- Soldier Piles & Lagging Walls
- Auger Cast Piles
- Drilled Shafts
- Elevator Jackshafts
- Helical Piles
- Dewatering Services
Soldier Piles & Lagging Walls
Soldier piles and lagging walls, also called Berlin Walls or king piles, are an earth retention technique that retains soil. The way that soldier piles and lagging walls retain soil is through vertical steel piles and horizontal lagging.
Soldier piles and lagging walls are one of the oldest forms of deep excavation used in retaining systems, used in cities around the world since the 18th century. They are also one of the least expensive techniques used and are very fast to construct.
Soldier piles are most suitable in conditions where well-constructed walls will not result in subsidence, such as overconsolidated clays, soils above the water table if they have some cohesion, and free draining soils which can be effectively dewatered, like sands. Additionally, they are often used when property lines dictate exactly where construction must be.
Permanent Systems Overview
While most soldier piles and lagging walls are used to temporarily retain soil in an excavation site, temporary lagging walls can become permanent when the soil needs to be retained for at least 36 months, according to current Washington state law. The most important consideration when installing a permanent lagging wall is that soil conditions are suitable. The retained earth cannot be prone to shift easily (such as with sand or soft clay) or have a high water table. For areas that may experience large amounts of precipitation, lagging walls must be built to drain water away from them, as weeping holes built into the wall aren’t sufficient.
Temporary Systems Overview
Soldier piles and lagging walls are often temporary installations used to retain soil in an excavation site. Temporary lagging walls are differentiated from permanent systems by the length of time in use. For Washington state, temporary lagging walls can be in use for up to 36 months, after which need to be removed or converted into permanent lagging walls. Temporary lagging walls and soldier piles are easy and quick to install and utilize lower-cost materials, as they do not need to withstand long-term stresses from loads and corrosive soil conditions. Temporary systems aren’t well-suited for long-term use because retained earth can shift, which can cause stress exceeding the load capacity over time. In addition, corrosion from water can degrade the system’s integrity. Short-term construction projects don’t need to worry about these long-term effects, making them excellent low-cost options for retaining earth while installing a deep foundation
Auger Cast Piles
Auger Cast Piles are a quiet and cost-effective process for casting deep foundation piles. Also known as continuous flight augering (CFA), piles are cast in-situ by using a continuous flight auger with a hollow center to inject liquid cement as the auger is removed.
The auger cast pile process is very economical for foundations in soft ground, as other techniques would require casings or support fluids to keep the ground in place. Auger cast piles are faster to install than bored piles and cause less noise and vibration during installation than driven piles, ideal for noise and environmentally-sensitive areas. Auger cast piles are also stronger than prefabricated piles because of the increased friction of the soil surrounding the pile caused by in-situ casting.
A common use for auger cast piles is to build secant (interlocking) piled retaining walls. It is important that the pressure and volume of liquid concrete is carefully controlled in order to cast a well-formed pile. This process can be used in ground containing clay, water-bearing sands, gravel, and soft rocks, but the soil conditions must be well-understood before drilling begins.
Drilled shafts and piling covers multiple pile types used in deep foundation construction, all of which require a hole to be bored before setting the pile. Also known as caissons, drilled piles can be formed in a wide variety of ground conditions, ranging from dense, dry strata to softer, water-logged strata. These piles can be used in many types of construction projects, and are especially effective for structures like tall buildings, bridges, and tanks. Drilled piles can withstand compression, tension, or lateral loads.
Drilled piles are excellent in case where the site requires low noise and vibrations, and can withstand heavier loads than prefabricated piles. In addition, the least amount of soil is displaced, eliminating the need for large-scale excavation, soil removal, and subsequent soil backfill. Wider diameter piles can be formed using this technique, which can remove the need for caps over pile groups.
While adaptable to most ground conditions, drilled piles must be constructed carefully, as the environment largely defined how the pile should be constructed. In a soft soil, an incorrectly-formed pile can bulge in places, greatly reducing load capacity. Drilled piles are not recommended for contaminated sites, as the contaminants can corrode the pile over time.
Elevator Jackshafts are shafts used to hold hydraulic jacks for elevators. Hydraulic jacks are the most common mechanical device for lifting elevators, representing around 70% of elevators installed in new building structures. Elevators of this type utilize a single plunger jack installed underneath the elevator car. Hydraulic jacks are ideal for low and medium rise buildings (typically 2-5 floors), given their low mechanical complexity. Elevator Jackshafts can reach depths up to 75 feet.
The cost of installation for an Elevator Jackshaft and hydraulic jack are approximately half the cost of a traction elevator, and utilization of underground space to hold the jack allows for more efficient use of space, as an overhead machine room is not required.
Helical piles, also called screwpiles, are hollow tubular piles that have a screw or helix design. They are commonly used as ground anchors for building deep foundations. The screw design is fabricated by welding helical steel plates (called blades or flights) to the pile shaft, with positioning and plate thickness determined by load requirements, ground conditions, and expected design life.
Originally used for building lighthouse foundations, helical piling systems are now used in many structure types, especially where fast installation is required or the construction site is close to existing structures. Screwpiles are cost-efficient and have a smaller environmental impact, since they displace less soil than traditional boring techniques. They are useful in sites with high water tables, and are easy to remove when a foundation is no longer needed. Helical piles can be used immediately after installation, not requiring concrete to cure.
Dewatering services remove groundwater from a construction site through pumping or evaporation. Well dewatering is a common solution, and hundreds of dewatering wells are constructed and decommissioned in Washington state every year.
Dewatering is important in facilitating construction, stabilizing and landslide, or protecting an aquifer, and should often be performed before subsurface excavation for a foundation begins. Dewatering can also be used to lower the water table in a construction site. Pearson Drilling offers customized dewatering service solutions, including bypass pumping systems and jetting, to suit your construction needs.
Given the small footprint of well dewatering equipment, it is an effective method for removing groundwater in tight construction sites, where larger equipment cannot maneuver easily. Well dewatering is also well-suited for a variety of soil conditions, including harder to manage conditions including clay and sand.
If you have any questions regarding our drilling services or if you would like to discuss your project drilling needs with an expert, please contact us today.425-672-4826