Wind Turbine Site Characterization by the MASW Method
Approaches for Site Characterization (also see Vs30m evaluation)
As demand for wind energy grows worldwide, so is the demand for utilizing new technologies to make the construction of a wind turbine site more robust, safer, and more cost
effective. Recently, the MASW method has been applied to site characterization efforts to replace (or reinforce) the conventional drilling approach at several places in the west and
midwest United States. Park Seismic LLC has recently participated in several projects in Texas and New Mexico. The first wind turbine site characterization by the MASW method
was reported by Park and Miller (2005a; 2005b) following its successful application at eighty-four (84) proposed turbine sites for the second phase construction in the Blue
Canyon Wind Mill Farm (Park and Miller, 2005a) (Fig. 1) near Lawton, Oklahoma, and also at twenty selected sites near Elk River in Kansas (Park and Miller, 2005b) (Fig. 2).
Fig. 1. Location map of eighty-four (84) turbine sites in Blue Canyon Wind Mill Farm near Lawton,
Oklahoma, surveyed by the MASW method (from Park and Miller, 2005a).
Fig. 2. Location map of the turbine sites near Elk River in Kansas surveyed by the
MASW method (from Park and Miller, 2005b).
Fig. 3. Illustration showing the relative advantage of seismic survey in
comparison to conventional drilling.
A wind turbine site has special characteristics that must be
considered before and during the construction of the tower. For
example, the heavy weight of the tower structure is built on a
relatively small area on the ground (for example, 30 ft by 30 ft) and
following construction the ground volume below and around the
tower will experience continuous vibration caused by the rotating
blades. Because of the vibration, the dynamic properties of ground
materials provided from a seismic survey, therefore, can be
especially pertinent from geotechnical engineering perspectives.
On the other hand, considering the extent of ground materials
related to the safety and sustainability of the tower being much
more extensive than the direct area occupied by the tower, the
conventional approach of drilling one or more places at the tower
center may not be sufficient to ensure the overall safety and
stability. A few instances of fatal crane failure caused by collapsed
ground during the tower construction have been reported, so it
seems this safety zone may need to be expanded even further.
The seismic investigation usually deals with the bulk-property
evaluation of the ground with the bulkiness increasing with depth. It
usually performs a Vs30m survey for a 1-D profiling, or a continuous
survey to generate a 2-D (and 3-D) cross-section image of the
property, usually in stiffness as depicted by shear-wave velocity (Vs)
information. Shear-wave velocity (Vs) is often used as a direct
indicator of the shear and Young’s moduli. The seismic survey is,
therefore, a more thorough and appropriate approach for site
characterization than conventional drilling (Fig. 3). Because a
seismic survey does not need the bulky, heavy equipment that
drilling does, the convenient accessibility to the site is another
advantage. Overall cost is also usually some fraction of the drilling
Seismic Site Characterization for Vs30m