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By N. D. Cristescu

The aim of the present paper is to show how a mathematical modeling of a creeping rock and that of an yieldable lining can allow us to obtain an optimization of the lining design and generally of the whole procedure and sequence of excavation-lining application. We follow the procedure presented by Cristescu (1989) Chap. 13, and Cristescu et al.(1987); for some other approaches see the literature mentioned, for instance, by Ladanyi and Gill (1988). We have in mind to describe the creep of the rock, i.e. the tendency of the tunnel to close in time, and to take into account that the lining itself may be deforming, i.e. possesses some rheological behavior. We start from the well known fact that "intelligent" lining, which are yielding to the pressure of the rock, may be much more successful in supporting creeping rocks than excessively strong, badly designed supports which are unable to resist to pressure of the rock, though these are oversized supports (too strong, too stiff, installed too early, etc.). In order to optimize the lining to be used for a certain rock, it is absolutely necessary to study in the laboratory the main mechanical properties of that specific rock and to formulate for it a reasonably simple mathematical model. Standard triaxial test results are quite enough to determine the model for the rock, combined with some creep tests which have to reveal the long-term behavior of rock (the so-called rheological model). What concerns the lining, we consider several kinds of linings existing today, for which a mathematical model was also formulated. One shows which is the interaction between the creeping rock? and the yielding lining and how can it be formulated in mathematical terms. Once written in mathematical terms, an optimization of the lining design and that of the excavation layout and support application sequence is possible. We will try to make the exposure as simple as possible, avoiding details and having in mind to give only a sketch of the problem, while the mathematical details could be worked out quite easy.

Jan 1, 1994

By Emad Farouz

The resistance of very dense glacial outwash formations consisting of sand, gravel and cobble formations can be quite high, and techniques for measuring the strength and deformation properties often cause engineers to underestimate the strength of these layers in drilled shaft design. More realistic measurements of this dense formation can be achieved with slotted steel casing pressuremeter tests. To minimize disturbance and achieve accurate measurements, drilling a pilot hole prior to probe insertion is necessary. Characterizing geologic formations that contain significant amounts of gravel and cobbles is challenging because of scale factor. Inserting a standard pressuremeter probe into this formation without damaging the membrane is difficult. This paper presents a case study for the IR-75 project in Dayton, Ohio, USA, where these dense materials were characterized using a slotted casing pressuremeter, optimizing design by providing more realistic properties of these materials.

Jan 1, 2006

By D. Marsh

The feasibility study for the Grasberg Block Cave mine, finalized in May 2008, indicated a production capacity of 160,000 tonnes per day. A rail haulage system was an integral part of the mine design. This paper describes the simulation process used in optimizing the design and discusses the key factors and variables that impact the capacity of the system. The final recommendations for the haulage level layout and associated equipment are also included.

Jan 1, 2010

By Behdeen Oraee, Amirhossein Bangian, Kazem Oraee

"Determination of the optimum design of chain pillars has a significant effect on the economics and safety of longwall operations. Most pillar design formulae are based on empirical methods and supplemented by local experience. They therefore lack versatility of application under different geotechnical conditions.In this paper, in order to illustrate the shortcomings of the above, a typical real coal pillar in Tabas coal mine has first been studied and the conventional formulae have been used to determine the optimum dimensions. The results show that a wide difference exists between the predicted and the real field data. The Oraee-Hosseini formula has then been applied to this mine in order to determine the optimum design. The results from this formula demonstrate a close fit between the theoretical VALUES (and those produced by laboratory tests and in practice. It is further demonstrated that the wide discrepancy between the results obtained from the two formulae is attributed to the dissimilarities between geotechnical conditions of Tabas and the original regions whose data were used to devise the empirical formulae.It is finally concluded that the application of numerical simulation methods and experimental equations together with engineering judgment used by the mining design engineer, will provide the most accurate design characteristics.INTRODUCTIONLongwall is an underground mining method which has a high rate of production capacity and mechanization ability. This mining method, which is appropriately applied for soft rock fiatlying bedded ore bodies, gradually became a widespread mining method amongst European coal mines at the beginning of the 19'h century. It was then applied in some of the U.S. coal mines with the development of self advancing support mechanisms in early 1960's (Oraee, 2001).Underground coal production around the world using Longwall mining method doubled during 1990s. The main reasons for this improvement were: the high level of mechanization, increased 10 safety, adequate design of panels, and well designed ventilation systems (Peng, 2006)."

