Abstract: Tianchiping tunnel is a very long single track tunnel from Lanzhou to Guangyuan of Lanyu railway, which is located at Tanchang couty of Gansu province. The total length of the tunnel is 14. 528 km. In the exploration area, a total of 26 hydrofracturing tests in 4 vertical exploration boreholes drilled from the ground surface are carried out. The results suggest that the present stress field of Tianchiping tunnel is dominated by horizontal stress, and the maximum horizontal stress is dominantly oriented NNW-NW-NWW. Stress magnitude is extreme high stress level. At the same time, the maximum horizontal stress orientations are closely consistent with those in the general contemporary stress field in southeast of Gansu Province. The maximum horizontal stress orientations in measurement hole No. LY1 is N40° W-N45°W. The angle is large between the maximum horizontal stress orientations and those along tunnel axis, which is a great disadvantage to the tunnel stability. Based on the geological conditions and rock mass properties, a 3D mechanical model is established, and the regional geo-stress field of tunnel area is analyzed by 3D multivariate FE regression from limited stress data of in-situ geo-stress measurement. The results of macro geo-stress field indicate that the transverse stress values are lager than 10 MPa along the tunnel axis,the lateral pressure coefficients is between 1 and 2,and stress concentration due to topography and other factors on local areas results to a great large lateral pressure coefficients. The results of macro geo-stress field are very important for dynamic design and construction.

Key words: tunnel engineering;Tianchiping tunnel;hydraulic fracturing method;geo-stress measurement;regression analysis;FEM