Piles subjected to torsional cyclic load: Numerical analysis

© 2019 Nimbalkar, Punetha, Basack and Mirzababaei. Pile foundations supporting large structures (such as high-rise buildings, oil drilling platforms, bridges etc). are often subjected to eccentric lateral load (in addition to the vertical loads) due to the action of wind, waves, high speed traffic, and ship impacts etc. The eccentric lateral load, which is usually cyclic (repetitive) in nature, induces torsion in the pile foundation. This paper presents a numerical model based on boundary element approach to study the performance of a single pile subjected to the torsional cyclic load. The model is initially validated by comparing it with the experimental data available from the literature. Thereafter, the model has been utilized to conduct a parametric study to understand the influence of the torsional cyclic loading parameters on the axial pile capacity. The results indicated that the model is able to capture the degradation in the axial pile capacity due to the torsional cyclic loading with a reasonable accuracy. Moreover, the parametric study showed that the frequency, amplitude and number of cycles play a significant role in the torsional cyclic response of the pile. The present study is essential for the development of design guidelines for pile foundations subjected to torsional cyclic load

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

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

Reinforcement of clay soils using waste carpet fibres.

It is reported that about 500,000 tonnes (i.e. 2% of the total waste) of waste carpet fibres are plunged into landfills annually in the UK. Municipalities and environmental authorities are increasingly concerned about the growing amount of carpet waste produced by household, commercial and industrial sectors. The notion of reusing such waste in industry has therefore attracted substantial attention in recent years by researchers and environmentalists. There have been a large number of studies in utilisation of virgin fibres in soils and other civil engineering applications. However, by contrast there have been relatively few studies of waste fibres especially waste carpet fibres in this context and in particular in cohesionless soils. In this study, the mechanical behaviour of composite cohesive soils (i.e. clay soils) with proportionate concentration of two types of waste carpet fibre is investigated. A series of consolidated undrained triaxial shear tests, Oedometer tests, swelling pressure tests and unconfined compression tests have been carried out to evaluate the effectiveness of the waste carpet fibres in improving the mechanical properties of cohesive clay soils including; shear strength and compression strength as well as reducing swelling pressure and consolidation settlement of such soils. The results have shown that waste carpet fibres do increase the shear strength and unconfined compression strength of clay soils proportional to fibre content. It was found that relative increase in unconfined compression strength or reduction in swelling pressure of the fibre reinforced clay soils is dependent on the initial dry unit weight and moisture content of the clay. A neural network analysis was conducted on the results of the triaxial shear tests to construct a predictive model for estimating the maximum deviator stress in consolidated undrained triaxial tests as a function of fibre type, fibre content, dry unit weight and consolidation pressure. The modelled behaviour was shown to be a perfect fit with the experimental data. Model slope tests were also carried out using a large scale laboratory test tank (L:800mm x W:300mm x H:500mm) to investigate the load bearing pressure of the slope made of fibre reinforced clay soil under strip footing load. The results confirmed that bearing pressure of the model slopes increased significantly with increased fibre content. Particle image velocimetry (PIV) method was used to track the displacement of the soil particles in the exposed front view of the model slope and contours of displacement and slip surfaces of the model slopes were determined and compared

Assessment of clay soil fabric using scanning electron microscope (SEM)

This paper introduces the way of assessing the soil fabric using outlines given by Collins and McGown (1983).The physical and mechanical properties of soils depends particularly on their fabric. At micro levels, the fabric of a soil sample consists of different elemental particles as well as it does at visible range of view. The arrangements of elementary particles and their sizes and shapes predict its mechanical behavior and characteristics. One of the best ways to recognize the fabric of a soil sample is to utilize scanning electron microscope. In this paper first the fundamental alphabets of scanning electron microscopes are explained then the soil fabric classification system given by Collins and McGown is fully described. Three clay soil sample were selected. Six specimens were prepared for swelling test, three of them without any treating agents and remains were treated with apolymeric agent. After applying swelling test according to ASTM D-4546 the samples were scanned using scanning electron microscope (SEM) and 18 micrographs were taken. For clarifying the terms used in the classification system, all micrographs were fully interpreted