Earth pressures in confined cohesionless backfill against tall rigid walls — a case history

Earth pressures exerted on tall, rigid retaining walls by confined backfill zones are not well understood. Many factors, such as the complex nature of the soil-structure interaction, soil arching within the backfill zone, vertical shear transfer (downdrag) on the back faces of walls, seasonal temperature effects, and variable methods of construction, affect the earth pressures. The new monolithic wall for the McAlpine Locks replacement project, constructed in Louisville, Kentucky, for the US Army Corps of Engineers, was instrumented to measure earth pressures and temperatures for 2 years, through continuing construction of monolith L-11. Earth pressures appeared to vary with changes in backfill temperature because gauges were not calibrated for thermal expansion–contraction of oil in the pressure chambers of the gauges. A temperature calibration and data filtering procedure was developed and verified through laboratory testing, as reported elsewhere. Adjusted pressure data are presented herein to illustrate the effects of compaction procedures and environmental factors. Earth pressure data reflect soil arching and vertical shear effects, roller-compacted concrete wall movement, and surcharging effects. Measured earth pressure values are compared to predictions based on classical theory and arching theory.