Development of Hard Rock Drilling Method Using Waterjet System for Pile Foundation Installation

Nowadays, utilization of underground spaces of cities in various ways, such as energy supply facilities, transportation facilities, and safety-related facilities, is ever increasing. Preparations for geo-risk (e.g., earthquakes) related to safety issues are required. In order to secure the geo-risk resistance of a structure, a suitable foundation structure must be anchored to the bedrock. In general, rock drilling for foundation structure anchoring is performed by a mechanical means. This methodology causes various problems such as dust, noise, vibration particularly when drilling hard rock such as granite. These problems also cause various civil complaints when construction is carried out in the city. Waterjet methodology for rock drilling can be effectively used to overcome problems associated with mechanical rock drilling means. The waterjet method uses only water and abrasives. Drilling is possible even if the bedrock has high uniaxial compressive strength, and dust and vibrations generated during the drilling process are minimized. In this study, hard rock drilling using the waterjet system was proposed, and its drilling performance was analyzed. Equipment capable of this drilling was designed with two water jet nozzles rotating in a circle. This equipment was designed to drill standard boreholes for anchored pile-type foundation structures. In addition, a drilling trial was performed using this equipment for granite with a uniaxial compressive strength of 200 MPa or more, and its performance was analyzed. This new drilling method is expected to be useful in installing pile foundations in hard rock.