Field Monitoring of Active Zone and Cracked Retaining Wall

Abstract

In this study, the causes of distress (crack movement) in the face panels of a 244 m (800 ft) long and 4.6 m (15 ft) high retaining wall was investigated by instrumenting the active zone adjacent to the wall. The foundation of the retaining wall was placed in a CH soil few feet below the surface and the ground water table was about 7 feet below ground. Total of three boreholes were instrumented to determine the vertical and horizontal ground movements in the active zone and to determine the variation of matric soil suction adjacent to the wall. The instrumentation included tensiometers, extensometers and an inclinometer. Two additional boreholes were instrumented with extensometers and pore-water transducers to determine the consolidation settlement. The crack opening and closing in the retaining wall panels were measured regularly. Based on the measurements over period of nine months, greatest vertical and horizontal displacements were observed in the top five feet of the ground. The tensiometers measured the changes in the matric suction pressures during this period. The pressures varied from 77 kPa to 10 kPa in the dry and wet weather conditions. Highest vertical settlement and swelling in the active zone were -0.51 cm (-0.2 in.) and 2.03 cm (0.8 in.) respectively and were in phase with suction pressure measurements. The lateral movement in the top five feet, during the monitoring period was about 1.02 cm (0.4 in. ) (moving away from the wall). The consolidation settlement was about 0.25 cm (0.1 in.), much smaller than what is being observed in the active zone. Hence the movements in the active zone have had the greatest influence on the crack movement in the face panels of the retaining wall.