Case Studies: Securing Cavities Area by a very high Tensile Strength Geosynthetic Reinforcement

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tensilestrength-casestudyA1Problematic
The sinkholes present a major problem in roads construction and urban development. The classical solutions used to limit the risk of cavities collapse are: filling of the void, construction of concrete bridges across the cavity areas, reinforcement by masonry piles, etc. Even if these methods offer a durable solution for long term security and stability, they present several inconvenient and limitations, such as the need of important material quantities; high CO2 emis-sions; need to localize the cavity and very high cost. Therefore, the use of a geosynthetic is a more attractive and economic solution.

Project Description
The project is located in Arras city (north of France) and concerns the securing of a public park built over an aban-doned chalk quarry. The cavities are 6 m high, 3.5 m wide and located between 14 and 20 m in depth. The main risk consists of the occurrence of a sinkhole with significant diameter.

Solution “Very high tensile strength geosynthetic reinforcement”
Usually, the geosynthetic reinforcement solution is used to secure the infrastructures over cavity zones, in association witha high embankment and good granular material. This case study presents a real challenge; it is one of the few or may be the only project where the installed geosynthetic has a tensile strength higher than 1800 kN/m. This project presents other specific conditions, they concern the low thickness of the soil over the geosynthetic layer and the reuse of the local materials for the embankment. So, the geosyn-thetic design and the construction steps required to take into ac-count particular hypotheses.

tensilestrength-casestudyA2Design Method
RAFAEL design method (issued from national French research pro-ject) is used with some simplifications: no arching effect; no shear strength of the collapsed soil column; specific expansion coefficient for SLS and ULS.

tensilestrength-casestudyA3Geosynthetic Reinforcement
The choice of the geosynthetic is done according to several criteria: the characteristic tensile strength of the product, the nature of the polymer, application requirements. The product designed for this project is the geocmposite Geoter® FPET 1800. Is manufactured by warp knitting process combining woven geotextile with high te-nacity polyester cables. It combines reinforcement, filtration and separation. It allows water flow during the service stage and pre-vents fill material going through the geosynthetic in case of cavity collapse.

Further Information
For more information on Texinov Geosynthetics visit www.texinov.fr or contact geo@texinov.fr

Case Studies: Roadway Reinforcement Applications

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Application Subgrade Stabilization and Rein-forcement Job owner Iberdrola Renewables, LLC
Location Hertford, NC Engineer Barr Engineering
Product Mirafi® RSi-Series Contractor Wanzek Construction
Quantity 205,000 yd2 – RS380i

120,000 yd2 – RS580i

Date of Installation

(m/y)

December 2015 – June 2017

THE CHALLENGE: What was the objective of project?
What were the soil conditions for the project (CBR, type of soil, etc.)

The contractor was responsible for constructing over 66 miles of access roads for the 104 turbines in the first phase of the Desert Wind Farm project. Since these access roads were the only source of entry, they had to support construction traffic over soft, wet North Carolina farmland soil. They were used by aggregate and concrete trucks, delivery tractor trailers (with heavy turbine components) and for moving the cranes between the wind turbines. The original design specified geogrid with 10” of Dense Graded Aggregate (DGA). The subsurface investigation revealed that the in-situ soils consisted of peat and organic clays with a CBR value as low as 0.7% and silty/clayey sands with a CBR value of less than 4.0%.

The end of 2015 and 2016 proved to be unusually wet times in costal NC. From the start of the project, the grading contractor had troubles with the roadways being too saturated. Multiple attempts at stabilizing the subgrade with geogrid were unsuccessful. The mud oozed through the apertures causing severe rutting and eventually the geogrid ruptured in multiple locations and wrapped around the truck axles.

The only way to stabilize the roads was to add additional stone. However, the aggregate imported by railcars was very expensive. The contractor tried cement stabilization as an alternative, however this method required too much cement and an excessively long curing time. This option was immediately ruled out for both time and cost reasons.
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THE DESIGN: What were the recommendations of overcoming the challenge/objective? Were any other op-tions considered or tried? Did the designer use MiraSpec and if so what was the unreinforced design vs. the reinforced design?
A site visit was made by one of TenCate’s Engineering Business Managers to observe the subgrade and to perform field vane shear tests to determine the CBR values of the soils. The field vane shear tests confirmed that the soils were less than 1.0% in many locations. Designs were recommended after the engineer evaluated the subgrade soils along with the anticipated truck and crane loadings. The parties agreed to the need for a high modulus reinforcement product that would integrate (1) superior water flow characteristics to minimize pore water pressure build-up, (2) AASHTO M288 separation criteria to minimize fines contamination into the overlying aggregate. Three different de-sign options using Mirafi® RSi-series were recommended to make the project more economically feasible.

