This paper presents an improved discrete element model, which incorporates stochastically distorted contact mechanics, for the simulation of double-twisted hexagonal wire meshes that are commonly used in rockfall protection. First, the characteristics of such meshes are investigated by conducting quasi-static and dynamic experimental tests. Second, the discrete model for the simulation of such meshes is presented. A stochastically distorted contact model is introduced to account for distortions of the wires and hexagons, allowing a more realistic representation of the mechanical response of the mesh from the deformation point of view and the force point of view. Quasi-static tensile tests of a plane net sheet, subjected to a constant strain rate, are used to study the effect of the stochastically distorted contact formulation and to calibrate the numerical model. Finally, the dynamic response of an impacting block on a horizontal mesh sheet is used to compare the numerical predictions against experimental results in order to validate the proposed approach.

ABSTRACT:This work presents a comparative study between multi-view 3D reconstruction using various digital cameras and a terrestrial laser scanner (TLS). Five different digital cameras were used in order to estimate the limits related to the camera type and to establish the minimum camera requirements to obtain comparable results to the ones of the TLS. The cameras used for this study range from commercial grade to professional grade and included a GoPro Hero 1080 (5 Mp), iPhone 4S (8 Mp), Panasonic Lumix LX5 (9.5 Mp), Panasonic Lumix ZS20 (14.1 Mp) and Canon EOS 7D (18 Mp). The TLS used for this work was a FARO Focus 3D laser scanner with a range accuracy of ±2 mm. The study area is a small rock wall of about 6 m height and 20 m length. The wall is partly smooth with some evident geological features, such as non-persistent joints and sharp edges. Eight control points were placed on the wall and their coordinates were measured by using a total station. These coordinates were then used to georeference all models. A similar number of images was acquired from a distance of between approximately 5 to 10 m, depending on field of view of each camera. The commercial software package PhotoScan was used to process the images, georeference and scale the models, and to generate the dense point clouds. Finally, the open-source package CloudCompare was used to assess the accuracy of the multi-view results. Each point cloud obtained from a specific camera was compared to the point cloud obtained with the TLS. The latter is taken as ground truth. The result is a coloured point cloud for each camera showing the deviation in relation to the TLS data. The main goal of this study is to quantify the quality of the multi-view 3D reconstruction results obtained with various cameras as objectively as possible and to evaluate its applicability to geotechnical problems.

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This paper presents a novel approach for the simulation of rockfalls behind drapery systems which can be used to accurately assess the residual rockfall hazard involved with such systems. A discrete element model of drapery systems installed on rock slopes is presented where all the relevant interactions are taken into account. The approach is based on the classical discrete element method, where the block is represented by a rigid assembly of spheres. The slope is represented by triangular elements and the drapery is represented by spherical particles which interact remotely. The model is calibrated and validated by comparing the numerical predictions with experimental results. It is shown that the model can accurately predict block trajectories and block velocities for rockfall analysis with and without drapery.