CONTINUOUS SURFACE WAVE TESTING
Part of our Data Acquisition Solution
Continuous surface wave testing offers a faster, safer and more cost-effective solution for soil and ground strength profiling, eliminating the need for large rigs, reducing risks and time associated with intrusive investigations.
What is Continuous Surface Wave Testing?
Continuous surface wave testing uses a seismic shaker source and a small linear array of geophones to record time-series data, enabling the empirical determination of client-specific parameters, such as shear and Young’s moduli, at depths of up to 30 metres below ground level. The laptop-based software uses the data to provide a stiffness versus depth profile.
CSW testing provides valuable information for a wide range of applications, including (but not limited to) crane pad design, track-bed analysis, highway substrate profiling, earthwork progression and general geophysical surveys. Our team has extensive experience with CSW across diverse environments including highways, rail and construction, and has successfully delivered high-profile contracts for industry leaders such as Network Rail and HS2.
CSW reporting meets bespoke client requirements. Information is delivered in both PDF and Excel formats, and results can be tailored to meet specific designer specifications. Parameters, such as bulk density, Poisson’s ratio and strain softening can be customised and tailored to the site and specific geological settings for the truest to ground dataset possible.
CSW data is robust; it is stacked and evaluated live on site, eliminating the need for extensive post-processing. Additionally, a brief Spectral Analysis of Surface Wave (SASW) hammer shot is performed to validate and enhance the CSW dataset.
Key Benefits of CSW Testing
Rapid
Six to ten tests can be completed in a single day
Safe
Avoids the risk associated with intrusive work
Turnaround
Indicative results may be evaluated live on site and verified with an additional SASW test. Simple inversions can be fully processed and reported within 48 hours of site work.
Portable
All site gear fits within and can be operated from a single 4×4 survey vehicle, and be operated by a two-person crew
Penetration
Typical depths achieved span 5-10m with a maximum possibility of up to 30m, providing an alternative to shallow boreholes
Advanced Inversion Capability
With plentiful ground truthing information and satisfactory data, a full advanced inversion analysis can also be performed for the site inferring layering systems and material identity
Adaptable
Effective in both man-made and natural substrates
Cost
Avoids the necessity for large mobilisations and large numbers of staff to operate
Size
The smaller size of the equipment enables the technology to work closer to key points of interest while minimising the potential for damage or adjustments required
Case Study: Parsons Tunnel to Teignmouth
Key Project Details
Location: Dawlish, Devon
Client: Network Rail
Sector: Rail
Services: Continuous Surface Wave (CSW) Testing
The setting of this case study is on the Parsons Tunnel to Teignmouth project based near the Exeter to Plymouth rail line in Dawlish, Devon. Dawlish station and the Great Western Railway see the transport of over half a million passengers every year along the South Devon coast.
Jacob’s, on behalf of Network Rail, instructed Central Alliance (CA) to perform a ground stiffness analysis in a variety of settings pertaining to the operation of MLN1, as part of a geological investigation across two phases: Phase 1 in May 2022 and Phase 2b in March 2023. The point profiles would be produced with the aim of complementing intrusive information obtained from borehole drilling and identifying geological strata and voids in the subsurface.
There are a variety of geophysical methods available that can be used to establish this, including lightweight deflectometry (LWD) and multi-channel analysis of surface waves (MASW). CAs Applied Technologies division, however, deployed its’ bespoke advanced continuous surface wave (ACSW) system to tackle this specific challenge.
Cumulatively, Jacob’s gave Central Alliance (RSK) the objective of completing 6 CSW surveys on public and private land across Dawlish and Teignmouth. A frequency band of 10-250Hz would be tested at each location with bespoke increments.
The stiffness of the ground would be assessed and quantified with depth at each position in Shear and Young’s Moduli; any layering present would be modelled with an advanced inversion, and evidence inferring the presence of significant voids would be reported upon.
Central Alliance (RSK) successfully deployed its’ CSW team whom thanks to the system’s rapid testing and swift turnaround, and moreover the experience of its engineers, completed both site visits within a single day, and completely processed and reported simple inversion data to the client within a 48 hour turnaround.
An advanced inversion methodology had been trialed using Geopsy (Wathelet, 2020) in the months between phases, and a layer analysis was requested by Jacob’s. This was successfully performed as part of the service for the first time. Within 1 week, Central Alliance (RSK) using intrusive information from the simultaneous geotechnical investigation, modelled and constrained the layering inverse problem down to a 2.3-4.6% misfit. Discrete layers and geological boundaries were identified and relayed to the client successfully.
Through rigorous testing and repeated attempts initiated from live data analysis on site, the presence of voids was inferred to the client and proofed by intrusive investigations, who found assumed zones of core loss in the same areas. The ground models generated by the advanced inversion also correlated well with intrusive means of strength testing, such as SPTs.