孟加拉帕德玛大桥钢管桩桩侧压浆施工技术

孟加拉帕德玛大桥水中40个主墩采用直径3.0m钢管桩基础,其中11个主墩共计77根钢管桩在桩身周围均布了10道压浆槽,对每道压浆槽进行桩侧压浆,以提高钢管桩承载力。桩侧压浆水泥浆采用超细水泥配置而成,以适应密实超粉细砂地质条件。先将10道压浆槽内泥砂清除至设计标高;再布置2条线路对2道压浆槽进行同步换浆和桩侧压浆,压浆速度控制在10L/min以内,压浆压力按1,2,3MPa分级设置。压浆量达到设计压浆量或压力达到3 MPa且无法继续注浆时,继续注浆10min或保压10min,即完成该压浆槽桩侧压浆,按轮次连续完成其它压浆槽桩侧压浆。荷载试桩和工艺试桩结果表明,通过实施桩侧渗透压浆技术,可提高钢管桩与土体之间的摩阻力约58.2%,有效提高了钢管桩承载力。

Key Shaft Grouting Techniques for Steel Tubular Piles of Padma Bridge in Bangladesh

A number of 40 river piers of Padma Bridge stand on pile foundation formed of 3.0 m diameter steel tubular piles.For the 77 steel tubular piles of 11 river piers,each pile shaft contained 10 grouting slots,through which the piles were grouted to enhance their load bearing capacities.The mortar was made from superfine cement to suit the geological condition of dense superfine sands.First,the sediments in the 10 slots were dredged to design elevation.Then,two routes were selected to conduct simultaneous mortar replacement for two grouting slots and simultaneous shaft grouting,with the grouting speed controlled within 10 L/min,and grouting pressure set at three grades of 1,2 and 3 MPa.Once the grouting amount reached the design amount,or the pressure rose up to 3 MPa where the grouting was unable to continue,and the grouting should not be stopped,but kept on for 10 minutes,or with the pressure sustained for 10 minutes,then the grouting process was finished.The operation was repeated to complete the grouting at other slots following the specified shifts.The results from pilot loading and technique-checking tests on trial piles indicate that the shaft grouting helps improve the friction force between the steel tubular piles and surrounding soil by about 58.2%,as a result,the load bearing capacity of steel tubular piles can also be effectively enhanced.