Analysis Of Influence Of Foundation Pit Dewatering Excavation On Settlement In Fuzhou Coastal Area

With the construction of the subway station,the surrounding surface settlement caused by the excavation of the foundation pit project of the station has gradually been paid attention to.At present,the Fuzhou subway is in the stage of large development,but the foundation pit for the special hydrogeology in Fuzhou area.There are relatively few studies on precipitation.The article focuses on the analysis of the impact of precipitation excavation on the surrounding environment in the foundation pit under the geological conditions of the weak water-rich soil layer in the coastal area of Fuzhou.Taking Luqi Metro Station as an example,the permeability coefficient and influencing radius parameters are obtained through pumping test,and the parameters in dewatering scheme are modified.Midas GTS NX is used to simulate the surface settlement outside the foundation pit caused by the change of water level in the foundation pit dewatering process by setting the height of nodal head.The comparison of monitoring data proves the feasibility of the method.Meanwhile,based on the Luqi metro station model,the influence of different unloading modulus of soil,depth of precipitation in pit,depth of water-stop curtain,permeability coefficient and recharge condition of pit on surface settlement is analyzed.The research shows that:(1)The settlement curve of the ground surface outside the foundation pit presents a "spoon shape".As the depth of the foundation pit increases,the maximum settlement value will appear at a certain distance from the edge of the foundation pit,and the location of the maximum settlement value and the depth of the foundation pit excavation will occur.It is related to soil quality.The maximum settlement generated by the construction of Luqi subway station is 28mm,which is 14m away from the edge of the foundation pit.(2)With the increase of soil elastic modulus and permeability coefficient,the settlement value of the earth surface will decrease and the ground will be uneven.The settlement is also reduced.After the elastic modulus reaches 12MPa or the permeability coefficient increases to 2×10-2m/d,the influence on the settlement is drastically reduced,and the elastic modulus and permeability coefficient of the soil are on the distance foundation pit.The influence of surface settlement outside the edge of 100m is also small;(3)The precipitation-excavation process of the foundation pit will cause "concave" settlement around the construction site.The settlement outside the pit is closely related to the precipitation time.If the precipitation is too fast,the pore water pressure drops too fast,and the settlement speed and settlement of the earth's surface will also increase.In the actual project,the groundwater level should be avoided as much as possible,and the groundwater level should be evenly reduced.Water velocity,can effectively control the uneven settlement.