17-07-2013, 03:24 PM
Effect of Waste Polymer Materials on Shear Strength of Unsaturated Clays
Waste Polymer Materials .docx (Size: 1.67 MB / Downloads: 42)
ABSTRACT
Improvement of shear strength of the soil may be undertaken by a variety of ground improvement techniques like stabilization of soil, adoption of reinforced earth techniques like stabilization of soil, adoption of reinforced earth techniques etc. reinforced earth technique is considered as an effective ground improvement method because of it’s cost effectiveness, easy adaptability and reproducibility. In the present investigation, the waste polymer materials
has been chosen as the reinforcement material and it was randomly included in to the clayey soils with different plasticity indexes at five different percentages of fiber content (0%, 1%, 2%, 3%, 4%) by weight of raw soil. the main objective of this study had been focused on the strength behavior of the unsaturated clayey soils. reinforced with randomly included waste polymer fiber. the reinforced soil samples were subjected to direct shear tests. The results have clearly shown a significant improvement in the shear strength parameters (C and φ) of the treated soils. The reinforcement benefit increased with an increase in fiber contents.
INTRODUCTION
The soil reinforcement technique is well established and is used in variety of applications like improvement of bearing capacity, filter and drainage control, shear strength, among others. Reinforced soils can be obtained by either incorporating continuous reinforcement inclusions within a soil mass in a defined pattern or mixing discrete fibers randomly with a soil fill. The concept and principle of soil reinforcement was first developed by Vidal (1969). . He demonstrated that the introduction of reinforcement elements in a soil mass increases the shear resistance of the medium. The primary purpose of reinforcing soil mass is to improve its stability, increase its bearing capacity and reduce settlements and lateral deformation (Hausman, 1990; Prabaker and Sridher, 2002; Yarbasi et al, 2007) many investigators have experienced on natural, fabricated and by product materials to use them as stabilizers for the modification of clayey soils (Aitcin et al., 1984; Sandra and Jeffrey, 1992; Kayabal, 1997; Asavasipit et al., 2001; Kalkan and Akbulut, 2004; Akbulut et al., 2004; Yetimoglu et al., 2004; Kumar et al., 2006; Cetin et al., 2006; Kalkan, 2006; Tang et al., 2006).
Randomly distributed fiber-reinforced soils have recently attracted increasing attention in geotechnical engineering.
TESTED MATERIALS
Three clayey soils with different plasticity indexes used in the present experimental testes were obtained from the mines in Malayer-Hamedan in north of Iran (soil A), Saveh in center (soil B) and Khorasan (soil c) in west of Iran. They are defined as high plasticity soils (CH) according to the Unified Soil Classification System.
TESTING PROGRAM
This experimental work has been performed to investigate the influence of Plasticity Index and percentage of waste polymer materials on the shear strength of waste polymer materials on the shear strength of unsaturated clayey soils. For this purpose, clayey soils with different
plasticity Indexes were used and mixed with different percentage of waste materials to investigate the shear strength parameters of unreinforced and reinforced samples in terms of direct shear test.
The clayey soils were dried and then ground before using in the Mixtures. At first the required amounts of clayey soils and waste reinforcement fibers were blended together under dry conditions. The contents of scrap tire rubber fibers were chosen as 0, 1, 2, 3 and 4 % by total weight of dry soil.
RESULTS AND DISCUSSIONS:
The effect of waste polymer fibers addition in soil on compaction, shows that the shape of the compaction curves are similar to that of unreinforced samples.
The effect of fiber content on Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) are presented in figures 2 and 3.
An increase in fiber content causes a reduction in dry density. This is due to reduction of average unit weight of the solids in the soil-fiber mixture. The maximum dry density of soil A range from 1.61 to 1.7 (g/cm3), in soil B from 1.62 to 1.74 (g/cm3) and in soil C from 1.7 to 1.79 (gr/cm3).
The OMC decreases with increase in fiber content. The OMC ranges of soil A is between 18.24% and 18.5 %, for soil B is between 19.72%and 19.9% and for soil C is between 21.42% and 21.5 %.
CONCLUSIONS
This study was undertaken to investigate the effect of plasticity index and fiber content on the shear strength parameters (c and φ) of randomly distributed fiber-reinforced soil by performing direct shear tests. The results of this study bring forth the following conclusions:
* The peak shear stresses are significantly affected by fiber content , specially at high normal stresses.
* The initial stiffness at the same normal stress for reinforced and unreinforced soils remains practically the same.
٭ The percentage of fiber content played an important role in the development of shear strength parameters c and φ of the fiber reinforced soil.
٭ When the soil is reinforced with the waste polymer fiber, it reduce the dry density of the soil due to a low specific gravity and unit weight of polymer fiber. The increase in the fiber content also reduces the optimum moisture content (OMC) of the soil. The variation is linear for
both cases.