Empirical and Physically Based Thresholds for the Occurrence of Shallow Landslides in a Prone Area of Northern Italian Apennines

Rainfall thresholds define the conditions leading to the triggering of shallow landslides over wide areas. They can be empirical, which exploit past rainfall data and landslide inventories, or physicallybased, which integrate slope physical–hydrological modeling and stability analyses. In this work, a comparison between these two types of thresholds was performed, using data acquired in Oltrepò Pavese (Northern Italian Apennines), to evaluate their reliability. Empirical thresholds were reconstructed based on rainfalls and landslides triggering events collected from 2000 to 2018. The same rainfall events were implemented in a physicallybased model of a representative testsite, considering different antecedent pore-water pressures, chosen according to the analysis of hydrological monitoring data. Thresholds validation was performed, using an external dataset (August 1992–August 1997). Soil hydrological conditions have a primary role on predisposing or preventing slope failures. In Oltrepò Pavese area, cold and wet months are the most susceptible periods, due to the permanence of saturated or close-to-saturation soil conditions. The lower the pore-water pressure is at the beginning of an event, the higher the amount of rain required to trigger shallow failures is. physicallybased thresholds provide a better reliability in discriminating the events which could or could not trigger slope failures than empirical thresholds. The latter provide a significant number of false positives, due to neglecting the antecedent soil hydrological conditions. These results represent a fundamental basis for the choice of the best thresholds to be implemented in a reliable earlywarning system.

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Characteristics of nonlinear response of deep saturated soil deposits

Bulletin of the Seismological Society of America ◽

10.1785/bssa0870020342 ◽

1997 ◽

Vol 87 (2) ◽

pp. 342-355 ◽

Cited By ~ 1

Author(s):

Shean-Der Ni ◽

Raj V. Siddharthan ◽

John G. Anderson

Keyword(s):

Resonant Frequency ◽

Soil Properties ◽

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Saturated Soil ◽

Soil Conditions ◽

Base Excitation ◽

Soil Deposits ◽

Stress Dependent

Abstract Recent EPRI seismic design guidelines call for dynamic soil properties (shear modulus ratio and damping) and liquefaction strength curves to be characterized as a function of the effective vertical stress (or depth). A modified version of the DESRA2 constitutive model for saturated soil has been applied to study the nonlinear seismic response including liquefaction of medium dense soil deposits of various thicknesses. The results of the stress-dependent soil properties model show lower deamplification and higher first-mode (resonant) frequency than that of the stress-independent soil properties model. By using the stress-dependent model with impulse base excitation, the nonlinear behavior of various soil deposits has been investigated under a variety of conditions. The results show that (1) the saturated soil deposit has a smaller surface amplitude and significantly lower resonant frequency than the unsaturated soil deposit of the same thickness; (2) for the saturated soil conditions, the larger the base excitation, the lower the surface amplification and the resonant frequency; (3) the deep soil deposits show lower surface amplification and resonant frequency compared to the response of shallow deposits; (4) when shallow and deep deposits are compared, the shallow deposits develop much higher residual pore-water pressure; and (5) the amplification and residual pore-water-pressure response of deposits deeper than 100 m or so are very similar. The application of the method has also been illustrated using a strong synthetic base excitation applied to the base at a site near Reno. The results in general are consistent with those computed using the impulse loading. The study reveals that the response predicted from the conventionally used stress-independent soil properties model is unconservative for deep deposit.

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Discontinuous slope failures and pore-water pressure variation

Journal of Mountain Science ◽

10.1007/s11629-015-3528-4 ◽

2016 ◽

Vol 13 (1) ◽

pp. 116-125 ◽

Cited By ~ 6

Author(s):

Xiao-jun Guo ◽

Yong Li ◽

Peng Cui ◽

Wan-yu Zhao ◽

Xing-yuan Jiang ◽

...

