Influence Of Soil Layer Deformation On Metro And Safety Risk Assessment Of Metro In Shanghai

Under the influence of partly soil deformation and regional soil deformation,the metro suffered serious uneven deformation in shanghai.Based on the longitudinal monitoring data of the metro,the regional soil deformation data and the monitoring data of nearly 70 excavations,firstly,the deformation characteristics and trends of the metro were analysed.Then,the influence of regional soil deformation on the metro was studied.After that,the influence of partly soil deformation caused by excavation on the metro was explored.Finally,four indicators of absolute settlement,deformation rate,curvature radius and relative bending,and two models of risk degree value and risk grade were to evaluate the deformation safety risk of metro at different locations.The main contents and conclusions of this paper are as follows:(1)By analyzing the longitudinal deformation data of the metro,the differences and trends of the metro deformation in different time and space are clarified.Results show that: the metro exhibit different deformation characteristics in different space,which is mainly affected by regional soil deformation and partly soil deformation.Before December 2008,the metro showed the characteristics of settlement,and the settlement rate gradually decreased.After that,the metro deformation is dominated by uplift,and the uplift rate increases firstly and then decreases.(2)Based on the deformation data of the metro and regional soil layers,the reasons for the settlement and uplift deformation of the metro and the difference of the metro deformation in different regions are revealed.Results show that: the slope of the fitting function between the metro and ground settlement is about 1.45,and that between metro and deformation of soil under the metro is about 1.The first,second,third and fifth aquifers under the metro exhibit elastic deformation characteristics;however,the fourth confined aquifer shows elastoplastic and plastic deformation characteristics.The weak permeable aquifers below the metro mainly exhibit compression deformation,but a small amount of expansion deformation occured in the partly soil layer.The reason for the settlement of the metro is that the compression which dominated by the fourth confined aquifer was greater than the expansion of the expansive soil layer.The reason for the uplift deformation of the metro is that the expansion of the first,second,third and fifth confined aquifers were increased,and the compression of the fourth confined aquifer and the weak permeable aquifers decreased dramatically,and even the expansion deformation occured in some areas.The main reason for the difference of the metro deformation in different regions is that the deformation of the fourth confined aquifer is different.(3)Combined with the monitoring data of the metro near the excavation,the influence of the partly soil deformation caused by excavation on the metro at different locations is revealed.Results show that: when the metro is located in the upper of the excavation,the excavation cause the metro to exhibit settlement and horizontal displacement towards the excavation.The maximum settlement and maximum horizontal displacement of the metro decrease with the increase of the lateral distance and longitudinal distance of excavation and the metro.When the metro is located near below the excavation,the excavation cause the horizontal displacement of the metro towards the excavation,and the vertical displacement to present settlement or uplift deformation.The maximum uplift of the metro decreases with the increase of the lateral distance and longitudinal distance of the excavation and the metro;the maximum settlement and horizontal displacement of the metro increase first and then decrease with the increase of the lateral distance;the maximum horizontal displacement of the metro decreases as the longitudinal distance increases.When the metro is located directly below the excavation,the excavation causes the metro to rise.When the excavation and the metro share the same underground continuous wall,the excavation cause the metro to rise and displace horizontally toward the excavation.(4)Combined with the four indexes of absolute settlement,relative bending,radius of curvature and deformation rate,the risk degree value and risk grade evaluation model are established,and the safety risk of metro deformation at different locations is evaluated.Results show that: the greater the vertical deformation and the deformation rate,and the more serious the non-uniform deformation,the greater the risk of metro deformation safety;on the contrary,the degree of metro deformation security risk is smaller.Both evaluation models can distinguish the influence of regional soil deformation and partly soil deformation on the deformation safety risk of the metro,and the risk degree value and risk level have a good correspondence with the cumulative deformation curve of the metro.Therefore,the evaluation results are reasonable.