Report No. : GEO Report No. 99

Report Title : A Review of Downhole Geophysical Methods for Ground Investigation (2000), 69 p. (Reprinted, 2002)

Author : K.C. Lau


One question raised in the December 1996 SSTRB meeting (Slope Safety Technical Review Board, 1997) that relates to the Phase 2 of the Assessment of Geological Features Related to Recent Landslides in Volcanic Rocks of Hong Kong study was "What methods of site investigation are available and should be adopted to establish the continuity and thickness of kaolin seams?" In response to this question, a research study on downhole geophysical methods for ground investigation in Hong Kong was initiated.

The objective of the study is to evaluate the capabilities and applicability of downhole geophysical and optical methods to 1) characterise discontinuities, in particular clay-infilled sheeting joints, within weathered rock in Hong Kong, and 2) determine small strain stiffness properties of weathered rock masses.

In this report, a review of downhole geophysical methods was conducted. Based on the existing data on the conditions of discontinuities, in particular clay-infilled sheeting joints, within a weathered rock mass in Hong Kong preliminary downhole geophysical methods were selected for the field trials to be conducted in the next phase of the study.

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