Geosynthetics, Forging a Path to Bona Fide Engineering Materials: Honoring Robert M. Koerner

An increasing demand for construction quality assurance (CQA) for large landfill liner and final cover projects is being driven by three key recent trends: (1) the consolidation and closure of large municipal solid waste (MSW) landfills; (2) the expansion and/or closure of large coal combustion residual (CCR) landfills, and (3) the closure of large CCR surface impoundments. The unprecedented size of these emerging construction projects is cause to examine existing CQA practices and evaluate their projected efficacy for upcoming construction. Destructive seam testing for geomembranes deployed in the field is an area of particular interest because this kind of CQA testing has a direct impact on the quality, schedule, and cost of installations. This paper examines available probability-based quality assurance methods and considers their impact on risk of poor performance for large liner and final cover systems. Data from completed projects are used to illustrate the implementation of these methods and to simulate how a CQA program can manage risk.

This paper describes ongoing research into the monitoring of two adjacent landfill cells with different liquids management strategies at an active municipal solid waste (MSW) landfill. One is a conventional dry cell and the other is a wet, or bioreactor, cell. To understand the waste materials behavior and associated geomembrane long-term behavior, the in-situ conditions are needed and how the various parameters change over time. In this regard, measurements have been taken at both cells for approximately 20-years and are continuing. Both dry and wet cells are monitored for changes in gases, leachate, waste and geomembrane temperatures. Knowing this information will allow for making longevity predictions in regard to both solid waste degradation and geosynthetics behavior. In addition, the data gives insight so as to fine-tuning the design-by-function approach for various situations and materials.

From 1984 to 1986, Dr. Koerner was graduate advisor of my master’s program, which focused on geoenvironmental and geosynthetic studies at Drexel University. This program of study was very unique and groundbreaking for its time. In honor of Dr. Koerner, the following case history addresses the topic of the former Fort Gillem (Gillem) Base redevelopment, which has required particular use of all the technical skills that I acquired while studying under his advisement. For the past seven years I have been involved with this project which, from a geoenvironmental perspective, has been the most technically challenging project of my 30-year career. I have served as the technical director for all environmental and geotechnical matters related to the Gillem Base transfer from the U.S. Army (Army) to the Urban Redevelopment Authority of the City of Forest Park (URA) through the process of redevelopment. Key technical challenges have included the following: (i) geotechnical issues related to difficult soil conditions; (ii) the evaluation of environmental concerns resulting from 60 years of Army use; (iii) regulatory negotiations; and (iv) an evaluation of two existing dams for future use or demolition. This case history presents key technical, regulatory, and business challenges faced by the major stakeholders who were critical to the success of the process: the owner, Army, legal counsel, master developer, environmental consultant, and end user.

It is well known that the bearing resistance against a geogrid’s transverse rib is transferred through the geogrid junction when the geogrid is embedded in soil and subjected to pullout or tensile loading. However, there is not an established technical approach that can be used by design engineers to estimate the load transferred to the geogrid junction confined in granular soil. In this paper, a theoretical analysis is performed to estimate the maximum load transferred to the geogrid junction. The results of the analysis are presented in mathematical expressions that can be easily used by design engineers to estimate the maximum geogrid junction load which will allow the proper specification of the required geogrid junction strength accordingly. Geogrid junction strength is determined by using either the Geosynthetics Research Institute (GRI) GG-2 test method or the ASTM International (ASTM) D 7737 test method. Currently, the required junction strength is typically specified as a percentage of the geogrid rib strength (i.e., junction efficiency). Typically, the required junction efficiency can range from 10 to 90% of the single rib strength. This paper provides insight into establishing a proper geogrid junction strength specification based on using a factor of safety and the estimated maximum geogrid junction load. The paper also presents a historical prospective with regard to the development of the geogrid junction strength test methods GRI GG-2 and ASTM D 7737-11.

This paper examines the use of geogrids to effectively stabilize particles and form a mechanically stabilized layer or layers. Historically the geosynthetic and geotechnical community have referred to the use of geogrids for reinforcement. This was born out of their widespread use in wall and slope or grade separation structures. However, when these materials are utilized in transportation applications they provide the primary function of stabilization. This paper will highlight recent modelling, laboratory and full scale field testing which demonstrate that this is in fact the case.

