Geosynthetic Interface Shear Testing

Fabricated Geomembrane Institute - Webinar

Robert H. Swan, Jr. Drexel University [email protected]

Presented on 22 January 2019

• Methods of Measuring Interface Shear Strength • Test Standards of the Industry • Who, Who & When Regarding Tests • Accreditation of Laboratories • Details of the Interface Direct Shear Test Concept • Details of the Interface Direct Shear Test Equipment • Selection of Interface Direct Shear Test Conditions • Data Reporting • Development of Interface Shear Testing Work Plan • Questions

• Direct Shear • Torsional Ring Shear • Cylinder Direct Shear • Tilt Table • Pullout • Triaxial Shear

• ASTM D5321/D5321-17 – Standard Test Method for Determining the Shear Strength of Soil-Geosynthetic and Geosynthetic-Geosynthetic Interfaces by Direct Shear. ASTM D 5321 was originally approved in 1992.

• ASTM D6243/D6243M-16 – Standard Test Method for Determining the Internal and Interface Shear Resistance of Geosynthetic Clay Liner by the Direct Shear Method. Was originally approved in 1998.

• ASTM D7702/D7702M-14 – Standard Guide for Considerations When Evaluating Direct Shear Results Involving Geosynthetics

Who Requests Tests to be Conducted?

• Design Engineers (Design Phase)

• Contractors and Installers (Construction Phase (MQA/CQC))

• Manufacturers (R & D, Product Development , (MQC/MQA))

• Owners/Owners Reps. (CQA/CQC)

• Regulators (R & D, CQA, Failure Analysis, etc.)

• Lawyers (Failure Analysis)

Who Performs the Tests to be Conducted?

• Commercial Laboratories (Third Party, Independent Labs)

• Institutional Laboratories (University , GRI)

• Manufacturers (R & D, Product Development, (MQC/MQA))

When should the Tests to be Conducted?

• During Design Phase (Site Specific Testing)

• During Material Selection / Qualification (Pre Construction)

• During Manufacturing Of Materials (MQC/MQA)

• During Construction (CQC/CQA)

• During Failure Analysis (Hopefully, this will not be needed, but failures do happen. At this stage in a project, this should not be the first time tests are conducted for a project!!!)

• There are various forms of Accreditation (ISO, GAI-LAP, UL, CE, Army Corp, DOT, etc.).

• The Geosynthetics’ Industry relies on GAI-LAP.

• GAI-LAP represents the Geosynthetic Accreditation Institute – Laboratory Accreditation Program which is part of the Geosynthetic Institute under the direction of Dr. George Koerner, P.E. & CQA.

• GAI-LAP is an Accreditation by Test and requires annual audits with an on-site audit every 5 years. Laboratories must have a QP consisting of a QM and SOPs.

• There are over 75 laboratories involved ranging from one test to 155 tests.

After Koerner (1998)

DIRECT SHEAR TESTING AND INTERFACE DIRECT SHEAR TESTING CAN ONLY MEASURE TOTAL STRESS SHEAR STRENGTH

• Equipment Type • Shear Box Size • Normal Stress Loading • Shear Force Loading • Equipment Calibration

GeoTest

GeoComp

• The standardized size of the shear box has minimum plane dimensions which are the greater of 12 in. by 12 in. (300 mm by 300 mm), 15 times the d85 of the coarser soil used in the test, or a minimum of 5 times the maximum opening size (in plan) of the geosynthetic tested.

• The depth of each container that contains soil must be a minimum of 2 in. (50 mm) or 6 times the maximum particle size of the coarser soil tested, whichever is greater.

• The guidance from ASTM allows the use of smaller shear boxes if it can be demonstrated that the data generated from the smaller devices contain no bias when compared to data generated by the standard minimum box size of 12 in. by 12 in.

• Typically it is believed that the larger the shear box the better the test results are, due to the reduction of boundary effects caused by using too small of a device.

• Shear box sizes up to 30 in. by 30 in. (762 mm by 762 mm) have been used to conduct interface testing.

