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By Noakes MJ, Willsteed TV

In the past few years an elevated gold price has resulted in the evaluation of many small scale surface gold deposits in Australia typically containing about 2-3 g/t Au. Operators have tended to assume that at the lower end of the grade spectrum only heap leaching is economically possible whereas above some assumed "cut-off" grade, carbon-in-pulp or similar techniques can be considered to have economic advantages.Studies made on a number of these prospects has indicated that this rather arbitary choice of treatment method can be mis-leading.A case study has been prepared assuming a "typical" situation and is presented. The deposit contains three million tonnes of ore assaying 3 g/t Au and is amenable to open pit mining methods. The mine site is remote but accessable and existing infrastructure is minimal. There are no unusual environmental constraints.

Jan 1, 1984

By M. K. Larson

The U.S. Bureau of Mines and Cyprus Shoshone Coal Corp. conducted a study of deformation mechanisms around a longwall gate-road system in an underground coal mine. Of particular interest was roof deformation over the headgate entry. The strata above and below the coal seam are very weak, carbonaceous mudstones that have planes of weakness oriented along the bedding. Visual observations of previous gate roads over several years suggested that deformation was time dependent and resulted in creep along joints or crack growth. Instruments were installed at a test site to measure deformation around the entry, strew changes in the pillar, and loads transferred to support systems. Multipoint extensometers, instrumented bolts, instrumented trusses, biaxial stressmeters, borehole pressure cells, and single-point extensometers were installed. Monitoring continued until the longwall face passed the test site by 38.7 m (127 ft). Results show that fracture zones arched over the entry from both ribs, most bolts and trusses were loaded past their yield point, and the largest change in secondary principal stress was almost horizontal in the pillar. Displacement measurements in the roof showed classic primary creep.

Jan 1, 1995

By John C. Stankus

The 3 Right pre-developed longwall recovery entry at Signal Peak Energy?s Bull Mountain No. 1 mine was designed to prevent the abnormal roof conditions encountered in its firsttwo recovery entries. Unique geological conditions, such as the low overburden of approximately 200 feet and prevalence of roof joints in the sandstone overburden, contribute significantly to abnormal conditions during longwall recovery. The 3 Right recovery entry was 42 ft wide and developed in two stages, 21 ft wide in each stage. The entry roof was reinforced with steel wire mesh/non-metallic recovery mesh, high-capacity primary bolts and cables. After all the support was installed, the entry was completely backfilled with specially designed, cuttable, low-density cement. The roof bolting and backfilldesign were based on current practices in this mine and successful practices in other mines in the U.S. and Australia. Extensive instrumentation was installed in the recovery entry for continuous monitoring of load transfer as the face approached and cut into the recovery entries. The support design was completely successful with a smooth cut-through on January 29 and 30, 2014, significantly reducing the shield recovery time and meanwhile protecting the safety of miners. Based on actual observance and practices of the 3 Right recovery entry, recommendations on improvement and modificationsof roof support for 4 Right recovery room are presented.

Jan 1, 2014

By K. Viking

It's well known that conventional impact hammers, usually are the method to use in order to drive precast prestressed concrete piles. However sometimes the vibratory technique might be considered as a suitable alternative due to favourable soil conditions. It is also well known that piles driven into granular soils can be installed more efficiently by the use of a vibratory driver compared with impact hammers. However, the use of the vibratory technique is seldom regarded as the first choice, since the technique is constrained by several uncertainties related to the pile capacity, and concrete piles to cope with tensile stresses. With the opportunities of having suitable subsurface conditions and a fair amount of piles to be installed, it was anticipated that the use of the vibratory method could result in a significant reduction of the installation costs. Part of the uncertainties of using a vibrator was intended to be eliminated by restriking the vibratory driven pile with an impact hammer and use a Pile Driving Analyzer? (PDA) to correlate recordings of soil resistance to driving with measured rate of penetration, and to evaluate the static capacity and load/settlement characteristics of the vibratory driven pile by conducting static load test. The conducted test study of using a vibrator to drive the precast prestressed test pile (14-in. square by 30-ft-long) did not turn out to the author's complete satisfaction. The present paper focuses mainly on a numerous practical engineering issues in relation to the use of the vibro-technique to drive precast prestressed concrete piles in granular soils. The obtained experiences of using a PDA to monitor vibro-driven piles, with its potential and limitations, is presented and discussed. Furthermore, a simple method of how to subjectively pre-estimate the soil resistance due to vibratory driving is presented and discussed. The reasons for the partly unsuccessful test study are discussed in great detail based on the obtained experiences. Suggestions of how to better approach a similar situation in the future are also provided in great detail

