This work explores the phenomena of instability in low stress tilt-testing of dry sands using novel imbedded shear stress and strain sensors to capture quantitative data of constitutive behaviour leading up to and during instability. A unique strategy of testing dry soil enabled the investigation of instability in isolation from pore pressure consequences. Six shear stress and shear distortion sensors were distributed along the transparent sidewall and centre of the tilt-table, which was then rotated until instability and failure. Shear strain measured next to the transparent sidewall were 50% of those measured along the table centerline. Friction reduction strategies were successful in significantly reducing, but not eliminating, this discrepancy. Soil layers tilted until reaching instability, unloaded, and subjected to a second tilt cycle only exhibit instability at angles in excess of the first instability event. This phenomenon, analogous to the Kaiser effect, reveals the importance of void ratio with respect to instability. Tilt-table testing, when equipped with internal shear distortion sensors, was shown to be able to capture the modulus degradation curve over the strain range of 10 −5 to 10 −1 providing a promising new experimental technique to explore the stiffness degradation curve at very low confining pressures.

Dam breach analyses for tailings dams currently rely heavily on relationships and methods derived for water retaining dams, despite significant differences in design, construction, dam materials, and geometry; particularly, the upstream face of the dam. Conventional tailings slurry deposition from the dam crest typically forms low angle upstream beaches (1-2 % inclination) within the impoundment. In this paper, we isolate the effect of tailings dam beach geometry at the time of overtopping on breach characteristics using physical and numerical modeling. Five 1 m high homogeneous fine sand dams with beach heights of 0.5 to 0.9 m and a beach slope of 5 % were brought to failure by v-notch overtopping. The laboratory data revealed that a threshold beach height existed above which the peak discharge was progressively limited by the geometry of the reservoir. Numerical simulations, performed in XBeach, captured this effect in the outflow hydrographs, with differences between physical and numerical model peak outflow generally within 25 %. Another key model parameter in tailings dam breach analysis is the volume of tailings solids lost through erosion during breach. Comparison of terrestrial laser scanning elevation profiles, cut through the centreline of the physical model, with XBeach simulations indicate XBeach can replicate the bulk characteristics of erosion when a tailings-style beach is present. These findings show that hazard analysis for overtopping failure in tailings dams should consider the effect of tailings dam beach geometry on the outflow hydrograph, and forms a growing case of evidence to support the use of XBeach for simulation of dam breach.

The Hudson Bay Railway in Northern Canada traverses over a thousand kilometers of challenging ground conditions, including peatlands, discontinuous permafrost, and continuous permafrost. Monitoring climate change impacts to the rail corridor is challenging, as ground conditions are changing rapidly, and access to remote locations is limited. As a result, the unknown rate of thaw settlement hampers quantitatively-informed maintenance and rehabilitation strategies. In this manuscript, we evaluate a workflow to transform normalized track geometry measurements (in the form of Surface 62) into absolute profiles of track surface elevation. Field validation of the method was undertaken at three strategically chosen field sites: Site A, a simple isolated subsidence feature located at the transition zone between a low-lying fen and a peat plateau; Site B, a more complex subsidence feature exhibiting clear signs of an advanced stage of permafrost degradation; and Site C, a bridge crossing experiencing track heave due to frost jacking of pile foundations. Validation of the method against LiDAR measurements illustrates that peak depth or heave of a feature can be estimated within 6 %. Furthermore, given the high temporal resolution of the track geometry measurements, this method can capture the rate of thaw subsidence and track settlement. This rate, observed to be 0.26 mm/day at Site A, illustrates the enormous challenge posed to infrastructure owners tasked with maintaining track geometry in permafrost environments under a changing climate.

Laboratory landslide flume studies have revealed that saturated granular flows experience greater mobility than their dry counterparts, being notably faster, farther reaching, and experiencing enhanced spreading. The ability to reliably measure basal pore water pressures is critical for developing, evaluating, and validating constitutive relationships linking the effects of pore pressure to the mechanisms causing increased mobility. Unfortunately, experience has shown that two identical sensors installed in the base of a landslide flume can yield wildly different responses to the same multi-phase landslide. In this paper we explore the hypothesis that the elevation of pore water pressure sensor filter elements can influence sensor readings. A unique experimental strategy of simplifying the flow into a single fluid phase is used to validate sensor readings, prior to application in multi-phase flows. Dam-break releases of 600 kg of water at the top of the inclined flume slope are used as a parametric study to provide evidence to support the hypothesis that sensor roughness significantly impacts the pore pressure recorded in high velocity flows. These results are then contrasted to observations of releases of multi-phase flows to derive best practices for the reliable measurement of pore pressure in landslide flume tests.

