重力嵌岩式锚碇深基坑开挖施工技术

棋盘洲长江公路大桥主桥为(340+1 038+305)m钢箱梁悬索桥,北锚碇为重力式嵌岩锚,平面尺寸为61.5m×60.0m,总高42.0m。锚碇深基坑开挖采用机械、人工、爆破相结合的方法,松散土层、全风化岩石采用机械开挖,局部转角处采用人工开挖修整,强风化岩石层、中风化岩石和微风化岩石采用钻孔爆破。基坑形成后采用螺旋便道出渣,高峰期每昼夜可出渣2 300m^3。基坑防水分为坑外截水和坑内排水。边坡采用锚杆支护及挂网喷射C20混凝土的方法进行防护。在基坑关键位置布设位移监测点,各测点位移及其变化速率均未超过规范要求,基坑施工质量良好。

Key Foundation Pit Excavation Techniques for Gravity-Type Rock Tunnel Anchorage

The main bridge of Qipanzhou Changjiang River Highway Bridge is a steel box girder suspension bridge with three spans of 340,1 038 and 305 m.The north anchorage is the gravitytype rock tunnel anchorage measures 61.5 mby 60.0 m,42.0 min total height,and stands on spread foundation.The anchorage is located in the hilly area hemmed in on three sides by water.The deep foundation pit was excavated by mechanical and manual digging as well as blasting.The loose soil and fully decomposed rocks were mechanically excavated,with manual excavation and grinding at local corners.Whereas the decomposed,moderately decomposed and light decomposed rocks were excavated by drilling and blasting(stepped blasting in shallow holes and laddered blasting in deep holes).After taking shape,the foundation pit was dredged using spiral ramps,with a peak-time dredging amount of 2 300 m^3.The waterproof of the foundation pit is realized by cutting off water outside the pit and draining water inside the pit.Slopes of the foundation pit were protected by adding anchor rods,placing mesh and casting C20 shotcrete.Displacement measuring points were distributed in the critical locations of the foundation pit.The displacement and variation rate registered at each testing point did not exceed the values prescribed in the code,and the construction quality of the foundation pit was good.