Swelling Capacity and Hydraulic Conductivity of Polymer-Modified Bentonite under Saline Water Conditions  
[PERSON]  
1 Department of Civil and Environmental Engineering, Seoul National University, Seoul 08826, Korea; [EMAIL_ADDRESS]  
2 College of Architecture and Civil Engineering, Taiyuan University of Technology, Taiyuan 030024, China; [EMAIL_ADDRESS]  
[PERSON]  
2 College of Architecture and Civil Engineering, Taiyuan University of Technology, Taiyuan 030024, China; [EMAIL_ADDRESS]  
[PERSON]  
3 Coastal Disaster Prevention Research Center, Korea Institute of Ocean Science and Technology, Busan 49111, Korea; [EMAIL_ADDRESS]  
Correspondence: [EMAIL_ADDRESS]; Tel.: +82-2-880-8356  
November 8, 202  
are prominent characteristics of bentonite, which always depend on the salinity of the contact solution and can change the microstructure of the bentonite [16]. Saline water can increase the hydraulic conductivity of bentonite and thus reduce its swelling capacity and sealing performance [17; 18; 19]. [PERSON] [20] found that the swelling pressure of bentonite was reduced in saline conditions and the pressure reduction increased with increasing bentonite density. Owing to the concentration gradient between the pore water and external salt solution, osmotic flow from the lower salinity solution to the higher salinity solution would cause a reduction in the swelling pressure of bentonite under saline conditions [21].  
Modified bentonite (MB) has been developed to improve bentonite's performance in saline conditions [22]. [PERSON] [23] found that salt tolerance could be enhanced when adding some types of high-molecular-weight polymer to bentonite. The MB solved the leakage problems in agricultural irrigation and led to a significant water-saving. In [PERSON] study, bentonite was treated with 2% and 8% polymer (carboxymethyl cellulose) by weight of bentonite, and the swelling ability increased as the polymer content increased, which has implications for bentonite barrier resistance in seawater [24]. [PERSON] [25] developed a superior clay with enhanced hydraulic performance. The treatment with an anionic polymer can improve the sealing, hydraulic, and membrane properties of clays. Polymer addition can enhance the solution viscosity and decrease the hydraulic conductivity of bentonite-aggregate mixtures [26]. Thus, such polymer-improved bentonite mixtures can be effectively used as barrier layers [27]. Different from other previous studies, guar gum was selected as an additive for bentonite modification. Guar gum has a higher hydrophilicity than other polymers, therefore it dissolves easily in water and combines with bentonite molecules to form MB [28]. Due to the high stability and relatively low price of guar gum, it has much potential as an additive in MB that can be used in hydraulic barrier materials for civil engineering applications [29].  
In this research, bentonite was modified with guar gum and a MB was developed for anti-seepage projects under saline water conditions. To investigate the hydraulic performance, hydraulic conductivity testing of the MB was carried out. To study the swelling characteristics of MB, swelling strain tests (load/unload conditions) and swelling pressure tests were conducted in saline water conditions. In addition, unload swelling strain tests of MB under fresh water conditions were performed as a control. Based on the test results, relationships between initial dry density, swelling time, swelling strain (load/unload), and swelling pressure were separately established.