The Influence Of Multi-storey Underground Space Building To The Groundwater Seepage In Tianfu New Airport

Tianfu new airport underground space excavation with its spatial structure and geological conditions on the uniqueness.Underground space is multi-layered and cross-traffic corridor: The first layer of comprehensive transport hub buried depth is-8m,the roof elevation of the second storey subway station is-9.42 m,and floor elevation is-11.1m,the third layer for the subway and high-speed railway station,the buried depth is-23.3m.The deep excavation of underground space and staggered layout increase the difficulty of underground space construction.Tianfu new airport is located in the east of Longquan Mountain,west of Tuojiang,in the area where the hills are all over,the reservoir is concentrated,surface water is very rich.As the new airport is located in the northwest wing of the retreat of the jingyang nose,the stratum is spread as a stratigraphic flat monoclinic sandstone interbedded stratum,although the red water area is relatively poor,the local weak water pressure makes the hydrogeological conditions in the field become complicated.Combined with the above characteristics,Tianfu new airport underground space excavation on the seepage field is more complex,each step of the subtle differences in operating conditions are affecting the seepage field fluctuations.Based on the data of geological conditions,hydrogeological conditions and underground engineering in the study area,this paper simulates the change of groundwater seepage field under different working conditions by Mod Flow,and suppose to reduce unnecessary construction steps boldly,observing whether the surrounding groundwater environment changes or not.Based on the above results as proposing reasonable optimization measures to the construction program.According to a series of simulation results,the following conclusions are obtained:(1)After the level,the small tributaries of the Lanhua Reservoir were landfilled and landfilled from the groundwater discharge area to the groundwater supply the runoff area,the relationship between groundwater and the Lanhua reservoir,the Jinji River and the Juren River were not changed,but the intensity of supply Runoff became weaken.Due to the strong change of the terrain in the site,the underground water and water ridge disappeared,the local groundwater was high,and the height was 0.04 m.(2)After the field level,the water level in the foundation pit should be reduced to 0.5m below the bottom of the foundation pit and then excavated.The simulation results show that the influence radius of the foundation pit is proportional to the length of the filter tube.Three-layer foundation pit precipitation has a radius of about 270 ~ 650 m,which is far away from the surface water system,we may not set the water curtain.(3)Dewatering of foundation pit will cause the groundwater seepage field to be reversed,and provide a new way of drainage for groundwater,and the blocking effect of underground structure on groundwater is weakened.The interbedded structure of the monoclinic sand and mudstone causes some subsurface flows,and the precipitation of the first and second foundation pit will speed up the runoff velocity of the subsurface structure.(4)As the construction of the third floor subway and high-speed railway station only reduced the original cross-section of 7%,and with the groundwater flow was large angle intersection,the construction of the station on the groundwater interception is weaker,groundwater seepage field has the higher water level on the side of subsurface structure and the lower on the other side,but the phenomenon of groundwater obstruction is not found.(5)The second floor subway station is located in the sandstone layer,the water cross section is reduced by 19.87%,and the long axis direction of the station is 90° angle with the groundwater flow.Therefore,compared with the third floor of the station,the layer of groundwater blocking effect increased slightly.When the second floor of the station and the third floor of the station at the same time,the groundwater level of the underground structure is higher than that of the back surface,and the two are interrupted by the runoff from the northern part of the study area.The seepage field of the high water level is consistent with the outline of the underground structure.(6)Compared with the third-stage foundation pit backfill,the backfill of the second layer foundation pit is more favorable to the recovery of groundwater seepage field.After the backfill of the foundation pit,the groundwater level of the second floor station is reduced by 1.03 m,while the third floor foundation falls only 0.33 m after backfilling.(7)During the operation phase,groundwater can be discharged to the surrounding rivers only because the road surface is hardened to cut off the infiltration and drainage of the groundwater.The water level is generally declining and the high water level area gradually dissipates.