Field observations of debris flows often show that a deep dry granular front is followed by a progressively thinner and increasingly watery tail. These features have been captured in recent laboratory flume experiments (Taylor-Noonan et al. , J. Geophys. Res.: Earth Surf. , vol. 127, 2022, e2022JF006622). In these experiments different initial release volumes were used to investigate the dynamics of an undersaturated monodisperse grain–water mixture as it flowed downslope onto a horizontal run-out pad. Corresponding dry granular flows, with the same particle release volumes, were also studied to show the effect of the interstitial fluid. The inclusion of water makes debris flows much more mobile than equivalent volumes of dry grains. In the wet flows, the formation of a dry front is crucially dependent on the heterogeneous vertical structure of the flow and the velocity shear. These effects are included in the depth-averaged theory of Meng et al. ( J. Fluid Mech. , vol. 943, 2022, A19), which is used in this paper to quantitatively simulate both the wet and dry experimental flows using a high-resolution shock-capturing scheme. The results show that velocity shear causes dry grains (located near the free surface) to migrate forwards to create a dry front. The front is more resistant to motion than the more watery material behind, which reduces the overall computed run-out distance compared with debris-flow models that assume plug flow and develop only small dry snouts. Velocity shear also implies that there is a net transport of water to the back of the flow. This creates a thin oversaturated tail that is unstable to roll waves in agreement with experimental observations.

The dry fringe that appears beneath a footprint on a beach is a visual manifestation of dilation. Dilation causes the sand to attempt to increase in volume on shearing, resulting in negative pore pressure and enhanced bearing capacity. Conventional theory cannot explain this increase in strength, suggesting instead that bearing capacity with the phreatic surface at the sand surface should be approximately half that of the dry case. To explore this apparent contradiction, ten load-controlled bearing capacity experiments were performed on transparent soil with phreatic surfaces ranging from 100 mm below to 30 mm above the footing. For phreatic surfaces deeper than the footing width, failure occurred within the dry material. In shallower phreatic surface conditions, bearing capacity increased as the phreatic surface approached the surface. Air entry was observed to initiate along the top surface of the saturated layer and extend to the depth of the bearing capacity mechanism. For the case of the phreatic and soil surfaces being coincident, the bearing capacity was observed to be more than double that of the dry case. In submerged cases bearing capacity was less than values at the surface, as there was no air–fluid interface to enhance the development of negative pore pressure.

Catastrophic breaches of water and mine waste retaining impoundments in recent history have emphasized the severity and consequences to the downstream environment. In this study, the applicability and suitability of the XBeach numerical model for modelling earth dam failures driven by overtopping with water is explored by detailed comparison with controlled experimental data. The XBeach model is applied to simulate laboratory-scale breaches caused by overtopping failure of dams constructed with uniform sand at the Queen's University Landslide Flume by Walsh et al. (2021a). The model sensitivity to boundary conditions for different virtual flume sizes, different sediment transport equations that influence erosion rates, and the process of avalanching are investigated. The model results are in best agreement with laboratory measurements when the Soulsby-van Rijn sediment transport formulation is used, which depends on grain size, and the avalanching module is activated, indicating the importance of these processes. The model is also run for different dam geometries to investigate the influence of upstream slope angle, which is relevant for tailings dam breach analyses. The results indicate that for flatter slopes the model is in closer agreement with observations of the peak discharge, while for steeper slopes the model results are better for breach duration time. Overall, XBeach provides promising results for the prediction of the dam breach outflow hydrograph at the laboratory scale and has potential to improve understanding of earth dam failure outcomes with further investigation.