Jan 1, 2004

By Dave Forrester

Mining subsidence over shallow abandoned coal mine workings is unfortunately not an uncommon experience in the coalfields of North America and there is a significant knowledge and literature base addressing the phenomenon and related issues. From time to time, however, a case history arises which is outside the more routine occurrence. This paper addresses one such case and presents an overview of a subsidence Event above abandoned coal workings, which badly damaged a two-story High School building. The subsidence at the Cape Breton & Victoria Regional School Board (CBVRSB)'s MacDonald High School in Dominion, N.S., Canada on October 30, 2002 led to a detailed investigation. It was concluded that the ground movement and associated building damage had been caused by mining subsidence in underlying old underground coal mine workings of the 1890s, only 150 ft deep at the School. The Event was not isolated and a similar but smaller event happened nearby a few months later. The paper describes the events and summarizes the subsequent investigations and findings. The 17-year old High School building was eventually demolished.

Jan 1, 2004

By Hung Tran, Qian Liu, Patrick Andrieux, Dave Counter

Blast damage in open stope mining has been an important concern in controlling ore dilution. Severe damage to the surrounding rock mass can result in the caving of waste rock and/or backfill materials, as well as general instability of the ground. The blast damage study conducted at Kidd Mining Division in 1995 was aimed at measuring the damage zone around blastholes and at identifying other factors which influence the damage. An approach and methodology developed mainly by Blastronics, together with Noranda under a project with the Mining Research Directorate, was adopted for this project. The principle was to combine vibration measurement results with borehole camera observations to derive the blast damage criteria at the specific site. The Holmberg-Persson Equation was used for the regression of near-field vibration data. The damage criteria was examined with both borehole camera observation results and rock elastic and mechanical properties. Details of this methodology, including instrumentation, are reviewed in this paper and an implementation case study of the blast damage evaluation is presented.

Jan 1, 1998

By Stephen P. Signer, John L. Lewis

This paper presents the results of a case study conducted in a two-entry gateroad in a coal mine where excessive roof deformation and bolt loading resulted in failure of many roof supports. The instruments consisted of 16 fully grouted, strain-gaged resin bolts, load cells on both full and partially grouted cable bolts, and vertical deflection multipoint extensometers. These instruments were installed on-cycle to measure loading on bolts in an existing support pattern and to determine if cable bolts could be used to improve roof stability. Results showed significant amounts of movement within the bolted zone. In some cases, these movements were enough to load the supports past their ultimate strength. Geology appeared to be a significant factor in localized roof degradation; that is, a very weak rock layer in the immediate roof overlain by a very strong rock layer contributed to the development of shear planes. Only one instrumented bolt had a maximum strain of less than 2,000 microstrain, which was the yield point of the steel. The average maximum strain on all bolts was 20,000 microstrain. However, electrical continuity to many gages was lost and a pattern was noted that would indicate possible bolt failure. Wire mesh and concrete cans installed as secondary support performed very effectively.

By Stephen P. Signer

This paper presents the results of a case study conducted in a two-entry gateroad in a coal mine where excessive roof deformation and bolt loading resulted in failure of many roof supports. The instruments consisted of 16 fully grouted, strain gaged resin bolts, load cells on both full and partially grouted cable bolts, and vertical deflection multipoint extensometers. These instruments were installed on-cycle to measure loading on bolts in an existing support pattern and to determine if cable bolts could be used to improve roof stability. Results showed significant amounts of movement within the bolted zone. In sonic cases, these movements were enough to load the supports past their ultimate strength. Geology appeared to be a significant factor in localized roof degradation; that is, a very weak rock layer in the immediate roof overlain by a very strong rock layer contributed to the development of shear planes. Only one instrumented bolt had a maximum strain of less than 2,000 microstrain, which was the yield point of the steel. The average maximum strain on all bolts was 20.000 microstrain. However, electrical continuity to many gages was lost, and a pattern was noted that would indicate possible bolt failure. Wire mesh and concrete cans installed as secondary support performed very effectively.

