Metal grade dilution is the main production disadvantage of the sublevel caving method, and overcoming this problem has been investigated over the years using different methodologies. Herein, numerical simulation using the discrete element method is used to analyze the influence of friction and fragmentation change in caved rock mass on ore dilution and recovery. The individual and mutual change of each parameter is analyzed. It is considered that at the beginning, the friction angle can be lower or higher than the basic friction angle, and after a certain moment, it will come close to the basic friction value, while fragmentation always decreases. The results showed that both friction and fragmentation, when decreasing, are influencing the higher dilution due to smaller kinematic resistance in the caved mass. If lower friction than the basic one is considered, with the drop of fragmentation, the decrease of dilution occurs. Once the basic friction angle is reached, the fragmentation of the caved mass becomes the dominant influencing factor, and its decrease will continuously increase the dilution until the end of production. However, identifying periods when these changes occur, the possibility for better production planning opens at the design stage, as well as the application of different sublevel designs.

A common technique in hard rock tunneling, and underground excavation in general, is drilling and blasting. This method of excavation assumes that damage will be done to the surrounding rock mass depending on its quality. Herein is a proposal for how to estimate blast-damaged zone extent and shape, and how to quantify rock mass properties in this zone. Comparison was made, using FEM, between models with and without blast-damaged zone consideration through analyzing its impact on the support load. Results showed greater support loads in the case of blast-damaged zone modeling. Also, comparison was made between the proposed method for blastdamaged zone quantification and quantification using blast damage factor D. Results showed that in both cases, the support loads are in same magnitude order. In other words, compared to the blast damage factor D method, the proposed is more objective and makes it possible to describe the blasting process before it is actually done.

Optimizing blast fragmentation and reducing the damage from it are two important research subjects in this field. Detonation and explosive charge induces three sets of tension cracks in the monolith rock. Radial tension cracks are formed under the influence of the pressure wave whose cylindrical propagation induces tension. Along with the explanation of how radial cracks are formed, formulation is given as to how their length can be calculated using laboratory and drill and blast parameters. Cracks subparallel with the free surface (face) are related with amounts of absorbed and recoverable strain energies. The distance between subsequent cracks can be calculated using the results of simple load-unload laboratory tests. Third sets of tension cracks are formed as a result of excessive deformation of the beam or cantilever formed by radial cracks. Once the length of the cracks and the distance between them are known, it is possible to apply these results for estimation of fragment sizes and blasting pattern design.

Important parameters that describe successful sublevel stoping operation are optimal fragmentation and low damage of rock mass around stopes. In current state of operation fragmentation of blasted material is not optimal since high percentage of fragments are oversized which requires additional sizing. Also, excessive damage of surrounding rock mass is found. By proposing new blasting pattern with slightly increased amount of drilling, but with decreased hole diameter decrease of explosive usage is obtained for more than 100kg. Along with better charge distribution it is expected that rock mass damage is to be decreased as well.

The main aim of a coal deposit model is to provide an effective basis for mine production planning. The most applied approach is related to block modeling as a reasonable global representation of the coal deposit. By selection of adequate block size, deposits can be well represented. A block has a location in XYZ space and is characterized by adequate attributes obtained from drill holes data. From a technological point of view, i.e., a thermal power plant’s requirements, heating value, sulfur and ash content are the most important attributes of coal. Distribution of attributes’ values within a coal deposit can vary significantly over space and within each block as well. To decrease the uncertainty of attributes’ values within blocks the concept of fuzzy triangular numbers is applied. Production planning in such an environment is a very hard task, especially in the presence of requirements. Such requirements are considered as target values while the values of block attributes are the actual values. To make production planning easier we have developed a coal deposit model based on clustering the relative closeness of actual values to the target values. The relative closeness is obtained by the TOPSIS method while technological clusters are formed by fuzzy C-mean clustering. Coal deposits are thus represented by multi-attribute technological mining cuts.

Analysis of rock wedge stability plays important role in tunneling and hard rock mining. Today there are many procedures for prediction of wedge formation and their stability. These procedures consider preexisting joints in rock mass, and there is no procedure that considers blast-induced cracks and their impact on structural stability of excavations. Using main principles of new rock blasting theory it is possible to assess length and density of radial cracks around blastholes. Herein, one simple excavation situation in hard rock is presented, where only two joint sets were present. This made it impossible for rock wedges to form. After blast-induced crack with limited persistence was added to analysis as result unstable rock wedge was formed. in addition to presented problem it is suggested how mechanical properties of blast-induced cracks could be estimated using Barton-Bandis failure criterion. As final result it was clear that without blast- induced cracks no wedge stability analysis is complete