DEEP FOUNDATIONS
A deep foundation transfers load to soil or rock that is typically much further below the surface than a shallow foundation does. Whether Condon-Johnson is providing deep foundations for new or existing structures, the company has the engineers, experience, and equipment to provide the most cost-effective solution to your challenging project. Our geotechnical professionals continue to be at the forefront of innovation, developing and applying progressive design and construction techniques for a wide range of deep foundation types, from large 13 foot diameter CIDH piles to small 6 inch diameter micropiles. Condon-Johnson is recognized as a leader in the industry, applying decades of experience, innovation and equipment technology to successfully complete hundreds of deep foundations for major public and private projects across the Western United States.
Auger Cast Piles (ACP) or Continuous Flight Auger (CFA) piles are created by rotating a continuous flight auger into the ground to a specified depth and then slowly withdrawing the auger while pumping cementitious grout under pressure to create the pile as the auger is retracted. As the auger is retracted, the spoils on the auger are continuously removed from the auger at the ground surface by an auger cleaner attached to the base of the mast on the drill rig. Once the pile has been grouted and the auger is completely removed from the pile, reinforcing cages may then be wet set into the previously placed grout.
The quality of the auger cast pile is largely dependent on the skill and experience of the contractor performing the work coupled with the use of real-time data acquisition that allows the operator to monitor grout injection volumes and pressures before pulling the auger up to the next stage. This type of control is essential to consistently constructing ACP that achieve the minimum diameter. Condon-Johnson is continuously selected for auger cast pile installation due to our vast experience and positive reviews from designers, contractors, and owners on previous projects.
Auger Displacement Piles are similar to Auger Cast Piles, but unlike ACP, displacement piles produce essentially no drill spoils. The specialized displacement tool displaces the soils laterally toward the borehole walls to increase the density of the surrounding soils and increase the capacity of the resulting pile. Since the displacement pile creates essentially no drill spoils during the installation process, the project saves the cost of spoil handling and disposal. Displacement piles reduce the hazards of handling contaminated soils and can offer substantial cost savings.
As the specialized displacement tool is advanced to the design depth, the soil is displaced laterally. When the displacement tool reaches the design depth, a high slump cementitious grout is then injected to create a pile with the minimum diameter of the displacement tool. While continuously injecting grout as it is withdrawn, the displacement tool is retracted to the ground surface.
After grouting of the pile is complete, a reinforcement cage can be installed. The inherent soil improvement process of displacement pile installation results in greater lateral/vertical capacities compared to conventional ACP or drilled shafts. Displacement piles also offer a low-noise, vibration-free installation process, ideal for sensitive deep foundation areas where noise and vibrations are not allowed. By using displacement piles, Condon-Johnson clients can avoid excessive noise, vibration damage to adjacent properties and any unnecessary project delays, claims and settlements associated with conventional deep foundations.
Condon-Johnson is proud of a long and successful record of installing drilled shafts of all sizes and depths. Drilled shafts, also known as drilled piers, Cast-in-Drilled-Hole Piles (CIDH piles) or Cast-in-Situ piles are used to transfer structural loads and moments through the relatively weak upper strata of many sites to deeper, stronger soils which have sufficient capacity for the anticipated loading.
Drilled shafts are deep, cylindrical, cast-in-place concrete foundations reinforced using full-length rebar cages and formed by a drilled borehole excavation. They can range in diameter from 18-inches to greater than 20-feet and reach depths over 250 feet. They are often used as a structural support where seismic loadings create large moment requirements that ultimately govern the bridge foundation design. Drilled shafts have additional foundation uses, including building support, cantilevered signs, communication towers, and landslide retention.
Construction methods depend on the geology of the site and on-site access. Condon-Johnson is competent with dry, wet (slurry), and oscillated/rotated cased drilling methods. Dry drilling methods are used in non-caving, cohesive soils, which are generally located above the local ground water table. An auger is advanced (it must be removed periodically to remove the borehole soils) until bottom of pile elevation is reached. A cleanout bucket is then used to ensure the bottom of hole is free of debris.
Wet or slurry drilling methods are used where caving of the drilled borehole is probable, typically when the local ground water table is located within the length of the shaft. By maintaining the slurry above the ground water table while drilling, a positive pressure will be exerted on the sides of the shaft to prevent the inward flow of water and to reduce the potential of caving.
Casing construction methods are applicable to caving ground conditions above or below the ground water table. The cased method uses a temporary steel casing that is installed in advance or concurrent with the advancement of the excavation to provide the lateral support necessary for maintaining the integrity of the hole.
