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By P. N. Worsey, M. Schmidt

Many advanced military systems and civilian power generation concepts postulate the availability of compact sources of electrical power capable of delivering gigawatts over microsecond time scales. For example, such a compact power source is essential for future practical pulsed high-powered microwave sources. An explosive-driven flux-compression power generator (EDPG) could fill this requirement. A basic strength of this concept capitalizes on the inherent high energy density storage capacity of modern chemical explosives. It relies on the physics of magnetic flux compression to convert that stored chemical energy into very large amounts of electrical power over short time scales. The generator also has the additional advantage of employing the same types of explosives that are already routinely used in conventional munitions. However, the self-destructive nature of this type of power generator places serious limitations on power pulse-lengths and ranges of applications. This paper describes how a multi-disciplinary team led by researchers from the University of Missouri-Rolla (UMR), Texas Tech University (TTU), and Texas A&M University was awarded a grant by the U.S. Air Force Office of Scientific Research to perform basic research to resolve several fundamental EDPG problem areas. Described are the utilization of UMR’s extensive explosives research expertise and facilities to investigate questions of energy conversion efficiency and the mechanics of energy production. Also, UMR explosives researchers will provide inputs to improved dynamic computer models of the complex, intertwined physics and chemistry operative in these devices. In addition to explosives expertise, UMR provides facilities for basic explosives material research, as well as the storage, machining, and formulation of explosives. UMR researchers are also using test facilities and data collection equipment at the Rock Mechanics and Explosives Research Center and at the UMR Experimental Mine to perform “proof of principle” and subscale tests of explosive-driven flux-compression power generator components. An integral part of the paper is a description of the development of an extreme intensity flash system by UMR and TTU to allow for the high-speed photography of EDPGs in operation. This multi disciplinary research program offers major advances regarding the size, weight, and electrical characteristics of compact EPDGs. Such breakthroughs could dramatically accelerate the practical realization of systems currently under study. Also, these power sources may have far reaching relevance to other Department of Defense and certain commercial compact power applications.

Jan 1, 2000

By B. A. Day

The traditional view taken of commodity prices is that they are cyclical, with strong demand boosting prices and attracting new suppliers. The resulting increased supply pushes prices down with consequent exit of the higher cost producers. And so the process repeats itself. Little attention is given to shifts in underlying global issues and their effect on the traditional process which is seen as being controlled by ?amorphous? market forces with producers profiting from the good times and trying to survive in the bad.. The questions posed are: does this still apply and will it apply into the future? What new factors are affecting the cycles? Can we expect to find the traditional commodity cycles repeated in the 21stcentury? Are producers powerless within the forces of the cycles? Forces likely to affect future commodity prices will be suggested, using gold, zinc, copper, tin and coal as case studies. The long-term downward trend in the real price of commodities is identified.

Jan 1, 2000

By Ian Martin

A precious metals refinery’s switch to personal computer-based, three-dimensional piping design saved many hours in the design of a South African precious metals refinery. Bateman Minerals and Industrial provided engineering, procurement and construction management services for Impala Platinum Limited-Refineries’ new $60 million refinery in Springs, South Africa. This project is one of the largest platinum refineries in the world. Bateman evaluated a new design method during this project that involved developing a three-dimensional model for the project. The new method saved time by reducing the man-hours required to generate complete project documentation, including plans, sections, isometrics and material takeoffs. The new method also saved design and construction time by allowing designers to detect clashes before construction began.

Jan 1, 2000

By Shoji Taniguchi, Lifeng Zhang, Kaike Cai

"In the present paper, based on the two-phase (Eulerian-Eulerian) model, the 3D fluid flows in gas-stirred systems, i.e., air-stirred water vessel and argon-stirred liquid steel ladle, are simulated. In the Eulerian-Eulerian two-phase model, gas and liquid are considered to be two different continuous fields. The phases are assumed to share space in proportion to their volume fractions. The exchange between the phases is represented by source terms in conversation equations. Turbulence simulated by the k- e model is assumed to be the property of the liquid phase. The following effects of mathematical treatments and operational factors on the fluid flow are discussed, such as interphase drag force, turbulent model, the size of bubble, and gas injection mode.Some interesting results are derived. Except the interphase drag force, the interphase lift force should be taken into accounted in order to exactly simulate the fluid flow in gas-stirred systems. Suitable turbulent model and drag coefficient have effect on the mathematical simulation. Injecting small bubbles can realize a well mixing flow condition. The distance between the two gas-injection nozzles has effect on the fluid flow."