The primarily function of carbon black (CB) is to protect the polymer from ultraviolet degradation. That said, conflicting results have been reported regarding the improvement of the long-term performance of the polymer by combining CB with antioxidants (AOs). This paper presents the effects of CB on the depletion of two types of AOs in high density polyethylene (HDPE). Carbon black with a particle size of 75 nm were blended with HDPE resin in the amount of 0 and 2.5 wt.%. Antioxidants, Irganox 1010 (I-1010) and Irgafos 168 (I-168), at different concentrations were then added to the samples with and without CB. Ten test formulations were generated. The interaction between the CB and AOs were accelerated by incubating samples in a forced air oven and in a water bath at a temperature of 85°C. The antioxidant depletion rate was monitored using the oxidative induction time (OIT) test. For unstabilized HDPE samples (with 0% of AO), the CB delayed the onset of oxidation. On the other hand, a strong interaction between the CB and AOs was found in samples that consisted of both, as indicated by a rapid decrease of the OIT value in both incubation environments. Furthermore, the depletion of AOs in CB samples was significantly faster in water than air environment, particularly in the initial 90 days. The hydrolysis/leaching of AOs as well as the enhanced CB/AO interaction due to ingress of moisture may be the factors for such an accelerated depletion rate.

The paper describes research on separation geotextiles performed at the University of Washington and supported largely by the Washington State Department of Transportation. The studies involved forensic investigations of separation geotextile installations throughout Washington State, repeated plate load tests on laboratory model soil-geosynthetic-aggregate test sections, and a full scale road test with end-of-construction and two subsequent forensic investigations. The results of all these studies are summarized and an extensive reference list is provided. We found that geotextile separators, if they survive construction and installation stresses, perform exactly as intended. All geotextiles worked well, although some performed better than others, depending on site specific conditions. On very soft subgrades, bearing capacity increased, rut depths decreased, and induced pore pressures in saturated subgrades dissipated faster with a geotextile; thus subgrades consolidated and gained strength, mostly in the first few months after construction. Short-term benefits of separator geotextiles appear to be more important than long-term for pavement performance.

An update to Robert M. Koerner’s 1969 equations for minimum and maximum dry density of soils, based on intrinsic soil properties, is presented. The original equations used coefficient of uniformity (C_u), 10% by weight particle size (D₁₀) and particle sphericity defined by the ratio of projected particle area to the area of the smallest circumscribing circle. The updated equations are written for maximum and minimum void ratio. They utilize C_u, Wadell particle roundness (R) and sphericity (S) now defined as the ratio of particle width to length. The R and S values for sands, glass spheres, crushed aggregate and rice spanned a wide range of sizes and shapes. Computational geometry was used to obtain the R and S values from images of three-dimensional particle assemblies. The paper also discusses the developed image analysis methods and the significance of intrinsic soil properties to soil-geotextile, soil-geomembrane and soil-geogrid interface behavior.

Several reinforced soil retaining walls of height 15.3 m were modeled in the Columbia University centrifuge under an acceleration field of 50-g. Nevada sand was used as backfill material and gabion blocks were used as wall facing to replicate the wire mesh system. A fiber glass mesh of length 35 cm was used to model the reinforcement layers having prototype length of 17.5 m. Two basic cases with different reinforcement layouts were tested, with vertical reinforcement spacings of 2 cm and 4 cm (prototype spacings of 1 m and 2 m), respectively. The retaining wall model was constructed in 4 stages. The models were prepared under 1-g, but were spun to 50-g after each wall height increment. The results obtained from staged construction compared favorably to the field measurements.

Engineered reinforcement of soils has revolutionized the methods for constructing soil retaining structures, man-made slopes, and development of foundation soils. Both the geosynthetic reinforcement in the form of geogrid or woven geotextiles and metal strips have been very successful in construction. Fiber reinforcement, while it caught the attention of some researchers, never proved to be as useful, and the amount of research generated on the topic today is disproportional to the utility of the method in engineering practice. Development of the models describing the strength of fiber-reinforced soils, however, forced engineers to consider such issues as the yield condition, flow rule, and anisotropy. All of these are important in considering stability of municipal solid waste landfill slopes. Although a comprehensive yield condition for municipal solid waste has not been developed yet, an effort is presented indicating how the existing methods describing reinforced soils can be used to develop an anisotropic yield condition suitable for the description of solid waste. It will be shown that a homogenization scheme, sometimes referred to as the principle of macro-homogeneity, is a useful tool in developing the yield surfaces suitable for fiber-reinforced composites, thus also for fibrous solid waste.

