Estimating in-situ rock stress from spalling veins: A case study

Stress-induced failures have typically been considered as engineering disasters in deep underground excavations. This paper highlights the importance of stress-driven rock failures as a means to estimate the in-situ rock stress at the depth. The method, which is based on the observation and documentation of a failure mode referred to here as “spalling” in deep tunnels or caverns, is put forward and presented to estimate the macro-scale rock stress. Using the proposed method, the orientation of the principal stresses in-situ can be deduced by the spalling intensity and associated stress-induced spalling veins in the rock mass surrounding the opening, and the magnitude of the principal stresses can be estimated by the assumed crack initiation stress required to generate spalling in the given rock by careful documentation of spalling failure characteristic in the field. A real case study at Baihetan powerhouse site has been carried out and indicates that the proposed method is an available way to enriching recognition of in-situ rock stress and a helpful supplement to traditional methods of stress measurements after strictly numerical verification. Analysis of the regional tectonic setting as well as measurements of in-situ stress supports the results by the suggested approach.