Case Study: Design, Installation, and Analysis of Column Supported Embankment Systems at I-295/I-76/Route 42 Direct Connection Contracts 1 and 2

At the I-295/I-76/Route 42 Direct Connection project in Camden/Gloucester Counties, New Jersey, column supported embankment systems (CSES) are used to limit settlement and accelerate construction of large embankments bearing on compressible soils. At present, the I-295/I-76/Route 42 interchange does not provide a direct connection for I-295 thru traffic. The reconfiguration of the interchange will allow access from I-295 directly to I-76 and Route 42 without the use of low-capacity ramps. Due to the project size, traffic flow, and safety concerns, expedited reconstruction of the existing roadway system is necessary and CSES are an ideal solution to treat the soft soils. Without ground improvement, unimproved settlements were estimated to be up to 30.5 cm; with ground improvement, the post-construction settlement was limited to 2.5 cm. This paper presents the project background, site challenges, ground improvement design, analysis of load test data, and quality control measures used on-site at the 295 Direct Connect Project Contracts 1 and 2. The project is divided into 4 contracts. The majority of the rigid inclusions were installed in a relatively homogenous soil profile consisting of 15.2 meters of low plasticity clay whose stiffness increases with depth. Thus, the rigid inclusions CSES design calculations relied on skin-friction capacity in cohesive soils. The design met the project performance requirements for settlement, bearing capacity, and external stability of the walls and embankments. The design was completed using finite element software including Plaxis and RocScience Slide as well as traditional deterministic analyses. Ten rigid inclusions static load tests were performed in Contract 1 and seven rigid inclusions static load tests were performed in Contract 2 to validate design assumptions. The rigid inclusion shaft resistance estimated in the clays during design was compared with actual shaft resistance values from the strain gauge data collected during the load tests. The walls were instrumented and monitored and the instrumentation indicated the system performance was well-aligned with design models. Finally, the numerous quality control measures employed on the project are discussed.