NMR-based analysis of shear strength of weakly expansive clay in sodium chloride solution

A series of direct shear and nuclear magnetic resonance (NMR) tests were performed on a compacted weakly expansive clay saturated by sodium chloride (NaCl) solutions with different concentrations to study the effect of NaCl solution on the shear strength and its mechanism. Results from the direct shear tests show that the shear strength decreases slightly with increasing the NaCl solution concentration when the concentration is less than 1.0 mol/L. The results of NMR tests show that the smaller transverse relaxation times (T2) of specimens saturated by NaCl solutions with concentrations of 0.5 and 1.0 mol/L are less than that of the specimen saturated by deionized water. This means that the amount of smaller pores in the specimens saturated by deionized water is greater than that in specimens by NaCl solutions. That is, the specimen saturated by deionized water is denser than those by NaCl solutions under the same vertical pressure, and thus the shear strength of weakly expensive clay decreases with increasing the NaCl solution concentration.