Runout Simulation Research Articles

A well-balanced numerical scheme for debris flow run-out prediction in Xiaojia Gully considering different hydrological designs

To simulate debris flow run-out, the governing equations for free-surface shallow flow are corrected by setting the basal flow resistance coefficients with the quadratic rheological friction model. A well-balanced numerical scheme is developed for its run-out simulation over irregular topography. A linear reconstruction is adopted for improving the spatial accuracy of the numerical scheme. Considering the complex friction terms of governing equations of debris flow, they are estimated with a full implicit scheme for ensuring stability of the numerical scheme. The validity check of run-out simulation is implemented based on general knowledge of fluid, and a well-studied case occurred in the Xiezi Gully in Yingxiu Town, Sichuan Province of China. For practical purpose, the present numerical scheme is used for run-out prediction of debris flow in Xiaojia Gully of Panzhihua City, Sichuan Province of China. Our work aims to present a well-balanced numerical scheme for debris flow run-out simulation prediction, which can be applied quite conveniently to solve other kinds of debris flow models and helpful to promote the development in debris flow numerical calculation.

Hybrid simulation of the initiation and runout characteristics of a catastrophic debris flow

On 13 August 2010, a catastrophic debris flow with a volume of 1.17 million m3 occurred in Xiaojiagou Ravine near Yingxiu town of Wenchuan county in Sichuan Province, China. The main source material was the landslide deposits retained in the ravine during the 2008 Wenchuan earthquake. This paper describes a two-dimensional hybrid numerical method that simulates the entire process of the debris flow from initiation to transportation and finally to deposition. The study area is discretized into a grid of square zones. A two dimensional finite difference method is then applied to simulate the rainfall-runoff and debris flow runout processes. The analysis is divided into three steps; namely, rainfall-runoff simulation, mixing water and solid materials, and debris flow runout simulation. The rainfall-runoff simulation is firstly conducted to obtain the cumulative runoff near the location of main source material and at the outlet of the first branch. The water and solid materials are then mixed to create an inflow hydrograph for the debris flow runout simulation. The occurrence time and volume of the debris flow can be estimated in this step. Finally the runout process of the debris flow is simulated. When the yield stress is high, it controls the deposition zone. When the yield stress is medium or low, both yield stress and viscosity influence the deposition zone. The flow velocity is largely influenced by the viscosity. The estimated yield stress by the equation, τ y = ρghsin θ, and the estimated viscosity by the equation established by Bisantino et al. (2010) provide good estimates of the area of the debris flow fan and the distribution of deposition depth.

Numerical runout simulation of debris avalanches in the Faroe Islands, North Atlantic Ocean

The Faroe Islands in the North Atlantic Ocean are susceptible to flow-type landslides in coarse-grained highly organic colluvium. Following several hazardous debris avalanche events, research work has been initiated to quantify landslide risk. A central task in this work is to predict landslide runout behavior. From numerical simulation of four debris avalanches, this study provides a first screening of which rheology and appertaining input parameters best predict runout behavior of debris avalanches in the Faroe Islands. Three rheologies (frictional, Voellmy, and Bingham) are selected and used for individual back analysis of the events in the numerical models BING and DAN3D. A best fit rheology is selected from comparing predicted and observed landslide runout behavior. General back analysis to identify the optimal input parameters for the chosen rheology is performed by cross validation, where each debris avalanche is modeled with input parameters from the three other events. Optimal input parameters are found from the model run producing the most accurate runout length and velocity. The Bingham is selected as the best fit rheology, a result differing from similar studies of coarse-grained landslides. A reason for why particularly the frictional rheology proves unsuitable is its tendency to produce too long runout lengths of the low-weight runout material, a result showing important limitations for using the frictional rheology in DAN3D. Optimal Bingham input parameters are τy = 980 Pa and μb = 117 Pa/s. However, future studies performed in 2D models are needed for precise parameterization before results can be used for landslide risk assessment.

