Instantly calculate concrete volume in cubic yards, rebar cage weight, and 2025 installation cost for bored pile (drilled shaft) foundations across the USA — per ACI 318-19, AASHTO LRFD, and IBC 2021 standards.
Enter pile geometry, quantity, and project details to calculate concrete volume (yd³), rebar weight (lbs), and estimated 2025 installation cost.
Common USA sizes: 18, 24, 30, 36, 42, 48, 60, 72, 96 in
Measured from cut-off elevation to pile toe
Total pile count for this foundation group
Bell height is typically 1/3 of shaft diameter
ACI 318-19 minimum f'c = 4,000 psi for drilled shafts
Accounts for borehole overbreak and slurry displacement
A bored pile — called a drilled shaft or caisson in standard US practice — is a deep foundation element formed by mechanically drilling a cylindrical excavation into soil or rock, inserting a steel reinforcement cage, and filling the hole with cast-in-place concrete. Unlike driven piles, bored piles are formed in-place without driving impact forces, making them the preferred deep foundation solution when vibration and noise restrictions apply, when large-diameter high-capacity piles are needed, or when soil and rock conditions prevent driven pile installation. The primary US design references are ACI 318-19, the FHWA Drilled Shafts Construction Procedures and Design Methods Manual (NHI-10-016), and AASHTO LRFD Bridge Design Specifications 9th Edition.
Bored piles transfer structural loads to competent bearing strata through a combination of skin friction (shaft resistance along the pile surface) and end bearing (resistance at the pile toe or bell). In cohesive soils like Chicago Blue Clay, skin friction often dominates — while in gravels, sands, and rock, end bearing is the primary load transfer mechanism. Pile diameter in US practice ranges from 18 inches for light residential caissons up to 10–12 feet for major bridge foundations, with shaft lengths commonly ranging from 15 to 150 feet depending on bearing stratum depth.
In the United States, the terms drilled shaft, bored pile, drilled pier, and caisson are often used interchangeably for the same cast-in-place deep foundation element. "Drilled shaft" is the preferred term in FHWA and AASHTO publications. "Caisson" is the common term in Chicago and Midwest building practice. "Bored pile" is more common in geotechnical engineering publications and internationally. All refer to the same type of deep foundation: a drilled, reinforced, cast-in-place concrete element transferring load to competent bearing material.
ACI 318-19 Section 26.4.1 requires a minimum concrete compressive strength of f'c = 4,000 psi for cast-in-place concrete piles and drilled shafts in the USA. Concrete for drilled shafts must be highly workable (slump 7–9 inches or use SCC) to flow around the rebar cage and fill the borehole without segregation. Water/cement ratio should not exceed 0.45 for piles in aggressive soil environments (sulfates, chlorides).
Longitudinal reinforcement in US drilled shafts typically ranges from 0.5% to 3.0% of gross cross-sectional area per ACI 318-19 Section 10.6. Minimum cover is 3 inches to the spiral/hoop ties for piles in soil, and 3 inches for piles in permanent casing, per ACI 318-19 Table 20.6.1.4. Spirals or circular hoops are used rather than rectangular ties for circular pile cross-sections.
Bored pile concrete quantities always exceed theoretical volume due to borehole overbreak (drilling beyond nominal diameter), slurry displacement, and soft-bottom concrete that is trimmed during quality control. A 20% overpour factor is standard for soil conditions; 30–50% may be needed in soft, caving, or water-bearing soils. FHWA recommends always ordering 15–25% more concrete than theoretical calculations indicate.
Calculating the concrete volume for bored piles requires computing the cylindrical shaft volume, adding the bell volume for underreamed piles, applying the overpour factor, and converting to cubic yards for ordering. The rebar cage steel weight is then estimated from the longitudinal rebar ratio and pile dimensions.
In US drilled shaft construction, the concrete at the top of each pile is contaminated with drill cuttings and slurry and must be cut off and removed after the concrete hardens — typically 2–4 feet of concrete is wasted per pile. This "overpour" at the top is in addition to borehole overbreak and must be included in concrete quantity estimates. On a project with 10 piles at 24-inch diameter, the cutoff concrete alone represents approximately 2–4 cubic yards of wasted material that must be ordered and paid for.
