CemOptics – Northern Line Extension

CemOptics – Northern Line Extension


Sector: Rail
Scope:  Thermal integrity profiling: 74 x 60m bearing piles of 1.2-2.4m diameter and 116 diaphragm wall panels (including corner panels and T-shaped panels)

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The upgrading of the A14 encountered a wide range of ground conditions in locations for bridges and abutments. To fully understand these conditions and assist the design team, geotechnical testing was needed. This included static load testing of eight preliminary piles with applied loads of up to 21MN.

Each pile was installed with at least four lengths of distributed fibre optic sensors (DFOS) alongside temperature compensating fibres. The fibres were attached to the reinforcement cages that were placed into rotary bored piles.

Fibre optic instrumentation was installed alongside traditional instrumentation, with some piles including up to 36 vibrating wire strain gauges and extensometers. The success of the fibre optic monitoring yielded a valuable set of data from which an efficient design was produced. What’s more, on one of the test piles – at a critical location for the project – the data from the fibre optics revealed the exact location of a significant change in ground conditions.

With traditional instrumentation, it would have been impossible to identify the boundaries of this feature or successfully back analyse the results from the test pile, once more demonstrating the benefits of DFOS.

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