In order to investigate the influence of train load and groundwater on tunnels after subways'operation,the settlement and deformation of a subway shield tunnel section in a city with sandy soil layer during 6 years in operation were observed on-site.According to the settlement laws obtained from the actual measurement,a scale model test was designed and carried out to study the settlement laws of tunnel caused by the variation of groundwater level under the condition of vehicle-induced vibration.The results showed that the data obtained from each monitoring point in tunnel showed a certain trend of cyclical rise and fall over time:in the first two years,the tunnel generally rose,then slightly went down;after the third year,although there were fluctuations,basically it did not further settle;and at last the maximum value of tunnel settlement after 6 years did not exceed 3 mm.In sandy soil layer,the variation of groundwater level led to the internal stress change of remolded soil stratum,and the restructuring of soil particle structure to dense caused by vibration load led to the tunnel settlement easily.Therefore,the adverse effects of construction precipitation around the subway on tunnels could not be ignored.The tunnel rising and settling were joint actions of soil vibration density and buoyancy caused by groundwater.Compared with the soft soil stratum,the settlement rate of shield tunnel in sandy stratum was obviously lower with basically shorter settlement time.The settlement laws and influence factors under two strata were completely different,and the settlement analysis theories under each stratum could not be applied to each other.
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