Jan 1, 2000

By B. Q. Li, R. A. Mirshams

"A numerical algorithm is described for the simultaneous prediction of the thermomechanical behavior of the materials and microstructure evolption during metal forging. The numerical development is based on the finite element solution of the thermoviscoplastic deformation of metals coupled with the internal state variable model describing the microstructure evolution involving work hardening, recovery, recrystallization and grain size distribution. The finite element code for rigid viscoplastic deformation is developed based on the modification of the existing code for the thermal and fluid flow calculations. The code is tested against and compares well with the results reported in literature. The procedures for the integration of the · rnicrostructure model into the macro finite element model are described. Results are presented showing the characteristics of materials dynamics and mechanical deformation during simple metal forging processes.IntroductionIn industrial deformation processes such as hot rolling and forging, the workpiece undergoes both macroscopic plastic deformations and microstructural evolution. A computer model that allows to predict both materials dynamics and macroscopic deformation is obviously more useful for both fundamental understanding and deformation process optimization. For some industrial applications, especially those involving novel, light and high strength materials, such an integrated model is critical in that both materials and thermomechanical 'behavior during forging must be carefully controlled to obtain the products that meet the desired strength requirement [I]."

Jan 1, 2000

By R. P. Jensen

This is a sampling of the papers presented at the conference, the proceedings can be bought from the SAIMM Arbitrary Lagrangian Eulerian (ALE) computational techniques allow treatment of gases, liquids and solids in the same simulation. ALE methods include the ability to treat shock waves in gases, liquids and solids and the interaction of shock waves with each other and with media from one of the other categories. ALE codes can also treat explosive detonation and the expansion of the explosive gases and their interaction with air and solids. ALEGRA is a 3-D ALE code that has been developed at Sandia National Laboratories over the past few years. ALEGRA has been applied to a 2-D simulation of presplitting using decoupled explosives in rock blasting with very interesting results. The detonation of the explosive at the bottom of the hole sends a shock wave up the borehole driven by the explosive gas expanding into air. The explosive gas compresses the air against the stemming column where it rebounds and recompresses at the bottom of the borehole. This type of ringing takes several cycles to damp out. The explosively induced expansion of the borehole is also treated by ALEGRA as well as the shock wave imparted to the rock. The presentation of this paper will include several computer animations to aid in understanding this complex phenomenon.

Jan 1, 2000

Various aspects of judgment and decision-making are key themes in this book. The model presented here serves as a loose structure for the chapters that follow this one. The notion of a model is introduced because growing research interest in the subjective aspects of group and individual behavior has led to a debate over whether judgment is a skill that can be understood scientifically. A related point of contention is whether such an understanding could lead to the development of methods for estimating people's ability to make good decisions during an emergency. There is some literature that supports the potential usefulness of this approach. However, little agreement seems to have been reached on how to define and operationalize even those basic concepts necessary to assess the soundness of decisions from within their environmental and group contexts [Jensen and Benel 1977; Godden and Baddeley 1979; Baumann and Bourbonnais 1982; Brecke 1982; Stone et al. 1985]. A look at the real-world process is clearly needed. The need to attempt a better understanding of judgment and decision-making properties stems from those occasions in the existence of an organization when there is a lot at stake. The process of decision-making (which is part of the exercise of judgment) has been analyzed in situations such as corporate takeovers [Janis and Mann1977], military combat [Begland1979], clinical emergencies [Baumann and Bourbonnais 1982], and aviation events [Billings and Reynard1984]. The fundamental assumption of these analyses is that, while there are untold successes, there are also notable numbers of failures resulting from decisions that can be ascribed to one or more errors in judgment. From a cognitive perspective, any person engaged in decision-making (either alone or in a group) is actively involved in a process characterized by certain elements. These were mentioned in chapter 1, but are reiterated briefly at this point: (1) detection of a problem, (2) definition or diagnosis, (3) consideration of available options, (4) choice of what is perceived as the best option given recognized needs, and (5) execution of the choice based on what has transpired [Flathers et al. 1982; Baumann and Bourbonnais 1982]. At any moment in this process, there are factors at play that have a large impact on one's ability to solve complex problems in a limited time: (1) an internal state [Hedge and Lawson 1979] is the sum of a person's psychomotor skills, knowledge, attitudes, etc.; (2) uncertainty [Brecke 1982] is caused by faulty or incomplete information received from the external environment; (3) stress [Biggs 1968; Jensen and Benel 1977] is generated both by the problem at hand and any background problem that may exist; and (4) complexity, as it is used here, refers to the number of elements involved that must be attended to. These variables are depicted in figure 5.1, and their relationship to each other and to an outcome is indicated. This schema is designed to suggest interaction, because while the judgment and decision-making process may be conceptualized as discrete stages, experience tells us that this is not the way people function in real-world situations.

