A Method for Horizontal Directional Drilling in Difficult Soil Conditions

Horizontal Directional Drilling (HDD) is highly sensitive to geological conditions, particularly in gravelly or stony grounds with low cohesion. Problems often occur when relatively large diameter boreholes have to be drilled. This is mainly due to the fact that the borehole is only supported by drilling mud. Therefore, in unstable soil conditions, the borehole might collapse after a certain period of time and might lead to a stuck pipe during pre-reaming or pull-back operation. This paper proposes a way for HDD to solve borehole stability problems in sandy gravel soil conditions. It combines the advantages of the pipe-jacking method to avoid the HDD disadvantages. The borehole is supported by intermediate pipes during the pre-reaming and pull-back stage. This method can lower the jrisk during installation and extend the range of HDD applications.