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ACSW testing for Geotechnical Design
Geotechnical Design is at the heart of SoilSafe. We aim to provide our clients with support by listening and understanding their needs. Providing expert advice and guidance on how ACSW testing can benefit them.
Settlement Analysis
ACSW Stiffness Measurement
Traditional methods of determining ground stiffness can be cheap but inaccurate (for example empirical relationships such as with SPT N value) or accurate but expensive (for example large scale load tests or pressure meter testing).
ACSW testing provides accurate stiffness profiles at reference small strain levels, non-intrusively, down to typical 10 to 15m depth for about the cost of a plate load test. Since 20 tests can normally be completed in an 8-hour shift, ACSW testing can be carried out rapidly and cost effectively to allow accurate whole site characterisation.
Since stiffness is measured by ACSW at small strain levels where stiffness is constant, strain softening functions can be applied to E0 to give a design E value at the appropriate strain. ACSW test data is provided in an Excel format which allows the user to adjust any assumed parameters, including design strain.
Settlement Calculations
Routine Analysis
For simple, routine analysis suitably strain softened ACSW stiffness data can be used directly in hand calculations adjusting for stress distribution and soil strata.
Refined Analysis
An improved level of accuracy can be provided through the use of a step wise analysis approach. This methodology allows the non-linear stiffness behaviour of soils to be simply modelled and improves accuracy where operational strain levels are uncertain or where only light loadings are being applied and strain levels are low.
Advanced Analysis
Where the settlement problem is complex, or the highest level of accuracy is required, then Finite element methods may be appropriate. Certain FE software provide small strain models with inbuilt softening functions (i.e. PLAXIS) which permit the direct input of small strain G0 stiffness values. In this case the soil stiffnesses across the FE mesh are determined based on individual element strains permitting the accurate modelling ground stiffness around rigid structure boundaries.
VIB testing
We use our Validated Independent Base testing (VIB testing) approach to ensure that all foundation bases across the site have their independent settlement limited to the structural engineer’s design criteria. This method uses our ACSW stiffness profiling test to ensure that we know the ground conditions at every single foundation location. Given that our tests take around 5 minutes to complete and the results are in real time, this method is cheaper and safer than vibro stone columns, deep soil mixing or CMC foundations which are largely impossible to validate to their full depth.
Validated Independent Base Design
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The use of CSW stiffness data, coupled with simple analysis techniques... provided a far better prediction of settlements than the complex finite element analysis
Heymann et al, 2017