The Zymoetz River landslide, British Columbia, Canada: description and dynamic analysis of a rock slide–debris flow

The Zymoetz River landslide is a recent example of an extremely mobile type of landslide known as a rock slide–debris flow. It began as a failure of 900,000 m³ of bedrock, which mobilized an additional 500,000 m³ of surficial material in its path, transforming into a large debris flow that traveled over 4 km from its source. Seasonal snow and meltwater in the proximal part of the path were important factors. A recently developed dynamic model that accounts for material entrainment, DAN3D, was used to back-analyze this event. The two distinct phases of motion were modeled using different basal rheologies: a frictional model in the proximal path and a Voellmy model in the distal path, following the initiation of significant entrainment. Very good agreement between the observed and simulated results was achieved, suggesting that entrainment capabilities are essential for the successful simulation of this type of landslide.     

Results of Back-Analysis of the Propagation of Rock Avalanches as a Function of the Assumed Rheology

Summary. Numerical simulation can provide a useful tool for investigating the dynamics of phenomena like rock avalanches, within realistic geological contexts and in the framework of a better risk assessment and decision making. Difficulties in numerical modelling of a heterogeneous moving mass are mainly linked to the simulation of the complex behaviour assumed by the mass during propagation. The numerical code RASH3D, based on a continuum mechanics approach and on the long wave approximation, is used to back-analyse two cases of rock avalanches: Frank (1903, Canada) and Val Pola (1987, Italy). The two events are characterised by approximately the same volume (about 30 × 10⁶ m³) while the run out area morphologies are widely different. Three alternative “rheologies” (Frictional, Voellmy and Pouliquen) are used. Comparison among obtained results underlines that the validation of a “rheology” requires not only a good agreement between the numerical simulation results and the run out area boundaries but also in term of depth distribution of the mass in the deposit. In case of a Frictional rheology, the obtained calibrated dynamic friction angle values are in a range of 15 ± 1° for both the cases; while assuming a Pouliquen or a Voellmy rheology it emerges a different behaviour of rheological parameters for each of the considered events. Besides the calibration of rheological parameters to better back-analyse each of the considered events, it is investigated how the behaviour due to the assumed rheology is influenced by the geometry of the run out area (e.g. narrow or broad valley). Authors’ addresses: Marina Pirulli, Department of Structural and Geotechnical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129 Torino, Italy; Anne Mangeney, Equipe de Sismologie, Institut de Physique du Globe de Paris, Université Denis Diderot, 4 Place Jussieu, 75005 Paris, France     

Debris-flow event in the Frangerello Stream-Susa Valley (Italy)—calibration of numerical models for the back analysis of the 16 October, 2000 rainstorm

Three debris-flow simulation model software have been applied to the back analysis of a typical alpine debris flow that caused significant deposition on an urbanized alluvial fan. Parameters used in the models were at first retrieved from the literature and then adjusted to fit field evidence. In the case where different codes adopted the same parameters, the same input values were used, and comparable outputs were obtained. Results of the constitutive laws used (Bingham rheology, Voellmy fluid rheology and a quadratic rheology formulation which adds collisional and turbulent stresses to the Bingham law) indicate that no single rheological model appears to be valid for all debris flows. The three applied models appear to be capable of reasonable reproduction of debris-flow events, although with different levels of detail. The study shows how different software can be used to predict the debris-flow motion for various purposes from a first screening, to predict the runout distance and deposition of the solid material and to the different behaviour of the mixtures of flows with variation of maximum solid concentration.     

Characteristics and numerical runout modelling of a catastrophic rock avalanche triggered by the Wenchuan earthquake in the Wenjia valley,Mianzhu, Sichuan,China

