Special Applications of Micro Piles for Construction of a Bridge Well Foundation-Paper

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The paper describes the design and construction of a circular micropile retaining wall for deep excavation around the caisson foundations of two railway bridges at T49A, Sumbar, Jammu and Kashmir. The work formed part of slope stabilization for the Banihal–Katra Railway project, in a seismically active Zone V area with weathered-to-fresh quartzite bedrock and significant landslide hazards.<br /><br />The initial square micropile-and-anchor proposal was revised to a circular wall to provide a secure working area for constructing the bridge piers’ well foundations. The system used 273 mm-diameter micropiles at approximately 475 mm centres, embedded at least 4 m into the ground. A 750 × 750 mm reinforced-concrete capping beam connected the piles at the top. As excavation proceeded in stages, paired ISMC 150 steel waler sections and self-drilling anchors provided additional lateral support.<br /><br />Design involved calculating active and passive earth pressures with GEO5, then modelling the piles, capping beam and walers in STAAD. Checks included construction surcharges, wheel and crane loads, structural stresses and deflections. The reported maximum wall deflection was 10.676 mm, below the 73.33 mm allowable limit; the differential deflection between waler levels was also within the stated limit.<br /><br />Construction used ODEX drilling through overburden and down-the-hole drilling into hard strata. Permanent casing, reinforcement cages and M35 concrete or grout formed the micropiles. Excavation then proceeded in stages, with the capping beam and successive waler-and-anchor levels installed as required. The completed circular wall served as temporary formwork and ground support during construction of the well foundations.

Keywords

micropile retaining wall

deep excavation

circular retaining wall

railway bridge foundations

slope stabilization

Banihal-Katra Railway

seismic Zone V

quartzite bedrock

self-drilling anchors

construction deflection