Dizhi lixue xuebao (Jun 2023)
In-situ stress measurement and inversion analysis of a large hydropower project in southeast Tibet
Abstract
As a control and regulating project, the hydropower station in the Yigongzangbu basin of Tibet plays a vital role in meeting the electricity demand of the Tibetan power grid. Identifying this hydropower station’s present-day in-situ stress environment and understanding the characteristics of in-situ stress distribution at critical locations such as underground plants and diversion tunnels are essential to ensure its engineering safety. Based on the tectonic and geological background and rock conditions of the project area, we carried out hydraulic fracturing in-situ stress measurements by placing boreholes and obtained in-situ stress data from 4 measurement points (8 boreholes). A finite element three-dimensional geological model was established according to the existing geological conditions. The measured stress state revealed the loading conditions, and the inverse analysis of the stress field in the engineering area was made. The maximum horizontal principal stress ranges from 4.17 to 16.93 MPa in the 2D test and 14.2 to 16.23 MPa in the 3D test. The maximum horizontal principal stress orientation is NE 38°to NE 47°, and the NE direction dominates the present-day tectonic stress field. In the 2995-meter elevation horizontal plane of the underground plant area of the power station, the stress values of σ1, σ2, and σ3 range from 11.70 to 12.12 MPa, 9.81 to 10.74 MPa, and 5.22 to 6.85 MPa, respectively. The maximum principal stress value of σ1, σ2, and σ3 along the diversion tunnel range from 11.8 to 14.05 MPa, 10.13 to 12.83 MPa, and 4.56 to 8.49 MPa, respectively. The axis direction of this hydropower station’s underground plant and the diversion tunnel’s axis direction intersect at a slight angle with the direction of the measured maximum principal stress, and the ground stress field is favorable to the stability of the project cavern. It is necessary to consider the actual geological conditions and adopt suitable tunnel construction technology in the later construction process. The construction monitoring should also be strengthened to ensure the project’s safe construction.
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