Dr Klaus Thoeni

© 2018 Australian Geomechanics Society. Recent advances in photogrammetry and computer vision have seen a growing interest in 3D image-based modelling. Semi-automatic workflows for processing large image sets are now available as commercial and open-source solutions, and coupled with low cost photo-imaging sensors, a new era of slope visualisation opportunities has begun. This paper investigates the application of low-cost image sensors, including a smartphone, two off-the-shelf compact digital cameras and a Raspberry Pi camera module, and low-cost aerial platforms, including one quadcopter with an action camera and another quadcopter with a built-in camera, to geotechnical problems. The study showed that reliable rock surface models can be created from images acquired by any of the different sensors tested, with the photogrammetric models able to match a laser scanner model to within 5 to 11 mm for the majority of areas on the slope. Reliability decreased for areas that were in heavy shade at the time of image acquisition, with errors of as much as 28 mm in extreme cases, although these were unusual. Models derived from terrestrial and aerially-mounted sensors performed similarly well, except for images acquired by a low-cost UAV for which the only positional control was an on-board GPS, which could only achieve an accuracy of 80-150 mm for the majority of points. Dips inferred from features in the virtual model were generally accurate to within 1 to 2 degrees. The variation in the dip direction is bigger, and in some cases even more than 12 degrees. Several of the steeper virtual measurements also have reversed dip directions. The reversed virtual dip measurements were a numerical anomaly, associated with the interpretation of very steep dip angle values from the model.

© 2016 Informa UK Limited, trading as Taylor & Francis Group. This paper presents a new methodology for estimating the expected energies and first impact distances at the base of a rock cliff, subject to the geometry and properties of the cliff and the representative block being known. The method is based on a sensitivity analysis, conducted by means of kinematic simulations and carried out for a large range of input parameters and their combinations, taking into account the uncertainty associated with their estimate. The proposed approach is validated by comparing predictions to experimental data and shows great potential for a quick qualitative hazard assessment.

This paper investigates the factors affecting the shear strength of granular materials by means of the tilt box test. The test involves the titling of a specifically designed split-box and measuring the angle at which the upper half of the box slides off. This angle can be interpreted as the peak friction angle of the sample for a low stress state. Experimental tests and numerical analyses using the Discrete Element Method (DEM) are carried out and compared. The study is carried out for two different materials, a rounded and an angular aggregate. It is shown that rolling resistance is needed to match the experimental results if only spheres are used but this is not the case for non-spherical particles. © 2015 Taylor & Francis Group, London.

This work consists of a preliminary numerical study on the impact behaviour of rock blocks on muckpiles using the Discrete Element Method (DEM). A contact law using a linear hysteresis model for normal contacts and a Mohr-Coulomb model for tangential contacts is used. In addition, two dissipative laws are introduced consisting of a moment transfer law and normal viscous damping law. One of the aims of this study is to investigate if the contact law enables a realistic modelling of the rebound characteristics of a block during impact on a muckpile. A parametric study is carried out in order to investigate the influence of the constitutive model parameters and the presence of clumps. Numerical predictions are compared to experimental results. It is shown that clumps in the muckpile are essential to reproduce realistic results. © 2015 Taylor & Francis Group, London.

This paper presents a discrete modelling approach which allows the simulation of rockfalls behind drapery systems. The falling rock is represented by a rigid assembly of spheres whereas the slope is represented by triangular elements. Energy dissipation during impact on the slope is considered via friction and viscous damping. The drapery is represented by a set of spherical particles which interact remotely. The numerical model is used to investigate the efficiency of a drapery system. Various simulations with two different block sizes are performed and the numerical predictions of simulations with drapery are compared to simulations without drapery in order to assess the performance of the protection system.