Jan 1, 2010

By Marian W. Otrebski, Julian A. Korneck

Long distance, overland conveyors require significant capital outlay of which up to 70% may be contributed to the cost of belting. Significant savings may be achieved by identifying possible risk areas and applying modern technology methods to reduce or eliminate risk. Recently, Sasol Coal commissioned an overland belt conveyor system comprising three belt conveyors of 7 km, 5 km and 4.5 km in length. These were designed and constructed taking the above into consideration. Contained in the paper are the belt conveyor system requirements, designing assumptions and methods applied in the designing process as well as ways and means to eliminate or at least reduce risks.

Jan 1, 1998

By Sugie Prawono

Jacked pile is the only piling system in which the load capacity of the pile, at any penetration depth, could be monitored directly during its installation process. Each installed pile could have a graph of jacking load versus depth of penetration. For safety purposes, the maximum applied jacking load during installation of a pile could be assumed as the minimum load capacity of the pile. This load capacity will increase with time since the drop in soil strength due to the installation process will recover later on. In order to determine accurately this jacking load, a research was carried out by comparing the load capacity of a pile at certain depths to the jacking load recorded during the installation process. The load capacity could be calculated using cone resistance, qc, and local friction, fs, from Dutch Cone Penetration Test. A graph could be drawn of the load capacity against the depth. By applying a correction factor, a, to the data of local friction, the calculated graph could be matched to the graph of recorded jacking load. The a factor is found to depend on the soil type, which is in this case, represented by the magnitude of cone resistance. The soil type is divided into 3 categories according to qc values (qc < 500 Kpa; 500 Kpa < qc < 2000 Kpa and qc > 2000 Kpa). Graphs of the a factor versus depth and a sample of calculation are presented in this paper for easy application.

Jan 1, 1999

The central thickened discharge system of tailings disposal takes advantage of the natural beach slope formed by sub-aerially discharged tailings, and the non-segregating properties of thickened tailings, to create a homogeneous conical stack. The need for containing embankments can be largely avoided leading to capital and operating cost savings. Methods for estimating beach slopes and tailings density, essential parameters for the design of such a system, are described. Case histories from three mining operations are used to illustrate the application of the technique, There are also seen to be potential advantages in the areas of water management, seepage, and rehabilitation. Laboratory and in-situ testing enable parameters to be determined.

Jan 1, 1991

By T. M. Barczak, S. C. Tadolini

Reduction in the recovery time required and improvements in safety during a longwall face move have compelled coal mine operators to examine and use pre-driven longwall recovery rooms. The recovery entry is developed at the longwall stop position and supported ahead of time so that the required combinations of standing and internal supports can be installed before the longwall face approaches. A calibrated three-dimensional finite element model, developed in conjunction with an underground test area, provided the critical components and design principals for a comprehensive parametric study. The study indicates that vertical, horizontal, and shear stresses concentrated on the outby abutment pillar corner of the recovery room resulting in deformations in the immediate roof above the primary roof support anchorage level. The results of the numerical model and field site observations indicated that the combination of the internal bolting system and the standing concrete supports are critical for the successful and safe extraction of the longwall equipment. Cable supports installed at and angle over the pillars can help stabilize the disturbed zone above the adjacent fender and outby pillars, however; standing supports are required in most sedimentary roof conditions to increase stability and assure a safe longwall extraction.

By T. M. Barczak, S. C. Tadolini

Reduction in the recovery time required and improvements in safety during a longwall face move have compelled coal mine operators to examine and use pre-driven longwall recovery rooms. The recovery entry is developed at the longwall stop position and supported ahead of time so that the required combinations of standing and internal sup-ports can be installed before the longwall face approaches. A calibrated three-dimensional finite element model, developed in conjunction with an underground test area, provided the critical components and design principals for a comprehensive parametric study. The study indicates that vertical, horizontal, and shear stresses concentrated on the outby abutment pillar corner of the recovery room resulting in deformations in the immediate roof above the primary roof support anchorage level. The results of the numerical model and field site observations indicated that the combination of the internal bolting system and the standing concrete supports are critical for the successful and safe extraction of the longwall equipment. Cable supports installed at and angle over the pillars can help stabilize the disturbed zone above the adjacent fender and outby pillars, however; standing supports are required in most sedimentary roof conditions to increase stability and assure a safe longwall extraction.

