Tamrakar, Surendra Bahadur creator Kohgo, Yuji Chairperson Balasubramaniam, A.S. Examination Committee Shibuya, Satoru Examination Committee Government of Japan Scholarship Donor text series technical report th Bangkok Asian Institute of Technology 1997 continuing eng 167 leaves : ill. + 1 online resource In order to investigate the unsaturated shear behavior of Khon Kaen loessial soil, triaxial tests were carried out in a specially modified triaxial apparatus. Specimens were statically compacted so that they had 1.2 kN/m3 initial density and 8 % initial water content which were similar to the field conditions. Consolidated drained triaxial tests were performed at three different confining pressures (50, I 00 and 200 kPa) with constant suction condition of 0, 10, 50,100 and 200 kPa. Axis translation technique was used for the making the initial suction condition before starting the tests. The apparatus being specially designed, we could measure the overall volume change of the sample more accurately than in conventional triaxial apparatus. Hence the shear behavior could be observed more precisely. Also, pore-air and pore-water pressures could be controlled separately in this test. The tests were performed in accordance with the programming. The test results showed that the amount of suction greatly influence the shear behavior of the soils. Stress-strain relationship of test results showed that initial slope (stiffness) of the curves are lower at the lower suction values, but the slope increases with the increase in suction. It is also seen that suction effect; an increase in suction increases the yield stress is dependent on the confining pressure. At lower confining pressure the effect of suction is higher than at the higher confining pressure where it decreases. From results of the volumetric strain and axial strain relationship, it is seen that with the increase in suction there is a decrease in volume change of the specimens. This is due to the increase in inhibition of plastic deformation of the sample with the increase in suction. Also, from e - logp' lines during shearing, we can see the decrease in slopes of these lines as the suction increases. At higher suction values, the amount of drainage increases with the mcrease m suction whereas at lower suction values, water goes into the sample. All of the changes in shear behavior of the unsaturated soils are due to the effect of suction which are explained by the Kohgo's elastoplastic model with two suction effects; (i) an increase in suction increases the effective stress and (ii) an increase in suction increases both the yield stress and stiffness against plastic deformation. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Civil Engineering Thesis (M. Eng.) - Asian Institute of Technology Shear strength of soils Testing Strains and stresses Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B13423 http://203.159.5.9/ait-thesis/detail.php?q=B13423 970807 20260818213901.0