Drilled shafts (also referred to as caissons) are high capacity concrete foundation elements. Drilled shafts are often used in cases where high axial and/or lateral loads need to be resisted. They are constructed using specialized equipment that can generate very high torque and crowd forces. In some cases, drilled shafts can be completed using “open hole” drilling. In other cases, casing or drilling slurry is required to maintain hole stability during shaft excavation and concrete placement. Drilled shafts range in size from approximately 18″ in diameter to in excess of 10 feet in diameter. Shaft depths are also highly variable and are determined by the specific shaft design. Shafts can be completed in many types of soil and rock. When drilling into rock, equipment with very high torque and crowd transfer is required when using conventional drill tooling. Alternatively, rotary percussion drill tooling can be used to excavate rock sockets in very hard formations.
The same methods and equipment that are used to construct drilled shafts can be used to pre-drill for piles. Pre-drilling for piles (H-piles, pipe piles, etc) can be advantageous when installing piles in areas that are particularly sensitive to noise, vibration, or lateral clearances.
H.B. Fleming has experience with the following types of drilling:
- Drilled shafts for Sound Wall foundations
- Drilled-in-place soldier piles
- Design-Build sign foundations in accordance with AASHTO/FHWA Specifications
- Rock socketed piles for building and bridge foundations
- Tower and pole foundations for CCTV poles and radio/cell towers
We are able to mobilize our drilling equipment quickly and we are able to quickly react to construction challenges, thanks to our ability to perform much of our engineering in-house. These abilities help get projects under way in a timely fashion, and help to maintain continued momentum on site.
Below are some examples of drilling work we have recently completed.
Pre-drilling for soldier pile installation can be an effective way to mitigate concerns regarding construction related vibration transfer. The photos below show a project in Hopkinton, MA where H.B Fleming was able to construct a soldier pile and lagging excavation support system within a few feet of a historically significant library with a very sensitive rubble foundation. Pre-drilling for the piles allowed the piles to be installed to a strict tolerance requirement, mitigated the potential for vibration transfer, and allowed for removal of cobbles and boulders that would have otherwise caused the piles to fall short of their required embedment depths.
In order to accommodate a severely sloping ledge profile, the Maine DOT elected to use rock socketed piles in place of conventional driven piles for the below project in Meddybemps, ME. Maintaining pile location using conventional pile driving techniques would have been difficult with this subsurface condition.
The photos below are of a recent project in Portland, ME. H.B. Fleming was hired to install three drilled shafts that will support a cell tower owned by the City of Portland. Each shaft was 48″ in diameter and extended approximately 30 feet to rock. Each shaft was then socketed 4 feet into sound rock.