure of active grouting,and the construction conditions that are not conducive to the control of building settlement are excluded.At the same time the reinforcing laws of active grouting are obtained when consider the active grouting pressure,then the optimal grouting reinforcing scheme is proposed and the mechanism of active grouting reinforcement is analyzed.(4)The reinforcing effect can be maximized by combining the reinforcement of anchor piles with the reinforcement of active grouting,and the joint reinforcing scheme with construction economic and effectiveness is obtained,and the best balance between reinforcing effect and construction economic is achieved through calculation.(5)The reinforceming measures are applied to the practical project,and the measured data of the construction are compared with the results of numerical simulation to verify the correctness of the numerical simulation and the effectiveness of the reinforcing measures.