Slope Protection and Seepage Control Measures for Deep Excavation Adjacent to Lake

Paper

Pdf Summary

The case study describes construction of the P2 pylon foundation for the Dhurgam Cheruvu extra-dosed bridge in Hyderabad, adjacent to a lake. The foundation required excavation to hard rock about 7 m below ground, while a 4 m-high temporary earthen bund retained lake water. HDPE sheeting, sandbags and sump pumping were used to limit seepage and keep the excavation workable.<br /><br />Excavation slopes were designed using borehole data and PLAXIS 2D, but actual ground conditions differed: residual soil extended deeper than anticipated, leaving less weathered rock. The resulting flatter soil slope encroached on the foundation footprint and reduced the space needed for formwork. The bund therefore had to be shifted about 5 m toward the lake, and steeper slopes were adopted despite persistent seepage.<br /><br />Precast concrete blocks formed toe-protection walls to create additional workspace. Blasting for deeper rock excavation caused these walls to collapse, so blasting near them was stopped; manual drilling was used instead, and steel beams were added to improve stability. Drains directed seepage into a sump, where two 5 HP submersible pumps removed the water.<br /><br />Despite delays and remedial work, the foundation was successfully constructed with a continuous concrete pour of approximately 1,000 m³. The authors emphasize that unexpected subsurface conditions can invalidate excavation designs, causing cost and schedule impacts. Thorough investigation, suitable retaining and dewatering measures, adaptable slope protection, and careful coordination of excavation methods are essential for deep excavations beside water. The temporary bund was to be removed after construction to restore the lake environment.

Keywords

P2 pylon foundation

Dhurgam Cheruvu bridge

Hyderabad construction

deep excavation

hard rock excavation

temporary earthen bund

seepage control

PLAXIS 2D analysis

dewatering pumps

foundation construction