Viscous Debris Flow Research Articles

Significance of coarse clasts in viscous debris flows

Debris flows are flowing mixture of water and sediments (from clay to boulder-sized particles). The sediments control both occurrence and characteristics of debris flows, however, the relevant literature has concentrated mainly on fine debris. Considering their large fractions in debris flows, the significance of coarse clasts (≥0.005 mm) is investigated by comparing the crude debris (CD, the fractions of <10 mm and <5 mm of the Jiangjia Gully debris-flow deposit) with the reconstituted debris (RD, prepared by replacing the coarse clasts of the CD with the corresponding sizes of the Dongyuege debris-flow clasts following the gradation of the CD). Rheometrical tests, propagation tests, and pore-pressure measurements are made on the CD and RD samples in a systematic manner.Aggregation of data collected in 39 tested debris-water mixtures leads us to conclude that the coarse clasts can greatly affect the slurrying susceptibility of debris masses and bulk behavior of slurries. The debris-flow indices (Id) from the CD to RD slurries with maximum grain sizes of 10 and 5 mm decrease by 29% and 17%, respectively. The CD slurries possess higher yield strength and viscosity than their RD counterparts with the same solid volumetric concentrations (Cvs). The areas inundated by 10 CD slurries with maximum grain sizes of 10 and 5 mm are approximately 17%–39% of those of their RD counterparts. The excess pore pressures in the RD slurries dissipate more quickly than those in the CD slurries. The shape and surface texture of coarse clasts regulate slurrying of debris masses, as well as influence their liquefaction potential, which in turn has an impact on the mobility and persistence of subsequent slurries.The platy/flaky debris-producing mountain catchments generally experience lower-magnitude/higher-frequency, lower Cv debris flows of relatively less destructive power, and the debris flows dominated by equidimensional clasts are often more powerful and hazardous, despite their potentially lower frequency.

Experimental investigation of blocking and discharge regulation function of window-frame dam in viscous debris flow control

The blocking of a window-frame dam and the discharge regulation are both important basic control features for characterizing the regulatory effect of a window-frame dam on debris flow. To better understand the regulatory effect of a window-frame dam on debris flow, physical model tests were carried out to investigate the flow pattern, trapping, and regulating characteristics when debris flow passed through a window-frame dam. The results revealed that the opening size of the dam and bulk density of the debris flow were the main factors affecting the blocking degree of the dam, followed by flume gradient. And a new comprehensive criterion for the blocking degree is proposed considering the multiple factors. Window-frame dams can regulate the discharge of debris flow to a certain extent under different conditions, and the control effect of discharge of viscous debris flow is not only reflected on the reduction of peak discharge, but also on the delayed effect of viscous debris flow. Moreover, the reduction rate of the peak discharge of debris flow is related to the blocking degree of the dam, which implies that designers should consider more factors in the determining the opening parameters of window-frame dams.

Gradation and Rheological Characteristics of Glacial Debris Flow along the Kangding–Linzhi Section of Sichuan–Tibet Railway

To date, most research on the characteristics of glacial debris flow along the Sichuan–Tibet railway has focused on numerical simulations and remote sensing, resulting in a lack of direct experimental data from debris flow samples. Therefore, in the present study, a field investigation was conducted along the Sichuan–Tibet railway, and 55 samples of glacial debris flow deposits were systematically analyzed to determine their grading and rheological properties. This is the first systematic experimental study on glacial debris flow deposits. The results showed that the proportion of coarse particles was high and the proportion of fine particles was low in the glacial debris flow along the Sichuan–Tibet railway. The average gravel and sand contents were 37.8% and 58%, respectively, and the average contents of silt and clay were 3.7% and 0.47%, respectively. The average fractal dimension was 2.1507, which is much greater than that of viscous debris flow. Under the same gravity and shear rate, the stress of typical glacial debris flow was significantly less than that of viscous debris flow, whereas the variability of the stress was more significant. These findings will contribute to revealing the movement rules and disaster risk of glacier debris flow along the Sichuan–Tibet railway and have considerable theoretical and practical significance for ensuring safety during both its construction and later operation.

