Estimation of the present-day stress field using in-situ stress measurements in the Alxa area, Inner Mongolia for China's HLW disposal

The Alxa area is a candidate site for China's high-level radioactive waste (HLW) repository. In-situ stress measurements using hydraulic fracturing were performed to directly estimate the present-day stress field of the Alxa area. Variation of the in-situ stress components with depth in two sub-sites (i.e., Nuorigong, and Tamusu) was analyzed based on valid hydraulic fracturing data obtained from two sub-vertical boreholes. The results reveal that the horizontal stresses in the Alxa area present an intermediate or low level. The in-situ stress magnitudes are consistent within the crustal frictional strength range that predicated using the Coulomb frictional-failure theory incorporating frictional coefficients of approximately 0.6-1.0. The maximum horizontal stress in the Alxa area is dominantly oriented in the NNE-SSW direction which is consistent with the direction of the tectonic stress field of northwest China. The estimation of the in-situ stress measurement results provides critical knowledge of the engineering geological characteristics of this candidate area, and support on potential underground excavation.