The experiments reported herein examine the self-healing of slits in GCLs upon hydration with deionized water under a confining stress of 2 kPa. Consideration is given to self-healing of 15 mm-wide, 25 mm-wide, and 30 mm-wide × 120 mm-long single slit in the center of a GCL specimen. The single 15 mm-wide slit fully self-healed after 65 days. Neither the 25 mm-wide × 120 mm-long nor 30 mm-wide × 120 mm-long single slit fully self-healed and a fully penetrating hole remained after full hydration. The self-healing of GCL specimens with 15 mm-wide × 240 mm-long double parallel slits is also examined. Full self-healing was observed when there was a 20 mm-wide strip of undamaged GCL between the slits. However full self-healing did not occur when the widths of this strip of bentonite between slits was reduced to 10 mm and 5 mm. This study also raises a number of questions such as what is the effect of stress, hydrating conditions, and mass of bentonite in the GCL that require further investigation.

The aim of this study is to investigate effective and sustainable measures to contain heavy metal contaminated sediments inside a geotextile tube during the dewatering process. A series of batch adsorption and pressure filtration tests (PFT) evaluated the efficacy of cellulosic materials (kraft pulp, jute fibers, and peanut hulls) on adsorption of selected heavy metals (Pb²⁺, Cu²⁺, Zn²⁺, and Cd²⁺) and the dewatering performance inside a geotextile tube. The batch adsorption tests conducted on two soils, sandy and silty in composition (Tully sands and Tully fines) with metal ions show that they have a very high affinity towards Pb and Cu compared to Cd and Zn. The maximum adsorption capacity as calculated from the batch adsorption of Tully sand to Pb and Cu are 33.12 and 6.54 mg/g, respectively. The Tully fines had even higher adsorption capacities of 57.3 mg/g Pb and 9.48 mg/g Cu. The concentration of filtrate collected from PFT, measured using ICP OES (inductively coupled plasma optical emission spectrometry), also shows that Tully fines were able to adsorb 99% Pb and Cu, 88% Cd, and 83% Zn. Meanwhile, Tully sand adsorbed 96% Pb, 90% Cu, 81% Cd, and 76% Zn. Although significant adsorption was accomplished by both soils rich in reactive minerals illite, chlorite, and calcite, the addition of cellulosic materials provided additional benefits in dewatering. Among three cellulosic materials, the addition of jute fibers significantly reduced the water content of the Tully sand filter cake by 44%. Since kraft pulp has a tendency to adsorb water and swell, water content as high as 40% was measured. The water content did not change significantly with the use of peanut hulls. All the cellulosic materials were successful in improving the overall turbidity of the filtrate. A drop in turbidity of more than 60-80% was observed with the addition of jute fibers.

Exposed geomembranes provide a tool for the more sustainable operation of solid waste landfills. Common sustainable landfill practices involve the purposeful treatment of the landfilled solid waste to stabilize the disposed materials more rapidly. Exposed geomembranes have been successfully employed to control liquid balance issues associated with wet landfills. They can be used to greatly enhance gas collection efficiency, including periods earlier in the operation life of a landfill, and to overcome many of the challenges of collecting gas from wet landfills. Employing an exposed geomembranes as a protection emissions control feature instead of a traditional landfill cover system offers the operator the opportunity to more efficiently utilize disposal capacity and implement landfill reclamation. These benefits result in an overall reduction of the net carbon footprint for a landfill site. Regulatory, engineering, and operational challenges remain to fully implement this approach, but the benefits suggested offer sufficient justification to continue to explore the role exposed geomembranes play with respect to sustainable landfill practices.