The table below shows pre-calculated concrete volumes for common US drilled shaft sizes using a 20% overpour factor, for both straight-shaft and belled piles per ACI 318-19 and FHWA design practice.
| Pile Dia | Length | Pile Type | Net Volume / Pile | Ordered (20% OP) | Approx. Cost (Midwest) |
|---|---|---|---|---|---|
| 18 in | 20 ft | Straight | 0.73 yd³ | 0.88 yd³ | $350–$700 |
| 24 in | 30 ft | Straight | 1.74 yd³ | 2.09 yd³ | $835–$1,670 |
| 24 in | 30 ft | Belled (1.5×) | 2.26 yd³ | 2.71 yd³ | $1,085–$2,170 |
| 36 in | 40 ft | Straight | 5.24 yd³ | 6.28 yd³ | $2,510–$5,025 |
| 36 in | 40 ft | Belled (1.5×) | 6.60 yd³ | 7.92 yd³ | $3,170–$6,340 |
| 48 in | 50 ft | Straight | 11.64 yd³ | 13.97 yd³ | $5,590–$11,180 |
| 60 in | 60 ft | Straight | 21.82 yd³ | 26.18 yd³ | $10,470–$20,940 |
| 72 in | 80 ft | Straight | 62.83 yd³ | 75.40 yd³ | PE Stamp Required |
The USA uses several bored pile configurations depending on soil conditions, load requirements, and project type. Here are the most common types encountered in US building, bridge, and infrastructure projects.
The most common US bored pile type — a constant-diameter reinforced concrete shaft drilled into soil or rock. Used for building columns, bridge piers, retaining walls, and sign foundations. Designed per FHWA NHI-10-016 and ACI 318-19. Diameters range 18 in to 10+ ft. Both skin friction and end bearing contribute to capacity.
A straight shaft with an enlarged bell excavated at the base using a belling bucket — typically 1.5–2.5× the shaft diameter. Greatly increases end bearing area and uplift resistance without increasing shaft size. Common in Midwest USA (Chicago, Kansas City) where stiff clay and hardpan soils exist. Not feasible in cohesionless or water-bearing soils.
A steel casing (temporary or permanent) is advanced ahead of or concurrently with drilling in caving, water-bearing, or contaminated soils. Temporary casing is recovered during concrete placement; permanent casing is left in place. Required in coastal areas, high water table conditions, and near existing structures where slurry cannot be used.
In soft or water-bearing soils, the borehole is stabilized with mineral slurry (bentonite or polymer) instead of casing. The rebar cage is lowered into the slurry-filled hole and concrete is placed by tremie pipe from the bottom up, displacing the slurry. The wet method is standard practice for large-diameter drilled shafts in US coastal, delta, and alluvial deposits.
A drilled shaft socketed into competent bedrock to develop high end bearing and socket friction capacity. The rock socket depth is typically 1–5× the shaft diameter, depending on rock quality (RQD). Rock socket design follows FHWA NHI-10-016 Chapter 13 and uses rock mass strength parameters from geotechnical investigation. Common in Northeast USA, Appalachia, and mountainous terrain.
Small-diameter (18–24 in) hand-excavated or machine-drilled bored piles used for residential foundations in Midwest cities, particularly Chicago, where deep bearing clays require foundations extending 20–30 ft below grade. Typically 4,000 psi concrete, 4 longitudinal #8 bars, spiral ties at 6 in pitch. Designed by a licensed Structural PE in Illinois, Wisconsin, and other Midwest states.
Proper concrete placement and quality control in bored piles is critical — defects are difficult to detect and extremely expensive to remediate. Here are the most important best practices from FHWA Drilled Shafts Manual and ACI 318 commentary for US contractors and engineers.
Concrete in slurry-drilled or water-bearing bored piles must be placed using a tremie pipe (minimum 8-inch diameter) extending to within 6 inches of the bottom. The tremie must be kept embedded in the fresh concrete at all times during placement — a minimum of 5–10 feet — to prevent slurry or water from entering the concrete. Never free-fall concrete into a wet borehole. Tremie placement is required by FHWA NHI-10-016 and is considered the most critical quality control step for wet-method drilled shafts in the USA.
The most common costly defects in US bored pile construction are: (1) Neck formation — concrete diameter reduces below nominal due to caving soil squeezing into the shaft before concrete hardens; (2) Soil/slurry inclusions — contaminated concrete zones caused by improper tremie procedure; (3) Soft bottom — inadequate base cleaning leaving loose debris that reduces end bearing; (4) Rebar cage float — rebar cage rises during concrete placement due to buoyancy in fresh concrete. All are preventable with proper construction methods per FHWA NHI-10-016.
Official design manuals, standards, and technical resources for US drilled shaft projects.
The Federal Highway Administration's Drilled Shafts Manual is the primary US reference for drilled shaft design and construction — covering LRFD capacity methods, construction procedures, quality control testing (CSL), and inspection requirements for highway and bridge drilled shaft foundations.
FHWA Drilled ShaftsACI 318-19 governs the structural design and concrete material requirements for cast-in-place concrete piles and drilled shafts in US building construction — including minimum f'c, rebar requirements, cover, and confinement reinforcement for seismic applications.
Visit ACIThe Deep Foundations Institute (DFI) is the primary US industry association for drilled shaft, driven pile, and deep foundation contractors and engineers — providing technical publications, inspection guidelines, training courses, and contractor directories for all US deep foundation types including bored piles.
Visit DFI