• Shear box sizes of 6 in. by 6 in. (150 mm by 150 mm) and 8 in. by 8 in. (200 mm by 200 mm) are used by some when conducting very high normal stress interface testing.

Normal stresses are typically applied using various applications:

• Dead Weight (Steel, lead, concrete plates/blocks) – Perfect for Very Low normal stress conditions from 50 up to 800 - 1000 psf (2.4 up to 38 – 48 kPa) on a 12 in. by 12 in. (300 mm by 300 mm) test specimen.

• Pneumatic Cylinders – good for normal stress conditions between 500 to 3000 psf (24 to 144 kPa) on a 12 in. by 12 in. (300 mm by 300 mm) test specimen.

• Pneumatic Bladders – good for normal stress conditions between 800 to 21600 psf (38 to 1035 kPa) on a 12 in. by 12 in. (300 mm by 300 mm) test specimen.

• Hydraulic Cylinders – OK for applying very high normal stress conditions. However the loading system must be able to relive itself during load application.

• Electric Stepper Motors with servo-controls requires continuous feed back to control to prevent overloading of test specimen. OK for full range of loading conditions, still would use dead weight for very low normal stress conditions.

All normal stress loading systems should include a method to verify the applied normal load on the test specimen (i.e., load cell and/or pressure transducer).

Shear Forces are typically applied using various applications:

• Hydraulic Cylinders – using a constant rate flow pump to maintain a constant displacement loading rate applied to the test specimen. Typically, unable to maintain very slow shear rate (Drained) conditions.

• Screw-drive (ACME or Ball Screw) connected to constant rate/constant torque electric motor or electric stepper motor with servo-controls allowing for continuous feed back to control the constant displacement loading rate applied to the test specimen. Electric stepper motors allow for very accurate shear rate control at extremely slow shear displacement rates.

The shear force loading system must be able to maintain a constant rate of displacement in a direction parallel to the direction of travel of the shear boxes. The point of force application to the traveling shear box must be in the plane of the shearing interface and remain the same for all tests.

Most of the currently used shear boxes measure the applied shear force as it is applied to the traveling shear box. By doing so the shear loading system must be calibrated to account for friction that develops within the loading system as the test specimen is sheared. These additional frictional forces must be removed from the actual measured shear force during the test. A more traditional design of a shear loading system incorporates the measurement of the shear force from the stationary shear box.

Fixed Box Fixed Box Shear Force Traveling Box Shear Traveling Box Force

Typical Shear Box Design Traditional Shear Box Design Where shear force is measured Where shear force is measured in the loading harness via as a reacting force from the pushing or pulling. stationary box. The moving box is either pushed or pulled. Durham Geo, GeoTest, GeoComp Presenter’s design

All Test Equipment Must Be Calibrated On A Regular Basis

What needs Calibration and When?

• Internal Friction Of Direct Shear Device – Minimum Every 6 Months

• Normal Stress Distribution – Minimum Every 6 Months

• Electronic Load Cells – Minimum Every 2 Years (Typically Yearly)

• Electronic Displacement Devices - Minimum Every 2 Years (Typically Yearly)

• Computer Data Acquisitions – Minimum Every 2 Years. The DA systems should be used when the load cells and displacement devices are calibrated.

• Other support equipment – Scales, Balances, Ovens, Soil Test Equipment, etc.

• Determine configuration of test setup. • Sample Preparation. • Soil Compaction Controls. • Wetting, Saturation, Submerged, and Consolidation Controls. • Shear Rate / Loading Controls.

• Determine what you want to have tested.

• Should you include the soils and other geosynthetics above and below the interface of interest?

• Doing so tends to give a more realistic representation of the field conditions.

• Using rigid sub/super stratums tends to give a more conservative result.

• Should you conduct single interface tests or multi-layer interface system (aka a “sandwich” type) tests? This will be discussed in more detail in an upcoming webinar by Dr. Tim Stark.

• Do you need to maintain the same orientation of the sample materials as they are placed in the field?

• Should the soil materials always be compacted directly on the geosynthetics that they come in contact with in the field?

• Sample preparation is usually left up to the test laboratory/staff.

• Do not be afraid to give specific guidance to the laboratory if you want to model and/or evaluate a specific set of conditions or specific locations on a roll of material.

