Load Support Publications

Railways

NPA Geocell for a Railway Line in a Permafrost Region

Poharel, S.K., Norouzi, Breault, M.
IFAI [ATA] Geosynthetics Magazine
2021

Abstract
This case study looks at the repairs on a single-line railway in the northern Manitoba, Canada city of Churchill. This line sustains damage due to the permafrost conditions and lack of timely service and upgrades, causing service interruptions. The authors examine the use of NPA geocell reinforcement in railway subtrack structure repairs in this arctic environment. Design concepts, construction methods, and geosynthetic materials are discussed. The authors conclude that the use of NPA geocell-reinforced design of the railway embankment is a solution for strengthening and maintaining the railway structure. It allowed the railway to end a two year nonoperational period and resume operation shortly after the rehabilitation project began. The design saved construction time and budget. Based on more than two years of operation post rehabilitation, the authors recommend this design as a viable method for future infrastructure projects in permafrost environments.

Roads

Sustainable Road Construction for Heavy Traffic using High Strength Polymeric Geocells

Poharel, S.K., Norouzi, M., Martin, I., Breault, M.
Resilient Infrastructure
2016

Abstract
Construction Sustainability has been the focus of debate ever since the Brundtland commission report ‘Our Common Future’ defined Sustainable Development. Kyoto Protocol and subsequent climate change conferences leading upto the Paris submit this year has put still more emphasis on this agenda. Construction of heavy traffic unpaved access roads require huge amount of aggregate mining and long haulage in the areas of scarce virgin aggregate. Conventional practices in these road constructions seek structural adequacy but never specifically address the sustainability issue. Innovative technology that can reduce the volume of aggregate material while maintaining the structural integrity is required to address the sustainability issue of these roads construction. This paper discusses the construction of these roads with high strength Geocell (Neoloy) reinforcement giving special reference to Oil Sand region of Alberta. These Geocells improve the modulus and strength of the reinforced composite and durability of the road structure by drastically reducing the required quantity of aggregate material. Operation of these access roads has also demonstrated saving on running cost, maintenance and down time. Neoloy Geocells also make it possible to use recycled and locally available cheaper materials for road construction still exceeding the overall performance of conventional construction. In terms of sustainability the benefit will be more visible when the carbon footprint is analyzed for the virgin material mining and haulage to the construction site. A basic analysis of CO2 emission reduction and how it is applied to new emission standards in Alberta industry with this innovative method is also discussed.

Staged Road Construction in Very Weak Subgrade Using Polymeric Geocell

Chatterjee, A., Poharel, S.K.,
Breault, M.
Innovations in Pavement Management, Engineering and Technologies TAC Conference & Exhibition
2022

Abstract
The ongoing development of the energy industry in Canada, especially for pipeline-related structures, demands innovative ways of access construction. Most of these are at remote locations and under difficult geotechnical conditions making access a challenge. A 4.1km long unpaved access road leading to a proposed compressor station in Blainville, Quebec was planned for the construction of the station pad and future access. The road was expected to serve as a material haul road for the 200m x 250m gravel pad, regular compressor station construction loads, and future traffic. Construction of the pad was scheduled to start before the winter of 2020. The proposed road alignment had very soft to soft subgrade conditions with saturated peat. There were problems with limited right of way, a landslide-prone zone, a creek crossing, and overhead power lines. The road geometry was to be designed such that there was enough clearance from the overhead power lines and the slide-prone area and maintain the minimum turning radius required for the long and heavy trucks carrying compressor units. Additionally, there were constraints imposed in permits and other aspects of the project that left a short 6-week window for the construction of the road.

Geocell-Reinforced Lateral Support for Anchoring Structural Foundations

Chatterjee, A., Pokharel, S.K.,
Breault, M.,
Canadian Society of Civil Engineers Annual Conference
2021

Abstract
With the advancement of portable quick install structures, there is an observed increase in demand for anchoring light structural foundations to natural grounds. For example, installation of floating fence needs pounding rods anchored to the existing subgrade at defined intervals. Even anchoring temporary portable foundations can leave permanent footprint on environment. Particularly, when the existing natural ground is soft, the structural footprint of the foundation anchors can interfere larger area requiring extra material to be shipped, which ultimately lead to increased carbon emission. Considering foundation designs on weak natural existing organic soil, long term stability of structure becomes a challenge. In such scenario, hybrid-designs with geocell reinforced stratum could be a viable alternative solution to the conventional design. This sustainable solution is economical, readily available, and easy to install. Over the past decade there has been substantial research on ground reinforcement technology with geocell. Overwhelming stress related study on geocell has been on lateral stress distribution for vertical load. However, when it comes to anchoring rods or pile foundations, the critical forces are lateral. Building the topsoil structure reinforced with high modulus and high strength polymeric geocell, filled, and compacted with naturally available granular material, plays a significant role in improving foundation design capacity. This innovative hybrid-design technology can reduce conservatively 25% of pile sectional area as compared to conventional design for specific assumed soil conditions. This paper discusses the innovative approach to optimize deep foundation designs using geocell reinforced soil.

