REPLACING TOP LAYER OF SOFT CLAY WITH COMPACTED ENGINEERING FILL TO IMPROVE THE LATERAL CAPACITY OF PILES-Paper

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The paper examines a method for improving the lateral capacity of piles supporting two 89 m-diameter LNG storage tanks at a coastal site in Odisha. The site was formed using seabed dredgings and had soft clay extending to about 20 m. The tanks are supported by 436 bored cast-in-situ piles each, 1,200 mm in diameter and 58–63 m long.<br /><br />Structural analysis required each pile to resist a 534 kN lateral load under free-head conditions. Analysis using the existing soil properties predicted 106 mm of deflection, exceeding the 75 mm allowable limit; the estimated lateral capacity was insufficient for design requirements.<br /><br />To strengthen the soil around the upper pile lengths, the project replaced the top 3 m of soft soil with engineered granular fill (crusher run/GSB). The fill was laid over geotextile in 150 mm compacted layers, each achieving at least 98% of the specified heavy-compaction density.<br /><br />An initial lateral load test applied up to 1,335 kN—2.5 times the design load—and recorded a maximum deflection of 76.06 mm, within the project’s 125 mm test limit. The test results were used to derive equivalent fill properties for further L-pile analysis: a unit weight of 23.3 kN/m³, friction angle of 38°, and subgrade reaction modulus of 57,015 kN/m³. Initial and routine load tests confirmed the improvement.<br /><br />The study concludes that replacing weak near-surface soil with well-compacted engineered fill to a depth of 3 m can increase pile lateral capacity and help meet design requirements for heavily loaded structures.

Keywords

lateral pile capacity

LNG storage tanks

soft clay improvement

engineered granular fill

bored cast-in-situ piles

lateral load test

pile deflection

geotextile reinforcement

subgrade reaction modulus

coastal Odisha site