Underpinning 324 Building: Supporting Hanford Nuclear Site Remediation Efforts-Paper

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The 324 Building at the Hanford Site housed research involving highly radioactive materials. After contamination was discovered beneath its B-Cell, remediation required removing contaminated soil while maintaining structural support and limiting the spread of radioactive material.<br /><br />Nicholson Construction designed and installed a micropile underpinning system to support the B-Cell during excavation. The design also included a permeation-grouted retaining wall to help prevent soil collapse and contamination migration. Micropiles were selected over the original jet-grouting proposal because they offered better control of drilling spoils, required less space, and were less vulnerable to inconsistent ground conditions.<br /><br />Extensive verification testing informed the final design. Seven micropile load tests confirmed performance and supported a design bond strength of 200 psi, exceeding the initial estimate. The production piles were approximately 31 feet long, with 18.3-foot bond zones.<br /><br />Construction took place in a restricted Category II nuclear facility, with limited overhead clearance and close proximity to the B-Cell wall. Crews worked in protective clothing with powered respirators and continuous radiological monitoring. The team developed airtight drilling and spoil-handling systems, used HEPA-filtered negative-air equipment, and established detailed radiological, administrative, and personal-protection controls. Mockups and contingency planning helped prepare crews for drilling and grouting under these conditions.<br /><br />The final 13 micropiles were successfully installed in December 2022, enabling contaminated soil removal. The project demonstrated the importance of thorough verification, advance planning, and realistic mockups when applying conventional foundation techniques in a highly contaminated nuclear environment.

Keywords

Hanford Site

324 Building

B-Cell

micropile underpinning

permeation grouting

contaminated soil remediation

nuclear facility

radiological controls

load testing

soil stabilization