The Multi-Channel Analysis Of Surface Waves (Masw) Method As A Tool For Ground Improvement Certification

Ground improvement techniques such as High Energy Impact Compaction (HEIC) of fill requires testing to allow certification of the compaction process. HEIC is often performed on mixed, unengineered and rock fill layers up to 8m in thickness. Experience has shown that conventional geotechnical testing techniques, including nuclear densometer tests, penetration tests (CPTs, SPTs, DCPs) and plate load tests have great limitations in testing such fill profiles. The MASW method is a useful tool for assessing ground improvement as it addresses many of the problems associated with more conventional tests. The MASW method has been used by Black Geotechnical on ground improvement projects since February 2006. The ground improvement methods often create a very stiff raft of fill over soft natural soils that become gradually stiffer. This very stiff-soft-stiff profile is not optimal for MASW as Lamb waves can be easily introduced and it is often difficult to define the base of a soft layer when there is a gradual transition to stiffer soil. Lamb waves, modes and artifacts contribute to making the use of MASW as an absolute stiffness measurement difficult at times. Pre and post compaction MASW surveys enable the method to be used as an effective relative measure of ground improvement.