Research On The Seismic Response Characteristics Of The Lengzhuguan Rock Slope

China is located in the Mediterranean Himalayas earthquake belt and circum-pacific seismic belt, and it distributed in the Himalayas earthquake region and Taiwan earthquake region and other active seismic regions. So earthquake may happen easily in these regions of China, especially in southwestern of China, the earthquakes caused a lot of slope instability and failure, which lead to landslides, avalanches, debris flow and other geological disasters chain. And many people's lives were hurt and properties were damaged. Based on geological studies and theoretical modeling, many authors have reported that topographic amplification effects occur at protruding topography and at slope breaks during earthquakes, leading to more slope failures at those locations than at other parts of the slopes. Therefore, research on the seismic response characteristics of the slope has particularly prominent, important, theoretical and practical significance in deep-cutting gorge and high intensity seismic region.Due to the current seismic active period in western Sichuan province, we set up a monitoring section in Lengzhuguan near the Xianshuihe fault as a natural field experiment. The seismic response characteristics could be studied in different topography and structural characteristics with different earthquake magnitude and propagation. Furthermore, a 3D numerical stimulation model is also set up to analyze the dynamic response characteristics of the slope. The main results are as follows:(1) The Lengzhuguan earthquake monitoring adit stations are located on both sides of the Lengzhuguan river valley where it flows into the Dadu River and on the right bank of the Dadu River. The study area belongs to the eastern margin of the Tibetan Plateau, which is deep-cutting gorge landform. A "peninsula" isolated ridge strikes approximately 15-25 ° and the ridge width ranging from 50-1000 m which is located on the right bank of Lengzhuguan ditch. A nearly linear slope strikes approximately EW and dips steeply(about 40°) to NW, and altitude difference is about more than 1000 m.(2) It concluded that the different slope shape and terrain conditions have different seismic response effect, and the "peninsula" isolated ridge is most obvious, slope break followed, and nearly linear slope is weakest. Monitoring data reveals that the PGA amplification factor on the top of the “peninsula” isolated ridge reach the maximum to 5.7-11.5, and spectral ratio analysis also show the direction perpendicular to the ridge is responded sharply.(3) Monitoring data showed that ground motion response parameters like PGA, RMS acceleration and Arias Intensity were larger with greater magnitude of the earthquake, but the amplification factor of the parameters did not keep consistent with this law. Meanwhile, PGA or PGA amplification factor was larger when the seismic wave propagation direction was agreement with the slope direction than the reverse.(4) The data revealed that the horizontal peak acceleration at each monitoring site decreases with the increase of depth. It decreases greatly within the surface range and at the inner slope falls at a slow rate. And Fourier spectrum varied with the same change laws of the PGA. Traditional spectral ratio method and HVSR pole graph showed that the range of amplification frequency in different depths were almost at the same level, and the directional effect of seismic response were nearly uniformly.(5) Numerical analysis showed that the maximum unbalanced force of the system model was positively correlated with the input seismic wave characteristics, and the model was still in steady state finally. Result showed that different terrain conditions had different seismic response to the earthquake. The PGA amplification factor reached to 2.0 on the top of the isolated ridge slope, while the linear slope was about 1.2 in horizontal direction and 1.7 in Z direction. And the PGA was decreased with the increases of the depth at the same altitude. Compared with the slope in different wave propagation direction, the PGA amplification factor was bigger at the back side than the welcome.