Lock Inspection

The walls in the 425-foot chamber section were monitored during dewatering. Engineering Division monitored chamber wall movement throughout the dewatering/repair period. Targets had been installed along the lock wall at four locations on each side of the channel to monitor lateral movement at the locations. Eight lasers will were mounted on the second floor of Coast Guard Facilities in order to sight the targets. A sketch showing the approximate set-up is as shown on encl. 1. The equipment remained in place throughout the dewatering period. The survey data was continuously read in real time and fed to a computer. Readings were checked hourly while the water level was being lowered and for three days thereafter. Henceforth, data was read every eight hours. Vertical movement had been measured by a survey party. Vertical control benchmarks had been established and approximate locations were shown on encl. 2. Readings were checked hourly while the water level was lowered and for three days thereafter. Henceforth, surveys were read once daily. Vertical displacement, elevations, were accurate to 1/16 inch (0.005 Feet). If movement approached the listed tolerances the hourly surveys were extended as deemed necessary by Engineering Division. If lateral movement exceeded the permissible amount the dewatering was to be immediately halted and the lock chamber refilled. Under those emergency conditions, there was no limitation on the rate of rewatering the chamber. In order to continue repairs, ten feet of backfill had to be removed and stockpiled as shown on encl. 3.