APPLICATION OF FRACTURE-MECHANICS TO CRACKING OF SALINE SOILS

Salt-affected cracking clay soils are common to many irrigated, relati vely arid regions of the world. The structural changes of these soils having changing water contents lead to a pattern of macroporosity of c oncern to water management and groundwater contamination. Herein, we b riefly describe the different morphologic observations and attempts at quantifying aspects of the soil-cracking phenomena. After a brief rev iew of fracture mechanics theory, we outline the equations appropriate for its application to soils. Results of the theoretical analysis are compared with field observations of crack morphology in Tulare basin soils irrigated with Na2SO4 waters having Total Dissolved Solids (TDS) concentrations of approximately 400, 4500, and 9000 mg/L. The theoret ical analysis indicates that widely opened shallow cracks require high tensile stresses for propagation and that sodium-affected soils requi re yet greater energy to extend crack depth. Combining the theory with field observations indicated that changes in crack width and depth in the high salinity treatment soils required roughly twice the energy a s that in the low salinity soils. In addition, we found that the chang e in water content necessary to induce crack growth increases as the s oil dries and that at any given water content, the stress associated w ith crack growth was less in the high salinity soils. Overall, fractur e mechanics, coupled with measurements of soil physical properties can be used to determine quantitatively the propensity of soils to crack and the extent to which cracking will occur. However, additional labor atory and field studies are necessary to verify estimates of strain en ergy release rates from the fracture mechanics theory.