Landslides comprised of a wide range of particle sizes (e.g. debris flows) exhibit flow structures arising from particle size segregation. Segregation influences the mobility of the flow, the development of debris fans, and the resulting impact forces to be expected when designing barriers and containment structures. In order to capture the flow dynamics of segregable materials in numerical simulations, experimental datasets quantifying segregation in the final deposit are required. However, the measurement of segregation is not a straightforward task as segregation observed at an external transparent boundary may not be indicative of segregation within the bulk of the landslide mass due to sidewall friction. In this paper, we explore the use of four different strategies to optically measure particle size segregation in large landslide flume tests, comparing measurements taken (i) at the external transparent flume boundary; (ii) using a thin transparent plane as a splitter plate along the centre of the flow; and using a (iii) vertically or (iv) horizontally inserted transparent plate into the static deposit after flow arrest. Relationships between concentrations measured by projected area (i.e. sidewall image) to concentrations by mass are derived and validated for a tridisperse mixture to assess which sampling method most closely represented the original source volume. Of the four strategies tested, the transparent splitter plane method was identified to cause the least amount of out-of-plane segregation of particles, provides a rich database of highly detailed observations of segregation of tridisperse granular flows that can be used to evaluate future numerical model outcomes, and is recommended for future laboratory flume investigations.

Field observed shrinkage was quantified and compared for one geosynthetic clay liner (GCL) type left covered only by a black geomembrane, a white geomembrane, and 0.3 m of gravel cover. Shrinkage is reported for up to 28 months field exposure of an additional four GCLs beneath a black geomembrane. All GCLs were needle-punched geotextile encased: one containing fine granular bentonite, two with powdered bentonite, one with polymer amended granular bentonite, and one multicomponent GCL with a film coating installed film up. All the GCLs examined have the potential to shrink with the magnitude of the shrinkage primarily dependent on the thermal/moisture cycles to which it is subjected and the degree of adhesion between panel overlaps. It is shown that the panel overlap adhesion can be highly variable and this is primarily attributed to condensation of water vapour below geomembrane wrinkles during daily thermal cycles. With a an initial GCL overlap of 300 mm, the shrinkage observed over 28 months left ≥32% of the original overlap; however, if the overlap had been only 150 mm, then gaps or ineffective seams would have occurred for several GCLs. Guidance regarding mitigating GCL panel shrinkage is provided.

Liquefaction can have devastating consequences by causing increased mobility of debris flows, tailings dam breaches, and settlement following seismic shaking. Observations on the consolidation behaviour of liquefied soils in 1-g or centrifuge shake table tests have permitted significant advancements in analytical and numerical methods to predict the rate and magnitude of consolidation settlement. However, advanced consolidation models introduce material parameters which are currently difficult to define quickly and at low cost. The objective of this paper is to demonstrate the development of a simple, low-cost test that can be used to quickly estimate the spatially and temporally varying coefficient of consolidation, which controls post-liquefaction settlements. Using the proposed simple set-up, experiments were conducted on four uniformly graded sands of varying grain size and on one well-graded mixture. A range of analytical and numerical approaches from literature were assessed for their ability to back-analyse the observed pore pressure dissipation and settlement. Estimated values for the coefficient of consolidation were comparable between models and estimates of surface settlement matched well the experimental results. The simplicity of the proposed test combined with its low-cost and mobile nature, raise significant possibilities for quick estimations of the evolution of the coefficient of consolidation post-liquefaction.

Climate change is making coastal regions increasingly vulnerable to hazards, including rapid subaerial and submarine landslides, which can result in catastrophic tsunamis. Due to the complex geomechanics of failure, limited physical modeling studies have been conducted that encompass the entire problem including the triggering of granular landslides, the waves generated by partially and fully submerged mass failures, and the runup of these waves on local and distal slopes. In the present study, for the first time, waves in both the seaward direction (in the direction of failure for both submarine and partially submerged slides) and the landward direction (opposing the direction of failure only for submarine slides) are investigated during morphological evolution of the granular material. A series of large-scale experiments are conducted under varying levels of submergence in water by releasing columns of gravel-sized material into a range of different reservoir depths. This is accomplished using a pneumatically actuated vertical lift gate designed specifically for these experiments. The wave amplitudes measured in the seaward direction agree with empirical relationships developed in a previous study using smaller-scale models, and a new analytical solution relating the column submergence to the trough-led wave amplitudes in landward direction is presented. These novel predictions of wave amplitude and runup in both the seaward and landward directions indicate strong dependence of the wave behavior on the submergence depth and granular properties, improving our understanding of tsunamis generated by mass failures in coastal regions. Landslides can occur from above water or underwater, and both types can generate hazardous waves. Climate change is destabilizing slopes and causing more landslides into water, and there is a need to study how these waves form and how they impact coastal areas in detail. In the present study, a series of large-scale laboratory flume experiments are conducted to examine this problem by measuring waves with digital cameras and probes. The experiments each begin with a vertical column of gravel-sized particles that are released by rapidly opening a gate specifically designed for this research. The collapse of the granular material generates waves in the forward direction (seaward) and in the backward direction (landward) and both waves also cause runup on slopes at each end of the flume. Different column heights and water depths are tested to obtain results over a wide range of conditions. Based on the measurements, the results agree with previous studies that used smaller-scale models, and a new equation for calculating the wave size in the landward direction behind the failure (landward direction) is presented. The results are useful for understanding tsunamis generated by both submerged and partially submerged landslides into water. A new rapid vertical release gate system is designed to experimentally generate tsunami from large-scale granular collapse For the first time, the amplitude and runup of waves in both the seaward direction and the landward direction are investigated A new momentum-based relationship is developed to predict the landward wave amplitude that impacts local coastal regions

