Adaptive Design and Contractual Approaches to Address Geotechnical Uncertainties in a Design-Build Ground Improvement Project-Paper

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The paper presents a design-build case study of an elevated water tank in East St. Louis, Illinois, where limited geotechnical information and challenging soil conditions created significant design and cost uncertainty. Loose, variable sands and compressible soils posed risks to bearing capacity, settlement, and earthquake-induced liquefaction. Initial seismic analyses predicted substantial settlement, exceeding the tank’s strict tolerances.<br /><br />After evaluating deep foundations, earthquake drains, and ground improvement, the project team selected a shallow ring foundation supported by a combination of ground improvement methods. Vibro-compaction densified granular soils to about 30 feet; compaction grouting treated deeper soils to approximately 65 feet; and aggregate piers reinforced weaker near-surface soils. Test sections, supplemental site investigations, cone penetration testing, and real-time grouting data informed adjustments to the design and construction criteria. Post-treatment testing confirmed substantial soil improvement.<br /><br />A central lesson was the value of collaboration among the owner, tank contractor, geotechnical engineer, and specialty ground-improvement contractor. Rather than relying entirely on fixed lump-sum pricing, the parties used lump-sum costs for predictable items and iterative, time-and-material or cost-plus pricing for work dependent on newly collected geotechnical data. This approach supported adaptive design, improved transparency, and allocated uncertainty more appropriately.<br /><br />The authors conclude that early specialist involvement and progressive verification can produce a cost-effective solution for complex ground conditions and settlement-sensitive structures. Rigid lump-sum contracting under incomplete information could instead lead to inflated bids, contractual qualifications, or costly change orders.

Keywords

elevated water tank

East St. Louis

geotechnical uncertainty

ground improvement

vibro-compaction

compaction grouting

aggregate piers

shallow ring foundation

soil settlement

seismic liquefaction