An Overview of Geocell-Reinforced Pavement Structure State Of Practice in Canada

Norouzi, M., Pokharel, S.K., Breault, M.,
TAC-ITS Canada Joint Conference on Innovation in Geotechnical and Materials Engineering
2019

Abstract
Geocell reinforcement at the base and subbase courses of pavement structures is one of the recent developments in the field of geosynthetics soil reinforcement. Geocells are honeycomb-shaped threedimensional materials usually made from polymeric alloys and High-Density Polyethylene. Geocells improve the modulus and strength of the reinforced soil composite and durability of the road structure by providing lateral confinement, wider load distribution and also through a semi-rigid slab or beam effect. Novel Polymeric Alloy (NPA) is the latest technology used as geocell material which provide increase tensile strength, higher modulus and creep resistance compared to the geocells made from other types of material. Geocells can be used in both paved and unpaved roads contributing to the sustainability of the project by reducing the overall thickness of the pavement structure and decreasing the amount of virgin aggregate required. This in turn decreases the environmental footprint of the project and reduces the overall construction cost. Over the past decade a number of roads (paved and unpaved) have been constructed in Canada using the NPA geocell reinforcement. This paper discusses the current state of the practice in designing pavement structure with geocells. Few projects designed with geocell reinforcement are also discussed in detail to provide insight into the challenges faced during construction, long-term performance of the geocell-reinforced pavement structure and contribution of the geocell in each project to reduce environmental footprint and construction cost of the projects. In summary geocells have enabled the owners to save on the construction cost and lower the CO2 emission associated with the construction while improving the pavement performance and reducing pavement distresses.

New Advances in Novel Polymeric Alloy Geocell-Reinforced Base Course for Paved Roads

Norouzi, M., Pokharel, S.K.,
Breault, M.,
Transportation Association of Canada [TAC] Conference
2017

Abstract
Seventh Street in Nisku industrial hub of Alberta was in very poor serviceability condition for the heavy traffic of the industrial area. In 2012, the County of Leduc decided to rehabilitate the road structure with asphalt pavement on cement treated base (CTB). Typical to most of the roads in cold climatic regions the conventionally designed CTB work satisfactorily at the beginning but start to show signs of failure as soon as the first freeze-thaw cycle completes with block cracks and other forms of pavement distress. To find a reliable solution to the problem the County decided to install a trial section with a Nano Polymeric Alloy (NPA) geocell-reinforced granular base and compare the performance over time with the conventional practice of CTB. Commercially available higher strength geocells made from NPA material were used to reinforce the base course. Two test sections were constructed over a total stretch of 1000m of the road, 500m each of the CTB and NPA geocellreinforced granular base on either side of the railway track. The University of Alberta conducted initial research and monitoring on the test sections. During the following years, non-destructive testing and monitoring of both the sections was carried out by the Leduc County employing independent organizations. Monitoring of the tests sections conducted after consecutive freezethaw season have demonstrated the increasing benefit of using NPA geocells over CTB. This paper discusses the construction, immediate tests and monitoring done over three years on the road and compares the performance based on the findings.

Validation of Geocell Design for Unpaved Roads

Norouzi, M., Pokharel, S.K.,
Breault, M., Martin, I.
IFAI [ATA] Geosynthetics Conference
2015

Abstract
Based on cyclic plate load and moving wheel tests Pokharel (2010) proposed a design method for unpaved roads using Neoloy based Geocell with a theoretical base from the Giroud and Han (2004) design method for planar reinforcement. To validate it under real time traffic, unpaved haul roads, well pads, and logging yards were designed. To the possible extent locally available cheaper poorly graded but environmentally friendly materials were used as infill. In case of extremely soft subgrades, construction layer of poorly graded sand reinforced with Geocell provided a driving surface for the construction equipment. The performance of the structures was evaluated on the rutting criteria, maintenance requirement, and visual serviceability after one year of service. This paper discusses the design method used in a number of projects in Western Canada including the Oil Sands region that face extreme cold weather conditions. The limitations of the design method are also discussed.

Experimental Study on Bearing Capacity of Geocell-Reinforced Bases

Pokharel, S.K., Han, J., Parson, rlL., Qian, Y., Leshchinsky, D., Halahmi, I.

