An underground mining project is the process of creating technical solutions for issues such as the location, size and shape of excavations and rock supports, and the sequence and application of support systems. In open pit mining, the optimum slope angle for each pit level should be selected along with other design aspects and slope reinforcement. Development design is a dynamic process that is modified and improved, as more information appears during the work as a result of observation and control. Empirical, observational and analytical design methods are commonly used.
Empirical methods often use a rock mass classification system (several such schemes have been developed, such as the Rock Mass System and the Rock Tunnel Quality Index), and are complemented according to project recommendations based on knowledge of accepted practice. Several empirical design methods such as Stability Graph Method have been successfully applied to open slope development.
Observational methods are based on the actual control of ground movement during excavation to detect measurable instability and on the analysis of the solid rock and support interactions. Examples of this approach include the new Austrian tunneling method and the convergence restriction method.
Analytical methods use stress and strain analysis around mining sites. Some of the earliest stress calculation methods used closed form mathematical solutions or elastic photographic models, but their application was limited due to the complex three-dimensional shape of most underground excavations. A number of machine numerical methods have recently been developed. These methods provide a means to obtain approximate solutions to stress, displacement and collapse problems in the surrounding solid rock.
Recent enhancements have included the introduction of 3D models, the ability to model structural blotches, rock-support interactions, and the availability of user-friendly graphical interface surfaces. Despite their limitations, numerical models can provide real-world insight into complex rock behavior.
The three methodologies described above should be considered essential parts of an integrated underground design approach rather than independent methods. The engineer developing them must be prepared to use a wide range of tools and re-evaluate the project strategy when required based on the amount and quality of information available.
The main purpose of solid rock support is to help the rock support itself. When the rock is strengthened, rock anchors are installed inside it. With solid rock support such as that provided by steel or wood sets, external support is provided for the rock mass. Support methods have not found widespread use in surface mining, partly due to the uncertainty of the final excavation geometry, and partly due to the susceptibility of the respective structures to corrosion. A wide variety of rock anchor systems are available worldwide. Factors that determine the choice of a particular solid rock support system include its conditions, planned excavation lifetime, ease of installation, availability, and cost. There are solid rocks for sale.
The mechanically anchored rock anchor consists of an expansion shell (there are various designs to suit different types of rocks), the actual steel anchor (threaded or forged head) and a face cup. The expansion casing usually consists of toothed ductile iron plates with a tapered wedge threaded into one end of the anchor. As the anchor rotates within the hole, the cone slides into the plates and presses them against the borehole walls. The expansion casing increases grip on the rock as the stress on the anchor increases. Anchors are available in various lengths, along with a range of accessories. Mechanically anchored rock anchors are relatively inexpensive and are therefore most widely used for short-term support in underground mines.
The friction stabilizer usually consists of a steel pipe cut along its entire length, which, when driven into a slightly smaller borehole, contracts and develops friction between the steel pipe and the rock. It is necessary to control the borehole diameter within tight tolerances for this anchor to be effective.
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