A parkade regularly used for youth programming and other activities was awarded a donation for an expansion to be made on the 1970’s building. During the construction of the addition, the area was backfilled with ¾ crushed stone to prepare for concrete to be poured. A spread footing was built and the framing was constructed for the future wall. Unfortunately, the fill was improperly compacted and could not support the weight of the footing. The project engineers and contractor were concerned that the gravel would also settle under the weight of the slab after it was poured. So they contacted their local concrete lifting and stabilization contractor.
The concrete lifting contractor team designed a plan to stabilize the gravel and increase the load bearing capacity. This plan consisted of two parts. The ﬁrst part was a layer of polyurethane foam to be installed to bind together the loose gravel. HMI HF 402 was chosen because of its unique foam characteristics.The second and ﬁnal stabilization technique was to install FillFoam™ to ﬁll in around the stone and lock into place. Precision laser measuring equipment was utilized to monitor for movement and identify when foam was installed until refusal. It was very evident when installing pipes at depth that the lower layers of gravel were not compacted.
Various densities of FillFoam™ were installed throughout the project. Higher densities that were more ﬂuid were installed where further ﬂow was required. This allowed material to ﬂow under the stairwell. In other areas, ﬂow was limited by installing a lower density FillFoam™. With HMI/FillFoam’s engineering support, the local contractor was able to successfully stabilize the gravel for the building addition.
1,800 lbs of HF 402 Fast were installed for the top layer. 2,119 lbs equivalent to 8 cubic yards of FillFoam™ were installed into the loose gravel. The next day, crews poured the slab over the top of the stabilized gravel.