Most commonly, Condon-Johnson uses segmental casing that can be advanced with a drill rig, an oscillator, or a rotator. Segmentally cased holes are the safest and most reliable manner of advancing drilled shafts through caving or slaking ground conditions. Segmental casing can be used for drill shaft diameters from two to 10 feet.
All wet drilled shafts are tested using non-destructive testing techniques, including CSL testing, Gamma-Gamma Testing, and Thermal Integrity Profiling.
Micropiles are 12-inch or less in diameter and constructed using high-strength steel casing and/or threaded bar. Micropiles are designed to carry compressive or tensile loads and can exceed depths of 200 feet with loads over 300 tons. The micropile casing typically ranges in diameter of 5 to 12 inches and is made of high-strength N-80 steel. The casing extends to the top of the bond zone or it can be plunged several feet into the bond zone to provide a stiff cross section and limit elastic deformation of the pile under load.
Condon-Johnson uses the latest technology and equipment for limited access and low headroom micropile installation for virtually any location and every ground condition with minimal vibration and disturbance. The grouting techniques used with micropiles result in much higher bond stress than conventional drilled or driven piles, which means that micropiles have much higher tensile capacity than conventional deep foundations. With higher tensile capacities, micropiles are the preferred alternative for seismic loading.
Condon-Johnson’s micropile drill rigs allow for installation in areas with low headroom and restricted access with minimal disturbance to normal facility operations. Micropiles are often used to underpin existing buildings or to increase the foundation capacity for building upgrades or seismic retrofit.
Condon-Johnson offers design/build services for micropile installation and works closely with engineers, contractors, and owners to ensure a pile cross section that meets the performance requirements of the structural engineer and an installation method that achieves the necessary capacity while minimizing the disturbance to building occupants and existing foundations.
Tiedowns are vertical ground anchors used in tension only to provide resistance to uplift forces. Tiedowns are typically used to resist hydrostatic uplift forces on underwater slabs and static or seismic overturning moment uplift forces in retaining walls or shear walls. Tiedown design should consider both individual anchor capacity and overall stability of the ground mass where the tiedown is anchored. Tiedown load is carried in steel reinforcement and transferred by friction into surrounding ground.
Driven Precast Prestressed Concrete Piles are a Displacement Pile that can be used in friction and end bearing design applications. They are a common pile type in California and provide an effective, low-cost pile that can be fabricated to custom lengths. Precast pile sizes can range from 12” to 24” and can be square, round or octagonal. Condon-Johnson has installed precast piles up to 220 feet long and in the right conditions, could install longer ones. Precast piles can be spliced when headroom restrictions are encountered or for transportation advantages. Because precast piles are installed with impact hammers, we can provide sound mitigation solutions to reduce noise as necessary.
The Driven H-Pile is a perfect pile for highly variable end bearing strata profiles that make predicting lengths difficult. These piles have been installed in lengths over 250 feet. The H-pile typically comes with thicker section as opposed to other steel piles. This allows piles to penetrate through or into dense strata layers like weather bedrock. The H-pile also provides higher lateral strength in the strong axis of the pile which is beneficial when directional lateral loads are required. H-piles range from 8” to 18” and are available in various thicknesses to maximize performance.
Driven Pipe Piles come in two common types, open and closed-ended, and can range from 8 inches to 14 feet in diameter. With either open and closed-ended, the pile can be filled with concrete or left with soil plug. The concrete-fill option allows the pile to be designed for high lateral and vertical stiffness. This provides value in material costs by not requiring the pipe to pick-up the complete load and allows the concrete and/or cage to handle the higher moments when the project requires.
The Torqued-In Pile is a closed-ended pipe pile with a specialty tip, designed to advance the pile to the designed tip elevation. Condon-Johnson uses a variety of tips that provide penetration advantages in different soil conditions. These piles, like all displacement piles, increase friction performance due to densification to the soil. Because the Torqued-In pile is a steel pile, it allows Condon-Johnson to extend pile length by welding. This enables us to work in low headroom conditions and to install piles to longer depths, upwards of 180 feet. The most common diameters are 12.75 to 20 inches.
The Bottom Drop Pile is a closed-ended pipe pile. Named because of the installation technique, the pile is installed with an internal drop hammer. This method maximizes headroom by utilizing the hammer in the pile as opposed to installing the pile from the top. Other advantages of the Bottom Drop Pile are reduced noise and vibration. Since the impact takes place below ground at the bottom of the pile, the vibration is reduced significantly. With each blow and advancement of the pile, noise and vibration are reduced as the impact takes place farther from the ground surface. These piles provide advantages to sites with low headroom conditions as well as to unique sites adjacent to water, long reaches, and those sensitive to noise and vibration.
Condon-Johnson & Associates – Geotechnical Contractors & Engineers
