Practical approach to predict the shear strength of fibre-reinforced clay

yesCarpet waste fibres have a higher volume to weight ratios and once discarded into landfills, these fibres occupy a larger volume than other materials of similar weight. This research evaluates the efficiency of two types of carpet waste fibre as sustainable soil reinforcing materials to improve the shear strength of clay. A series of consolidated undrained (CU) triaxial compression tests were carried out to study the shear strength of reinforced clays with 1%, to 5% carpet waste fibres. The results indicated that carpet waste fibres improve the effective shear stress ratio and deviator stress of the host soil significantly. Addition of 1%, 3% and 5% carpet fibres could improve the effective stress ratio of the unreinforced soil by 17.6%, 53.5% and 70.6%, respectively at an initial effective consolidation stress of 200 kPa. In this study, a nonlinear regression model was developed based on a modified form of the hyperbolic model to predict the relationship between effective shear stress ratio, deviator stress and axial strain of fibre-reinforced soil samples with various fibre contents when subjected to various initial effective consolidation stresses. The proposed model was validated using the published experimental data, with predictions using this model found to be in excellent agreement

Analysis of strip footings on fibre reinforced slopes with the aid of Particle Image Velocimetry (PIV)

YesThis paper provides results of a comprehensive investigation into the use of waste carpet fibres for reinforcement of clay soil slopes. The interaction between laboratory scale model slopes made of fibre reinforced clay soil and surface strip footing load was examined. Results for the influence of two variables namely fibre content and distance between the footing edge and the crest of the slope are presented and discussed. Particle Image Velocimetry (PIV) technique was employed to study the deformation of the slope under the surface loading. The front side of the tank was made of a thick Perspex glass to facilitate taking accurate images during the loading stage. To study the stress induced in the slope under footing pressure, excess pore-water pressure and total stress increase were measured at predetermined locations within the slope. The results showed that fibre reinforcement increased the bearing resistance of the model slope significantly. For instance, inclusion of 5% waste carpet fibre increased the bearing pressure by 145% at 10% settlement ratio.The post-print of this article will be released for public view when the version of record has been published by ASCE

Rubber powder-polymer combined stabilization of South Australian expansive soils

This study examines the combined capacity of rubber powder inclusion and polymer treatment in solving the swelling problem of South Australian expansive soils. The rubber powder was incorporated into the soil at three different rubber contents (by weight) of 10%, 20% and 30%. The preliminary testing phase consisted of a series of consistency limits and free swell ratio tests, the results of which were analyzed to arrive at the optimum polymer concentration. The main test program included standard Proctor compaction, oedometer swell–compression, soil reactivity (shrink–swell index), cyclic wetting and drying, crack intensity, and micro-structure analysis by means of the scanning electron microscopy (SEM) technique. The improvement in swelling potential and swelling pressure was dependent on the rubber content, with polymer–treated mixtures holding a notable advantage over similar untreated cases. A similar dependency was also observed for the crack intensity factor and the shrink–swell index. The beneficial effects of rubber inclusion were compromised under the cyclic wetting and drying condition. However, this influence was eliminated where the rubber powder was paired with the polymer agent. A rubber inclusion of 20%, preferably paired with 0.2 g/l polymer, was suggested to effectively stabilize South Australian expansive soils.A. Soltani, A. Deng, A. Taheri, M. Mirzababae

Interfacial shear strength of rubber-reinforced clays: a dimensional analysis perspective

The present study aims towards the development of practical dimensional models capable of simulating the interfacial shear strength of rubber-reinforced clays. Two types of recycled tire rubbers (of fine and coarse categories) were each incorporated into the soil at four different contents (by weight), and statically compacted at their respective Proctor optimum condition for direct shear testing. The rubber inclusions amended the soil through improvements achieved in two aspects: (i) frictional resistance generated as a result of soil–rubber contact; and (ii) mechanical interlocking of rubber particles and soil grains. In general, both amending mechanisms were in favor of a higher rubber content, and to a lesser degree a larger rubber size. The dimensional analysis concept was extended to the soil–rubber shear strength problem, thereby leading to the development of practical dimensional models capable of simulating the shear stress–horizontal displacement response as a function of the composite's basic index properties. The predictive capacity of the proposed models was examined and validated by statistical techniques. The proposed dimensional models contain a limited number of fitting parameters, which can be calibrated by minimal experimental effort and hence implemented for predictive purposes.A. Soltani, A. Deng, A. Taheri, M. Mirzababaei, H. Nikra

Swell-shrink behavior of rubberized expansive clays during alternate wetting and drying

The present study examines rubber’s capacity of improving the swell–shrink potential of expansive clays. Two rubber types of fine and coarse categories with different geometrical features were considered. The test program consisted of standard Proctor compaction and cyclic wetting–drying tests. Scanning electron microscopy (SEM) analysis was also performed to identify the soil–rubber amending mechanisms, and to observe the evolution of fabric in response to alternate wetting and drying. Cyclic wetting–drying led to the reconstruction of the soil/soil–rubber microstructure by way of inducing aggregation and cementation of the soil grains. The greater the number of applied cycles, the lower the swell–shrink features, following a monotonically decreasing trend, with the rubberized blends holding a notable advantage over the virgin soil. The tendency for reduction, however, was in favor of a larger rubber size, and more importantly the rubber’s elongated form factor; thus, predicating a rubber size/shape-dependent amending mechanism. The soil–rubber amending mechanisms were discussed in three aspects—increase in non-expansive content, frictional resistance generated as a result of soil–rubber contact, and mechanical interlocking of rubber particles and soil grains. The swell–shrink patterns/paths indicated an expansive accumulated deformation for the virgin soil, whereas the rubberized blends manifested a relatively neutral deformational state, thereby corroborating the rubber’s capacity to counteract the heave and/or settlement incurred by alternate wetting and drying.Amin Soltani, An Deng, Abbas Taheri, Mehdi Mirzababaei and Sai K. Vanapall

