The drilling process monitoring (DPM) has been used in site characterization. Information from the drilling monitoring can be added to the existing geological information for more accurate identification of the rock discontinuities and weathered degrees of soils and rocks, because a larger number of drilled holes from rotary-percussive drilling can be used. In this paper, two sets of DPM data from two adjacent holes are examined. The two holes were drilled with two different rotary-percussive drills in soil nailing construction. Based on the monitored data, the interaction of the most important drilling parameters is assessed. The parameters are the drilling rate, the air pressures and the effect of work powers of different drills. The effect of the different drill work powers on the drilling data is identified. So, only the rock dependant variation can be left for site characterization. The results demonstrate that the drilling parameters from different drills can be normalized.
1. INTRODUCTION
Site characterization in weathered rock mass is important in rock mechanics and rock engineering. It is often based on the factual data from drillhole exploration and geological mapping. To obtain an accurate characterization of ground rock mass condition, more and additional factual data about the ground condition are always useful and needed. One of the additional factual data which can be used to characterize weathered rock mass is the data from automatic and digitally monitoring of drilling in ground investigation and in construction. The digital data from drilling monitoring can provide additional geological information for better site characterization. Particularly, air-driven rotary-percussive drilling with down-the-hole hammer can be used to drill hundreds and thousands production holes in geotechnical construction. Over the last ten years, Yue and his research team [1, 2, 3, 4, 5, 6] have developed a new in-situ technique for characterization of rock mass and the associated spatial distribution in ground. It is the DPM system. It comprises seven pressure transducers and digital data logger. It can automatically monitor the drilling process of air-driven rotary-percussive drilling machines in real-time and in a digital manner. Based on the monitored digital DPM data, a data analysis method has been developed. This paper reports a continued effort on the DPM methodology for rock mass characterization. To examine the influence and interaction of the most important variable factors concerned in rock drilling- namely, air pressures, work condition of drilling machine and drilling rate, two drilling machines are used to drill two adjacent holes and the corresponding drilling processes are monitored by DPM system. A full drill analysis is applied to divide the monitored drill data into many sub-processes such as pushing-in, pulling-back, and drilling. Work conditions of the two drilling machines are examined in these sub-processes by two aspects: thrust motor effect and effect of drill rod, down-the-hole hammer and drill bit. The case study demonstrates that the different drill work powers on the drilling data can be identified and the DPM methodology can be applied into different drilling machines.