The 2008 Wenchuan earthquake triggered more than 100 rock avalanches with volumes greater than 10 million cubic metres. The rock avalanche with the longest runout amongst these destructive landslides occurred in the Wenjia valley, Mianzhu, Sichuan, China. The landslide involved the failure of about 27.5 million cubic metres of sandstone from the source area. The displaced material travelled about 4,170 m with an elevation descent of about 1,360 m, equivalent to a fahrböschung of 16.9° and covered an area of 1.5 million square metres, with the final deposited volume of approximately 49 million cubic metres. The catastrophic event destroyed the village of Yanjing, killed 48 people and buried some houses at the mouth of the Wenjia valley. On the basis of a detailed field investigation, we introduce basic characteristics of the rock avalanche and find that the rock avalanche resulted in two run-ups and a superelevation along the runout path, and downslope enlargement due to the entrainment of path materials. A numerical model (DAN3D) is used to simulate the post-failure behaviour of the rock avalanche. By means of trial and error, a combination of the frictional model and Voellmy model is found to provide the best performance in simulating this rock avalanche. The simulation results reveal that the rock avalanche had a duration of about 240 s and an average velocity of 17.4 m/s.     

A non-hydrostatic model for the numerical study of landslide-generated waves

This paper proposes and demonstrates a two-layer depth-averaged model with non-hydrostatic pressure correction to simulate landslide-generated waves. Landslide (lower layer) and water (upper layer) motions are governed by the general shallow water equations derived from mass and momentum conservation laws. The landslide motion and wave generation/propagation are separately formulated, but they form a coupled system. Our model combines some features of the landslide analysis model DAN3D and the tsunami analysis model COMCOT and adds a non-hydrostatic pressure correction. We use the new model to simulate a 2007 rock avalanche-generated wave event at Chehalis Lake, British Columbia, Canada. The model results match both the observed distribution of the rock avalanche deposit in the lake and the wave run-up trimline along the shoreline. Sensitivity analyses demonstrate the importance of accounting for the non-hydrostatic dynamic pressure at the landslide-water interface, as well as the influence of the internal strength of the landslide on the size of the generated waves. Finally, we compare the numerical results of landslide-generated waves simulated with frictional and Voellmy rheologies. Similar maximum wave run-ups can be obtained using the two different rheologies, but the frictional model better reproduces the known limit of the rock avalanche deposit and is thus considered to yield the best overall results in this particular case.     

基于GIS和Voellmy模型的泥石流运动堆积过程模拟

泥石流流体具有速度快、破坏力强的特征,严重威胁着山区城镇的发展建设、群众生命财产安全。如何针对泥石流运动堆积过程进行模拟一直是泥石流研究的热点和难点。本文基于GIS技术以及近似Voellmy解的连续介质理论,建立了泥石流动力模型,采用数值模拟仿真的方法,以一典型泥石流沟为研究实例进行分析,通过模拟泥石流运动、堆积的动力过程,分析其最大速度、压力、过流量、堆积高度以及堆积面积,为后期泥石流危险性评价区划及防治提供有力支撑。     

Some observations on the prediction of the dynamic parameters of debris flows in pyroclastic deposits in the Campania region of Italy

Over the last 20 years, many tools have been developed for the prediction of the post-failure behaviour of rapid landslides. However, as pointed out by several researchers, knowledge may be improved by the performance of back-analyses using different models and the evaluation of their reliability. This paper reports the back-analysis, conducted using numerical models, of 57 rapid landslides that have occurred in the Campania region. The back-analysis has been performed using the 2-D DAN_W code (version 2003) with two different rheological models: the Voellmy and the frictional models. The latter has been immediately discarded because it did not match the observed data. Instead, using the Voellmy model, the best-fit values of the parameters (friction μ and turbulence ξ) for different types of flow (channelled, un-channelled and mixed flows) have been researched. With these values a parametric study has been carried out on four representative slope profiles of the Campania region, enabling the prediction of runout, velocity and depth of flow (dynamic parameters) of potential debris flows.

