Abstract: The determination of deep rock stresses is a focused and difficult issue in the study of regional stress field. Most estimating methods for deep rock stresses depend on the extrapolation of fitting empirical formula, which are short of theoretical basis and unreliable. This research proposed the lateral pressure coefficient polygon with reference to stress polygon theory, combined with stress factor R to better constrain stress distribution polygon. The Zijingguan fault belt in Yi county, Hebei province was chosen as the application area. Based on focal mechanism and in-situ stress measurement data in this area, , the maximum lateral pressure coefficient, and , the minimum lateral pressure coefficient, were estimated for the deep rock masses of 6 km, 11 km and 19 km respectively. The results showed that at three depths are 1.07 0.07, 1.14 0.14, 1.09 0.09 and are 0.85 0.15, 0.88 0.12, 0.86 0.14 respectively. The relative deviation of results is between 6% and 17%. The orientation of the maximum horizontal principal stress, jointly determined by hydraulic fracturing and focal mechanism methods, is N44.4°E. The method proposed and established in this research provides a new estimate means for deep rock stresses.

Key words: deep rock stresses, Zijingguan fault belt, stress polygon, stress factor, hydraulic fracturing method