Effect of Fiber Content on the Mechanical Behavior of Fiber-Reinforced Clay

A. Palat, M. Roustaei, M.T. Hendry

Dans les comptes rendus d’articles de la conférence: GeoSt. John's 2019: 72nd Canadian Geotechnical Conference

Session: Laboratory Testing

ABSTRACT: Existing models of soil behavior have been developed based on the understanding of interaction between particles, much of it is conceptually based on sand and modified to describe the behaviors of clayey soils. There are other classes of fibrous soils and soils amended with fibers for which the current understanding of soil behavior does not represent well. The research presented within this paper is an investigation into the engineering properties of fiber reinforced clay soil and to understand the impact of adding fibers. This paper includes the results of undrained triaxial compression tests performed on soil-fiber composite to evaluate the pore pressure response, strength and stiffness properties. Parametric studies are performed for three different fiber contents (0%, 1% and 2%). In near future, the results of this testing will be evaluated within the context of material models developed to explain the anisotropic properties of fibrous peat (stiffness and strength) as a result of the fibrous composition. This work is fundamental in nature, but the results are anticipated to be applicable to the undrained anisotropic behavior and strength of fibrous organic soils and soils reinforced with elements that act in tension. RÉSUMÉles particules, une grande partie de celui-ci est conceptuellement basé sur le sable et modifié pour décrire les lesquelles la compréhension actuelle du comportement du sol ne représente pas bien. La recherche présentée dans ce document est composite sol-fibre pour évaluer la réponse de la pression interstitielle, la résistance et les propriétés de rigidité. Des études paramétriques sont effectuées pour trois teneurs en fibres différentes (0%, 1% et 2%). Dans un avenir proche, les résultats de ces essais seront évalués dans le contexte des modèles de matériaux développés pour expliquer les propriétés anisotropes de la tourbe fibreuse (raideur et résistance) à la suite de la composition fibreuse. Ce travail est fondamental dans la nature, mais les résultats devraient des sols organiques fibreux et des sols renforcés par des éléments qui agissent en tension. 1. INTRODUCTION Modification by inclusion is one of the potential methods for improving the properties of existing soil. Traditional methods of soil reinforcement involved the use of continuous planar reinforcements (metallic strips, geotextiles etc.) that requires large anchorage length and demands anchoring to a competent material on both sides (Zornberg, 2002). Even though the tensile strength of the soil mass is improved, these continuous reinforcements introduce a plane of weakness as the shearing resistance along the soil reinforcement interface is less than the soil alone (Li, 2013). There is also a greater chance of pullout when planar reinforcements are placed in the soil. The best alternative solution is to add short, discrete fiber reinforcement to a soil mass, mix in the same way as lime or cement, and followed by subsequent compaction. Randomly fiber-reinforced soil mass shows an isotropic increase in the shear strength of soil mass and no planes of weakness are introduced (Li, 2013). The objective of this study is to reinforce kaolinite clay soil with randomly oriented polypropylene fibers, and to quantify the strength and stiffness properties of this soil through extensive laboratory techniques. Most of the existing studies are performed on fiber-reinforced sands and a very few have been performed on fiber-reinforced clay soil. This is mainly due to the difficulty in sample preparation and the difficulty in quantifying the pore pressure response and interface shear strength between soil and fibers. Adding to that, the models used to describe the mechanical behavior of soil, more specifically the critical state family of models (e.g. Schofield & Wroth 1968, Roscoe & Burland 1968), assume isotropic elasticity. However, according to Quigley, 1980, most post glacial clays are deposited vertically. They are subjected to equal horizontal stress, but the properties do vary from top to bottom and are referred to as transversely isotropic or cross-anisotropic. To date, no studies have been attempted

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