Deep Excavation with Well Point Dewatering in Soft Soil-Paper

Paper

Pdf Summary

A thermal power plant’s coal-handling complex in Haldia, India, required excavations 8–12 m deep in very soft soil with groundwater close to the surface. Initial open excavation for the track hopper failed at depths of 5–6 m, halting construction. The original proposal for extensive sheet piling and well sinking was costly and time-consuming.<br /><br />A site pumping test provided hydraulic data for designing a dewatering system. The adopted solution used single-stage well points for the track hopper and tunnels, and a two-stage system for the deeper wagon tippler and transfer points. Groundwater was lowered and maintained below excavation levels, enabling safer, extensive open excavation. Excavation profiles were optimized, reducing excavation volume by about 20%.<br /><br />The lower groundwater level also allowed substantial revisions to the sheet-pile design. Sheet piles were shortened from 19 m to 12 m, while the protected length was reduced from about 1,000 m to 190 m. Strutting and excavation were planned to account for changing loads during construction.<br /><br />The underground works, covering a roughly 400 m by 120 m area, were completed safely in about four months, without interruption and nearly two months ahead of schedule. The approach delivered significant cost savings and transformed the site into a manageable construction environment.<br /><br />The case demonstrates the importance of investigating site-specific soil and groundwater conditions before deep excavation. Classical seepage and cofferdam design methods can support effective solutions, provided they are based on reliable field data. Dewatering and support systems also require careful installation, operation, inspection, and maintenance; software outputs should be checked against the underlying assumptions and limitations.

Keywords

thermal power plant

coal-handling complex

deep excavation

dewatering system

well points

groundwater control

sheet piling

soft soil

excavation optimization

site pumping test