Edited by Christina Fisher
"Trench density is the single most important factor on a land development project once the mass excavation and utility trenches have been dug," says Jay Burnett, superintendent with Gramling Bros. Contracting, Inc.
Multifunctional equipment like the Bomag BMP-851 and Bomag BW-145DH-3 compactors play a critical role in achieving the required compaction densities on a project. Both are drum rollers that quickly and easily convert to either a narrower or wider trench roller or a general duty pad foot compactor. Blue Eagle Equipment Rental and Sales in Spartanburg has been instrumental in providing Gramling Bros. Contracting with specialized machinery.
Jay Burnett's current project is the North Grove Medical Complex site in Spartanburg, S.C. It involves a 55-acre development with about 350,000 cubic yards of mass excavation. The material was balanced on-site, with the deepest cut about 16 feet.
Here, according to John Gramling III, president of Gramling Bros., they are involved in turning a bare ground location into a productive building package. This encompasses stripping and stockpiling original earthwork, balancing cuts and fills, and the installation, compaction and backfilling of storm water runoff piping, sanitary sewers and other underground utility lines.
The first phase of the stripping and the cut and fill earthwork is being handled by Caterpillar 615 and 620 single- and double-engine scrapers pushed by D-6 and D-8 dozers for site grading and leveling.
A Caterpillar 325C LCR hydraulic excavator with a reinforced 4-cubic-yard bucket is digging the initial 16-foot-deep trench. It is followed closely by a Caterpillar 322C excavator side casting the recently excavated material away from the trench to the safe angle of repose as is required for safety by OSHA. A trench box is used when there is no room to layback the excavated material.
The Cat 325C is also handling most of the required 3,000 feet of pipe. The pipe ranges in size from 36 inches to 48 inches in diameter, along with some smaller sewer pipe.
Initially, the backfill is put in around the pipe in 8-inch lifts and compacted with a BT: 60/4 Bomag tamper. This continues until the fill is near the top of the pipe. From there work continues in 6-inch lifts until the fill is 24 inches over the pipe. A Bomag BMP-851, which can be either manually or remotely controlled, compacts the fill at this point.
The last compaction effort is made with a converted BW-145DH-3 smooth drum roller. Gramling Bros. uses the optional three-segment, bolt-on shell kit to transform the smooth drum roller to a pad foot soil consolidation compactor. The lifts are usually 12 inches to 18 inches thick yet still need the 95-plus-percent compaction specified for this open site location. The soil in this area of the state has clay with silt, which makes for cohesive, tightly compacted backfill material.
"Trouble is certain to follow if both the proper backfill and density aren't achieved during initial pipe installation. This includes under, around and over the line. Settlement will occur sooner or later, especially under streets and roads, where impact traffic is heaviest. This is where we are often able to employ multifunctional equipment which provides us with both added convenience and value," says Burnett.