Keyword(s):

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Pressure Variation ◽

Slope Failures

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Numerical study of soil conditions under which matric suction can be maintained

Canadian Geotechnical Journal ◽

10.1139/t04-006 ◽

2004 ◽

Vol 41 (4) ◽

pp. 569-582 ◽

Cited By ~ 63

Author(s):

L L Zhang ◽

D G Fredlund ◽

L M Zhang ◽

W H Tang

Keyword(s):

Steady State ◽

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Water Storage ◽

Matric Suction ◽

Rainfall Infiltration ◽

Soil Conditions ◽

Soil System ◽

Coefficient Of Permeability

The effect of negative pore-water pressure is often ignored in slope stability studies. There is a perception among geotechnical engineers that negative pore-water pressures will dissipate with rainfall infiltration and cannot be relied upon in design considerations. The objective of this paper is to illustrate that under certain conditions soil suction can be maintained. Based on the theory of infiltration and seepage through a saturatedunsaturated soil system, steady state and transient finite element seepage analyses were conducted using Seep/W on a 20 m high slope inclined at 30°. The results of the analysis showed that under steady state conditions, the most important factor influencing the permanency of matric suction in the soil is the magnitude of rainfall flux expressed as a percentage of the saturated coefficient of permeability of soil. For the analysis under transient seepage conditions, the results showed that the pore-water pressure profile depends on the magnitude of the rainfall flux, the saturated coefficient of permeability, the soil-water characteristic curve, and the water storage function. For a soil with a low coefficient of permeability and a large water storage capacity, the matric suction needs a substantial amount of time to dissipate and thus may be maintained over a longer time period than the rain is likely to fall, even if the ground surface flux is equal to or greater than the saturated coefficient of permeability. Engineers should address more appropriate engineering design assumptions that can be related to the permanence of matric suction in soil slopes based on the numerical analysis. Measures such as slope cover or surface recompaction can be taken into consideration to minimize the rainfall infiltration and thus maintain active matric suction in slopes.Key words: unsaturated soils, slope, rainfall infiltration, matric suction, permeability.

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NUMERICAL MODELING OF UNSATURATED LAYERED SOIL FOR RAINFALL-INDUCED SHALLOW LANDSLIDES

Journal of Environmental Engineering and Landscape Management ◽

10.3846/16486897.2017.1326925 ◽

2017 ◽

Vol 25 (4) ◽

pp. 329-341 ◽

Cited By ~ 4

Author(s):

Chih-Yu LIU ◽

Cheng-Yu KU ◽

Jing-En XIAO ◽

Chi-Chao HUANG ◽

Shih-Meng HSU

Keyword(s):

Numerical Modeling ◽

Slope Stability ◽

Pore Water ◽

Numerical Solutions ◽

Pore Water Pressure ◽

Water Pressure ◽

Characteristic Curve ◽

Shallow Landslides ◽

Layered Soil ◽

Richards Equation

In this paper, a pioneer study on numerical modeling of rainfall-induced shallow landslides in unsaturated layered soil using the variably saturated flow equation is presented. To model the shallow landslides, the infinite slope stability analysis coupled with the hydrological model with the consideration of the fluctuation of time-dependent pore water pressure and Gardner equation for soil water characteristic curve was developed. A linearization process for the nonlinear Richards equation to deal with groundwater flow in unsaturated layered soil is derived using the Gardner model. To solve one-dimensional flow in the unsaturated zone of layered soil profiles, flux conservation and the continuity of pressure potential at the interface between two consecutive layers are considered in the numerical discretization of the finite difference method. The validity of the proposed model is established in three numerical problems by comparing the results with the analytical and other numerical solutions. Application examples have also been conducted. Obtained results demonstrate that the fluctuation of pore water pressure in unsaturated layered soil dominates slope stability of landslides and the lowest factor of safety may occur at the interface between two consecutive layers. The findings observed in this study are a fundamental contribution to environmental protection engineering for landslides in areas with higher occurrence and vulnerability to extreme precipitation.