Internal deformation of a muddy gravity flow and its interaction with the seafloor (site C0018 of IODP Expedition 333, Nankai Trough,SE Japan)

The processes of flow deformation of marine mass-transport sediments, including their ability to affect the underlying substrate and add mass during sediment flow events, are addressed based on sedimentological analyses of strata from the distal part of a ～61-m-thick mass-transport deposit (MTD 6) drilled during Integrated Ocean Drilling Program (IODP) Expedition 333. Our analyses, supported by 3D seismic data, show a cohesive density flow deformed by folding, faulting and shear, except for its lowermost part (～7 m), where no deformation and sediment entrainment was identified. While the lowermost part moved as rigid sediment, the underlying sand layer acted as the basal shear zone for this part of the distal MTD 6. This shear zone was restricted to the sand, not involving the overlying sediments. From this, the studied part of MTD 6 was found to represent a case where the flow behaviour at least partly depended on the location and properties of the underlying sand layer, a situation that so far has received little attention in studies of marine flows. Our results also show that shear-induced mixing, located by the initial layering, is an important process in the flow transformation from cohesive slumps to mud flows and that this may occur over short distances (<4 km) without involving disintegration into blocks, probably due to only moderate prefailure consolidation of the sediments involved. In conclusion, we find that the bulk part of the flow was self-contained from a mass balance point of view and that that the overall amount of entrainment was limited.     

Comparison of 2D debris-flow simulation models with field events

Three two-dimensional (2D) debris-flow simulation models are applied to two large well-documented debris-flow events which caused major deposition of solid material on the fan. The models are based on a Voellmy fluid rheology reflecting turbulent-like and basal frictional stresses, a quadratic rheologic formulation including Bingham, collisional and turbulent stresses, and a Herschel–Bulkley rheology representing a viscoplastic fluid. The rheologic or friction parameters of the models are either assumed a priori or adjusted to best match field observations. All three models are capable of reasonably reproducing the depositional pattern on the alluvial fan after the models have been calibrated using historical data from the torrent. Accurate representation of the channel and fan topography is especially important to achieve a good replication of the observed deposition pattern.     

孔隙水压力对岩石裂纹扩展影响的数值模拟

应用岩石破坏过程渗流-应力-损伤(FSD)耦合分析软件F-RFPA2D,通过对孔隙水压作用下岩石试件加载破坏过程的数值模拟,对孔隙水压力大小和梯度对岩石试样中裂纹的萌生和扩展进行了数值模拟研究。模拟结果再现了孔隙水压力作用下裂纹萌生扩展的全过程,表明孔隙水压力大小和梯度对岩石中裂纹的萌生和扩展模式都有很大的影响。     

Application of a SPH depth-integrated model to landslide run-out analysis

Hazard and risk assessment of landslides with potentially long run-out is becoming more and more important. Numerical tools exploiting different constitutive models, initial data and numerical solution techniques are important for making the expert’s assessment more objective, even though they cannot substitute for the expert’s understanding of the site-specific conditions and the involved processes. This paper presents a depth-integrated model accounting for pore water pressure dissipation and applications both to real events and problems for which analytical solutions exist. The main ingredients are: (i) The mathematical model, which includes pore pressure dissipation as an additional equation. This makes possible to model flowslide problems with a high mobility at the beginning, the landslide mass coming to rest once pore water pressures dissipate. (ii) The rheological models describing basal friction: Bingham, frictional, Voellmy and cohesive-frictional viscous models. (iii) We have implemented simple erosion laws, providing a comparison between the approaches of Egashira, Hungr and Blanc. (iv) We propose a Lagrangian SPH model to discretize the equations, including pore water pressure information associated to the moving SPH nodes.     

雅鲁藏布江色东普沟冰崩—堵江—溃决灾害数值模拟

为了揭示雅鲁藏布江色东普沟2018年10月17日冰崩—堵江—溃决灾害链的动力演化过程,基于Massflow数值模拟仿真平台,使用Fortran编程语言,根据研究区域地质条件特征对程序进行二次开发以优化Voellmy模型,模拟冰崩—泥石流动力过程;将模拟泥石流得到的堰塞坝体嵌入地形中,运用ArcGIS计算堰塞湖范围及体积,通过Manning模型模拟堰塞湖溃决洪水动力过程。采用分段模拟法再现冰崩—泥石流—堵江—堰塞湖—溃坝的完整动力过程,对泥石流运动过程中的流速、流深,坝体高度,溃决洪水的流深、流速等参数进行定量化研究,为色东普流域的防灾减灾工作提供有效支撑。为了揭示雅鲁藏布江色东普沟2018年10月17日冰崩-堵江-溃决灾害链的动力演化过程,采用Massflow数值模拟仿真平台,以Fortran语言为编程手段,根据研究区域地质条件特征对程序进行二次开发优化Voellmy模型,模拟冰崩-泥石流动力过程;将模拟泥石流所得到的堰塞坝体嵌入地形中,采用ArcGIS计算堰塞湖范围及体积,通过曼宁模型模拟堰塞湖溃决洪水动力过程。采用分段模拟法再现冰崩-泥石流-堵江-堰塞湖-溃坝的完整动力过程,对泥石流运动过程中的流速、流深,坝体高度,溃决洪水的流深、流速等参数进行定量化研究,为色东普流域的防灾减工作提供有效支撑。     

