Risk Management On Pile Foundation Underpinning For Shield Tunnel Down-traversing Existing Buildings

In recent years,with the speeding up of urbanization,the urban subway construction density is becoming more and more big.Due to the existing dense buildings,city metro will often encountered going through buildings or structures in construction process,which increases the difficulty to the subway construction,also puts forward a new serious issue to the safety of subway construction.Subway next to wear both buildings usually adopt the method of shield tunnel construction process,need to adopt pile foundation underpinning technology to realize the protection of buildings when shield tunnel down-traversing existing building,therefore,for the sake of safety of pile foundation underpinning for shield tunnel down-traversing existing building,establish a scientific and reasonable risk evaluation method is very important.Based on the analysis of the shield tunnel influence law of strata,pile foundation,building,establish risk management system of pile foundation underpinning for shield tunnel down-traversing existing buildings.Combined with Guangzhou Metro shield tunnel under wear YUZHU coal A7 dormitory building engineering,analyze the main risk factors of the pile foundation underpinning process when shield tunnel down-traversing existing buildings.and formulated the corresponding risk dynamic control system for the main risk factors.Provided a scientific basis for pile foundation underpinning when shield tunnel down-traversing existing buildings.The main work is as follows:(1)Analyzing the relationship between subway,formation,pile foundation,upper buildings.This article first analyze the relationship between subway,formation,pile foundation,upper buildings,and find controlling strata deformation is the core element to guarantee the shield to go through both buildings.Then respectively introduce the characteristics of shield tunnel construction,shield tunnel construction on the influence of the formation,the influence of formation deformation on existing pile foundation and the influence of stratum deformation effect on existing buildings.(2)Established risk management system of pile foundation underpinning when shield tunnel down-traversing existing buildings.On the basis of analyzing the shield tunnel influence law of strata,pile foundation,building,pile foundation underpinning risk management system is established when shield tunnel down-traversing existing buildings,Identify 7 categories and 36 risk factors including shield tunnel construction risk and building their own risk.Using expert knowledge established Bayesian network topology after the data processing,and in accordance with the parameter learning features of GeNIe2.0 software to get more reasonable pile foundationunderpinning security risk Bayesian networks when shield tunnel down-traversing existing buildings.(3)Guangzhou Metro shield tunnel under wear YUZHU coal A7 dormitory building engineering as an example application of risk management system.With reference to established pile foundation underpinning risk management system when shield tunnel down-traversing existing buildings,Under the combination of Guangzhou Metro shield tunnel under wear YUZHU coal A7 dormitory building engineering,make the basis of the questionnaire for risk assessment data after the identified risk factors,conduct reliability analysis and validity analysis to basic data by SPSS22.0 software.Conduct pile foundation underpinning security risk Bayesian networks when shield tunnel down-traversing existing buildings for the reverse reasoning,sensitivity analysis,and the most general chain analysis by algorithm brought by the Bayesian networks,to find greater influences of pile foundation underpinning when shield tunnel down-traversing existing buildings.In allusion to the greater safety risk,formulate corresponding dynamic risk monitoring system and control system.Monitoring system includes monitoring of the main beam stress,the building tilt and the building structure deformation monitoring,the monitoring of subsidence pillars and one thousand catties by force.Guarantee the shield tunnel construction safety when shield tunnel down-traversing existing buildings by the monitoring data reflecting various risk factors in real time.