Assessment of depth-averaged method in analysing runout of submarine landslide

Depth-averaged method (DAM) is one of the widely used numerical methods to back analyse the post-failure deposits of submarine landslides due to its high efficiency. However, its simplifications of the velocities along the thickness of the slide cannot capture complex behaviours such as shear band propagation. A novel non-averaged method, material point method (MPM), is used to validate the DAM analysis. The runout distances and morphologies of viscous debris flows predicted by the DAM and MPM are compared with those predicted by experiments and computational fluid dynamics analyses. The ranges of the shear strength, viscosity and sensitivity parameters are investigated to determine the feasibility of the DAM. The conventional DAM algorithm specialised for no-slip bases is enhanced to reproduce the phenomenon of block sliding of slides on frictional bases by considering the stability of the front and rear faces. Then, a spreading of horsts and grabens due to shear band propagation is presented with the MPM analysis. Two real cases of submarine landslides, Southern Mediterranean slide and Finneidfjord slide, were back-analysed with the DAM and MPM.

Numerical Simulation of Non-Homogeneous Viscous Debris-Flows Based on the Smoothed Particle Hydrodynamics (SPH) Method

Non-homogeneous viscous debris flows are characterized by high density, impact force and destructiveness, and the complexity of the materials they are made of. This has always made these flows challenging to simulate numerically, and to reproduce experimentally debris flow processes. In this study, the formation-movement process of non-homogeneous debris flow under three different soil configurations was simulated numerically by modifying the formulation of collision, friction, and yield stresses for the existing Smoothed Particle Hydrodynamics (SPH) method. The results obtained by applying this modification to the SPH model clearly demonstrated that the configuration where fine and coarse particles are fully mixed, with no specific layering, produces more fluctuations and instability of the debris flow. The kinetic and potential energies of the fluctuating particles calculated for each scenario have been shown to be affected by the water content by focusing on small local areas. Therefore, this study provides a better understanding and new insights regarding intermittent debris flows, and explains the impact of the water content on their formation and movement processes.

Impact characteristics of gustiness debris flow on check dam

The gustiness is a common motion form of debris flow, especially viscous debris flow. However, few researches have considered the gustiness into the impact characteristics of debris flow, which needs further research. In this study, the check dam was used as the load receptor to study the impact characteristics of gustiness debris flow. The results show that, under the same general flow depth, the dam stress considering the impact of gustiness debris flow is far less than that of disposable continuous debris flow. The impact force increases with the increase of the times of gustiness debris flow, and the impact torque increases linearly. Under the impact of gustiness debris flow, the displacement and stress of the dam vary in the same rule. The safety factors of anti-sliding and anti-overturning of the dam under the effect of gustiness debris flow are larger than those of disposable continuous debris flow, and the decrease rate of the safety factors increases with the increase of the times of gustiness debris flow. And under the condition of the same total flow depth, the increase of the debris flow depth can significantly decrease the stability of dam. The conclusions can provide reference for the design of blocking structures of gustiness and frequent debris flow.

Experimental study on the performance characteristics of viscous debris flows with a grid-type dam for debris flow hazards mitigation

A grid-type dam, which is an open-type dam, is an active structural countermeasure employed to mitigate the potential risk from and damage by debris flows. Although grid-type dams are widely used to control water-stone flows in Japan and other countries, they are not used in China due to the lack of knowledge regarding their suitability for controlling viscous debris flows. Viscous debris flows with a wide grain-size distribution are common in southwestern China. Using the known characteristics of such debris flows, we performed a series of flume tests designed to take three main factors into account: debris flow bulk density, channel gradient, and grid size. The goal of these tests was to investigate the dynamic processes and the performance of a grid-type dam in controlling viscous debris flows. The results of our analysis indicated that grid-type dams could effectively trap and regulate viscous debris flows. The sediment storage rate increased with the bulk density, concomitantly with a decrease in the reduction rate of bulk density and peak discharge; however, all parameters decreased with grid opening size. Additionally, based on theoretical analyses and experimental results, dimensionless relationship equations for grid-type dams were established that considered sediment storage rate, bulk density reduction rate, and peak discharge reduction rate. These equations make it possible to predict the effectiveness of controlling transported sediment using a grid-type dam. Moreover, they represent a reference for designing grid opening size, which could provide technical support for further practical engineering. Finally, we applied these equations to a case study of the Sandaoqiao Gully, where they were shown to be effective as a guideline in designing a grid-type dam to control a viscous debris flow.

