MODELING OF RAPID FINE-GRAINED MATERIAL FLOWS

Gravitational mass movements, such as debris and mud flows, are among the most destructive natural hazards, leading to substantial fatalities and extensive economic damage worldwide. Improving our understanding and modeling of these processes is essential for developing effective risk management and early warning strategies. When debris and mud flows pass through a curved channel, centrifugal forces may cause a difference in flow height between the inner and outer banks of the channel. This height difference, known as superelevation, can be described using analytical models that establish a relationship between the superelevation height and the flow velocity.Analytical models often employ a forced vortex approach, incorporating parameters such as the cross-sectional slope of the flow surface, flow width, and bend radius. These models, however, rely on assumptions such as a linear flow surface between mud deposits on the banks, a rectangular cross-section, and neglect both complex rheological behaviors and solid-fluid interactions. As a result, an empirically determined correction factor is required within the formula. The absence of a clear mechanical rationale for this correction factor presents challenges, as it is currently derived only through field investigations and laboratory experiments.This study presents an enhancement to the existing forced vortex approach by incorporating insights from numerical modeling. A coupled SPH-DEM numerical model is employed, where DEM particles represent coarse solid particles, and SPH accounts for the fluid phase, comprising fines and water. The SPH-DEM coupling is based on the no-slip interaction model, with simulations performed using a GPU-based solver to ensure enhanced computational efficiency. To validate the approach, a parametric test is conducted, initially back-calculating laboratory-scale experiments. The study further involves varying the water content in debris and mud flows to examine its impact on flow behavior and superelevation. Larger water contents lead to an increased superelevation angle. Results from the parametric test reveal a clear correlation between water content and the flow surface shape in curved channels. Specifically, mud flows are characterized by convex upward surface shapes, whereas more granular debris flows typically exhibit concave downward shapes.The distribution of material within the cross-section of the flow is governed by the equilibrium between boundary forces and centrifugal forces acting on the flow, which directly influences the superelevation. Numerical investigations are conducted to determine a correction factor and assess the extent to which inertial effects contribute to this correction factor for different material mixtures. Furthermore, we demonstrate that the effect of the flow surface shape is significant and is currently only accounted for by the empirical correction factor. This study offers new physical insights for the back-calculation of debris flow velocities in curved sections marked by mud deposits. Large-scale SPH-DEM simulations of a real debris flow event at Illgraben (Switzerland) are performed, showing good agreement with field data and its potential for further real-scale modeling.

A physically-based multi-hazard risk assessment platform for regional rainfall-induced slope failures and debris flows

Effect of water content and soil texture on consolidation in unsaturated soils

Debris flow is a very common and destructive natural hazard in mountainous regions. Pore water pressure is the major triggering factor in the initiation of debris flow. Excessive pore water pressure is also observed during the runout and deposition of debris flow. Debris materials are normally treated as solid particle–viscous fluid mixture in the constitutive modeling. A suitable constitutive model which can capture the solid-like and fluid-like behavior of solid–fluid mixture should have the capability to describe the developing of pore water pressure (or effective stresses) in the initiation stage and determine the residual effective stresses exactly. In this paper, a constitutive model of debris materials is developed based on a framework where a static portion for the frictional behavior and a dynamic portion for the viscous behavior are combined. The frictional behavior is described by a hypoplastic model with critical state for granular materials. The model performance is demonstrated by simulating undrained simple shear tests of saturated sand, which are particularly relevant for the initiation of debris flows. The partial and full liquefaction of saturated granular material under undrained condition is reproduced by the hypoplastic model. The viscous behavior is described by the tensor form of a modified Bagnold’s theory for solid–fluid suspension, in which the drag force of the interstitial fluid and the particle collisions are considered. The complete model by combining the static and dynamic parts is used to simulate two annular shear tests. The predicted residual strength in the quasi-static stage combined with the stresses in the flowing stage agrees well with the experimental data. The non-quadratic dependence between the stresses and the shear rate in the slow shear stage for the relatively dense specimens is captured.