Jan 1, 1998

By A. B. Cecala

An evaluation was recently performed on a district recirculation system at a trona mine in Granger, Wyoming. A 1.52m (5 ft) diameter, 37.3kw (50 hp) vane axial fan was installed in a crosscut between the intake and return airways and recirculated approximately 31.4 m'/sec (66,578 ft'/min) of air back into the intake. This amounted to a recirculation factor of approximately 20 pct of the return air. This air was part of the primary ventilation to three different continuous miner sections at operating distances of between 6l0m (2,000 ft) and 1,829m (6,000 ft) from the recirculation fan. The mine environment was constantly monitored for respirable dust, methane, and carbon monoxide in the operating sections and in the main intake and return entries. In addition, air samples were taken with and without the recirculation system during the evaluation and analyzed using gas chromatography. The results of this study showed only small increases in dust, while all other mine contaminants remained at such low levels that it was impossible to determine any relative changes from the recirculation system. Because of this, a brief SF. tracer gas analysis study was subsequently performed to more precisely determine an increase in a mine contaminant with the recirculation system.

Jan 1, 1991

By Kaustuv Bhattacharya, Manish Kumar, Nirbhay Singh, Prodyot Kr. Ray, Praveen Soin

This paper highlights salient features of an excavation 38 m (Length) by 10 m (Width) by 24 m (Depth) carried out in Central Kolkata. Secant pile wall (SPW) formed using a combination of alternating 1200 mm & 800 mm diameter piles was used. Six layers of struts and waler beams, including bottom slab were utilized as lateral restraints to piles. The geotechnical profile for excavation zone was predominantly silty sand to sandy silt. The profile is characteristic of river channel deposit usually encountered in Kolkata. Temporary stage analysis (including seepage analysis) and design were carried out in FEM softwares. Design checks for clay bursting, piping, bottom heave, etc. were also carried out. Extensive instrumentation and monitoring were carried out during the excavation period to check parameters such as ground movement, pile movement, piezometric heads, etc. as per review levels. During excavation, ground improvement using Tube-a-manchette grouting technique was also required to be carried out as per field observations. The paper discusses some of the major challenges faced as well as measures taken to counter them, during deep excavation carried out in silty soils in a very congested Urban setting in the heart of a Megacity.

Sep 1, 2022

By Choon Sunwoo, Chang-Ha Ryu

There are various methods available for the recovery of dimensional stone in open pit quarries. Explosive blasting has more advantages in the economic point of view over the other methods but was not widely used in Korea because owner was concerned about much economic loss when it failed. Several years of efforts have been made in order to develop more effective cutting methods and to spread to the quarries for strengthening the competitiveness in the market. Rock cutting by jet flame and black powder was generally used in the early stage. Black powder was applied to cut the last horizontal plane after forming other vertical planes using the jet flame. Jet flame operation, however, is time consuming and produces excessive noise, and as the result, brings adverse effects on the operator as well as the complaints from the residence adjacent to the quarry. Some mechanical methods such as the slot drill, diamond wire saw or in-situ scale of diamond saw cutting were introduced. Most effective cutting methods using the explosive blasting were developed and applied successfully. Black powder was replaced with the detonating cord. A new air decking technique where plug was not used was developed. This paper reviews the technology for dimensional stone cutting and case study in Korea.

Jan 1, 2003

By Changa-Ha Ryu, Hae-Moon Choi, Sang-Don Lee

The rock mass to be excavated is classified using data obtained from the initial site investigation, and the design of excavation and support is then made based on the rock class. Rock classification provides an empirical design with guidelines for tunnel support compatible with rock mass quality and the method of excavation. Although most clients provide standard patterns corresponding to each rock class, the patterns of drilling and blasting have only been used in estimating the excavation cost and not used in the construction stage. The purpose of the study presented in this paper is to establish a standard blast pattern to yield optimum blasting performance along with an attempt to reduce a difference between design and construction. A series of test blasts were carried out at two tunneling sites of Central Inland Highway crossing the country. Long hole blasting was tested in rock mass whose RMR value is over 60. The blasting results were evaluated by measuring degree of fragmentation, advance rate, muckpile distribution, overbreak, etc. Based on the results of test blast, several patterns were proposed for a twolane highway tunnel.