At impact with water, the velocity and thickness of a landslide are the key factors that govern momentum transfer and wave generation. These properties are not only a function of the size of the slide, but also a function of the landslide material, grain size, pore fluid, and other rheological parameters. The objective of this study is to determine the amplitude of waves generated from realistic landslides composed of both granular material and pore fluid in comparison with the waves generated by end-member landslides composed of only dry granular material or only fluid. To achieve this, laboratory experiments are conducted in a large-scale landslide flume and observations are collected using high-speed digital cameras and wave probes. Different source materials consisting of dry granular material, saturated granular material, and water are released down the landslide slope into the reservoir to generate impulse waves. The waves are analyzed to determine the amplitude and shape, and the effective time and length scales over which each landslide generates a wave. The observations are used to develop a mobility factor for all three landslide types based on the linear relationship between the length of forcing and the time of wave release. The measurements are compared to a predictive momentum-based relationship, and a modified equation is developed to account for the bulk mobility of the landslide. The improved equation can be applied to predict the maximum wave amplitude generated by a wide range of conditions for realistic landslides.

Over the past four years, a graduate module has been offered at the University of Cambridge to provide a ‘hands-on’ experience of using a small-scale centrifuge to investigate a geotechnical engineering problem. The problems chosen in recent years include the well-known geotechnical problems of embankments on soft clay, and foundations on soft clay. These problems have been selected to demonstrate construction rate effects, the presence of layers of varying permeability, and the application of ground improvement technology. The contents of the module are presented, along with example data and interpretations prepared by the students. Finally, we conclude that centrifuges such as the mini-drum centrifuge have a significant role to play in the teaching of modern Geotechnical Engineering.

