In a uniform granite gneiss study area in central Zimbabwe, lineaments oriented parallel to the maximum regional compressive stress orientation exhibit the thickest regolith development, while lineaments oriented perpendicular to the maximum compressive stress show the shallowest development of weathered regolith. The principal fracture set orientations were mapped using aerial imagery. The regional stress field, estimated from global stress maps, was used to determine the stresses acting on each principal lineament orientation. Multi-electrode resistivity profiling was carried out across fractures with different orientations to determine their subsurface regolith conditions. The results indicate that the 360 and 060° lineaments, which are sub-parallel to the principal compressive stress orientation (σ1) exhibit maximum development of the regolith, while 130° lineaments perpendicular to σ1 do not exhibit significant regolith development. Since regolith thickness has been positively correlated with groundwater resources, it is suggested that fractures with orientations sub-parallel to the principal compressive stress direction constitute favourable groundwater targets. Knowledge of the regional stress field and fracture set orientations can be used as an effective low cost tool for locating potentially higher yielding boreholes in crystalline rock terrains. 相似文献
The influence of pore structure, water transport properties and rock strength on salt weathering is evaluated by means of
a thorough rock characterisation and a statistical analysis. The pore structure was described in terms of its porosity, pore
size distribution (quantified by mean pore radius) and specific surface area, density and water transport was characterised
by means of water permeability (saturated flow) and capillary imbibition (unsaturated flow); whilst the rock strength test
was carried out using uniaxial compressive strength, compressional and shear wave velocities, dynamic elastic constants and
waveform energy and attenuation were obtained from the digital analysis of the transmitted signal. A principal component analysis
and a stepwise multiple regression model was carried out in order to examine the direct relationships between salt weathering
and petrophysical properties. From the principal component analysis, two main components were obtained and assigned a petrophysical
meaning. The first component is mostly linked to mechanical properties, porosity and density whereas the second component
is associated with the water transport and pore structure. Salt weathering, quantified by the percentage of weight loss after
salt crystallisation, was included in both principal components, showing its dependence on their petrophysical properties.
The stepwise multiple regression analysis found that rock strength has a predominant statistical weight in the prediction
of salt weathering, with a minor contribution of water transport and pore structure parameters. 相似文献
The crystallisation of soluble salts within the pores of the stone is widely recognised as a major mechanism causing the deterioration
of the stone-built architectural heritage. Temperature, in turn, is one of the main controls on this process, including salt
precipitation, the pressure of crystallisation and the thermal expansion of salts. Most laboratory experiments on decay generated
by salts are just carried out with convective heating regimes, while in natural environments building stones can undergo radiative
and convective heating regimes. The thermal response of stone to these different heating regimes is noticeably different and
might influence the crystallisation patterns of a salt within a stone. The aim of this work is to raise awareness on the different
patterns of crystallisation of NaCl within a porous stone tested with different heating regimes (convection and radiation)
and the implications that this could have on the design of experimental modelling of natural weathering conditions in laboratory
simulations. Results show that heating regime affects the sodium chloride distribution within a stone with high percentage
of microporosity. In this case, radiation heating facilitates the generation of subefflorescences, while convection heating
promotes efflorescences. This has a clear implication both on the stone decay in natural environments and on the methodologies
for testing salt decay, as subefflorescences are more destructive than efflorescences. In this sense, the use of convective
heating in laboratory experimentation might underestimate the potential damage that sodium chloride may generate. This counsels
the use of radiation heating test methods in addition to convection for the laboratory study of salt crystallisation. 相似文献
In spite of the considerable area covered by argillaceous sedimentary rocks (comprising shales, mudrocks and siltstones) in Brazil and the number of engineering works associated with these materials, little is known about their geotechnical, physical, chemical, mineralogical and textural characteristics and the effects of weathering processes on them. This work presents results obtained in a research project aiming primarily at identifying degradation processes responsible for the weathering of some of these rocks in Brazil. The rocks under investigation come from two different parts of the country, each one related to a specific engineering problem and to different geoenvironments. The project involved a comprehensive laboratory testing program for basic characterization (chemical and mineralogical composition, index properties, etc.) and evaluation of durability characteristics of these rocks. The present paper describes the testing program carried out and discusses the results obtained. 相似文献
Since 1998, BHP Billiton has mined diamonds at the Ekati Diamond Mine™ near Lac de Gras in the Northwest Territories of Canada. Current operations are based on mining multiple pipes by the open-pit method, but as some pits deepen, converting to underground mining is being considered.
