Auger (Drilling Equipment)
A rotating drill that bores holes for piers, caissons and posts.
Quick Answer
An auger is a rotating, screw-shaped drilling tool that cuts and lifts soil to bore holes for drilled piers, caissons, posts and piles. In estimating it is an equipment and subcontract item. The work is measured as the number of holes, drilled linear feet and the concrete volume, not the auger itself.
The Full Picture
An auger bores a vertical hole by rotating a helical screw, which loosens soil and lifts it out. Small earth augers mounted on a skid steer or tractor drill fence and sign posts. Large rig-mounted augers drill the shafts for drilled piers (also called caissons or drilled shafts) that support columns, retaining walls and light poles, and a continuous-flight auger can place concrete as it is withdrawn when used for auger-cast piles.
The estimator seldom takes off the auger. What is measured is the foundation the auger creates. Drilled pier schedules on the structural sheets give the shaft diameter, depth or minimum embedment, bell size if any, and reinforcing. The geotechnical report supplies the soil profile, groundwater and rock, which decide whether the pier needs casing, slurry, rock drilling or a different rig. Division 31 (earthwork, which includes drilled piles and caissons) and Division 03 cover the work, so confirm the section in the project manual.
How it is quantified: piers are counted each by diameter, drilled depth is totaled in linear feet, and the excavated volume is cubic yards computed from the cylinder, pi x radius squared x depth, divided by 27. Concrete is measured in cubic yards (often with an overbreak allowance), rebar cages in each or by weight, and spoil haul-off in cubic yards with swell. Mobilization of the rig, casing, and drilling through obstructions or rock are normally lump sum or time-and-material items, which is how the equipment cost shows up in the estimate.
Typical pricing mistakes include assuming a single soil condition across the site when the boring logs show layers, leaving out casing in caving soils or below the water table, forgetting to count mobilization for a small number of piers, and not carrying spoil removal, which is sometimes contaminated or wet. Subcontractors often bid piers on a per-foot basis with stated assumptions, so the estimator has to match those assumptions to the geotechnical report.
Real Examples
Common Misconceptions
People assume: The auger is a quantity item that appears in the takeoff.
Actually: The auger is the means of drilling. The takeoff measures piers (EA), drilled depth (LF), concrete (CY), reinforcing and spoil. The rig and its mobilization are cost lines in the estimate.
People assume: Pier concrete volume equals the theoretical cylinder volume.
Actually: Actual volume is higher due to overbreak, irregular walls and casing removal. Estimators usually add an allowance, and the amount varies by soil and method.
Frequently Asked Questions
What is an auger used for in construction?
Augers drill holes for drilled piers or caissons, auger-cast piles, fence and sign posts, utility poles and soil borings. Size and rig type vary with hole diameter and depth.
How do you estimate drilled pier quantities?
Count each pier by diameter, total the drilled depth in linear feet, and compute concrete volume as pi x radius squared x depth divided by 27 for cubic yards. Add reinforcing, casing, spoil removal and rig mobilization as separate items.
Is the auger a line item in the estimate?
Usually it appears as equipment rental, or inside a drilling subcontractor's price. The takeoff quantities, such as piers, LF drilled and CY of concrete, are what drive that price.
Where do I find drilled pier information?
The structural drawings carry pier schedules and details, and the geotechnical report carries the soil profile and groundwater. Specifications for drilled piers or caissons set tolerances, casing and inspection requirements.