Potash Mine Research Articles

Pressure solution creep and non-associated plasticity in the mechanical behavior of potash mine openings

During the process of analysis and investigations associated with a potash mine rock mechanics project, a great amount of information regarding underground creep deformations was obtained from a long-term, extensive in situ instrumentation campaign under different opening geometries and geological conditions. Over 300 samples were tested in laboratories to define the elasto-plastic parameters of the seven existing different layers of the Saline Formation. The analysis of all this information by regression analysis, optimization numerical search techniques, and by the numerical modeling simulation of several control stations, where measured and calculated room movements were matched, made it possible to demonstrate that the in situ mechanical behavior of fine-grained salt rocks under actual mining conditions is controlled by non-associated plasticity and by pressure solution creep mechanisms, that is, under equivalent stresses, temperatures and strain rates, below 25 MPa (3625 psi), 100°C and 10 −11 sc −1 , respectively.

The effect of the reunification of Germany on the water chemistry and ecology of selected rivers

SummaryWe review several studies and provide new data previously unpublished to show that there has been a substantial decline in pollution of German riverine waters since the beginning of German political reunification in 1989. This reduction is notable in the Elbe, which originates in eastern Germany and the Czech Republic. Pollutants such as many of the chlorinated hydrocarbons have fallen substantially in concentration, while others such as arsenic have declined only slightly. Total nitrogen has declined by only a small amount, but ammonium has fallen substantially, while nitrates have increased. Nitrification is no longer a significant drain on oxygen in the tidal stretch of the Elbe, but decomposition of algae from the middle Elbe is now a greater problem in the lower Elbe. The river-bed sediments of the middle Elbe have a higher species diversity. Fisheries are improving, and concentrations of pollutants in fish such as eel and bream have declined significantly. The river Werra has also improved in quality due to reduction in salt loadings from earlier potash mining.

Interpretation of RIM Surveys in Underground Potash Mines

RIM surveys in underground potash mines in Saskatchewan, Canada, have been undertaken for several years with generally positive results. The methodology is similar to surveys carried out in underground coal mines in the U.S. and Australia, where TEM-mode magnetic-field amplitudes are measured and subsequently processed to produce absorption-coefficient images of the seam being exploited. The primary differences between the coal and potash situations are the great transmission range possible in potash, which exceeds 3000 m, and the nature of the target anomaly, which for potash is always the anomalous presence of brine. The RIM method responds to zones of anomalous conductivity in a manner that does not well match the commonly-applied ray assumption. There is a difference between how two rays respond to the same anomaly where one of the rays has both end points outside the anomaly and the other has either the beginning or end of the ray within the anomaly. In each case grossly different measurements are made of essentially similar volumes of earth which, if unrecognised, can lead to serious interpretational pitfalls. These effects have been recognised in field data and turned to advantage: if both ray modes traverse the same anomaly the thickness and conductivity of the anomalous material can be derived by a curve-matching method.

MORTALITY FROM CARDIOVASCULAR DISEASES AMONG POTASH MINERS EXPOSED TO HEAT

We assessed mortality rates in a cohort of French potash miners between 1977 and 1987. The cohort comprised all workers of a potash mine active on January 1, 1977, or subsequently hired, with at least 3 years of employment. We compared the mortality of the subcohort exposed to heat from underground work (U) with the mortality of those who had never worked underground (D). The overall mortality was low [standardized mortality ratio (SMR) = 0.89, based on 570 deaths] and was lower among underground workers (age-standardized mortality rate = 660 per 100,000 person-years, 266 deaths) than among daylight workers (age-standardized mortality rate = 710 per 100,000 person-years, 304 deaths). Mortality from ischemic heart diseases (IHD) was higher for underground workers than for daylight workers (relative risk = 1.6). As exposure to heat decreased over time, we analyzed the mortality according to period of hire: within underground workers, we observed a downward trend for mortality from IHD which contrasted with a stable mortality from IHD among daylight workers. Among subjects who left for medical reasons, IHD mortality was five times greater in the heat-exposed group compared with daylight workers. The data are consistent with an increased risk of ischemic heart diseases from a hot environment that is offset by a strong healthy worker effect.