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A model of landslide triggering by transient pressure waves

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-11-2355-2014 ◽

2014 ◽

Vol 11 (2) ◽

pp. 2355-2390

Author(s):

G. W. Waswa ◽

S. A. Lorentz

Keyword(s):

Diffusion Model ◽

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Ground Surface ◽

Shallow Landslides ◽

Diffusivity Coefficient ◽

Saturated Zone ◽

Transient Pressure ◽

Additional Energy

Abstract. Previous studies indicate that most rainfall-triggered shallow landslides are initiated by a spike in rainfall intensity, which does not usually occur at the beginning of a critical storm, within which the slide is triggered, but after several minutes (or hours) of the storm. The critical storm is also usually not positioned at the beginning of a rainfall season, but after several days of antecedent period. Rainfall triggers landslides via rapid increase in pore water pressure, commonly associated with the change in water content. Consequently, many hydrologic pressure wave models assume that rapid pore water pressure responses are as a result of rapid infiltration of rainwater. On the contrary, this paper argues that, based on the above timings of landslide occurrences and the knowledge that infiltration rate decays with the soil wetness, the rapid increase in pore water pressure that triggers shallow landslides is as a result of rapid introduction of additional energy into the tension saturated (or nearly saturated) zone by the intense rainfall at the ground surface, without infiltration. Antecedent and critical precipitations are significant in creating a tension saturated zone, necessary for rapid transmission of the introduced energy from the ground surface to the lower soil horizons during the critical storm. These arguments are supported by a newly proposed one-dimensional diffusion mathematical model, which, when solved for the appropriate boundary conditions, can yield pore water pressure at any time and depth of a tension-saturated soil profile, without infiltration. The newly proposed diffusion model is mathematically similar to Iverson's model (Iverson, 2000), except that the hydraulic diffusivity parameter in the latter is substituted with a newly proposed energy diffusivity coefficient in the former. A combination of the new diffusion model and the infinite slope model can predict the stability of a shallow slope as a result of transient pore water pressure.

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Pore Water Pressure as a Trigger of Shallow Landslides in the Western Ghats of Kerala, India: Some Preliminary Observations from an Experimental Catchment

Physical Geography ◽

10.2747/0272-3646.29.4.374 ◽

2008 ◽

Vol 29 (4) ◽

pp. 374-386 ◽

Cited By ~ 19

Author(s):

Sekhar L. Kuriakose ◽

V. G. Jetten ◽

C. J. van Westen ◽

G. Sankar ◽

L. P. H. van Beek

Keyword(s):

Pore Water ◽

Western Ghats ◽

Pore Water Pressure ◽

Water Pressure ◽

Shallow Landslides ◽

The Western Ghats

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TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

HUE UNIVERSITY JOURNAL OF SCIENCE TECHNIQUES AND TECHNOLOGY ◽

10.26459/hueuni-jtt.v128i2b.5424 ◽

2019 ◽

Vol 128 (2B) ◽

pp. 29-41

Author(s):

Trần Thanh Nhàn

Keyword(s):

Cyclic Loading ◽

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Clayey Soils ◽

Loading History ◽

Cyclic Shear ◽

Wide Range ◽

Primary Consolidation ◽

Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

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Conjectures, Hypotheses, and Theories of Drumlin Formation (In memory of Stanislaw Baranowski)

Journal of Glaciology ◽

10.3189/s0022143000011552 ◽

1981 ◽

Vol 27 (97) ◽

pp. 503-505 ◽

Cited By ~ 1

Author(s):

Ian J. Smalley

Keyword(s):

Shear Strength ◽

Pore Water ◽

Stress Level ◽

Critical Stress ◽

Pore Water Pressure ◽

Water Pressure ◽

Glacial Till ◽

Forming Process ◽

Stress Levels

AbstractRecent investigations have shown that various factors may affect the shear strength of glacial till and that these factors may be involved in the drumlin-forming process. The presence of frozen till in the deforming zone, variation in pore-water pressure in the till, and the occurrence of random patches of dense stony-till texture have been considered. The occurrence of dense stony till may relate to the dilatancy hypothesis and can be considered a likely drumlin-forming factor within the region of critical stress levels. The up-glacier stress level now appears to be the more important, and to provide a sharper division between drumlin-forming and non-drumlin-forming conditions.

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