Study On Engineering Properties Of The Moraine In Sichuan-Tibet Transportation Corridor

Sichuan-Tibet line cross the cold alpine mountain in the earthquake-prone.This prone will encounter glacial debris flow、landslide blocked river、earthquakes and other disasters.The subgrade in this prone offen build along the river and will encounter many problems. So the stability of the subgrade built along the river in the earthquake-prone is particularly prominent. Firstly, By extensive data collection and analyzing, we conclude the factors of the subgrade stability which is along the river and in the alpine mountain of earthquake-prone. Then, we study emphasis on the stability of the subgrade along the river when it is in seismic action and occur dramatic changes of the water level by means of GEO-SLOPE software.At last, according to the influencing factors, we put forward control measures. The primary coverage as follows:1. The stability influence factor of the subgrade along the river in cold alpine mountain and earthquake-prone includes water immersion、scouring, collapse, rock-fall, landslide, slope foundation unstable, earthquake, dramatic changes of the water level.2. We use pseudo-static method to analyze the stability of the subgrade along the river when earthquake occur in SLOPE/W module. On the same water level, as the earthquake acceleration increases, subgrade safety coefficient decreased; On the same earthquake acceleration, the higher of the water level, the bigger of the subgrade safety coefficient. The higher of the subgrade along the river, the smaller of the subgrade safety coefficient. The slower of the transverse slope, the bigger of the subgrade safety coefficient.3. First, we analyze the seepage of water in the subgrade when the water level sharp rise and sharp decline in the SEEP/W module. Then we import the results in the SLOPE/W module to analyze the stability of the subgrade The results show that water seep from outward of the subgrade along the river to inside when water level sharp rise and the safety coefficient increase. In the early time, the safety coefficient increases slow; in the late time, increase fast. Water seep from inside of the subgrade along the river to outward when water level sharp decline and the safety coefficient decline. In the early time, the safety coefficient decline fast; in the late time, decline slow. The faster water level decline, the bigger pore water pressure and the smaller safety coefficient. When the subgrade experiencing water rising then falling, the safety coefficient will reduce. When water falling into the lowest level, there is the smallest safety coefficient. As pore water pressure dissipating, the safety coefficient will increase, but it’s a long time. We compare different height (from 5 m to 7.5 m) subgrades’safety coefficient when the subgrade experiencing sharp decline. The research shows that The higher of the subgrade along the river, the higher the risk of it; By comparing the subgrade safety coefficient on different water level, we found that the most dangerous position is falling to 0.5～0.9 times subgrade slope height from subgrade surface. By changing the filling parameters, We found:increasing c or phi value will increase the safety coefficient; phi value effect the safety coefficient more than c value. Setting up embankment retaining wall before the subgrade will increase the subgrade safety coefficient during rapid drawdown.4.We put forward control measures for the influence factor of the stability of the subgrade. The stone cage and riprap can prevent water immersion and scouring, active network/passive network can prevent collapse and rock-fall, cutting side load、supporting and retaining can prevent landslide; Cleaning soft loose layer, setting reinforced concrete lateral restraint pile, using composite foundation to prevent slope foundation unstable; Seismic intensity region should control the height of subgrade and take seismic measures if necessary, such as geogrid、geotechnical cancellous. Choosing drainage, high phi value materials as subgrade filler, keeping subgrade drainage and setting embankment can enhance the stability when the water level dramatic changes.