Seattle Transportation initiated four engineering studies in April 1999. The City of Seattle owns and maintains approximately 500 retaining walls. Most were built during the initial grading or widening of streets, and several walls were built after a landslide damaged a street. Retaining walls typically have drain systems that control subsurface water build-up behind the walls. Walls have weep holes or drain pipes connected to an existing main line, or a combination of both.
Drain lines require maintenance.
Management of subsurface water in steep slope and slide prone areas plays a big role in slope stability. Slope movement may cause drain lines to break that may cause a concentration of water, which in turn aggravates slope stability. As a slide preventive measure, we researched our records and located all drain lines in our retaining walls. Knowing these locations, we can better manage drainage maintenance and also expedite slide prevention measures and risk assessment of retaining walls in slide prone areas. Our consultant started this contract in early July 1999 and completed it in September 1999.