We analyzed multi-time satellite images of the Central Caucasus glacial zone and interpreted more than thirty rock avalanche events in the 21st century with a total damage area of more than 25 km2 (including the collapse zone of the Kolka Glacier disaster). The highest rock and rock-ice avalanche activity is detected in the section of The Greater Caucasus range (northern and southern slopes) with a length of about 20 km between the Bashkara and Kulaktau peaks (16 rock avalanches) and in the section of the Kazbek-Dzhimaray Massif (series of rock avalanches to the surface of Kolka, Suatisi and Devdoraki glaciers). The feature of the rock and ice-rock avalanches is the large runout distance. For 12 events (about 40%) the distance was more than 2000 m. One ice-rock avalanche from the Mount Kazbek (excluding the Kolka Glacier disaster in 2002) reached the runout distance more than 10 km. In some areas, the rock avalanches occurred several times. In particular, a large number of avalanches were in the cirque of the Kolka Glacier; the last of them at the end of 2019. Thrice шт each case, rock avalanches originated from Mount Bashkara, in the cirques of the Murkvam Glacier, the East Shtulu Glacier, and the Devdoraki Glacier. Ice and rock avalanches were the initial stage of the complex process of the Kolka Glacier disaster and following catastrophic glacial debris flow in the Genaldon/Gizeldon River valley in 2002. Also, they were causes of glacier surges, formation of dammed lakes, and debris flows. As a result of the collapse of the hanging glacier and bedrock, the former right tributary of the Kolka Glacier surged to 200 m in 2006. Ice-rock avalanche from Mount Kazbek in 2014 load up the former right tributary of the Devdoraki Glacier and caused its advancing in 2015–2019, at a distance of more than 400 m. The avalanches caused catastrophic debris flows in the Amilishka/Kabakhi River valley in 2014, the Mestiachala River valley in 2019. Rock avalanches can cause outbursts of lakes and debris flows. Two dammed lakes formed as a result of the rock avalanche from the cirque above the Seri Glacier in the Tviberi River valley of the in May 2016. The lakes (total area was more than 0.05 km2) have outburst at the end of August 2017 after heavy rains. Rock avalanches of the 20th century led to an abrupt deceleration in the retreat of the Yusengi, Bartuytsete, East Shtulu and Mosota glaciers. The formation of rock avalanches in the 21st century took place at high altitudes (an average of about 3900 m). Possibly, the reason was associated with an increase of the «0» isotherm and of the high border of the zone of intense frost weathering due to climate warming. Some rock avalanches in the section of the Kazbek-Dzhimarai Massif have been caused by endogenous factors (seismicity and volcanism).

The turbine engine that is operating will generate vibrations that are transmitted by the foundation into the soil layer. This causes the pore water pressure in the soil to increase, which causes the shear strength of the soil to decrease and can reduce the carrying capacity of the soil as a foundation resting place, which results in a reduced bearing capacity of the foundation as well. The pore water pressure in the soil consists of static pore water pressure and excess pore water pressure. Static pore water pressure is hydrostatic pressure that depend on Ground Water Level (GWL), while excess pore water pressure is the pore water pressure that occurs due to changes in undrained soil stress. Therefore, a study was conducted on the effect of gas turbine engine vibration on pore water pressure in sand and clay soils with a depth of 8,5 m (fine to coarse sand), 10,5 m (silty clay), and 12,5 m (medium to coarse sand). From the research results, the value of the pore water pressure ratio for each layer of soil was 0,32, 0,02, and 0,49, which can reduce the bearing capacity of the pile, especially in sandy soils and if the value is greater than one, it can be concluded that the soil has the potential for liquefaction.

Stresses and pore water pressure induced by machine foundation on saturated sand

Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid‐fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ∼10 m³ of poorly sorted, water‐saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse‐grained surge fronts have little or no pore fluid pressure. In contrast, finer‐grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate permeability of the debris. Realistic models of debris flows therefore require equations that simulate inertial motion of surges in which high‐resistance fronts dominated by solid forces impede the motion of low‐resistance tails more strongly influenced by fluid forces. Furthermore, because debris flows characteristically originate as nearly rigid sediment masses, transform at least partly to liquefied flows, and then transform again to nearly rigid deposits, acceptable models must simulate an evolution of material behavior without invoking preternatural changes in material properties. A simple model that satisfies most of these criteria uses depth‐averaged equations of motion patterned after those of the Savage‐Hutter theory for gravity‐driven flow of dry granular masses but generalized to include the effects of viscous pore fluid with varying pressure. These equations can describe a spectrum of debris flow behaviors intermediate between those of wet rock avalanches and sediment‐laden water floods. With appropriate pore pressure distributions the equations yield numerical solutions that successfully predict unsteady, nonuniform motion of experimental debris flows.

