Real-time drilling process monitoring for soil nailing works for slope upgrading works

摘要

Soil nailing is a commonly adopted technique for upgrading substandard slopes in Hong Kong. The Landslip Preventive Measures (LPM) Programme was first introduced by the Hong Kong Government in 1977 and the design and construction practices of slope upgrading works are continuously being improved by use of new technology and research. One of the innovative technologies, called Drilling Process Monitoring (DPM), has been developed by the Department of Civil Engineering of the University of Hong Kong (HKU) to monitor and record the drilling process of soil nailing works (Yue et al, 2004). Several sensors for recording position of drill chuck, pressure for percussion, thrust and rotation movement, are mounted onto a pneumatic rotary percussive down-the-hole drilling machine and its control panel. A set of data representing the whole drilling process is recorded automatically and continuously. The real-time DPM raw data together with the calculated penetration rate are presented graphically on a designated website.Site trials of real-time drilling process monitoring were carried out at two sites under a Landslip Preventive Measures (LPM) Contract. One of the sites is a 20m high cut slope comprising bouldery Colluvium. The other is a 12m high loose fill slope. Some soil nail drillholes at the above two sites were selected for carrying out DPM with real-time monitoring. Some cavities and joints were suspected during drilling. Closed circuit television (CCTV) survey was conducted in those drillholes with suspected cavities and joints. In the DPM result of the selected drillholes, the deviation of penetration rate was correlated with the features such as cavities and joints in the drillholes as observed in the CCTV survey.Real-time DPM for soil nailing works was confirmed to be an effective means of remotely verifying the depth of the hole and monitoring of ground conditions and progress. Portions of slopes with difficult ground conditions such as excessive grout loss or drillhole collapse can be identified in the early construction stage and a better planning or arrangement of site works can be made.