Jan 1, 2000

By Fathi Habashi

Laboratory autoclaves for hydrometallurgical investigations are available in a variety of sizes, models, and materials of constructions. They vary in sizes from 25 mL to 2 liters for laboratory studies and 5 to 50 gallons for pilot plant work. They are essential tools for studying aqueous oxidation of sulfide concentrates, dissolution of oxide minerals at high temperature and pressure and hydrothermal precipitation reactions. The maximum pressure and temperature at which any pressure vessel can be used will depend upon the design of the vessel and the materials used in its construction. Since all materials lose strength at elevated temperatures, any pressure rating must be stated in terms of the temperature at which it applies. A review of existing models and their accessories will be given.

Jan 1, 2000

By M. F. Handley

Sequential grid mining has been employed as the primary mining strategy at the AngloGold West Wits Elandsrand Mine since the inception of stoping operations from the sub-vertical shaft system in 1988. Little has been published on sequential grid mining as a mining strategy since, and the purpose of this paper is to describe sequential grid mining, its history, its implementation at Elandsrand, and the outcome to date. The results obtained using sequential grid mining have been evaluated from seismic data, productivity statistics, and rock related accident statistics. Comparisons with neighbouring mines namely Western Deep Levels and Deelkraal, have been made to substantiate the improved conditions observed at Elandsrand, and to compare sequential grid mining directly with longwall mining in similar conditions and at similar depths. Sequential grid mMining is shown to be cost-effective, more flexible, and safer than long wall mining in similar conditions, at least on the Ventersdorp Contact Reef in the western part of the Carletonville Goldfield. More work is necessary to establish it as the favoured mining strategy at depths exceeding 3000 metres, and for reefs other than the Ventersdorp Contact Reef.

Jan 1, 2000

By K Nesbitt

Draw control at Premier Mine is considered important to avoid conditions of isolated draw, which results in early waste ingress, compaction of the kimberlite ore and loss of ore reserves. The Premier Mine kimberlite pipe is unique in that the pipe is cut at a depth of 400 metres below surface by a 75 metre thick gabbro sill. All cave mining at Premier is below the sill and failure to exercise good draw control could cause early ingress of gabbro waste. Gabbro causes problems in the diamond recovery plant and the amount of gabbro sent to the plant needs to be closely monitored. Fortunately coarse gabbro fragments are easy to recognise in drawpoints. It was anticipated that only 85 per cent of available ore would be drawn from the blocks immediately overlain by the gabbro sill before excessive gabbro waste forced the closure of drawpoints. Data on tons drawn per drawpoint and loaded per LHD as well as the tons tipped per pass is gathered by the vehicle monitoring and control (VMAC) system and information recorded by the load-haul-dump (LHD) drivers. Draw control staff monitor drawpoints on a shift basis and record the occurrence, type and height of hang-ups. Information pertaining to the status of the drawpoint in terms of support, waste and availability is also recorded. A database has been compiled that has been used to analyse the overall pattern of draw control, the frequency of occurrence of different types of hang-ups, secondary blasting efficiencies and drawpoint and LHD productivity. The gabbro sill has provided a unique marker horizon that has allowed the arrival of rock from a level 100 metres above the production level to be recognised. Data shows that ore migrates extensively towards groups of drawpoints that are heavily drawn with many drawpoints more than 100 per cent drawn before gabbro waste was recognised. This indicates that an accurate mixing algorithm is essential for good draw control. Data on tons drawn, drawpoint availability, productivity and the occurrence of various types of hang-ups has allowed better control of the mining operation and provided data for planning future caves. In the BA5 mining block a drawpoint spacing of 22 metres, horizontally across the major apex, has still allowed drawpoints to be pulled to waste with no loss of ore. In the BB1E mining block the drawpoint spacing has been increased to 23 metres and no problems have been experienced to-date. Future initiatives centre on improving the data gathering integrity of the vehicle monitoring and control system and a linear programme that will optimise draw control and productivity.

