Study On The In-situ Stress Field Of A Deep-incised Valley

More and more hydropower plants are or will be built in the deep-incised valleys andcomplex tectonic region of the western region in China, which sites in high in-situ stressand high seismic intensity zone. To ensure hydropower plants’s smooth construction andsafe operation in complex geological conditions and special in-situ stress field, it is veryimportant to deeply study the in-situ stress field characteristics of deep-incised valley tochoose sites, design and construct safely. In this paper, to study the stress field problem ofdeep-incised valley in a hydropower plants, it carried out the following studys:(1)The dissertation summarizes regional tectonic background and engineeringgeological conditions, the characteristics of regional geological tectonic and the "stagingerosion" process of valley growth, which provide geological basis for the elevation oferosion basis and tectonic stress in the process of evolution simulation.(2) To establish a deep-incised valley elastic-plastic finite element model of the stressfield, three different elevation of erosion basis in valley erosion process and the number ofpossible tectonic stress field mode are considered.The simulation results of erosion basisand surface weathering influencing valley stress field show it has less effect. Thesimulation results of different tectonic stress patterns influencing valley stress field showthat tectonic stress direction has greater impact on stress concentration band at the bottomof the valley and deep rock and less impact on the stress of slope surface.(3)According to measured results, the Simulated Annealing technique(SA) isintroduced into the Particle Swarm Optimization(PSO) in the study of the entire stressfield of deep-incised valley. To build neural network training samples, the forwardcalculation carrys out by appling multiple tectonic stress including the aforementionedvariety of tectonic stress mode to the finite element model. Inversion results could matchmeasured results well. There is a small angle intersecting between regional tectonicorientation and the river trend. Affected by topography, the slope rock stress of the rightbank is greater than the left bank’s. With the increasing of horizontal buried depth, theorientation of maximum horizontal stress of rock slope at left and right banks deflect fromthe NE to NNE direction, intersect in a large angle with the direction of the segment ofnujiang, and transfer into parallel. At the bottom of the riverbed, rock stress concentrationis significantly and mainly in horizontal direction.There is a large angle intersecting to thedirection of the segment of nujiang. With the increasing of vertical buried depth, the direction also transfer into regional tectonic stress orientation.