Grain Silo Slab Leveling

Wednesday, February 20th, 2019 by Jorge Figueroa

Challenge

The slab of a 60-foot diameter grain silo had experienced about 12 inches of differential settlement. The settlement caused the interior grain delivery augers and floor sweep system to become inoperable. This required manual removal of the grain from within the silo. The silo’s concrete slab was 10-inches thick and the auger/floor sweep system was supported by a footing structurally integral with the slab. The grain silo owners were looking for a slab leveling solution rather than removal and replacement.

Solution

PolyLevel® polyurethane injection was selected as the preferred option based on the cost effectiveness, speed of repair and the ability to use the facility immediately after placement of the material. PolyLevel® is a two-part urethane that expands into a rigid foam used to fill voids, stabilize slabs and lift concrete. Once injected through small 5/8-inch drilled holes through the slab, a chemical reaction converts the liquid urethane components to a strong, rapidly-setting foam material. In its foam state, PolyLevel® is extremely light, weighing two to six pounds per cubic-foot (pcf). Other void-filling or lifting materials can weigh upwards of 120 pcf, adding significant weight to supporting soils or base materials and potentially contributing to further settlement.

With a typical compressive strength of 70 to 80 pounds per square inch (psi) and an in-place density of about 4 to 6 pcf, PolyLevel® 400 was proposed to relevel and support the concrete slab and floor sweep foundation. The injection holes were located on approximate 5-foot centers across the slab. An access hatch was used to gain entry to the sweep delivery system and drill injection holes through the footing, on approximate 4-foot centers. Prior to injecting the polyurethane foam, the augers and sweep assembly were removed. A total of 7,580 pounds of PolyLevel® 400 was injected below the concrete slab and delivery system footing. The PolyLevel® injection process filled voids and lifted the slab/sweep delivery foundation approximately 7 inches, which then enabled the system to be operational. After installation, the strength of the PolyLevel was tested by measuring the floor elevation prior to and after full loading of the grain bin with a variation of less than 1/8 inch. The project took three days to complete using a crew of three people.

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