Jan 1, 2004

By X. Y. Hou

The design practice of several circular underground projects with large diameter is summarized. By taking the advantages of load-bearing of circular structure, a rational annular tensile bar support system and a new design method are proposed. Calculation for a car park shows that remarkable results are brought in by this design technique.

Jan 1, 2010

Provide longwall operators with practical information and guidelines concerning mine design to reduce problems associated with the interaction of adjacent workings in multiple-scam longwall mines. Background The high productivity achieved by longwall mining demonstrates its potential to provide a substantial segment of underground coal production. Longwall mines produce more than 30 pct of underground coal, up from pct just 15 years ago. However, the continued growth of this mining method without appropriate multiple-seam planning may increase the cost and risk of mining. Research by the U.S. Bureau of Mines (USBM) indicates that 25 longwall mines (32 pct of the total number in the United States) have mining in adjacent coalbeds either above or below. About half of these longwall mines report some type of interaction problem with the adjacent workings, such as caving due to subsidence. Optimization of mine design factors is the best means for controlling interactions between operations in adjacent scams. To avoid higher mining costs, operators should focus on adopting practices and procedures that prevent and control interactions in multiple scams. The USBM, in an effort to improve longwall mine planning, has been investigating multiple-seam longwall design and development.

Jan 1, 1994

By N. Mphathiwa

When slope angles are designed during open pit optimization, there is a risk factor applied in steepening the slopes. The steepening of slope angles has implications for the safety and economics of the mining operation. The steeper the slope angles, the greater the probability of slope failure. Although a slope failure will result in added costs, the challenge is to compile an accurate cost-benefit exercise optimizing the economic benefits of the project without exposing mine workers and equipment to unacceptable risk of rockfalls. A balance between the safety of the operation and the economics of the investment is therefore required. The ideal situation is to have a slope monitoring system that will predict slope failure by detecting any ground movement before the actual failure occurs. This early warning will allow the risk factor to be applied with a high degree of confidence, knowing that the risk will be adequately mitigated. The objective of this paper is to provide guidelines on how to design an optimal survey slope monitoring system. It is the authors? view that for a survey monitoring system to yield desirable results, it should adhere to survey principles such as working from the whole to part and consistently cross-checking. The case study used is Jwaneng Mine, and the design strategy outlined can be used as a guideline for developing a new slope monitoring system or to optimize an existing one.

Jan 1, 2014

By Werner Burger

The last decade has witnessed a rapid development and application of slurry and EPB type tunnel boring machines. Both soft ground types are able to excavate tunnels in unstable ground conditions below the water table with positive face support. The most significant component of the excavation process is the cutterhead and tool con-figuration were the excavation and face support meets the geological challenge. The TBM downstream processes cannot take place unless the cutterhead and tools effectively do their job. This paper will review the current state of the art design for both slurry and EPB cutterheads and highlight both common as well as geological specific design features.

Jan 1, 2007

By Ian S. Ross

The emphasis in this paper is focussed on dry bulk car go or the same cargo converted to slurry form for ease of handling. It is this type of cargo which is of primary interest to the mining industry whose products it represents to a large extent. The design problems associated with the handling of liquid bulk and of unitized cargo are sufficiently different to be treated separately. This paper then will consider the port handling facilities of dry bulk commodities as part of a system consisting of (1) the movement of products to the port area, (2) the movement of products out of the port area and (3) the handling of products within the port area itself. Expanding within these three components of the total transportation system, the paper will discuss the various difficulties encountered concerning the mode of transport into the port area and the method of handling product from transport to stockpile. Secondly, and before discussing the port area itself and in order to complete the conditions under which the port must operate, the movement of products out of the port area will be covered dealing with such items as the accommodation of the ship, problem associated with the very large ships, optimum berthing arrangements and the need to consider the various costs associated with the vessel. Finally the paper will review within the port or interface area such items as stockpiles, method of recovery, inventory control and an outline of the common design difficulties encountered. In all cases the relative influence on the total transportation costs of each of these dry bulk transportation system components will be considered.

