When A 96-inch diameter storm drain at the Dundalk Marine Terminal in Baltimore, MD was discovered to have ovalized and was determined to be close to failure. Further evaluation showed that the drain line had been installed through chromite ore processing residue (COPR) materials. COPR is known to expand with time. The increase in soil volume had, in turn, increased the lateral pressure on the drain, causing it to distort. Moretrench was contracted by the Maryland Port Administration to provide emergency interim lateral load relief to the drain in the form of a soil- bentonite slurry trench.
Scope of Work
The 185-foot long slurry trench followed a parallel alignment just four feet from the drain in order to maximize lateral relief, and extended through the COPR stratum to key into the underlying clay layer at up to 17 feet below grade. The trench backfill was designed to be compressible in order to accommodate the additional calculated rate of expansion of the COPR over a prescribed time period. Components consisted of bentonite slurry, excavated soil, COPR, dry bentonite, and Styrofoam pellets, by proportion.
The slurry trench operation utilized a central slurry mixing plant and backfill mixing area. In situ soils were excavated under bentonite slurry to ensure sidewall stability. The excavated material was segregated on site to minimize the amount of excess COPR disposal. Clean soils were incorporated into the backfill, which was then placed into the trench.
Following completion of the backfilling work, 10-inch diameter, PVC volume relief ports were installed at 25 foot centers along the trench to provide additional stress relief. A concrete cap, HDPE liner, clean fill and asphalt pavement were then installed to restore the area.
Alleviation of the excessive lateral pressure through the installation of the slurry trench prevented failure of the drain and provided the Maryland Port Administration with the time it needed to effect a permanent solution.