| Lanzhou metro line 1 Wulipu station is built near the main road of Lanzhou city.The surrounding buildings are dense,engineering geology and hydrogeological conditions are complex.There is a tertiary water-rich semi-diagenetic sandstone(red sandstone)in the stratum,which is of special nature and poor water quality.The groundwater in this area is rich,making excavation difficult and slow.In this paper,the method of field investigation and laboratory test is used to analyze the red sandstone in the station strata.The groundwater treatment effect of the station is analyzed and evaluated by field measurement.In order to solve the problem of underground water treatment of the subway station in the tertiary red sandstone stratum.The main research results are as follows:(1)Tertiary red sandstone is red in appearance with high price iron(Fe+3).The sandstone is divided into two types: burial type and exposed type.The first one is located in Limasha ditch,Luogu ditch,the north of Shajingyi,the Dasha ditch and the valley of the south of Chengguan.The second one is distributed in the Chengguan,Qili river,Anningbao and Xigu basin.The results show that the sandstone is a fine grained sandstone with narrow particle size and uniform distribution.Without disturbance,the strength is higher and the stability is better;It is difficult to excavate the foundation pit because of disturbed or disintegrating water,rapid decrease in strength,destruction of structure and mud sandstone.(2)After investigation,the groundwater in the Wulipu station site is divided into bedrock fissure water in the Quaternary pore dive and red sandstone in the pebble layer.The water level of the dive is relatively high and the depth of burial is 8.4 to 9.4 meters.When the foundation pit is excavated,the water level difference between the inside and outside of the pit is too high,which results in excessive lateral pressure on the envelope structure,and collapse of the pit wall and inrush of the pit bottom.The red sandstone in the pit encountered water disintegration,and the fissure water emerged in the pit,resulting in too much water in the pit and difficult excavation of the pit.(3)In view of the unfavorable influence of underground water on the excavation of foundation pits,after research,bored occluded pile was used as a foundation pit enclosure to serve as a water stop curtain to block the internal and external hydraulic contact between the pits;The water level in the middle dive is reduced to the sandstone layer;the water leveling platoons are stratified and collected in the pit to ensure the excavation of the foundation pit.(4)Due to the large depth of excavation at the Wulipu station and the long retaining piles,the construction quality is difficult to control accurately,and problems such as slanted piles and poor occlusal quality occur,which results in water leakage and sand leakage of the enclosure structure.After field experiments,because of the fine granularity of red sandstone and the disintegration of the red sandstone,cement-water glass two-fluid grouting cannot form impervious “stones” in the soil,resulting in poor plugging effect.The sand-conducting and water-conducting measures using water-guiding water diversion,instantaneous concrete and transient cement blocking can prevent the loss of soil particles outside the pit and meet the plugging requirements.(5)The excavation of the foundation pit to the vicinity of the basement resulted in the disintegration and softening of red sandstone and the difficulty in pouring the floor slab.According to the study,light well-point dewatering measures are taken at a depth of 1m above the basement,and the depth of precipitation is 5m.Through the precipitation of multiple wells,the water level in the fractured red sandstone near the basement is reduced,and the smooth pouring of the floor is ensured.The above research results can provide reference for the design and construction of deep foundation pits in the third station water-rich semi-diagenetic sandstone section. |
PDF Full Text Request