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ScrewFast Foundations Ltd have recently successfully installed and tested piles for loads of over 800kN in compression, 600kN in tension, and 75kN laterally to simulate the applied loads from a large super-span portal gantry. Each foundation comprised a single row of 8 piles supporting a large circular beam grillage. The axial load tests were made with a beam and reaction piles and the lateral load tests were made against a pair of reaction piles as can be seen in Fig.3. The testing was completed in accordance with the Highways Agency Series 1600 Specification for Piling and Embedded Retaining Walls.
The piles were only 7m long with 3 helical plates: a 450mm diameter plate at 6.5m bgl, and 600mm diameter plates at 5.5m and 4.5m bgl. The sub soil was clay.
Each pile was installed in approximately 45 minutes to a torque of 130kNm . Large diameter shafts up to 298 x 10mm CHS were installed to cope with the large design moment and lateral loads. A traditional pile relying on skin friction would need to be 7m in length and have a diameter of 1m to achieve the same ultimate capacity, in the same soils.
The benefits gained by the use of helical piles combined with the innovative steel grillages, or pile caps, are:
a) smaller piles
b) lighter installation equiptment
c) no spoil
d) rapid installation.
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