Lime Cake as an Alternative Stabiliser for Loose Clayey Loams

Lime Cake (precipitated calcium carbonate PCC), a by-product of sugar production, is proposed as a stabiliser for improvement of loose silty clayey loams. Two inorganic pedogenic and organic precipitated calcium carbonate polymorphs are artificially synthesized into a base loosely compacted loamy soil. Formation, micromorphology, quality of cementing bonds, and physiochemical interactions in the interlayer are modelled at molecular level and verified by a suite of micro-analytical spectrometry techniques. Emphasis is put into determining the impacts of polysaccharides on soil strength and implications on soil pore anatomy. Erodibility, compressibility, volumetric change, and hydro-mechanical behaviour of base, and modified soils at yield and post-yield states are studied. Anomalies in suction-controlled post-yield stress–strain behaviour of modified soils are discussed and explained within the tenets of mechanics of composite soils with double porosity. PCC-reinforcement offers the closest possible packing at optimum water content. Desiccation cracking remains likely, but at relatively higher lower-bound water contents. Under low confinement levels and unsaturated state, strain-hardening prevails. Loss of shear strength on saturation is minimal. When saturated, PCC-reinforced soil develops substantially high levels of shear strength at all strain levels. Higher levels of confinement are needed for organic fibrous and onion-skin coating matters to effectively encrust the soil pore network; such high levels, however, leads to formation of an unwelcomed brittle, strain–softening stress–stress behaviour

Discussion on “Effects of lime addition on geotechnical properties of sedimentary soil in Curitiba, Brazil” [J Rock Mech Geotech Eng 10 (2018) 188–194]

The present discussion aims at complementing the original work published by Baldovino et al. (2018) by outlining a novel point of view. In light of the inherent limitations associated with the empirical model suggested in the original article, the dimensional analysis technique was introduced to the soil-lime strength problem, thereby leading to the development of simple and physically meaningful dimensional models capable of predicting the unconfined compressive and splitting tensile strengths of compacted soil-lime mixtures as a function of the mixture's index properties, i.e. lime content, initial placement (or compaction) condition, initial specific surface area and curing time. The predictive capacity of the proposed dimensional models was examined and validated by statistical techniques. The proposed dimensional models contain a limited number of fitting parameters, which can be calibrated by minimal experimental effort and hence implemented for predictive purposes. © 2018 Institute of Rock and Soil Mechanics, Chinese Academy of Science

Discussion of "compaction and strength behavior of tire crumbles-fly ash mixed with clay" by Akash Priyadarshee, Arvind Kumar, Deepak Gupta, and Pankaj Pushkarna

The dimensional analysis concept was successfully extended to the clay–tire crumbles–fly ash CBR problem, thereby leading to the development of a simple and practical dimensional model capable of predicting the CBR (at both unsoaked and soaked conditions) as a function of the mixture’s basic index properties, i.e., stabilizer content, initial placement (or compaction) condition, specific surface area, grain-size distribution, and curing time. The predictive capacity of the proposed dimensional model was examined and further validated by statistical techniques. The proposed dimensional model contains a total of four model (or fitting) parameters, which can be calibrated with little experimental effort and further implemented for predictive purposes. The model parameters can be adequately estimated by a total of four unsoaked or soaked CBR tests. Four scenarios consisting of the clay soil with no additives, a desired clay–tire crumbles mixture (no fly ash), a desired clay–fly ash mixture (no tire crumbles), and a desired clay–tire crumbles–fly ash mixture are recommended for the calibration phase. The choice of tire crumbles and fly ash contents are arbitrary; however, from a statistical perspective, median contents are expected to yield a more reliable estimate of the model parameters (Mirzababaei et al. 2018)

A sulphonated oil for stabilisation of expansive soils

The efficiency of a commercially manufactured sulphonated oil (SO) agent in treating a highly expansive soil was investigated through an extensive experimental program. A total of six SO to water mass concentrations, i.e. 0.25, 0.5, 0.75, 1, 1.25 and 2.5%, were examined. The test program included swell–load oedometer, unconfined compressive strength and cyclic wetting and drying tests. SO-stabilisation amended the soil’s mechanical behaviour through improvements achieved in swelling and strength characteristics. The reduction in swelling potential and swelling pressure was dependent on SO concentration, while the effect of curing time was found to be insignificant. A similar dependency was concluded for the unconfined compressive strength and stiffness of the stabilised soil. Both dependencies suggested an SO concentration of 1.25% capable of yielding an optimal stabilisation scheme. Results of the cyclic wetting and drying tests indicated that the beneficiary effects of SO-stabilisation at optimum concentration, particularly in ameliorating the adverse effects of swell–shrink-related volume changes and to some extent increasing the strength, are strongly preserved under the influence of alternate wetting and drying.Amin Soltani, An Deng, Abbas Taheri and Mehdi Mirzababae