Managing rock slopes adjacent to highway infrastructure involves consideration of possible rock slope instability and making decisions about how to manage potential mitigation efforts for rockfall. The selected method often involves the removal of loose blocks by slope scaling, re-establishing the catchment area, and/or the construction of a variety of types of rockfall barrier structures to retain the debris. When designing a slope scaling program, a rockfall catchment area or a rockfall barrier structure, the potential trajectories of the rocks released from the slope must be considered. In order to make appropriate preparations for rock slope scaling, such as protecting the highway surface, existing rockfall barrier structures, and adjacent waterways, rockfall fragments must also be considered. Sometimes temporary barricades will be erected to retain the rock fragments generated by slope scaling in a controlled manner. Generally, the potential path and distribution of falling rocks is modelled using a rockfall simulation model. Given the variability and uncertainty in modelling rockfall physics, reasonable ranges of input parameters are inputted into the simulation in order to assess the potential hazard. The results are used to evaluate the trajectory, bounce height, energy and runout distance of potential rockfall events, in a probabilistic sense. Most of the models available are based on the physics of a single block, moving as a solid non-fragmenting lumped mass, by bouncing, rolling and sliding along a 2D section cut through the 3D model of the slope surface. The implementation of a 3D slope surface and a realistically shaped block is available in only a very few models. Experience with rockfall simulation indicates that the use of readily available, easy to use rockfall models, which utilize a single circular block on a 2D surface, tend to significantly overestimate the length of travel path taken by real falling blocks of rock. This in turn leads to more expensive and extensive protection being used, than is required, during rock slope maintenance and slope scaling work. No commercially available software package currently simulates rockfall fragmentation, or considers the presence of joints and pre-existing geological structure within the rockmass. In recent years, our ability to model rockfall is being transformed by the adoption of the engines created for the video gaming industry (Harrap et al, 2019). Game engines incorporate sophisticated representation mechanisms for materials, physics engines, databases to store unique and repeating spatial features, methods for procedural generation of entire environments, dialog and interaction AI systems, and physically accurate models for light and sound. The physics engines generally include at least two core components – i) collision detection / collision response, and ii) simulation of dynamics to solve the forces acting on the moving, simulated objects. These are in the form of standardized libraries contained within the engines that support generalized spatio-temporal simulations. In addition, the engines provide easily implemented world building tools that can accept complex geometry. The physical parameters are defined for each game object and, when the game is run, the behaviour of the object under various forces is simulated. In the case of rockfall, this includes fragmentation of the falling blocks and interaction between fragments. Recent work by Ondercin (2016), Sala (2018) and Sala et al (2019) has demonstrated that rockfall models built in game engine environments replicate the observed pathway and fragmentation sizes of rockfall events observed from change detection between time sequential point clouds. The implementation of realistic 3D surfaces, based on data from LiDAR or photogrammetry models, and the potential to model fragmentation and block interaction, creates models that appear much more realistic. By varying the rockfall physics parame

The objectives of the research work are to: 1. Develop a field data collection methodology to observe rockfall events, generated by scaling projects. Develop a detailed database of rockfall events, collected and analyzed from DOT rock slope scaling projects, and utilize this database to define ranges of input parameters needed to simulate rockfalls. 2. Build a user interface with the selected physics engine to permit model self-calibration based on observations, and generate numerous simulations providing probabilistic output data. Define and produce useable metrics such as runout distance for a defined % of the volume, bounce height and energy etc. 3. Determine the basis for decisions related to goodness of fit of simulations, and simulate many known rockfall events to define appropriate ranges of input parameters to generate realistic fragmental rockfall models for different geological settings and slope condition states. 4. Simulate the interaction between falling fragments and the underlying slope, considering geology, geometry and whether the blocks will be impacting outcropping rock, talus, soil, and possibly vegetation, to refine the fragmentation model.

Phase 1 – Development of field data collection techniques / review of existing information to define the behaviour of real rockfall cases, including block fragmentation. Phase 2 – Rock slope and rockfall field data collection from partnering agency locations during slope scaling operations, development of a database to store the information, and development of modeling/simulation tools. Phase 3 – The interpretation and simulation of the field data that has been collected, definition of calibration workflow, and a review of the software functionality. Phase 4 – The development of simulation software, a user’s manual that includes input parameter guidance related to rockfall behaviour and fragmentation and training, and recommendations for future management and maintenance of the software program.

The estimated cost of the overall project is $700,000 and will be led by the Washington State Department of Transportation (WSDOT). The project will commence once we receive enough commitments and/or fund transfers to begin Phase 1 & 2. The project is estimated to be completed in 4 years. The minimum partner commitment is $30,000 per year for four years for planning purposes of the project. However, we will accept one year commitments as well at any dollar amount. Partners may include public sector and international entities.