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A complete stress determination has been performed by hydraulic tests on pre-existing fractures conducted in two inclined boreholes for a railway cavern in Hong Kong, China. A total of ten complete tests including normal stress and fracture plane orientation determination have been successfully carried out in the zone where the cavern is located. The test depth in two holes varies from 101 to 120 m beneath the ground surface. After a brief introduction to the test system, procedures, and results in this paper, the inversion method for in situ stress field, neglecting both the vertical and horizontal stress gradient, is reported. Moreover, the genetic algorithm is applied to search for the optimal solution, which minimizes the misfit function, and the misfit associated with this solution is used to evaluate the 90 % confidence level domain with the Monte Carlo Technique. The results of this study are useful for a better understanding of the stress level of the planned railway cavern and also helpful for the safety design of the cavern.

This technical note summarizes and discusses the results of the in situ stress measurements by hydraulic fracturing conducted in 7 holes at depths ranging from 21 to 111 m in planned dam sites, and in 13 holes at depths varying from 28 to 532 m in planned tunnel sites in the Western Route of South to North Water Transfer Project in China. The measured maximum and minimum horizontal principal stresses increase linearly with depth in tunnel sites, and piecewise-linearly in dam areas. The horizontal stresses are greater than the vertical stress, indicating a thrust faulting regime at all tested locations. Such a stress regime is confirmed by local geological structures. The direction of the maximum horizontal principal stress is generally NEE–SWW, which is highly correlated with the tectonic plate movement and crustal deformation in the study area, and consistent with that revealed by focal mechanism solutions from earthquakes. The results in the present study may provide in situ stress information for the design of planned dams and tunnels, and make a good complement to the World Stress Map.