Blasting & Boulder Busting

Production blasting is the workhorse method for bulk rock removal on highway cuts, quarry benches, foundation excavations, and tunnel approaches. Holes are typically drilled 2 to 6 inches in diameter on a 6 to 12 foot pattern, loaded with bulk emulsion or ANFO at powder factors of roughly 0.5 to 1.5 pounds per cubic yard, and detonated in a delay sequence that breaks the rock toward each successive free face. Fragmentation is sized to feed the loading and crushing equipment, and the muck pile is shaped to support efficient digging. On highway projects production blasting is followed by presplit or smooth-wall trim work along the design face to produce a stable long-term cut, and the production face is offset roughly 5 to 10 feet from the design line so the trim row defines the final geometry.

Pre-split blasting fires a row of small-diameter holes on the design face line before any production blasting takes place, propagating a fracture between the holes that intercepts and reflects the production-shot energy. Pre-split holes are typically 1.5 to 3 inches in diameter at a hole spacing of 12 to 24 inches, loaded with decoupled string charges of roughly 0.08 to 0.50 pounds of explosive per linear foot, and detonated simultaneously or in close succession. The result is a clean, stable rock face that requires minimal scaling, supports rock-bolting and mesh installation more efficiently, and reduces the long-term loosening behind the cut. Pre-split is the standard for permanent rock cuts on FHWA-funded highway projects and on aesthetic exposed cuts where the final face will remain visible.

Cushion blasting (sometimes called smooth-wall or trim blasting) is a controlled method in which the design-line row is fired after the adjacent production rounds, with reduced charge per hole and decoupled loads similar to pre-split. The technique is typically used where pre-splitting is not practical or where the rock mass would not hold a presplit fracture cleanly, for example in heavily jointed rock or in soft sedimentary units. Hole diameter and spacing match the production rounds, but the charge per linear foot is reduced and the holes are stemmed with crushed gravel or air decks to soften the peak pressure pulse against the final face. The cushion row is delayed last in the firing sequence and detonated against the relieved face left by the prior production rounds, producing a smoother result than untrimmed production work without the additional drilling required for a separate presplit row.

Non-explosive methods extend the toolkit into work where blasting is restricted by regulation, vibration limits, or proximity to occupied structures. Hydraulic rock splitters use steel wedges driven into a pre-drilled hole by a hydraulic ram, generating splitting forces of several hundred tons that fracture the surrounding rock along controlled planes. Expansive demolition grouts (Dexpan, Bristar, and similar products) are slurries poured into pre-drilled holes that develop expansive pressures of 6,000 to 12,000 psi over several hours as the chemistry hydrates, fracturing the surrounding rock without explosion, vibration, or airblast. Both methods are slower than blasting on a per-cubic-yard basis but are routinely the only feasible option in occupied building basements, near gas mains and high-pressure pipelines, and in urban demolition work where any explosive charge would exceed the site's vibration envelope.