硅藻土地区桥梁灌注桩成孔测试研究

Study on Borehole Test of Bridge Cast-in-place Piles in Diatomite Area

硅藻土作为一种特殊的黏性土,在分布上具有一定的区域性,目前针对该类型土的工程特性以及硅藻土地区灌注桩成孔方法的研究都较少。以杭绍台高铁项目为工程依托,为了研究硅藻土层中灌注桩的成孔方法,开展了灌注桩成孔方法现场试验;分别采用冲击锤锤击成孔、旋挖干钻成孔和旋挖泥浆护壁成孔三种方法进行施工,对三种方法的成孔质量进行分析对比。研究结果表明:在硅藻土地区施工灌注桩,旋挖干钻成孔工艺施工速度较快,效率高,桩长、桩径、桩位偏差和垂直度均能满足设计要求,成孔后孔壁稳定性好,成孔质量更为可靠;冲击锤法成孔,成孔速度较慢,且存在桩孔扩径现象;旋挖泥浆护壁法成孔后平稳性较差,波动性较大,且存在局部塌孔现象,成孔效果较差。因此建议硅藻土地段优先考虑采用旋挖干钻法施工桥梁灌注桩。

Diatomite is a special type of clay,which has a certain regional distribution.At present,there are relatively few studies on the engineering characteristics of this type of soil,especially on the drill method of cast-in-place piles in diatomite area.Based on the Hangzhou-Shaoxing-Taizhou highspeed railway project,field test was carried out according to the field condition to study the drill method of cast-in-place piles in diatomite layer.Three types of drill methods,including the impact hammer drill method,dry rotary drill method and rotary drill method with mud wall protection,were used to construct the holes.The quality of the pile holes by the three methods was analyzed and compared.The results show that the rotary dry drill method is faster and more efficient in diatomite soil area.The length,diameter,deviation and verticality of piles can all meet the design requirements.The borehole wall is stable and the quality of bored piles is more reliable.The impact hammer method has a slow drill speed,and pile hole enlargement phenomenon exists.Rotary drill with mud wall protection method has poor stability of pile holes and undulation hole wall.There sometimes is local collapse of holes wall,resulting in poor hole forming effect.Therefore,it is suggested that the dry rotary drill method should be preferred in the construction of bridge cast-in-place piles in diatomite soil areas.The research results can provide reference for similar engineering applications in the future.