During the IGS Council plenary session in Seoul, Korea, the newly formed Egyptian Chapter of IGS (IGSE) was selected to host GeoAfrica 2021 in Cairo, Egypt. GeoAfrica 2021, the 4th African Regional Conference on Geosynthetics will follow the great successes of the previous GeoAfrica conferences in South Africa, Ghana and Morocco.
GeoAfrica establishes a gateway for geosynthetics into Africa by providing a forum for engineers, practitioners and academia to explore current and future potential applications for geosynthetics while offering an active market place for the promotion of geosynthetic products and technology to users throughout the African continent.
The use of geosynthetics in infrastructures and mega projects has immensely increased in Egypt and the region in recent years. Projects including major expansions of highways and railroads in challenging soil conditions, new cities and urban centers, industrial and commercial zones, ports, tank farms, landfills, mine tailings, and major utilities have seen extensive use of geosynthetic products in various applications. IGSE has therefore chosen a conference theme to be “Geosynthetics in Sustainable Infrastructures and Mega Projects”. IGSE believes that this theme will attract the attention of many practitioners in Egypt and the region. The technical program of the conference shall be developed to cover the different applications of geosynthetics with a preference towards infrastructures and mega project applications.
The IGS Technical Committee on Barrier Systems (TC-B) hosted its 1st GeoBarrier Workshop in Munich, Germany on June 6 – 7, 2018 and had 69 participants from all around the world.
This open event for researchers, designers, consultants, manufacturers, industry insiders and any interested group addressed considerations of technical consensus versus continuing technical needs, educational efforts, and potential publications.
The two day workshop allowed a lot of discussions in the fol-lowing topics and the selected chairmen served as facilitators to foster discussion and interaction.
• Geomembrane Durability (chairman: George Koerner, USA)
• Geomembrane protection (chairman: Richard Brach-man, Canada)
• GCL hydration and controlling factors (chairman: Malek Bouazza, Australia)
• Standard protocols for Construction/Installation Quality Assurance and Quality Control (chairman: Kerry Rowe, Canada and Boyd Ramsey, USA)
Following is a short summary of the Sessions from the June 2018 IGS TC-Barrier Workshop
Geomembrane Durability chaired by George Koerner, Session Chair and Director of the Geosynthetic Institute (GSI), Folsom, USA
The IGS welcomed over 69 civil and geotechnical engineer-ing professionals from around the world to the TC-B work-shop. This unique gathering combines high-level presenta-tions from leading practitioners in the field with significant audience discussion time, enabling participants to share project experience, exchange technical concerns and solutions and network with colleagues who influence diverse applications (projects) containing geosynthetics.
GSI’s involvement over the two days was significant. GSI’s task at the event was to chair the opening morning session of the TC-B workshop on durability. The agenda was stacked with heavy hitting presenters from Germany, the USA and Canada.
Andreas Woehlecke started us off with an overview of the German regulation for geosynthetic used in waste disposal. The BAM mandates that only a relatively thick 2.5 mm HDPE be used in liner systems in Germany. The geomembrane is used in a single composite configuration and can only be made via the wide mouth die case process. It needs to be a monolithic layer of HDPE and cannot be a blended or layered material. The agency’s perspectives on geomembrane durability, service life and end of life is that all materials used in lining system need to exhibit 100 year performance.
Helmut Zanzinger of SKZ was the next speaker in the session. He discussed an autoclave exposure technique to accelerate incubation for Arrhenius modeling. This worked tied in nicely to the first presentation and answered the question of how the Germans verify 100 year performance of materials.
Sam Allen of TRI Environmental was next and thru the audience a major curve ball. He went against convention and discussed other materials than monolithic HDPE geomembranes. He delved into all kinds of issues (sampling, testing, seaming etc.) with multi-component (layered) geomembrane durability. He left the session with the question: There are many different geomembrane formulations that exhibit fantastic physical, mechanical, hydraulic and endurance properties, why don’t we consider broadening our options for containment.
Kerry Rowe of Queen’s University ended the presentation portion of the session with a discussion on antioxidant depletion. He challenged the validity of both the standard and high-pressure DSC tests by contrasting predicted performance with actual field verifications. Much of his findings showed that performance is application specific where extreme environmental conditions will challenge commodity materials but can be managed by high performance geomembranes.
With the conclusion of the presentation phase of the session the discussion began. In true workshop fashion we opened the floor to 90 minutes of exchange. The Questions & Answers were fast and furious. Some of the better examples are listed below;
• Should we restrict the comonomer used in the manufacturer of HDPE (oxtane, heptane, butane etc.)?
• What are the risks if a GM fails?
• Should we insist that the GM exhibit isotropic behavior?
• Should we be making application specific materials (i.e. covers/liners, landfills, brine ponds, high chlorine)
• Do all GM pass a TCLP (Toxicity Characteristic Leaching Potential) test?
• Can someone explain how the anti-oxidant (AO) package diffuses throughout the polymer cross section of a geomembrane with time?
• How do geomembrane seams age? Are they as durable as the parent material?
• What is the durability of textured versus smooth geomembrane?
