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钻孔灌注桩由于具有单位承载力造价较低,桩长现场施工控制,减少了浪费,且大直径钻孔灌注桩单桩承载力大等优点,常作为公路、桥梁、高层建筑等的基础设计。目前钻孔灌注桩的理论与实际操作尚有较大的差距。下面结合施工实际,谈谈自己的一些体会。 一、护筒的埋设。《灌注桩工程设计计算与施工》一书中谈到“把钻孔中心位置标于坑底,再把护筒吊放进坑内,用十字架在护筒顶部或底部找山护筒的圆心位置,然后移动护筒,使护筒中心与钻孔中心位置重合。”此法在实际操作中较难实现,且偏差很难满足规范要求。在此首先得改变一种观念,即认为护筒中心必须与钻孔中心重合,而实际上应该是桩机在水平的情况下其转盘(回旋钻机)中心与钻孔中心在同一条垂线上,因而可通过主桩点(钻孔中心)引出四个副桩点A、B、C、D,副桩点起转点作用(见示意图),副桩点离主桩点三倍半径左右,然后开按护筒坑、下放护筒,挂线AC、BD,只要其交点O距护筒壁的最小距离比设计孔半径大7厘米即可。埋好护筒后将四个副桩点引至护筒壁上,分别为
Bored cast-in-place piles have the advantages of low cost per unit of bearing capacity, long-term construction control of piles, reduced waste, and large bearing capacity of large-diameter cast-in-place bored piles, and are often used as basic designs for roads, bridges, and high-rise buildings. . At present, the theoretical and practical operation of bored cast-in-place piles still has a big gap. The following combination of construction practice, talk about some of their own experience. First, the casing buried. The book “Calculation and Construction of Pile-pile Projects” mentioned in the book “The position of the center of the drill hole is marked at the bottom of the pit, then the casing is suspended in the pit, and the cross is used to find the position of the mountain casing at the top or bottom of the casing. Then the casing is moved so that the center of the casing coincides with the center of the drill hole.” This method is difficult to implement in actual operation, and the deviation is difficult to meet the specification requirements. First of all, we have to change the concept that the center of the casing must coincide with the center of the drill hole. In fact, the center of the turntable (rotary rig) and the center of the drill hole should be on the same vertical line when the pile driver is horizontal. Therefore, four secondary pile points A, B, C, and D can be induced through the main pile point (drilling center), and the secondary pile point can act as a turning point (see diagram). The secondary pile point is about three times the radius of the main pile point. Then open the protection pit, put the protection tube, hang AC, BD, as long as the minimum distance between the intersection of O and the casing wall is 7 cm larger than the design hole radius. After burying the casing, the four secondary pile points are led to the casing wall.