Southdowns is the lead noise and vibration specialist for the design and build contractor (Alstom TSO Costain JV,) with responsibilities that include the final detailed design sign-off of the proposed Standard Track Systems for the tunnelled sections of the alignment under central London.
The track has been designed to achieve prescriptive groundborne noise and vibration requirements in overlying buildings and includes several generic trackform types including: resilient baseplates; bi-block and monobloc booted sleeper systems; and two variants of floating track slab in sensitive locations. Other design related elements include: the optimisation of fixed nose switch and crossing units to minimise groundborne noise and vibration; the field measurement of vibration transfer functions between tunnels and buildings; the management of combined wheel / rail roughness to control groundborne noise and vibration; and calculation of Insertion Gains to assess the predicted changes in track system parameters associated with design changes. The work package also includes liaison with Local Authorities on technical matters to ensure that Project commitments are achieved and also to interface on issues with the future Infrastructure Maintainer.
In addition to the design input, Southdowns is also responsible for the construction noise and vibration management during track construction and M&E fit-out. This includes: temporary track laying trains in tunnels; FTS construction using high density concrete pumping via shafts from the surface; preparation of and submission of Section 61 consent applications, dispensations and variations; routine Best Practicable Means audits and attended monitoring; vibration risk assessments and monitoring the effects on heritage assets.