Cold Climate Publications

Permafrost

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.

Winter Construction

High-Strength Geocell and Geogrid Hybrid Reinforcement- Compressor Station Gravel Pad on Soft Subgrade

Poharel, S.K., Yii, T., Breault, M., Norouzi, M.
IFAI [ATA] Geosynthetics Magazine
2020

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).

Freeze Thaw

Role of Geosynthetics in Improving Freeze-thaw Resistance of Bases- A Literature Survey

Poharel, S.K., huang, M., Lin, C.
IFAI [ATA] Geosynthetics Conference, Kansas
2023

Abstract
Freeze-thaw (F-T) cycles are a major cause of road damages in seasonal frost regions. Different measures have been
implemented to mitigate the F-T damage to roads, which include chemical stabilization (e.g., lime or cement stabilized
bases) and physical stabilization (e.g., improving drainage, creating capillary barrier, replacing weak bases with gravels,
etc.). Although geosynthetics have been widely applied to enhance the performance of cold regions roads, the beneficial
effect of geosynthetics in improving the freeze-thaw resistance of paved and unpaved roads is not well appreciated. This
paper aims to fill this research gap through a survey of the state-of-the-art research in literature and presenting the progress
results of the authors’ research. The survey is focused on the limited cases of field trials and model tests of geogrid,
geotextile, and geocell reinforced bases under seasonable F-T cycles while the authors’ research is focused on the
development of custom-made model test apparatus and the use of it to investigate the F-T responses and bearing
pressures of geocell-reinforced base courses after F-T cycles. Both the survey and the experimental tests indicated that
geosynthetics could be effective in reducing the frost heave and thaw settlement and improving the bearing pressure of
the bases

Freeze-thaw Effects on Mechanical Behavior of Geosynthetic-Reinforced Sands from Element and Model Test

Huang, M., Lin, C., Pokharel, S.K.,
Breault, M.,
International Journal of Geosynthetics and Ground Engineering
2021

Abstract
Freeze–thaw (F–T) cycles are a major cause of pavement distress in seasonal frost regions. It has been demonstrated in practical applications that geocell-reinforced roads are effective in resisting F–T damage. However, this beneficial effect has not been quantified, and the underlying mechanisms are not well appreciated either. To address these questions, this study carried out two types of laboratory-scale tests, namely element tests (single geocell) and model tests (multiple geocells) to investigate the mechanical properties (stiffness and ultimate bearing pressure) of geocell-reinforced sands subjected to various freeze–thaw cycles. The experimental results showed that although the poorly graded sands used in this study were classified as frost insusceptible, both mechanical properties (stiffness and ultimate bearing pressure) of the sands were reduced up to 20% after five F–T cycles. The mechanical properties of both unreinforced and reinforced sands were decreased with the increased F–T cycles. At different F–T cycles, geocells improved the mechanical properties by 30–110%. The test results showed high variability at a small number of F–T cycles in the element tests, but the variability diminished at a higher number of F–T cycles. The discrepancy of test results between element tests and model tests might be due to scale difference that resulted in different soil conditions prepared and thus different water distributions inside the soils.

Model Tests of Freeze-Thaw Behavior of Geocell-Reinforced Soils

Huang, M., Lin, C., Pokharel, S.K., tura, A., Mukhopadhyaya, P.
Journal of Geotextile and Geomembrane
2021

Abstract
Freeze-thaw cycles are a major cause for destabilizing pavements in cold regions. Among countermeasures for freeze-thaw damages, use of geocells to reinforce pavement bases is an effective solution in practice. However, as opposed to widespread applications, research concerning freeze-thaw behavior of geocell-reinforced bases is limited, probably due to a lack of proper devices for conducting experimental tests. This paper presents a new model-test device capable of performing both freeze-thaw tests and plate loading tests on geocell-reinforced soils. A thermodynamic numerical model was developed to assist with the design of freeze-thaw component of the device, while the design of plate loading component was developed by referring to features of existing devices. Eleven tests were run on geocell-reinforced and unreinforced sands to confirm the effectiveness of the proposed device. The test results showed the device successfully provided vertical heat transfer in sands during freeze and thaw. After five freeze-thaw cycles, geocells reduced peak frost heave and thaw settlement of sands by 18% and 34%, respectively, and increased the stiffness and bearing capacity by 40% and 253%, respectively. It was found a temperature drop occurred at the interface between cooling plate and sands, which was due to the existence of thermal contact resistance.