This paper describes, from field exposures, temporary excavations and borehole core, the pedogenically altered fluvial deposits found in the UAE termed the Barzaman Formation. This formation comprises a sequence of rocks dominated by variably cemented conglomerates thought to be middle Miocene to Pliocene in age. The sequence is interpreted as an alluvial fan succession (or "bajada") laid down in response to uplift and erosion of the Hajar Mountains. A ground model for this formation is described to explain the distinct lithological features of the formation, comprising terrestrial fluvial and alluvial plain deposits that have been modified by cementation and dolomitisation, duricrust formation and pedogenic processes during arid periods over repeated climatic cycles. Four principle lithologies thus typically occur as a rhythmic alternation of a basal conglomerate (composed predominantly of clasts of ophiolite and chert) overlain by an irregular bed of white conglomerate and "calcisiltite" and passing upwards into a pale grey to green clay and siltstone "breccia". The white conglomerate and calcisiltite largely represent deposits of dolomite-palygorskite duricrust. The well established Clarke & Walker (1979) descriptive scheme currently used for describing the formation is reviewed and a simple visual descriptive lithological classification proposed. The classification is described in terms of the three principal lithological components visible in hand specimen: mottled white calcisiltite matrix/cement, palygorskite rich marl and clasts derived from the Oman Mountains (gabbro, chert and weathered ultramafic rock). Data on the mineralogy and microstructure of the rock constituents is also presented and some implications for geotechnical characterisation of the formation briefly discussed.

Realistic finite element (FE) modelling of the tunnel construction process has been restricted by the computational effort needed to incorporate the three-dimensional (3D) aspects of the tunnelling operation. Two-dimensional (2D) plane-strain models have therefore been widely adopted by practitioners and researchers in their studies of the effects of tunnelling. However, 2D modelling suffers the drawback whereby a volume loss must be assumed at the outset as the input for the FE model. This paper presents an analysis of measured surface ground movements induced by a sprayed concrete lined tunnel in London Clay. This was achieved using computationally efficient, non-linear, 3D modelling and Oasys LS-DYNA software. By modelling the problem using a non-linear small strain BRICK soil model, which incorporates anisotropic behaviour, good agreement with the actual Gaussian distribution of surface settlement was obtained. This was achieved without any initial assumptions regarding volume loss, but rather by realistically modelling the excavation sequence and time-dependent gain in lining strength. On the basis of this work it is considered that 3D modelling techniques can provide an effective means to estimate ground settlement and the associated effects on nearby structures, without dependence on empirical methods alone.

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This paper describes a geological model for the ‘conglomeratic carbonate siltstone’, otherwise known as the Barzaman formation, which comprises the principal founding stratum for deep structures in coastal Dubai, UAE. It identifies and highlights some important considerations for future engineering works in this stratum. A brief review of the geology and geotechnical characteristics of the stratum is provided, followed by a discussion of recent work on those aspects of the mineralogy and geotechnical properties that indicate potential constraints to future development.