Rockfalls detached from a lateral moraine during spring season. 2010 and 2011 events observed at the Rebaixader debris-flow monitoring site (Central Pyrenees, Spain)

Instability processes at glacial deposits represent an important hazard in mountainous areas. During the spring seasons of 2010 and 2011, two falls of large boulders (18 and 55 m3) initiated in a lateral moraine in the Rebaixader catchment (Central Pyrenees, Spain). Detailed information was gathered due to the debris-flow monitoring system installed along the torrent. Meteorological data showed that the two rockfalls were triggered without important rainfall amounts. Field surveys, ground vibration acquired at geophones and the movie recorded with a video camera provided unique information on the rockfall occurrence and dynamics. In addition, the information gave an excellent opportunity to show the importance of monitored data for the calibration of model parameters for runout simulations. The analysis focussed on the 2011 event and showed that the boulder passed rolling and bouncing through the monitored torrent reach. The velocity estimates in this reach range from 3 to 9 m/s. The 2011 rockfall was also back-analysed by a two-dimensional physically based model, which was fitted by the monitored and field data. The results of the simulation coincided well with recorded measurements, although the output could be improved by the application of a three-dimensional model.

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

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.

A SPH depth integrated model for Popocatépetl 2001 lahar (Mexico): Sensitivity analysis and runout simulation

Lahars are debris flows of volcanic origin, which can endanger or even destroy communities located near the flanks of volcanoes. Lahars are not always triggered by eruptions; they can form during heavy rainfall or after hydrothermal alteration and volcanic edifice collapse. Decision makers need lahar hazard maps to devise hazard prevention measures that will prevent casualties, so lahar modelling is an important tool for assessing flow behavior and determining inundation areas. The depth integrated numerical model used in this study is derived from the velocity–pressure of the Biot–Zienkiewicz model and was discretized using the smoothed particle hydrodynamics (SPH) method to simulate a lahar that occurred at Popocatépetl volcano in 2001. In order to investigate the convergence of the model, we used a range of different SPH mesh resolutions. Once the optimum mesh resolution was bounded, we analyzed the model's sensitivity to the initial lahar volume, the density of the geomaterial, and the rheological parameter of the Bingham fluid. The results show that the SPH depth integrated model produced a highly accurate simulation of the distribution and velocity of the 2001 lahar. The study also shows the effects of SPH mesh resolution and the relevant influence of rheological parameters.

Hazard investigation of the Portillo Rock Avalanche site, central Andes, Chile, using an integrated field mapping and numerical modelling approach

This paper reports a detailed rock slope hazard investigation of the Portillo Rock Avalanche site located in the rugged mountains of the Andean Cordillera of central Chile. The site is important as it lies along the International Santiago–Mendoza Highway Corridor connecting Chile and Argentina, and a major ski resort is located on its deposits. A number of large lobate-shaped diamicton deposits were mapped and dated by cosmogenic nuclides ( 36Cl), with the results showing that they correspond to two significant prehistoric rockslide events. An integrated field mapping and numerical modelling investigation was subsequently carried out to assess the threat posed to the area by further rocksliding activity. Distinct-element modelling was used to back analyze the failure mechanism and identify the geological model that best reproduced the Portillo Rock Avalanche failure surface. Results show that a stress-controlled failure at the toe of the slope followed by sliding along volcaniclastic bedding was the likely failure mechanism. A 3-D dynamic runout analysis was carried out to back analyze which combinations of rheologies, material properties and rockslide sequencing were best able to reproduce the current distribution of rockslide deposits. Results indicate that two separate sliding events originating from different sources had occurred, with each involving different combinations of frictional and Voellmy rheologies depending on the level of entrainment that occurred along each travel path. Insights gained from the back analysis were then used to carry out a forward analysis to assess the potential for a recurring major rockslide under several different triggering scenarios. Results suggest that a low probability M 7.8 earthquake would be required to trigger another rockslide from the original source area. The rock slope was otherwise found to be stable, even following high precipitation events. Nevertheless, runout simulations for the estimated large-magnitude earthquake-triggered rockslide volume showed that for both a highly frictional and non-saturated path (i.e. dry season) and a snow covered path (winter), the leading edge of the flow would override part of the International Santiago–Mendoza Corridor with the debris coming to rest in a flat-lying area in the upper part of the valley. Overall, the results from this integrated hazard assessment suggest that the hazard level is low.

