The stability of landfills and leach pads is becoming more important with each new project failure and the increasingly difficult terrain of some sites.  Shear strength of geosynthetic interfaces is one of the primary, and more contentious, variables used in stability analysis.  The continued growth of the geosynthetics industry has led to a constant influx of professionals working in waste facility design and slope stability evaluation for the first time.  These engineers, together with geomembrane and geosynthetic clay liner (GCL) manufacturers, have long complained of the difficulty in achieving good, reliable interface strength parameters.

The standard test method for the evaluation of friction between geosynthetics and geosynthetics, or geosynthetics and soil, is ASTM D5321, large scale direct shear test for geosynthetics, and ASTM D6243 for GCLs.  While these tests are simple in concept, the generated test results are significantly affected by the test parameters defined and the procedures used.  As a result, understanding the specification of interface friction testing and how to interpret and use generated test results has become a crucial part of an engineer’s job.  In fact, the cost for not understanding ASTM D5321 and D 6243 tests and test data can be enormous.  Unfortunately, the waste industry has several examples of this cost.

This course had been specifically targeted to those persons who have a need to understand and specify interface friction/direct shear tests, and use generated results in subsequent design.  These persons include:

• Design/Certifying Engineers
• Construction/Quality Assurance Project Managers
• Manufacturers
• Installers
• Third Party Inspectors
• Regulators

This course will be presented in two parts, each complementing the other to provide maximum benefit.  The first will focus on the designer’s use of interface strength including sources of interface strength, peak vs residual strength, normal stress and failure envelopes, friction angle, adhesion and slope stability calculations.  Included will be detailed forensic analysis of several slope failures.

The second part of the short course will provide a detailed explanation of ASTM D5321, including detailed discussion of test parameters.  Procedural implications of specimen anchorage, normal stress application, machine friction and calibration, rate of shear and reporting mechanisms will be evaluated.  In addition, limitations of the D 5321 test will be explored, with explanation of alternative tests including torsional shear, tilt table and double interface shear.  Special emphasis will be placed on specifying a meaningful shear test that will best serve the user.

November 5, 2025
Course runs 8:00 am - 5:00 pm US Central Time both days, breakfast & lunch included

Overview of Materials, Stress, and Environment
Background – Shear Strength and Slope Stability Concepts
Bottom Linear Stability and Strain Softening Concepts
Bottom Liner Interface Shear Testing
Veneer Stability
Veneer Interface Shear Testing
Open Discussion and First Day Closing

November 6, 2025

Welcome and Recap Quiz
Reliability and Risk
Seismic Stability
Internal Shear Strength of GCL, GC, and Soil
Evaluation of Test Results
Clear Specifications and Test Prescription
Challenging Specifications and Test Prescription
3rd Party Lab Conclusions and Recommendations
Designer and CQA Conclusions and Recommendations
Open Discussion and Closing

Richard Thiel, PE is President of Thiel Engineering. He is an engineer with 30+ years experience specializing in containment design applications for geotechnical projects, waste containment, secondary containment of fuel, and leach mining applications. He has participated extensively in the feasibility evaluation, permitting, design, and construction of waste facilities and surface impoundments. He is experienced at being an expert witness, performing design peer reviews, economic evaluations, failure analyses, design of liner systems with soils and geosynthetics, leachate management systems including pipelines an pump stations, geotechnical site reconnaissance and resource inves­tigation programs, construction quality assurance (CQA), and assistance in developing state solid waste regulations. He is currently the instructor for the ASCE seminars on containment liner and cover systems design, as well as other courses related to geosynthetics and liner system design. Before his specialization in containment system design, Mr. Thiel participated in the design of several large rock-fill clay-core dams.

Jeffrey Kuhn, PhD, PE is the Executive Director for TRI Environmental, Inc. His doctoral work principally focused on alternative/evapotraspirative cover design and evaluation for the EPA, and he performed research with expansive clays for the Texas Department of Transportation (TxDOT). Prior to joining TRI, he served as a consulting engineer, where he worked on the design and installation of the Circuit of the Americas Formula One Race Track over expansive clays with tight differential movement criteria. Since 2012, he’s led the expansion of TRI’s geotechnical laboratory capabilities and reach within the geotechnical community.

* Commercial Rate: $850/person
* Government Rate: $350/person

Commercial entities save 5% on 2 or more registrations in a single transaction.

TRI Environmental, Inc. (TRI) is a full-service independent laboratory serving a variety of related polymer-centric industries around the world. At our core is a deep understanding of geosynthetic materials and the characteristics critical to performance. TRI tests, certifies, performs research, develops equipment and provides consulting on geosynthetic materials used in civil, environmental and geotechnical engineering as well as protective clothing.

Materials including geomembranes, geosynthetic clay liners, geotextiles, geogrids, geocells, plastic pipe, rolled erosion control products, protective clothing and the like have been tested by TRI for over three decades. However, our knowledge and understanding goes deeper than just testing… TRI performs research, develops test equipment, develops standards and provides education for each of the industries it serves.

