Basement Excavation: Cost Effective Retention System for a Multi Storeyed Structure-Paper

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The paper presents a cost-effective foundation and earth-retention solution for a multi-storey residential building in Chennai, where restricted urban space made open excavation impractical. The project required heavy-load foundations and a 168 m-long retaining system for basement excavation reaching approximately 10 m below finished ground level.<br /><br />Because the near-surface soils could not support the building’s estimated column loads of 150–350 tonnes, 600, 750 and 900 mm diameter bored piles were installed, socketed 3 m into competent siltstone. The retention system combined contiguous bored piles (CBP), vertical grout columns behind the wall to limit soil erosion from seepage, and a single level of inclined ground anchors. A capping beam was constructed, and the anchors were stressed and locked before excavation proceeded. Plaxis 2D was used to assess stability and predict wall behaviour through construction stages.<br /><br />Wall deflections were monitored using a total station, with measurements initially taken daily. At full excavation, the maximum observed deflection was approximately 8 mm, compared with a predicted maximum of about 39 mm. The authors report that observed deflections were lower than anticipated, while monitoring was still ongoing.<br /><br />The project demonstrates how coordinating pile foundations, retention works, testing and monitoring through a single specialist contractor can simplify delivery, improve construction speed and reduce overall cost. The authors emphasize that effective solutions depend on careful assessment of site conditions, construction requirements and appropriate monitoring.

Keywords

bored piles

retaining system

basement excavation

ground anchors

contiguous bored piles

Plaxis 2D

wall deflection

siltstone socketing

urban construction

foundation design