A wide range of problems involving geosynthetics have been and are being studied using geotechnical centrifuges. In the late 1970’s when geotechnical centrifuge testing began to gain popularity in the U.S., there was some doubt as to the usefulness of centrifuge modeling for geosynthetics applications. However as the field matured and experience was gained, it became apparent that the use of centrifuge modeling has certain distinct advantages in the area of geosynthetics, and thus geosynthetic centrifuge modeling is a very active area. A brief history of centrifuge modeling in the U.S. is presented, plus three projects utilizing centrifuge modeling involving geosynthetics applications: a slope stabilization scheme, dynamic interface experiments, and the use of geosynthetics to protect underground structures from explosive effects. Emphasis is on the experimental design and the scaling relations, to illustrate that even where all parameters are not scaled correctly, the modeling is correct and the results are valid. Detailed results can be found elsewhere and are referenced. Some advantages and limitations of centrifuge modeling are also discussed.

The objective of this paper is to assess the formation of capillary barriers on soils in contact with nonwoven geotextiles that have been placed with the primary function of acting as a separator between clay and gravel. This includes a comprehensive experimental program that involved a number of soil column infiltration tests conducted using a variety of material combinations to assess the hydraulic performance of interfaces between the unsaturated clay and the geotextile. Soil moisture was recorded using time domain reflectometers. The acrylic soil columns custom made for this study were comparatively small (20 cm diameter and 17 cm tall) in order to facilitate test setup and reduce total testing time. Eight column tests were conducted, which included four different nonwoven geotextiles selected to observe the geotextile characteristics that may affect the formation of a capillary barrier. The tests were all performed using the same configuration, soils, relative compaction, initial unsaturated water content, and inflow rate, in order to assess the impact of different geotextiles on the hydraulic performance. Based on data from the moisture sensors, all tests were found to show a clear formation of a capillary barrier, which resulted in additional moisture storage in the overlying fine-grained soil layer. The test results show that currently available standard nonwoven geotextiles will create a capillary barrier and restrict moisture flow into the underlying soil layer until the overlying fine-grained soil has become nearly saturated. The strength of the capillary barrier was found to be similar for the multiple standard polypropylene nonwoven geotextiles investigated in this study.

The characteristic flow equation (CFE) is a quadratic formula consisting of two terms; one that is proportional to the flow velocity and one that is proportional to the velocity squared. The first order term is referred to as the Darcy friction term, while the second order term is the “Inertia” term. This latter variable is based on the equation that describes flow through an orifice which explains the curved shape of the flow rate versus head plots generated in both permittivity and transmissivity tests, countering the commonly accepted supposition that the concave downward shape is due to turbulence. In this paper, The CFE is used to provide increased accuracy and utility for hydraulic measurements of geosynthetic flow capacity. This paper summarizes the features of the standard permittivity test procedure, ASTM D4491, Standard Test Methods for Water Permeability of Geotextiles by Permittivity, and reports test results using the CFE formula and air and water flow measurements to determine the permittivity of the same test specimens.

This paper presents a review of available information on leachates from several U.S. Department of Energy (DOE) Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) waste disposal facilities (WDFs) in order to characterize radioactivity doses and chemical exposures for high-density polyethylene (HDPE) geomembrane liners used in them. This exposure information is compared to the results of studies performed to evaluate the effects of radiation and chemical exposure on the physical and mechanical properties of HDPE materials. Case study data from laboratory geomembrane-leachate compatibility testing programs performed for several CERCLA WDFs and other relevant projects are also presented and discussed. From this information, it is concluded that the radiological doses to which HDPE geomembrane liners will be exposed in CERCLA WDFs are well below the threshold doses likely to induce geomembrane physical and mechanical property changes. Consistent with this finding, the physical and mechanical properties of HDPE geomembrane liners were not measurably degraded in the CERCLA WDF leachate compatibility testing programs described in the paper. In addition to radionuclides, the paper also reviews information on pH levels, trace metal concentrations, and volatile organic compound concentrations in CERCLA WDF leachates. The conclusion is reached that the service life for HDPE geomembrane liners in these facilities should be well in excess of the 200-year minimum facility performance period of DOE Order 458.1 and may approach the DOE performance-period goal of 1,000 years “to the extent reasonably achievable.” To maximize service life, it is recommended that relatively thick geomembranes (e.g., 2.0-mm thick) be used in CERCLA WDF applications. Lastly, the paper briefly discusses the implications of this long geomembrane service life in the context of the design philosophy for CERCLA WDFs and provides suggestions for further studies.

