Evaluation of Laser Doppler Vibrometry for Long-Range Remotely-Sensed (Touch-Free) Seismic Data Acquisition
Can LDV be implemented in a manner that is technically and economically feasible for rapid and effective collection of remotely-sensed (e.g., touch-free) seismic data for the sake of detecting and imaging concrete structure defects/damage/ deterioration in a field-scale implementation scenario? What are the main technical and practical capabilities and limitations for LDV to replace standard seismic surveying techniques on large concrete structures? What replacing or augmenting standard seismic surveying techniques on earthen surfaces or earthen structures?
Need and Benefit
Need: Reclamation has several needs for various types of seismic surveying services, with applications that range
from geologic mapping, void detection, seismic site classification, embankment and foundation imaging, landslide
assessment and imaging, slope stability analysis, and concrete infrastructure defect imaging. Many of these surveys
involve costly data production rates and limited spatiotemporal data coverage, due to the need for wired sensor
installation and physical access to oftentimes difficult or dangerous areas. Reclamation has several large concrete
dams and other large concrete infrastructural components that are considered to be "high-risk" due to their critical
functions and locations relative to large downstream population centers (e.g., large economic losses and loss of life
for downstream populations in the event of a catastrophic failure).
Benefit: LDV technology could be deployed for collection of various active and passive seismic survey types, including
active and passive seismic surface-wave interferometry surveys, seismic refraction tomography surveys, and seismic
reflection surveys, all without the need for wired geophone systems that are limited in the number of sensor channels,
geometric configurations, and the need for physical access to sensor locations. This would translate to immense cost
savings, increases in data coverage and production rates, and overall value of information obtained from various
seismic surveying efforts. A particularly poignant benefit of from the application of this technology is the potential to
rapidly detect and image defects, damage and deterioration across large vertical concrete structures or large
infrastructural components without the need to access or touch the target structure's surface with sensors, and
potentially without the need to apply active seismic sources across the structure's surface (e.g., alleviate the need for
ropes team access for placement of geophones and hammer impacts). Hence, this approach could potentially allow
for extremely rapid, cost effective, safe, and spatiotemporally comprehensive assessment and imaging of concrete
structures throughout Reclamation's entire inventory of infrastructure. If deemed a successful approach to collection
of "touch-free" remotely-sensed seismic data, LDV technology could be used to more comprehensively assess the
state of disrepair of critical infrastructure and high-risk structures/miscellaneous structures, and help to guide and
optimize repair and mitigation efforts. Additionally, the results of application of this technology could help to guide
efficient and intelligent placement of more costly and invasive investigations, including the placement of coreholes
along the crest of concrete dams, or across the vertical/sub-vertical faces of concrete structures.
Urgency: The location, spatial extent and severity of concrete structure defects are usually poorly understood, and
typical assessment methods are often conducted "blindly" (e.g., random placement of coreholes (and geologic
boreholes, in the case of earthen structures), without the use of additional information or prior knowledge of defect
location/severity). As a result, there is the ever-present chance of underestimating the severity of damage to these
structures and the subsequent overly liberal estimate of safety factors/risk.
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