Review and assessment of in-situ rock stress in Hong Kong for territory-wide geological domains and depth profiling

Abstract

Hydraulic fracturing is a favorably used technique to measure in-situ rock stress orientation and magnitude for the design of underground excavations. In Hong Kong, studies prior to 2000 revealed a general WNW-ESE maximum horizontal stress orientation and established stress ratio depth profile. However, there is a paucity of geological assessment on the in-situ stress. By examining 380 no. of in-situ stress test results from 65 boreholes at depth ranging between 18 and 300 mbgl and the review of the associated raw data, such as pressure-time records and impression packer test results in the test reports, this study updates the map of Hong Kong regional major principal stress orientation. Besides, the study also reviews whether the major geological domains in Hong Kong have any major impact or influence on in-situ stress magnitudes and orientations. Depth relationships on principal in-situ stress orientation is also explored.

From the study, the following conclusions can be drawn: • High KH and Kh at shallow depth and the overall WNW-ESE orientation of maximum horizontal stress are observed. The results are consistent with the published measurements in previous studies. • The rock type imposes no prominent effect on the stress magnitude. • No apparent depth relationship on principal in-situ stress orientation is observed