Late-Variscan fluid migration at the Variscan thrust front of Eastern Belgium: numerical modelling of the palaeothermal and fluid flow field

Modelling of the palaeothermal field at the Variscan thrust front in eastern Belgium indicates significant temperature modifications by late-Variscan palaeofluids migrating from internal to peripheral parts of the orogen. A detailed set of calibration data (chlorite geothermometry, microthermometry, organic rank) gives evidence of temporary palaeotemperature variations at the Variscan thrust front obviously connected to the migration of hot, low saline palaeofluids. These thermal events likely enhanced organic maturation (vitrinite reflectance, conodont alteration) of Devonian and Carboniferous sediments, which accumulated long before the Variscan orogeny occurred. Numerical simulation (2D Finite Element method) of the palaeothermal field includes coupled heat transport by thermal conduction and fluid flow. Palaeothermal scenarios yield successive palaeotemperatures (200–300°C), which are indicated by the control data, due to relatively short-term fluid ascent along the detachment and the imbricate thrust front. The simulated flow velocities are up to tens of metre per year lasting several thousand years (non-steady-state solution). In the scenarios modelled, these thermal events occur in a realm of enhanced bulk temperatures due to elevated basal heat flow densities (90 mW m⁻²) and an additional burial depth of some kilometres. The simulated temperature enhancement due to fluids ascending at the Variscan thrust front is several tens degrees. The scenarios demonstrate long-distance fluid migration during or after deformation of the Palaeozoic basin and its effect on the palaeothermal field.     

Numerical modeling of debris avalanche propagation from collapse of volcanic edifices

Debris avalanches produced from the collapse of volcanic edifices are destructive events that involve volumes up to two orders of magnitude larger (cubic kilometer) than most non-volcanic rock and debris avalanches. We replicate the motion and spreading of several volcanic collapses by means of a depth-averaged quasi-3D numerical code. The model assumes a frictional internal rheology and a variable basal rheology (i.e frictional, Voellmy and plastic). We back analyzed seven case-studies against observations reported in the literature to provide a set of calibrated cases. The ASTER and SRTM satellite-derived digital elevation models were used as topographic data. The numerical model captures the main features of the propagation process, including travel distance, lateral spreading and run up. At varying triggering factors and material characteristics the best fitting parameters span in a narrow interval and differ from those typical of non-volcanic rock and debris avalanches. The bulk basal friction angles (the sole parameter required in the frictional rheology) range within 3° and 7.5° whereas typical values for non-volcanic debris avalanches vary from 11° to 31°. The consistency of the back analyzed parameters is encouraging for a possible use of the model in the perspective of hazard mapping. The reconstruction of the pre-event topography is critical, and it is associated to large uncertainty. The quality of the terrain data, more than the resolution of the DEMs used, is relevant for the modeling. Resampling the original square grid to larger cell sizes determines a low increase in the back analyzed rheological parameters, as a result of the lower roughness of the terrain.     

Structural controls on fluid flow and related mineralization in the Xiangshan uranium deposit, Southern China

The Xiangshan uranium deposit of Southern China is a Mesozoic volcanic uranium deposit where mineralization is closely associated with regional rock deformation and fluid flow. To better understand the genesis of this deposit, we have carried out coupled deformation and fluid flow modeling to explore the relationship between mineralizing fluid flow and structural deformation processes. The numerical modeling results demonstrate that fluid transport and focusing are predominantly controlled by deposit scale structures and associated rock deformation.     

