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It’s been testing, testing, testing on the METRONET Byford Rail Extension as structural works scale up with the building and measuring of not one, but two test piles.
The name gives a hint but what exactly is a test pile, how is it built and what is it testing?
A test pile is a reinforced concrete pylon built before construction of the viaduct begins. Put simply, its role is to test whether the piles will be able to carry the weight of the elevated rail infrastructure and if any design changes are required.
The test piles are built by drilling a hole 21m deep x 1.8m in diameter and removing the dirt – a process that typically takes around four days. If water or sand are encountered during drilling, a jelly like substance called polymer is used to stabilise the walls of the hole. Following this, a steel reinforcing cage is placed in the hole with a test cell and measuring instruments and the hole is filled with concrete and left to cure for 28 days.
The test cell enables the pile to be put at a depth under pressure, pushing the base of the pile downwards and the shaft of the pile upwards. The cell then provides information on friction measurements, which informs the design of the pile and ultimately ensures structural stability of the design structure.
The testing method used on the Byford Rail Extension is an Osterburg Bi-directional load cell test. This is a modern method of testing which provides highly accurate results that minimise wastage and conserve resources as structural works take place.