Coupled elastoplastic and viscoplastic analysis of a potash mine : P. R. Oyanguren & L. R. A. Monge, in: Geomechanics 93. Proc. conference, Ostrava, 1993, ed Z. Rakowski, (Balkema), 1994, pp 203–210

Coupled elastoplastic and viscoplastic analysis of a potash mine : P. R. Oyanguren & L. R. A. Monge, in: Geomechanics 93. Proc. conference, Ostrava, 1993, ed Z. Rakowski, (Balkema), 1994, pp 203–210

Testing and modeling of backfill used in salt and potash mines : Van Sambeek, L L Proc International Symposium on Rock Support, Sudbury, 16–19 June, 1992P583–589. Publ Rotterdam: A A Balkema, 1992

Testing and modeling of backfill used in salt and potash mines : Van Sambeek, L L Proc International Symposium on Rock Support, Sudbury, 16–19 June, 1992P583–589. Publ Rotterdam: A A Balkema, 1992

High resolution seismic reflections in a potash mine : Gendzwill, D J; Brehm, R GeophysicsV58, N5, May 1993, P741–748

High resolution seismic reflections in a potash mine : Gendzwill, D J; Brehm, R GeophysicsV58, N5, May 1993, P741–748

En echelon crack-arrays in potash salt rock

There are two types of fracture patterns in the yield pillars of the potash mines of Saskatchewan. The individual members of both patterns are tensile (extension) fractures that propagate parallel with the maximum principal stress trajectory (perpendicular to the minimum principal stress). The difference between the two patterns lies in the arrangement of the member fractures. In theen echelon tensile crack-array, the macroscopic fracture consists of individual tensile cracks that are slightly offset from each other. They have only a small overlap and the child crack seems to form randomly on either side of its parent. Consequently, the en echelon tensile crack-array inherits the axial orientation of its members. In contrast, the tensile cracks of anen echelon shear crack-array, have a larger overlap and their lateral displacement from each other is biased in one direction. Therefore, the crack-array is no longer axial but inclined 20–25 degrees from the maximum principal stress direction. With increasing stress, the shear crack-array often collapses, forming theenvelope orhourglass structures of the potash mines.

In situ tests on backfilling and surrounding host-rock in the case of a radioactive waste disposal in a layered salt formation

In situ experiments carried out by ANDRA in a deep and homogeneous salt layer of a French mine (Amélie mine — Alsace Potash Mines S.A.) tested the behavior of the different components of a multibarrier system, designed for high-level waste disposal and particularly for heat-generating wastes. Canisters were placed in blind boreholes. The experimental field is located at a depth of 520 m where two major tests have been carried out since 1987. The first test (1987–1989) tested the backfilling by heating different types of crushed salt (max. 130°C) emplaced in large-diameter boreholes. One hole remained empty as a control. The second experiment started in 1989 with the opening of a gallery and the boring of three different boreholes (7 m depth, 250 mm diameter) where the annulus between the cylindrical heating cell and the salt mass differs fundamentally in configuration: as tight as possible, empty, or backfilled with crushed salt. The first configuration was tested at the end of 1991. In both test fields, a complete series of measurements has been carried out to record temperatures, pressures and deformations on the heating devices, as well as in the surrounding media. Backfill and host rock are monitored with sensors placed in different boreholes. High-resolution tiltmeters and accurate levelling complete the field of investigations. Thermo-mechanical behavior and the properties of the materials have been considered in detail using laboratory test results. Calculations showed how thermo-mechanical interactions behave and generally agreed in a satisfactory manner with the measurements of the test field. Finally, after cooling and dismantling of the experiment, the microscopic change of the different crushed salts used for the backfilling is analysed.