This paper focuses on the use of recycled cross-linked polyethylene foam aggregates in conjunction with nonwoven geotextiles to produce a composite used for floating covers. These floating geosynthetic cover systems provide effective odor and air emissions control for manure storage structures, waste retention ponds and other odorous lagoons. This design approach allows rainwater to pass through the cover while scrubbing the odorous gases—thus avoiding collection, pumping, and associated maintenance/cost. Additional benefits include insulating properties that aid in the anaerobic process, blockage of sunlight to preclude algae growth, and water loss reduction due to evaporation. Heretofore typical available permeable covers to offer an aerobic environment were made from straw, peat-moss, or similar organic materials. However, these organic materials exhibit performance deficiency with respect to buoyancy and structural integrity. Further, they are vulnerable to wind, rain, hail, and fire damage.

Stress cracking (SC) in high density polyethylene (HDPE) has been a problem, an interesting research topic, and an agent for improved geomembrane performance. The Geosynthetic Research Institute and Professor Robert Koerner have been front and center in this effort over the years since about 1984. In this paper we take a look back and a look forward at this still developing story. The internationally accepted GRI.GM13 standard for HDPE geomembranes specified SCR (SC resistance) from 200 hr to 300 hr, recently increased to 500 hr in the ASTM D5397 standard test procedure. And some geomembranes have SCRs exceeding 2000 hr. However, we have not seen an end to SC yet, and we may even see in increase in SC events as older HDPE geomembranes reach the ends of their natural service lives, oxidize, and crack. But there are excellent new high performance, premium, high temperature, and hot liquid rated HDPEs, some using quite different resins, to take their place. And as SCRs increase conformance testing times increase which engenders further research into accelerated methods to generate stress cracking resistances rapidly. One of these methods is to assess SCR from the post-yield strain-hardening segment of a uniaxial tensile stress/strain curve; a test that can be done very quickly.

“How long will my geomembrane last?” That question had been asked throughout the engineering community for many years following their introduction. The question inevitably morphed into warranty time on manufactured geosynthetics. The initial response was “20 years” (or thereabouts) based on nominal service lives of building roofing systems where use of geosynthetics had increased the most. Geosynthetic sealing technology moved into the geo-environmental realm in the last decades of the 20th century for use in containing environmental and human health toxins associated with waste disposal (municipal solid and hazardous waste). The stakes were now much higher than simply crafting an appropriate capital recovery amortization schedule to replace the roof before it started to leak. The “warranty” answer quickly became an unsatisfactory solution. Also since such warranties originated from exposed membrane conditions, they were completely inapplicable for landfill base liners. Geosynthetic science as provided by the Geosynthetic Institute has evolved to the point such warranties are really an archaic device that no longer serve a useful purpose. This technical paper will discuss the GRI legacy to the geosynthetic industry with regard to geosynthetic longevity and demonstrates how initial field data is confirming to the initial conclusions the GRI is drawing from its laboratory studies.

Since 2009 the St. Lawrence County Highway Department in New York State has constructed seventeen GRS-IBS bridges. This is as a result of a bridge inventory which showed that there were 81 county-owned bridges that were labeled as deficient. Twenty-seven of the 81 were placed on a 2014 priority replacement list due to a condition rating of ≤ 4.5 out of 7. There was a need to find a faster, more economical and better method for the replacement of these bridges. Thus the decision was made to use the GRS-IBS approach. This paper will present a case study of one such structure constructed by the St. Lawrence County Highway Department.

Surface impoundments (aka, ponds) lined with geomembranes are susceptible to geomembrane uplift caused by trapped gases below the liner. This paper provides a method to analyze the shape, internal pressure, stresses, and strains in a geomembrane bubble (also called “whales” or “hippos”) whose pressure is caused by the gases and surrounding impounded fluid.