Jan 1, 2005

By H. Sato, B. Thornton, K. Nishi, A. Usui

"Northwestern Pacific submarine seamounts are believed to be future marine mining areas of ferromanganese crusts, which contain hi-tech industrial metals, such as Co, Ni, Te, Ti, Pt, and REEs. The Takuyo No. 5 seamount is a member of the Cretaceous super-plume seamounts in the north Pacific, located within a Japanese EEZ (100 nm from the Minami- Torishima Is. or Marcus Is.), and only 300 nm away from the Japan’s Licensed area for exploration of Co-rich ferromanganese crusts under the ISA. This is an on-going program supported by independent academic communities but not a state-run program or managed by private funding.We have observed, sampled, measured, and analyzed the occurrences, distribution, physical properties, and microbiological environments at a selected flat topped seamount named Takuyo No.5 as a model area for scientific study of ferromanganese crusts within the Japanese EEZ. We then characterized crust structures, composition, age, and growth history, resulting in an understanding of the overall nature and distribution of these deposits from wide range of areas, water depths and geological environments. The study started with a ROV (Hyper-Dolphin 3K of JAMSTEC) exploration jointly with universities and national institutions (Japan Agency for Marine-Earth Science and Technology, Japan Oil, Gas, and Metal Exploration Corporation, and Geological Survey of Japan) in 2009 using marine geology vessels, remotely-operated vehicle, an oceanbottom drill machine, deep-tow TV camera, as well as conventional dredges and corers. We have been studying the topography, geology, nature of the bottom material of the seamounts using delicate sampling devices and measurement tools, and characterized the distribution patterns of the metal-rich ferromanganese deposits from chemical, mineralogical, and microbiological points of view."

Sep 1, 2014

By D. F. Malan, L. Scheepers

Seismic risk in the deep gold mines of South Africa has been studied for many decades. A clear understanding of the effect of geotechnical conditions on the seismic hazard nevertheless remains elusive. Certain reef types seem to be associated with a higher risk of rockbursts. The stability and deformation behaviour of excavations on the different reef horizons are affected by the rock types and the varying strength properties. The seismic response to mining is therefore also expected to differ according to the geotechnical conditions. As a case study of this behaviour, the seismicity at Mponeng mine was investigated. On the VCR (Ventersdorp Contact Reef) horizon, two areas can be delineated. On the eastern side of the mine, the footwall is shale, and on the western side it is a strong brittle quartzite. More large-magnitude events occur in the area with the shale footwall than the area with the quartzite footwall. Moment tensor analyses indicated that the majority of the large-magnitude events are not related to geological structures, but are face-related, implying that shear failure of intact rock is occurring ahead of the mining front. Preliminary modelling indicated that the closure volume for the shale footwall may be higher than that for the quartzite footwall, providing a possible explanation for the observed difference in seismic response.

Mar 2, 2022

By Yoginder P. Chugh, K. V. K. Prasad, R. Missavage

This paper presents results of field monitoring and finite element studies to analyze and improve a room-and-pillar retreat mining system. Fie1 d instrumentation was utilized to monitor pi11ar load changes, roof to floor convergence and differential roof strata movement as retreat mining progressed and to determine in-situ horizontal stresses. A two-dimensional finite element model depicting strata behavior at this mine was developed and used to analyze existing and alternate improved mining geometries. The results showed excellent correlation between fie1 d observed and model predicted behavior. Some of the recommended changes in mining geometry based on the study were incorporated in the mining system.

Jan 1, 1986

The Bureau of Mines, U.S. Department of Interior, is currently investigating strata interactions associated with the mining of multiple coalbeds. Strata interactions due to subsidence are a result of undermining. This study involves underground investigations at a mine where room and pillar panels are actively being developed through an area of the Sewickley Coalbed which was subsided by undermining of the Pittsburgh Coalbed. Research to date indicates that undermining had little effect on upper mine pillar stability, but had a more severe effect on the development and maintenance of entries. Roof-to-floor measurements recorded over four times more convergence in entries developed over gob as compared with entries developed over support pillars in the lower mine. Consequently, this has led to major roof falls in the active panels, resulting in considerable production delays and supplemental roof support costs.

