| Shield method refers to use shield to excavate tunnela soft foundation or brokenrock.Strata displacement of the construction stage and late initiation is caused bysubsidence and adjacent structure (building) the main reason of ground deformation anddamage of buildings.Conventional control standards emphasis on construction area ofground settlement control,the consideration of the buildings around is notcomprehensive,sometimes only use the maximum settlement and the maximum amountof tilt to assess the extent of damage of buildings.How to improve the existingsettlement control standard and take effective measures for settlement control is a veryimportant problem,having practical engineering significance.This paper makes shield tunnel of Ningbo Metro Line1and line2a phase of theproject as the project background,Collation and analysis the geological and hydrologicalconditions, plane and vertical section design, tunnel shield construction parameters andthe ground settlement and deformation monitoring data of five interval in theconstruction and the built environment.In the light of the construction of shieldtunneling method in Ningbo area settlement control standard and control measures arestudied,the main work is as follows:①Collate and summarize past research theory,analysis surface subsidence anddeformation mechanism, influence factors, building standards and control measures tocontrol settlement deformation law at home and abroad as well as in practicalengineering andmake evaluation;②Research on a large number of engineering data，analysis the law andinfluencing factors of settlement in shield tunnel ground and building in Ningbo;③Use the finite element analysis software ANSYS to simulate the effect onadjacent building foundation excavation of the tunnel under differentconditions,considering the influence of tunnel and tunnel levels based on soil conditions,spacing, type of foundation and other factors on the settlement results;by using the finitedifference software FLAC3D to simulate the excavation process of four pile foundationeffect,and compared with the measured data;④Based on a large amount of data analysis and finite element numericalsimulation，put forward Ningbo rail traffic shield interval of ground and buildings settlement deformation control standard value,and further on the settlement controlmeasures.The conclusions in this paper are as follows:①The curve of cumulative settlement of the surface monitoring point is above theactual tunnel is not in accordance with the law theory,that is not a single settlementlaw,early settlement curve is not a normal distribution,but in the shield by section andgradually developed into a normal distribution curve;②Building settlement rule have difference with the surface during the singlepropulsion,but the overall downward trend,in the latter part of the settlementstabilized,after the double track,the two construction significantly increased thebuildings near the side of the vertical displacement of the tunnel,lead to the building oflateral and longitudinal inclination change has the very big difference;③In practical engineering，surface and building settlement factors deformation isnot single,settlement deformation are generated in the influence of a variety offactors,research methods mainly depend on the test and numerical simulation ormodel,effect of single influencing factor in practical engineering is not obvious.④The numerical simulation of shield crossing group of pile foundationshowthatground subsidence trough is the normal distribution curve, which is similar withpeck formula; The pile foundation has limit with the existence of strata displacement;Pile foundation of different location have different response in the process of tunnelexcavation.⑤Put forward Ningbo rail transit land and buildings settlement deformationcontrol standard value，and combined with the actual project,divided the measures ofconstruction control of shield divided into passive control measure and active controlmeasure. |
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