Jan 1, 2000

By Steve Collinsworth

Sometimes, for those of us in the right place at the right time with the right product, necessity creates opportunity. Such is my case at a West Virginia coal mine where a mine manager was desperately seeking a way to eliminate coal damage on cast shots while maintaining cast percentage without the expensive process of secondary drilling. This paper will focus on how bottom hole air decking is solving the problem.

Jan 1, 2000

By C. Mattich, A. L. Beyzavi

The Waelz Plant at Taiwan Steel Union Co. Ltd. (TSU) was erected within nine months from September 1, 1998 to May 15, 1999. The nominal capacity of the plant is 50,000 tonnes per year of electric are furnace dust (EAFD). The plant, consisting of material handling, a waelz kiln, a waste gas cleaning system, waelz oxide leaching and waste water treatment, was commissioned within three months from July 1, 1999 until October 12, 1999. The specific problem of the plant is the high chlorine content in the EAFD pellets which is up to 6 %. Lurgi Metallurgie GmbH, Frankfurt, Germany was responsible for the engineering erection and commissioning of the plant.

Jan 1, 2000

By Raymond A. Binns

Drilling into an active hydrothermal system linked to convergent-margin felsic magmatism is a listed priority of the Ocean Drilling Program that addresses several fundamental geoscience issues. Solid and fluid products of felsic rock-water interaction, and the consequences for global chemical fluxes and for ore deposition, should differ from those in basaltic mid-ocean ridge environments already successfully tested by Legs 106, 139, 158 and 169. So, too, will fracturing controls on fluid pathways, and sources for metals and ligands. Researching the subsurface volcanic, structural/hydrologic, and mineralisation/alteration architecture of a drilled felsic-hosted system also has economic implications, especially for land¬based mineral exploration. A first-order hypothesis to be tested states that fluids derived from volatile-rich magmas are more important than recirculated seawater in convergent-margin hydrothermal systems - economic geologists increasingly appeal to this for creating "world-class" massive sulfide orebodies. Another hypothesis proposes "subhalative" massive sulfide deposition within hydraulically expanded volcanic products as a factor in generating large orebodies. Many second-order hypotheses such as leaching fractionated volcanics to cause gold enrichment in back¬arc systems also need testing. The thoroughly surveyed, active, PACMANUS hydrothermal field in the Eastern Manus back-arc basin of Papua New Guinea will be the site for ODP Leg 193 commencing in November 2000. It lies near the crest (1655-1750 m) of high-standing Pual Ridge, a 40 km-long edifice of dacite/rhyodacite with basal andesite all having geochemical and isotopic affinities with modern arc volcanoes of nearby New Britain. PACMANUS includes at least three focussed, high-temperature "smoker" sites with Cu+Au-rich massive sulfide deposits, and a field of diffuse, lower temperature venting through intensely altered dacite where modelling indicates significant subsurface mineralisation. Isotopic characteristics of deposits and vent fluids suggest magmatic contributions to the mineralising fluids.

Jan 1, 2000

By D Mukendi-Ngalula, G Hearn

Beach sand minerals from the volcanic rock structures of the Drakensberg, Kwazulu-Natal, (South Africa) have been processed. Screening, flotation, spiral concentration and magnetic separation methods were used either separately or successively in an attempt to concentrate monazite minerals. Products thereof and those from a long time (up to 72 hours) microwaves treatment of the finally produced ilmenite-bearing minerals have been studied using the M÷ssbauer effect spectroscopy. The 57Fe M÷ssbauer effect spectroscopy has demonstrated its versatility and power in monitoring the ilmenite internal reduction mechanism and products and, in characterising the iron-bearing phases contained in different products from the beach sand minerals processing. Microwaves heating of ilmenite for up to 38 hours reduced internally the Fe3+ from the ilmeniteÆs structure. A more prolonged microwaves heating (up to 72 hours) re-oxidised the mineral. 61 per cent natural ilmenite recovery was obtained in the floating products of a spiral concentrated -212+106 ¦m screened and beach sand minerals fraction. A preferential concentration of hematite with a 62 per cent recovery was found in the sinking products while the combination of screening-spiral separation-magnetic separation and flotation yielded a floating product with the highest ilmenite and the highest hematite abundanceÆs (71 per cent, 19 per cent respectively). A natural ilmenite containing 87 per cent ilmenite and 13 per cent hematite could be produced and extracted from the sinking products of the flotation process collected subsequently to the spiral concentration and the initial screening.

