Shear strength of bentonite saturated with saline solutions exhibiting variety of cations

Investigation of saline solutions on the shear strength (SS) of compacted bentonite is desideratum to evaluate the safety of engineered barriers in order to safely dispose of the high-level radioactive waste. Undrained shear experiments were carried out on Na-bentonite saturated with CaCl₂, KCl, and NaCl solutions. The stress-strain relationship of all the bentonite samples exhibits strain softening behavior, and the peak stress increases with the increase of the saline solution concentration. The SS of samples in saline solutions at 0.1 mol/L (M) follows the order of NaCl< KCl < CaCl₂, whereas, in 0.5 M salt solutions it follows the order of NaCl<CaCl₂ < KCl, indicating that the cation exchange process has a major impact on the SS of bentonite. The modified effective stress concept p’ was used to express the SS in various salt solutions based on Mohr-Coulomb criterion. The results further revealed that the solution concentration had minimal effect on the angle of internal friction φ’. In addition, the strength envelope remains the same when samples are saturated with different concentrations of NaCl solution, unlike the samples saturated with KCl and CaCl₂. At lower salinity concentration (0.1 M), the SS in CaCl₂ solution approaches maximum value because of higher osmotic suction. On the contrary, the SS of bentonite saturated with KCl attains the highest value at high concentration (0.5 M), which is attributed with strong K-linkage and low hydration energy of potassium ion.