• What is the effect on durability of CaCO3 or talc in the geomembrane formulation?
In all, the session was exciting and fun. The audience was great and energized the panel to stretch and give many suggestions for going forward and improving geomembranes.
Richard Brachman, Session Chair and Professor, Queen’s University, Canada reports from his session:
The session on Geomembrane Protection reviewed and reflected on where practice is today, and presented findings from recent research to stimulate discussion with the overall goal of advancing practice and guiding future research.
Geomembrane protection chaired by Richard Brachman (Queen’s University, Canada)
Richard Brachman began the session with an overview of the engineering mechanics of geomembrane deformations from coarse gravel. He emphasized that the geomembrane is part of a system, meaning that long-term deformations of one or more components of the system can lead to additional deformation of another. Proper consideration of engineering mechanics was encouraged to understand limitations of past empirical approximations; resolve why some tests show no long-term rupture, while others do; and select an appropriate protection layer to ensure long-term environmental protection.
Kerry Rowe (Queen’s University, Canada) spoke on “Why we need to limit long-term strains”. He presented recently published work (Abdelaal et al. 2014, Ewais et al. 2014) along with additional new findings from an on-going, two-decade-long effort to resolve the issue of whether a poly-ethylene geomembrane can rupture from sustained local gravel indentations. Kerry Rowe presented data that con-firms the end-of-life mechanism for landfill geomembranes involves: i) consumption of protective antioxidants, ii) polymer oxidation, iii) decrease in stress crack resistance, and iv) brittle rupture when combined with sufficiently large sustained tensions from local gravel deformations. His presentation highlighted the importance of considering the effects of modelling the system as it really exists (including the compacted clay or GCL that can deform with time be-low a geomembrane), chemical interaction, and temperature if one is to realistically represent the overall system interactions.
George Koerner (Geosynthetics Institute, USA) presented “Preventing puncture: A US approach”. A review of the original experiments (Narejo et al. 1996) used to derive an equation for the mass of nonwoven geotextile required to prevent geomembrane puncture (Koerner et al. 1996) was presented. These short-term experiments were not in-tended to limit geomembrane strains to a certain level, but rather to find the external pressure required to cause the geomembrane to puncture for a given protrusion height and mass of geotextile, predominately based on hydrostatic pressure testing with truncated cones (Koerner et al. 2010). Findings from four, 10-year-long hydrostatic pressure tests with truncated cones conducted at 22°C (Koerner et al. 2010) were then summarized. There was no puncture with 12-mm-high protrusions at pressures of 430 and 580 kPa, while one puncture occurred for a 38-mm-high protrusion at 52 kPa. The findings were used to update the long-term factor in the puncture equation.
Ulrich Sehrbrock (ICP, Germany) presented “Limiting strain: The German Approach”. He described that the geomem-brane is loaded under vertical pressure with project specific gravel above the geomembrane and a rubber layer beneath the geomembrane (provisions also exist to site specific materials beneath the geomembrane). There are specific requirements for test pressure, temperature and time. Indentations in the geomembrane are recorded by placing a thin, deformable metal sheet beneath the geomembrane. A measure of geomembrane strain is then calcu-lated from the measured indentations. The geotextile protection layer is deemed acceptable if that calculated strain is limited to 0.25%. From his own professional experience, he noted that specifying coarse (16/32 mm) gravel with rounded particles can lead to sharp-edged grains from particle breakage, that need to be considered in the protection layer testing. Last, he commented on the beneficial effects of using sand a protection layer to limit geomembrane indentations.
Richard Brachman gave the final presentation titled “Why allowable strain depends on how it’s measured and calcu-lated”. In terms of how strain is calculated, he showed how consideration of average vs. maximum membrane strain, neglecting bending strains, or neglecting large-displacement effects lead to underestimates of actual geomembrane strain (Eldesouky and Brachman 2018). He clarified that the German method of strain calculation results in an aver-age membrane strain along the indentation and explained that this value is limited to 0.25% with the intent that the maximum extreme fibre strain (considering bending) is below a long-term target of 3% strain, as detailed by Seeger and Müller (2003). In terms of test conditions, he showed how the type of subgrade (none, rubber, clay layer), clay compressibility, temperature and time impacted the strains resulting from the test and presented a new screening method (Brachman et al. 2018) to help select protection layers to limit long-term strains to target allowable limits.
The discussion session was productive and involved debate on why the Abdelaal et al. (2017) and Ewais et al. (2014) studies resulted in brittle rupture, while that of Koerner et al. (2010) did not, and discussion on: how test boundary conditions (boundary friction, flexible vs. rigid load) effect the measured results, construction issues related to place-ment of a sand protection layer, the extent to which whether wrinkles impact geomembrane protection, consideration of different/new materials for applications other than landfill bottom liners, the chemical resistance of polyester vs polypropylene nonwoven geotextiles, and allowable strain limits.
GCL Hydration and Controlling Factors chaired by Malek Bouazza (Monash University, Australia)
Malek Bouazza presented about myths and facts about GCL hydration and informed about conditions in field and how the bentonite hydrates but as hydrates less if the subsoil has a similar suction capacity as the bentonite.
