- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
In 1983, a catastrophic landslide occurred in Saleshan, Dongxiang, Gansu, China, which resulted in the death of 237 people and the destruction of 585 houses. Saleshan landslide was a typical rapid moving landslide in loess area, China, which moved with extremely high speed and long run-out distance on a gentle sliding surface. This paper reviews the characteristics of the landslide and its consequence, analyzes the possible triggers and the processes of development, and back-calculates the kinematic characteristics of the landslide. The digital elevation models (DEMs) of the study area before and after the event were used to analyze the geomorphological characteristics before and after the event. The authors inferred the possible deformation and failure processes of the landslide based on available observations. Direct shear tests were carried out to obtain the parameters of the soil involved in the failure and postfailure process, which was adopted in the following simulation using an energy-based runout model. The velocities of moving materials at a different time stage together with the variation of runout distance and maximum flow height are presented. The authors also compared the calculated results with field observations and previous simulation results. Sensitivity analysis was conducted to understand the effect of internal and basal friction angles on the kinematic characteristics. This study indicates that the Saleshan landslide was a fast-moving landslide with long traveling distance. The landslide lasted more than one minute with a maximum velocity of approximately 25 m/s according to the calculation using the energy runout model, which was consistent with the estimations based on the observation of eyewitness. This study also gives an insight on the progressive failure mechanism and explains the high mobility of Saleshan landslide in details, which provides a reference for hazard zonation for areas along loess platforms.
Discussion and conclusions
Figure 19a indicates the precipitation before and after the event. The accumulative precipitation before the event in 1983 was around 15 mm, and no precipitation was recorded three days before the Saleshan landslide. In 1982, the accumulated rainfall was approximately 430 mm, close to the average annual precipitation that is 485 mm. However, the precipitation from October to December in 1982 was 66.3 mm, seven times more than the average precipitation in the same period previous years (Han, 1986). This would very likely result in a larger variation of the underground water table in the following few months, compared with the resulted variation of the water table in the previous years. Figure 19b shows average temperature in 1983. In January and February, the average temperatures were -8.2 ºC and –4.4 ºC. However, the average temperature rose up to 0.9 ºC, which probably caused an increase of water table as the result of the infiltration of meltwater along the seepage path located in the The cracks behind the crest of the slope and fissures developed in the soil accelerated the infiltration of the water (Figure 5). The cracks can also store the perched water to supplement the groundwater. The infiltration of water played a significant role in the progressive failure process which could lead to the reduction of shear resistance that can further accelerate the failure process. In the post-failure process, the existing water in the sliding zone significantly decreased the shear resistance of the soil in the sliding zone and decreased the effective stress applied on the alluvial sand due to the excess pore water pressure. The sliding zone in the slope was developed progressively, and the landslide exited from the bottom of the slope. The weathering and loss of structural strength resulted in the development of fissures and cracked in the soil. A local shear surface was then formed after a long period and extended to the toe of the slope and bottom of the tension cracks behind the slope, as proposed by Petley et al. (2005). The comparison of the DEMs before and after the event together with the borehole information indicated that the toe of the slope had been mobilized and landslide exited from the toe of the slope.