BBV HS2 MWC North Rayleigh Waves

Description

BBV intends to appoint their preferred bidders on the basis that risks are owned by those best able to manage the risk. Successful tenderers will be required to provide the equipment, labour and supervision to carry out the measurement of the shear waves velocity and ensure delivery of their package of works with the interpretation of the results via a report included. Each offer is required to identify the areas where shared responsibility or a change in responsibility would offer value to the project. Rates to include reports, staff, preliminary visits, site inductions, testing, equipment's, calibration of equipment to enable contractor to carry out the measure of the shear waves velocity. The measure of shear waves velocity would be happening during the hold period on the weather protection layer to limit the interaction with other parties and affect the collection of data. The depth of measuring should be up to 7m depth and on 1 lane of measurement. All reports are to be supplied in an agreed format, such as PDF/Word/Excel. Any agreed format and colours mapping is not to be changed without agreement. Reports are to be emailed to agreed email addresses within 2 weeks after completion of the site measures. Where client specification is supplied this is to be included on report. No external agencies can be subcontracted to without the approval from BBV. Method of testing Two (2) method of testing might be proposed in the tender, but it should be clearly defined. The tenderer should justify of using this method previously and provide suitable references. MASW method (Multichannel Analysis of Surface Waves) The geophysical survey used MASW to generate and record surface wave energy. The recorded energy was analysed to produce modelled S-wave velocity profiles. The MASW method relies on surface wave seismic energy (specifically Rayleigh waves) which can be generated by an active source (usually an impact event). The propagating surface wave energy was recorded with a linear array of geophones. The captured dataset from a single source event is referred to as a 'shot gather.' The shot gathers are analysed to measure the Rayleigh wave 'dispersion' (velocity as a function of frequency). Dispersion of Rayleigh waves occurs because their depth penetration is dependent on wavelength. Higher frequency (shorter wavelength) Rayleigh waves will typically propagate at a relatively low velocity, representing shallow materials, while lower frequency (longer wavelength) Rayleigh waves will typically propagate at a higher velocity, representing deeper materials. CSW method (Continuous surfaces Wave) The CSW testing system uses a vibrating source with an operating range of 5 to 100 Hz to produce surface or Rayleigh waves that propagate across the ground. These waves are detected by a system of geophones and analysed using software to provide a stiffness versus depth profile. If required, office-based post-processing can provide