Study On The Construction Control Measures Of Peat Soil Large Slope Shield Under Dense Buildings

Kunming Metro Line 6 is a metro line connecting Kunming Changshui International Airport and the main urban area,with a total length of 25.6km and an underground line of15 km.The section line between Juhua east railway station and East passenger station is mainly arranged along Guishi road.The line starts at the intersection of Kunhe railway and Jinma Road,then turns to the north and passes Guishi West Road and Hongqiao interchange.After crossing the extension line of Renmin East Road,it connects with the East passenger station.The buildings along the line are densely distributed.Peat soil is widely distributed in Kunming area,and its engineering mechanical properties are very poor.In terms of geological structure,the project section is located in the sedimentary environment of piedmont alluvial diluvial fan and ancient lakeside in Dianchi water system,with a wide range of peat soil deposits.With the rapid development of urban traffic,the engineering environment of subway construction in peat soil layer is inevitable.Shield method is the main construction method used in the project area.To control the ground settlement is one of the main engineering problems to be solved in the peat land area.Construction in peat soil with poor mechanical properties is very easy to disturb the stratum,thus endangering the safety of personnel and municipal facilities.Underpass construction is a necessary engineering situation in metro tunneling,and the maximum shield slope in the work area can reach 28.33 ‰,which puts forward higher requirements for strict control of surface settlement,and also increases the difficulty and danger.The improvement of physical and mechanical properties of peat soil layer by grouting is the main control means of settlement control in construction.The mixing ratio of clean slurry material and the thickness of reinforcement ring layer are important grouting control parameters.Based on the interval project from juhuadong station to East passenger station of Kunming Rail Transit Line 6,this paper studies the physical and mechanical properties and distribution characteristics of peat soil in the section,and carries out laboratory tests of compression modulus of different mixing ratio of clean slurry materials,and puts forward the best improvement parameters and compression modulus of peat soil.According to the indoor pressure test,the organic matter content of peat soil in the project area is 25.94%,and the compression modulus is 2.92 mpa,which is high compressibility soil.In order to prevent the settlement of the building group under the shield from exceeding the control range,it is necessary to improve and strengthen the stratum by grouting.According to the test results,the proportion of slurry filling in the gap at the tail of shield should not be less than 70%,and the compression modulus range from 4.53 mpa to 7.34 mpa at the content ratio of 70% to95%.In addition,with the help of PLAXIS 3D numerical simulation software,the surface settlement value of shield construction passing through the building complex under the improved parameters is monitored,and the field construction situation and monitoring data are compared,and the following conclusions are drawn:(1)peat soil surrounding rock reinforcement is carried out by filling slurry in the gap at the tail of shield,and the mixing ratio of clean slurry material reaches 90%,the compression modulus of equivalent layer reaches 7.34 mpa,and the slurry continues to be increased In addition,the effect of equivalent layer surface settlement control is not obvious,so this parameter is taken as the index of equivalent layer improvement;(2)the surface settlement value of the shallow overburden under the shield is proportional to the slope;(3)when the thickness of the radial grouting reinforcement ring is 3 meters,it can strictly meet the requirements of ground settlement control and tunnel forming quality.