Research on the numerical model for the routing of viscous debris flow considering the interface

Based on the interface theory, taking the corresponding surface of the yielding depth of debris flows as the interface, the viscous debris flows can be divided into the ideal fluid and the Bingham fluid. Thus, a vertical layered numerical model and its relative algorithm are developed to simulate the routing of viscous debris flows. The model is based on the motion feature of the debris and takes the velocity differences of debris flows in different layers into account. Therefore, it reasonably describes the routing mechanism and its impact on the morphology of debris flow due to the flow velocity. In addition, the model fully considers the phenomena of ‘tongue-like’ and ‘debris flow head’ of actual viscous debris flows and thus accurately depicts the motion state of the debris flow during the routing. A series of model experiments are adopted to verify the proposed numerical model and the algorithm. Compared with the measured data, the relative errors of the inundation areas and maximum accumulation thicknesses are within ±5%. Then, the comparison between the proposed model and other models further testifies the rationality of the proposed model.

The Model for Dilution Process of Landslide Triggered Debris Flow —A Case of Guanba River in Tibet Southeastern Plateau

Understanding and modeling the downstream dilution process of a landslide triggered debris flow is the foundation for recognizing the boundary condition and dilution mechanism of this type of debris flow, and this serves as the theoretical basis for the categorized control of viscous debris flows, diluted debris flows, hyperconcentration flows and flash floods in a drainage basin. In this study, taking as an example a typical debris flow that occurred in the Guanba River on Tibet’s southeastern plateau on July 6th, 1998, empirical models are used to calculate the density, water flow discharge, debris flow discharge, average depth of loose materials and channel gradient at 11 cross-sections upstream to downstream in the debris flow. On this basis, the dilution characteristics and debris flow dilution process are analyzed in this study. According to the correlation between the debris flow density and the water-soil ratio and channel gradient, we have established the density evaluation model for the debris flow dilution process, which can predict the dilution process of a landslide triggered debris flow. The study results include the following four aspects: (1) The key factors in the dilution process of landslide triggered debris flows are the water flow discharge, average depth of loose materials and channel gradient. (2) The debris flow dilution characteristics in the Guanba River in 1998 include the occurrence of the debris flow dilution process after a significant increase in the water-soil ratio; an increase in the proportion of fine particles after dilution of the debris flow; and the size distribution of grain is “narrowed.” (3) In accordance with the density and dilution characteristics, the debris flow dilution process in the Guanba River can be divided into the upstream viscous debris flow section, midstream and downstream transitional debris flow section and downstream diluted debris flow section. (4) The density evaluation model for the debris flow dilution process is expressed by the Lorentz equation, and this model can reflect the debris flow dilution process such that the debris flow density will decrease gradually with an increase in the water-soil ratio and decrease in channel gradient. The density evaluation model for the debris flow dilution process has been verified by three debris flow cases, which include Gaoqiao Gully, Haizi Valley, and Aizi Valley

Experiment study of mud to the moving process influent about viscous debris flow along slope

Mud is the main component of viscous debris flow. The physical model experiments of viscous debris flow were carried out through the mixing mud with different density and fixed components of coarse particles. The width, longitudinal movement distance and motion velocity were recorded by video cameras during experiment. Through viscous debris flow physical model experiments, the influence of mud to transverse width, longitudinal movement distance and motion velocity was discussed. The physical model experiment results show that the motion forms change from inviscid particle flow to viscous debris flow and to the whole mass sliding with the increase of mud density; the width and the length along the slope decrease with mud density increasing; the movement process has classified phenomena about viscous debris flow composed by different mud densities: the velocity increases rapidly with time and the change gradient is steady when the density of mud is lower than 1.413g/cm3; the movement process can be divided into two stages when the density of mud is higher than 1.413g/cm3: the movement velocity is lower and the gradient change is small in the initial stage; but in the second stage, the movement velocity increases quickly, and the gradient is higher than the first stage, and with steady value.