Kerry Rowe then explained how well GCLs hydrate and self-heal as well as factors and effects. It was clear that a GCL under a geomembrane with no confining stress there might be concerns with a GCL. Particularly gran-ular bentonite GCLs seemed to show in the investigated test plot a higher shrinkage and downhill erosion effect than powder bentonite. However, it was mentioned that covered geomembrane/GCL solutions will very likely prevent any of the above mentioned issues.
Craig Benson (University of Wisconsin-Madison) went then in Detail into the topic “Hydration, Swelling, and Hydraulic Conductivity of Bentonite-Polymer Composite GCLs for Aggressive Leachates” and showed lab tests with polymer modified bentonites but also mentioned that there is still a lot to do on research, such as detect-ing the amount of polymer used as well as classifying the polymer type.
Gemmina Di Emidio (Ghent University, Belgium) then introduced research from her work at the University with a special produced polymer-bentonite composition. The topic was “Wet and dry ageing of modified bentonites for GCLs under aggressive conditions”
Standard protocols for Construction/Installation Quality Assurance and Quality Control chaired by Kerry Rowe (Canada) and Boyd Ramsey (USA)
The fourth session focused on installation and installation related issues; problems that were either caused by or could be mitigated and reduced by the use of experienced knowledgeable installation staff and management. Wrin-kles were a key topic: both wrinkle management and the effect and relationship between wrinkles and leakage rates. Regulation and more specifically regulation with enforcement were discussed and emphasized as an important factor in leak prevention and groundwater protection. Electric leak location surveys were another critical and highly effective leakage rate reduction tool with Abigail Gilson Beck’s documentation on the clear numerical relationship between electrical leak surveys and leakage rates being highlighted. Perhaps most important were multiple requests within the session and the surveys to host a focused seminar on geosynthetic installation, perhaps in conjunction with the International Association of Geosynthetic Installers.
Even though it was the end of the last day of the workshops (for some it was the second day but for others it was the fourth workshop day as they also joined the workshop on TC-Reinforcement) all participants had a heavily discussion over 90 minute. The Questions & Answers brought up the following topics, which are listed in no particular order:
• Global improvement in communications with envi-ronmental regulatory bodies. IGS to a national EPA for example.
• Germany/BAM has published a welding manual – utilize or promote globally?
• A description of how to best manage unconfined geosynthetic clay liner materials in the field (and avoid panel separation if at all possible).
• Promote the credentialing and regimented qualifi-cation of welders and installers (with or without IAGI?)
• Conduct a seminar focused on geosynthetic in-stallation.
• How to best support the expansion of the requirement for electric leak location surveys.
• How to best support the required planning and construction details to support electric leak location surveys.
• Create a duplicate of the video shown by Kerry Rowe illustrating wrinkle leakage and head effects.
• How to best support a requirement to require electronic data management of geosynthetic installations.
• How to promote the agglomeration and utilization of “big data” sets for welding, interface friction tests, or other purposes.
Again, we would like to thank all involved people, including the chairmen, the speakers, the participants, the Univer-sity helpers on site, and Dagmar Bräu as well as Terry Ann Paulo our IGS Secretariat Manager.
Kent von Maubeuge, (Chairman TC-Barrier Systems and Corporate Committee)
The International Geosynthetics Society Technical Committee on Rein-forcement (TC-R) hosted its 1st GeoReinforcement Workshop 4 – 5 June 2018 in Munich, Germany and had 90 participants from all around the world.
This open event for researchers, designers, consultants, manufacturers, industry insiders and any interested group addressed considerations of technical consensus versus continuing technical needs, educational efforts, and potential publications.
The two day workshop allowed a lot of discussions in the following topics and the selected chairmen served as facilitators to foster discussion and interaction.
• Facings of Walls and Steep Slopes (Chair: Ian Fraser, United Kingdom)
• Use of Recycled and Amended Marginal Backfills in MSE and Reinforced Embankments/Slopes (Chair: John Sankey, USA)
• Design of Load-carrying MSE Bridge Abutments (Chair: Jorge Zornberg, USA)
• Reinforced Veneer Stability (Chair: Pietro Rimoldi, Italy)
PDF files of the presentations are available for the participants only and are distributed for most sessions already. Following are short summary of some sessions from the June 2018 IGS TC-Reinforcement Work-shop prepared by the session chairs – many thanks for their effort in organizing and finanlizing their session in this out standing way! The missing summary will be pre-pared for the next issues of IGS News.
Gerhard Bräu, TC-R Chairman
Facing of Walls and Steep Slopes
Ian Fraser highlighted the importance of the performance of facings from the end user’s perspective. It was noted that, other than satisfactory performance of the required engineering function like soil retention and load bearing, the end user’s principle concern is the appearance of the structure which is almost entirely judged on the facing. Examples were shown of the variety of facing types available and illustrations of the choice of facing to suit application, environment and design life.
Reinforcement Loads and Facing Connection Capacity in Reinforced Soil Walls: Measured vs Predicted?
