Undrained behaviour of clay reinforced with surplus carpet fibres

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Undrained Behaviour of Clay Reinforced with Surplus Carpet Fibres
M. Mirzababaei1, M. Miraftab1, P. McMahon2 and M. Mohamed3

University of Bolton, Centre for Materials Research and Innovation, Bolton BL3 5AB, UK 2 University of Bolton, School of Built Environment & Engineering, Bolton BL3 5AB, UK 3 University of Bradford, Geotechnical Engineering, Bradford BD7 1DP, UK

Acollaborative research programme between University of Bolton and Bradford University is investigating the effect of surplus carpet fibres on the strength as well as other important geotechnical properties of cohesive soils. Initial work concentrates on the manner in which the fibres affect the quick undrained properties of the reinforced soil. Four different surplus carpet fibre types are being usedduring the study (most popular in United Kingdom) mainly containing fibres from “top-finishing” and “shredded segments” of carpets. Relatively low plasticity index clay has been prepared using commonly available clay within the North-West Region of the UK. A series of quick undrained (UU) triaxial compression tests is scheduled for 76mm in height by 38mm diameter soil specimens reinforced withtarget concentrations of 1%, 5%, and 10% of ‘surplus’ carpet fibres (by dry soil mass) compacted at optimum water content for the light (2.5kg) BS1377 method. The mixing efficiency of the surplus carpet fibres within the cohesive soil is of critical importance alongside the methodology for preparing samples to a uniform standard for research purposes. Later stages of the work intend to extend theinvestigation into effective stress path testing, exploration of practical methods of mixing and compaction in the field for civil engineering applications.

1. Introduction
The roots of soil fibre reinforcing can be traced in history of human kind to thousands of years ago. The remainder of houses built with thatch, plant roots and other natural fibres as reinforcing elements to prevent cracking inmasonry materials proves this historical fact. Such buildings can still be found in some rural places where people use low strength fibre-like materials like straw to reinforce low strength masonry walls. From past decades, the beneficial effect of fibres in geotechnical engineering and construction engineering has become a known fact to all engineers. Several researchers have utilised differentfibres including natural fibres and/or synthetics for reinforcing problematic soils specially for increasing shear strength of low strength granular soils. Fibres can be utilised for reinforcing soils either in continuous insert form (sheets like woven/non woven geotextiles, strips and bars) or as randomly orientated

discrete inclusions. The first method involves introducing oriented layers ofplanar sheets into several layers of soil. Although planar inclusions increase the shear strength of soil between successive layers and introduce ‘tensile strength’ into reinforced soil, they at the same time decrease the shear strength of the composite soil at the interfaces due to less bonding strength between planar inclusions and soil rather than soil against soil. When failure occurs incontinuous sheet systems it most probably happens first through the interface between the soil and planar inclusion. Moreover, in this method the orientation of fibrous inclusion, number of layers and distance between layers are also important for reinforcement purposes. With randomly orientated discrete fibres, where fibres are spread over the whole volume of the reinforced soil randomly by virtue ofthe mixing process, there should not be any discernible planes of weakness in the reinforced soil.

2. Objectives and scope
Statistics show that there are about 400 million tones of waste produced annually in the UK of which 2% of its weight is attributed to textiles generally in the form of carpet waste. One of the reasons for concentrating on carpet wastes is because they have a high...
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