Jan 1, 1972

By Birger Schmidt

The design of underground nuclear waste disposal facilities poses new problems related to the requirement of long term safety against radionuclide migration. The degree and effects of rock disturbance caused by construction and by the long term thermal effects from the hot waste must be predicted with confidence. Computer modeling can, to an extent, be verified by accelerated near-surface tests. Credible extrapolation to deep, long-term conditions requires successful near-surface modeling verification, proper characterization of near-surface and deep rocks, and successful determination of in-situ stresses. Excavation induced disturbance may be assessed primarily by empirical evidence.

Jan 1, 1981

By P Andersson, P Marklund

Evaluation of different techniques for bottom fill stabilisation showed that frozen fill was the most economical method. In order to test the method a full-scale field test was performed in the Rehnstr÷m mine. The test was instrumented with temperature gauges and extensometers. Before the field test, frozen fill was tested at the laboratory. The mechanical properties of the frozen fill were determined by uniaxial compression and creep tests. A deformation model for the frozen fill was set up. Calculation procedure for design of spacing between the freezing tubes, time for freezing and calculation of the necessary capacity of the refrigeration plant was developed. These procedures were calibrated against the field test. The results of these investigations allow the following conclusions: From a mechanical point of view, frozen fill has excellent properties as a structural member and it also has excellent properties to support itself and the fill above. Methods for the thermal and mechanical design of freeze stabilisation have been developed and found adequate. The need to place the freezing tubes several years in advance of the future sill pillar mining, requires careful long-term planning and accurate documentation.

Jan 1, 1998

By Richard A. Allwes

A procedure is presented for the design of an arch canopy for the application of rehabilitating a high-roof-fall area. This procedure is specifically developed for evaluating an unbackfllled arch canopy, which Is subjected to an impact load (roof fall). Dynamic line loading of the arch canopy at its crown is only considered and the procedure does not account for an unsymmetrical loading condition. The evaluation of whether an arch canopy is suitable for a particular installation is dependent upon many variables, including in-nine conditions and the engineering properties of the structure. However, a general evaluation can be based upon a comparison of the arch&apos;s maximum crown deflection and a prescribed allowable crown deflection. A single spring-mass system is used as an idealized model to represent the dynamic behavior of the arch canopy at its crown. An energy approach is taken to determine the maximum crown deflection of an arch rather than solving a differential equation of notion derived from dynamic equilibrium. The design procedure is based on the concept that when an arch canopy is subjected to impact loading at its crown and deflects from its unloaded state to maximum crown deflection, the structure absorbs strain energy, both elastic and plastic. As a result, this strain energy can be calculated from a static load-displacement diagram for the structure. The significance of this design procedure Is that It gives mine personnel an analytical tool to select an arch canopy to meet the dimensional and functional requirements of a mine entry and a prescribed allowable crown deflection.

Jan 1, 1986

A wide range of materials are used in hydraulic backfilling operations and the pipeline flow behaviour of these mixtures varies considerably. It is shown that despite the large differences in constituent materials and flow behaviour, a common approach can be applied to analysing the flow of all hydraulic backfills. This is extended to include a rational design approach for backfill distribution systems. The use and limitations of pipe loop tests as a design aid is discussed. Backfill quality control is identified as a key area where improvement needs to be made to enhance the reliability of backfill system operation.

Jan 1, 2001

Provide mine personnel with a convenient means of determining the optimum installation geometry of roof trusses in bedded roof. Background Mine operators frequently ask the following questions concerning roof truss installations: 1. Where should the bearing plates or brackets be placed or where should the inclined holes be started? 2. At what angle should the holes for the inclined chords or angle holts be drilled? 3. What tension should be put into the inclined chords so as to achieve the most effective results for the effort and expense? Truss hardware manufacturers have responded to these questions with answers based on what seems to work best. While designs based on past experience are frequently reliable, there was a need for a rational approach that could accommodate a variety of conditions. The Bureau has developed a procedure that enables mine operators to optimize roof truss installations in bedded roof.

Jan 1, 1989

By D. G. Mirakovski, B. Krstev

The paper presents models of auxiliary ventilation systems with leaky ducts and algorithms for calculations of pressure loss, air leakage, and volume flow ratio and pressure fans. Two basic models are discussed: 1st model for a duct with leakage through the flange joints; 2nd model for a duct with an equivalent longitudinal aperture. The present analytical system has been successfully applied to developing of computer software named DAVentS. A. sample problem is used to illustrate efficiency and accuracy of DAVents software in solving most common problems in process of designing AVS.

Jan 1, 2002