Procedure for the selection of runout model parameters from landslide back-analyses: application to the Metropolitan Area of San Salvador, El Salvador

The existing procedures for the selection of runout model parameters from back-analyses do not allow integrating different types of runout criteria and generally lack a systematic approach. A new method based on receiver operating characteristic (ROC) analyses and aimed at overcoming these limitations is herein proposed. The method consists of estimating discrete classifiers for every runout simulation associated with a set of model parameters. The set of parameters that yields the best prediction is selected using ROC metrics and space. The procedure is illustrated with the back-analyses of a rainfall-triggered debris flow that killed 300-500 people in the Metropolitan Area of San Salvador in 1982. The selected model parameters are used to estimate forward predictions for scenarios that correspond to different return periods. The proposed procedure may be useful in the assessment of areas potentially affected by landslides. In turn, this information can be used in the production or updating of land use plans and zonations, similar to that currently being carried out by the Office for Urban Planning of the Metropolitan Area of San Salvador in El Salvador.

Integrated back and forward analysis of rock slope stability and rockslide runout at Afternoon Creek, Washington

Hazard assessments involving large rock slopes are often problematic, given the influence of geology on failure kinematics and the subsequent influence of the failure kinematics on the rockslide runout. The 2003 Afternoon Creek rockslide in northwest Washington is one such example, where 750 000 m3 of rock slid from a steep ridge harmlessly into Afternoon Creek. However, topographic and structural controls at the source area unexpectedly redirected a small volume (<10%) down the opposite side of the ridge along a much steeper travel path, impacting the highway below. Postfailure investigations indicate that the slope still presents a danger. To address this, a framework was developed that links back analyses with forward modelling of failure initiation and runout. Field mapping and data collection were specifically tailored for these analyses. Advanced numerical modelling was used to assess likely rockslide source areas, volumes, and controlling features. These were then used to guide a series of three-dimensional runout simulations to model rockslide travel path, reach, and velocities. The results show that a rockslide originating from the ridge could occur again and that the topography would again direct a small percentage of material down the backside which would reach the highway below.

Hazard assessment and runout analysis for an unstable rock slope above an industrial site in the Riviera valley, Switzerland

This paper presents a detailed field investigation and hazard assessment for an unstable rock slope above an industrial site in the Riviera valley in the Canton of Ticino in southern Switzerland. An integrated framework was used to counter issues of geological complexity and uncertainty, linking geological mapping and numerical modeling to develop an understanding of the acting instability mechanism to 2-D and 3-D dynamic runout simulations to predict the travel path and reach in the event of a large volume rockslide. The results from the numerical stability analysis provided a means to constrain failure volume estimates, whereas a series of calibration simulations were used to constrain the input parameters required by the rheological model used for the runout analysis. Results from this assessment suggest that current protection measures in place may not be sufficient, helping local authorities to define hazard zones and aid further development plans for the region.

Incorporating the effects of topographic amplification and sliding areas in the modeling of earthquake-induced landslide hazards, using the cumulative displacement method

A procedure that considers topographic effects and runout behavior is proposed for analyzing seismic landslide hazards. The theoretical topographic amplification factors and corresponding amplified ground motion are calculated. By using the amplified motion, a cumulative displacement map is generated through the Newmark's displacement method. The high displacement areas are defined as the source areas of landslides. A runout simulation that identifies sliding routes and the final deposition areas of the sliding material from these source areas is performed. Finally, the complete set of landslide zones, including source, and sliding and deposition areas, is predicted. The landslide hazard maps of the Mt. Baishiya region, Nantou, Taiwan are evaluated, and the maps of actual landslides triggered by the September 21st, 1999, Chi-Chi earthquake are compared with the prediction. The results show that the proposed procedure, which combines topographic effects and runout simulation, can generate more accurate predictions for seismic landslide hazard analysis. However, this slight improvement over the procedure that only considers topographic effects is within the uncertainty levels of the input parameters. This slight improvement is obtained by a relatively complex and time-consuming procedure, and further research is required towards evaluating the viability of the proposed model when topographic effects cannot be neglected.

