Identification of interface of earth fill with weathered granite in site investigation of Hong Kong

A hydraulic rotary drillrig instrumented with a drilling process monitoring system (DPM) was used in site investigation of Hong Kong. The penetrating parameters such as effective thrust force, rotational speed, flushing pressure, penetrating rate and displacement of the bit were monitored in real time. A varying slope was defined as a significant index for identification of dominative and subsidiary interfaces in the granite site. It was shown by the result of t-test that the confidence of the DPM in identification of the geotechnical interfaces was 99%. Besides, the analysis of variation of the penetrating parameters on the interfaces indicated that there were different fluctuations on the interfaces in the variation of the parameters with borehole depth. The response degree of the effective thrust force and the penetrating rate to variation of rock strength at the interfaces was 81.82%.