Repair methods

Drilled piers for foundation repair

Every other pier on this site is forced into the ground — pressed, driven or screwed. A drilled pier is built in the ground: a hole is bored, steel is lowered in, concrete is poured. That single difference decides where the method works, what it costs, and how you know it worked.

How the installation works

  1. Establish access. A drilling rig needs room to reach each location and room to turn. This is the first question on a tight lot, and occasionally the one that rules the method out.
  2. Bore the shaft. An auger cuts down to the design depth. On a rock-bearing design that means drilling until competent limestone is reached and often a short distance into it.
  3. Form the bell, if the design calls for one. An underreaming tool widens the base of the shaft into a cone.
  4. Inspect and record. What the auger encountered and at what depth is the evidence that the pier is founded on something. On a cast-in-place method this record is not paperwork — it is the verification.
  5. Place the reinforcing cage and pour the concrete, filling the shaft from the bottom up.
  6. Cure, then connect. Once the concrete has gained sufficient strength the structure is supported on the completed piers, with jacking and shimming if elevation recovery is part of the plan.
Four foundation support methods in cross-section Cross-sections comparing a concrete pressed piling made of stacked segments, a steel push pier driven as a pipe, a helical pier with screw plates along its shaft, and a wide drilled pier bored down to rock. foundation beam foundation beam foundation beam foundation beam Concrete pressed piling pressed with the house as the reaction force Steel push pier driven through the clay to load-bearing strata Helical pier screwed in; torque readings give capacity on install Drilled pier bored and poured where rock sits close to the surface Strata active clay stiff clay load-bearing strata / rock
The method is chosen for the soil profile and the load the pier has to carry, not arbitrarily — which is why two contractors can propose different systems for the same house. It is a fair question to ask any contractor why the method they have proposed is the right one for your soil.

Cast in place, not driven — the difference that matters

A pressed piling, a push pier and a helical pier are all finished products forced into the soil, and in each case the act of installing them measures something. A push pier reaching refusal under the weight of the house has demonstrated it can resist that load. A helical pier generates a torque reading that correlates with capacity. The installation is the test.

A drilled pier is different in kind. You make a hole, then you make a pier inside the hole. Nothing about that process loads anything, so nothing about it proves anything. Three consequences follow, and they are the whole character of the method:

  • Verification comes from the drilling record, not from installation force. What the auger hit, at what depth, and whether the hole was inspected before the pour.
  • Load transfer waits for cure. Concrete needs days to reach usable strength and weeks for its design strength. Steel piers carry load immediately.
  • Lifting is a second operation. With push piers, driving and lifting are one continuous process. Here the pier must exist and cure before anything can be jacked against it.
What to ask for instead of a torque log

On a helical job the thing worth having in writing is the torque reading at each pier. There is no equivalent here, so ask for what replaces it: the drilling log recording what was encountered and at what depth, confirmation that the shafts were inspected before concrete went in, and whether concrete test cylinders were taken. On karst terrain — the Edwards Aquifer recharge zone across north Bexar County in particular — that record matters more than usual, because what the drill finds is less predictable. More on that ground on our Stone Oak page.

Two kinds you will meet in Texas

Rock-socketed drilled piers

The straightforward case. Where competent limestone sits within reach, the shaft is bored down to it and frequently a short way into it, and the pier bears on rock that is not going anywhere. This is the standard method across the western edge of the Metroplex around Benbrook and out toward Aledo, north of the Balcones Escarpment in San Antonio, and on the limestone west side of Austin.

It is also why pressed pilings and helical piers are the wrong tools in those places: you cannot press a concrete cylinder into rock and you cannot screw a helix through it. The soil has already chosen.

Drilled and underreamed — the bell-bottom pier

A Texas signature, and the reason a great many houses in this state are sitting on drilled piers already without their owners knowing it. The base of the shaft is widened into a cone by an underreaming tool before the pour.

The bell does two things. It spreads load across a much larger area at the bottom, which matters in soil that cannot carry much per square foot. And — the reason the design took hold here specifically — it resists uplift. When expansive clay takes on water and swells, it grips the sides of a pier shaft and tries to lift it. A straight shaft has little to resist that with. A belled base is anchored under a mass of soil and holds the pier down.

That matters if your house was originally built this way, because the repair conversation changes. A belled pier that has failed has usually failed for a specific reason — inadequate depth below the active zone, a bell that was never properly formed, or soil conditions that changed — and establishing which is a better use of money than assuming the original design was simply wrong. More on how Texas clay behaves on our Texas page.

Where drilled piers are the right call

  • Shallow rock — the primary case, and the one where no other method competes
  • Expansive clay where uplift is the problem, using a belled base to anchor against heave rather than only resisting settlement
  • High loads per point, where a large-diameter shaft carries what several smaller elements would be needed for
  • New construction, additions and new loads — the pier can be cast before the thing it will carry exists
  • Where there is room to work, which on a typical suburban lot with a driveway there usually is

Where they are not the answer

  • Tight access. The single biggest practical limitation. A drilling rig needs space that a compact helical machine does not, and no amount of soil suitability overcomes a gate the equipment cannot pass through — that is what helical piers are for.
  • Deep saturated soil and a high water table. An open hole in water-bearing ground can collapse or flood, which means casing or drilling slurry and a materially higher cost. It is one reason the Gulf Coast favors driven methods — see push piers in Houston.
  • Where support is needed immediately and concrete cure time is not acceptable.
  • Where precise elevation recovery is the main goal, which hydraulic push piers do more directly.
  • Light structures — a porch or a deck rarely justifies a drilling rig when a helical would carry it for less.
  • Problems that are actually plumbing. A leak under the slab moves a foundation on its own, and piering around it means paying twice.

