High speed and conventional trackbed design
ACSW testing provides accurate trackbed formation stiffness measurements without the need to excavate or unclip track. Tests can be undertaken on ballast along the 4-foot in possession and will automatically provide Rayleigh wave velocities for the design of high speed track.
Testing equipment can be mounted on a rail skate or trolley if required and the speed of ACSW testing maximises possession working opportunities. The portable nature of GSS ACSW equipment also means it can be easily removed from track, reducing the risk of possession overruns.
Pile design for lateral loading
ACSW has been successful used for lateral pile design optimisation – in one case demonstrating 2 to 3 times less movement than the conventional approach to determining stiffness parameters. 1
For large schemes such as railway electrification the saving of reducing individual pile lengths or reinforcement can be very significant, but optimising these designs is not possible without representative high quality stiffness parameters as provided by ACSW testing.
1Deighton, M & Rigby-Jones, J (2016) Improved estimation of ground stiffness for railway projects using Continuous Surface Wave testing, Ground Engineering
Accurate settlement analyses
Due to the poor quality of most easy to obtain stiffness data, routine settlement analysis often provides very inaccurate results. To improve accuracy normally requires very expensive and time consuming testing such as instrumented large scale load tests.
ACSW testing has been demonstrated to provide representative stiffness data equivalent to the most expensive stiffness measurement but can be undertaken rapidly and at a fraction of the cost. 1
Heymann G, Rigby-Jones J, & Milne C A (2017) The application of continuous surface wave testing for settlement analysis with reference to a full-scale load test for bridge at Pont Melin, Wales, UK. J. S. Afr. Inst. Civ. Eng. 2017:59(2)
Analysis of basements and retaining structures
High quality stiffness data is required for the design of deep structures. Traditionally stiffness data for Finite Element analysis has been obtained using pressuremeter or specialist triaxial testing, but this is expensive, requires boreholes and can be very time consuming.
ACSW testing offers a low cost alternative whilst providing data of similar high quality. The size of ACSW testing equipment means that it can be easily used in difficult to access locations such as excavations.
Ground improvement design and control testing
GSS ACSW provides a rapid and cost effective alternative to zone testing for ground improvement. The ‘simple inversion’ average stiffness profile generated on site can be used to demonstrate the improvement during ground treatment to depth, avoiding the uncertainly provided by shallow plate load testing and without the need for heavy plant.
Since 12 tests can be completed in a normal shift validation across the site can be undertaken rapidly with out disruption to other site activity.
Real-time consolidation assessment
Optimising the start time for construction on reclaimed or surcharged material is essential. CSW testing allows stiffness improvements to be assessed in near real time and to depth.
The speed of GSS ACSW testing means that 12 test are typically completed per shift, allowing assessment of stiffness variations and greater confidence in decision making.
Stiffness profiling to identify discrete layers, such as rockhead variation
Where there is a variation in stiffness with stratigraphy, such as at rockhead, ACSW testing can be used to give an approximate ground profile, supplementing intrusive investigation, particularly where access is difficult. ACSW has also been used to identify zones of poor ground, such as collapsed mineworkings.
Use of ACSW testing in these circumstances avoids the risk and delays associated with intrusive investigation, particularly where there are sensitive services.
Preliminary site assessment
GSS ACSW testing provides accurate shear wave velocity (Vs) profiles for which published corrections exist for a wide range of soil parameters including shear strength, SPT N value and CBR. In addition to providing accurate stiffness profiles ACSW can therefore provide an initial indication of other design soil parameters to supplement existing test data or where opportunities for intrusive investigation are limited (for example services sensitive locations).
Seismic and liquefaction assessment
ACSW testing provides the shear wave velocity (Vs) ground profiles required by seismic design standards such as US ASCE and Eurocode 8. Using ACSW provide an accurate way to determine in-situ wave velocity profiles directly without the need for boreholes.
Shear wave velocity can also be used to reliably assess liquefaction susceptibility, another key concern for earthquake engineering.
Ground characterisation for stiffness modelling in 2D and 3D or BIM
The speed of GSS ACSW testing and allow large data to be obtained which details variation in stiffness with depth and laterally.
As a result representative 2D and 3D modelling of stiffness for site characterisation and BIM output is now possible for sites with suitable grids of ACSW test data.