Assessing potential debris flow runout: a comparison of two simulation models

Abstract. In the present paper some of the problems related to the application of the continuum mechanics modelling to debris flow runout simulation are discussed. Particularly, a procedure is proposed to face the uncertainties in the choice of a numerical code and in the setting of rheological parameter values that arise when the prediction of a debris flow propagation is required. In this frame, the two codes RASH3D and FLO2D are used to numerically analyse the propagation of potential debris flows affecting two study sites in Southern Italy. For these two study sites, a lack in information prevents that the rheological parameters can be obtained from the back analysis of similar well documented debris flow events in the area. As a prediction of the possible runout area is however required by decision makers, an alternative approach based on the analysis of the alluvial fans existing at the toe of the two studied basins is proposed to calibrate rheological parameters on the safe side. From the comparison of the results obtained with RASH3D (where a Voellmy and a Quadratic rheologies are implemented) and FLO2D (where a Quadratic rheology is implemented) it emerges that, for the two examined cases, numerical analyses carried out with RASH3D assuming a Voellmy rheology can be considered on the safe side respect to those carried out with a Quadratic rheology.

Velocity and runout simulation of destructive debris flows and debris avalanches in pyroclastic deposits, Campania region, Italy

The Campanian Apennines are characterized by the presence of monocline ridges, mainly formed by limestone. During the periods of volcanic activity of the Somma-Vesuvius and Phlegrean Fields, the ridges were mantled with pyroclastic materials in varying thickness. The pyroclastics have been involved in destructive landslides both in historical time and in the recent past (1997, 1998, 1999). The landslides occur following intense and prolonged rainfalls. In some cases, landslides extended up to 4 km into the surrounding lowlands and reached towns, causing severe destruction and over 200 deaths. Generally, the landslides begin as small debris slides that develop into large, shallow debris avalanches or debris flows involving pyroclastic horizons and colluvial soils (0.5–2 m thick) on steep and vegetated slopes, often at the heads of gullies. During motion, the landslide materials eroded vegetation and soils from the slope, so that the moving material volume tended to increase. Then, proceeding towards and beyond the base of the slopes, the phenomena evolved into hyperconcentrated streamflow due to dilution by incorporating water. The results of motion analyses are described. An empirical rheological relationship was used including two principal terms that depend on the total normal stress and on the flow velocity. On this basis, the model has simulated the velocity and duration of debris avalanches and the distribution of the deposits. The selected areas were those of Sarno/Quindici and Cervinara, where a large amount of data is available both on the material properties and geomorphological setting. It was found that the majority of the cases at the two sites can be simulated successfully with only one specific pair of rheologic parameters. This provides the possibility for first-order predictions to be made of the motion of future landslides. Such predictions will be a valuable tool for outlining potential hazard areas and designing remedial measures.

Displacement Accuracy of Discontinuous Deformation Analysis Method Applied to Sliding Block

Discontinuous deformation analysis (DDA) is a discrete element method that was developed for computing large deformation in fractured rock masses. In this paper, we present an alternative derivation of the basic theory of DDA for planar (two-dimensional) problems, and we address the accuracy of the DDA method for sliding blocks using sensitivity analyses. Results of analyses with different parameters show that the residual and relative errors in the displacement of a frictional sliding block are controlled by the perturbation in the initial time steps of the simulation. In addition, we expose a systematic error induced by the DDA penalty formulation. Overall, the initial perturbation of the solution decreases with decreasing friction angle and increasing contact penalty and, counterintuitively, decreases with increasing time step size. All analyses show that the long runout behavior of the system trends toward the analytic solution, independent of the initial perturbation. The resulting precision of the long runout simulation is more than sufficient for all problems of engineering interest.

Non-repeatable runout measurement and simulation of fluid lubricated spindles

The non-repeatable runout (NRRO) of small self-acting air bearing spindles is investigated using high precision capacitance probe transducers. Transient NRRO, spindle start-up time, and power consumption are determined at start-up for horizontal and vertical spindle orientation. The design of fluid spindles for magnetic recording disk drive applications is optimized by means of finite element-based numerical simulation. Advantages and disadvantages of fluid lubricated spindles are discussed.