Parametric Study on Dynamic Response of FRP Masonry Structures under the Impacts of Debris Flow

The aim of this study was to investigate the influences of different parameters on the performance of fiber reinforced polymer (FRP) masonry structures under debris flow using finite element models that were established using the software LS‐DYNA. The overall structural responses under the impacts of viscous debris flows were analyzed based on an in‐depth parametric study of some key factors (fiber types, relative impact positions, etc.). The results show that the diagonal and intersecting parallel types of FRP arrangements elicit better performances than horizontal types. Use of wider fiber cloths leads to the minimization of the structural response after its impact by debris flow. In addition, glass fiber reinforced polymer (GFRP) yields the best results among all studied materials in reducing local damage, while carbon fiber reinforced polymer (CFRP) yields a better overall structural response. Impact positions at the center of the wall are more unfavorable than those at the corners.

Experimental study of viscous debris flow characteristics in drainage channel with oblique symmetrical sills

In this study, experiments were performed in a 6-m-long flume to determine the characteristics of viscous debris flows in a new type of drainage channel with oblique symmetrical sills. The debris flow velocity was measured and subsequently used to characterise the viscous debris flow. The influences of the channel slope, transverse length of sills, and row spacing of sills on the debris flow velocity and the velocity reduction ratio P were investigated. The experimental results indicated that the viscous debris flow velocity increased as the channel slope increased from 0.10 to 0.15. However, the velocity decreased as the ratio of the transverse length of sills to the row spacing of sills increased from 0.13 to 0.53. Different combinations of the channel slopes, transverse lengths of sills, and row spacing of sills reduced the velocity by 14.2%–51.1% compared to the velocity in a smooth channel. The effects of the channel slopes, transverse lengths of sills, and row spacing of sills on P could be described using a power-law equation. Most of the errors in P prediction ranged from −25.0% to 25.0%. A comparison of P in drainage channels with different deceleration measures indicated that P increased with an increase in the length of a channel with deceleration measures. These experimental results serve as a useful reference for the design of drainage channels with oblique symmetrical sills.

Experimental Study on the Additional Load Occured in Viscous Debris Flow

To the bridge covered by viscous debris flow sludge in highway, there has seriously potential safety hazards at the bridge structure, and it is easy to be damaged by the gradual covering load. The viscous debris flow sludge is prepared, whose bulk density is 19.75±0.14kN/m3 and the slurry viscosity is 1.31±0.03Pa.s. It can be found that the surface layer of the viscous debris flow sludge will dehydrate and form crust after been placed for almost 10 days, and a prominent additional load will affect on the inner debris flow sludge, which will achieve 140kPa and almost 9 times more than its gravity stress. The research results find the main reasons for the damage of the bridge structure covered by viscous debris flow sludge, and are propitious to do further study on the formation mechanism of additional load of viscous debris flow sludge to bright out handling methods to strengthen structures covered by viscous debris flow sludge.

Natural consolidation characteristics of viscous debris flow deposition

: Pore water pressure and water content are important indicators to both deposition and consolidation of debris flows, enabling a direct assessment of consolidation degree. This article gained a more comprehensive understanding about the entire consolidation process and focused on exploring pore water pressure and volumetric water content variations of the deposit body during natural consolidation under different conditions taking the viscous debris flow mass as a study subject and by flume experiments. The results indicate that, as the color of the debris changed from initial dark green to grayish-white color, the initial deposit thickness declined by 3% and 2.8% over a permeable and impermeable sand bed, respectively. A positive correlation was observed between pore water pressure and depth in the deposit for both scenarios, with deeper depths being related to greater pore water pressure. For the permeable environment, the average dissipation rate of pore water pressure measured at depths of 0.10 m and 0.05 m were 0.0172 Pa/d and 0.0144 Pa/d, respectively, showing a positive changing trend with increasing depth. Under impermeable conditions, the average dissipation rates at different depths were similar, while the volumetric water content in the deposit had a positive correlation with depth. The reduction of water content in the deposit accelerated with depth under impermeable sand bed boundary conditions, but was not considerably correlated with depth under permeable sand bed boundary conditions. However, the amount of discharged water from the deposit was greater and consolidation occurred faster in permeable conditions. This indicates that the permeability of the boundary sand bed has a significant impact on the progress of consolidation. This research demonstrates that pore water and pressure dissipations are present during the entire viscous debris consolidation process. Contrasting with dilute flows, pore pressure dissipation in viscous flows cannot be completed in a matter of minutes or even hours, requiring longer completion time - 3 to 5 days and even more. Additionally, the dissipation of the pore water pressure lagged the reduction of the water content. During the experiment, the dissipation rate fluctuated substantially, indicating a close relationship between the dissipation process and the physical properties of broadly graded soils.

