Completion of a portion of the highway loop around Tulsa, Oklahoma, required that State Highway 11 (SH-11) cross an old strip mine/uncontrolled landfill area located in north central Tulsa. A grade separation was required where SH-11 crossed Yale Avenue, a major city street. The entire project involves the bridge structure, approach embankments with a maximum height of approximately 9 m and the roadway paving. The foundation conditions varied from remnants of intact shale existing between the strip mined areas to layers of disturbed shale covering layers of trash varying in thickness from approximately 1 m to nearly 6 m. At both ends of the project, ground water was present.
Dynamic compaction was selected over other options (i.e. grouting or elevated roadway) to prepare the foundation material to support the embankments. As part of the dynamic compaction quality assurance program, three instrumented field test sections were constructed to verify the adequacy of dynamic compaction. In the portion of the project where the thickness of the trash layers was the greatest, the potential for additional settlement following dynamic compaction seemed large, so it was decided to support that section of the embankment on stone columns constructed using the dynamic compaction process. An on-site evaluation of different impact sequences was conducted to determine the most efficient method for stone column construction. Approximately 95 stone columns were constructed, using the selected procedure, in the area with the thickest trash. Following completion of the embankment, several locations were instrumented (settlement gages and piezometers) to observe the long term settlement performance of the embankment.
Dynamic compaction of the materials resulted in average settlement over the approximately 9 hectare site of 66 cm. Reasonable strength improvements were measured at each of the test sites. Settlement records show a maximum settlement of approximately 30 cm since completion of the embankment in Spring 1986. The major portion of the settlement occurred rather quickly (i.e. in a few months) with subsequent settlement being minimal.