Richard J. Bathurst – GeoEngineering Centre at Queen’s-RMC, Canada
Richard Bathurst concentrated on modular block walls and polymeric geosynthetics and started by presenting a wide range of connection types available in the market and posed the question ‘Are connections and connection strengths really important?’ to which his answer was definitely yes. Methods for prediction of connection strength were presented and Richard Bathurst then focused significantly more time discussing actual connection strengths measured in both field and full scale laboratory situations, including face connection failures. Down-drag related to poor construction practice was cited. Methods and re-search in connection capacity testing were extensively dis-cussed leading to conclusion that connection capacity cannot be predicted in the absence of full-scale testing. Finally, Richard Bathurst addressed connection creep and associated research taking the view that creep calculated from the geosynthetic alone was generally a safe worst-case assumption.
Stress Conditions and Connection Requirements of Rein-forced Soil Block Walls including the German EBGEO Perspective
Lars Vollmert – BBG Bauberatung Geokunststoffe
Lars Vollmert reminded us of the need for both ULS and SLS design consideration and noted that most facing issues clearly fell under SLS. He then presented the effect that a range of facing types from rigid (eg full height panels) to flexible (eg wraparound) have on the stress conditions close to the face. There followed a discussion on the compar-ison of measured lateral stress near the facing compared with active earth pressure with the conclusion that the former is invariably much lower and that the consideration of active earth is effectively invalid. Lars Vollmert discussed the EBGEO approach to the calculation of earth pressure and then shared some measured stress data on both flexible and rigid facings. There was a consideration of geosynthetic stiffness in addition to facing stiffness and lastly Lars Vollmert suggested that reduced lateral stresses allows for simplified connections and construction techniques.
Incorporation of Connection Strength in the Design of Reinforced Soil Modular Block Walls including Seismic Con-siderations
Mike Dobie – Tensar International
Mike Dobie focused on modular block wall connections and stated clearly from the outset that connection type and strength was normally very important but was critical in seismic areas. Mike Dobie then demonstrated how the 2 Part Wedge design method could very effectively take account of connection strength in an “appropriate” way. He outlined a representation of the ‘envelope of available resistance’ for each reinforcement layer and described the importance of the hinge height of the facing and how this could be calculated. Mike Dobie then overlaid the seismic considerations and in particular demonstrated the critical situation developed under upward seismic acceleration. In conclusion Mike strongly advocated the adoption of the 2 Part Wedge design method.
Flexible Reinforced Soil Structure Facings and associated Design Considerations
Philippe Delmas – Conservatoire National des Arts et Métiers
Philippe Delmas provided many examples of successful flexibly faced soil structures of significant height (>20m) from around the world and illustrated a range of facing types. The importance of appropriate facing type selection and construction detailing was emphasised. The criticality of the correct construction procedures was also highlighted. It was clear that flexible facing structures had the advantage of visibility thereby providing an opportunity to learn via the observation of their behaviour over time. It was generally concluded that many of these structures had extremely well and some had significantly outperformed expectations in respect of facing deformation and durability.
Facing and Connection Considerations for Concrete Wall Systems
Yassine Bennani – Terre Armee
Yassine Bennani focused on concrete panel walls and he highlighted a range of connection types and design con-siderations including flexibility, strength and adequate drainage. In terms of flexibility the design, the capacity for any connection to accommodate, the contrast between potential down-drag due to infill settlement and the compressibility of the facing was discussed. Yassine Bennani emphasized the need to avoid such settlement via good construction practice but nevertheless design to accommodate was deemed prudent. In particular the design of suitable panel bearing pads was discussed together with potential adjustment of the reinforcement strip placement. Finally Yassine Bennani shared some panel connection capacity test procedures and results.
Four impromptu presentations were given. The first by Jay McKelvey (Earth Engineering Incorporated) discussed and reinforced soil and soil nailed hybrid face in a very visible location at the Pocono Raceway, USA. Colin Jones (Newcastle University) presented a case study from China which demonstrated some limitations of segmental block facings used with large structures if great care is not taken. Jorge Zornberg (University of Texas) discussed the distribution of facing connection loads with height and the settlement induced connection load failure pattern. Lastly Satish Naik (Best Geotechnics Pvt Ltd) shared his experience of constructing a 40m high reinforced soil slope in a remote location in India using a soil bag vegetated facing.
Following the impromptu presentations there was a lively discussion for over 30 mins. Topics raised included stress conditions behind the face and in the fill, creep limited strength to the split of responsibility between the manufacturer, designer and the contractor and the consequent need for continuity. The importance of connection strength and flexibility, adequate drainage and good construction practice was emphasized. It was clear that it was key to adopt a holistic approach that matched the nature of the structure and facing to the available fill material, sophistication of the construction practices and application. So in summary, a range of tried and tested reliable solutions are available but they rely on making a number of the correct choices based on the individual circumstances – ‘horses for courses’.
Ian Fraser, TCS Geotechnics
Use of Recycled and Amended Marginal Backfills in MSE and Reinforced Embankments/Slopes
The session was the second of the day presented during the IGS Reinforcement Workshop held in Munich, Germany on June 4 and 5, 2018. John Sankey of Terre Armee/Reinforced Earth chaired the session composed of 5 main presentations and 6 impromptu presentations. At the start, Chungsik Yoo of Sungkyunkwan University in Korea made a brief announcement on the forthcoming 11th International Conference on Geosynthetics to be held in Seoul, Korea between September 16 to 21, 2018.
