Case History of Roadway Embankment Construction over Very Weak Clay

In this paper, a case history is presented of staged construction of a 25-ft high roadway embankment over very soft saturated clay. The roadway needed to pass over a creek bed. Anticipating the construction of the embankment near the creek area was complicated, the original design called for the construction of a bridge over the creek area. Due to the high cost of the bridge, the authors were requested to evaluate if and how a roadway embankment can be constructed instead. The authors completed a detailed geotechnical investigation and laboratory testing program at the site. The field and laboratory data were used to perform detailed slope stability and settlement analyses. The stability analyses indicated that construction of the embankment using typical methods would lead to embankment failure. However, the analyses showed that staged construction will result in acceptable factors of safety for stability. Furthermore, the consolidation data suggested the soft clay will consolidate relatively quickly, making staged construction feasible. The authors developed an instrumentation and monitoring plan to collect settlement and pore-pressure data during the embankment construction. This data was used to estimate when a new lift can be placed. The roadway embankment construction was completed successfully.