Challenging Ground Conditions During Flooding Leads to Innovative Deep Foundation Design Process and Load Test Evaluation-Paper

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The Fairfax-BPU floodwall in Kansas City, Kansas, protects more than $2 billion in infrastructure. A 2006 assessment found that it could lose foundation support if floodwaters reached the wall’s top. Flood-driven underseepage raises artesian groundwater pressures beneath the landward side, reducing effective stress and the drained soil resistance supporting the existing piles.<br /><br />The design modification combined two measures: 14 relief wells to lower artesian pressures and a row of seven 24-inch-diameter drilled shafts for each standard floodwall monolith. Because conventional foundation software could not directly represent the site’s changing effective stresses, engineers adjusted the modeled unit weight of the blanket soils to reproduce flood-condition stresses.<br /><br />Axial and lateral load tests were used to verify the design. Testing took place under unsaturated soil conditions, unlike the saturated, artesian conditions that governed the design. The team therefore estimated soil suction and unsaturated shear strength, used test results to calibrate soil–shaft friction and axial response, and matched lateral responses by adjusting soil-modulus values. These calibrated parameters were then incorporated into group analyses of the foundation system.<br /><br />The revised analysis confirmed the design’s adequacy. Predicted monolith deflection under flood loading was 0.83 inches, below the 1.5-inch limit, and structural checks passed. The drilled-shaft support was completed in 2014; the relief-well system and pumping-plant modification were planned for completion in 2016. The project demonstrates a method for designing and validating foundations where flood-induced groundwater pressures control performance and load tests occur under different soil-water conditions.

Keywords

Fairfax-BPU floodwall

Kansas City Kansas

floodwall foundation

underseepage

artesian groundwater pressure

relief wells

drilled shafts

soil suction

axial load tests

lateral load tests