ACSW PROFILING APPLICATIONS
ACSW testing provides high quality stiffness and shear wave velocity data to optimize engineering solutions.
RAILROAD BED DESIGN
ACSW testing provides accurate roadbed formation stiffness measurements without the need to excavate or unclip track. Tests can be undertaken on ballast and will automatically provide Rayleigh wave velocities for the design of high-speed track.
Testing equipment can be mounted on a rail skate or truck if required and the speed of ACSW testing maximizes 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 optimization – in one case demonstrating 2 to 3 times less movement than the conventional approach to determining stiffness parameters. 1
For large projects such as railway electrification, the savings realized by reducing individual pile lengths or reinforcement can be very significant, but optimizing these designs is not possible without representative high quality stiffness parameters, such as those 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 (and thus commonly used) stiffness data, routine 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 equipment to provide reaction force.
Since 12 tests can be completed in a normal shift, validation across the site can be undertaken rapidly without disruption to other site activities.
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 tests are typically completed per shift, allowing assessment of stiffness variations and providing 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 or zones of karst collapse.
Use of ACSW testing in these circumstances avoids the risk and delays associated with intrusive investigation, particularly where there are sensitive underground utilities.
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 provide an initial indication of other design soil parameters, to supplement existing test data or where opportunities for intrusive investigation are limited (for example utility corridors).
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 provides an accurate way to determine in-situ wave velocity profiles directly and 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 allows large data sets to be obtained, detailing variations in stiffness with depth and spatially.
Consequently, 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.