THE CONSTRUCTION: Installation. Any special benefits our product provided to speed up or improve construction?
The contractor called the local TenCate distributor on a Saturday and asked to try the “orange fabric”. The distributor brought 3 rolls of Mirafi® RS580i to the site that same day and the contractor was able to place 900’ of roadway in 45 minutes. The contractor was so excited with the results, they bought the remaining rolls from the distributor’s inventory on Monday and ordered another truckload at the same time. Depending on how soft and wet the subgrade was, the contractor used either Mirafi® RS380i or RS580i with approximately 10” of aggregate. Occasionally the contractor had to use a little more aggregate in some of the most extreme cases of saturated soils. The contractor successfully installed approximately 325,000 yd2 of Mirafi® RSi-series.

THE PERFORMANCE: How did our material(s) make a difference? What was achieved? What was the cost savings/value proposition that the product allowed?
Due to the integration of the separation, reinforcement, filtration and confinement functions into a single product, Mirafi® RS380i and RS580i allowed the contractor to optimize overall costs while minimizing construction delays of the access roads over soft, saturated soils.

With the demand for renewable energy growing, TenCate Geosynthetics will continue to provide the highest quality geosynthetic solutions to create a safe and successful environment.

Further Information
For more information on Tencate Geosynthetics Americas visit www.tencate.com or contact J.McKay@TEN-CATE.COM

Case Studies: Hybrid Sheet Piling – Fiberglass Rein-forced PVC Profiles

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This case study shows how we introduced to the market new hybrid material to manufacture sheet piling that would bridge the gap between vinyl polychloride and steel. We present here how we conducted the research, developed the manufacturing line, followed by lab and field tests to ultimately introduce the patented product to the market.

Case-fiberglassABridging the Gap
Sheet piling made of polyvinyl chloride is a long-lasting prod-uct of high resistance to corrosion, as well as the majority of chemical agents. In contrast to steel piling, profiles made of PVC are lightweight, which allows to make savings, as far as the transport and assembly costs are concerned. Aesthetic look is an additional advantage of PVC. On the other hand, the largest limitation of this type of sheet piling is their consid-erably lower resistance to bending, which limits the scope of application, especially in case of projects where long ele-ments are used.
The above limitations made us conduct a comprehensive research aimed at improving the mechanical parameters of vinyl sheet piling and, at the same time, maintaining all advantages of PVC profiles. The Pietrucha Group R&D department has developed a technology of reinforcing PVC sheet piling with fiberglass in form of roving.

Step One – the Research
The initial stage of the research assumed the development of surface, layered model of a profile, with five variations as far as the fiberglass location was concerned. The fiberglass content did not exceed 10 percent of the total mass of the composite. In the next phase, the team conducted finite elements analysis. The results of the analysis helped to select the optimal location of fiberglass core, i.e. reinforcement of horizontal walls and corners of the profile. The next stages of the research included analysis of different reinforcement mass share. In addition, the team analysed further variations of the initial reinforcement location and validated the results of the finite element analysis with the numerical analysis of the 3D spatial model.

Step Two – the Tool
The research results helped to determine the optimal geometric and quantitative location of fiberglass reinforcement within the polymer matrix, so as to achieve the highest mechanical parameters of the profile. Then, the team moved on to design and assemble the extrusion tool for fiberglass reinforced GW700. The available technologies of PVC reinforcement used for small profiles, such as window frames etc. were reviewed. In a consortium with the World’s pioneer in fiberglass technology, we have adapted this solution to strengthen large scale profiles. A complete manu-facturing line was assembled, equipped with tools that would enable coextrusion of profiles with fiberglass reinforce-ment

Step Three – Lab Tests
Then, the manufactured hybrid geotechnical profiles were tested at the Silesian Science and Technology Centre of Aviation Industry. The Silesian Centre specializes in testing the strength parameters of advanced geo-composites used in the aviation industry, inter alia, by Boeing. The static and fatigue analysis included 4-point bending of the profile using a specially designed testing unit. During the experiment the force and the material shift were monitored on a continuous basis. Thanks to the obtained results the Young Modulus and the flexural rigidity parameters of the product were calculated.

Step Four – Field Tests
Moreover, the results of bending tests have confirmed the improvement of the new hybrid material mechanical prop-erties. The samples’ stiffness parameter of the fiberglass reinforced vinyl sheet piling nearly doubled in comparison with sheet piling made solely of PVC. In order to confirm the results, and the ability of the hybrid material to bear constant tension, field tests were conducted. The tests were run in real-life conditions. The walls made of hybrid material were submerged in the ground and subjected to bending. The results of the field tests were repetitive and confirmed the lab assumptions.

