Modification in Current BRE Approach for Designing Pilling Rig Working Platforms on Soft Subgrades-Paper

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The paper proposes modifying the BRE BR470 method for designing geogrid-reinforced working platforms for piling rigs on soft ground. The existing method models platform failure as punching shear and accounts for geogrids mainly through their tensile strength. According to the authors, this overlooks geogrid–aggregate interaction and therefore can produce overly conservative designs.<br /><br />The proposed modification incorporates the increased shear strength and internal friction angle of the reinforced aggregate, reflecting the lateral confinement and interlocking provided by the geogrid. Large-scale laboratory tests found improved bearing capacity and reduced deformation in reinforced sections. Field monitoring of a crane platform also recorded low geogrid strain (maximum 0.48%) and settlement of about 9.5 mm, supporting the importance of reinforcement stiffness at low strain. The field results were used to validate a numerical model and the revised approach.<br /><br />The authors report that the modification can reduce platform thickness by 50–75% compared with an unreinforced design, and by 35–70% compared with current reinforced-platform approaches. In a Northshore Hamilton case study, the revised design reduced costs by more than 40% against the unreinforced option and over 12% against the original reinforced design.<br /><br />The method relies on improved shear parameters established through testing, and its results may vary with the geogrid and aggregate used. Designers should therefore use relevant product-specific evidence and ensure reinforcement is distributed through the platform.

Keywords

BRE BR470

geogrid reinforcement

working platform

piling rigs

soft ground

punching shear

bearing capacity

shear strength

aggregate interlocking

lateral confinement