Characteristics of viscous debris flow in a drainage channel with an energy dissipation structure

A new type of drainage channel with an energy dissipation structure has been proposed based on previous engineering experiences and practical requirements for hazard mitigation in earthquakeaffected areas. Experimental studies were performed to determine the characteristics of viscous debris flow in a drainage channel of this type with a slope of 15%. The velocity and depth of the viscous debris flow were measured, processed, and subsequently used to characterize the viscous debris flow in the drainage channel. Observations of this experiment showed that the surface of the viscous debris flow in a smooth drainage channel was smoother than that of a similar debris flow passing through the energy dissipation section in a channel of the new type studied here. However, the flow patterns in the two types of channels were similar at other points. These experimental results show that the depth of the viscous debris flow downstream of the energy dissipation structure increased gradually with the length of the energy dissipation structure. In addition, in the smooth channel, the viscous debris-flow velocity downstream of the energy dissipation structure decreased gradually with the length of the energy dissipation structure. Furthermore, the viscous debris-flow depth and velocity were slightly affected by variations in the width of the energy dissipation structure when the channel slope was 15%. Finally, the energy dissipation ratio increased gradually as the length and width of the energy dissipation structure increased; the maximum energy dissipation ratio observed was 62.9% (where B = 0.6 m and L/w = 6.0).

Experimental analysis on the impact force of viscous debris flow

AbstractA miniaturized flume experiment was carried out to measure impact forces of viscous debris flow. The flow depth (7.2–11.2 cm), velocity (2.4–5.2 m/s) and impact force were recorded during the experiment. The impact process of debris flow can be divided into three phases by analyzing the variation of impact signals and flow regime. The three phases are the sudden strong impact of the debris flow head, continuous dynamic pressure of the body and slight static pressure of the tail. The variation of impact process is consistent with the change in the flow regime. The head has strong–rapid impact pressure, which is shown as a turbulent‐type flow; the body approximates to steady laminar flow. Accordingly, the process of debris flows hitting structures was simplified to a triangle shape, ignoring the pressure of the tail. In order to study the distribution of the debris flow impact force at different depths and variation of the impact process over time, the impact signals of slurry and coarse particles were separated from the original signals using wavelet analysis. The slurry's dynamic pressure signal appears to be a smooth curve, and the peak pressure is 12–34 kPa when the debris flow head hits the sensors, which is about 1.54 ± 0.36 times the continuous dynamic pressure of the debris flow body. The limit of application of the empirical parameter α in the hydraulic formula was also noted. We introduced the power function relationship of α and the Froude number of debris flows, and proposed a universal model for calculating dynamic pressure. The impact pressure of large particles has the characteristic of randomness. The mean frequency of large particles impacting the sensor is 210 ± 50–287 ± 29 times per second, and it is 336 ± 114–490 ± 69 times per second for the debris flow head, which is greater than that in the debris flow body. Peak impact pressure of particles at different flow depths is 40–160 kPa, which is 3.2 ± 1.5 times the impact pressure of the slurry at the bottom of the flow, 3.1 ± 0.9 times the flow in the middle, and 3.3 ± 0.9 times the flow at the surface. The differences in impact frequency indicate that most of the large particles concentrate in the debris flow head, and the number of particles in the debris flow head increases with height. This research supports the study of solid–liquid two phase flow mechanisms, and helps engineering design and risk assessment in debris flow prone areas. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Mechanism of downcutting erosion of debris flow over a movable bed

