This paper attempts to synthesise available information in parallel with recent work by Skipper et al (2005), who provide an updated understanding of the geology of the DBC.Having assessed the effects of sampling disturbance, the paper characterises the various formations and sub-units of the DBC. The interpreted material behaviour is related to observed engineering performance. It was found from the behaviour of earth retained structures that intact, clayey, DBC formations are 2 to 3 times stiffer than assessed from high quality laboratory tests on block samples. DBC is shown to be significantly stiffer than other well-characterised tills. Relatively inexpensive Multi Channel Surface Wave techniques (MASW) can give very reliable estimates of in situ small strain stiffness. High undrained triaxial compression strengths were measured and it appears that simple UU tests on high quality specimens give good results. Significant strength anisotropy was suggested by undrained triaxial extension strengths that were only 30% to 50% of the triaxial compression strengths. Field horizontal permeability values of the intact clayey till units have a representative mean of about 10 -9 m/s and when compared to laboratory values suggest that the material may exhibit some degree of anisotropy of permeability.Overall, the measured engineering parameters for the DBC are favourable for many construction projects. Further work is required in order to understand the in situ horizontal stress profile and the stiffness anisotropy of the till. From an associated wealth of borehole investigations, in-situ tests, laboratory tests, excavation exposures and monitored field performance, these projects have provided much more detailed information on the superficial deposits in Dublin.Technical data are now available from a concentration of such projects in Dublin, but these are not in the public domain and have not been interpreted and correlated on a (geological) formation-level scale. There are significant economic benefits in understanding the characteristics of the DBC as it underlies much of the city, see Figure 1. A parallel study is reported by Skipper et al (2005), which provides a more detailed understanding of the geology of the DBC, and serves as a backdrop to this paper.Much of the data are from the Dublin Port Tunnel Project (DPT, Site 1), which has been augmented by information from other important developments, as listed below and shown in Figure 1. Site 1: Dublin Port TunnelThe central part of the DPT project comprises 12m external diameter twin bored tubes, with lengths of cut and cover tunnel at either end. The project involves the excavation of about 1.5 million cubic metres of soil and rock. Although project wide information is 4 considered, focus in this paper is placed on experience gained at the northern cut and cover section and shaft WA2, where excavations were carried out in the superficial deposits to about 25m depth, see Figure 1. Further details of the project and a review of case histories associated with it ar...

This paper presents a case study of the Bolu highway twin tunnels that experienced a wide range of damage during the 1999 Duzce earthquake in Turkey. Attention is focused on a particular section of the left tunnel that was still under construction when the earthquake struck and that experienced extensive damage during the seismic event. Static and dynamic plane-strain finite element (FE) analyses were undertaken to investigate the seismic tunnel response at two sections and to compare the results with the post-earthquake field observations. The predicted maximum total hoop stress during the earthquake exceeds the strength of shotcrete in the examined section. The occurrence of lining failure and the predicted failure mechanism compare very favourably with field observations. The results of the dynamic FE analyses are also compared with those obtained by simplified methodologies (i.e., two analytical elastic solutions and quasi-static elastoplastic FE analyses). For this example, the quasi-static racking analysis gave thrust and bending-moment distributions around the lining that differed significantly from those obtained from full dynamic analyses. However, the resulting hoop stress distributions were in reasonable agreement.

The ground investigation and construction for the North Cut and Cover Section of the Dublin Port Tunnel (north Dublin, Co. Dublin, Ireland) involved high resolution ground investigation and excavation logging. As a result, our interpretation of the glacially derived Quaternary geology encountered presents a more complex picture than previously described. A detailed description of the stratigraphy and lithology of the glacial deposits formerly known as the ‘Dublin Boulder Clay’ is presented, and palaeoenvironmental interpretations are suggested for the various units. The ‘Dublin Boulder Clay’ is reinterpreted to comprise four major units and associated subunits. Possible construction hazards, including discontinuities, lithological variability, glacio-tectonic rafting and the presence of large water-bearing units, are identified and linked with the stratigraphy. Preliminary data on the geotechnical and engineering behaviour of each unit are presented. The encountered lithologies generally demonstrated high in-situ strength and stiffness but low permeability and plasticity.