Step Five – the New, Patented Product
Application of the innovative technology resulted in the creation of hybrid sheet piling made of fiberglass reinforced polyvinyl chloride. Thanks to comparable mechanical parameters, the new type of material occurs to be a strong competition to light steel piling. Furthermore, aesthetic look, resistance to corrosion and lower price are some of the additional advantages which make our product more attractive.

Further Information
For more information on Pietrucha visit www.polgrid.com or contact export@pietrucha.pl

Case Studies: Kaytech Stabilises XtraSpace Storage Facility

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In May 2017 Endecon Ubuntu Consulting Engineers contacted Kaytech for a solution on a differential settlement problem at a site in Centurion, Gauteng where a new branch of XtraSpace, a container storage facility, was to be constructed.

When Endecon engineers discovered dolomite pinnacles at a depth of 150 mm below the natural ground level, they realized that even once the Wad and weak soils were removed and replaced with higher quality fill material, differ-ential settlement might still occur. As a mineral composed of calcium magnesium carbonate, dolomite provides a higher load bearing capacity than fill material. Since the containers would easily span any voids and settlement, the main concern was to adequately reinforce the access roads between the rows of containers.

Case-kaytechxtraSpaceAfter a site inspection, a Kaytech representative consulted with Tensar, the manufacturers of TriAx geogrids. A de-cision was made to crush a portion of the dolomite rocks and mix this with the in-situ material to create a G6 aggregate that would be included in the Tensar analysis to create a specific design for this project.

The rigid polypropylene triangular geometry of this geogrid, a significantly different structure compared to bi-axial geogrids, provides numerous advantages, including near uniform radial stiffness through 360o, and greater reduction in aggregate layer thickness. This reduces the quantity of natural aggregates required as well as the volume of material to be excavated.
The design generated included compaction of the in-situ material to 100 mm above the top of the dolomite peaks to serve as a “cushion layer”, covering this by simply unrolling a layer of Tensar TriAx TX160 geogrid. Prior to surfacing, two 150 mm layers of the G6 material were installed above the geogrid.

The triangular structure of the geogrid, in conjunction with increased rib thickness and junction efficiency, provides significantly improved aggregate confinement and interaction, leading to improved structural performance of the me-chanically stabilised load-bearing sub-base. With tensile stiffness in three principal directions, this multi-directional product shows near isotropic properties.

Further Information
For more information on Kaytech products and systems, visit www.kaytech.co.za

Case Studies: Sunich Reinforced Green Slope Project (Iran)

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case-greenslope1Objective
Sunich factory is one of the main production of fruit juices in Iran. At the moment, Phase 1 and Phase 2 of the Firouzkooh plant are in progress. Phase 1 involves the construction main factory production line. Phase 2 was landscaping and making storage areas. The pro-ject was constructed in mountainous area and there were different terrace levels for each factory building. The 1000 m section was proposed to be constructed with reinforced slope with green surfaces.

The Challenge
An integrated system consisting of PET Woven Ge-ogrid (40 and 60 KN/m) was qualified for reinforcing (i) the bottom of the slopes for basal reinforcement (ii in the reinforced slopes. Needle-punched nonwoven ge-otextiles weighing 300 g/m² were specified as cush-ions as filter layer in facing. At the surface level (in front of geogrid reinforced slope), a 10 cm Perforated textured Geocell was specified to separate the exist-ing reinforced slope the surface layers of a typical 30 cm thick agricultural soil for plantation. Some water proofing with HDPE Geomembrane is used for waterproofing the foundations.
case-greenslope2
The Solution
Following the specifications of the design for reinforced slopes, Geosakht Geosynthetics provided needle-punched nonwoven geotextiles weighing 300 g/m² namely Hytex3 and PET Woven Geogrids namely GG40 and 60. Different slopes in height designed and covered with geotextile and Geocell cover. Finally, a green slope is constructed in a very harsh weather condition with using Geosynthetics materials.

Further Information
Fore more information about Geosakht visit www.geosakht.com, or contact Rezaashgbousi@gmail.com

Case Studies: Nuevo Aeroporto Internation de la Ciu-dad de Mexico (NAICM) – Runway 3

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case-Nuevo-Aeroporto1Client: CARGI-PROPEN SA DE CV
Engineer: PARSONS & TASANA
Main Contractor: GACM
Subcontractor CETEAU BV / COFRA BV JV

Scope of works
• Production of more than 30 million linear meters of Prefabricated Vertical Drain (PVD) with record quantities delivered per week of 1 to 2 million lin-ear meters.
• Implemented local PVD manufacturing facility where, in addition to the manufacturing in The
Netherlands, the highly specified material was produced whilst meeting all the ISO standards demanded by the Client.
• Installed more than 30 million of PVD´s with more than 10 rigs to depths ranging from 15 to 28 mt.

