The purpose of this web manual is to provide highway engineers with a basic knowledge of geophysics and nondestructive test (NDT) methods for solving specific engineering problems during geotechnical investigation, construction, and maintenance of highways. The web manual is not intended to make engineers experts in the field of geophysics, but rather to provide them with tools that will assist them in the use of suitable geophysical and NDT techniques to evaluate problems for design, planning, construction, or remediation efforts.
The application of geophysical imaging and NDT methods has been increasing in site Characterization and geotechnical investigations during highway constructions because they offer accurate and timely information for design quality and performance. Detailed knowledge of unforeseen, highly variable subsurface ground conditions reduces project risk and costs associated with "change of conditions" claims, and improve construction and safety. In this web manual, the term NDT is used to refer to condition evaluation of engineered structures. Condition evaluation includes integrity assessment for defects and corrosion, and the determination of unknown geometry, such as unknown foundation depths or extent of foundations.
This web manual provides a broad range of practical methods, including almost all traditional geophysical methods. These have been adapted to provide solutions more specific to a variety of engineering problems pertaining to transportation. For example, conventional geophysical methods have been used to evaluate the physical properties of soil and rock, such as seismic methods which are used to calculate the depth to bedrock or locate underground voids. In the NDT applications, the same seismic methods have been adapted for condition evaluation with great success, producing a technique known as the Ultraseismic test method. In this method, the concrete structure itself is used instead of the earth for the transmission of the acoustic energy with reflection events coming from either the bottom of a structure, as in a bridge foundation, or a defect zone. Similarly, the ground penetrating radar (GPR) geophysical method, originally developed for high resolution imaging of the subsurface, is now used routinely in condition evaluation of pavements, concrete slabs, and walls. These types of NDT geophysical investigations are used in the transportation and infrastructure systems to evaluate new procedures for Quality Assurance (QA) and existing structures for forensic and Quality Control (QC) purposes. To this end, many state and federal Department of Transportations (DOT's) have added various NDT testing standard specifications to their construction codes and will continue to do so with continued deployment of geophysics and NDT in the construction projects.
This web manual is divided into two parts. The first part is problem oriented and provides a range of geophysical and NTD methods that can be used to solve a particular problem. The second part describes the geophysical techniques in greater detail.