Coupled distinct element method computational fluid dynamics analyses for reservoir landslide modelling

The Vajont landslide involved a large mass of rock splashing at high speed into the reservoir which in turn generated a highimpulse water that overtopped the dam and swept away the downstream village. In several cases of reservoir landslide, albeit the flood defence structures may remain intact, a catastrophe still occur due to the generation of a ‚tsunami‘ wave. Since the features of the tsunami wave strongly depend on the physics of the rock splashing and the subsequent rock –water interaction, a numerical tool accounting for such physics is required for predictions to be reliable. Here, the formulation of a coupled 3D Distinct Element Method (DEM) – Computational Fluid Dynamics (CFD) code used to simulate the rock slide from onset to impact with the reservoir and the subsequent generation of the impulse wave, is presented. To run realistic simulations in an affordable runtime, coarse graining is employed. The main results of quasi 3D analyses in plane strain along two cross-sections representative of the eastern and western slope sectors are presented. The results show to be in broad agreement with the available recorded observations

Non-invasive portable geophysical tool to monitor water content in earthen long linear infrastructures

The use of electrical conductivity measurements from a non-invasive hand held electromagnetic probe is showcased to monitor the water content of earthen embankments at routine inspections. A methodology to convert the electrical conductivity measurements from the electromagnetic device into water content values is illustrated. The methodology is based on measuring the soil electrical conductivity variation with respect to a baseline reference condition and calibrating a water content - electrical conductivity relationship by comparing electrical conductivity readings from the electromagnetic probes with water content readings taken from geotechnical probes installed in a few sections of the embankment. The values of water content converted from the conductivity measurements according to the proposed procedure were found to be in very good agreement with independent measures of water content taken at times well beyond the calibration period

Landslides and geophysical investigations: advantages and limitations

This special issue is dedicated to the geophysical methods applied to investigate, characterize, and monitor landslides. Over the years, both the advantages and limitations of these techniques have been highlighted, and some drawbacks are still open. Some papers were submitted to this special issue, and, after a thorough peer review process, only five articles were selected to be included in this special issue. This relatively small number is probably caused by the difficulty in applying geophysical techniques on slope movements given hard-operating conditions (e.g., high slopes, distance from access roads, and lack of security for the technical operator) and not because the methods limitations are greater than the advantages

Cost-benefit methodology for road slope stabilisation

\ua9 2024 The Author(s). Cost-benefit analyses are conducted to evaluate the cost efficiency of road slope stabilisation measures to aid road planning, design, maintenance, and repair. Most cost analyses are based on a statistical framework that requires a database of slope failures. However, databases can be costly to compile, and they tend to compare options that satisfy the same global factor of safety or partial factors of safety (e.g. EC-7) neglecting the fact that each measure reduces the risk of slope failure by a different extent. Here, we present a novel methodology to evaluate the cost efficiency of different road slope stabilisation measures based on direct costs and a rigorous but parsimonious mechanistic and probabilistic geotechnical slope stability assessment. Unlike other cost analyses for slope stability, our methodology accounts for uncertainty in slope geomaterial characteristics, as well as for hillslope hydrology. Probabilistic slope stability analyses accounting for the effect of time-varying slope seepage are performed using the CUTSTAB-P methodology to estimate the frequency of slope failure. The methodology is demonstrated on a cut slope in Nepal, assessing four different road slope stabilisation measures that are implemented in Nepal: (1) the cut slope with no additional support; (2) reprofiling to a shallower inclination; (3) a mortared masonry wall; and (4) an anchoring system. We find that an anchoring system is the most cost-efficient road slope stabilisation measure for this cut slope, and that a mortared masonry wall is least cost-efficient. This is despite the mortared masonry wall having much lower initial investment costs than the anchoring system. Mortared masonry walls are hugely common along roads in Nepal. We also make an approximation of indirect costs. With this addition, we find that the anchoring system remains the most cost-efficient method

Dynamic Fragmentation of Jointed Rock Blocks During Rockslide-Avalanches: Insights From Discrete Element Analyses

