Browsing by Author "Rinne, Mikael, Associate Prof., Aalto University, Department of Civil and Environmental Engineering, Finland"
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- Excavation damage zones, fracture mechanics simulation and in situ strength of migmatitic gneiss and pegmatitic granite at the nuclear waste disposal site in Olkiluoto, Western Finland
School of Engineering | Doctoral dissertation (article-based)(2015) Siren, TopiasIn Finland and Sweden, the geological nuclear waste disposal is heading for the implementation phase in the next ten years or so. In the disposal concept, the knowledge of the in situ stress state, the excavation damage zone (EDZ), rock mass strength, hydraulic conductivity and other rock mass properties are important for long-term safety. In this dissertation, the EDZ, rock strength and rock failure mechanisms have been researched in Posiva's ONKALO underground characterization facility, located in Olkiluoto, Western Finland. The experiments included a prediction–outcome (P–O) component in order to test the current predictive capability. Fracture mechanics modelling in anisotropic rock has been developed and tested, in relation to the in situ experiments. The ground penetrating radar measurements and observations both in ONKALO and the Äspö hard rock laboratory (HRL) indicate that excavation induced damage can be distinguished into a construction-induced excavation damage zone (EDZCI) caused by blasting or by mechanical excavation and into a stress-induced excavation damage zone (EDZSI) as a result of the evolution of the secondary stress state. The EDZCI is evident around the full tunnel perimeter, whereas the effects of the EDZSI are typically noticeable in areas where stress peaks or tensile conditions exist. Previous experience and research of rock strength in ONKALO and executing the POSE in situ experiment revealed that rock mass failure in Olkiluoto is governed by fracture growth at lithological borders. A two-fold failure criterion is proposed in this dissertation based on the onset of rock mass damage strength at 40 MPa and the rock mass strength 90 MPa. By comparing the experiment prediction and outcomes, the fracture mechanics prediction can capture the fracture growth realistically in the anisotropic rock mass, although the in situ experiments revealed a behaviour that was unpredictable. Based on the POSE experiment the structurally controlled failure is distinguished as a new rock mass failure mechanism. In this dissertation the applicability of the horizontal and vertical disposal concepts were evaluated for nuclear waste disposal. Based on the in situ experiments and modelling, the vertical disposal concept is not particularly sensitive if the trend of the tunnel is within 30° of the direction of the major principal stress. In the thermal period, the vertical disposal concept may suffer from the initiation of new fractures sometime after excavation, but neither of the disposal concepts is expected to be affected by any significant rock mass failure. Based on the dissertation, rock damage in Olkiluoto is modest and the site is well-suited for nuclear waste disposal from a rock mechanics perspective. - A new method to improve operating performance for underground hard rock mining - with new scheduling, controlling and forecasting techniques
School of Engineering | Doctoral dissertation (article-based)(2015) Song, ZhenIn underground mining, there are missing links among mine planning, mining machines and mineral processing. They have significantly affected the overall performance of the entire mining process. There have been quite few studies aiming to improve the mining process of underground mines. In underground mines, mobile mining equipment is mostly scheduled instinctively, without theoretical support for these decisions. Furthermore, in case of unexpected events, it is hard for miners to rapidly find solutions to reschedule and to adapt the changes. Furthermore, the underground mining process is constrained by the geometry and geology of the mine. The various mining operations are normally performed in series at each working face. The delay of a single operation will delay the starting time for the next process and the completion time of the entire process. Moreover, safety stock of mining production is kept to prevent stock-out, due to the existence of high uncertainty in mining operations and various unforeseen geological conditions. Any shortage of ore supply from its mine would cause the insufficient utilization of the mill and financial loss. Mining production has its own features, which require a tailor-made strategy of safety stock. This dissertation has reviewed a wide range of the optimization techniques used in mine planning and scheduling, as well as analyzed other techniques which are used to solve the problems jointly. A technical package of decision support instrument is proposed and described to address the above issues. The software structure, input/output, and related algorithms of scheduling are presented. It also presents a new approach to the process control for underground mining. Additionally, a real options technique was developed to determine the safety stock of mining production. The proposed methods were tested by using real data of the Kittilä mine located in Finland. The result suggests that the proposed methods can improve the working efficiency and reduce the working time of the underground mining. It shows the critical operations can be detected and the completion time can be estimated more accurately. It also shows that the real options approach can provide miners with a more accurate and reasonable result, and also give a useful indicator for a mine's future production planning.