Authors
1
Islamic Azad University, Estahban Branch, Iran
2
Islamic Azad University, Estahban, Iran .
3
Department of Civil Engineering,, Zand Shiraz Higher Education University, Shiraz, Iran,
4
Department of geology, Estahban Branch, Islamic Azad University,Estahban,, Iran
Abstract
In the present study, the effect of chitosan biopolymer on the mechanical properties of marls was investigated. To this aim, different amounts of chitosan (0, 0.02, 0.04, 0.08 and 0.16%) were mixed with soil and different samples were made to perform experiments. Then the samples were cured for 7 and 28 days and finally subjected to 0, 1, 4 and 8 freeze-thaw (F-T) cycles. Finally, unconfined compressive strength (UCS) and direct shear tests were performed on the samples and variations of stress-strain, secant modulus, peak strain energy modulus, cohesion and internal friction angle were evaluated under different freeze-thaw cycles. The results showed that the marl soil alone had a diminutive strength equal to 180 kPa, especially after successive F-T cycles, so that after 8 cycles, its UCS reached about 90 kPa. However, the strength increases significantly in the samples stabilized with chitosan, so that in the sample containing 0.16 chitosan as the optimum composition, after 7 days of the curing period, the UCS reached about 409 kPa. According to the results obtained from Eu and E50 parameters for different samples, it was found that the addition of chitosan causes, in addition to greater stiffness, much more energy to break the sample. Moreover, the values of cohesion and internal friction angle for the optimum mixture after 7 days of curing were equal to 38.76 kPa and 21.07°, which was much higher than 21 kPa and 18.26° related to the initial marls.
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