Iron ore reserves are normally found within a few meters from the ground surface, and most of the major mines of the world are operating an opencut system, which requires little sophistication, except in terms of the equipment used and the quantities needed to be mined for operations to be cost-effective. This chapter will look at case studies that define how mining of ore is conducted today. Examples of mining sites are described from the major mining areas of the Pilbara in Western Australia and Minas Gerais in Brazil. The deep mining of iron ore is unusual in the modern era, but in northern Sweden, ore is mined from considerable depth largely aided by the application of automation and remote control equipment. Kiruna has been chosen as the example for a more detailed review of underground techniques. However, in order to provide an historical context of the early smaller scale of iron ore mining, the chapter begins by examining two examples of historic underground mining in the United Kingdom, these being the underground mining of iron ore in Cleveland and also the Frodingham Ironstone of North Lincolnshire.

Cracks in the rock are among crucial defects affecting its deformation and strength characteristics. Particularly in underground or mining engineering, the initiation and development of cracks due to cyclic unloading are critically affected by the fracture of the rock mass. In order to scrutinize the mechanical behavior of rocks with different crack angles, a true triaxial cyclic loading and an unloading test are carried out on sandstone samples with prefabricated cracks of various angles. The cracked sandstone samples do not considerably expand under action of triaxial stresses, commonly exhibit non-ideal elastic characteristics, and mainly undergo shear failure. As the crack angle grows, the tensile properties become pronounced, and the fracture surface morphology of the cracked samples presents a huge difference. The change rules of the irreversible axial and lateral strains are apparently different, and the rate of change of the irreversible lateral strain in terms of the applied stress is more sensitive than that of the axial irreversible strain. The energy evolution law of the hysteresis loop formed in the sample cyclic load test has no evident influence on the crack angle of the sample; however, the larger the crack angle of the sample, the more energy consumption during failure. Based on the equivalent irreversible strain and the hysteretic loop energy dissipation indicators, the damage law of sandstone samples can be described. It is also revealed that the damage rule determined according to the equivalent irreversible strain index is more conducive to characterizing the initial characteristics of damaged samples. Additionally, the damage rule determined based on the hysteretic loop energy dissipation index would better describe the damage rule associated with the understudy samples. There are obvious discrepancies in the morphological characteristics of the fracture surface in the scanning electron microscope images of the typical fracture surface of the samples with various crack angles, indicating that the damage and destruction of the sample acted upon by the shear and tensile shear are wholly dissimilar.

The impact of high temperatures on rocks is a topic of growing importance in geotechnical engineering due to its relevance to applications such as underground nuclear fuel storage, geothermal energy resource exploration and underground coal gasification. This paper presents results from tests performed on samples of sandstone treated to a range of temperatures between 20 and 1000°C. Sandstone samples obtained from underground coal gasification trial sites in Poland were selected for the tests. Multistage triaxial tests were used to determine the mechanical properties of the samples. X-ray diffraction and thermal analyses were performed to investigate the changes in physical and chemical properties of the samples under increasing temperature. Micro-computed tomography analyses were carried out on selected samples in order to show the microstructural changes that take place as a result of the heating process. Three-dimensional characterisation of sample porosity and pore-size distribution was performed to obtain a quantitative comparison between samples subjected to different temperature treatments. The relationship between microstructure and macro-mechanical characteristics of sandstone at high temperatures is discussed. The results illustrate that the mechanical properties of sandstone are closely related to alterations of microstructure that result from increased temperatures.

Research Programme of the Research Fund for Coal and Steel (RFCS), grant numbers RFCR‐CT‐2003‐00011.

Probabilistic analysis and numerical modelling techniques have been combined to analyse a deep coal mine roadway. Using the Monte Carlo method, a correlation control algorithm and a FLAC 2D finite difference model, a probability distribution of roof displacements has been calculated and compared to a set of measurements from an actual mine roadway. The importance of correlation between input parameters is also considered. The results show that the analysis performs relatively well, but does tend to over predict the magnitude of displacements. Correlation between parameters is shown to be very important, particularly between the three model stresses.

The collapse of abandoned and often hidden mine shafts is a serious problem in the UK and many parts of Europe. The collapse of these shafts is often related to the failure of the shaft lining. Understanding the mechanisms of ground movements around deforming/collapsing mine shafts is, therefore, important in the assessment of mine shaft location as well as lining condition. This paper presents an experimental study of the mechanisms of soil failure around a deforming shaft lining. Geotechnical centrifuge modelling of reduced-scale buried mine shafts was tested to determine the magnitude and pattern of ground deformations that occurred during loss of internal support pressure. An axis-symmetric centrifuge container was used along with half-cylindrical model shafts. These allowed for the acquisition of digital images of the sub-surface soil and mine shafts which enabled the measurement of soil and shaft deformation using image analysis techniques. The results from two model shaft tests are presented. The first test involved the loss of internal support along the entire shaft length, whereas the second test studied the effect of a discrete weakened zone within the lining.

