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The grab survey is undertaken along the outfall using a suitable seabed sampler. Inshore operations using small grabs, such as Van Veen and Shipek, are sometimes not successful. In these cases we use a hydraulic clamshell grab which is considered the most suitable for achieving representative samples although a Hamon grab is also utilised, in particular for benthic work, as this instrument is recommended by CEFAS for this type of operation.
Sampling of surface sediments (the top 5cm) is normally required on and off the pipe-route at regular intervals.
Samples collected are retained and sub-sampled into double-lined plastic bags prior to chilling within a cool chest. Samples are transported back to the laboratory for sieve analysis in this fashion.
Additional samples are collected for benthic fauna analysis using the Hamon grab which has been specifically designed to minimise washout of surface sediment as the grab is raised from the seabed. This means that the sample is completely enclosed within the grab. Samples are representative of around 0.1m² of the seabed. The recovered material is initially described and subsequently sieved through a 1mm mesh.
Organisms retained on the sieve are fixed immediately in 10% buffered saline formalin solution (4% formaldehyde), the volume of fixative used exceeding the volume of the sediment sample by a factor of at least two.
Large stones are returned to the sea following in situ inspection by the scientist onboard, recording the retention of attached fauna.
Cone Penetration Testing (CPT) is generally carried out in accordance with BS 1377 Part 9 section 3 with the exception that a 5cm² cone is used.
The Cone Penetration Test is based on pushing an instrumented cone into the ground at a constant speed, with continuous measurement of the cone end resistance, the friction along the sleeve of the cone and the pore water pressure.
These measurements make it possible to evaluate accurately the ground conditions and stratigraphy over the penetrated depth. The system is designed to use 2, 5, and 10cm² piezocones.
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he probe is pushed into the seabed using a well proven 25kN nominal, 40kN maximum thrust, electric powered ROSON friction wheel drive unit.
Maximum penetration is in the order of 5.0 metres although in specific conditions greater penetration may be feasible. Our preferred method of operation is to utilise 5 cm² cones pushed into the soil with a maximum thrust setting of 20-30kN. Use of 5cm² cones is included in NEN (Dutch) standards.
High strength rigid steel rods reduce the risk of deviation and breakage compared with coiled tubing.
When using a 10cm² cone the base dimension and weight can be increased to 4.0 m² and 5 tonnes respectively.
Read about the real-time data acquisition, the CPT rig and the advantages of using our advanced CPT service.
Recent advances in current flow measurement technology have provided Clydeside Surveys with the tools to gather current profiling data in a variation of marine environments.
For pipe and outfall route applications we use an RDI Workhorse. This tool can either be mounted aboard the survey vessel or for long duration surveys mounted in a seabed frame.
For measuring non-stop across the flow field, RDI’s Horizontal ADCPs give horizontal profiles with as many as 128 individual points of measurement.
Installed in estuaries to define complex circulation patterns, in ports and harbors monitoring surface currents for navigation and safety, in rivers to measure discharge rates, and on oil platforms and seismic vessels during oil exploration and production.
An innovative and powerful way to measure waves and currents at once. More than a wave gauge — ADCPs (Acoustic Current Doppler Profile) measure a complete frequency-direction wave spectrum and can operate in shallow and deep waters.
Better than a directional wave buoy — ADCPs distinguish waves from multiple directions and operate with less risk of loss or damage. More powerful than a single instrument — the ADCP measures velocity profiles, water level and wave frequency-direction spectra at once.
We can measure waves like never before — for more capability and better performance than the traditional choices for measuring waves.