Intelligent construction using irregular, untooled rock

Field: Engineering (Physical Sciences)

Current methods in the construction industry leave much to be desired in terms of efficient material use and a result of this is high consumption of resources with high greenhouse gas emissions. Traditional methods tend to involve the use of concrete or steel. The increased awareness of the limited amount of resources has sparked a desire to move away from these materials. It is suggested that earthen materials are a suitable replacement as they have low energy requirements and are available globally. Furthermore, waste materials such as construction demolition waste or mining rock that would otherwise go unused is suitable for geotechnical structures such as drystone retaining walls or embankments. With the increased computational power available there lies potential for improving techniques of construction using a high intelligence, low resource method. Autonomous construction performed by robot is an area gaining interest that utilises such capabilities. Previous work sees construction of drystone walls made from large boulders and construction demolition waste. However, placement of the material is based on suitability for fitting a designed shape and stability of the particle. Improvements can be found by determining position to optimise the shear strength of the structure. The purpose of this thesis is to produce a packing technique that selects placement on criteria derived from the shear strength of soil structures. Parameters are derived from literature and based on commonly seen features in these systems. Low void ratio, high contact area of a particle with other particles and coordination number are all selected for the basis of an objective function to score placement. Additionally, the centroid of the particle is considered as it is shown to be a sign of stability when particles are located further down in a system indicating less potential energy. The packing algorithm is designed to pack all particle shapes that can be defined by a closed-loop coordinate system in clockwise order for both convex and concave shapes. Two scenarios are tested to ensure this is the case, one based on the packing of irregular, untooled rock particles to replicate the autonomous construction method. This is based in two-dimensions to keep the problem simplied and to reduce computational times. The other replicates the Tetris videogame. Tetris is seen as a scenario where a clear objective to minimise void ratio is present for simplified, orthogonal shapes. As a result, it is adopted as a verification that the algorithm works as intended. Results for particle placement in the Tetris scenario using an objective function based on the features of high shear strength soil structures is shown to be an efficient method of packing. Minimal gaps between particles are observed and when compared to the deepest-bottom-left method for bin packing it was found to outperform this heuristic. As such, it is suggested that this could be adapted to be a novel approach for the bin packing optimisation problem with the further comparison to other bin packing solutions. The packing of rock particles is also achieved and it is shown that structures can be produced by the algorithm. Void ratio is thought to be a good indication of mechanical strength for systems of soil however it should not be taken as an individual measure for this. Therefore the number of disrupted running joints was adopted as an indication of shear strength of the structure. However, packing in the soil particle scenario found that there is no correlation between disruption of running joints and void ratio of the packing and therefore it was difficult to conclude on the efficiency of the algorithm in terms of optimising shear strength. Results of the algorithm using rock particles presents well packed structures in a domain. From this visual inspection it is determined that the algorithm could be adopted as a novel approach for specimen generation for fields such as DEM modelling. Verification of strength through rotating drum to measure angle of repose is suggested with structures of high shear strength exhibiting higher angles of repose.