• Typically, test specimen are removed randomly on a diagonal method. Make sure the laboratory receives plenty of material for testing. Don’t be shy unless material is very limited for some reason (i.e., a failure investigation, etc.)

• Be clear in your specification or guidance given to the laboratory on how the testing should be conducted: if hydration, saturation, and/or consolidation are required; specify, applied normal load and duration, etc, and if additional wetting or other test conditioning is required.

• Remember, the responsibility of the laboratory is to conduct the requested test as accurately as possible under the requested conditions. If your conditions are not properly conveyed to the laboratory they may not conduct the test as expected. The laboratory is not responsible for the engineering of the project. (See Appendix of ASTM D6243 for a handy check list for specifying tests)

• Soil Moisture and Compaction Methodology (Remold Criteria).

• Soil compaction can typically be controlled to within +/- 0.5 pcf • Soil moisture can typically be controlled to within +/- 0.5 %

• Compaction directly on test interface.

• Compaction away from test interface.

• Development of over consolidated condition at interface.

• Think about what you are trying to model.

From RHS Data Base

• Wetting at interface

• Soaking of materials / interface

• Are you saturated?

• Consolidation

• Submerged Interface

• Measurement of sample and interface moisture.

• Simulates condensation that can develop during a warm day and a cool night.

• By spraying the interface with a controlled amount of moisture allows the moisture to be placed where you want it.

• When coupled with consolidation and other soil conditioning , a saturated state can be achieved.

• Free Swell

• Under Load

• Duration

• Typical wetting front from the top down

• Water has access to all sides of sample except the interface directly.

• May not model reality

Dry

Soaked

• In the Laboratory probably YES

• In the Field probably NOT?

• What is the correct situation to model? That’s an engineering decision.

• Some states like California allow an averaging of dry shear strength and hydrated/soaked shear strength.

• 1/3 dry strength + 2/3 hydrated strength

• 1/4 dry strength + 3/4 hydrated strength

• One Time Loading • Incremental Loading • Duration • Submerged? • Dissipation of pore pressure • Important for Clays (fat & lean) and GCLs • Monitoring of Consolidation • Log of Time • Square Root of Time • Can be used to demonstrate if soil is in a saturated state through compression by squeezing air voids and allowing the soil to approach the zero air voids curve (saturation).

From RHS Data Base

• When should it be used?

• What does it model?

• Should lab account for soil buoyancy?

• Measuring initial moisture of soil sample for remolding • Measuring final moisture from interface surface • Measuring the moisture content of GCLs • What will it show? • Effect of spraying (wetting) • Effect of consolidation • Remember shearing is occurring within the immediate soil at the surface of the interface.

• Discussion on various shear rates in test standards

• Default shear rates in ASTM D 5321 – 0.2 ipm (geosynthetic-geosynthetic) and 0.04 ipm (soil-geosynthetic)

• Default shear rates in ASTM D 6243 – 0.04 ipm (GCL-geosynthetic) and 0.004 ipm (internal strength of GCL)

• Both standards recommend a constant rate of displacement that is slow enough to dissipate soil pore water pressures unless the test conditions that are to be modeled are for rapid loading to simulate field conditions.

• What is appropriate?

• How to determine the best shear rate?

• The appropriate rate of shearing depends on several factors, including the geosynthetic, the materials on both sides of the geosynthetic, the soil, the normal stress level, the hydrating conditions, and the drainage conditions.

• For drained shearing the following equation can be used for guidance:

R = df / 50 * t50 * Θ where:

R = rate of horizontal displacement

df = estimated horizontal displacement at peak shear stress

t50 = time required for specimen to reach 50% consolidation under the current normal stress increment. This time is typically determined from ASTM D 2435 One-dimensional consolidation test.

Θ = factor to account for drainage conditions on the shear plane.

Well Behaved

Refer to ASTM D7702/D7702M-14 Standard Guide for Evaluating Direct Shear Results Involving Geosynthetics Not Well Behaved

• A good laboratory report starts with good quality laboratory testing.

• It is important to have multiple levels of review for an interface testing program.

