Relationship between pH value and electrical conductivity and strength characteristics of cement treated Shanghai clayey soil

Drilling core samples, standard penetration test, and load test are common methods for checking the quality of soil-cement columns in China. They have disadvantage of high requirements and ineffective in time and test cost. Because of these reasons, a new method for checking the strength of soil-cement columns is proposed. The method includes measurement of the pH value and the electrical conductivity at the initial stage to determine the unconfined compressive strength and the characteristics of cement treated soil. In this study, the fourth layer of Shanghai clayey soil is used. The cement content of variables, cement treated soil's chemical properties and strength characteristics researching tests were done. The relationship among pH value, electrical conductivity, and cement content, curing time, unconfined compressive strength are investigated. Test results show that when pH value and the electrical conductivity at initial stage are larger than 11.5 and 0.09 s/m respectively, cement treated soil starts to get strength. After that, the strength grows with the increase of pH value slowly. However, when pH value reaches 11.8, the strength grows with the increase of pH value rapidly. Characteristics of relationship between electrical conductivity and strength can avoid inaccuracy and risks brought by using single chemical index to determine the unconfined compressive strength. These results can provide a test basis for the judgment of the strength of cement treated Shanghai clayey soil.