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

Effect of density and total weight on flow depth, velocity, and stresses in loess debris flows

Debris flows that involve loess material produce important damage around the world. However, the kinematics of such processes are poorly understood. To better understand these kinematics, we used a flume to measure the kinematics of debris flows with different mixture densities and weights. We used sensors to measure pore fluid pressure and total normal stress. We measured flow patterns, velocities, and depths using a high-speed camera and laser range finder to identify the temporal evolution of the flow behavior and the corresponding peaks. We constructed fitting functions for the relationships between the maximum values of the experimental parameters. The hydrographs of the debris flows could be divided into four phases: increase to a first minor peak, a subsequent smooth increase to a second peak, fluctuation until a third major peak, and a final continuous decrease. The flow depth, velocity, total normal stress, and pore fluid pressure were strongly related to the mixture density and total mixture weight. We defined the corresponding relationships between the flow parameters and mixture kinematics. Linear and exponential relationships described the maximum flow depth and the mixture weight and density, respectively. The flow velocity was linearly related to the weight and density. The pore fluid pressure and total normal stress were linearly related to the weight, but logarithmically related to the density. The regression goodness of fit for all functions was >0.93. Therefore, these functions are accurate and could be used to predict the consequences of loess debris flows. Our results provide an improved understanding of the effects of mixture density and weight on the kinematics of debris flows in loess areas, and can help landscape managers prevent and design improved engineering solutions.Peer ReviewedPostprint (published version

Reconstructing ice dynamics in the central sector of the last British-Irish Ice Sheet

The central sector (NW England and Scottish borders) of the last British-Irish Ice Sheet exhibits a palimpsest glacial geological and geomorphological signature characteristic of multi-phase ice flow and ice-marginal fluctuations. Despite its influential position at the heart of the British-Irish Ice Sheet, sourced from major ice dispersal centres of the northern Pennines, Lake District and Southern Uplands, and drained via fast-flowing outlets such as the Irish Sea Ice Stream, the region remains poorly constrained, both temporally and in terms of ice-flow dynamics. The principle goal of this thesis was therefore to reconstruct the palaeoglaciology of the central sector of the British-Irish Ice Sheet during the last glacial cycle, focusing on: (1) ice-flow dynamics with respect to palaeo-ice divides, ice-dispersal centres, flow trajectories and flow phasing; (2) the relative chronology of ice flows during advance and decay of the ice sheet; and (3) evidence for ice stream activity either within or sourced from the study area. The thesis adopted a dual approach involving both geomorphological mapping and sedimentological analysis. A 5 m resolution NEXTMap DEM was used to map over 9,000 individual landforms including subglacial lineations, hummocky terrain, moraines, meltwater channels, eskers and glaciofluvial sediment accumulations. Subglacial lineations were subdivided into discrete flow sets demarcating distinctive flow phases, and a relative chronology produced from cross-cutting relationships. Thirteen field sites, concentrated in the Solway Lowlands, supported by data collected from over 200 boreholes enabled detailed stratigraphic and sedimentological analysis to be carried out. This included stratigraphic logging, the collection of macrofabrics, particle size and geochemistry analysis on till matrixes, clast lithological counts, varve analysis and microstructural (thin sections) data. Results from this study have demonstrated that the central sector of the ice sheet was characterised by repeated ice-flow switches, initiation and termination of ice streams, drawdown into ice streams, repeated ice-marginal fluctuations (the Scottish and Blackhall Wood Re-advances) and the production of large volumes of meltwater, often impounded to form ice-dammed lakes. Six main stages of ice flow have been recognised in the region, of which stage I is thought to indicate the period of maximum ice expansion, while stages II-VI record the deglacial history. A pre-stage I event is also discussed and can be reconciled with the initial expansion of ice out of upland dispersal centres. Stage I was characterised by ice flowing eastwards across the country through major topographic lows of the Stainmore and Tyne gaps. The Tyne Gap was occupied by a topographic ice stream, which was heavily influenced by the changing dominances of both Lake District and Southern Upland ice-dispersal centres. Migration of ice divides back towards upland dispersal centres during stage II resulted in the flow of ice through the Stainmore Gap being cut-off, while the northern edge of the Tyne Gap ice stream was breached by a SE ice flow down the N Tyne Valley. Despite the maintenance of the Irish Sea Ice Stream off the western coast of Cumbria throughout stage III, the Tyne Gap and Solway Lowlands underwent widespread deglaciation. Meltwater from the Tyne Gap was routed into Glacial-Lake Wear via a major proglacial drainage network in the South Tyne Valley, while the natural basin of the Solway Lowlands also ponded-up (Glacial-Lake Blackhall Wood) as drainage became impeded by the Irish Sea Ice Stream. The overall pattern of retreat was reversed during the Blackhall Wood Re-advance (stage IV), during which ice was vigorously drawn down into the Irish Sea Ice Stream. Stage V was characterised by the continued retreat of ice out of the central sector of the British-Irish Ice Sheet; with the vast amounts of meltwater generated impounded in ice-marginal lake systems (Glacial-Lake Carlisle), or routed through meltwater channel networks or evolving glacier karst (Brampton kame belt). The landforms of the Brampton kame belt can be reconciled with ice stagnation on the reverse slope of the Tyne Gap, and is thought to have formed one component of a much larger, time-transgressive drainage network involving the Pennine escarpment and Tyne Gap meltwater channel systems. The final recognised stage in the glacial history of the region was the Scottish Re-advance, a brief incursion of ice, sourced from the Southern Uplands, onto the fringe of the Solway Lowlands. A large glacial lake is identified to have formed at the ice front, dammed against ice in the Irish Sea basin and delimited by a large deltaic complex at Holme St. Cuthbert

An experimental investigation of the debris flow surge phenomenon

A review of theoretical, experimental and field work on debris flow surges was undertaken. A new hypothesis concerning the nature of debris flow surges was proposed and tested in the laboratory. The hypothesis is that a debris flow surge can be analytically explained by what was termed a "moving shearing granular dam (MSGD)" model. It proposes that any surge can, in principle, be analyzed macroscopically without knowing the internal details of individual grain motions using a physical description involving three essential forces on the surge head/body. These forces are; an upslope internal frictional force, a downslope gravity force and a downslope hydrostatic force. The quantitative testing was carried out in a 9m long by 150 mm wide flume with transparent walls flume. Quasi-steady state coal grain (diameters up to about 4mm) and wall paper paste surges were produced which propagated down the flume. During these runs an unsaturated region, termed the “wetting front,” was observed within the surge front. Field evidence for the wetting front was established from measurements made on debris flow deposits at Bullock Creek, North Canterbury. The results of the analyses of several runs were found to be consistent with the observed quasi-steady surge front translational motion. Several observations from the literature review of debris flow surge field behaviour are consistent with the central concept underlying the MSGD hypothesis while no observations were found which appear to conflict with the idea

Advances in Modelling and Prediction on the Impact of Human Activities and Extreme Events on Environments

YesThis book is an edition of the Special Issue Advances in Modelling and Prediction on the Impact of Human Activities and Extreme Events on Environments that was published in Water journal