The execution of grouting, associated with drainage, is very important for the control of seepage through concrete dam foundations. Most of the uplift pressure criteria used nowadays for dam design are based on methods, which are both deterministic and empirical, originated from accumulated experience under certain specific geological and geometrical conditions. When such criteria are used for a specific site, peculiar geological features may not be reflected on the data basis used as previous experience. In this work, grouting and drainage systems efficacy are evaluated in a probabilistic way, using statistical methods to analyze data obtained during grouting execution, which provide good assessment for the variability of foundation properties. A probabilistic analysis methodology is proposed, based on Monte Carlo Simulation principles, randomly generating hydraulic conductivity scenarios according to statistical distributions obtained from Lugeon tests carried out during site investigation. By means of finite element numerical simulations, adopting foundation permeability coefficients following those statistical distributions, it is possible to obtain a statistical distribution for uplift forces. Reliability analyses can be performed, and the probability of occurrence of any particular uplift force value can be assessed, such as values leading to failure, values predicted by any empirical criterion or even instrumentation readings.
Sergio A. B. da Fontoura, Carla Carrapatoso, Carlos Emmanuel R. Lautenschaler, Guilherme Righetto, Nelson Inoue
405 - 416
The petroleum industry has shown great interest in the study of drilling optimization on pre-salt formations given the low rates of penetration observed so far. Rate of penetration is key to economically drill the Brazilian pre-salt carbonate rock. This work presents the results of numerical modeling through finite element method and discrete element method for single cutter drilling in carbonate rocks. The work is relevant to understand the mechanics of drill bit – rock interaction while drilling deep wells and the results were validated with experimental data obtained under simulated downhole conditions. The numerical models were carried out under different geometrical configurations, varying the cutter chamfer size and back-rake angles. The forces generated on the cutter are translated into mechanical specific energy as this parameter is often used to measure drilling efficiency. Results indicate that the chamfer size does not change significantly the mechanical specific energy values, although the cutter aggressiveness is influenced by this geometrical characteristic. Results also show there is a significant increase in drilling resistance for larger values of back-rake angle.
Inmaculada Mining Project, located in the south of the Peruvian Andes (4500 metres above sea level), in the department of Ayacucho, mainly operates its Angela Vein which has silver and gold mineralisation. The vein dips 60° towards the southeast, and measures 2 kilometres long, has a height of 200 to 400 metres and a thickness ranging from 2 to 15 metres.
Geomechanical evaluation is one of the most important aspects in mining for the operation of an ore deposit. The main objective is to ensure the overall stability of the mine in a productive and safe way throughout the mining cycle.
The aim of this study is to select the optimum mining method according to the geomechanical and geometrical vein conditions. As well as to determine the size of the openings or stopes through empirical methods and confirm them by numerical methods, ensuring the stability of the ore and the surrounding rock mass, in order to obtain low dilution.
The conventional fill compaction procedure usually controls the dry density ρd and the water content w referring to the maximum dry density (ρd)max and the optimum water content wopt determined by laboratory compaction tests performed at a certain compaction energy level (CEL). However, (ρd)max increases and wopt decreases with CEL, while, since Proctor (1933), CEL practically available in the field has been increasing and the required ρd value has generally been becoming higher for more satisfactory performance of soil structures. Besides, the values of (ρd)max and wopt change with soil type. In a single earthwork project, the actual CEL and soil type may vary and it is very difficult to accurately estimate the field CEL and identify the actual soil type at a given moment at a given place. Therefore, the actual values of (ρd)max and wopt are usually unknown. On the other hand, the optimum degree of saturation (Sr)opt defined as Sr when (ρd)max is obtained for a given CEL and the ρd/(ρd)max vs. Sr−(Sr)opt relation are rather independent of CEL and soil type. The unsoaked and soaked strength and stiffness and the saturated hydraulic conductivity are a function of ρd and compacted Sr not including CEL as a variable. It is proposed to control Sr of compacted soil to be close to (Sr)opt and ρd to be large enough to achieve the physical properties required in design, together with pre-compaction control of water content.