(1. School of Civil Engineering and Mechanics，Yanshan University，Qinhuangdao，Hebei 066004，China； 2. School of Energy Science and Engineering，Henan Polytechnic University，Jiaozuo，Henan 454000，China； 3. School of Civil and Environmental Engineering，University of Science and Technology Beijing，Beijing 100083，China； 4. Institute of Geomechanics，Chinese Academy of Geological Sciences，Beijing 100081，China)
Abstract：Hydraulic fracturing is an efficient method for determining the stress field and is suitable at the early stages of projects when no underground access exists. Wanfu coal mine is located in the southwest of Shandong Province，China，which is prepared to construct with great annual coal capacity. The overburden soil layer is the alluvium of the Yellow River with the thickness of over 700 m. The depth of coal deposit is about 1 004.12 m. Determination of both the orientation and magnitude of in-situ stresses at great depth is quite difficult，so some new stress measurement techniques are employed. In the exploration area，a total of 37 hydrofracturing tests in 7 vertical exploration boreholes drilled from the ground surface are carried out. The results suggest that the maximum horizontal stress is dominantly oriented NEE-SWW. This stress direction is also in agreement with the direction derived from the focal mechanism in the area. At the same time，the maximum horizontal stress orientations are closely consistent with those in the general contemporary stress field in southwest of Shandong Province. The ratio of maximum horizontal principal stress to vertical principal stress is 1.44–3.22 with the average of 1.97 in 37 measuring points. It is shown that the prevailing stress field in Wanfu coal mine is controlled by the tectonic horizontal stress. Based on the geological conditions and rock mass properties，a 3D mechanical model is established and a regressive method for obtaining regional stress from limited stress data by using a 3D finite element method is proposed. According to the spatial distribution of the stress filed，the curves of principal stress for coal roof are plotted；and some adverse geological phenomena are discussed.
