Design and Field Comparison of Ground Improvement and Bored Piles for Large Diameter Steel Water Tanks-PPT Presentation

PPT Presentation

Pdf Summary

The presentation compares ground improvement and bored-pile foundations for large-diameter steel water storage tanks. Tank foundations must meet bearing-capacity and settlement limits, including circumferential differential settlement of 13 mm over 10 m and edge-to-center dishing limited to 1:120 under API 650. Poor investigation or design can lead to tank-bottom buckling, shell stresses, tilting, and damage to piping.<br /><br />Two projects illustrate how foundation choice depends on ground conditions. At one site, weak, alternating sand and clay layers over denser sand were treated with stone columns for a 50 m tank. Verification included zone load tests and plate load tests. At a nearby pumping station, deep soft clay and silty soils made ground improvement unsuitable, so a 41 m tank was founded on piles.<br /><br />A second case involved three tanks, each 106 m in diameter and 20 m high, with a design bearing pressure of 285 kPa. At one tank, variable-density sand over hard silt and clay was improved using vibroreplacement stone columns. Post-treatment CPTs and a zone load test assessed performance. At design load, measured settlement was 4.66 mm, compared with a predicted 8.65 mm, supporting the design assumptions.<br /><br />The presentation concludes that no single foundation solution is best for every site. With suitable investigation, design, and field verification, either deep foundations or ground improvement can meet performance requirements. Ground improvement can also reduce construction time, cost, material use, and environmental impacts, though additional measures may be needed near tank edges to control settlement.

Keywords

ground improvement

bored-pile foundations

steel water storage tanks

bearing capacity

differential settlement

API 650

stone columns

vibroreplacement

CPT testing

zone load test