John Sankey provided the first presentation of the session titled “Overview of Reinforced Structure Design, Applica-tions and Uses with Recycled and Amended Backfills”. The presentation first described the main components of MSE and reinforced fill embankments, followed by a more detailed listing of materials that have been considered for the main component, which is select backfill. Materials addressed included foundry sands, fly ash, bottom ash, recycled asphalt, recycled concrete, ferrous slag, recycled tires, lime amended soils, cement amended soils and others. The main considerations for use of recycled and amended backfills are their compatibility with the geosynthetic or steel reinforcement, strength characteristics and in place density. Simple use of recycled and amended backfills was also noted to not necessarily be an immediate determination of sustainability value depending on means used to process the materials and transportation requirements.
Chaido (Yuli) Doulala-Rigby of Tensar International Limited followed with a presentations titled “Use of Polymeric Geogrids in Structures with Non-Standard Reinforced Fills”. Her talk also gave a further history of MSE walls and embankments reinforced by geogrids. She followed with an overview of non-standard reinforced fills with selection criteria, design considerations and benefits indicated. Specific case studies were cited. Backfill materials addressed in the talk included pulverized fuel ash, landfill waste, chalk, expanded polystyrene, lightweight expanded clay ag-gregate.
The third presentation of the session was delivered by Robert Lozano of the Reinforced Earth Company on the subject of “Treated Marginal Soils in MSE Structures”. The talk first defined the basis of lime and cement treated marginal soil as using a soil stabilizer with a high pH environment that creates a pozzolonic reaction and results in a monolithic block. Specialized equipment is needed for preparation, which in itself must be considered with respect to the presence of reinforcements for MSE wall applications. The creation of a monolithic block makes for use of a wider range of marginal soils, but the MSE wall is less flexible and the high pH environment needs evaluated for reinforce-ment compatibility purposes. Attention needs to be paid to effects on wall fascia connections, environment, filtra-tion/drainage and long term repair needs.
Oliver Detert of Huesker Synthetic presented the fourth topic of the afternoon on “Construction and Long Term Experiences with Marginal Fill in GRS Walls”. The talk started with an overview of Geosynthetic Reinforced Soil (GRS) walls and the cautionary needs when using marginal backfills. A good listing of the physical definition of marginal fills was described including recycled materials, contaminated granular soils, cohesive soils and mixtures of the aforementioned. The challenges of marginal fill placement with cement treatment and compatibility in a GRS structure were then discussed. Focus was given to the issue of hydrolysis of PET reinforcements when using cement stabilization. The talk concluded with project applications.
The fifth and final full length presentation was delivered by Castorina Silva Vieira from the University of Porto on “Use of Mixed Construction & Demolition Recycled Materials in Geosynthetic Reinforced Structures”. A discussion was first given on the outlook of construction and demolition waste use prepared by the European Commission, which addresses growth, environmental consid-erations and generation. This then led to considerations of recycled construction and demolition waste in geosynthetic reinforced structures including GRS walls and embankments. Studies have been directed toward characterization of the waste, characterization of the geosynthetics used, characterization of interfaces and numerical modeling. Full scale research on GRS walls was addressed along with damage trials in embankments. The talk concluded with outcomes of physical and leachate generation evaluations.
After the main presentations were given, six (6) impromptu audience participation presentations were given as fol-lows:
• “Ground Improvement with Electro-Osmosis for Soil Nailing” by Colin Jones, Electrokinetic Ltd
• “Clay Fills – Comments on Drainage” by Michael Dobie, Tensar
• “Red Soil Backfill for Double-Sided MSE Walls” by Dandung Sri Harnianto, Geoforce Indonesia
• “Geosynthetics as Support for Tunnel Muck” by Guilia Lugli, Maccaferri
• “Reinforcement of Marginal Soils Using Geosynthetics with In-Plane Drainage Capabilities”, Jorge Zornberg, University of Texas
• “A GRS Wall Failure” by Chungsik Yoo of Sungkyunkwan University
Two to three questions were taken from the audience for each of the full length presentations and impromptu presen-tations. In the last 20 minutes of the session, the main presenters were asked to the stage to answer further questions from the audience in round table fashion. The session was concluded with thanks to the presenters and audience.
John Sankey, Terre Armee/Reinforced Earth
Reinforced Veneer Stability
The fourth session of the GeoReinforcement Workshop took place in the afternoon of 5th June 2018, for discussing the topic “Reinforced Veneer Stability”.
The Session Chairman, Pietro Rimoldi, introduced this session by explaining that the topic was different from previous sessions, which were dealing with reinforced soil walls (RSW); in fact, RSW foundation is horizontal, the stability depends mainly on the horizontal soil thrust, and different failure mechanisms may occur with many potential failure surfaces; while reinforced veneers stay on an inclined plane and the failure occurs only by sliding along the inclined plane; the reinforcing geosynthetic, placed below the veneer soil at the interface with the failure plane, can provide the required tensile forces only if it is properly anchored at the top of the slope.