Early 2017, CeTeau BV is awarded by CARGI-PROPEN SA DE CV the contract for the manufacturing and installation of more than 28 million linear meters of Prefabricated Vertical Drain to be in-stalled under the future RUNWAY 3 for the NAICM. Given the scope and availa-ble timeframe CeTeau teamed up Cofra BV.
case-Nuevo-Aeroporto2
The wick drain solution was chosen with the purpose of accelerating the rate of consolidation of the very soft soils pre-sent at the site. At one point during the work execution, more than 10 Rigs were deployed at the site for 8 months, work-ing 24/7. Work was commenced in Feb-ruary 2017 and successfully completed in September 2017. Further to comple-tion of the original contract, procurement and installation of additional PVD´s has been re-quested by the Client and continues as of March 2018. CeTeau is a world class PVD (wick drain) manufacturer with an annual capacity exceeding 150 million meter and Spe-cialty Geo Contractor, it operates locally in Mexico through its Mexican Subsidiary, Mexi-can Wick Drain, SA de CV.

Further Information
For more information about CeTeau BV visit www.ceteau.com or contact info@ceteau.com.

Case Studies: Detention Pond under the Freeway Over-pass, Taichung, Taiwan (R.O.C.)

Background
Numerous typhoons swept across Taiwan during 2012 and 2013 bringing along abundant rainfall, leading mud flow and flooding to rolling and pouring down along the west side of Dadu Mountain. The torrent was arbitrarily pouring along the main road of Taiwan Boulevard, Taichung City, causing severe inundation to Shalu District located on the west foot of Dadu Mountain. Frequent flooding not only afflicted residents but also further affected the local housing prices. Thus, Taiwanese government initiated to investigate and deal with the drainage problem of Shalu District so as to ensure the security of life and property of Shalu residents.
case-DetentionPond
Problem (Tasks)
Causing the disasters of Shalu District usually resulted from (a) incomplete rehabilitation of partly creeks and rivers (b) earth and stone caused by collapsed slope of Dadu Mountain block the drainage system (c) unconnected up-stream and downstream drainage paths (d) the drainage construction of Shalu District is unable to catch up the speed of regional development (e) because the construction projects on the foot of Dadu Mountain increase rapidly, making impervious areas and the surface runoff increased as well. In order to resolve flooding problem of this district, the government makes plans for drainage treatment on upstream slope while drainage improvement project on down-stream urban area. This construction project included in the treatment plan uses the spare space between bridge piers under the Shalu overpass of the Freeway No.3 located on the slope of Dadu Mountain to construct a detention pond with 1,026m3 volume. The detention pond allows surface runoff to be stored temporarily within it and thus achieves the effect of flood storage; moreover, it is able to reduce flood peak flow produced by rainstorm or delay the arriving time of peak flow, and then decrease flooding condition of low-lying Shalu district downstream during rainy seasons.

ACE Solution
The geology of Dadu Mountain area is laterite on Toukoshan formation which is mainly composed of gravels with high permeability. Considering the influence of water conservation volume caused by water retention facility, land-scape, economy and ecology, the construction utilize local materials, natural granular backfill to form mechanically stabilized earth (MSE) wall as the wall structure around the detention pond. The bottom of detention pond uses RC board of 30 cm thickness as back over to intercept floods on the southern side of detention pond. In addition, this case uses a single-stage reinforced slope with 7.5 m to 8.5 m height, and uses ACEGrid® GG geogrids with 220*110 kN/m tensile strength as reinforced material. Every 4 m vertical height of the reinforced slope lays out light gravel drainage layer of 20 cm thickness with horizontal and vertical ACEDrain S geocomposite drainage panels of 2 m spacing, so that the seepage water in the soil layer behind the slope enables to divert into the pond to release the water pressure and maintain the stability of the long-term reinforced slope. Moreover, the reinforced slope uses durable erosion control bags which are filled with in-situ selected soils and staked on the slope with ACEGrid® GG geogrids wrapping around, allowing the slope to have stable foundation for vegetation and to reach the effects of greening and ecological friendliness.