When the slurry shield tunneling in water rich sandy gravel stratum, it is easy to have problems such as difficult to form the filter cake and poor stability of the excavation face, and the filter cake is the key factor to maintain the stability of the slurry shield excavation face. Using finite element software, a three‐dimensional fluid solid coupling model of slurry shield tunneling is established. The influence of slurry parameters (slurry pressure and permeability coefficient of filter cake) on pore water pressure and excavation face stability during slurry shield tunneling is studied. The variation laws and internal relations of slurry parameters, pore water pressure and displacement are obtained. The results indicate that the slurry pressure and the permeability coefficient of the filter cake play an important role in maintaining the stability of the excavation face. Too large or too small slurry pressure will lead to forward or backward displacement of the excavation face, which is not conducive to the stability of the excavation face and causes large surface displacement. The excess pore water pressure will occur during tunneling, and the excess pore water pressure will decrease with the distance away from the center of the excavation face. When the slurry pressure is small, the excess pore water pressure is larger. With the shield away, the excess pore water pressure gradually recovers. When the permeability coefficient of the filter cake is large, it will accelerate the seepage of pore water in the excavation face, which will increase the excess pore water pressure value and lead to the increase of surface settlement.

Sand strata located 5 to 10 miles seaward of the major active passes of the Mississippi River have been buried by more than 100 ft of rapidly deposited clay. As a result of rapid deposition the clay is underconsolidated and contains pore water at pressures in excess of hydrostatic values. Results of soil borings drilled as part of foundation investigations in the region have indicated that in some instances the sand strata also contain excess pore water pressures. The existence of pressurized shallow sands of this type has been verified by direct measurement at a location in 200 ft of water near Southwest Pass. Using a piezometer installed at a penetration of over 200 ft in the bottom of a borehole, pore pressure 2.6 ksf greater than the hydrostatic was recorded. Excess pore pressures of this magnitude may cause problems during pile installation if jetting is used to clean out the soil plug. Sand below the pile tip may become quick and flow into the pile as a result of the excess head in the sand relative to the pile. The excess pore pressure would reduce pile end bearing and skin friction capacity in the sand. The stability of soil deposits beneath a sloping seafloor may also be adversely affected by excess pore pressures. The geologic conditions leading to the development of pressurized sands are examined using an example from the Mississippi River delta. A method of estimating the in situ excess pore pressure in clay soils using laboratory test data is presented. The method is applied to the clay soils which confine a pressurized sand stratum and the results are compared to a piezometer measurement of excess pore pressure in the sand. INTRODUCTION Soil borings performed in the Gulf of Mexico as a part of foundation investigations usually penetrate 300 to 400 ft below the seafloor as required for the design of structure-support piling. Sand strata which are encountered in such investigations offshore Texas and western Louisiana generally appear to have interstitial pore pressures at normal hydrostatic pressures. In such conditions, the pore pressure at any point in the strata is equal to the product of the unit weight of seawater and the distance below sealevel. The relatively slow sedimentation processes on the continental shelf have allowed time for these sands and clays to adjust to the increasing weight of overburden through drainage of water from the pores of the soil to the seafloor, and for transfer of the loads to intergranular stresses. Exceptions exist near the mouths of rivers where rapid sedimentation results in the formation of under-consolidated clays, in soils charged by gas and in artesian aquifers charged by onshore sources at higher elevations. Excess pore pressures may also form in deep-lying confined beds where the drainage paths for the escape of water are so great in length that sedimentation and changes in tectonic stresses induce pore pressures which cannot be effectively dissipated. High pore pressure sands are not unusual, for example, at depths below 8000 ft in some Louisiana Gulf Coast reservoirs.

Debris flow modeling: a review

Pavement pumping can significantly reduce the overall strength of pavements, even rigid or flexible pavements. The fine contents in the subbase material underneath the pavement slabs move up to the pavement surface through the cracks in the slabs due to pumping, resulting in the erosion of the subbase and decreased structural support. Pumping occurs when water that has accumulated underneath a slab is pressurized when the slab deflects under traffic loading. Therefore, the pore water pressure behavior in the granular subbase is an essential factor in clarifying the pumping mechanism. Model tests were conducted in this study to observe the pore water pressure behavior under various conditions. The model was a small-sized circular road simulator, consisting of a transparent cylindrical soil chamber made of acrylic, a transparent slab, and a rotational wheel loader. The slab had a single artificial joint in the radial direction simulating a pavement crack. The soil chamber had manometers equipped on the side wall to measure the pore water pressure in the ground. The experimental results showed that the excess pore water pressure generated under the load was greater at the leave slab side than at the approach slab side. It was also observed that the excess pore water pressure was larger in the case of a slower traveling speed, which implies that the larger slab deflection under slower loading resulted in larger excess pore water pressure.

