Development of Rainfall Hazard Envelope for Unsaturated Infinite Slope

다국어 초록 (Multilingual Abstract)

Rainfall during summer season is one of the major causes of slope failure in Korea, especially in unsaturated weathered granite soils. The current slope design procedure for the rainy season is to just raise the ground-water level, which is not adequate for the unsaturated soil slope. Previous rainfall hazard envelopes only tend to use rainfall intensity and duration as the main variables, not considering mechanical and hydraulic characteristics of unsaturated soils. The general equation for Factor of Safety (FS) in infinite unsaturated slopes is derived to consider the rainfall infiltration. The three important factors governing the equation are as follows:rainfall characteristics such as intensity and duration to determine a wetting front depth using an infiltration model, shear strength theory for unsaturated soil, and variation of suction profile during rainfall. The minimal FS is calculated from the FS profile with depth for a given rainfall intensity and duration, and a rainfall hazard envelope considering soil infiltration characteristics is built for a given slope angle. The procedure to develop a hazard envelope for various slope angles is applied to three unsaturated weathered granite soils in Korea.

참고문헌 (Reference)

1 정상섬, "지속강우특성에 따른 불포화 풍화토사면의 안정성분석" 대한토목학회 29 (29): 1-9, 2009

2 Fredlund, D. G., "The shear strength of unsaturated soils" 15 (15): 313-321, 1978

3 Caine, N., "The rainfall intensity–duration control of shallow landslides and debris flows" 62 (62): 23-27, 1980

4 Guzzetti, F., "The rainfall intensity-duration control of shallow landslides and debris flows: an update" 5 : 3-17, 2008

5 Lu, N., "Suction stress characteristic curve for unsaturated soil" 132 (132): 131-142, 2006

6 Green, W. H., "Studies on soil physics I. The flow of air and water through soils" 4 (4): 1-24, 1911

7 Collins, B. D., "Stability analyses of rainfall induced landslides" 130 (130): 362-372, 2004

8 Rahardjo, H., "Shear strength characteristics of a residual soil" 32 (32): 60-77, 1995

9 Chleborad, A. F., "Rainfall thresholds for forecasting landslides in the Seattle, Washington, area - exceedance and probability" U.S. Geological Survey 2006

10 Mein, R. G., "Modeling infiltration during a steady rain" 9 (9): 384-394, 1973

11 NIDP, "Model development to evaluate geotechnical disaster on steep slope considering rainfall and infiltration characteristics" National Institute of Disaster Prevention 2010

12 Iverson, R. M, "Landslide triggering by rain infiltration" 36 (36): 1897-1910, 2000

13 김재홍, "Influence of rainfall-induced wetting on the stability of slopes in weathered soils" 75 : 251-262, 2004

14 ASCE, "Hydrology handbook, In ASCE Manual No. 28"

15 Cho, S. E., "Evaluation of surficial stability for homogeneous slopes considering rainfall characteristics" ASCE-AMER SOC CIVIL ENGINEERS 128 (128): 756-763, 2002

16 Fredlund, D. G., "Equations for the soil-water characteristic curve" 31 (31): 521-532, 1994

17 Li, A. G., "Comparison of field and laboratory soil-water characteristic curves" 131 (131): 1176-1180, 2005

18 Lee, M. L., "A simple model for preliminary evaluation of rainfall-induced slope instability" 108 (108): 272-285, 2009