Quarry site design put on hold for more testing

Results of initial geotechnical testing by Palmerton & Parrish Engineers of Springfield show that the property’s approximately 100-foot fill of soil, rock and other organic material is settling quicker than expected, at a rate of between one feet and three feet per year, according to company President Brad Parrish. The data, however, was collected February through April, an unusually wet period because of record rainfall.

“It’s so much that it would have to be re-graded,” Parrish said of the need to refill the sinking land over time. “The maintenance would be so excessive that I think the city would rather wait and have a better handle on what to expect before they proceed.”

The Jordan Valley Advisory Committee has recommended suspending the design process over the summer instead of moving to the next step of developing construction documents, according to a city news release.

Meanwhile, Palmerton & Parrish will do additional testing in the next several months, possibly including some bore drillings, to further assess the settlement rates and stability of the property.

Parrish said there is a thin strip of land on the quarry’s south end that’s more stable than the rest of the site, and the firm will work to determine exactly how large that area is. Depending on its size, more of the gateway plaza’s heavier, structural elements, such as a pavilion, could be placed there, while flexible elements, such as benches, would be placed on the less stable areas.

Palmerton & Parrish has been working with Portland, Ore.-based firm GreenWorks on the nine-acre property’s conceptual design, revealed in March. Parrish said the design already takes into account the fact that the quarry will settle over coming years, but knowing just how much it will settle helps in planning.

Those involved in the project have been considering a number of options to account for the settlement, Parrish said. The project could be conducted in phases, starting with the south side. Another option would be to preload – to fill the quarry even higher and heavier than necessary in order to speed up the settlement process, and then remove the extra fill, he said.

The firm will make recommendations to the city when it concludes the additional testing.

During the summer, work also will continue on the required environmental assessment of the property, clarifying boundary lines, and studying the best way to address methane gas production at the site’s southwest corner, the release said.

The project is funded through $2.2 million in earmarked federal grants.