One of the most pressing needs for research in the geotechnical area is on the issue of the use of marginal soils (e.g. silts, soft rock, etc.) for fills and as backfill material for walls and bridge abutments. The lack of availability of higher quality materials and the added costs for these materials will eventually force engineers to use marginal soils when in the past these marginal soils were replaced with materials of better quality. Often however, high water content and low workability of these soils pose difficulties for construction projects. Frequently, additives such as lime, cement, fly ash, lime-cement-fly ash admixture, cement kiln dust, emulsified asphalt, Geofiber, and polymer stabilizers are used to improve their engineering properties. The choice and effectiveness of an additive depends on the type of soil and its field conditions. Nevertheless knowledge of mechanistic behavior of treated soil is equally important as selecting the stabilizer.
This study first presents a critical examination of the use of various additives on soil improvement projects. It then presents a comprehensive examination of the effectiveness of cement treatment on geotechnical properties of soils from Aberdeen, Everett, and Palouse regions from the state of Washington. The addition of cement was found to improve the drying rate, workability and compaction characteristics of the soils. Significant improvement in unconfined compressive strength and modulus of elasticity are attained by cement treatment of these soils.
Results of undrained triaxial tests showed that while cement treatment improved shear strength significantly, the type of failure behavior varied greatly. Non-treated, 5%, and 10% cement treated soils displayed ductile, planar, and splitting type of failure, respectively. For 10% cement treated soils pore pressures rose rapidly to confining pressures resulting in zero effective confining pressure at failure. Consequently, specimens split vertically. Therefore, while increase in strength can be achieved by cement treatment, high percentages of cement should be used with extreme caution in field applications.
The results of triaxial tests on Aberdeen soil were interpreted using the critical state framework. As a result of cement treatment, interlocking increased, critical state friction remained constant and soils displayed anisotropic behavior. The anisotropic model presented by Muhunthan and Masad (1997) was used to predict the undrained stress path. A combination of this model with extended Griffith theory can be used to predict the complete shear behavior of cement treated soil in q-p΄ space.
The main contributions of this study to practice are on quantifying improvement in mechanical behavior due to cement treatment and highlighting the fact that higher percentages of cement could turn stabilization from a beneficial to an extremely dangerous practice.