• From the beginning when the samples arrive at the laboratory to when the report leaves the laboratory the person reviewing the test results for technical accuracy should be involved in the project.

• All work should be checked for accuracy and correctness via a peer review process.

• The person running the test should not be the person reviewing the report, unless that person is a Geotechnical Engineer with extensive experience in conducting testing and understanding material behavior.

• By taking the time to check the results for technical soundness helps eliminate project delays, embarrassment to client and laboratory, expensive retesting, etc.

When contracting for interface shear tests, a user should require the following: 1. Regular calibration of shear testing device for accuracy of normal stress and shearing force (minimum once per year recommended) 2. Specimen gripping surfaces that can impart uniform shearing to the test specimen without slippage 3. Full GCL hydration is achieved (if applicable) before consolidation of the GCL to the desired shearing normal stress (if applicable) 4. Consolidation of a GCL in small increments to minimize bentonite extrusion 5. Measurement of specimen volume change during hydration, consolidation, and shearing 6. Thorough inspection of failed specimen(s) 7. Measurement of initial and final GCL water contents and sub grade soil water contents (if applicable).

When contracting for interface shear tests, a user should provide the following: 1. GCL material(s) (from actual project site or designated for actual project site if possible), 2. Subgrade soil(s) (if applicable), 3. Geosynthetic interface material(s) (if applicable), and 4. Hydration liquid (if different from tap water).

When contracting for interface shear tests, a user should specify the following: 1. Specimen selection, trimming, and archiving procedures, 2. Number and type of tests, 3. Specimen configuration (bottom to top), 4. Soil compaction criteria (if applicable), 5. Number of interfaces (single or multiple) to be tested at the same time, 6. Orientation of GCL or GCL interface (machine or transverse direction), 7. Hydration normal stress and hydration time duration (or termination criterion), 8. Consolidation procedure, including load increments (or load-increment-ratio) and load increment duration (or termination criterion), and 9. Shearing procedure, including shearing normal stress levels, magnitude of shear displacement, and shear displacement rate.

When receiving the results of interface shear tests, a user should expect the following:

1. Description of specimen selection, trimming, and archiving procedures, 2. Description of testing equipment, 3. Description of specimen configuration and preparation conditions, 4. Description of test conditions (hydration, consolidation, shearing), 5. Shear stress–displacement relationships, 6. Specimen volume change data during hydration, consolidation, and shearing, 7. Peak and large displacement shear strengths, 8. Location and condition of failure surface(s) within test specimens, and 9. Initial and final GCL water contents and subgrade soil water contents (if applicable).

Fox and Stark 2004

• Interface Direct Shear Testing is not as simple as it sounds.

• Remember you just can’t specify ASTM D 5321 or ASTM D 6243 and expect to get accurate test results.

• Interface Direct Shear Testing is a performance test whose results are dependent on the test conditions that are applied to the test specimen.

• Be careful for what you ask for and take the time to properly specify the test conditions which are needed for the testing.

• Remember failure to specify correctly may lead to the failure of the project.

Robert H. Swan, Jr. Drexel University [email protected]

Presented on 22 January 2019

FGI’s 2019 Webinar Calendar

. Feb. 28 – GCL Shear Testing

. March 12 – Multi-Interface Shear Testing

. April 9 – Geomembrane Fabrication and Installation

. May – Geofoam for Roadway Applications

. June – Coal Combustion Residuals

. August – Coal Combustion Residual (CCR) Regulations

. September 10 – Geosynthetics for Shale Oil and Gas Ponds

. October – Geomembrane Durability

. November – Geomembrane Wrinkles

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Robert H. Swan, Jr. Timothy D. Stark Associate Teaching Professor Professor of Civil & Environmental Engineering Department of Civil, Architectural and University of Illinois at Urbana-Champaign Environmental Engineering Technical Director Drexel University Fabricated Geomembrane Institute [email protected] [email protected]

Andy Durham Jen Miller FGI Member Coordinator GMA Executive Council Fabricated Geomembrane Institute Owens Corning University of Illinois at Urbana-Champaign [email protected] [email protected]