Anyway veneer stability is equally challenging as wall stability, and it may even require much stronger reinforcement, as shown in the following comparison example:
Hence the economical value of the reinforcement required for a veneer can be even higher than for a RSW.
Therefore the topic of reinforced veneer stability has been addressed through five invited presentations, followed by extensive discussion with the audience.
The first presentation was delivered by George Koerner (Geosynthetic Institute) on “General approach to veneer stability, testing and monitoring”:
• the basic principles of veneer stability were intro-duced, with the distinction between the stabilizing and destabilizing forces acting on the veneer block, which is usually divided in two parts: the top part which is prone to sliding down due the self weight of the soil veneer and other loads; the bottom part, which is buttressing against the top part and provide resistance to sliding by friction and passive resistance;
• stability analyses require: proper testing of the friction properties at the interface between the veneer soil and the inclined surface, often made up of a geomembrane or another low friction material; wide width tensile tests on the reinforcing geosynthetics, pullout and connection tests for designing the top anchorage;
• the presence of water in the veneer soil, due to rainfall and/or runoff from upstream, can dramatically reduce the Factor of Safety of the veneer: hence water shall be properly drained and/or considered in stability analyses;
• the consequences of a veneer failure may be dramatic for persons and constructions downstream, hence a proper monitoring program should always be designed, where both conventional and recent instrumentation (like Lidar) can be employed for surveying of the surface displacements and early alerts.
The second presentation was delivered by Jorge G. Zornberg (The University of Texas at Austin) on “Selection of design alternatives for water and seismic actions on reinforced veneer stability”:
• There are few design alternatives for steep veneer slopes:
o Unreinforced veneer
o Uniaxial reinforcements along the slope
o Fiber reinforcement
o Uniaxial reinforcements placed horizontally
• Design shall consider extreme loadings:
o Seismic loads
o Seepage conditions
• Preliminary design consideration can be drawn by focusing on infinite slope configuration, and with the con-sistent definition of the Factor of Safety (FS): FS = (Available soil shear strength) / (Soil shear stress required for equilibrium)
• Final Remarks:
o Innovative approaches have been recently implemented involving the use of reinforcements in landfill and mining projects
o Care shall be used, when comparing alternatives, about the definition of the Factor of
o Seepage forces and seismic loads can be accounted for using approaches similar to those used for un-reinforced slope analysis
o Solutions are available for analysis of unreinforced, slope parallel‐reinforced,
o horizontally‐reinforced, and fiber‐reinforced veneers
o Increased total height (or length) of the slope does not affect detrimentally the efficiency of horizontally‐reinforced and fiber‐reinforced slopes
o Solutions for analysis of reinforced veneers can easily incorporate the effect of seepage forces and seismic loads
o The yield acceleration used in displacement based seismic evaluations is significantly increased with the use of reinforcement
o Excellent field performance has been reported in recent case histories.
The third presentation was delivered by Jay McKelvey (Earth Engineering Inc.) on “Effects of equipment on veneer stability”:
• The stability of the veneer is heavily influenced by the movement of equipment up and down the slope;
• Based on Giroud and Beech (1989) analytical approach for the two-wedge analysis, it is possible to introduce equipment loads in the stability equations, both for tracked equipment, rubber tire equipment, and compaction equipment;
• Dynamic loads produced by acceleration and deceleration of equipment can be introduced as well in stability equations;
• It is possible to design a taper cover soil, rather than a constant thickness veneer, to reduce the loads.
The fourth presentation was delivered by Pietro Rimoldi (Consultant) on ”Semi-probabilistic approach to veneer sta-bility according to EuroCodes”:
• The existing methods for veneer stability (like Koerner and Soong, 1998) can be revised and adapted to the semi-probabilistic method in Ultimate Limit State (ULS) conditions, according to EuroCodes.
• In the semi-probabilistic approach in Ultimate Limit State (ULS) conditions, according to EuroCodes, loads are amplified by Amplification Factors, while resistances are reduced by Reduction Factors. The analysis of forces in the free body diagrams of the active and passive wedges allows to calculate the active and passive inter-wedge forces, Ea and Ep. The stability check is satisfied if: FS = (Ep / Ea) ≥ γR where FS is the Factor of Safety and γR is the partial factor R1 or R2 required by the EuroCode norms for sliding analysis.
• Design equations for calculating FS have been derived for the following conditions:
o Only gravitational forces in static conditions
o Veneer reinforcement with high strength geosynthetics
o Tracked construction equipment forces
o Seismic forces
o Horizontal seepage buildup and parallel-to-slope seepage buildup;
• The stability of the veneer cover shall be analyzed in the following Ultimate Limit State (ULS) conditions:
o At the end of veneer construction, with equipment moving down the slope, in static conditions, without seismic actions nor seepage forces applied; being a short term analysis, if reinforcement is used, the Reduction Factors for creep, chemical and biological damageshall be set equal to 1.0.
o At the end of the design life, in static conditions, without seismic actions but with seepage forces ap-plied, either for horizontal seepage buildup or parallel-to-slope seepage buildup; being a long term anal-ysis, if reinforcement is used, all the Reduction Factors (for installation damage, creep, chemical and biological damage) shall be applied.
o At the end of the design life, in seismic conditions, with seismic actions and seepage forces applied, either for horizontal seepage buildup or parallel-to-slope seepage buildup; the vertical seismic accelera-tion shall be considered both as downward (+Kv) and upward (-Kv), while the horizontal seismic accel-eration shall always be considered as outward; being a long term analysis in seismic conditions, if rein-forcement is used, the Reduction Factors for installation damage, chemical and biological damage shall be applied, while the Reduction Factor for creep shall be set equal to 1.0.