Four selected projects from the last twenty years are briefly presented in chronological order. They all include pioneering elements in terms of engineering solutions, development and application of innovative geosynthetic reinforcement. They are the following: (1) Bridging a sinkhole on the German National Highway B180 near Eisleben, Germany in 1993. Geogrids from aramid (AR) with 1200 kN/m were developed, produced and installed for the first time worldwide. Ten years later the sinkhole reactivated. The solution performed even better than expected and actually saved human life. (2) Intermediate capping system of a landfill near Stuttgart, Germany in 1998 to allow the overbuilding of the old landfill so as to increase capacity. Differential settlements had to be equalized and an old gas dome to be overbridged. Geogrids from polyvinylalcohol (PVA) with 900 kN/m were developed and used to reinforce the soils of the intermediate layer system. (3) Upgrade of the intercity rail link Berlin-Hamburg in Germany at Büchen for train velocities of up to 260 km/h in 2003. The subsoil was of insufficient dynamic stability. The solution comprised a flat geogrid-reinforced embankment from cemented sand on top of mixed-in-place columns. Two layers of PVA-geogrids with 400 kN/m were applied. This allowed building the flattest railroad embankment over piles known to exist. (4) Heavy stockyard of the TKCSA steel plant, Sepetiba, Brazil in 2006-2008. It included stock beds and runways and had to be constructed on soft saturated clays. To ensure both the ultimate and serviceability limit states a wide range of PVA-geogrids and -woven geotextiles with up to 1600 kN/m were installed. It is the biggest project worldwide using PVA-geosynthetic reinforcement (887,000 m²) and possibly the biggest one in terms of total installed geosynthetic strengths.

The use of exposed geomembranes for the rehabilitation of concrete and masonry dams was introduced in Italy in 1976, when the entire upstream face of an 11 m high masonry dam was lined with a 2 mm thick PVC (polyvinyl chloride) geomembrane as the waterproofing element (Lago Miller). In subsequent applications, the system progressively evolved. From 1988 to present, this technique underwent several other changes, mainly thanks to the use of additional geosynthetics, such as geonets and as thick nonwoven needle-punched geotextiles which allow to avoid the surface irregularities before the geomembrane installation. In all of these applications, the geomembranes were left exposed on the upstream face, without any external protection, to environmental factors and weather conditions, especially to UV rays, which are very intense because many of these dams are at high elevation (typically around 2.000 m above the sea level). On the other hand, the fact that geomembranes are exposed makes it easier to control and monitor their behavior over time. Therefore, in order to verify the performance of the waterproofing system, several geomembrane samples have been taken in different years from a considerable number of dams. These samples have then been subjected to physical and mechanical tests, in order to observe the change of the properties of the geomembranes over the years. In several cases, particularly when the results of tests on virgin samples were available, it was possible to evaluate the residual life of exposed geomembranes on the different types of dams. The main updated results of this large research program will be reported in the paper.

This study investigates the performance of a geosynthetic-reinforced modular block retaining wall backfilled with cohesive soil during seismic loading. A shaking table test was performed to understand the seismic behavior of the ½ scaled model wall with the dimensions 190 cm height, 280 cm length, 50 cm width. Scaled versions of the recorded El Centro and Kobe earthquakes at different amplitudes were applied. A 12.5^° battered facing was constructed with modular hollow concrete blocks. Polyester woven geogrid was used in the test. Maximum and residual displacements on the front wall, acceleration amplification ratios on the front wall and inside the backfill, strain values implying the tensile loads on the reinforcements, and the visual observations for the facing and backfill surface were the results of this test to evaluate the performance of the cohesive backfilled model wall. As a conclusion, it can be said that the model wall with cohesive backfill performed within acceptable limits under seismic loading conditions when compared with the limit design values described in previous studies.

In the late 1980s a shear-resistant sandwiched product of geosynthetic textile layers and bentonite clay was invented and introduced to the field of geotechnics in Germany. The product consists of a needle-punched nonwoven/woven fabric combination as carrier layer, a powdered layer of bentonite clay as sealing element and a second needle-punched nonwoven as cover layer, all layers connected by a needle-punching operation. By this needle-punching operation a long-term shear-resistant connection of all layers is achieved to transmit shear forces from the cover layer across the bentonite layer (very low internal shear strength when hydrated) to the carrier layer. Very rapidly this new product was accepted around the world as a new sealing element in geotechnical and hydraulic engineering applications. Currently, more than about 1 billion m² has been used worldwide up to now, saving about 1 million tons of natural clay. Today the “shear-resistant geosynthetic clay liner” (shear-resistant GCL) is a standard geosynthetic product being produced and used all around the world. Early applications were in hydraulic and environmental applications, but also many others, such as waterproofing in construction engineering, infrastructure applications and many more. The GCL applications development was accompanied by significant research with activities around the world which also leads to new questions and answers for clay sealings in general. Professor Robert M. Koerner supported the GCL development as prominent leader with great personal commitment and visions.

