Performance Monitoring of Mixed Ground Working Platform for a CCR Surface Impoundment-Paper

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The study evaluated the geotechnical performance of a working platform built on soft coal combustion residuals (CCR) for a deep soil mixing (DSM) pilot project. The platform and access route consisted of five feet of cement-stabilized, mass-mixed CCR, geogrid, and 1.5 feet of coarse aggregate. An automated monitoring system tracked settlement, lateral movement, porewater pressure, and vibration during load testing, equipment transport, and DSM construction.<br /><br />A staged load test applied about 1,200 psf—approximately 1.3 times the estimated DSM rig pressure. Settlement reached 1.2 inches during the two-week loading period, with only minor rebound after unloading. The subsequent rapid load test produced less than 0.05 inches of settlement.<br /><br />During the rig’s 500-foot journey to the platform, settlement remained below 0.1 inches and lateral movement below 0.05 inches. Excess porewater pressure peaked at roughly 30–50 psf and dissipated within about 20 minutes. The maximum vibration recorded during transport was 0.12 inches per second.<br /><br />DSM installation generated larger responses: total settlement reached approximately 2.4 inches, and lateral deformation reached 0.5 inches. Excess porewater pressure was greatest at depth, reaching about 550, 800, and 1,700 psf at depths of 20, 30, and 60 feet, respectively; dissipation took up to about 10 hours. Surface vibration monitors detected no significant vibration during mixing, though rig movements produced higher readings, indicating that deeper geophones could improve monitoring.<br /><br />Overall, the instrumentation provided near-real-time information to assess platform behavior and support safe construction. The results showed that equipment mobilization caused limited, largely recoverable movement, while DSM operations produced more substantial settlement, lateral displacement, and porewater-pressure increases.

Keywords

geotechnical performance

working platform

coal combustion residuals

deep soil mixing

settlement monitoring

porewater pressure

lateral movement

load testing

vibration monitoring

cement-stabilized fill