• A practical example of stability calculations according to Eurocodes have been shown.
The fifth presentation was delivered by Felix Jacobs (IGB Ingenieurgesellschaft mbH, Kiel) on “EBGEO approach to veneer stability”:
• The topic discussed here is the specifically the resistance of anchor trenches at the top of the veneer slope;
• The proof of anchorage is: Effect of actions from slope ED ≤ Resistance of anchor trench RD
• The EBGEO 2010 / 2011 approach requires an interaction model for the resistance of anchor trenches, devel-oped using pullout tests, model tests and instrumented field tests; moreover, the tensile stiffness of reinforce-ment, geogrid junction strength, and serviceability limit states have been considered;
• The possible design approaches include the detailed model and the modified EBGEO 2010 / 2011 approach;
• The Model Factor value has been validated for various geogrid types.
The five presentations were followed by a long and interesting discussion, where the presenters and all the audience debated about several specific topics, including the best way of testing the friction properties at the interface below the veneer (direct shear test and inclined plane test were compared), the influence of water and equipment on sta-bility, how to consider the seismic action and the seismic displacements.
The interest and attention gained by this topic at the GeoReinforcement Workshop has shown that reinforced veneer stability deserves research and developments by the geosynthetics technical community.
Pietro Rimoldi, Session Chairman
The International Geosynthetics Society hosted two high-level, two-day geotechnical engineering workshops 4 – 7 June 2018 in Munich, Germany: 1st GeoReinforcement and 1st GeoBarrier. Each workshop was divided into 4 hot topics that were presented and discussed very lifley for mostly half the time of each session half day each. The presentations are available as pdf-files only for the participants.
These events, with their international speakers, attendees, and engineering issues, were a great success and provided the most advanced IGS Technical Committee-led workshops to date. The format will be continued.
And for sure not only the technical aspects, but also the social contacts made the events a success and the participants happy!
GeoAfrica 2021, the 4th African Regional Conference on Geosynthetics is fast approaching following the great successes of the previous GeoAfrica conferences in South Africa, Ghana and Morocco.
GeoAfrica is establishing a gateway for geosynthetics into Africa by providing a forum for engineers, practitioners and academia to explore current and future potential applications for geosynthetics, while offering an active market place for the promotion of geosynthetic products and technology to users throughout the Africa.
The International Geosynthetics Society – IGS calls for proposals in hosting GeoAfrica 2021
The proposal shall include, as a minimum, a letter from the proposing chapter/committee outlining the structure of the event, proposed location and dates with a general outline of the technical programme. The proposal should contain a high-level budget proposal demonstrating the feasibility of the event (including fees for IGS Members and possible sponsorship packages).
The official language of the conference must be English for the written version of the papers. However, presentations may be presented in another language provided that simultaneous translation into English is provided in all technical sessions.
The proposing committee must demonstrate its ability to manage a high-level conference with international attendees and a technical programme covering a variety of geosynthetic topics. Previous experience in similar events is recommended or the inclusion of a professional conference organizer is advised.
GeoAfrica 2021 shall follow the “Guidelines of the International Geosynthetics Society Regarding Regional Conferences on Geosynthetics” available through the IGS Secretariat.
A call for Proposal should be submitted not later than 7th September 2018 and the vote by the IGS Council will take place during the 11th International Conference on Geosynthetics to be held in Seoul, Korea in September 2018. Although not a requirement, presentations to the IGS Council are welcome but they do not necessarily influence the decision of the IGS Council in the award of the next GeoAfrica 2021 Conference.
IGS meetings open for all IGS Members
|Sep. 17 (Mon), 2018||12:40 – 13:40||TC Hydraulics – Membership Meeting|
|Sep. 18 (Tue), 2018||12:30 – 13:30||TC Filtration – Membership Meeting|
|Sep. 19 (Wed), 2018||12:30 – 13:30||TC Reinforcement – Membership Meeting|
|Sep. 20 (Thur), 2018||12:30 – 13:30||TC Barriers – Membership Meeting|
|Sep. 21 (Fri), 2018||10:30 – 12:30||IGS Regional Activities Committees|
|Open to all IGS Members – Concurrent meetings|
|Sep. 21 (Fri), 2018||13:30 – 16:30||IGS Council Committee Meetings|
|Open to all IGS members – Corporate, Communications, Education – Concurrent meetings|
IGS Technical Committee Sessions
Drainage and Filtration for Reinforced Soil Walls
Organizer: Pietro Rimoldi (IGS TC Hydraulic Applications)
Geosynthetic Barriers – Current Hot Topics
Organizer: Kent P. von Maubeuge (IGS TC Barrier Systems)
New design and research approaches for fundamental geosynthetic – soil reinforcement applications
Organizer: Gerhard Bräu (IGS TC Soil Reinforcement)
And much more…
We hope to see you in Seoul! We welcome your questions. Contact the IGS Secretariat (IGSsec@GeosyntheticsSociety.org).
