Abstract:Wanfu coal mine is located in south-west of Shandong Province,China. The overburden soil layer in the mine is over 700 m thick of the alluvium of Yellow River. The burial condition of the coal layers in the mine makes the mining very difficult. In order to provide reliable engineering-geological information for the mining design,in-situ stress measurement in the mine is carried out. Because the mine is just in the early exploration stage and there is no entrance to underground positions,the only reliable stress measurement technique in this stage is hydraulic fracturing technique. To save the measuring cost,the hydraulic fracturing stress measurement is performed in the exploration boreholes. There are 29 exploration boreholes in the mine,in which 7 boreholes are meticulously chosen for hydraulic fracturing tests. Among the 7 boreholes,6 boreholes are near or over 1 100 m in depth,and the deepest measuring point is 1 105 m deep. It is a new record of measuring depth for in-situ stress measurement using hydraulic fracturing technique in China. In order to make the sealing and impression packers to pass the thick overburden soil layers smoothly and ensure the hydraulic fracturing tests to be successful at the depth more than 1 000 m,a series of special equipment and measuring techniques are developed. Successful hydraulic fracturing tests are carried out at 3–6 measuring points in each borehole and altogether 37 hydraulic fracturing tests are completed in 7 boreholes. Through the measurement the in-situ stress state and its distribution law in Wanfu coal mine are obtained. The ratio of maximum horizontal principal stress to vertical principal stress is 1.441–3.224 with an averaged value of 1.97 in 37 measuring points. It shows that the in-situ stress field in Wanfu coal mine is dominated by tectonic horizontal stress. The stress measurement results provide a solid basis for construction and mining design in the mine.