This is the published version of the paper.This version of the publication may differ from the final published version. This research concerns the influence of ribs on the ultimate capacity of a bored pile in overconsolidated clay. Ribbed bored piles are known to give increased shaft capacity in comparison to conventional straight-shafted bored piles. The investigation seeks to explore the effectiveness of ribs at increasing the ultimate capacity of a pile, and furthermore to understand how this enhanced capacity is derived. The scale pile test results are analysed using several industry standard methods. A plastic failure envelope for the base of the pile rib is identified. This plastic failure envelope is used to provide a detailed design solution for the ultimate capacity of a ribbed pile. The design solution is simple and requires a summation of the constitutive contributions from each rib and from the base and shaft of the pile. This method has been used successfully to predict the ultimate capacity of any pile tested to within ±8%.
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The construction of deep basements in urban areas is associated with many risks and problems among Which is the possible damage to existing structures and services resulting from settlements near the excavation. A number of methods are routinely employed to attempt to control these movements (e.g. top-down construction, use of stiff diaphragm walls). This paper discusses the methodology and practicalities of a series of centrifuge model tests designed to investigate the effect of deep basement construction. Two sets of experimental apparatus are described in detail and their effectiveness in terms of robustness and generation of repeatable data are assessed. It is shown that using relatively simple techniques and equipment it is possible to model many of the features associated with top-down construction.
This is the accepted version of the paper.This version of the publication may differ from the final published version.
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AbstractThis paper describes the concept and field testing of a 1200mm diameter x 30m deep hollow cast in situ rotary bored pile foundation. The aim of the foundation is to allow large diameter piles to be constructed using less concrete than in an equivalent conventional solid pile and with a view to allowing reuse at a later date. Reuse is made possible because the hollow core of the pile allows access for inspection after demolition of an existing structure. The new piles may also allow modification to enhance load capacity by augering through the base and extending their length. In addition, the piles are better suited than conventional piles for use as 'energy piles' to allow environmentally friendly heating and cooling. The geotechnical performance of the hollow test pile was comparable with a conventional solid pile constructed during the same trial. Details of construction are given including lessons learned.• A list of notations, defining all of the symbols used.•
An 8·2m diameter, 40m deep shaft for Crossrail is being constructed below the 10m deep basement of the Moorhouse development near Moorgate in the City of London. The depth of the shaft is such that it will penetrate through stiff London Clay and will be founded at the bottom of the Lambeth Group. The shaft is being constructed after the Moorhouse structure has been completed and the design of the Moorhouse foundations places tight constraints on acceptable ground movements due to construction of the shaft. Furthermore, the shaft needs to be designed to accommodate future ground movements associated with construction of Crossrail. The paper describes the complex relationship between the foundations of Moorhouse, the draught relief shaft and the future Crossrail assets. The optimised design includes extensive slip coating and base grouting of the Moorhouse piles, a complex temporary works dewatering system around the shaft and the option to carry out additional dewatering from within the shaft during construction. Control of ground movements through the Lambeth Group was perceived to be a particular problem in relationship to destressing the ground around the Moorhouse piles. To prevent longterm settlement of these piles, provision was made for radial grouting to “restress” the ground should the need arise.
This is the accepted version of the paper.This version of the publication may differ from the final published version. that support Moorhouse and the presence of these foundations placed tight constraints on acceptable ground movements associated with construction of the shaft. The depth of the shaft is such that it penetrates through stiff London Clay and is founded at the bottom of the Lambeth Group. The paper describes the contingency measures to deal with potentially difficult ground conditions including the water bearing layers of the Lambeth
Permanent repository linkGroup. The construction processes included a complex temporary works dewatering system around the shaft with the option to carry out additional dewatering from within the shaft during excavation. Provision was also made for radial grouting to "restress" the ground, to prevent long-term settlement of the Moorhouse piles, should the need arise. The success of the project was due, in no small part, to the detailed planning and consideration of contingency measures to deal with perceived risk.
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