Abstract: Abstract: Engineering accumulation, a kind of loose soil-sock mixture consisted of soil, parent rock and stone caused by various artificial engineering during producing and constructing process, is the most serious erosion-landform in production and construction areas because it can greatly change the terrain, soil and vegetation conditions of original landform in a very short term, thereby causing great soil and water loss under a certain rainfall-runoff condition, and making more difficult for ecological restoration in these project areas. In order to revel the runoff erosion mechanism and its process for engineering accumulations with different slopes and soil-rock ratios, we carried out field scouring experiments from August to November 2012 at the Soil Erosion Experiment Site for production and construction projects in Southwestern University, Chongqing (29° 48' 50.2" N, 106° 24' 48.8 "E). The field scouring experiments were conducted under the simulated runoff conditions according to the regional rainstorm occurrence frequency with the 5, 10, 15, 20, 25 L/min for purple soil deposits and 5, 7.5, 10, 12.5, 15 L/min for yellow sand deposits, respectively. In the experiment, some physical properties, hydraulic properties and runoff erosion process on underlying surfaces of engineering accumulations with different producing sources and soil-rock ratios were all comparatively studied. The results indicated that material composition and infiltration capacity of the two loose engineering accumulations were remarkably different from original landform. The yellow sand deposit was dominated by ≤0.25 mm particles with particles variation coefficient as high as 1.2-2.0 times than its original landform and its stable infiltration rate was 1.70-4.07 times than original landforms, respectively; while purple soil deposit was well-distributed, its' variation coefficient of particles was 2.2 times than original landform and the stable infiltration rate was 7.02-11.59 times than original landforms. The experiments also showed that soil-rock ratio change could influence the slope infiltration performance for the two engineering accumulations and the effects of engineering construction on the purple soil deposits were more powerful than that of the yellow sand deposits. Some dynamic parameters on underlying surfaces of engineering accumulations increased with increasing flow discharge, in which flow velocity of yellow sand deposits ranged from 0.155 to 0.318 m/s, flow shear stress varied between 27.632 and 57.154 N/m2, and soil detachment rate changed from 0.337 to 77.071 g/(m2·s); while the flow velocity, flow shear stress and soil detachment rate of purple soil deposits were 0.184-0.281 m/s，35.525-53.600 N/m2 and 1.445-61.910 g/(m2·s), respectively. For rocky underlying surfaces, runoff yield rate had continuously waving variations within 9 min after runoff yielded. When flow discharge increased gradually from 5 to 25 L/min, the average runoff yield rate of rock underlying surface from yellow sand deposit increased by 510.38%, 531.96 % and that of purple soil deposit increased by 73.20% and 57.61%, respectively; for same conditions, the cumulative runoff of underlying surfaces showed the similar trend of partial soil deposits larger than rocky deposits, and that of yellow sand deposit higher than purple soil deposit. For rocky underlying surfaces, sediment yield rate presented continuously multi-peak multi-valleys. When flow discharge increased from 5 to 25 L/min gradually, the average sediment production rate of rock underlying surface from yellow sand deposit were 0.001, 0.03, 0.542 kg/(m2·min), respectively, while that of purple soil deposit were 0.0003, 0.012, 0.034 kg/(m2·min), respectively. The collapse on gully wall caused by gravity from underlying surfaces was an important cause for the fluctuating variations of the sediment yield rate. These results provide essential parameters and technical supports for predicting soil water loss caused by production and construction projects and for selecting vegetation measures for soil and water conservation in similar areas.