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A switching station is planned to be built in Enshi City, Hubei Province, China. It locates in hill landform, and the elevation of the site is lower than that of surroundings. The site should be backfilled with surrounding soils. The embankment is of 4-16m in height, and is reinforced by TENSAR geogrid reinforcement. When the slope was backfilled about 8m in height, a series of sliding evidences was discovered at the northeast side of the slope, such as fissures, uplift, road damage and pinnate fissures. With the development of sliding, the dimensions of the landslide were 35m in width and 20m in length, the maximum horizontal displacement and vertical settlement were 2.5m and 1.5m, respectively. Through the stability calculation and field investigation, the designed slope is stable while the replaced gravel cushion was not set according to the design sketch during the construction, thus the reinforced soil slope slipped in push-sliding type. Besides, other failure causes were: (i) poor foundation, (ii) rainfall, (iii) bad drainage, (iv) no stepped excavation. Further geological survey and quantitative analysis reveal that the quick field judgment and stability analysis in this paper are reasonable. It is concluded that the soft soil improvement, drainage of surface and groundwater must be taken into great consideration, and carefully determined before the filling of reinforced soil slope.