Field monitoring of rainfall infiltration in a loess slope and analysis of failure mechanism of rainfall-induced landslides

Abstract A full-scale field experiment involving artificial rainfall has been conducted in an instrumented loess cut slope in an expressway in a loess plateau, Northwest China. Instrumentations including soil moisture probes, tensiometers, piezometers, vacuum sensors, water level sensors, and rain gauge were installed in the slope. After monitoring for about 2 years, artificial rainfall was induced at the site in April 2007. This paper presents the results from soil moisture probes, tensiometers, and water levels to reveal the surface infiltration process in an unsaturated soil. The results show that the top 0.7 m in loess is an active zone under the process of infiltration and evaporation, when subjected to a maximum rainfall intensity of 40 mm/day. The depth of the “wetting front” during the wet season was limited to the top 2 m of soil. During high rainfall intensity of 120 mm/day, the depth of the “wetting front” is about 3 m. Based on the variation of volumetric water content and matric suction in soil, a method to analyze the rainfall infiltration is proposed. By means of Gravity-Predominant Flow (GPF) concept, the infiltration rate is analyzed in the deeper soil. The results explain well the observations that loess slopes could be stable in the wet season, but it may tend to slide about 3–6 months later in the dry season. The surface infiltration has a very limited effect on the permanent groundwater table, which is at a greater depth.

[1]  Tsuyoshi Miyazaki,et al.  Water flow in soils , 1994 .

[2]  Leslie George Tham,et al.  Field-monitored variations of soil moisture and matric suction in a saprolite slope , 2005 .

[3]  B. Collins,et al.  STABILITY ANALYSES OF RAINFALL INDUCED LANDSLIDES , 2004 .

[4]  Malcolm G. Anderson,et al.  An integrated hydrological model for rain‐induced landslide prediction , 2002 .

[5]  D. Fredlund,et al.  Effect of rainfall on matric suctions in a residual soil slope , 1996 .

[6]  Richard M. Iverson,et al.  Landslide triggering by rain infiltration , 2000 .

[7]  Jeffrey P. Walker,et al.  In situ measurement of soil moisture: a comparison of techniques | NOVA. The University of Newcastle's Digital Repository , 2004 .

[8]  Rex L. Baum,et al.  Modeling regional initiation of rainfall-induced shallow landslides in the eastern Umbria Region of central Italy , 2006 .

[9]  D. R. Nielsen,et al.  On describing and predicting the hydraulic properties of unsaturated soils , 1985 .

[10]  M. Crozier.  Landslides: Causes, Consequences and Environment , 1986 .

[11]  D. Hartley,et al.  Interpretation of Kostiakov Infiltration Parameters for Borders , 1992 .

[12]  J. Jiao,et al.  In situ rainfall infiltration studies at a hillside in Hubei Province, China , 2000 .

[13]  M. Crozier.  Prediction of rainfall-triggered landslides: a test of the Antecedent Water Status Model , 1999 .

[14]  Giovanni B. Crosta,et al.  Regionalization of rainfall thresholds: an aid to landslide hazard evaluation , 1998 .

[15]  T. Tsai,et al.  Modeling of rainfall-triggered shallow landslide , 2006 .

[16]  Charles Wang Wai Ng,et al.  A numerical investigation of the stability of unsaturated soil slopes subjected to transient seepage , 1998 .

[17]  Thomas Glade,et al.  Applying Probability Determination to Refine Landslide-triggering Rainfall Thresholds Using an Empirical “Antecedent Daily Rainfall Model” , 2000 .

[18]  W. Durner.  Hydraulic conductivity estimation for soils with heterogeneous pore structure , 1994 .

[19]  S. Au.  Rain-induced slope instability in Hong Kong , 1998 .

[20]  C. F. Lee,et al.  Frequency–volume relation and prediction of rainfall-induced landslides , 2001 .

[21]  Toshitaka Kamai,et al.  Monitored and simulated variations in matric suction during rainfall in a residual soil slope , 2008 .

[22]  D. Fredlund,et al.  Soil Mechanics for Unsaturated Soils , 1993 .

[23]  David G. Toll,et al.  The effect of antecedent rainfall on slope stability , 2001 .

[24]  David G. Toll,et al.  Infiltration characteristics of two instrumented residual soil slopes , 2003 .

[25]  D. Zerihun,et al.  Modified Kostiakov Infiltration Function: Accounting for Initial and Boundary Conditions , 2006 .

[26]  C. F. Lee,et al.  Characterization of rainfall-induced landslides , 2003 .

[27]  E. Derbyshire,et al.  Geological hazards in loess terrain, with particular reference to the loess regions of China , 2001 .

[28]  Seung-Rae Lee,et al.  INSTABILITY OF UNSATURATED SOIL SLOPES DUE TO INFILTRATION , 2001 .

[29]  Yossef H. Hatzor,et al.  Large-scale infiltration experiments into unsaturated stratified loess sediments: Monitoring and modeling , 2008 .

[30]  Sang-Seom Jeong,et al.  Influence of rainfall-induced wetting on the stability of slopes in weathered soils , 2004 .

[31]  Z. Q. Yue,et al.  Comparison of field and laboratory soil-water characteristic curves , 2005 .

[32]  Harianto Rahardjo,et al.  INSTRUMENTATION OF AN UNSATURATED RESIDUAL SOIL SLOPE , 1999 .

[33]  Charles Wang Wai Ng,et al.  Influence of rainfall intensity and duration on slope stability in unsaturated soils , 1998, Quarterly Journal of Engineering Geology.

[34]  B. Huat,et al.  Water infiltration characteristics of unsaturated soil slope and its effect on suction and stability , 2006 .

[35]  D. G. Fredlund,et al.  Effect of soil suction on slope stability at Notch Hill , 1989 .

[36]  David G. Toll,et al.  CONTROLLING PARAMETERS FOR RAINFALL-INDUCED LANDSLIDES , 2002 .

[37]  Wang Wei-sheng.  Distribution regularity and forming condition of loess landslide , 2001 .

[38]  D. Montgomery,et al.  A physically based model for the topographic control on shallow landsliding , 1994 .

[39]  Van Genuchten,et al.  A closed-form equation for predicting the hydraulic conductivity of unsaturated soils , 1980 .