Rock mass characterization around Saskatchewan potash mine openings using geophysical techniques: a review : Gendzwill, D J; Stead, D Can Geotech JV29, N4, Aug 1992, P666–674

Rock mass characterization around Saskatchewan potash mine openings using geophysical techniques: a review : Gendzwill, D J; Stead, D Can Geotech JV29, N4, Aug 1992, P666–674

High‐resolution seismic reflections in a potash mine

High‐resolution seismic reflections underground in a deep potash mine in Canada have been collected using a hammer for a seismic source, 50 Hz geophones, and a digital, stacking seismograph with 0.1 ms sampling rate. Data were obtained with 12‐fold redundancy in both downward and upward directions from the mine openings. Reflections with dominant frequency up to 1100 Hz were observed between 20 and 80 ms time. Both single geophones and arrays of geophones were tested. For the roof profiles, geophones were bolted to the rock with specially designed base plates. Computer processing used deconvolution filters to remove spurious high‐frequency resonance of the geophones. Constant velocity for salt was used for all static corrections and normal moveout corrections. An unexpected result was the appearance of near‐vertical reflected waves that traveled both ways at the shear‐wave speed. These are thought to have been caused by near‐surface fractures or near‐surface anisotropy of the rock. Synthetic seismograms calculated from logs of a nearby well agree with the seismic reflection data. Normal stratification of the flat‐bedded sedimentary rocks and a small structure were mapped by the seismic data, confirming the vertical extent of geological anomalies observed at the mine level.

Archaeal halophiles (halobacteria) from two British salt mines

Summary: Samples were taken from the Winsford salt mine in Cheshire, England, which exploits bedded deposits from the Triassic Period (195-225 million years ago, MYA) and from Boulby potash mine in Cleveland, England, which is Permian (225-270 MYA) and is mined for the mineral sylvite (KCl). Halobacteria and obligately halophilic eubacteria were isolated from several different sample types. The halobacteria were characterized by chemotaxonomic methods and most but not all were shown to be very similar but not identical to those halobacterial types that dominate in highly concentrated surface brines. There was a high degree of similarity between the two mine populations, but some strains were particular to each mine.

Mining-induced deformation in potash yield pillars, Vanscoy, Saskatchewan

Mining-induced deformation of potash yield pillars in the Cominco potash mine at Vanscoy, Saskatchewan, has been documented by mapping deformational structures, determining changes in pillar width and in thicknesses of potash and interbedded clay layers, and analyses of rock fabrics in samples collected from three yield pillars. Pillar deformation over a period of 8 years can be shown to have involved progressive bulk rock flattening, followed by development of shear zones at pillar corners, development of shear wedges at pillar margins, and detachment of these wedges into adjacent rooms. Furthermore, this sequence appears to be repetitive. Strain in halite involves fracturing and displacement and rotation of fragments, strain in sylvite is continuous, and grain boundary sliding has been an important mechanism in the deformation. Although the fabric anisotropy cannot be used to assess total bulk rock strain, the component of strain related to sylvite shape change has been examined during progressive failure of the pillars. The values of strain in the principal strain directions based on sylvite shape are estimated as 42% shortening in the subvertical direction, 37% subhorizontal elongation perpendicular to the original openings, and 25% subhorizontal elongation parallel to the original openings. Key words : yield pillar, potash, fabric analysis, induced deformation.

The exchange process between river and groundwater on the Central Alsace floodplain (Eastern France)

The recent canalisation (in the nineteen sixties) of the upper Rhine has modified the exchange processes between the river and its groundwater in the floodplain of Alsace. The Rhine seeps through its gravelly bed and in this way feeds the nearby groundwater table by means of the so-called ‘Rhine filtrates’. Using a few groundwater stream examples, this paper presents the characterization and localisation of these infiltrations. The Rhine filtrates are characterized by a high level of chloride and a low level of nitrate, these compounds being hydrological tracers, specific for the Alsatian floodplain (chloride resulting from contamination by the potash mines in the south of Alsace). They are also defined by high levels of phosphate and mercury (very localized injection). Phosphate is responsible for eutrophication which is observable in the appearance of specific aquatic macrophyte communities. Groundwater contamination by mercury is reflected by its accumulation in the bryophyte Fontinalis antipyretica sampled in ground-water streams. Thus aquatic vegetation, and more particularly the distribution of macrophyte communities, is used as an ecological descriptor of the exchange between the Rhine and its groundwater. The maximum injection of Rhine filtrates occurs between two areas of stillwater (hydroelectric dams), where the Rhine dominates its plain and where the substrate is constituted of coarse gravels.