Jan 1, 2000

By Caroline B. Chapleau, Mélanie Proulx, Claude Bazin, Gaétan Lavoie

"Quebec Cartier Mining operates a pelletizing plant in Port-Cartier, QC. Grinding, agglomeration and pellets induration are the three main steps in the preparation of iron oxide pellets. In 1998, following different recommendations, the company increased the speed of one of its ball mill in order to increase the grinding efficiency of the machine. As expected, the increased speed lead to an increase of the power draught, which did not produce the expected increase of fineness of grind, neither its allows to increase the mill throughput. The change of behaviour of the mill could hardly be understood by comparison of discharge size distribution at initial and modified mill rotation speed. On the other hand, the use of the selection function from a population balance model provides an insight of the changes that occurred in the mill. This paper reviews the various steps required for the estimation of a grinding mill selection function. Results of the calibration to Quebec Cartier grinding mills show that the increase in the mill speed leads to higher rate of breakage of coarse particles, at the expenses of less efficient breakage of medium and fine size particles. In the case of the studied mill, breakage of coarse particles was probably not the critical step of the mill operation. INTRODUCTIONOre size reduction is the major energy consumption step in any mineral processing operations (Austin et al., 1984). Size reduction is required to either liberate valuable minerals from the gangue minerals in which they are imbedded, or to increase the specific surface of the ground material. Plant engineers continuously face the challenge to find grinding machines, operating conditions or grinding circuit flowsheet configurations that could improve the size reduction process at lower energy or m6dia consumption."

Jan 1, 2000

New Zealand depends on foreign investment for economic development. This also applies to the development of New Zealand's mineral resources. For this foreign investment to happen there must be some incentives to attract the investment. While prospectivity is the dominant parameter considered by investors it is not a variable that can be changed, only the perception of New Zealand's prospectivity. Other parameters likely to be considered are sovereign risk, red tape, green tape, land access, civil unrest, land claims, social risk, labour relations, infrastructure and natural disasters. Regulators and political will can vary some of these parameters. Where New Zealand fits internationally can be measured by investors' perceptions of these parameters. Following on from these perceptions New Zealand can be seen to have advantages in some areas and be disadvantaged in others. How to deal with the disadvantages to give investors confidence is not easy in the New Zealand environment where the development of mineral resources plays a small part in an economy dominated by agriculture. Added to this is the current global state of the minerals industry which offers even more of a challenge to attract foreign investment to develop New Zealand's mineral resources.

Jan 1, 2000

It is proposed to consider a new access, mining and hoisting system for underground deposits, as an alternative to the commonly used decline or vertical shaft access. The proposed system offers fundamental improvements in gathering of exploration data, reduction of capital expenditure and significant savings in mine operating costs. The cost reductions are achieved through:superior orebody definition by Supersucker winzing on ore prior to the commencement of capital development; considerable reduction of capital development in waste; full capitalisation on all benefits of a raisebored excavation; introduction of rubber tyred skip and rubber tyred Mine Rapid Response Vehicle; introduction of simplified ore handling system and reduction of underground mobile diesel fleet; and introduction of minimum maintenance shaft concept. The system is applicable to deposits ranging from shallow, low dip angle, narrow vein, high-grade to bigger, massive type vertical mineralisations accessed from the surface, preferably from the bottom of an open pit; it is also suitable as a down dip extension of an existing underground mine. The system is highly conducive to mine automation and emerging trend aimed to increase the ratio of mined metal/mineral to mined waste. It offers substantial reduction in diesel exhaust gas emissions to the mine atmosphere.

