Research On PBA Construction Method For Settlement Control Of Metro Stations Adjacent To Urban Rivers And Water-rich Sand And Gravel Strata

At present,the scale of subway construction in the country is developing at a high speed.Due to urban environmental conditions,there are more and more near,underpass,shallow buried,and long-span stations.The construction environment is becoming more and more complex.The impact of subway construction on the surrounding environment is mainly through station construction.The resulting ground settlement will be realized,and in serious cases,the adjacent buildings(structures)will be damaged and in turn affect the station construction.Therefore,it is necessary to study and analyze the settlement mechanism and control method of the subway station construction process under the complex urban environment.This article relies on the Honglian Nanli Station project of Beijing Metro Line 16 20,through "document review,field investigation,numerical simulation,theoretical analysis and on-site measurement" to control the settlement of the stratum during the construction process to ensure the station and surrounding environment Safety as a starting point,an in-depth and systematic study was carried out on "Structure scheme,construction sequence,settlement control method and implementation effect of settlement control on the surrounding environment of underground subway stations in water-rich pebble strata under complex environmental conditions".The research shows that:(1)Analyze the defects of the original 8-guiding tunnel design scheme,and put forward the PBA construction scheme of "single-layer 4-guiding tunnel + large-diameter pile foundation in the pilot tunnel" suitable for the characteristics of this station and successfully implement it.At the same time,the numerical simulation method was used to analyze and compare the mechanical mechanism and settlement control effect under the two schemes.After verification with the field measurement data,the results showed that the optimized scheme reached a satisfactory standard in terms of formation settlement control,ensuring the safety of the the station and the surrounding environment.(2)Taking the control of stratum settlement as the starting point,the station construction process is studied.The results show that: Based on the current complex geological environment,the station guide tunnel excavation adopts the method of lagging 5m first,then middle,respectively,and the second liner arch is divided into warehouses The form of jumping positions is "jumping one by one",the length of one position is 6～8m,and the order of the main second liner is the whole reverse operation and the local partial operation.The best settlement control effect is established.The dynamic control standard of the subsidence of the station,combined with the analysis of the actual monitoring data,shows that the subsidence control standards are met at all stages of the station construction.(3)In view of the complex construction steps of the station’s spatial intersections,and the proximity of dense areas with water and pressure pipelines,corresponding measures are proposed to protect the pipelines and intersections.The FLAC3 D numerical model is used to verify the effect of settlement control.The construction practice shows that : Advance grouting reinforcement measures taken during the construction phase,adjustment of the excavation scheme of the main arch of the station,and initial support structure strengthening measures effectively control the settlement of the stratum and protect the safety of dense pipeline areas.(4)Research on the implementation of station excavation and settlement control measures for the structures with high environmental control requirements such as bridges and rivers near the station.The results show that after the reinforcement measures are taken,the absolute settlement of the bridge piles,the differential settlement along the bridge direction,and the differential settlement across the bridge direction Both meet the settlement control standards;compared with the small pipe grouting measures taken by the channel protection and deep hole grouting measures of the station,the plastic zone does not penetrate the channel,the channel lining is not cracked,and the effect of the deep hole grouting to protect the channel lining is better than the small Catheter grouting.