Influence and Quality Control of Horizontal MJS Pile in Water-rich Silty Sand Stratum
The metro jet system(MJS)construction method has advantages of omnidirectional,high-precision,centralized mud discharge and shows high adaptability under unfavorable construction conditions such as complex geology and traversing existing stations by shield tunneling.The objectives of this study were to investigate the effects of horizontal MJS pile constructed within a silty sand stratum and to optimize the design and construction parameters of the horizontal MJS.MJS pile tests were conducted at Sujin subway station of Suzhou Rail Transit Line 6.Field tests were performed to examine the variations in the groundwater level,excess pore-water pressure,soil pressure,and deep horizontal displacement caused by horizontal MJS pile construction.The results show that the maximum excess pore-water pressure increases by 46.1 kPa during horizontal MJS shotcreting.The water level rises by a maximum of 3.6 m during shotcreting and decreases by a maximum of 1.5 m after shotcreting.The variation trend of the earth pressure is consistent with that of the pore pressure,and the maximum increment in earth pressure is 40.6 kPa.Because of the insufficient self-supporting capacity of the soil mass,the hole tends to collapse during the hole drilling process in the silty sand layer.In-situ experimental results show that during the hole drilling and shotcreting processes,the inclinometer had maximum inclinations of 1.2 and 2.2 mm,respectively.The maximum displacement of the station floor during the horizontal MJS construction at a subway station in Suzhou is 0.8 mm,which satisfies the specification requirements.During the construction of MJS piles within a silty sand layer,3%bentonite can be added to the cement slurry to prevent hole collapse and drilling-holding problems.
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维普
