DeWaal piles are reinforced concrete piles constructed by means of a screw-shaped tool that allows sufficient penetration into dense soil layers, while not allowing decompression of the soil. The soil is displaced laterally such that there are no surface spoils. Installation requires a fixed mast rig, high torque turntable, and crowd capability. Morris-Shea owns drill rigs capable of installing from 12″ through 24″ diameter DeWaal piles and depths of up to 120 feet. Working loads up to 250 tons have been achieved. Foundation support has been provided for chemical plants, pulp and paper facilities, steel mills, power plants, high-rise buildings, refineries and many other structures.
Morris-Shea purchased the exclusive rights to the patented DeWaal® pile system in 1992. Since then, we have successfully installed several hundred thousand piles on numerous projects throughout the US and Caribbean. This pile system is a full displacement cast in-situ pile, and as such, has the load capacity benefits of a displacement pile, along with the low noise and vibration-less advantages of an augercast or CFA pile.
HOW IT WORKS
Installation of DeWaal piles involves the advancement of the tool with a detachable end plate to the design tip elevation. As the tool is advanced, it is rotated to facilitate soil to be transported and ramped up to a full diameter section, called the displacement body. At this point, the soil is displaced laterally into the annular zone around the pile, resulting in densification. This process essentially creates a soil form.
Upon reaching the design tip elevation, a center bar is typically placed full length inside the drill stem and the 9-inch ID drill stem is filled to a level above grade with a rich and plastic concrete by means of a pump. The rig then withdraws the tool, while still rotating clockwise. The end plate is left behind; concrete flows out under hydrostatic pressure and fills the hole.
During extraction, the left-handed flight above the displacement body picks up any caved material and re-compacts it back into the soil. This pressure from the displacement body, in addition to hydrostatic pressure from the concrete in the 9-inch ID drill stem, ensures no decompression of the soils. This results in extremely high friction values. The degree to which displacement causes an increase in capacity is a function of soil type and the initial relative density. Increases in unit shaft friction over those typically observed for auger-cast piles range up to 30% in loose granular soils.
Upon concreting, a reinforcement cage is installed in the upper section of the pile. The inherent soil improvement process of DeWaal pile installation generates higher lateral capacities compared to conventional in-situ piles. Due to the high power of DeWaal rigs, pile production typically ranges between 25 and 55 piles per day. The DeWaal pile is a low-noise, vibration-free system. This can be advantageous where deep foundation support is needed in sensitive areas where noise and vibration are unacceptable. In areas of sensitive soils, vibration or pile driving can cause settlement or cracking from vibrations. DeWaal piles eliminate risk of such potential delays and claims. In addition, the lack of spoils removes risk of high costs and delays dealing with and disposing of contaminated soil. Drill rig instrumentation of drill depth, torque, auger rotation and concrete volume facilitate a controlled drilling and concrete process and provide a record of each pile instead.
DEWAAL CONSTRUCTION PROCESS
Step 1: Position DeWaal tooling over pile point and attach sacrificial endplate.
Step 2: Advance DeWaal tooling by rotating clockwise and applying crowd force. All material is displaced laterally; there are no spoils or vibrations.
Step 3: Penetrate into bearing layer as specified.
Step 4: Place full-length center reinforcing bar into tremie, then pump tremie full of concrete to a level above the ground.
Step 5: Withdraw DeWaal tooling using clockwise rotation while maintaining the concrete level within the tremie. The sacrificial end plate remains at the pile tip.
Step 6: Upon withdrawal of the DeWaal tooling, clean pile head of debris.
Step 7: Insert additional reinforcing steel as required to satisfy the specified pile load requirements.
BENEFITS OF DEWAAL PILES
- Increased unit shaft friction allows shorter or fewer piles to be used for the same loads as compared to augercast or driven piles
- Use of an end plate and the bottom discharge concreting method used precludes the need to pull the DeWaal stem up prior to pumping and results in higher end bearing than other cast-in-place piles.
- Lack of spoils
- Environmentally more acceptable than driven or augered piles
- High production rate allows accelerated schedules
- DeWaal pile integrity is not dependent on concrete pump rate during withdrawal
- Eliminates the need for long manufacturing lead times, large lay down space, and coordination of deliveries associated with pre-cast concrete piles