Analytical Investigation on the Benefit of Sisal Fibre Reinforcement of Expansive Clayey Subgrade using Fem
Binu Sara Mathew1, Gayathri Mohan2, Kuncheria P. Isaac3, Susan Rose4
1Binu Sara Mathew,  Asst. Prof, in Dept. of Civil Engineering, College of Engineering Trivandrum, Kerala, India.
2Gayathri Mohan, Former P. G Student, College of Engineering Trivandrum, Kerala, India.
3Kuncheria P. Isaac, Member Secretary, AICTE, New Delhi, India.
4Susan Rose,  Research Scholar, College of Engineering Trivandrum, Kerala, India.
Manuscript received on July 26, 2014. | Revised Manuscript received on August 10, 2014. | Manuscript published on August 30, 2014. | PP: 149-153  | Volume-3 Issue-6, August 2014.  | Retrieval Number:  F3356083614/2013©BEIESP

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Abstract: Well-built and maintained highways play a major role in nation’s development. The subgrade soil is integral part of pavements which provides support to the pavement. The subgrade soil and its properties are important in the design of pavement structure. Expansive soils are those soils, which have high swelling and shrinkage characteristics, extremely low CBR value and shear strength. The soil of Kuttanad region of Alappuzha district of Kerala in India is example of expansive soil entirely different from the normal well drained soils in their morphological, chemical and physical characteristics. Thus construction of roadbeds on or with these soils, which do not possess sufficient strength to support wheel loads imposed upon them either during construction or during the service life of the pavement is a commonly encountered problem. Hence extensive research is being done on improvement of strength properties of these types of soils. Ground improvement technique use locally available material to the maximum and hence found economical. It includes stabilization technique and reinforced earth technique. Lime when added to the soil, can substantially increase the stability, impermeability, and load-bearing capacity of the subgrade. Presently, the soil reinforcement technique is well established and is used in variety of applications like improvement of bearing capacity, filtration and drainage control. Conventional methods of reinforcement consists of continuous inclusions of strips, fabrics, and grids into an earth mass. An experimental investigation was done earlier by the same authors to study the effect of stabilization with lime, sand and sisal fibre on compaction characteristics, CBR value, swelling property, and elastic modulus of expansive soil. The optimum quantity of fibers was decided based on CBR value. The static triaxial test was conducted on unstabilized and stabilized soils at a confining pressure of 40 kPa. In this study, a finite element analysis was done to quantify the benefits of stabilization of clay. The stressstrain data from tri-axial test were used as input parameters for evaluating the vertical compressive strain at the top of subgrade soils using elasto-plastic finite-element analysis. It was observed that the elastic modulus value almost doubled as a result of stabilization. The vertical compressive strain at the top of unreinforced and reinforced subgrade soils obtained as an output from the finite element model was used for estimating the improvement in service life of the pavement or decrease in layer thickness and consequent reduction in construction cost. It was observed that a 14% reduction in construction cost and 7.3 times improvement in TBR value can be attained due to sisal fibre stabilization. Hence it can be concluded that the stabilization with sisal fibre after lime stabilization is as an efficient and economic method of stabilizing expansive subgrade soil.
Keywords: CBR, TBR, Subgrade, Fibre, Stabilization, Kuttanad, Alappuzha.