Many experimental and field trials have shown lime to be an effective clay stabilizer. As lime mainly affects clay minerals, it will come as no surprise that lime is more effective where clay content is higher. However, there is some evidence in the literature that the presence of high concentrations of organic matter in clay soil can lessen the chemical reaction between lime and clay minerals and have detrimental effects on engineering properties of soil. In particular, humic acid is a well-known constituent of organic matter with the potential to disrupt the soil stabilization process. Findings on the subject of lime stabilization by various researchers are presented in this section. The behaviour of lime stabilization is discussed at length with reference to clay, organic clay and peat soils.

The effectiveness of lime as a chemical additive for the stabilisation of organic clay is considered uncertain, especially in the long term. Previously, it was shown that a high humic acid content (i.e. > 1.5%) reduces the strength of clay undergoing the process of lime stabilisation. The results of tests carried out on lime-treated specimens revealed that lime may not be the only available option to stabilise organic clay comprising more than 1.5% humic acid. A mixture of 1.5% humic acid, at 5% optimum lime content was prepared to be stabilised with various amount of calcium chlorides, CaCl2) (0.5%, 2.0% and 5.0%). The strength properties of specimens were examined by undrained (CU) and drained (CD) triaxial tests. Curing periods of 7 and 28 days were chosen to assess the influence of salts for improving the properties of lime-treated organic clay. Overall, there was significant improvement in the properties of the lime-treated organic clay when the chloride salt (i.e. CaCl2)) was introduced. Changes in the soils' properties were discovered early (i.e. after 7 days) in each specimens.

During the last thirty years, the Boulby Potash Mine has replaced the concrete shaft linings in sections of both shafts on two occasions following progressive deterioration. A third replacement lining is now under construction in the man shaft. This paper reports the results of two-dimensional (2D) and three-dimensional (3D) numerical modelling of the shaft linings and their surrounding strata. The numerical modelling, using FLAC 2D and FLAC 3D has considered the detrimental effect to lining stability of a weak rock zone surrounding the shafts at depth. The 3D modelling work has also taken into account the formation of an inset and roadway leading from the shaft. This research aimed to identify the failure mechanisms of the shaft linings in the affected zone and their causes. The research also supplied reference data to allow the prediction of stress and deformation conditions in the newly designed third shaft relining system.

This paper is concerned with the stability assessment of Rossio railway tunnel, located in Lisbon metropolitan area, during its rehabilitation phase. Built in the nineteenth century, the 2.6-km long Rossio tunnel was constructed in the old central area of Lisbon for providing goods and services for the users of railway services. On several occasions, the breakdown of tunnel lining together with water inrush has caused total disruption of traffic operations resulting in necessary comprehensive rehabilitation of the tunnel. Almost 50% of the original brick support lining has been replaced by 50-cm thick reinforced concrete arches. In order to monitor the efficacy of both the new and the old support systems, a new special monitoring method was applied, using a perimeter bar extensometer incorporating fibre optics strain sensors together with an automatic convergences data acquisition and processing system for detecting abnormal roof displacements.

The paper is concerned with the hydrogeological appraisal of the proposed mining operations in the Thar Lignite field in Sindh, Pakistan containing lignite reserves >9 billion tonnes. The presence of three main aquifers surrounding three lignite seams induces pore pressure in the rock mass making the high wall slopes potentially unsafe. In order to dewater the surrounding rock mass before commencing mining excavations groundwater inflow predictions were carried out using a SEEP/W finite element software package. The simulation results for the three aquifers are presented indicating that the relative error of estimation between analytical and the numerical solutions vary from 3.4 % to 6.4%.

The effect of strain rate on mechanical properties has been reported in literature for some types of rock using uniaxial compression tests. In this paper, the authors investigated the phenomena of strain rate dependency of strength and stiffness in a silty mudstone, from the coal measure rocks of the UK. Using multistage triaxial testing, a series of experiments were conducted on both intact and fractured rock samples to cover the two ultimate structural conditions of the rock mass. The results showed that the rate-dependency of strength and stiffness is particularly significant in the fractured samples and this dependency varies according to the level of confinement.