The central pillars of a bridge belonging to a recently built high-speed railway line experienced an unexpected and continuous heave after the end of construction. Pillars were founded on 3 × 3 pile groups capped by a rigid slab. The tips of piles supporting the central pillars reached a hard Tertiary anhydritic claystone. Deep extensometers allowed the identification of an active layer, 12–15 m thick, located below the pile tips. Observations in recovered cores suggest that the heave is induced by the growth of gypsum crystals in discontinuities of the anhydritic claystone. No heave was observed in gypsum-rich claystones located above the anhydritic layer. Gypsum crystal growth is associated with dissolution of anhydrite and subsequent precipitation from a super-saturated aqueous solution. Boreholes and pile construction allowed a hydraulic connection of upper aquifers and the lower anhydritic formation. This hypothesis explains the role of the bridge construction in the triggering of a dormant heave phenomenon. The heave rate has been reduced to a small value by the weight added by an embankment 33 m high, which partially fills the original valley.

The ultimate earth resistance for a group of two side-by-side piles that are laterally loaded in clay is investigated using four different methods of analysis: three numerical (the displacement finite-element method, and the upper- and lower-bound finite-element limit analysis methods) and one analytical (an analytical upper-bound plasticity method developed in this paper). The results of the three numerical methods are shown to be in excellent agreement, while the analytical solution presents a theoretical upper bound that is very close to the numerical results. The results of the analyses are used to identify the predominant failure mechanisms for different pile spacings and pile–soil adhesions. They are also used to develop a design chart and design equations for determination of the ultimate lateral bearing capacity factor.

An existing 15·5 m high main dam embankment at Abberton Reservoir in Essex was completed in August 1938, since when its performance has been satisfactory. However, the upstream embankment shoulder of the original dam suffered a deep-seated failure through its foundation towards the end of construction in July 1937, 9 days before a similar and well-known failure occurred at Chingford Reservoir in close proximity to Abberton. Whereas the failure at Chingford became an important case in the history of soil mechanics through the involvement of Karl Terzaghi and marked one of the first applications of modern soil mechanics principles, the failure at Abberton has remained largely unknown, until recently when raising of the existing dam started to be considered. This paper describes advanced finite-element analyses which were carried out to investigate the failure of the original dam at Abberton and the stability of the existing main dam. The parameters used in the constitutive models were derived on the basis of the available site investigations and laboratory testing and on experience in the back-analysis of other failures in London Clay. The analyses demonstrated that the upstream shoulder of the original embankment failed through the mechanism of progressive failure, which involved the top of the stiff plastic London Clay rather than the overlying alluvium in the foundation. The relatively rapid rate of embankment filling, achieved by using modern earth-moving equipment, contributed significantly to the original dam failure. The analyses also demonstrated satisfactory behaviour of the existing dam during reconstruction, the first impounding and in the long term, with its response being similar to that observed. Thus the constitutive models used and parameters derived were successfully calibrated against the observed behaviour of both the original and existing main dams at Abberton, and could be used in predicting the behaviour of the dam during and after its proposed raising.

Increasing the speed and frequency of trains with the same static axle weight imparts higher dynamic axle loads more frequently. When this occurs on existing track which has not been designed for such loading there can be increased rates of ballast degradation, characterised by unacceptable deformation and lateral spread, leading to more frequent requirements for track maintenance. Recent studies carried out at the University of Wollongong highlighted that confining pressure and frequency have a significant influence on the permanent deformation and degradation of ballast. However, confinement required to keep the deformation and degradation of the ballasted track to an acceptable limit will depend on the train speed (frequency). In this context, a series of cyclic triaxial tests was conducted on latite basalt samples having an initial confining pressure of 120 kPa. After every 25 000 cycles, the confining pressure was decreased in steps to simulate the drop of confining pressure during heavy traffic. This test procedure was adopted to replicate the influence of train speed on the stability of ballast. Test results indicated that both the frequency and confining pressure have a significant influence on the permanent deformation of ballast. Resilient modulus is found to increase with an increase in confining pressure and number of cycles, but to decrease with increasing frequency. The results also showed that the ballast layer requires a minimum level of confinement for preventing an excessive amount of track deformation. An empirical equation is formulated to determine the required confining pressure and resilient modulus of the ballast layer for an allowable limit of track deformation at a given train speed.

Both plugged and coring behaviours are normally considered when analysing pile drivability. However, several authors challenge the idea that pipe piles can always plug. These views are argued partly on experience and engineering judgement, and partly on measured (although often proprietary) data. This paper proposes a new, objectively calculable criterion to determine whether a pile will plug during driving. The criterion is shown to agree with engineering judgement and be relevant to published data.

This paper describes recent advances in stability analysis that combine the limit theorems of classical plasticity with finite elements to give rigorous upper and lower bounds on the failure load. These methods, known as finite-element limit analysis, do not require assumptions to be made about the mode of failure, and use only simple strength parameters that are familiar to geotechnical engineers. The bounding properties of the solutions are invaluable in practice, and enable accurate limit loads to be obtained through the use of an exact error estimate and automatic adaptive meshing procedures. The methods are very general, and can deal with heterogeneous soil profiles, anisotropic strength characteristics, fissured soils, discontinuities, complicated boundary conditions, and complex loading in both two and three dimensions. A new development, which incorporates pore water pressures in finite-element limit analysis, is also described. Following a brief outline of the new techniques, stability solutions are given for several practical problems, including foundations, anchors, slopes, excavations and tunnels.

The paper describes the expansive phenomena affecting Lilla tunnel in Spain during construction and subsequent operation. The geology of the site and the performance of alternative support designs are described. Field observations are analysed to identify the causes of the observed swelling. It was found that long-term swelling in Lilla tunnel was the result of gypsum crystal growth in discontinuities. The phenomenon was a consequence of a few contributing factors: significant presence of anhydrite, existent or activated discontinuities, and the circulation of water. These conditions were present in the highly tectonised Tertiary claystone in Lilla. The original horseshoe cross-section was transformed into a circular one, and a reinforced concrete lining was built to resist swelling pressures. Long-term monitoring of the reinforced tunnel provided valuable data on the evolution of swelling pressures against the lining, and on the stresses developed in the resisting structure. The highly heterogeneous distribution of swelling pressures against the lining explains the low strains measured in reinforcement bars despite the very high maximum swelling pressures recorded.

This paper examines the performance of unsaturated soils under repeated loading. As part of the research, a triaxial system was developed that incorporates small-strain measurements using Hall effect transducers, in addition to suction measurements taken using a psychrometer. Tests were conducted on samples of kaolin under constant water mass conditions. The results address the effects of compaction effort and water content at the time of compaction on the overall performance of unsaturated soils, under different amplitudes of loading and different confining pressures. The results show that suction in the sample reduced with increasing number of loading cycles of the same magnitude. The resilient modulus initially increased with increasing water content up to approximately optimum water content, and then reduced substantially with further increase in water content.