A mechanism of pore pressure accumulation in rapidly sliding submerged porous blocks

Landslides are a common phenomenon in all the regions of Malawi. A number of historical landslides have been documented and are summarized here. This paper examines the occurrence of landslides in the Rumphi District of Northern Malawi. The study is based on a detailed study of 98 landslides that occurred in 2003 at Ntchenachena and Chiweta areas in the Rumphi District. This paper examines factors that contributed to and caused these landslides. The paper suggests that landslides were triggered by 206 mm of rain received in 2 days. The high percentage of medium to fine sand and abrupt rise in pore pressure accelerated the process of liquefaction at Ntchenachena. Cleft water pressure at the point between regolith and soil mass caused a number of slides in the Chiweta areas. High slope angles, deep weathering of the basement and high annual total rainfall contributed to the slope instability. Human activities through cultivation on steep slope, slope remodeling, and deforestation significantly altered the conditions of the slopes, thereby increasing the degree of landslide hazard present in these areas.

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“…The mechanism of pore pressure accumulation is provided in Musso et al (2004). The rainfall data (Sect.…”

Section: High Pore Pressurementioning

confidence: 99%

Landslides in the Rumphi District of Northern Malawi: characteristics and mechanisms of generation

Msilimba

Holmes

2010

Nat Hazards

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“…Interstitial pressures at the base of the mass can vary from null or hydrostatic value to high values, due to possible water pressure excess, related to very rapid changes of pore volumes, often localized along a thin layer in proximity of the sliding surface [3].…”

Section: Introductionmentioning

confidence: 99%

Coupled Effects of Energy Dissipation and TravellingVelocity in the Run-Out Simulation of High-SpeedGranular

Federico¹,

Favata²

2011

IJG

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The run-out of high speed granular masses or avalanches along mountain streams, till their arrest, is analytically modeled. The power balance of a sliding granular mass along two planar sliding surfaces is written by taking into account the mass volume, the slopes of the surfaces, the fluid pressure and the energy dissipation. Dissipation is due to collisions and displacements, both localized within a layer at the base of the mass. The run-out, the transition from the first to the second sliding surface and the final run-up of the mass are described by Ordinary Differential Equations (ODEs), solved in closed form (particular cases) or by means of numerical procedures (general case). The proposed solutions allow to predict the run-up length and the speed evolution of the sliding mass as a function of the involved geometrical, physical and mechanical parameters as well as of the simplified rheological laws assumed to express the energy dissipation effects. The corresponding solutions obtained according to the Mohr-Coulomb or Voellmy resistance laws onto the sliding surfaces are recovered as particular cases. The run-out length of a documented case is finally back analysed through the proposed model

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“…Furthermore, the average interstitial pressure at the base of the granular mass, which can vary between null and higher than hydrostatic values, due to the rapid change of pores volume related to the continuous rearrangement of grains, localized within the shear layer (Musso et al 2004), remarkably influences the runout length.…”

Section: Mechanical Behaviour Of Rapid Sliding Granular Massesmentioning

confidence: 99%

“…To simulate a p w value greater than the hydrostatic value (Musso et al 2004), d w < 0 must be assigned. If the different (inertial and frictional) regimes acting at the base of the sustained block are taken into account, the interstitial pressure's resultant may be expressed as follows:…”

Section: Power Balance Equationmentioning

confidence: 99%

An energy-based approach to predict debris flow mobility and analyze empirical relationships

Federico

Cesali

2015

Can. Geotech. J.

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Several empirical relationships allowing a preliminary estimate of debris flow runout distances have been proposed to correlate the runout length to the volume of the sliding granular mass, delimit potentially hazardous areas, and design safeguarding measures. To overcome their large variability and define their fields of applicability, an energy-based model, predicting debris flow mobility, is developed. The power balance of a granular mass sliding along two planar surfaces is written by taking into account the volume of the debris mass, the slopes of the sliding surfaces, an assigned interstitial pressure, the possible mass variation along the motion, the energy dissipation due to the grain inelastic collisions ("granular temperature" within a basal "shear layer"), and friction. A system of ordinary differential equations is obtained; its numerical solution allows, through parametrical analyses: (i) highlighting of the role of physical and mechanical parameters on the runout distance, such as grain size material, interstitial pressures, grain collisions, and erodibility of the crossed channel; and (ii) defining of the favourable conditions for debris flows mechanism generation. Finally, through the back-analysis of some cases, an original relationship to estimate the runout length, as well as to interpret the results of the empirical formulas, is proposed.Key words: sliding granular mass, granular temperature, shear layer, collisions, empirical relationships.Résumé : Plusieurs relations empiriques permettant d'effectuer une estimation préalable des distances parcourues par les écoulements de débris ont été proposées pour mettre en corrélation la distance parcourue par les écoulements et le volume de masse granulaire glissante, délimiter les zones potentiellement dangereuses et mettre en place des mesures de protection. Pour compenser la grande variabilité de ces relations et définir leurs champs d'application, on conçoit un modèle basé sur l'énergie, capable de prédire la mobilité des écoulements de débris. On décrit l'équilibre des forces d'une masse granulaire glissant sur deux surfaces planes en tenant compte du volume de la masse de débris, de l'inclinaison des surfaces de glissement, d'une valeur déterminée de pression interstitielle, de la possible variation de masse sur le parcours de l'écoulement, de la dissipation d'énergie due aux collisions inélastiques entre grains (« température granulaire » au sein d'une « couche de cisaillement » basale) et des frottements. On obtient un système d'équations différentielles ordinaires; la solution de ce dernier permet, par le biais d'analyses paramétriques : (i) de souligner le rôle des paramètres physiques et mécaniques (tels que la taille des grains de la masse glissante, les pressions interstitielles, les collisions entre grains, l'érodabilité du canal croisé) sur la distance du parcours des écoulements; (ii) de déterminer les conditions favorables au déclenchement du mécanisme d'écoulement de débris. Enfin, grâce à l'analyse rétrospective de certain...

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A mechanism of pore pressure accumulation in rapidly sliding submerged porous blocks

Cited by 12 publications

References 11 publications

Landslides in the Rumphi District of Northern Malawi: characteristics and mechanisms of generation

Landslides in the Rumphi District of Northern Malawi: characteristics and mechanisms of generation

Coupled Effects of Energy Dissipation and TravellingVelocity in the Run-Out Simulation of High-SpeedGranular

An energy-based approach to predict debris flow mobility and analyze empirical relationships

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