It has been theorised that seasonal pore water pressure cycles play a significant role in the progressive failure of clay embankments. This paper presents the development of an atmospheric chamber to build on the recent advances in techniques for matric suction measurement and texture-based image analysis of deformations to model these cycles in the centrifuge. The systems for regulating the relative humidity boundary condition are described, and the importance of a near-zero moisture loss environment emphasised. Through control of the relative humidity boundary condition, idealized seasonal pore water pressure cycles have been successfully created in the centrifuge. The resulting deformations observed over two years of modelling of an overconsolidated clay slope are presented. These results indicate that, although most of the deformation is normal to the soil slope, seasonal moisture cycles cause small, yet irrecoverable downslope displacement components. 2 PHYSICAL MODELLING OF SLOPES One of the first applications of the centrifuge as a tool for the physical modeling of geotechnical problems was that of slope stability (Lyndon & Schofield, 1970). Model slopes were subjected to increasing acceleration levels before reaching a “critical height” at which an undrained failure was observed. The popularity of slope modelling in the early days of centrifuge technology relied heavily on the fact that these tests did not employ a great deal of instrumentation, yet produced dramatic results which could be back analysed by limit equilibrium methods. Undrained failures initiated in this manner, are analogous to failure during construction due to excess pore water pressures, and do not address the problem of infiltration instability. The problem of rainfall-induced failure of soil slopes has been tackled in the centrifuge by applying moisture directly to the soil surface. The results of these tests indicate that soil slopes are very resilient to short-term, monotonic, pore water pressure increases despite having slope angles in excess of the critical state friction angle (eg. Jackson and Craig, 1998). Model testing of homogeneous soil slopes, therefore, inherently models behaviour consistent with mobilised peak soil strengths, potentially leading to dangerous conclusions. If seasonal pore water pressures drive progressive failure of soil slopes, both wetting and drying cycles must be modelled in the centrifuge. Of these two seasons, the dry summer poses a particular technological difficulty. Historically, the inability to reliably measure matric suctions has typically restricted centrifuge modelling to a saturated surface boundary condition. Recent advances in suction probe design and saturation techniques have allowed the measurement of matric suctions above the ‘false ceiling’ of 100 kPa which was traditionally thought to be the maximum directly measurable suction value. Based on the work of Ridley (1993), a new device has been developed for the measurement of matric suctions in the centrifuge environment (Take and Bolton, 2002). As a result, the drying phase of seasonal moisture boundary conditions can now be quantified in terms of matric suction. 3 ATMOSPHERIC CHAMBER An atmospheric chamber designed for the physical modelling of seasonal pore water pressure cycles is required to perform two functions: control of the relative humidity of the air contained within the chamber, and isolation of the internal environment from that of the centrifuge chamber. Figure 1. Manufacturer’s calibration for model rainfall intensity in model and field scales. Figure 2. Self-weight of nozzle pressure supply column and acceleration sensitivity of water pressure reducing valve. 3.1 Relative humidity boundary condition The relative humidity within the atmospheric chamber is increased by forcing high pressure water through small diameter nozzles to create atomised mist droplets of the order of 30 microns in diameter. Applying scaling laws for linear dimensions, these droplets would have a prototype dimensions of 1.8mm at 60g. In nature, rain droplets rarely grow larger than 5mm owing to the stability of the droplet under drag forces. Although no conscious effort has been placed on rainfall droplet similitude, model precipitation of a small droplet size will reduce the energy of impact, and therefore the propensity for the model rainfall to cause erosion. The rainfall intensity provided by the atmospheric chamber has been designed for low permeability clay slopes. To ensure a flooded slope boundary, two rows of nozzles have been provided at the appropriate distance from the soil surface to apply a uniform rainfall on the model slope. The manufacturer’s calibration for the atomising mist nozzles in terms of flow rate and scaled rainfall intensity as a function of inlet pressure is shown in Figure 1. The high pressure water supply to drive the mist nozzles is provided by the self weight of a column of water originating at the centre of the beam centrifuge and running the length of the centrifuge arm through an increasing radial acceleration field. The water pressure delivered to the atmospheric chamber is therefore dependent on the acceleration level, geometry of the centrifuge, and the mains water pressure (Figure 2). Once delivered to the atmospheric chamber, the water pressure is regulated using a water pressure reducing valve. The pressures are monitored with pressure transducers both up and downstream from the reducing valve. The sensitivity of the pressure reducing valve to centrifugal acceleration is shown in Figure 2. The nozzle pressure, originally set at a nominal pressure of 150 kPa for proof testing, increases at a rate of 1.7 kPa/g. Based on this result, the valve was set at 1g at a value of 400 kPa which, accounting for the drift under acceleration, results in a scaled rainfall rate of approximately 5 mm/h. The rainfall delivery system is shown in Figure 3a. The onset of model rainfall through the mist nozzles is controlled through a two-way solenoid valve. When energised, the valve delivers water to the mist nozzles. As shown in Figure 1, the nozzles do not perform well at low driving pressures – they tend to drip rather than form a fine mist. This can cause a potential problem at the end of the modelling of a wet winter. Upon cessation of model rainfall, the low pressure water remaining in the distribution system will empty through the nozzles, dripping onto the slope creating impact craters. This problem has been overcome through the use of a two-way solenoid valve. When deactivated, the solenoid relieves the pressure in the nozzle delivery system by routing it to atmospheric pressure. Dry air can be circulated through the atmospheric chamber to lower the relative humidity boundary condition within the atmospheric chamber. The initial design for the drying system consisted of two pairs of 50mm diameter fans mounted on the top plate of the atmospheric chamber to blow air from the centrifuge pit into the chamber and to extract the moisture laden chamber air. This system was abandoned because the fans behaved poorly under elevated acceleration levels, the presence of fans meant that the chamber could not be sealed, and the relative humidity could only be dropped to the ambient conditions on the test day. The latter two drawbacks also hampered a subsequent design which consisted of pneumatically controlled louvers and an air scoop. The problem of a consistent dry air supply was finally overcome using dried compressed air transferred via sliprings to the atmospheric chamber. As shown in Figure 3b, air enters the atmospheric chamber near the toe of the embankment through a solenoid valve, picks up moisture, and exits through Figure 3. Plan view of atmospheric chamber isolating a) rainfall modelling system, and b) drying system. Figure 4. Relative humidity during centrifuge acceleration and model rainfall in a non-sealed chamber. three large-bore solenoid valves at the crest of the embankment. Since a pressure gradient is necessary to drive air exchange, an air pressure transducer records the increase in air pressure within the atmospheric chamber. Running at a supply pressure of 150 kPa, the air pressure in the chamber rises by only 3 kPa when all three exit valves are opened. Therefore, the increase in air pressure associated with simulating seasonal dry conditions will result in only a small change in pore air and water pressures. Furthermore, as a safety precaution, a blow-off valve has been incorporated into the atmospheric chamber to ensure that, in the eventuality of malfunction, the air pressure cannot exceed 100 kPa within the atmospheric chamber. Finally, the drying system also has a provision for temperature control of the incoming air, if desired. This is achieved through the use of two process heaters situated to preheat the air as it is entering the chamber. 3.2 Near-zero moisture loss environment Soil, whether left on the laboratory bench, or in a exposed centrifuge model will experience moisture loss as water is transferred from the soil surface to the surrounding air. If situated in a sealed chamber, this process will be arrested once the surrounding air becomes saturated with moisture. However, if the air above the soil surface is constantly replaced, this equilibrium cannot be reached and moisture will be continuously stripped from the soil surface. This problem is especially pertinent to centifuge testing, as centrifuge chambers are inherently windy environments. Therefore, if the soil model is not protected in a sealed chamber, the constant circulation of air will desiccate clay soils generating hitherto unquantified matric suctions. This problem of moisture loss to the air has historically been acknowledged but remained unquantified in terms of pore water pressure (eg Malushitsky, 1981), or avoided by applying saturated boundary conditions (eg. Bolton and Powrie, 1988). Avoidance of the problem in this manner

