Experimental and statistical assessment of expansive soil treatment using artificial fiber and chemical stabilizer

Expansive soils are found in many parts of the world particularly in arid and semi-arid regions. They are considered a worldwide problem as they cause extensive damage to civil engineering structures. As a result، a clear understanding of the behavior of such soils is required for the effective design of structures and infrastructures on these soils. Researchers have demonstrated various methods to reduce expansive soils swelling potential، with one being soil treatment. In this paper an experimental program was developed to study the treatment of an expansive soil using mechanical and chemical techniques. Two different types of artificial fiber consisting of polyethylene (bar shaped) with a diameter of 0. 3mm and polypropylene (tape shaped) with a width of 3mm were used in order to randomly reinforce soil samples with various fiber contents of 0. 5%، 1% and 1. 5%; and fiber lengths of 10، 20 and 30mm. Chemical treatment was carried on using lime and cement as soil stabilizers with various percentages of 5%، 8% and 10%; for curing times of immediate، 3 and 7 days. Uniform and repeatable moist-compacted soil samples were prepared by static compaction at a chosen moisture content and dry density less than the optimum water content and maximum dry density from standard proctor compaction tests. Free swelling and swelling pressure tests were conducted using a one-dimensional oedometer apparatus. In addition multiple regression equations with 3 and 2 independent variables were developed based on experimental results. The proposed multiple regression equations present an understanding of the variation of free swelling and swelling pressure as a function of swelling time، fiber or chemical stabilizer content and fiber aspect ratio (fiber length divided to fibers diameter or width) or curing time for various values. Experimental results and statistical analysis indicated that soil treatment with artificial fibers and chemical stabilizers can indeed reduce swelling potential in expansive soils. Reduction of free swelling and swelling pressure in samples randomly reinforced with artificial fiber was seen to be dependent on fiber content، fiber length and fiber shape، where tape shaped fibers showed more reduction in free swelling and swelling pressure thus being more effective compare to bar shaped fibers. Furthermore reduction of free swelling in samples treated with chemical stabilizers were seen to be a function of percentage of chemical stabilizer and curing time with cement showing to be more effective compare to lime. In addition chemical stabilizers proved to be more effective in reducing soils swelling potential compare to artificial fibers. The suggested regression equations can predict and estimate the free swelling curve، final free swelling and swelling pressure for various swelling time، fiber or chemical stabilizer content and fiber aspect ratio or chemical stabilizer curing time with accuracy and a high degree of agreement between experimental and predicted values. Also، the regression equations can aid the performance of a sensitivity analysis which indicates the importance of each independent variable (fiber or chemical stabilizer content، fiber aspect ratio or chemical stabilizer curing time) in estimating final free swelling and swelling pressure.