ASTM D6460 and ASTM D7101 standard test methods were used to conduct the storm-water induced runoff and rain-splash soil erosion performance tests for two types of rolled erosion control products. The test soil is sandy silt obtained from a local river bed. Cold-resistant small leaf Bahia grass was chosen for this study. The test soil conditions included bare soil bed, vegetated soil bed, erosion control mat covered soil bed and vegetated erosion control mated covered soil bed. Six to eight weeks of vegetation was used in this study. Vegetation has more effect on increasing the Manning’s coefficient than the test RECP. Soil erosion was increased with increasing channel slope and pump capacity. Placing RECP over the test soil would significantly reduce the soil erosion. The soil erosion rates for all vegetated soil and vegetated RECP conditions are only around one percent. Four to six months vegetation period is required for using RECP for erosion control applications. Test soil containers were placed on a 36° inclined slope ramp. The test rainfall intensity was 100 mm/hr. The quantity of soil loss was measured and the bench-scale cover index (BSCI) determined for each test condition. The study results indicated that RECP and vegetation are important influence factors for soil loss rates.

The development of green geosynthetics, its background and technical concerns, are discussed using research results on polylactic acid (PLA) samples. A test method to evaluate biodegradability of PLA as a green geosynthetic is considered and suggested. The results show that the concept of biodegradability of green geosynthetics is applicable for many environmental applications. As a raw material for green geosynthetics, PLA 4032D (NatureWorks LLC)/PBAT (polybutylene adipate-co-terephthalate, BASF) (80/20) blend shows improvement of environmental performance as a green geosynthetic over that of PLA 4032D alone.

Structures of a geotechnical nature have been constructed for thousands of years and a brief review of this infrastructure over time shows that the use of filters and drains is a relatively recent development in a wide range of applications. The use of granular filter design criteria for sands and gravels has been common practice for a century whereas granular filter criteria for cohesive silts and clays evolved in the 1980s. It was at about this time that geotextiles as filters rapidly gained favor as use in many civil, environmental and mining applications. However their use as primary filters in critical applications such as the internal filters of embankment dams was not generally accepted, due to longevity concerns and construction considerations. A laboratory research programme and subsequent field investigation into the performance of both geotextile and granular filters is reported. This experience exposes the advantages and disadvantages of each filter material type. A world wide review of dam failures confirms the critical importance of preventing internal erosion or piping in critical applications especially during the first decade of service. Furthermore the use of filters and drains in critical applications such as in dams and in mono-waste disposal facilities requires filter systems to perform under diverse conditions of hydraulic gradient; wetting and drying; stress and strain; with varying quality of the permeating fluid. These conditions have an effect on the short and long term performance of filters and drains. This paper proposes the simultaneous employment of benefits from geotextile and from granular filter materials in composite filters in critical applications, such as the internal drainage of embankment dams and mono-waste disposal facilities. In such applications the geotextile serves as an adjunct to the granular filter and the granular filter supplements the geotextile filter performance, with resultant reduced risk of failure.

Testing of the oxidative resistance of polyolefin based geosynthetics in autoclaves at high oxygen pressure has been suggested as an alternative method to conventional forced-air oven aging. The intention is to shorten considerably the testing time and to ensure that aging is performed under the condition of rate-controlled and not diffusion-limited oxidation. We compare data from high pressure autoclave tests (HPAT) with data from oven aging and water immersion tests at 80 °C. For this, the stabilization of the samples has to be taken into account. Polyolefin based geosynthetics are usually stabilized by two types of “packages” of antioxidants (AO), designated here as P1 and P2. P1 consists of phenols and phosphites, P2 of hindered amine stabilizers (HAS) in addition to a marginal stabilization P1 of the resin for the manufacturing process. Phenolic and phosphite AO are quickly consumed in the HPAT. Failure time is tremendously reduced compared to forced-air oven aging or water immersion. The results are discussed within the framework of a basic autoxidation scheme. The reduction is much greater than expected from theoretical considerations. Therefore, a direct and degrading reaction of oxygen with the AO has to be assumed. In case of HAS, the time dependence of the degradation of tensile properties in the HPAT is significantly different from the dependence observed in conventional forced-air oven aging and their effectiveness is likewise strongly reduced. A conclusive interpretation of HPAT results needs a better understanding of what happens to the AO at high oxygen pressure.