Landslide tsunamis and impulse waves are hazardous events with severe socioeconomic impacts. A long standing problem with simulations of these events is the generation stage, where landslides and water interact. Depth-averaged models like the Saint-Venant or Boussinesq Equations lose their validity for such applications. Therefore, we have to rely on a full treatment of the hydrodynamics, for instance by applying the Navier-Stokes Equations and Computational Fluid Dynamics (CFD). However, applications of fully three-dimensional methods to landslide tsunamis are sparse, and have often been outperformed by depth averaged models when compared to experimental data. In this work, we evaluate the multiphase Navier-Stokes Equations as implemented in OpenFOAM® in terms of impulse wave generation. We focus on a simplified two-dimensional setup where the landslide consists of water, in order to circumvent additional complexities due to treatment of landslide rheologies. We conduct a thorough grid refinement study and compare results to experiments to investigate model convergence, stability, and accuracy. The simulations display good agreement with the experimental data if the Courant-Friedrichs-Lewy (CFL) condition is modified to account for the specific properties of the multiphase system. Further, we use the validated model for sensitivity studies and to review various scaling relations for landslide generated tsunamis. The application of numerical models allows us to perform broad parametric tests and dissect the underlying physics of these predictive equations systematically. We found that the first wave crest may be well estimated by solely the landslide mass in our setting. Including additional properties related to landslide momentum can improve the predictive skill, while other parameters lead to no substantial improvement.

