Drilled shafts (also known as drilled piers, bored piers, or caissons) are rigid, high-capacity, cast-in-place concrete elements that provide foundation and earth retention support for a wide range of structures and construction objectives.
McKinney Drilling Company (MDC) has been installing drilled shafts for over 80 years and maintains one of North America’s largest fleets of rotary-style large diameter vertical boring equipment. Our inventory comprises various makes and models of drilling units including standard height, low-overhead, and other specialty rigs, together with a variety of tooling systems and materials including augers, core barrels, reamers, muck buckets, air hammers, boulder busters, and casing.
We have the capability and experience to install shafts with diameters ranging from 18 inches to 12 feet and to cater to projects of any footprint size, from a single shaft to thousands of shafts. We serve the industry’s commercial building, heavy/highway, industrial, power, energy, private and residential sectors
- Structural support systems for buildings, bridge abutments and piers, tanks, communication towers, and high mast lighting
- Earth retention for retaining walls and sound barriers
- Sump wells
- Methane gas relief wells
Drilled shafts for structural support can be installed by the dry (open hole), stabilizing polymer slurry, or steel-cased methods. Permanent casing is typically only specified in corrosive environments, voided (open cavity) conditions, or for shafts drilled through water. For open hole shaft installation, temporary casing may also be required if adverse subsurface conditions are present (i.e., groundwater, caving soils, granular soils, sidewall loss, etc.).
A hole of the required diameter is augered to the required bearing stratum or design depth, cleaned out, and inspected. Inspection may be manual for shallow holes or with a Mini-SID (shaft inspection device) or down-hole camera. Large boulders encountered during auguring may prevent shaft continuity or required bearing capacity and must be removed, typically by drilling out. A core barrel or rooting tool may also be used. If reinforcement is required and the client elects to remove this from their scope, McKinney Drilling will purchase and fabricate the cage(s) on site. Following insertion of the steel cage, concrete is placed either by freefall or tremie methods. The casing, if temporary, is then withdrawn. The completed shaft can resist compressive and lateral loads and uplift forces.
Where project site restraints and low headroom conditions are a factor, McKinney Drilling can mobilize its low clearance drill rigs and other specialty equipment to complete the project safely and expediently.