Drilled Piers: Deep Foundation Support for Homes and Structures

When the soil under a house can no longer carry its weight, the repair has to reach past that soil to ground that can. Drilled concrete piers are one of the ways engineers do that, and the term comes up often once a homeowner starts researching settlement in California and Arizona. This page explains what a drilled pier is, when an engineer specifies one, and how the system compares with the two deep foundation systems Dalinghaus Foundation Repair actually installs, helical piers and push piers.

What Are Drilled Piers?

Drilled piers are deep foundation supports designed to hold heavy loads by reaching down to stable soil or bedrock. Unlike shallow footings that rely on surface soils, drilled piers foundation systems carry the load where surface conditions are weak.

According to Methods of Foundation Engineering, drilled concrete piers are created by drilling a large hole, placing a steel reinforcement cage inside, and filling it with high-strength concrete. The load from the structure above is then transferred deep below the unstable surface layers.

Sometimes called caissons or bored piles, drilled shaft foundations are engineered for the soil conditions at a specific site. That is why they turn up on projects built over expansive soils, soft clays, or ground that is known to shift.

Key Features of Drilled Piers

• Installed deep into stable load-bearing soils or bedrock
• Typically 18 to 60 inches in diameter
• Reinforced with steel rebar cages to handle heavy loads
• Used on large buildings, commercial structures, and heavy loads
• Sized and placed from a geotechnical soil report

When Do Engineers Specify Drilled Piers?

Arizona soils are unpredictable, ranging from clay-rich expanses to loose, sandy layers, and they react dramatically to moisture changes. Shrinking, swelling, and shifting soils put stress on shallow foundations, which shows up as cracks and uneven floors. A deep foundation system of some kind is the usual answer.

Drilled concrete piers bypass unstable soil and bear on stronger ground below it. A structural or geotechnical engineer typically specifies them when:

• The load is large, as on a commercial building, a bridge, or a heavy retaining wall
• The project is new construction and the foundation can be designed from scratch
• A soils report calls for a specific shaft diameter and depth that only a drilled shaft can deliver
• The site has room for a drilling rig, a concrete truck, and somewhere to put the spoils

That last point matters more than it sounds. Drilled piers are a design decision made before anything is built, on sites with open access. Most residential foundation repair is the opposite situation: an existing house, a finished yard, and a few feet of working room along the footing.

How Drilled Piers Are Installed

Installing a drilled pier foundation takes planning, engineering, and specialized equipment.

1. Site Evaluation and Soil Testing

The work starts with a soil analysis. A geotechnical engineer assesses the soil’s depth, type, and load-bearing capacity, and that report drives the pier design.

2. Drilling the Shaft

Large drilling rigs create shafts at the locations the engineer marked. The holes typically extend 10 to 40 feet, depending on soil conditions and the weight of the structure, until they reach load-bearing strata.

3. Reinforcement and Concrete Placement

Steel rebar cages are lowered into the open shaft and concrete is poured to form the pier. Casing or slurry is sometimes used to hold the hole open during drilling, especially in unstable soils.

4. Curing and Load Transfer

Once the concrete has cured, the weight of the structure is transferred to the piers. The cure time is part of the schedule, and it is the main reason drilled piers are a slower system than driven steel.

Strengths and Limits of Drilled Piers

Drilled concrete piers have real advantages, and real trade-offs that decide most residential jobs:

• Load capacity. A large reinforced shaft carries loads that lighter systems cannot.
• Designed depth and diameter. Each pier is sized from geotechnical data for the soil and the load.
• Durability. Reinforced concrete holds up well underground.
• Access and disruption. Drilling rigs need room, and drilling produces spoils that have to go somewhere. In a landscaped side yard, that is a problem.
• Cure time. The load cannot transfer until the concrete has cured.
• No proof during installation. Capacity comes from the engineer’s calculation and the soils report, not from a measurement taken as the pier goes in.

Drilled Piers Compared With Helical and Push Piers

Helical piers and push piers solve the same underlying problem, a footing sitting on soil that cannot hold it, with driven galvanized steel rather than poured concrete.

Drilled pier foundations suit large or heavy structures where other systems cannot supply the load capacity. For an existing house that has settled, helical and push piers usually fit the site better, install faster, and prove their own capacity as they go in.

Signs a Home Needs Deep Foundation Support

Certain warning signs point to soil that is no longer carrying the house, whatever system ends up being the right one:

• Foundation settling or sinking that keeps getting worse
• Cracks appearing in interior or exterior walls
• Uneven or sloping floors through the house
• Gaps forming around doors or windows that were not there before
• Water pooling or drainage problems near the foundation

If you see one or more of these, get the house measured before the movement goes further. Floor elevation readings and a look at the footings tell you what is actually happening.

What Dalinghaus Installs, and Why

Dalinghaus Foundation Repair does not install drilled concrete piers. Our deep foundation work on homes is done with helical piers and push piers, for reasons that come straight off the job site:

• The pier proves itself as it goes in. Helical pier installation torque correlates with soil capacity, and a push pier is driven against the weight of the house until the soil pushes back harder than the structure weighs. Both give a number on the day of installation.
• The equipment fits. Hydraulic drive heads work in side yards and tight access where a drilling rig cannot reach.
• No cure time. The load transfers to steel as soon as the brackets are set.
• Lift is possible. Where the structure allows it, we can lift toward level during the transfer, which often closes cracks that settlement opened.

If the evidence at your property points toward a drilled shaft system or anything else outside our scope, we will tell you that and point you to the engineer who should design it. That is a straighter answer than selling you the system we happen to carry.

Schedule a Free Evaluation

Foundation movement is easier to judge in person than from a photo. Schedule a free evaluation and a Dalinghaus specialist will walk the property with you, measure the floor elevations, and explain what the evidence shows in writing.

Get a free evaluation today