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Project Title: Mechanical Behaviour of Unsaturated Soil Reinforced with Carpet Fibres

  • PhD Student: Suleiman Saad
  • Supervisors: Dr Mostafa Mohamed and Dr Ashraf Ashour


In England, MSW amounted to 27.3 million tonnes in 2008/09, of which 50.3% were sent to landfill, and 49% recovered through recycling, composting, and energy recovery. Compared with data for the previous year, the portion of MSW recovered by recycling and composting, increased by 3.9% in 2008/09. The MSW recovered by recycling or composting accounted for 36.9% of the waste in 2008/09, while 12.2% was incinerated for energy recovery (Municipal 2008/09).

Recently in the UK, the total amount of solid waste generated yearly is about 400 Million tons (Mt), of which approximately 2% of its total weight (Wt) consists of textile and other carpet waste (Miraftab and Lickfold, 2008). Carpet waste (Fig. 1) represents by a high proportion of the waste weight, as it has a high volume to weight ratio, which means that it occupies a large volume compared to other constituents of landfill disposal (Mirzababaei et al 2009). Many studies investigated different methods for the treatment and reuse of carpet fibre waste to improve the physical and mechanical properties of soils, and cement or concert. Wang et al. (1999) recycled carpet waste fibres by mixing them with concrete to improve its physical properties. On the other hand, Tang et al. (2007) studied the influence of mixing of carpet waste that consisted of polypropylene polymer (PP) with uncemented and cemented clayey soils.

Figure 1. Carpet waste fibres (GBF) and clay soil used.

Figure 1. Carpet waste fibres (GBF) and clay soil used


The aim of this project is to study the mechanical behaviour of unsaturated soil and the effect of fibre waste on unsaturated soil reinforcement. The objective of the study is to:

  • Review current literature on: soil, fibre-soil reinforcement, fibre, clayey soil and unsaturated soil.
  • Review the mechanical behaviour of clay under unsaturated conditions.
  • Perform standard triaxial test methods for determining the physical properties of fully saturated and unsaturated soils, such as suction, volume change and shear strength.
  • Perform a series of advanced triaxial tests on unsaturated soil samples with different percentages of fibre inclusion (0, 1, 3 and 5%).



This clay was collected from the site in the North West of the United Kingdom. It is a type which can be found in most areas of the UK. The specific gravity of the soil was determined for soil according to BS1377-2:1990 standard procedures, the result was within the limits for clay, i.e. 2.65 to 2.75. Sieve analysis of clay soils was undertaken according to BS1377-2:1990. To prepare a clay soil with a plasticity index, the soil was selected based on liquid and plastic limits. The results have proven that the liquid limit (LL) of soil is 21.3%, the plastic limit (PL) is 10.36%, and the plasticity index (PI) is 10.94%.  It has low plasticity (CL) according to the Unified Soil Classification System.

Carpet waste fibre

In this investigation, we used this type of fibre as reinforcement for unsaturated soils. The fibres were composed of 60% polypropylene, 20% styrene butadiene latex rubber (SBR), 15% nylon and 5% wool. Moreover, the diameter of the fibre varied from 0.1 to 1mm and the length was between 2 and 20mm, with a specific gravity of 1.30. In terms of physical properties of the carpet waste, absorption of water for the polypropylene was 0%, for wool 13 to 15% and for nylon 4.1 to 4.5. The specific gravity of the polypropylene was 0.9, nylon 1.14, and wool 1.32 (Carpet Recycling UK). The fibre contents used in this investigation were 0, 1, 3, and 5%.

A series of fully saturated triaxial tests were conducted to investigate the mechanical behaviour of clay under full saturation, as well as the unsaturated triaxial test which investigated different values of suction.

Figure 2. Experimental set-up (not to scale).

Figure 2. Experimental set-up (not to scale)


Soil for civil engineering purposes, Part 2: Classification tests, British standard, BS 1377-2:1990, BSI 11-1998

Municipal Waste Management Statistics for England, 2008/09 report, at 2/01/2011.

Miraftab M., and Lickfold, A., Journal of industrial Textiles 38:2 (2008) 167-174.

M. Mirzababaei, M. Miraftab, P. McMahon and M. Mohamed, “Undrained Behaviour of Clay Reinforced with Surplus Carpet Fibres”, Second International Symposium on Fibre Recycling, 11-13 May 2009, Georgia Institute of Technology, Atlanta, Georgia, USA.

Tang, C., Shi, B., Gao, W., Chen, F., and Cai, Y. Geotexiles and Geomembranes, 2 (2007) 194-202.

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