PRACTICAL CONSTRUCTION CONSIDERATIONS FOR RUNWAY EXTENSION AND TAXIWAY EXPANSION OVER SOFT/ORGANIC SOIL USING A COLUMN-SUPPORTED LOAD TRANSFER PLATFORM-Paper

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The paper describes the design and construction of a column-supported load transfer platform (LTP) for extending runways and widening taxiways at a municipal airport in Marshfield, Massachusetts. The work crossed wetlands underlain by very soft organic soils, with groundwater near the surface. Environmental limits prevented excavation beyond the construction footprint, while the pavement transitions required negligible post-construction settlement.<br /><br />After considering soil improvement, excavation and replacement, and preloading, the project team selected timber piles to support an LTP. More than 2,000 piles supported approximately 5,500 square yards of platform. The design followed BS 8006-1:2010 and used a square pile grid at 5-foot spacing, 2-by-2-foot pile caps, and two high-strength uniaxial geotextile layers oriented perpendicular to one another. An aggregate layer separated the geotextiles; the reinforced layers transferred embankment and pavement loads to the piles. Design considerations included limiting geotextile strain, providing adequate anchorage, protecting the reinforcement from pile-cap edges, and meeting strict construction tolerances.<br /><br />The authors emphasize that full-time engineering oversight was essential. Inspectors monitored pile locations and installation, pile-cap dimensions and alignment, sand-cushion thickness, geotextile condition and placement, overlaps, and aggregate compaction. They identified and corrected issues while materials remained accessible, reducing the risk of defects that would be difficult to repair after paving.<br /><br />Settlement monitoring during construction showed negligible movement of the upper geotextile. The aggregate achieved the specified 100% compaction, and no measurable or observable settlement was identified after construction. Nearly two years later, airport staff had observed no noticeable runway pavement deformation. The authors conclude that the BS 8006 design method produced a reliable system and that detailed engineering oversight helped protect its intended performance.

Keywords

load transfer platform

timber piles

airport runway extension

taxiway widening

soft organic soils

wetlands construction

geotextile reinforcement

BS 8006-1:2010

settlement monitoring

engineering oversight