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Abstract of thesis entitled
Verification ofHKU-DPM Results by Pullout Tests and Drillhole Logs in Weathered Tuff
for the degree of Master of Philosophy at the University of Hong Kong
in March 2003
This thesis aims to verify the validity and usability, in terms of ground characterization, of a digital drilling process monitor (DPM) system recently developed by the Department of Civil Engineering of the University of Hong Kong for instrumented drilling in geotechnical engineering.
The prototype DPM was used to monitor hole drilling for installation of soil nails at a slope stabilization construction site in Hong Kong. The site was characterized by weathered tuff. The drilling work was carried out with percussive rotary drilling machines (or down-the-hole drills), and there were no samples for adequate geological logging. The study monitored the drilling of 39 soil nail holes. The DPM data were analyzed to obtain the variation of drill bit penetration depth with time and the penetration rate profile along each soil nail hole.
The existing vertical and inclined drillhole logs were further analyzed. The logs were compared with the DPM ground profile. This comparison revealed that the DPM penetration rate can be used to determine the weathering profile in the ground. In particular, a statistical correlation between the total core recovery from the drillhole logs and the DPM penetration rate was established.
The conventional soil nail pullout tests including specifications, arrangements and procedures were studied. Twenty pullout tests at the construction site were carried out and recorded. The test results were analyzed and further used to verify the findings on ground geological profiles from the DPM penetration rate. A mechanical model was proposed to check the pullout test results and to provide a comparison with the DPM penetration rate at the bond zone. The comparison revealed that a lower DPM penetration rate corresponds to higher pullout resistance in the ground, and vice versa.
The verification findings show that the DPM penetration rate, as a kinematical parameter, can be used to construct the weathering profile in the ground. This DPM ground profile can be used as factual data to verify geotechnical design and even to perform geotechnical design in weathered rocks during construction. To explore the potential for such applications, this study carried out a comparison between the DPM ground profile and the conventional contractor's records for drilling of soil nail holes.
The comparisons and verifications presented in this thesis have shown that the HKU-DPM penetration rate can be used to characterize ground conditions in weathered volcanic soils and rocks. The discovery that the DPM penetration rate is inversely related to conventional total core recovery and pullout resistance is of considerable importance, as a source of data with a number of possible applications in geotechnical engineering practice and geomechanical analysis.