As a test of underground mining methods and to provide access to the lower elevations of the Panda and Koala pipes, the Koala North pipe is being developed for underground mining. Initially, the top 40 m of the pipe were mined as an open pit to provide grade information and a prepared surface for the transition to underground mining. Currently, Koala North is being developed as an open-benching, mechanized, trackless operation. Although the method was successfully used at several De Beers diamond operations in South Africa, it has never been tested in an Arctic environment.
This case study describes basic geology, mining method layout and ongoing geological and geotechnical investigation. From the beginning of underground development, geotechnical daily routines have been fully integrated within the technical services department, which supports the operation. Geotechnical, geological and structural information obtained from underground mapping and core logging is compiled, processed, reviewed and analyzed on site by the geotechnical staff. Conclusions and recommendations are implemented as part of the operations in a timely manner. This ongoing “live” process enables the operators to make the most efficient use of resources both for ground support and excavations as well as to address safety issues, which are the top priority. 相似文献
For a mining operation to be successful, it is important to bring fundamental and applied science together. The mining engineer needs to understand the importance of geology, mineralogy and petrography, and how projects can benefit from the data collected during the exploration and pre-exploration stage. Geological scientists also need to understand the process of project development from the exploration stage through mine design and operation to mine closure. Kimberlite pipe or dyke emplacement, geology and petrology/mineralogy are three areas that illustrate how information obtained from the geological studies could directly influence the mining method selection and the project strategy and design. Kimberlite emplacement is one of the fundamental processes that rely on knowledge of the kimberlite body geology. Although the importance of the emplacement model is commonly recognized in the resource geology, mining engineers do not always appreciate its importance to the mine design. The knowledge of the orebody geometry, character of the contact zones, internal structures and distribution of inclusions could directly influence pit wall stability (thus strip ratio), underground mining method selection, dilution, treatability, and the dewatering strategy. Understanding the internal kimberlite geology mainly includes the geometry and character of individual phases, and the orientation and character of internal structures that transect the rock mass. For any mining method it is important to know “where the less and where the more competent rocks are located” to achieve stability. On the other hand, the detailed facies studies may not be important for the resource and mine design if the rock types have similar physical properties and diamond content. A good understanding of the kimberlite petrology and mineralogy could be crucial not only to the treatability (namely diamond damage and liberation), but also to the pit wall and underground excavation stability, support design, mine safety (mudrush risk assessment) and mine dewatering. There is no doubt that a better understanding of the kimberlite and country rock geology has a direct impact on the safety and economics of the mining operations. The process of mine design can start at the beginning of kimberlite discovery by incorporating the critical geological information without necessarily increasing the exploration budget. It is important to appreciate the usefulness of fundamental geological research and its impact on increased confidence in the mine design. Such studies should be viewed as worthwhile investments, not as cost items. 相似文献
Microbial biofilms are ubiquitous in aquatic and terrestric ecosystems as well as on man-made material. They are initial colonizers on all surfaces and take part in biogenic weathering on natural rocks as well as on building stone. The structure and function of the biofilm matrix, mainly extracellular polysaccharides (EP), is documented for biofilms on stone surfaces: the hydrated gel acts as glue between the organisms and the material surface. Besides EP, living cells, cell debris and mineral particles are embedded in the matrix. These particles appear to be deposited on the surfaces of cell walls and interfaces in the biofilm matrix. As an important function of the matrix, EP stabilizes the biological activity against periodic desiccation. It was demonstrated that in several polymers (alginate, dextran, levan and others) a typical extracellular enzyme, the alpha-amylase, develops enhanced resistance against desiccation stress. Consequences of EP production and biofilm development on surfaces are discussed.Special issue: Stone decay hazards 相似文献