Result
The detention pond of this case which was finished in 2014 has been attacked by numerous typhoons until now, but it still shows an excellent ability for flood storage. Using mechanically stabilized earth (MSE) on this construction not only fulfills the basic demand of security and economy in civil engineering but also conforms to the current trends of carbon reduction and ecological sustainability pursued by engineering industry. As a result, the constructions of subsequent detention ponds in this district all imitate the design of this case. It is strongly believed that after other drainage improvement and flood detention projects are completed in the Shalu region, Taichung, the flooding status here, will be greatly improved with minimal impact on the environment.
Further Information
For more information about ACE Geosynthetics, visit www.geoace.com or contact sales@geoace.com.

Case Studies: Landfill drainage and enhanced cover soil interface, Silent Valley Landfill, Ebbw Vale, Wales, U.K.

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case-Landfill-drainage-1Project Description
Silent Valley, which runs up from the Welsh town of Ebbw Vale, was restored and turned into a nature reserve managed by the Blaenau Gwent County Council and Gwent Wildlife Trust. The once post-industrial mining valley, contaminated with metal recovery waste has been cleaned up and the upper valley turned into a modern domestic landfill facility which is capped off and landscaped to become part of the nature reserve. Silent Valley is now one of the most beautiful natural environments in Gwent.

Challenges
With the finished landfill profiles incorporating 80m long 1 in 2.5 slopes the challenge was to achieve a stable cap without any reprofiling or use of geogrid reinforcement.

The aim was to install a multi-layered syn-thetic cap comprising a 1mm LLDPE textured geomembrane with a drainage capability above the membrane and a gas venting capa-bility below.

The challenge was to provide sufficient drain-age capacity on both interfaces and adequate interface shear strength to withstand the dead load of the 0.5m cover soil and live load of the construction traffic whilst placing the backfill material on this critical slope.
The required slope stability was not possible to achieve with standard geocomposites typically used for the landfill cap drainage. A geocomposite with enhanced performance was required for this 1 in 2.5 slope application.

case-Landfill-drainage-2Solution
Geocomposite drains have long been used as alternative to crushed stone. ABG is well known as a pioneer of cuspated drainage and in 1995 was the first to introduce a 4.4m wide drainage composite suitable for wide scale use in environmental projects. Since then, many millions of sqm of Pozidrain have been used on landfill and mine capping projects to provide sub-surface drainage above and below the barrier to improve stability. It has become clear that the interface shear strength is of critical im-portance. As slopes have become ever more steep, geomembrane texture and spikes have improved the barrier/geocomposite interface shear strength to the ex-tent that it is the cover soil to geocomposite interface that is often the limiting factor. ABG has invented and patented the Pozi G with a unique lattice core that has proven to give in excess of 20% improvement to the cover soil interface. Shown is an example project that used Pozi G on a 1:2.5 slope. Consideration of the inter-face friction was needed for the construction phase allowing for plant tracking up the slope to spread cover. Just like the original Pozidrain, Pozi G has MD and CMD flow which ABG believe is fundamental to true equivalence to crushed stone and for a realistic factor of safety. The ability for the water to flow in all directions equally guards against any possibility that a longitudinal flow channel is inadvertently compromised on site, as the water can simply detour around that zone and continue safely to the outlet pipe.
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Further information
For more information about ABG Ltd., visit www.abg-geosynthetics.comor contact liz@abgltd.com

New Board of the Czech Chapter

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from left: Martin Vanicek ‐ head of technical group, Petr Hubik ‐ treasurer, Zikmund Rakowski ‐ president, Dalibor Grepl ‐ secretary

For more information please visit www.igs.cz

12th Rencontres Géosynthétiques 2019 Nancy, France, 11 – 13 March 2019

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The 12th French Speaking Conference on Geotextiles, Geomembranes and Related Products
Organized by the French Chapter of IGS every two years since 1993, The Rencontres Géosynthétiques are the reference French speaking event for geotexiles, geomembranes and related products. They cover the whole range of applications of these materials in civil engineering and environmental protection. From the 11th to the 13th of March 2019 in Nancy (France), this conference will welcome experts, engineers and technicians coming from all Europe and northern Africa. The twelfth edition of the Rencontres Géosynthétiques will be the occasion to make a state of the art on recommendations of use and installation and standards, through the presentation of practical cases of use. The Rencontres Géosynthétiques will be a unique opportunity for practitioners to meet and exchange. On the first day, some short courses will be given (in French) to those attendees less familiar with geosynthetics on what geo-synthetics are, their basic properties and main uses in civil engineering and environmental protection.
More information can be found in http://www.rencontresgeosynthetiques.org/index.html

Reported by
Guillaume Stoltz, Assistant General Secretary of French Chapter of IGS