Analysis On The Stability Of The Bank Slope Of Ancangjiang Bridge Which Is In The Area With High Seismic Intensity

Lancangjiang Bridge is a large-scale bridge which is the part of Dali-Ruili railway that crosses Lancangjiang River. The position where it located at is under the valley with sharp terrain coming along . In this district there is the fault of Shande Bridge which lies 240m away from the direction of Lancangjiang Bridge's Dali lateral abutment,while the fracture of Pingpo is just 1km away in the same direction. And the rock mass on the mountain that lies behind the Lancangjiang Bridge's Ruili side abutment may be collapse with large rocks . The bridge located in Lancangjiang Fault zone. In this area, the stress field is very complex and there are lots of seismic activities. It is a area with high seismic intensity and the peak acceleration of earthquake activity can be 0.2g. Determined by the complex geological condition of its location, it is not only necessary but an urgent required for the project construction to put research on the bank slope stability of Lancangjiang Bridge.First of all, in the paper, we build a 2D stress inversion model. With adjusting the boundary stress of the model, we simulate the stress value and distribution characteristics of the in-situ stress in this area. According to the result of simulation, we can determine that the maximum and minimum principal stress of the area where Lancangjiang Bridge located have non stress concentration with the faults structure.Secondly, we build a 3D bank model. In this model, the rock mass of the bank slope is considered as homogeneous material. Through the model, we do static and dynamic analysis on the bank slope when it is natural, loaded by bridge and with water poured in. Especially, we do dynamic analysis on the bank slope when it is under the circumstances of both frequent and rare earthquake. The result of Static analysis shows that:1. Loading by the bridge without water, the rock mass near the arch abutment is stable. But the rock mass above the posterior margin of arch abutment is going to move outside of the slope, which causes unfavorable influence on the stability of the rock mass. And the rock mass below the posterior margin of arch abutment is going to move inside of the slope, which is favorable to the stability of the rock mass.2. Loading by the bridge with water in hydropower reservoir, the horizontal displacement of bank slope was affected more by the hydrostatic pressure than the bridge load. The trend of the rock mass moving outside of the bank slope is further increased because of the water storage in hydropower station. It is adverse to the stability of bank slope, but not enough to cause a high degree of damage or bring instability to the bank slope.The result of dynamic analysis shows that:1. The condition of frequent seismic has almost the same influence on stress characteristics and displacement characteristics of the rock mass while there are three combinations of slope rock mass working on it. Affected by frequent seismic activity, the maximum displacement of the rock mass has occurred on Dali slope which lies near the fault of Dali slope. The maximum horizontal displacement of rock on Dali slope is about 5mm, while it is about 2mm on Ruili slope. According to Moore Judgment Criterion, we find that the strength of rock mass near Dali slope and slope toe is damaged owing to frequent seismic activity. The great range damage to the strength of rock mass in Ruili slope leads to slope rock mass collapsing and sliding.2. The influences from rare seismic condition on stress characteristics and displacement characteristics of rock mass in three combinations of slope rock mass working condition are basically the same. Influenced by rare seismic activity, the maximum horizontal displacement of rock mass has occurred near the fault of Dali slope. Most of horizontal displacements in Dali slope are about 7mm, and the maximum number is about 8mm. The horizontal displacement of rock mass under the bridge foundation and below the slope is about 7mm. On the other side, horizontal displacement of rock mass in Ruili slope is between 2 mm and 5 mm, smaller than in Dali slope. The horizontal displacement that rock mass of bridge foundation in Ruili slope has made is about 3 mm. According to Moore Judgment Criterion, we find that the damage to the strength of rock mass in Dali slope and Ruili slope by rare seismic earthquake activity is basically the same as the frequent seismic activity, but the damage caused by rare seismic activity is deeper and broader than by frequent seismic activity. It can make a stronger impact on the stability of tow sides of the slope.