TRI’s personnel are active throughout the world’s standards development organizations and routinely provide short courses, seminars and tailor-made training services.

TRI is unaffiliated with any manufacturer or engineering firm, and thus provides services to regulators, manufacturer, engineering firms, contractors and installers. Laboratories perform testing in accordance with ASTM, ISO, BS, DIN and GRI test methods. TRI is GAI-LAP & ISO 17025 Accredited and is an official provider of testing services to NTPEP, USACE, AASHTO and other government and regulatory agencies.

Sam Allen (00:00):
It's good to see you. Thank you for participating in this year's Geo-U, the Geosynthetics University hosted by TRI in Austin, Texas. Thank you for lending your expertise to the field of interface friction and slope stability evaluations. And this is a chance to just ask you a few questions, and I'll start out, Rick, with sort of what you feel are the most recent slope stability issues that you encounter in your career, and will you be addressing some of those issues during the course?

Rick Thiel (00:38):
Well, thank you for inviting me, Sam. Yes. The slope stability failures that I typically encounter in my work is deals with containment lining systems, and they apply generally to landfills and heap leach pads and mining. They generally fall into two categories. There's large deep seated failures along the bottom liner systems, and then there are what we call shallow planer failure surfaces. Also, given the name of veneer failures.

Sam Allen (01:13):
Yeah,

Rick Thiel (01:14):
The veneer type failures are much more common than the deep seated ones, probably a hundred times more frequent and most often occur in final cover systems, but also in newly installed bottom liner systems. Often these smaller ones go unreported, whereas the more consequential, deep seated failures typically become public knowledge, and both of these types of failures are discussed in the

Sam Allen (01:41):
Course. Okay. Well good, very good. In terms of your experience encountering these issues during your career, what do you wish you had understood a little better or been more informed about when you first started after reviewing all your slope stability designs? What do you wish you had known very early on that now you certainly appreciate?
Rick Thiel (02:11):
Well, one thing is I always feel like many of us just don't take enough statistics. You don't have to be an expert in statistics, but they really help you gain an appreciation for the sensitivity of what contributes the most to a failure. And you can do simple probability analysis, which I'll go over in my course related to this is an appreciation for the variability of the material properties that affect slope stability. Things like poor pressures and sheer strengths and geometry and unit weight. And these factors can create localized failures and trigger failures. And when you understand what is the most sensitive variable of most significance, that helps you refine your design and give you confidence.
Sam Allen (03:11):
Yeah, makes sense. Yeah. And I guess that kind of leads me to my last question, and that is when you're working with younger engineers or when you're hiring somebody, what do you sort of wish that they had more education about as they're coming into their professional life? What do you yearn for them in the context of beginning that career in evaluating slope stability? What do you wish for them? What do you wish they knew more about?
Rick Thiel (03:53):
The area that is of most value that may or may not occur in somebody's opportunities is having hands-on laboratory and field experience. You can learn computer programs and how to do analysis, but there's nothing that can replace putting your hands in the dirt, feeling the geosynthetics, watching laboratory testing and seeing how construction actually occurs in the fields and how these materials interact. So I really encourage people to pursue getting out in the field and seeing how it actually happens. Other things that I think are critical is not just the analysis themselves, but the operations, the sequencing. Most failures that occur in slope stability with lined containment facilities are because of the fill sequencing. If the sequencing is done properly, many failures could be averted. And then next to gravity, the thing that brings down slopes the most is poor pressures. And getting a good understanding of where poor pressures come from and how they manifest is essential. And then, as I mentioned earlier, the variability of materials and getting a good feel for that. And that comes with field and laboratory experience. And finally, I would say good specifications and having an appreciation not to just copy the last ones, but to start from scratch and look at each project at its own merit.
Sam Allen (05:47):
Yeah, we often get asked the question, this is my profile. How much over that normal compressive load should I specify as a testing parameter or should I land right on it? So those kinds of things I'm sure will be discussed in the class. Well, again, thank you. I might mention with you that the class includes an open house, of course, at the TRI laboratories where people can look at interface friction boxes and evaluate the pluses and minuses of different designs and approaches to friction testing. So yeah, looking forward to this. And again, thank you very much for your time and looking forward to the class in early November.
Rick Thiel (06:37):
Very good. Thank you, Sam.

Materials including geomembranes, geosynthetic clay liners, geotextiles, geogrids, geocells, plastic pipe, rolled erosion control products, protective clothing and the like have been tested by TRI for over three decades. However, our knowledge and understanding goes deeper than just testing… TRI performs research, develops test equipment, develops standards and provides education for each of the industries it serves.

TRI’s personnel are active throughout the world’s standards development organizations and routinely provide short courses, seminars and tailor-made training services.

TRI is unaffiliated with any manufacturer or engineering firm, and thus provides services to regulators, manufacturer, engineering firms, contractors and installers. Laboratories perform testing in accordance with ASTM, ISO, BS, DIN and GRI test methods. TRI is GAI-LAP & ISO 17025 Accredited and is an official provider of testing services to NTPEP, USACE, AASHTO and other government and regulatory agencies.