Study On Construction And Application Of The MJS(Metro Jet System)for Soft Soil Stratum In Shanghai

With the deepening of underground space development in Shanghai,the shallow middle-level underground resources,which are marked by rail transit,are being consumed,the intensive development and deepening utilization of underground space have become the two ways to solve the current predicament.The traditional soil reinforcement process,represented by high pressure rotary jet,has great environmental impact and shallow depth of reinforcement,which cannot meet the demand of underground space development in Shanghai in the 21st century.The MJS improved the traditional soil reinforcement process in the environmental impact and depth of reinforcement and other deficiencies.Adopting unique porous pipe for grouting and underground pressure monitoring technology,within the advantages of the larger diameter rotary jet reinforcement construction,large depth of foundation improvement and low environmental impact,However,the MJS,which introduced into China from Japan since 2008,is still in the construction parameters and process of the exploratory stage.This paper describes the MJS of principles,characteristics,equipment composition,reinforce mechanism and its development process in China.Relying on the projects background in the Soft Soil Stratum of Shanghai,the construction parameters and technology of the MJS were verified by vertical,horizontal and inclined reinforcement test.Based on the background of Shanghai Expo,Shanghai Metro Line 9 and Line 12 projects.The MJS has been implemented to apply successfully in the field of large diameter rotary jet reinforcement,adjacent projects and the improvement of the large depth foundation by optimizing the MJS construction technology and construction parameters,common ditch hole and separate casing method of simultaneous lifting,information construction and other measures.The measured data show that the MJS can achieve the "micro-disturbance" to environment and the super-large diameter super-large depth foundation improvement in the Soft Soil Stratum of Shanghai,and has wide application prospect.