Implementation and monitoring thermomechanical tests in a salt formation of a French potash mine : Ghoreychi, M; Raynal, M; Roman, J Proc 33rd US Symposium on Rock Mechanics, Santa Fe, 3–5 June 1992P181–190. Publ Rotterdam: A A Balkema, 1992

Implementation and monitoring thermomechanical tests in a salt formation of a French potash mine : Ghoreychi, M; Raynal, M; Roman, J Proc 33rd US Symposium on Rock Mechanics, Santa Fe, 3–5 June 1992P181–190. Publ Rotterdam: A A Balkema, 1992

Rock mass characterization around Saskatchewan potash mine openings using geophysical techniques: a review

Saskatchewan potash deposits are found in relatively uniform, flat-bedded strata with few irregularities. Potash mines are highly automated and efficient, taking advantage of the uniform strata. However, anomalous geological conditions can lead to severe problems, especially with water inflows. One mine has been lost to flooding, and other mines now have or previously had large inflows of water. Geophysical techniques, especially the method of vertical seismic reflection from the surface, are used to predict anomalous geological conditions. Seismic, electric, and other geophysical methods are also used underground, sometimes in boreholes, to detect conditions around the mine openings such as the thickness of the salt cover over the mine, fractures around the opening, shale beds, the presence of water, and other rock properties. The mines generate seismic activity ranging from magnitude 3.7 earthquakes to tiny micro-earthquakes, and various field monitoring and laboratory testing programs have analyzed these. To avoid hazards discovered by geophysical methods, mine managers have often changed their plan of operation or even deleted large ore reserves. Key words : geophysics, potash mining, seismic, earthquakes.

Seismic activity in flooded Saskatchewan potash mine : Gendzwill, D J; Prugger, A F Proc 2nd International Symposium on Rockbursts and Seismicity in Mines, Minneapolis, 8–10 June 1988P115–120. Publ Rotterdam: A A Balkema, 1990

Seismic activity in flooded Saskatchewan potash mine : Gendzwill, D J; Prugger, A F Proc 2nd International Symposium on Rockbursts and Seismicity in Mines, Minneapolis, 8–10 June 1988P115–120. Publ Rotterdam: A A Balkema, 1990

The application of geostatistically controlled elliptical weighting techniques at Boulby potash mine, Cleveland

Abstract Statistical studies of a portion of the Boulby potash seam revealed that distinct subareas are present in which stationarity could be shown to exist and which are characterized by statistically distinct populations of seam thickness and % KCl. Semivariogram modelling in these sub-areas allowed the definition of the axes of anisotropism in each case and hence the dimensions and orientation of the search ellipses for ore reserve purposes. Inverse distance weighting was then applied to evaluate individual ore blocks and the efficiency of the method tested by cross-validation of actual borehole values. Considering the problems induced by the sampling method applied (low angle deflection of in-seam drill holes), the results were generally satisfactory and form the basis for a more detailed comparative study of inverse distance and kriging techniques at Boulby.

Time-dependent hydraulic fracturing in potash mines : Int J Rock Mech Min Sci V28, N2/3, May 1991, P187–197

Time-dependent hydraulic fracturing in potash mines : Int J Rock Mech Min Sci V28, N2/3, May 1991, P187–197

Borehole acoustic logging around underground potash mine openings : Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990 V2, P1037–1044. Publ Rotterdam: A A Balkema, 1990

Borehole acoustic logging around underground potash mine openings : Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990 V2, P1037–1044. Publ Rotterdam: A A Balkema, 1990