Project Summary/Scope:
The Tempe Marketplace property was historically used as a Municipal Solid Waste (MSW) and construction debris landfill for decades prior to the late 1990s. In 2015, the site was targeted for redevelopment as a thriving commercial and retail destination within Tempe. In order to stabilize the over 40 feet of highly variable landfill material underlying the site, a dynamic compaction program was conducted across the entirely of the development footprint. In areas to receive vertical construction, additional high-energy passes were completed to provide additional strengthening to the on-site soils. Following dynamic compaction, the new construction at the site was supported utilizing shallow foundation systems in conjunction with slab-on-grade construction. The dynamic compaction program consisted of two high-energy passes of a 20-ton weight dropped from a height of 60-feet, utilizing a 15-foot grid spacing with six drops completed at each point across the entire site. At the building locations, an additional two high-energy passes were completed using the same weight/height combination; however, 12-foot grids were used for the additional passes with six drops completed at each point. In calculating the depth of influence of the weight/height combination to be used, an n-value of 0.45 was chosen, indicative of the major component of the landfill layer being soil. When adding the four passes together, a total applied energy of 584 kJ/m3 was imparted to the landfill material.
Complementary Technologies Used:
None
Alternate Technologies:
None
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Performance Monitoring:
Ground response (i.e. crater depth) was monitored during the course of the work, along with vibration monitoring to assess the impact on off-site structures and utilities. Post-improvement testing consisted of plate load testing to assess the magnitude of settlement that could be expected under construction loads; the results of multiple tests indicated an anticipated post-construction settlement of less than one inch.
Cost Information:
The dynamic compaction work was completed on a unit rate basis of approximately $1.00/sf for the initial two passes across the site and an additional $1.25/sf for the additional two building passes; cost of the earthwork support is unavailable.
Case History Author:
Chris Woods, P.E., G.E., BC.GE, P.Eng, CEng MIEI, F.ASCE
Project Technical Paper:
Woods, C.B., Shaffer, R.A., and Drumheller, S.J. (2023). “Dynamic Compaction: A Proven Ground Improvement Alternative Method for Landfill Sites.” In proceedings for GeoCongress 2023, Los Angeles, California, March 26-29.