This paper compares simple constitutive models that are widely used in engineering practice with more sophisticated methods in the context of a case study. In particular, four constitutive modelling approaches have been considered: a simple elasto-plastic constitutive model (modified Cam-clay), with and without Rayleigh damping; the same model coupled with a cyclic non-linear model that can simulate pre-yield hysteresis; and finally an advanced kinematic hardening model, which is an improved version of the Al-Tabbaa & Wood two-surface model. These four approaches are used to analyse the seismic response of a section of the Bolu tunnels during the 1999 Duzce earthquake. To shed light on the performance of the constitutive models, simple site response finite-element analyses were first undertaken for the studied site, paying particular attention to the calibration of the Rayleigh damping parameters. The results of these analyses, in terms of maximum shear strain, were then used as input to an analytical elastic method (extended Hoeg method) for calculating the thrust and bending moment acting in the tunnel lining. Finally the results of dynamic time domain plane-strain analyses, employing the four adopted constitutive modelling approaches, are compared against field observations and results obtained by the extended Hoeg method, to investigate the ability of the models, of ranging complexity, to mimic soil response under seismic excitation. On effectue enfin une comparaison des résultats des analyses dans le domaine temporel de la déformation sur un plan, faisant usage des quatre méthodes de modélisation constitutives adoptées, avec les résultats obtenus à l'aide de la méth-ode étendue de Hoeg, pour examiner la capacité pour des modèles de complexité variable de simuler la réaction des sols à une excitation sismique. INTRODUCTIONUnderstanding the behaviour of geotechnical structures such as tunnels, earthfill dams and retaining walls during earthquakes is recognised as a necessary condition for their rigorous and safe seismic design. In order to predict the seismic response of these structures correctly, it is essential to develop and use constitutive models that can simulate soil behaviour appropriately under dynamic loading. Numerical analysis has developed significantly over the last decades, and nowadays a wide range of constitutive models is available. Equivalent linear models and simple non-linear models are used with acceptable accuracy for situations involving small to medium strains, whereas for higher strain levels coupling of a non-linear model with an elasto-plastic model, or the use of more advanced models, is needed. However, not all of the above-mentioned types of models are available in commercial codes. Therefore in engineering practice very simple elasto-plastic models (e.g. Mohr-Coulomb and/or

A good number of deep excavations have been recently completed in Dublin Boulder Clay, Ireland. These have included propped walls up to 25 m deep and permanent cantilevers 7 . 5 m high. Experience elsewhere in the world was used to design and construct these walls. However, case history data have shown that the behaviour of the walls in Dublin Boulder Clay is very rigid and much stiffer than comparable systems worldwide. It appears this behaviour is due to the inherent natural strength and stiffness of the soil and the slow dissipation of excavationinduced depressed pore pressures or suctions. There appears to be scope for developing more efficient designs and in particular for reducing propping requirements. For temporary works, the use of undrained parameters in serviceability limit state calculations together with implementation of the observational approach on site could be considered for future schemes. IntroductionOver the previous 15 years, economic growth in Ireland has led to an increase in the use of underground space, with some developments now including four underground levels. Valuable full-scale data have been obtained from a good number of these projects. The purpose of this paper is to provide an overview of aspects relating to the design, construction and behaviour of retaining walls in Dublin Boulder Clay. Specifically the paper will j briefly review the background geology and ground conditions j outline the presently used design approach j review in detail the general behaviour of walls in Dublin Boulder Clay by reference to four case histories namely: j lightly supported 'regular' wall for 6 m excavation at Leinster House where pore water and earth pressure changes were measured in additional to regular monitoring j 7 . 5 m excavation for relatively highly stressed anchored wall at Trinity College Library j 7 m cantilever wall excavation at Ballycullen Road where monitoring information for some six years is available j 17 . 5 m excavation at the northern cut and cover section of the Dublin Port Tunnel project, which is among the deepest excavations carried out in Dublin to date j present an overall summary of the behaviour of retaining walls in Dublin Boulder Clay compared to similar support systems worldwide j provide some overall conclusions and recommendations for the design and construction of future similar schemes.An exception to the general cover of Dublin Boulder Clay is an area north of the city centre where an old channel of the River Liffey has been infilled with fluvio-glacial sands and gravels. This period has also seen the development of marginal sites, for example areas of Dublin docklands, built on recent filling over soft alluvial soils to reclaim land. These sites previously would have been considered unsuitable for deep basement construction. Issues relating to the design, construction and performance of walls in these two areas are the subject of two separate papers by Long et al. (2012aLong et al. ( , 2012b. Background geology, ground conditions and soil parametersBedrock...