8th International Conference on the Bearing Capacity of Roads, Railways and Airfields, Illinois
2009

Abstract
Geocell, a three-dimensional interconnected geosynthetic made of polymer, has been used to improve base course properties by providing soil confinement to increase its stiffness and to reduce its permanent surface deformation. Research conducted in the past on geocell-reinforced base courses has shown apparent benefits over unreinforced ones. However, the use of geocell reinforcement for base courses on soft subgrade is limited due to lack of established design methods. In this study, laboratory tests were conducted to investigate the behavior of geocell-reinforced bases under static and repeated loading. Two base course materials, Kansas River sand and quarry waste, were used as infill materials. This study investigated the bearing capacity and stiffness improvement provided by geocell reinforcement and the effect of infill materials. This study also evaluated the permanent deformation and the percentage of elastic deformation of geocell-reinforced Kansas River sand and quarry waste compared with unreinforced bases. The test results show that the single geocell reinforcement can increase the bearing capacity, stiffness, and percent of elastic deformation for each cycle and reduce the permanent deformation.

Experimental Evaluation of Influence Factors for Single Geocell-Reinforced Sand

Pokharel, S.K., Han, J., Parson, R.L., Qian, Y., Leshchinsky, D., Halahmi, I.

TRB 88th Annual Meeting, Washington
2009

Abstract
Geosynthetics have been in use for subgrade stabilization and base reinforcement for last 40 years. Over the years, research conducted on geosynthetic-reinforced base courses, especially with planar reinforcements, have shown marked benefits over unreinforced ones. Geocell, a three-dimensional geosynthetic material with interconnected cells, can be used to improve the properties of base courses by providing lateral confinement to increase strength and stiffness and reduce permanent surface deformation. However, the use of geocells for base reinforcement is limited due to lack of established design methods. Literature review has shown a significant gap between the applications and the theories for geocell reinforcement mechanisms outlining the need for more research. This research utilized simple loading equipment to evaluate the influence factors of single geocell-reinforced sand. The tests investigated the effect of influence factors (geocell shape and type) on the bearing capacity and stiffness of compacted sand. The experimental results showed that the geocell reinforcement increased the bearing capacity and stiffness and reduced settlement of the base course. The magnitude of improvement varied with the type of geocells.

Behavior of Geocell-Reinforced Granular Bases Under Static and Repeated Loads

Pokharel, S.K., Han, J., Parson, R.L., Qian, Y., Leshchinsky, D., Halahmi, I.

TRB 88th Annual Meeting, Washington
2009

Abstract
Geosynthetics have been used for base reinforcement since 1970s. Numerous research has already been carried out for planar geosynthetic reinforcement but limited research has been conducted for three-dimensional geocell reinforcement. Literature review has also demonstrated a significant gap between the applications and theories of geocell reinforcement outlining the need for more research. This study was to investigate the behavior of reinforced bases using a single geocell under static and repeated loads on a loading plate. The experimental results show that the single geocell could increase the stiffness by approximately 50% and the maximum load by 100% as compared with those of the unreinforced base. The repeated test shows that the geocell-reinforced base had the percentage of elastic deformation increase with the number of cycles of the repeated load up to 95%.

Performance of Triangular Aperture Geogrid-Reinforced Base Courses Over Weak Subgrades Under Cyclic Loading

Qian, Y., Pokharel, S.K., Parson, R.L.

ASCE Journal of Materials in Civil Engineering
2013

Abstract
Geogrid (uniaxial or biaxial) is one type of geosynthetics that has been successfully used in slopes, walls, roads, and other applications. The main application of biaxial geogrid is to stabilize soft subgrade and reinforce weak base courses by providing lateral confinement. The confinement due to the interaction between aggregates and the ribs of biaxial geogrid depends on the geometry properties of the geogrid, such as rib shape and apertures size, the stiffness of the ribs, and the properties of aggregates. Research has shown that biaxial geogrid cannot provide uniform tensile resistance in all directions. To overcome this problem, a geogrid product with triangular apertures was developed and introduced into the market. Recent studies showed that the triangular aperture geogrid can provide nearly uniform tensile resistance in all directions and is more efficient in improving the performance of reinforced bases as compared with biaxial geogrid. However, the performance of triangular aperture geogrid-reinforced bases under dynamic loading and the influence of base course thickness on the confinement effect of triangular aperture geogrids have not been well evaluated. In this study, unreinforced and triangular aperture geogrid-reinforced bases at different thicknesses over a weak subgrade were constructed in a large geotechnical testing box at the University of Kansas and tested under cyclic loading. During the tests, surface deformations and vertical stresses at the interface between the base and the subgrade were monitored. The test results indicated that triangular aperture geogrids reduced permanent deformation and maximum vertical stress at the interface as compared with the unreinforced bases. The geogrids improved the performance of the aggregate bases at different thicknesses. The benefit became more pronounced when a heavier-duty geogrid was used. The back-calculations from the test data showed that the stress distribution angle and the modulus ratio of base course to subgrade decreased with an increase of the load cycles. The stress distribution angle increased with the increase of the base thickness. The vertical stress distributions were compared with the computed distribution by the layered linear elastic theory. These test data provide the basis for the development of a design method for triangular aperture geogrid-reinforced bases over weak subgrade in the future.