Cost, in general terms

About these figures

Foundation Repair IQ does not quote prices and does not perform repairs. The figures below are general industry ranges published for orientation only — not quotes, not estimates for your property, and not binding on any contractor. Foundation pricing is set by the contractor after an on-site evaluation, and your actual cost may fall outside any range shown here.

Drilled piers generally run in the region of $1,000 to $2,800 per pier installed, moving with depth to competent bearing, how hard the rock is once reached, shaft diameter, and whether a belled base is part of the design. That is well above the $300 to $600 of a concrete pressed piling and broadly comparable to a helical pier.

The per-point figure overstates the gap, though. Shallow rock means short piers, and a design bearing on rock may need fewer points than one relying on friction in clay. Compare totals rather than unit prices, and ask what happens to the number if the rock turns out to be deeper or harder than assumed. More on slab repair costs →

Questions worth asking

  • What are the piers bearing on, at what depth, and how was that established?
  • Will I get the drilling log, and were the shafts inspected before the pour?
  • Is a belled base part of the design, and if not, why not on this soil?
  • How long between the pour and load transfer, and what supports the house meanwhile?
  • Can the rig physically reach every location, or are some being relocated to suit access?
  • Is an engineer designing the layout, and does one sign off afterwards?

Questions about drilled piers

What is a drilled pier?

A reinforced concrete column formed in a hole bored into the ground, rather than a manufactured element forced down into it. A rig augers a shaft to the required depth, a steel reinforcing cage is lowered in, and concrete is poured to fill it. Once cured, the structure is connected to it and the load transfers down the column to whatever the base of the shaft is bearing on. You will also hear them called drilled shafts, bored piles, caissons, or — when the base is widened — drilled and underreamed or bell-bottom piers. They are the standard method wherever competent rock sits close enough to the surface to be reached, which across Texas means the western side of the Metroplex, north of the Balcones Escarpment in San Antonio, and west Austin.

What is a bell-bottom or underreamed pier?

A drilled pier with a widened, conical base — the bell — formed by a special underreaming tool at the bottom of the shaft before the concrete goes in. It is close to a Texas signature, and a great many houses across the state were originally built on them. The bell does two jobs. It spreads the load over a much larger area at the base, which matters in soil that cannot carry much per square foot. More importantly here, it resists uplift: when expansive clay swells it grips the shaft and tries to lift the pier, and a belled base anchors against that in a way a straight shaft cannot. That second function is the specific reason the design became standard in Texas clay rather than anywhere else.

Drilled piers or push piers — which is better?

Neither. They answer different ground. A push pier is driven down until it meets resistance, which makes it the method of choice where competent bearing is deep and you have to get past a lot of unstable soil to reach it — and the driving itself demonstrates capacity. A drilled pier is bored to a depth someone has decided on, which makes it the method of choice where you know what you are reaching for and it is not far away, typically shallow limestone. Trying to press a piling into rock a few feet down does not work; boring forty feet through saturated Gulf Coast clay is slow, expensive and may need the hole cased to stop it collapsing. The soil picks the method, and a contractor recommending the same one everywhere is not reading it.

How long before a drilled pier can carry the house?

Days rather than hours, which is the practical disadvantage of the method and worth planning around. A drilled pier is poured concrete, and poured concrete has to cure — it gains usable strength over several days and reaches full design strength over several weeks. Load cannot be transferred until it has got there. Push piers and helical piers carry load the moment they are installed, because they are finished steel going into the ground. For most repairs this changes nothing except the schedule, but it matters if the structure needs support urgently, and it means a job involving drilled piers has a gap in the middle where nothing visible is happening.

What do drilled piers cost?

Generally in the region of $1,000 to $2,800 per pier installed, varying with depth to competent bearing, how hard the rock is once reached, shaft diameter, and whether the design calls for a belled base. That places them well above concrete pressed pilings at $300 to $600 and broadly alongside helical piers. Where they look expensive on a per-point basis they are often not expensive overall, because shallow rock means short piers and a design may need fewer of them. The figure that moves the total most is what the drilling actually encounters, which nobody knows precisely in advance. General industry ranges only — see the cost guide.

Can drilled piers lift my house back to level?

Lifting is possible but it is a separate operation rather than part of the installation, and that is a real difference from push piers. With push piers, driving and lifting happen in one continuous process — the hydraulic equipment that drove the pipe is right there and can raise the structure against it immediately. With drilled piers the column has to cure first, and only then can the structure be jacked and shimmed against the completed piers. Most drilled pier repair work is about stabilizing rather than recovering elevation. As with any method on an older house, full recovery is often not the goal anyway, because forcing a structure back to a geometry it stopped having twenty years ago cracks finishes that had settled comfortably.

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