摘要
According to the collapse,borehole diameter shrinkage,slip of drill bit,large thickness of sediment in the bottom appeared in a viaduct project in soft soil layer with rotating drilling rig,the accident causes were analyzed; and casing lengthening,bit structure improving,drilling process optimizing,borehole cleaning by air-lift reverse circulation and slurry purifying methods,etc. were adopted with good effects. The construction experiences could be reference to the similar projects.