Piling System Projects
What is a Screw Pile?
History
The earliest known use of screw pile foundations was in 1833, when Englishman Alexander Mitchell designed the supporting foundations of a series of lighthouses in tidal regions in the Thames area and around England. These were manufactured in cast iron and apparently installed with a capstan and a number of horses drays! Also in England in 1863, the West Brighton pier was constructed utilising steel screw piles. A number of original piles where exhumed just recently, showing that even in the most extreme exposure conditions, they have lasted over 150 years, well beyond their design life.
This "emerging technology" was imported to Australia in 1872, and used to build the "Cape
Jaffa Lighthouse" erected to alert ships of the Margaret Brock Reef off the South Australian
coast.
The oldest known functioning screw pile structure in Australia is the Victor Harbour jetty,
known as the "Screw Pile Jetty" in South Australia which was built in 1881.
Similarly in India, the screw pile was used in Piers and Railway Bridges and associated
structures.
Japan also in the late 1800's began utilising the screw pile for similar applications.
There is not much documented on what was constructed with screw piles from this period until the 1950's, when the A.B.Chance company in the United States utilised screw piles primarily for tension applications.
In Australia since the early 1990's ,screw piles have been used extensively across the country in compressive , tensile and lateral load applications in new domestic and commercial buildings and structures. They are used in civil applications, as well as underpinning existing buildings. The rapid expansion of this industry is due to the cost effectiveness of the product, combined with the rapid installation technique as well as the "cleanliness" of the system.
Introduction & Development
Steel screw piles are the most cost effective foundation type available in the domestic and commercial construction industry. They are also the most rapid in installation, as well as causing the least disturbance to the soil profile during installation, eliminating the costly and time consuming removal of spoil.
The pile consists of a high tensile 350 to 400 Grade steel shaft, with a single or multiple
helix plate welded to the base of the shaft and a point of attack "bit" at the end, to assist
in penetrating the soil profile. The pile is screwed into the soil profile by a hydraulic
drive motor which is suspended off the boom of the excavator.
A pressure gauge is mounted in the cab for the operator to read the "torque" being
generated as the pile is screwed into the soil profile. The torques are measured and recorded
by the installer on the engineer's project log.
The design requirements for the torques are test proven from soil bearing capacity to torque
relationships which are related to Static Load results and C.P.T. comparisons.
The number and sizes of the helixes used is a function of the soil profile, with deep firm clay profiles requiring large plates and 2 to 3 helixes. This reduces the depth the pile would have to go, with conventional piles having to penetrate deeper into the profile. This "gearing" principle gives the screw pile considerable design flexibility. Shallower soil profiles over rock would require a small single helix plate.
The screw pile is a "displacement" pile, which as the title suggests, displaces soil as it screwed into the ground much the same as a timber screw is screwed into a plank. Unlike bored piers and driven piles, 90% of the load is generated from the helix plate at the base. Unlike bored piers and CFA piles, no spoil is excavated or removed from site, eliminating the potential issue of contaminated soils. Also due to the relatively slender shaft diameter, it far less likely to hit obstacles within the profile. Unlike driven piles, there is no vibration at all from the installation process.
Applications
Domestic Constructions
- replacing bored piers
- Replacing blinding concrete
- Replacing concrete pads and stumps for timber floors
- Angle of repose for easements and sewers
- for protection of tree roots and as root barriers
- for underpinning new or existing structures
- for eco-sensitive sites
Commercial Constructions
- replacing bored piers and CFA piles
- replacing driven piles
- Replacing blinding concrete
- Replacing concrete pads and stumps for timber floors
- Load capacities up to 2400Kn ultimate
- Unlimited length potential
- commercial high rise up to 6 storeys
- Angle of repose for easements and sewers
- for eco-sensitive sites
Civil Constructions
- Foundations for light poles and transmission towers
- Foundations for signs
- Foundations for Bridges and walkways
- Ground and land slip stabilisation
- Foundations for shade structures
Mining Applications
- Foundations for mining structures
- Foundations for pipelines and
- Foundations for conveyor Belts