The phenomenon of debris flow is intermediate between mass movement and solid transport. Flows can be sudden, severe and destructive. Understanding debris flow erosion processes is the key to providing geomorphic explanations, but progress has been limited because the physical-mechanical properties, movement laws and erosion characteristics are different from those of sediment-laden flow. Using infinite slope theory, this research examines the process and mechanism of downcutting erosion over a moveable bed in a viscous debris flow gully. It focuses specifically on the scour depth and the critical slope for viscous debris flow, and formulas for both calculations are presented. Both scour depth and the critical conditions of downcutting erosion are related to debris flow properties (sand volume concentration and flow depth) and gully properties (longitudinal slope, viscous and internal friction angle of gully materials, and coefficient of kinetic friction). In addition, a series of flume experiments was carried out to characterize the scouring process of debris flows with different properties. The calculated values agreed well with the experimental data. These theoretical formulas are reasonable, and using infinite slope theory to analyze down cutting erosion from viscous debris flow is feasible.

Model Tests of Catastrophic Initiation Mode and Transport Mechanism of Viscous Mudflows

Most previous studies on the initiation mechanism of debris flows have achieved some significant results by means of traditional linear methods, statistical analyses, and qualitative and single-factor analyses. In fact, however, a large number of field observation analysis indicate that the initiation of debris flows may be a complicated nonlinear process subject to many influencing factors, with its initiation mode showing typical and complex characteristics such as sudden happening and slow happening and so on, which we could not explain clearly till now. In other words, if the initiation conditions could be regulated and controlled, the prevention and control of debris flows should achieve the practical effect. Based on catastrophe theory, the characteristics and mechanisms of the initiation, transport, and sedimentation associated with viscous mudflows, which can be taken as representative of natural debris flows, are analyzed, described, and verified using flowing model tests on the well-designed test apparatus. The results show that not only does the initiation mode of viscous mudflows belong to the slow-starting mode, but also its transport mechanism is in accordance with the general characteristics of the cusp catastrophe model. This is of great significance not only with regard to the forecasting and controlling of viscous debris flows that occur frequently in mountainous areas, but to the enriching of the nonlinear theoretical system of debris flows initiation mechanism as well.

The 1988 glacial lake outburst flood in Guangxieco Lake, Tibet, China

Abstract. The 1988 glacial lake outburst flood (GLOF) in Guangxieco Lake is studied based on geomorphological evidence, interviews with local residents, field surveys in 1990 and 2007, and satellite images from different years. The findings are as follows. (1) The outburst event was caused by two major factors, namely, intense pre-precipitation and persistent high temperatures before the outburst and the low self-stability of the terminal moraine dam as a result of perennial piping. (2) The GLOF, with the peak discharge rate of 1270 m3 s−1, evolved along Midui Valley in the following order: sediment-laden flow, viscous debris flow, non-viscous debris flow, and sediment-laden flood, which was eventually blocked by Palongzangbu River. (3) A comparison between the conditions during the outburst in 1988 and the present conditions suggests a small possibility of a future outburst unless drastic changes occur in landscape and climate. Reconstructing the outburst conditions and the GLOF processes is helpful in assessing a potential outburst in glacier lakes in Tibet.

Characteristics of a drainage channel with staggered indented sills for controlling debris flows

The characteristics of a new type of drainage channel with staggered indented sills for controlling debris flows were studied. The intermediate fluid in the non-viscous debris flow exhibited a helical movement, whereas the fluid near the sidewall had a stop-start movement pattern; the viscous debris flow exhibited a stable structure between the indented sills. The experimental results indicate that the mean velocity of the debris flow increased with increasing channel gradients, and the debris flow velocity was slightly affected by the angle of the sills. The average velocity of the non-viscous debris flow increased in the range of (0.5-1.5) interval between the indented sills, whereas the average velocity of the viscous debris flow increased initially and then decreased in the range of (0.75-1.25) interval between the indented sills. The depth of the non-viscous debris flow tended to gradually increase as the channel gradients increased, whereas the depth of the viscous debris flow gradually decreased as the channel gradients increased. When the discharge of the debris flow was constant, the angle and the interval between the indented sills had a slight effect on the depth of the viscous debris flow, whereas the depth of the non-viscous debris flow exhibited a different trend, as the sill angles and intervals were varied.