Runup of landslide-generated waves is an important natural hazard in coastal regions, and can result in major damage to the natural and built environment. Past work has investigated the runup of non-breaking waves, whereas, in contrast, little data is available on the runup of waves at the point of breaking prior to interaction with the opposing shore. In the present study, impulse waves were generated in a series of laboratory flume experiments by releasing a range of different slide source volumes of highly mobile slide material (water) into different reservoir depths, to observe the runup of breaking and non-breaking waves at the point of arrival at steep slopes ranging from 25° to 45°. Water surface characteristics including the maximum wave amplitude were measured using wave probes and digital imagery was obtained using high-speed cameras. The maximum runup, and the cross-slope variability in runup, of each wave was captured using hydrochromic paint, which changes colour on contact with water. The experimental results indicate that in the near-field the runup of breaking waves is dependent on the wave amplitude relative to the water depth, and is nearly independent of the slope angle. Statistical analysis of the runup observations for breaking and non-breaking waves indicate that the variability of runup across the width of the slope increases with increasing incident relative wave amplitude. These observations, combined with runup data from previous studies, are used to develop a new semi-empirical equation for the maximum runup of breaking and non-breaking waves. The formulation is valid over an extended range of relative wave amplitudes, relevant for near-field runup that has been documented in major field cases. The experimental observations in the present study provide, for the first time, a comprehensive dataset of runup for impulse waves involving breaking and no breaking on arrival at a slope.

The granular column collapse experiment is an important benchmark case for the physical and numerical study of transitional mass flows. Unlike columns of dry granular materials, the presence of a relatively incompressible fluid, such as water, in the voids of saturated columns complicates the shear behavior of the column by becoming a function of the coupled shear and volumetric behavior of the grain–fluid system. Dilative or contractive behavior at the pore level will cause a decrease or increase, respectively, in the pore fluid pressure. These changes in effective stress, in turn, will define stability or instability and length of runout. Here we use the new opportunity provided by transparent soil to observe air entry within saturated columns to explore the hypothesis that the entry pressure provides the maximum contribution of capillary pressure at incipient failure, thereby providing a quantitative control on the stability of dilative granular columns. Furthermore, the mobility of densely packed saturated columns subject to collapse was significantly influenced by air entry. An analytical model, based on this assumption of limiting capillary pressure, is able to describe the stability of the experimental columns as well as the larger dataset from the literature, reframing the previous empirical stability threshold using limit equilibrium and soil material parameters. Our results demonstrate the importance of stress-dilatancy and air-entry phenomena on the rapid shear behavior of saturated granular materials.

Tailings dams differ from conventional water‐retaining dams in design, materials retained behind the dam and used in construction of the dam, and the inclination of the upstream face of the dam. In this paper, we isolate the effect of upstream slope angle on behavior during overtopping breach. Six 1 m high homogeneous fine sand dams were constructed with upstream slope angles varying between 10.0° and 30.0° and brought to failure by V notch overtopping. Slope angle was observed to define the height of flow over the erosional breach crest hydraulic control structure that forms in the upstream face of the dam, with higher peak outflow corresponding to steeper upstream slope angles. A semiellipse was observed to be an excellent approximation of the geometry of the breach throughout the rising limb of the hydrograph to peak outflow. This observation permitted the use of the Ramanujan approximation for perimeter of an ellipse to define a mathematical relationship between breach width and arc length. A simplified method to predict the rising limb of the outflow hydrograph was then proposed based on the assumption of linear growth of breach width coupled with a semielliptical breach geometry. These findings show that hazard analysis for overtopping failure should consider the effect of upstream slope angle on peak outflow.

The granular temperature is an index of the level of collisional activity in a granular flow, and increasingly important in the verification of extended kinetic theories. The granular temperature is related to the square of the difference between a particle’s velocity and that of the group mean. Image analysis of high-speed video is the most common method to measure granular temperature in experimental flows and depends on correlation of a search mask or a portion of the original image to the next image frame to determine the particle’s movement. This invariably involves some level of estimation of the location at a resolution finer than the pixels that make up the image. However, errors in determining particle movement at the subpixel level can be shown to have a significant impact on granular temperature identification. We show that taking particle movement to be a chain of displacement vectors provides context to the apparent impulses on the particle. Here we propose two novel methods for determining the granular temperature of experimental flows, namely a novel method of initializing Particle Image Velocimetry (PIV) for granular systems where each search subset is centred on a previously determined particle location to reduce bias, and a method of filtering the apparent impulses on a particle on a frequency basis. We term these methods Guided-PIV and Impulse Frequency Filtering (IFF), respectively. In a verification exercise using synthetically generated images, we show Guided-PIV to produce substantially more accurate results than ordinary applications of PIV. The IFF method is shown to greatly reduce the influence of analyzed framerate on granular temperature results. Our results demonstrate practical improvements for granular temperature identification from image analysis, throughout a range of experimental image quality levels, and we anticipate that these improvements will enable experimental assessment towards verification of theorized models of collisional-frictional granular flows.