Jan 1, 2000

Geophysics is playing an increasingly important role in the exploration industry. In the soft rock scene the application of seismic techniques is basically mandatory prior to any drilling program. Simply, this is because, in a majority of situations, the seismic method is ideally suited to mapping accurately relatively flat lying strata and displaying structures that may host oil or gas. It is worth stressing that seismic methods do not delineate oil or gas but they map well in two or three dimensions. In the base metal arena, geophysical methods used are generally focussed on direct detection methods with the mapping application not often used except in potential fields (magnetics and gravity). The success rate in the last decade has not been good but this does not only apply to the application of geophysics; it really applies across the board of exploration techniques. Both geological and geochemical exploration have not had a success rate commensurate with the funds injected. Basically in the last ten years we have failed as explorers! As explorers we have been negligent in mapping. As geoscientists we have let the basic mapping and observation skills diminish û the old adage æboots on the groundÆ is still applicable but are we doing enough of it? The answer is clearly no. As explorers the huge burden of bureaucracy, eg Government Acts û local, state and federal, safety compliance, environmental compliance, etc has reduced the ægeologicalÆ time dramatically. This has culminated in an over-reliance on quick fix solutions, eg spot the bump geophysics or geochemistry. This obviously simplistic scenario is arguable but there is no doubt in the geoscientific areas we have failed in the last decade to provide adequate geoscientific maps to assist in exploration. This failure could partially be responsible for the current demise of the industry resulting in a reduction in exploration dollars and, hence, people. This trend is seen acutely in the geophysical area where the head count in comparison with the geological fraternity is low. Other trends during this downturn are inevitable as explorers maximise the use of the dollar in exploration and diminish spending on advances in geophysics. Improvements are being seen however in geophysical equipment, although it is considered that the main improvement will be in the interpretation of data. Specifically, the trend will be towards integrating geophysical data into geological, geochemical and spatial data sets producing quality interpretation and providing low risk drill targets. Examples of the current trends in hardware and future directions are discussed below. In interpretive schemes there are very few examples of integrated interpretation but the possible trends will be discussed with limited examples.

Jan 1, 2000

By Hamid Maleki

Results of geologic investigations, in-mine instrumentation, and numerical modeling are presented for two longwall mines in which pillars with large width-to-height ratios (8 to 9) are used. These investigations revealed that wide pillars unload when subjected to sufficient stress and that pillar unloading is influenced by geologic conditions. Field measurements in mine 1 clearly indicated load transfer from the longwall area toward the gate roads, resulting in pillar failure near the margin of a fluvial channel. Loads were shown to transfer to a harrier pillar (width height ratio equal to 9), contributing to progressive failure of this pillar. Unloading of the barrier pillar was associated with significant load transfer to the two-seam submains to the north of the harrier, contributing to roof falls, floor heave, and rib spalling within the submains. Stress analysis results addressed pillar peak strength and unloading behavior that was in agreement with the measurements and underground observations. Underground observations and stress analyses were completed before and after longwall mining near a six-entry submain in mine 2. This submain was intended to he used as a temporary bleeder and tailgate for a small longwall block consisting of one to two panels, depending on the development schedule in other areas of the trine and observed ground conditions. Numerical modeling using both elastic and inelastic pillar behavior for submain pillars with a width-to-height ratio of 8 was completed before mining began. Results indicated that pillar unloading was likely. During retreat of the first longwall panel, pillars unloaded. as evidenced by progressive rib spalling along the cleats, This behavior was mostly confined to the immediate face area, an observation that was in agreement with the modeling results,

Jan 1, 2000

By J. Kuijpers

Failure and fracturing are often regarded as synonymous. While this is obviously true in an environment dominated by tensile stresses, it is still not clear how failure and macro fracturing are related in a compressive stress environment. Excavations at great depths are typically subjected to compressive stresses only. The fracturing observed around such excavations is therefore commonly assumed to be induced by such compressive stresses. The physics of such a phenomenon have unfortunately never been explained properly, so that the formation of these so-called extension fractures still remains a mystery. As the presence of fractures is an important factor affecting the stability of underground excavations, it is of practical relevance to understand their formation. In this paper, a possible explanation is proposed. It is argued that fracturing in a compressive stress environment is a secondary effect. Primary failure, in the form of micro fracturing and associated damage is assumed to precede the major fracture processes. The fractures are thus generated in response to material failure and may not directly be the cause of failure. The implications for material response and behaviour are discussed. Keywords: micro fracturing, macro fracturing, extension fractures, failure, compressive stresses, damage, excavations.

Jan 1, 2000