The problem was solved with a redesign of the base course structural section. Perforated Presto GEOWEB® Cellular Confinement System was substituted for the concrete slab. Geotextile fabric was first placed directly on top of the soil subgrade, and GEOWEB sections installed with aggregate base rock infill. While subgrade conditions were so soft that pumping of the soils was observed even when walking on top of the subgrade, the contractor was able to rapidly achieve base course compaction specifications of 95% Modified Proctor with the GEOWEB base reinforcement system in place and spreading the loading of the compactive effort laterally rather than downward into the saturated clay subgrade.
Wilshire Boulevard base reinforcement, Los Angeles, California
A City of Los Angeles street beautification effort for world famous Wilshire Boulevard provides a classic case study regarding the incompatibility of rigid pavements placed on top of rigid base layers. Wilshire Boulevard is constructed across areas of clay subgrade soils of very poor bearing strength. Soft subgrade conditions are a year around problem as the soils have a high affinity for water. In addition to miles of new concrete sidewalks and landscape features the City planned to reconstruct street crossings running parallel to Wilshire Boulevard with brick pavers placed on a thin sand bed above a concrete slab base layer. When the first of the new street crossings were placed into service they began to self destruct with brick pavers rapidly moving out of alignment under bus, truck and automobile traffic.