EFFECTS OF ADDITION OF POLYPROPYLENE FIBERS ON LIQUEFACTION CHARACTERISTICS OF SAND

Author

Sandip Dahal, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2016

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

Puri, Vijay

Abstract

During the past earthquakes major geotechnical hazards have occurred causing huge loss of property and damage to infrastructures. The liquefaction phenomenon which occurs mostly in saturated granular soils is the major causes of these hazards. The rise in pore water pressure resulting in the decrease of effective stress leads to loss of strength of soils during liquefaction. Extensive research has been done in this field to increase the strength of the soil against liquefaction. One of the key option in increasing the strength of soil is by the addition of monofilament fibers. However, many factors such as fiber length, fiber type, fiber aspect ratio and particle size of the soil affect the results. The objective of this study were: (i) to evaluate the shear strength parameter cohesion (c) and friction angle (φ) with the fiber inclusion during a direct shear test (ii) to study the influence of fiber addition on the shear strain development of the soil and (iii) to study the beneficial effects of addition of random fibers in increasing the cyclic resistance of sand. Direct shear test on clean sand and sand with 0.1%, 0.25% and 0.5% fiber content were carried out in a pneumatic direct shear equipment. The tests were carried out at 4 different normal stresses of 17.9, 25.5, 41 and 72.4 psi. The effect of fiber on the shear strength parameters and the volumetric strain was studied. In a cyclic triaxial test, consolidated undrained test was carried out on sample of clean sand and sand containing 0.25% fiber at a relative density of 30%. The tests were performed using an effective confining pressures of 5 and 10 psi. The number of cycles to reach initial liquefaction and the number of cycles to reach 2.5% of axial strain were recorded. The results from the direct shear test on dry samples showed that the cohesion and friction angle value kept on decreasing with the addition of fiber. However, the tests on sample at 5% moisture content showed increase in cohesion value with the addition of fiber but a decrease in the friction angle value. The volume of the sample of sand decreased during the tests and with the addition of fiber, there was a reduction in the decrease in the volume of the sample. In the case of cyclic triaxial test, the samples with fiber didn’t reach initial liquefaction compared with the clean sand samples. And the number of cycles to reach 2.5 % axial strain was higher in the case of sample containing fiber in comparison to the samples of clean sand.