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- PublicationRetaining wall behaviour in Dublin's estuarine deposits, IrelandPractising engineers in the Dublin, Ireland, area have much experience in dealing with the boulder clay which underlies much of the city. However, significant deposits of estuarine soils, some of them soft, exist along the east side of the city and in particular in Dublin docklands. Some construction difficulties have previously been encountered in these materials and significant developments, including a large tunnel project, are planned in the area overlying these deposits. Few published data exist on retaining wall schemes in the deposits. Data from nine sites, including three detailed case histories, are presented which confirm that construction of deep propped excavations and cantilever walls up to 7·5 m are feasible in these deposits and can perform well. A key issue is the soil that is located at excavation level and competent deposits here are essential to prevent large displacements or possible instability. The resulting movement will also be sensitive to the overall system stiffness. There seems to be scope for more efficient future design, including more use of cantilever walls, particularly for temporary works purposes. Beam-on-spring type computer analyses tend to give conservative results for these deposits and more sophisticated finite-element analyses may be warranted for future schemes.
1484Scopus© Citations 11
- PublicationRetaining wall behaviour in Dublin's fluvio-glacial gravel, IrelandPractising engineers in the Dublin, Ireland, area have significant experience in dealing with the Boulder Clay which underlies much of the city. However, the 45 m deep buried pre-glacial channel north of the River Liffey is infilled with fluvio-glacial deposits which behave very differently from an engineering point of view. Case history data from eight sites and a detailed examination of the retaining wall behaviour at two of the sites show that retaining wall movements appear to be governed by system stiffness (i.e. a combination of wall stiffness and support configuration). It seems that relatively simple beam–spring type computer programs will provide data for reasonably accurate designs of retaining walls for basements of up to two levels. Input parameters such as K 0, φ‘ and soil stiffness need to be carefully specified. Groundwater inflows can be significant but can be dealt with by providing a good cut-off into the underlying glacial till or bedrock and by conventional pumping techniques. Geophysical techniques such as multichannel analysis of surface waves, S/P waves and resistivity can be very useful for the determination of soil properties, such as degree of saturation, density and stiffness, and for material characterisation (i.e. distinguishing the presence of these materials in contrast to the Boulder Clay).
590Scopus© Citations 13
- PublicationRetaining walls in Dublin Boulder Clay, IrelandA 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 excavation induced 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.
1017Scopus© Citations 19