Jan 1, 1985

By Stephen P. Signer

A field test was conducted by the U.S. Bureau of Mines at the Cyprus Plateau Starpoint No. 2 Mine. near Price. UT. to study the support rock interaction mechanics. Twelve instrumented. fully grouted roof holts and eight sagmeters were installed in the roadway of a two-entry gate road to measure load changes and roof movements. Readings were taken during section development and as each longwall panel passed the test area. Loads that resulted from development of the en- tries were higher than would be expected if simple suspension of the roof rock was the sole cause of loading. When the first longwall face passed the test section massive beam behavior was exhibited over the entry and adjacent pillar. However, no significant localized bending was detected at any of the strain gauge locations. After the first panel passed the test section. all the roof bolts had at least one zone where the steel had yielded. Loading continued to increase. and when the face from the second panel was adjacent to the test section. 70 pct of the strain gauges at the 6-. 1%. and 30-in locations had passed the yield point of the steel roof bolt. However, even at these high load levels, the supporting pattern was sufficient to provide adequate reinforcement to the mine roof.

Jan 1, 1990

By J. H. Potgieter

This paper describes two cases of corrosion that occurred in dry-process, rotary, cement-clinker kilns. In the case of the kiln with five pre-heater stages, the attack occurred primarily from sulphates that probably originated in the raw feed and fuel being used in the plant and that penetrated the refractory lining. The corrosion was similar to ash-deposit corrosion often observed in steam boilers. In the second case the plant consisted of a long dry kiln with a single pre-heater fitted to the feed-end. In this case the corrosion could be ascribed to alkali chloride penetration through the refractory-brick lining and subsequent hot corrosion of the kiln shell.

Jan 1, 2004

By J. F. T. Agapito, J. B. Page

This paper describes part of a geotechnical study based on stress determinations and convergence measurements conducted to assess the long-term stability of an experimental room-and-pillar oil shale mine. A rock mechanics program was initiated in 1971 at the Colony Mine as part of a large study conducted for the design of a commercial operation. The Colony Development Operation is a joint venture currently consisting of four active members; Ashland Oil Inc., Atlantic Richfield Company (Operator of the project), Shell Oil Company, and The Oil Shale Corporation. Although oil shale commercialization plans are presently suspended, rock mechanics instrumentation has been continued as part of Colony's policy in maintaining readiness to proceed with a commercial shale oil plant when national energy policies became better defined. The property is located in the southern edge of the Piceance Creek Basin in northwestern Colorado, approximately 200 miles west of Denver. Experimental mining operations were conducted from 1965 to 1972 with one of the major objectives of the pilot mine being the assessment of opening and pillar sizes for the determination of extraction ratio and life of the property. Mining was conducted in a 60 foot thick portion of the Mahogany Zone in the Parachute Creek Member of the Green River Formation, at depths of 600 to 850 feet by a one-bench system. Pillar dimensions were 58 feet by 58 feet and rooms were 55 feet wide.

Jan 1, 1977

By Y. H. Wang

During the last two decades many research projects were conducted to study the load requirements for the powered supported longwall faces (1-6). Significant results had been achieved by these researches. Most of the previous studies were rarely designed to understand the mechanisms of interaction between the supports and the surrounding rock, or to correlate the stress conditions around longwall faces to the mining operations both in time and space. In case of the shield supported faces, the roof-to-floor convergence is very difficult to measure due to the high percentage of roof coverage. The external load on the supports can not be determined from the leg pressure data alone due to the existence of the lemniscate links. Therefore, there is a real need in that a simple engineering method be developed to monitor the variations of roof load on the shield supports, the roof-to-floor convergence and the roof stress restoration in the gob area as the mining proceeds. Only with the results of these measurements, a further understanding about the mechanisms of interaction between the supports and the surrounding rock can be achieved and a criterion of designing or selecting the optimum mechanical parameters of the shield supports can finally be developed.

Jan 1, 1986