In this study, the economical FlexiForce sensor, which is thin and flexible, was used to measure K0 and the excess pore water pressure during a 1D consolidation test on kaolinite clay samples. Before the sensor could be used in the measurement, a special waterproof coating was applied, after which sensor calibration was carried out. The coated FlexiForce sensor was incorporated into two types of tailor-made needle probes for the pore water pressure measurement. The experimental results demonstrate that the two types of needle probes can well capture the evolution of the induced excess pore water pressure during consolidation. Upon a loading increment, the measured excess pore water pressure at the middle of the sample continues to increase and reaches a maximum value at t = ∼4 min and subsequently start to decrease. There is a distinct change in the decreasing trend of the measured excess pore water pressure; the trend becomes mild after t = ∼480 min, indicating the end of primary consolidation. During secondary compression, the excess pore water pressure continues to decrease due to the continuous settlement. A constant K0 value, which is comparable to the prediction by Jaky's equation, is measured by the sensors in the loading path; during secondary compression, K0 increases with time.

High‐resolution images acquired by the Mars Global Survey Mars Orbiter Camera show gullies on the walls of impact craters and valley systems on Mars. Depositional aprons associated with these gullies have been interpreted byMalin and Edgett[2000]to be characteristic of debris flow and to indicate the presence of sources of liquid water at shallow depths below the Martian surface. By focusing on a terrestrial debris flow we test the application of Chezy‐type modeling to provide more direct estimates of the dynamics of proposed debris flows on Mars. Traditionally, planetary scientists, constrained by available remotely sensed data, have used a range of flow models to gain insights from deposits into the behavior and rheologic nature of features such as lava flows, debris flows, and gravity‐driven flows. On the basis of these model results, broad interpretations of the physics governing flows of granular materials have been tempting based on limited field‐derived data. This study tests and validates the extent to which the absolute value and relative variations of empirical parameters derived from the Chezy‐type models describe the behavior of the General's slide debris flow (38.24°N, 78.23°W) in Madison County, Virginia. The results indicate that extreme caution must be taken when interpreting model results for turbulent flows of granular materials. We obtained high‐precision topographic profiles, superelevation data, sedimentary facies, and sedimentary textural properties over the debris flow. This study focuses on the empirical parameterC, whose value gauges energy dissipation in a flow, thereby called flow resistance. Using field observations, both variations and absolute values ofCalong the debris flow have been computed using two approaches: (1) assuming constant volumetric flow rateQ, where only topography and high‐resolution images are required to compute channel dimensions, and (2) a variableQ, calculated using field derived data. Assuming near‐Newtonian flow conditions in the debris flow, estimated values ofCrange from 0.035 to 0.099. WhenQis fixed,Cdecreases as a function of distance downstream. WhenQvaries andCis computed from field‐derived flow speeds, its value tends to increase downstream slightly. These opposite results have been compared to the field observations to determine which best describes the behavior of the flow. The variations inCdownstream, obtained using the flow speeds, are most consistent with the geomorphic evidence for erosion of material by the debris flow and the presence of bends in the channel. The average values ofC, 0.036–0.33 for the General's slide, have been compared with computedCvalues for Newtonian and near‐Newtonian flows to assess the rheology of the flow during emplacement. Our terrestrial study demonstrates that advances in understanding of the dynamics of debris flows on the Mars depends on obtaining debris flow speeds in addition to channel topography and flow thickness, rather than just on channel topography, flow thickness, and the assumption thatQis constant. Mars Orbiter Camera (MOC) and Mars Observer Laser Altimeter (MOLA) data can be used to derive channel topography, flow thickness, and possibly flow speeds. Such data will provide more direct estimates of the dynamics of debris flows on Mars than are currently available.

Introduction Debris flows are climate change-driven geohazards that pose a significant threat to life and the built environment. These flows are unconfined, in which the water-laden mass comprising of soil, gravel, boulders, and trees surges down steep hill slopes and channelises into streams, trapping everything that encounters them. These hazardous flows impact the engineering and defence structures, transportation systems, and the environment. State of Knowledge Various researchers have performed numerous laboratory-to-field scale experiments to understand debris flow's dynamic morphological and rheological properties. The state-of-the-art approach to evaluating the effect of multiple factors, such as water content, pore water pressure, grain size distribution, topography, solid volume fraction, and basal friction parameters on the initiation mechanism, dynamics, and morphology, has evolved rapidly in the past few decades. Objective The present paper discusses the progress in the identification of rheological and morphological characteristics of the debris flow and the advancement in debris flow experimentation. Approach and Scope This review will help the readers get a consolidated overview of the recent advancements in debris flow experiments. The study complements the previous studies by identifying the latest developments in debris flow experiments, such as the effects of material and geometric parameters on flow dynamics, mechanisms of evolution of excess pore water pressure in saturated and unsaturated bed conditions, entrainment mechanisms, and the classification of experiments based on the type and size of experimentation. Discussion and Relevance The characteristics of debris flow are also discussed based on different phases in debris flows, such as the initiation phase, dynamic phase, morphological characteristics, and impact on the built environment.