Quick Verdict
Auger excavation drills clean, vertical, round holes into the ground for structural piers, deck and fence posts, sign footings, and drilled-pier foundations. Instead of digging an open pit, an auger -- a large rotating drill bit on an excavator, skid steer, or dedicated drill rig -- bores a precise column to depth. In Oregon, augering is the go-to method when you need many holes to an exact diameter and depth, or when a structure has to reach past soft clay to firmer soil or rock below. The method is fast and tidy, but Oregon's ground -- from valley clay to Central Oregon basalt -- decides which auger and which bit the job really needs.
What Auger Excavation Is
An auger is a helical drill bit. As it spins into the ground, the flighting lifts spoil up and out, leaving a round hole at a set diameter. The auger mounts on different machines depending on the job:
- Handheld or towable augers for small post holes.
- Skid-steer and mini-excavator auger attachments for decks, fences, and light footings.
- Excavator-mounted and dedicated drill rigs for large-diameter drilled piers and deep foundations.
The result is a repeatable hole -- same diameter, same depth, every time -- which is what makes augering the right tool when you have a grid of footings or piers to place. That precision is the same reason tight-tolerance jobs like elevator pit excavation sometimes use augered points for drainage or support.
Drilled Piers vs Post Holes
Not all augered holes are the same. The two big families:
- Post and footing holes are shallow to medium depth for decks, fences, pergolas, signs, and light structures. Diameter is modest and the hole is filled with concrete and often a post anchor.
- Drilled piers (also called drilled shafts or caissons) are deeper, larger-diameter holes that carry real structural load. They are reinforced with rebar cages and filled with concrete to transfer building loads down to competent soil or bedrock.
Drilled piers matter in Oregon anywhere the surface soil is too weak or expansive to support a structure directly -- a hillside home, a soft valley-bottom lot, or a deck on a slope. The pier reaches through the bad ground to something that will hold.
| Hole type | Typical use | Depth | Diameter |
|---|---|---|---|
| Post hole | Fences, decks, signs | Shallow | Small |
| Footing hole | Pergolas, light structures | Shallow to medium | Small to medium |
| Drilled pier | Structural foundations | Deep | Medium to large |
How Oregon Ground Affects Augering
The auger is only as good a match as the soil it meets:
- Willamette Valley clay augers cleanly when moist but can smear and stick; very wet clay holes may need casing to stop collapse, and the sticky spoil is slow to clear off the flighting.
- Central Oregon basalt and rock can stop a standard auger cold, calling for rock augers, core barrels, or a switch to hammering. Even a fractured rock layer over softer ground can throw the hole off vertical.
- Coastal and valley-bottom sand tends to cave, so sandy holes may need temporary casing or slurry to stay open until concrete is placed.
- High water tables can flood a hole faster than you can fill it, which changes the method and the schedule, and standing water in a pier hole has to be managed before concrete goes in.
Because augering often means many holes across a site, the utility risk is real -- every hole is a chance to hit a line. Call 811 before drilling. The same care applies to any trenching nearby, such as horizontal geothermal loop trenching that shares the yard.
What to Expect on Drilling Day
For a typical batch of holes, the day runs in a predictable order:
- Confirm 811 locates are marked and lay out hole centers to the plan.
- Position the machine, set the auger over the first center, and drill to depth.
- Clean spoil away from each hole and check depth and diameter against the spec.
- Set casing where sand or wet clay threatens collapse, then drop rebar cages on structural piers.
- Place concrete promptly so an open hole does not slough or take on water before it is filled.
On a structural pier job, an inspector often checks the hole -- depth, diameter, clean bottom, and rebar -- before concrete, so the holes are drilled and poured in a sequence that keeps them open the shortest time possible.
Permits and When an Engineer Is Involved
Post and fence holes are usually routine, but drilled piers that carry a building are engineered elements. A structural pier design comes from an engineer who sets the depth, diameter, rebar, and bearing requirement, and the work is permitted and inspected like any foundation. County and city permit rules vary, and a hillside or soft-soil lot may need a geotechnical report before the pier layout is even finalized. Getting that paperwork lined up before the rig shows up keeps a pier job from stalling with an open hole and a truck of concrete waiting.
What Auger Excavation Costs in Oregon
Pricing depends on hole count, diameter, depth, and how hard the ground drills. A row of fence-post holes in workable soil is inexpensive per hole; deep, large-diameter drilled piers through rock are a different scale entirely.
Industry Baseline Range: augered holes are often priced per hole or by machine time, with an excavator or skid steer plus operator at $125 to $350+ per hour, a mobilization fee of $250 to $800+, and haul-off of spoil at $250 to $750+ per load where it cannot stay on site. Drilled piers add rebar and concrete on top of the drilling.
These are industry baseline ranges for planning only -- actual pricing depends on site conditions, soil, access, depth, haul-off, and current market conditions. Get a site-specific quote.
- Hole count spreads mobilization across the job -- one hole is expensive per unit, fifty is efficient.
- Diameter and depth drive the auger size and machine class.
- Rock or caving soil can multiply time and require casing or specialized bits.
Current Market Reality
Real costs often run 2 to 3 times baseline when rock, caving sand, a high water table, permits, or disposal hit. A pier job that hits basalt and has to switch to a core barrel or hammer, or a sandy hole that needs casing, can double the drilling time per hole -- and an engineered pier carries design and inspection costs on top of the excavation. Most small auger jobs carry a $500 to $1,500+ minimum callout once a machine is on site.
The Bottom Line
When you need clean, accurate holes -- for posts, footings, or load-bearing piers -- augering beats hand digging every time, and on structural piers it is the only sane way to reach good ground. The trick in Oregon is matching the auger and method to clay, rock, sand, or water before the bit turns. Cojo is CCB licensed and insured, based in Hood River, serving statewide Oregon and the I-5 corridor. See our excavation services or request a free estimate with your hole schedule and we will spec the right rig.