Characteristics of in-situ stresses and engineering stability analysis on the south section of the cross-Bohai Strait passage project

The cross-Bohai Strait passage project is an important maritime traffic project which joins Northeast regions and Shandong Peninsula. The state of geostress provides an important reference for engineering design and construction decision-making. In order to better understand the present geostress characteristics and the distribution characteristics of the tectonic stress field in the southern section of the project, hydraulic fracturing tests for stress measurements were conducted at BGZ borehole in the range of 0～300 m depth at Beigou town, southwest Penglai district, Yantai city.By analyzing the measurement data, the result indicates that the in-situ stress field is controlled by horizontal tectonic stress in the study area，and the ground stress values are in the middle level as compared with that obtained elsewhere in Northeast -North China stress region; S_H（the maximum horizontal principal stress）、S_h（the minimum horizontal principal stress）and S_v（the vertical principal stress）change linearly with the depth of BGZ borehole; in the range of measurement depth, the shallow surface stress type of the crust is mainly reverse fracture type，that is the relationship of the three principal stresses is S_H＞S_h＞S_v；The measured S_H average azimuth angle in the borehole is N75.3°E, which is in good agreement with the direction of the tectonic stress field of North China stress zone that the study area belongs to, and is basically consistent with the direction of the regional tectonic stress field revealed by the focal source mechanism solution and GPS measurement. The Coulomb friction sliding criterion and the measurement data are applied to preliminarily evaluate the current accumulation level of geostress in the study area and its impact on engineering stability, it is believed that the overall level of stress accumulation in the region is relatively low, and the crust in the engineering area is currently relatively stable. In addition, based on the comprehensive discrimination criterion of surrounding rock burst σ_θmax / R_c, the possibility of rock burst of the surrounding rocks in the underground tunnel project of the cross-Bohai Strait passage is discussed. It is primarily concluded that there is currently no possibility of rock burst in the underground tunnel of the cross-Bohai Strait passage project, and the surrounding rock of the tunnel is in stablity. The findings in this paper can provide scientific basis for the optimization of the design, construction schemes and other schemes of the Bohai strait cross-sea channel project, at the same time, he study can also provide some basic data for research on active fault, seismogeology and regional dynamics in the survey area, etc.