This project developed and demonstrated the use of a hybrid sensor based on Bender Element and Time Domain Reflectometry technologies and an algorithm for the rapid assessment of the susceptibility of chemically-treated sulfate-rich soils to sulfate heaving. The developed sensor was embedded in lime- and cement-treated soils to monitor changes in both moisture content and shear wave velocity at various time periods. Laboratory assessments indicated that cement treated soils experienced higher stiffness losses as compared to lime treated soils. For field implementation and validation, a test section was chosen in the median area between Highway 114 and International Parkway near Dallas/Fort Worth airport. Sulfate tests conducted on the natural soils indicated the sulfate contents was in excess of 30,000 ppm. A 25-ft. x 60-ft. section was built in this area and the subgrade was treated with 6% lime. The developed hybrid sensor was embedded at a depth of 8 in. in the treated section. The treated section was watered three times a day to keep continuous supply moisture for uninhibited sulfate reactions in the treated soil. Field test results indicated a reduction in shear modulus with time in the lime treated test section. The results also reconfirm the laboratory findings that the shear modulus decreased in chemically treated sulfate rich soils owing to the deleterious reactions among soils and mineral and chemical stabilizers. Addition field testing and evaluation is needed before this technology can be implemented by highway agencies.
The contractor's final report is available.