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This webinar was co-sponsored by ASCE's Geo-Institute (G-I) and ASCE Continuing Education

Instructor:  Neil L. Anderson, P.Eng.

Course Length: 1.5 Hours

Purpose and Background

This webinar focuses on two geophysical methods that are routinely in support of geotechnical, hydrologic and/or environmental site investigations: electrical resistivity tomography (ERT) and multichannel analysis of surface waves (MASW).

The typical output of an ERT survey is a suite of one or more relatively high- resolution 2-D resistivity images of the subsurface. The resistivity of earth materials is a function of multiple parameters including salinity, porosity, permeability, lithology, clay content, water saturation and contaminant saturation. However, on a local scale, the resistivity of earth materials is often a function mostly of lithology. Hence, a 2-D resistivity image can usually be transformed into a lithological cross-section with scales of distance and depth. This is especially true if boring control is available or if the interpreter is familiar with the subsurface geology at the site being investigated.

ERT data (1-D, 2-D or 3-D) are generally interpreted with the objectives of mapping: variations in lithology (soil and rock), variable depth to the top of rock the top of the water table,, variations in moisture content, variations in clay content, faults, solution-widened joints, seepage pathways, variations in ground water salinity, contaminants, etc.

The output of a multichannel analysis of surface wave (MASW) survey is a suite of one or more 1-D shear-wave velocity profiles of the subsurface. The shear-wave of earth materials is a function of the shear modulus and density. Hence, a 1-D shear-wave velocity profile can often be transformed into a 1-D lithological profile. This is especially true if boring control is available or if the interpreter is familiar with the subsurface geology at the site being investigated. If multiple MASW data sets are acquired, the user can generate 2-D or 3-D shear-wave velocity images of the subsurface.

MASW data are generally acquired for earthquake site classification purposes and with the objectives of mapping: variations in the shear-wave velocity of soil and rock, variations in lithology (soil and rock) and variable depth to the top of rock.

Learning Outcomes

Upon completion of this course, you will be able to:

• Recognize the applications (geotechnical, hydrologic and environmental)
• Determine limitations of the electrical resistivity tomography (ERT)
• Identify multichannel analysis of surface waves (MASW) methods

Webinar Benefits

• Recognize the basic principles of the ERT and MASW methods.
• Apply the fundamentals of ERT and MASW data acquisition (methodology, crew size, data acquisition rates, potential field-related issues, etc.)
• Discuss the fundamentals of ERT and MASW data processing
• Explain the fundamentals of ERT and MASW data interpretation
• Understand the applications and limitations of the two subsurface imaging technologies

Assessment of Learning Outcomes

Students' achievement of the learning outcomes will be assessed via a short post-assessment (true-false, multiple choice and fill in the blank questions).

Intended Audience

Engineers engaged in geotechnical, hydrologic and/or environmental site characterization.

Webinar Outline

• Overview of the MASW method with emphasis on interpretation
• Presentation of MASW case studies with emphasis on applications and limitations
• Overview of the ERT method with emphasis on interpretation
• Presentation of ERT case studies with emphasis on applications and limitations

How to Earn your CEUs/PDHs and Receive Your Certificate of Completion

To receive your certificate of completion, you will need to complete a short on-line post-test and receive a passing score of 70% or higher within 1 year of purchasing the course.

How do I convert CEUs to PDHs?

1.0 CEU = 10 PDHs [Example: 0.1 CEU = 1 PDH]