A pore-scale numerical model for non-Darcy fluid flow through rough-walled fractures

This paper aims at developing a pore-scale numerical model for non-Darcy fluid flow through rough-walled fractures. A simple general relationship between the local hydraulic conductivity and the flow velocity is proposed. A new governing equation for non-Darcy fluid flow through rough-walled fractures is then derived by introducing this relationship into the Reynolds equation. Based on the non-linear finite element method, a self-developed code is used to simulate the non-Darcy fluid flow through fractures. It is found that the macroscopic results obtained by the numerical simulation agree well with the experimental results. Furthermore, some interesting experimental observations can be reproduced.     

基底侵蚀对高速流动性滑坡运动性影响的模拟分析

高速流动性滑坡运动距离远,破坏性强。这类滑坡在运动过程中常裹挟大量的松散物质,导致滑坡的体积和致灾范围增大,该现象被称为基底侵蚀效应。以往的研究指出基底侵蚀效应对这类滑坡的运动性有显著的影响,但却很少有研究考虑其对滑体性质的影响,以及如何对其进行量化。因此,本文基于动量守恒原理建立了考虑基底侵蚀效应的滑坡运动模型,利用有限差分法求解,并依据滑坡的侵蚀深度来计算侵蚀导致的滑坡性质变化。利用改进的模型对陕西泾河南岸的西庙店滑坡进行模拟分析。结果表明,滑坡运动可分为启动加速阶段（0~5 s）和运动减速阶段（5~14 s）。在启动加速阶段,基底侵蚀程度低,对滑体运动的影响较弱。而在运动减速阶段,基底侵蚀效应降低了滑带土强度,对该滑坡的运动产生了明显的促进作用,致使其发生远程运动。此外,对比考虑和不考虑基底侵蚀两种工况的模拟结果还发现,考虑这种影响时,模拟所得的运动范围及地形与实测吻合良好,而未考虑时模拟所得运动范围明显偏小。因此,本文的模型可对这类滑坡的运动过程进行更为有效的模拟。     

德兴斑岩铜矿床断裂与侵入体产状对成矿的控制作用:从力-热-流三场耦合数值模拟结果分析

斑岩矿床的成矿机制是一种典型的力-热-流多物理场耦合的岩浆-热液过程,因而从成矿动力学数值计算模拟的角度研究斑岩矿床成矿作用过程,对揭示斑岩岩浆-热液系统动力学演化机制及其成矿响应情况具有十分重要的意义.德兴铜矿(包括朱砂红、铜厂和富家坞)作为目前中国华南已发现的最大斑岩型铜矿床,是研究(大型/超大型)斑岩矿床成矿作用...     

Runout and entrainment analysis of an extremely large rock avalanche—a case study of Yigong,Tibet, China

An extremely large rock avalanche occurred on April 9, 2000 at Yigong, Tibet, China. It started with an initial volume of material of 90?×?10⁶ m³ comprising mainly of loose material lying on the channel bed. The rock avalanche travelled around 10 km in horizontal distance and formed a 2.5-km-long by 2.5-km-wide depositional fan with a final volume of approximately 300?×?10⁶ m³. An energy-based debris flow runout model is used to simulate the movement process with a new entrainment model. The entrainment model considers both rolling and sliding motions in calculating the volume of eroded material. Entrainment calculation is governed by a second order partial differential equation which is solved using the finite difference method. During entrainment, it is considered that the total mass is changed due to basal erosion. Also the profile of the channel bed is adjusted accordingly due to erosion at the end of each calculation time step. For Yigong, the profile used in the simulation was extracted from a digital elevation model (DEM) with a resolution of 30 m?×?30 m. Measurements obtained from site investigation, including deposition depth and flow height at specific location, are used to verify the model. Ground elevation-based DEM before and after the event is also used to verify the simulation results where access was difficult. It is found that the calculated runout distance and the modified deposition height agree with the field observations. Moreover, the back-calculated flow characteristics based on field observations, such as flow velocity, are also used for model verifications. The results indicate that the new entrainment model is able to capture the entrainment volume and depth, runout distance, and deposition height for this case.