It is our pleasure to invite all IGS Members to the 2018 IGS General Assembly with Awards Presentation at 3:30 pm on Wednesday 19th September 2018 at the 11th ICG in Seoul. It promises to be like no other! During this event we will review the progress of the IGS over the last four years, be introduced to the newly elected council, and recognize some of our Society’s outstanding service & technical contributions.
The Presentation of IGS Awards
• The IGS Award – Our society’s highest award, given to members for a substantive technical contribution to the geosynthetics discipline.
• Honorary Membership – An award to distinguish a person who has made a vast and long-term commitment to the Society and its aims.
• The IGS Service Award – Recognizes members of the IGS who have served the IGS in such a way as to sig-nificantly impact the IGS, its members and its aims.
• The Young IGS Service Award – To be presented here for the second time, the IGS Young Member Service Award is given to a Young Member of the IGS for outstanding contribution(s) to the society.
IGS North America Presents:
Introduction To Geopipe
Presented by Dr. Michael Pluimer, University of Minnesota – Duluth
Date: Thursday, July 12, 2018 @ 1:00 – 2:30pm EDT (includes Q&A time)
$20.00* – IGS-NA Members | $20.00 – IGS-NA Student Members
$60.00 – IGS Members | $80.00 – Non-members
* IGS-NA Members receive one FREE webinar coupon on paying annual dues
EARN 1 PDH
Presenter: Dr. Michael Pluimer, University of Minnesota – Duluth
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Introduction To Geopipe
In this webinar, Dr. Pluimer will open a series on applications, specifications, and test methods associated with geopipe. These polymeric pipe materials, commonly offered in corrugated and smooth varieties and a wide range of diameters and thicknesses, are essential to the success of modern infrastructures: water, wastewater, sewer, landfills, mining, residential and commercial development, utilities, etc. The session will detail types of geopipe (e.g., dual-wall pipe, polyethylene corrugated pipe, numerous other materials), raw material properties and resulting pipe properties, long-term durability, common specification requirements, and more. Essential engineering parameters such as stress cracking, oxidation resistance, UV degradation, and creep will be discussed.
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Key Topics Include:
- types of geopipe
- raw material properties and resulting pipe properties
- long-term durability
- common specification requirements
- and more
IIGS North America’s Introduction To Geopipe Webinar is ideal for environmental engineers, infrastructure-owning agencies, design engineers, municipal engineers, regulators, general contractors, and other stakeholders.
Presenter Bio: Michael Pluimer holds a PhD in Civil Engineering (2016) from Villanova University and a Master’s Degree in Mechanical Engineering (2002) from the University of Minnesota. His PhD research was on the performance of corrugated HDPE pipe manufactured with post-consumer recycled content in commuter railroad applications. Dr. Pluimer developed and validated a service life model for pipes in these applications relative to both the fatigue- and creep-related slow crack growth failure mechanisms. The service life model utilized ASTM F3181, the Un-notched Constant Ligament Stress (UCLS) test, a new test method developed for corrugated HDPE pipe materials containing recycled content.
IGS North America Presents:
Erosion Control with Geosynthetics
Presented by Markus Wilke, HUESKER
Date: Tuesday, May 29, 2018 @ 1:00 – 2:30pm EDT (includes Q&A time)
$20.00* – IGS-NA Members | $80.00 – Non-members
* IGS-NA Members receive one FREE webinar coupon on paying annual dues
EARN 1 PDH
Presenter: Markus Wilke, HUESKER
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Erosion Control with Geosynthetics
Erosion is a natural process, resulting from the interaction between water and soil. Unfortunately, this can cause severe damage to infrastructure and endanger people’s lives. Culverts, roads, bridge foundations, embankments, landfill slopes, MSE walls, and other critical pieces of infrastructure are susceptible. With greater urbanization occurring around the world and population centers swelling along coastlines and rivers, the collective need to better manage erosion threats has intensified.
Geosynthetics provide highly engineered solutions for solving all of these erosion problems.
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Key Topics Include:
- Naturally occurring erosion processes
- Available geosynthetic product and system approaches
- Geosynthetic mitigation measures
- Case studies
IGS North America’s Erosion Control Webinar Series is ideal for environmental engineers, infrastructure-owning agencies, design engineers, municipal engineers, regulators, general contractors, and other stakeholders.
Presenter Bio: Markus Wilke is an engineer and business development manager with HUESKER, one of the world’s oldest and largest geosynthetic manufacturing and design engineering companies. Wilke brings more than a decade of experience to the presentation, including a very deep background in hydraulic engineering and coastal protection and remediation. He has published extensively on topics such as dewatering, port maintenance, bank stabilization, and waterway engineering.