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This webinar was co-sponsored by ASCE's Geo-Institute and ASCE Continuing Education

Instructor:  Robert M. Koerner, Ph.D., P.E.,D.GE, NAE Dist.M.ASCE

Course Length: 1.5 Hours

Purpose and Background

Precast concrete block and vegetative faced retaining walls reinforced by geogrids or geotextiles are in a period of enormous growth. Estimates are that 35,000 of these walls exist and that they accommodate the entire range of practical design considerations. This webinar gives a perspective on the evolution of retaining walls in general and follows with results of a recent cost survey. It is seen that geosynthetic reinforced MSE walls are the least expensive of all wall categories and at all wall heights. Three design methods are then compared to one another using a numeric example showing that the modified Rankine method is the most conservative, the FHWA method is intermediate, and the NCMA method is the least conservative.

A survey of walls which suffered either excessive deformation or actual collapse is included. The causes for these cases of inadequate performance are (i) backfilling with fine grained silt and clay soils, (ii) lack of adequate quality control and inspection, and (iii) lack of proper drainage routing and control. The presentation includes a discussion of improper procedures with respect to these concerns. Lastly, the transition from precast concrete block to vegetated facings is illustrated by many actual situations in the transportation, geotechnical and geoenvironmental areas.

Learning Outcomes and Webinar Benefits

You will become familiar with geosynthetic (mainly geogrids) reinforced mechanically stabilized earth (MSE) walls and, by inference, steep soil slopes. Two types of facings will be emphasized; precast concrete blocks (also called segmental retaining walls) and welded wire mesh with geogrid backup (also called vegetated or green facings). Proper design will be illustrated by an example, but both improper design and improper construction will be emphasized by means of numerous examples. This exposure will hopefully lead to proper procedures going forward.

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

• Obtain cost comparisons of different wall types
• Identify the wide variety of wall applications
• Improve your understanding by comparison of three different design approaches
• Draw from examples of inadequate performance
• Determine specific concerns (both design and construction) in light of inadequate performance and benefit from recommendations in light of these

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

Federal, state and regional geotechnical, transportation, and geoenvironmental engineers; engineers from municipal districts and townships; private and municipal land developers, architectural and landscape designers; general civil consulting engineers; testing laboratories servicing these organizations; manufacturers and representatives of geosynthetic materials; contractors and installers of MSE walls and steep soil slopes; academic and research groups; and others desiring technically related information on this important aspect of our constructed environment will benefit from this webinar.

Webinar Outline

• Background and aesthetics
• Retaining wall costs
• Design approaches and MSE wall example
• Cases of inadequate performance
• Concerns regarding inadequate performance
• The new paradigm; vegetative wall facings
• Summary and conclusions

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]