Unpaved Roads: Tough Cell- Geosynthetic Reinforcement Shows Strong Promise

Han, J., Pokharel, S.K., Yang, X., Thakur, J.K.

Roads and Bridges
2011

Abstract
An estimated 80% of all roads in the world are unpaved. According to an AASTHO report, approximately 20% of pavements fail due to insufficient structural strength. Nowadays, it is challenging to optimally manage available natural and financial resources on construction of new roads and repair, maintenance and rehabilitation of existing roads. A sustainable option to overcome this problem is to develop an innovative pavement stabilization technique with a suitable reinforcement alternative that improves the overall structural strength, reduces operational costs, minimizes maintenance requirements and uses on-site or recycled materials. In the past four decades, planar geosynthetic reinforcement (geotextile and geogrid) has been used to improve the performance of roadways by subgrade improvement and base reinforcement. Geocell, a three-dimensional interconnected honeycomb polymeric cell, is another type of geosynthetic reinforcement that is ideal for soil confinement. The concept of lateral confinement by cellular structures dates back to the 1970s. The U.S. Army Corps of Engineers developed this idea for providing lateral confinement to poorly graded sand to improve its bearing capacity. For easy transportation, most geocell products have a foldable three-dimensional geometry and are often honeycomb-shaped after being unfolded. The use of geocell, especially for roadway applications, however, is limited by a lack of understanding of mechanisms and influencing factors for geocell reinforcement and an established design method. Research on exploring geocell reinforcement for roadway applications has been ongoing at the University of Kansas in cooperation with other research institutes. The objectives of this comprehensive research are to understand the mechanisms and influencing factors of geocell reinforcement, evaluate its effectiveness in improving roadway performance and develop design methods for roadway applications. This research includes laboratory box tests, accelerated moving wheel tests, field demonstration and development of design methods. A variety of base materials have been investigated, ranging from poorly graded beach silty sand and Kansas river sand, well-graded aggregate, quarry waste and recycled asphalt pavement. Simplified and mechanistic-empirical design methods for geocell-reinforced unpaved roads were developed.

Experimental Study on Geocell-Reinforced Bases Under Static and Dynamic Loading

Pokharel, S.K. 

Ph.D Dissertation, the University of Kansas
2010

Abstract
Geocells are a three-dimensional honeycomb type of geosynthetics used to reinforce weak soils and base courses of roads since the 1970s. However, this technology has been hindered by the lack of a reliable design method. The development of a reliable design method requires in-depth understanding of the geocell reinforcement mechanisms. In this study, laboratory model and full-scale moving wheel tests were conducted on geocell-reinforced granular bases over weak subgrade. Plate loading tests were conducted in the medium-scale and large-scale geotechnical boxes at the University of Kansas and full-scale moving wheel tests were conducted in the accelerated pavement testing facility at Kansas State University. Four types of geocells including one high-density polyethylene (HDPE) and three novel polymeric alloy (NPA) geocells were tested in the medium-scale plate loading tests.

Pads

High-Strengh Geocell and Geogrid Hybrid Reinforcement for Compressor Station Gravel Pad on Very Soft Subgrade

Poharel, S.K., Norouzi, M., Breault, M., Yii, T.
IFAI [ATA] Geosynthetics Conference
2019

Abstract
Planar geosynthetics have been used as soil reinforcement for many years; three-dimensional geocells are comparatively new. Geocell reinforcement usually utilizes geotextile for separation. Geogrid improves the stiffness of the reinforced soil by interlocking, lateral restraint and tension membrane; it reduces the applied stress on the soft soil and increases the bearing capacity while decreasing settlement (Qian et al. 2013). The performance of geogrid depends on aperture size and shape, material stiffness at junctions, and shape and stiffness of ribs (Giroud and Han 2016). Ever since the U.S. Army Corps of Engineers used geocell for reinforcing beach sand in the 1970s (Webster 1979), numerous research programs, experiments and monitored applications have been carried out to further understand the geocell-reinforcement mechanisms (Han et al. 2013). Vertical and lateral confinement, wider stress distribution and beam/slab effect are identified as the main reinforcement mechanism of geocell. Higher tensile stiffness, strength and creep resistance of geocell material provide the reinforced base with improved bearing capacity, higher modulus and extended design life (Pokharel et al. 2010, Thakur et al. 2013 and Kief et al. 2015). High-strength NPA geocell reinforcement also improves the creep resistance of the reinforced structure, which is a very important factor in the repetitive loading conditions, as it significantly reduces the initial deformation and rate of creep of the reinforced material (Thakur et al. 2013).