The dynamic fragmentation of jointed rock blocks during rockslide avalanches has been investigated by discrete element method simulations for a multiple arrangement of a rock block sliding over a simple slope geometry. The rock blocks are released along an inclined sliding plane and subsequently collide onto a flat horizontal plane at a sharp kink point. The contact force chains generated by the impact appear initially at the bottom frontal corner of the rock block and then propagate radially upward to the top rear part of the block. The jointed rock blocks exhibit evident contact force concentration and discontinuity of force wave propagation near the joint, associating with high energy dissipation of granular dynamics. The corresponding force wave propagation velocity can be less than 200 m/s, which is much smaller than that of an intact rock (1,316 m/s). The concentration of contact forces at the bottom leads to high rock fragmentation intensity and momentum boosts, facilitating the spreading of many fine fragments to the distal ends. However, the upper rock block exhibits very low rock fragmentation intensity but high energy dissipation due to intensive friction and damping, resulting in the deposition of large fragments near the slope toe. The size and shape of large fragments are closely related to the orientation and distribution of the block joints. The cumulative fragment size distribution can be well fitted by the Weibull’s distribution function, with very gentle and steep curvatures at the fine and coarse size ranges, respectively. The numerical results of fragment size distribution can match well some experimental and field observations

Manufacturing of PAV-ONE, a Permeator against Vacuum Mock-Up with Niobium Membrane

The Permeator Against Vacuum (PAV) is one of the proposed technologies for the Tritium Extraction System of the WCLL BB (Water-Cooled Lithium-Lead Breeding Blanket) of the EU DEMO reactor. In this paper, the manufacturing of the first PAV mock-up with a niobium membrane with a cylindrical configuration is presented. This work aimed to demonstrate the possibility of manufacturing a relevant-size PAV to be later tested in the TRIEX-II facility. The adopted prototypical solutions are described in detail, starting with the methodology developed to join the Nb tubes with a 10CrMo9-10 (A182 F22) plate. Dedicated manufacturing and welding procedures, based on vacuum brazing with a nickel-based brazing alloy, were developed to solve the problem. This new kind of brazing was first analyzed to check the morphology of the joint and then tested to check its capability to withstand the TRIEX-II operative conditions. In parallel, the compatibility with a lithium-lead environment was analyzed by exposing samples of niobium and 10CrMo9-10 (A335 P22) to a flow of the eutectic alloy at 500 °C up to 4000 h. Finally, the PAV mock-up was installed in the TRIEX-II facility

On the stability of fissured slopes subject to seismic action

A set of analytical solutions achieved by the upper bound theorem of limit analysis and the pseudo-static approach is presented for the assessment of the stability of homogeneous c, ϕ slopes manifesting vertical cracks and subject to seismic action. Rotational failure mechanisms are considered for slopes with cracks of either known or unknown depth and location. A validation exercise was carried out based on numerical limit analyses and displacement-based finite-element analyses with strength reduction technique. Charts providing the stability factor for fissured slopes subject to both horizontal and vertical accelerations for any combination of c, ϕ and slope inclination are provided. The effect of the direction of the vertical acceleration on slope stability is specifically analysed. Yield seismic coefficients are also provided. When the presence of cracks within the slope can be ascertained with reasonable confidence, maps showing the zones within the slope where they have no destabilising effect are provided. Finally, Newmark's method was employed to assess the effect of cracks on earthquake induced displacements. To this end, displacement coefficients are provided in chart form as a function of the slope characteristics. Two examples of slopes subjected to known earthquakes are illustrated

Investigation of rock fragmentation during rockfalls and rock avalanches via 3-D discrete element analyses

This paper investigates the characteristics of dynamic rock fragmentation and its influence on the postfailure fragment trajectory. A series of numerical simulations by discrete element method (DEM) were performed for a simple rock block and slope geometry, where a particle agglomerate of prismatic shape is released along a sliding plane and subsequently collides onto a flat horizontal plane at a sharp kink point. The rock block is modeled as an assembly of bonded spherical particles with fragmentation arising from bond breakages. Bond strength and stiffness were calibrated against available experimental data. We analyzed how dynamic fragmentation occurs at impact, together with the generated fragment size distributions and consequently their runout for different slope topographies. It emerges that after impact, the vertical momentum of the granular system decreases sharply to nil, while the horizontal momentum increases suddenly and then decreases. The sudden boost of horizontal momentum can effectively facilitate the transport of fragments along the bottom floor. The rock fragmentation intensity is associated with the input energy and increases quickly with the slope angle. Gentle slopes normally lead to long spreading distance and large fragments, while steep slopes lead to high momentum boosts and impact forces, with efficient rock fragmentation and fine deposits. The fragment size decreases, while the fracture stress and fragment number both increase with the impact loading strain rate, supporting the experimental observations. The fragment size distributions can be well fitted by the Weibull's distribution function.Wile

DEM of triaxial tests on crushable cemented sand

Using the discrete element method, triaxial simulations of cemented sand consisting of crushable particles are presented. The triaxial model used features a flexible membrane, allowing realistic deformation to occur, and cementation is modelled using inter-particle bonds. The effects of particle crushing are explored, as is the influence of cementation on the behaviour of the soil. An insight to the effects that cementation has on the degree of crushing is presented