Background: In general for bridge foundation subsurface investigations, borings are performed at each pier or abutment location, if they are known when the field testing is being conducted. Regardless, previous projects reveal that site conditions can be very erratic and more borings are needed for these situations. However, how many additional borings are considered to be enough to have an optimum and safe design is still to be resolved. This problem has been compounded by the increased use of single, large diameter, non-redundant drilled shafts as a deep foundation element. Even with a boring (or two) conducted at the location of the drilled shaft, the large area that is encompassed by the foundation element (which can be 10 to 15 feet in diameter) versus the small area that is actually tested by the boring (2 to 4 inches) can lend itself to a change of site conditions over the entire rock socket. Knowing this variability is essential for the designer to assign reasonable design values to the rock in order to accurately design the capacity of the drilled shaft. Without this information, typically the designer will lean toward very conservative values (resulting in a more expensive foundation system than what is needed), but it can also lead to unconservative estimates that can result in foundation failures (excessive settlements or collapses). The engineering properties of soft rock (e.g. Florida limestone) that are obtained from correlations based on results from conventional field testing, primarily the Standard Penetration Test (SPT), have proved to be unreliable for design and construction applications. In many instances the SPT results in low blow counts (and N-values) as a result of fracturing the rock during the process of driving the sampler into the rock formation. These lower values are misleading and result in the designer using very unconservative values. In addition, they can result in costly construction claims, especially during excavations since the material is much stiffer than is reflected on the plans. In the case of hard rock, laboratory testing should be performed on every core sample to obtain the engineering properties of the rock profile, but this only gives an indication of rock properties at the borehole location.

To incorporate geophysical testing into the field investigation program to assess the variability of rock formations and its geotechnical engineering physical properties. The emphasis will be utilizing geophysical testing to expand the coverage area of a typical subsurface investigation program, thereby gaining more information and/or data for assessing the variability of the site conditions. This not only will reduce the number of standard tests (i.e. borings or soundings) resulting in a reduction of the overall cost of the subsurface investigation program, it will give engineers more confidence in developing engineering properties for their designs. As such, the end result(s) of the research will be focused to incorporate geophysical testing methods with existing testing procedures and practices to optimize manpower and time resources. The focus of the research will be aimed at assessing properties of subsurface rock formations that will be associated with substructure design considerations.

Scope: The scope of work shall consider the following tasks: 1) Perform literature search. Search for existing and emerging test methods and technologies that can be applied for field investigations in assessing properties of rock formations. 2) Investigate case studies that are available for the applications under consideration utilizing various techniques and technologies. Emphasis should be placed on ease of use, lack of special qualifications for the user, timeliness of testing and analysis of data, accuracy and repeatability of test results, and ability of the technique to be incorporated with existing testing procedures and practices. 3) If applicable, develop or modify existing test methods to utilize geophysical techniques and technologies. If this task results in a specific piece of equipment, a unit will be supplied to each sponsoring state. 4) Perform controlled tests using promising techniques and technologies to establish acceptable range of performance for each method for each application under consideration. 5) Utilizing the results from (4), relate the geophysical test results to known geotechnical engineering physical properties that can be utilized in existing design procedures. 6) Perform field tests on project location sites using promising techniques and technologies to validate the results from Tasks (4) and (5) under real life situations. 7) Evaluate various techniques and technologies, and provide recommendations on the use of each technique and technology, including the identification of site conditions that allow for their successful use or that prohibit their use (for instance, above/below water table, presence of clay, etc.). 8) Provide guidelines on how to utilize test results and how to analyze the raw data, including how to develop engineering properties. Include statistical-based methods to assess the variability of the site by developing confidence intervals to predict the reliability of the test results over the range of the measured area. 9) Develop guidelines to optimize subsurface investigation programs utilizing a combination of geophysical and standard field testing methods. In this process, consider the area of influence of each of the test measurements to ensure that the maximum area of the project subsurface conditions is `measured¿. As part of the optimization, take into account the increased confidence levels in the actual subsurface conditions versus economic considerations. 10) Provide training guidelines to state agencies as required, particularly in the implementation of recommended test methods. Include any revisions to test procedures that are covered in Task (3). As part of the training, include examples of the analysis of raw data for each recommended test method, particularly how to obtain known geotechnical engineering physical properties that can be utilized in existing design procedure (Task 5). 11) Conduct a demonstration project utilizing the recommended test methods, including a workshop to display, analyze and report field data.