Research On Settlement Control Of Double-track Tunnels Detouring Ancient Buildings

In recent years,with the acceleration of urbanization process in China,the construction of subways in major cities is in full swing.At present,the construction of urban subways mostly adopts the shield method.The construction process will inevitably cause certain ground disturbances,cause surface settlement or uplift,and cause certain impacts on nearby buildings(structures).Especially when the railway line is close to ancient buildings,how to effectively predict the ground settlement during the construction process,select reasonable reinforcement schemes and determine reasonable construction control measures,strictly control the amount of ground settlement and deformation,and ensure the safety of ancient buildings becomes a key and difficult issues of the project.In this paper,Xi’an rail transit line of double tunnel around the ancient building construction section as the research object.Firstly,I predicted and analyzed the surface settlement of a,b and c sections by peck formula.Then,I built a three-dimensional finite element model to study the law of ground settlement caused by tunnel excavation.On the basis of the previous research,I optimized and analyzed the reinforcement plan of this project,and proposed corresponding construction control measures to ensure that the settlement deformation of the foundation of the ancient building and the maximum settlement of the ground are controlled within 5mm and 30 mm,respectively.The main research results of this paper are as follows:(1)The measured data of three typical cross-sections are used to revise the peck formula.On this basis,the surface settlement is analyzed by fitting.The results indicate that: The revised peck formula can be applied to the prediction of surface settlement of the project.The predicted value of settlement at the foundation of the ancient tower is greater than ±5mm of the foundation deformation control standard,and certain reinforcement measures need to be taken for the foundation of the ancient tower.In addition,the peck formula has a large deviation in the prediction results of the local reinforcement treatment.(2)The ABAQUS software was used to simulate the double-track tunnel bypassing the ancient tower project.The results indicate that: The lateral surface settlement curves of the three sections are in normal distribution.The maximum value of the settlement curve and the curve range are basically consistent with the measured value.In section b,the local settlement curve is suddenly steep due to the isolation piles in the foundation of the ancient city building,which is consistent with the actual situation;the longitudinal surface settlement curves of the three sections in this area are basically consistent with the measured values.Therefore,the numerical simulation method can be applied to the prediction of the ground settlement of the project,which can provide theoretical and technical support for the optimization of foundation reinforcement.(3)By establishing numerical models of three different reinforcement schemes(Weak reinforcement scheme A,cement grouting + bored piles + non-high pressure jet grouting pile water stop curtain;medium reinforcement scheme B,cement grouting + bored piles + 5m high pressure jet grouting pile water stop curtain,strong reinforcement scheme C,cement grouting + bored pile + 9m high pressure jet grouting pile water-stop curtain),the three schemes are compared and analyzed in terms of reinforcement effect and economy.The results indicate that: With the strengthening of the foundation of the ancient building of the tunnel,the maximum settlement of the tunnel surface gradually decreases.Both schemes B and C can meet the reinforcement requirements,but scheme B is more cost-effective than scheme C.(4)Analyze the relationship between shield tunneling speed and ground settlement through numerical simulation.The results indicate that: The maximum surface settlement increases with the increase of the excavation speed.The relationship between the two has a certain phase.When the shield tunneling speed is controlled within the range of 4m/d-5m/d,the maximum settlement of the ground surface can be controlled within 30 mm.