Earthquake Disaster Investigation Of V-Shaped Deep Vally And Research Of Disaster Itigation Countermeasures For Highway Reconstruction Engineering

Ⅴ-shaped deep vally is the normal geomorphology in southwestern mountain areas. It is usually the corridor for the highway. Yuzhi creek is the first tributary of the Ming River, and it is the typical Ⅴ-shaped vally. S303highway from Yingxiu to Wolong is along the Yuzhi creek, which locates the epicenter of the5.12Wenchuan-Earthquake. The distance between the Yinxiu-Genda sections (18km) to the earthquake center is about7km. Based on the engineering background, coseismic geological disasters and road damages were investigated. The forms of coseismic geological disasters of the Ⅴ-shaped vally in the near field region were researched. Combining the secondary disasters after the earthquake, the mechanism of the secondary disasters induced by the earthquake was studied. The contermeasures for the secondary disasters during the highway repair project were proposed. Based on this research, the universal contermeasures for the mechanism of highway earthquake disasters along the Ⅴ-shaped vally were proposed. The main conclusions are as following:1. During the formation process of the slope landforms caused by the mountain uplift, tectonic monement, and river erosion, the Ⅴ-shaped deep vally is at the the initial stage of the evolution of the vally landforms. The strss and strain in the shallow structure are released in the short period of time because of the earthquake. The release of the stress and strain before the evolution of the vally landforms induces the serious damages of the surface. Under the same lithology and the seismic intensity, collapse of the landslides caused by the earthquake in the Ⅴ-shaped vally is more serious than that in the U-shaped vally.2. Usually, the coseismic slope disaster is the collapse in the Ⅴ-shaped deep vally with hard bedrock. For highway, the main earthquake damage mode is the block of the road by the rock piles because of the collapse of the upper slope. The main earthquake damage mode for the bridge is the smash by the boulder. Due to the narrow of the vally, the river can be blocked easily by the rock piles from the collapse of the upper slope. The road is flooded by the multi-level quake lake. This is the typical earthquake damage in the Ⅴ-shaped vally.3. The main secondary damage after the earthquake is the debris flow in the deep vally. It has the characteristic of large scale and high frequency as Wenchuan earthquake zone. However, the Ⅴ-shaped vally is narrow, and the water transport ability is small. The debris flow can block the river directly, and raise the river bed substantially (up to35m by one debris flow). The highway may be buried even at high locations. This is the typical disaster mode for the V-shaped vally after the earthquake.4. According to the typical debris flow disaster mode for the V-shaped vally after the earthquake, the treatment principles are proposed by different types. The small scale debris flow with more afterward materials has high chance to form the large scale debris flow. The treatments are:detour, tunneling, and drainage canal. The large scale debris flow may have less afterward materials. The treatments are:improving the longitudinal slope, drainage canal, and retaining wall. For the large scale debris flow with more afterward materials, the treatments are:detour and tunneling. If the river is raised by the plug body and the road is flooded by water, the comprehensive measurements such as dredging and raising the road shall be used.