An experimental study has been carried out as part of a wider programme of research in order to examine some of the physico-mechanical properties of the Jiaozuo Sandstone after exposure to extremely high temperatures. The mechanical properties of the rock under examination are discussed before the results of the thermo-mechanical response of the sandstone are presented and analysed. The range of temperature to which the sandstone has been exposed is 20-1,200°C. The physical properties considered include the shape, volume, mass and density changes and the velocity of longitudinal and transverse elastic waves through the samples, before and after exposure to high temperature. The mechanical properties considered include the stress-strain response, the uniaxial compressive strength, the modulus of elasticity and the Poisson's ratio. The results are analysed and discussed and possible mechanisms for the observed thermomechanical response, are postulated.

In order to observe the impact of different water compositions on sludge dewaterability, assessments of floc sizes using a particle size analyzer and of sludge dewaterability based on the capillary suction time (CST) test were carried out. Synthetic raw water had small floc sizes, and synthetic domestic wastewater had both larger median floc sizes and a better correlation between sludge dewaterability and median floc sizes. The floc size distribution results showed that synthetic raw water is associated with a narrow particle size distribution. In comparison, synthetic domestic wastewater produced a wider distribution. However, the CST values were similar for both waters. Compared to synthetic wastewater, natural wastewater had the largest distribution with generally larger particle sizes.

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An historical review of the geotechnical behaviour of the Northwich Rock Salt is presented as a forerunner to a numerical modelling analysis of the current stability of the Winsford salt mine, Cheshire. Extensive laboratory and in situ tests have been historically undertaken by the mine to characterise the strength and stiffness behaviour of the rock salt. Recent proposals to store waste within the Bostock No. 5 panel of the mine have lead to increasing concerns as to the current stability of the workings, as well as to the long term stability of the mine. This present study uses the wealth of geotechnical data to assess the current mine stability using numerical modelling techniques and validates the results against in situ roof to floor convergence data. The results indicate that the mine structures are stable. Convergence simulation using the numerical model compare favourably with the in situ monitoring data allowing greater confidence to be placed in future predictions.

The hazards associated with the possible collapse of old mine workings underlying an active landfill site in northeast England have been identified as a significant concern to both the regulatory authorities and to the landfill operator. A quantitative assessment of the hazards and their perceived risks to the integrity of the composite lining system in place beneath the landfill has been undertaken using a combination of field observation, established mine subsidence prediction tools and numerical modelling techniques. Field observations have identified the presence of extensive fissuring within the limestone underlying the site, however, it is difficult to assess the extent to which mining has contributed to the development of these features. In light of this, an influence function technique has been used to attempt to predict the degree of fracturing that could have been experienced at the surface due solely to mining, with the intention of illustrating whether the scale of movements on pre-existing joints could be attributed to mining subsidence. The results of this analysis have subsequently been used within a finite-difference numerical model to assess the effect that a fracture of the scale predicted would have on the composite lining system.

The most significant operational cost in a treatment plant is related to the dewatering and disposal of sludge. In this research, different shapes of mixers (radial, axial, wheel, three-blade and magnetic) have been tested to assess their influence on sludge dewaterability testing. As well as the shape of mixers, different rapid mixing velocities, rapid mixing times and coagulants also have been used as test parameters. The capillary suction time (CST) test apparatus was used as a rapid measure to assess sludge dewaterability. Findings indicate that the use of magnetic stirrers leads to the lowest sludge dewaterability properties tested using the CST. The magnetic stirrer produced greater vortex and turbulence compared with other types of mixers, so rapid contact between the coagulant and the water occurred. The use of the other mixers produced similar results. However, the application of different coagulants results differently regarding the sludge dewaterability, when using different rapid mixing velocities. Different rapid mixing times did not lead to differences in the CST. During rapid mixing, Moringa oleifera produced the highest CST values followed by alum and ferric. This is likely due to the difference in sludge volume that is produced by each coagulant. Only M. oleifera produced contaminant agglomerates. In comparison, alum and ferric produced contaminant agglomerates and coagulant hydrolysis products.

The stability problems associated with a shallow, room and pillar ironstone mine have been analysed in detail using established, empirical approaches. Initial analysis centred on elastic beam theory and pillar strength formulae to establish the factor of safety against roof beam and pillar failure, respectively. The pillars have been shown to be inherently stable; even those that have been subsequently reduced in size as a result of pillar splitting have safety factors in excess of 3. The roof has been shown to be unstable using an elastic beam analogy, which is corroborated by the extensive surface damage. Confidence in the application of such approaches is shown to be difficult due to the lack of knowledge relating to the effects of time on mine stability; increased weathering of the mine structures may lead to weakening and ultimately failure at lower stresses than determined through the mine design approaches. Clearer definition of the rock mass behaviour is required in order to advance such techniques as valid approaches for the analysis of abandoned mines. However, the paper also highlights how such approaches are valid where failure mechanisms are well defined and understood. Probabilistic risk analysis has also been considered as an alternative approach. From a surface developer's perspective, such approaches are more useful.Résumé Des problèmes de stabilité, en rapport avec une mine de fer peu profonde exploitée par chambres et piliers, ont été analysés en utilisant la théorie des poutres élastiques et des formules de résistance des piliers. Ainsi, des facteurs de sécurité ont été définis respectivement pour la stabilité du toit et pour la stabilité des piliers. Les piliers s'avèrent fondamentalement stables. Même ceux dont la taille avait été significativement réduite, du fait du phé-nomène d'écaillage, ont un coefficient de sécurité supérieur à 3. Le toit s'avère instable d'après la théorie des poutres élastiques, conclusion corroborée par les dommages de surface résultant du développement de nombreux fontis. Bien que la confiance dans de telles approches est probléma-tique du fait que le facteur temps et les processus d'altération associés ne sont pas pris en compte, l'article met en lumière leur intérêt pour des situations où les mécanismes potentiels de rupture sont bien définis et compris. L'analyse probabiliste du risque est considérée comme une autre approche des techniques d'analyse de stabilité.

There is a large number of masonry arch bridges on the rail networks in Europe and other parts of the world. However, the mode of response of masonry arch structures subjected to railway loading is little understood. To address this, an experimental study involving large-scale physical models of backfilled masonry arch bridges subjected to railway loading conditions was conducted. The study explored the influence of the rail track–bed system on bridge behaviour and load-carrying capacity. The tests results indicated that the track–bed system fundamentally alters the mode of response of the bridge system and significantly increases load-carrying capacity. Using the same test facility, load tests were also used to explore and characterise the behaviour and performance of damaged arch bridges. The results obtained suggest that, although there is likely to be a reduction in overall capacity, even a significantly damaged arch bridge can still perform adequately under loading. This has important implications for bridge owners and assessment engineers.