ABSTRACT
America could produce on the undrained shear strength parameters normally used for geotechnical design.
Since many factors can affect the shear strength parameters of cohesive soil it is imperative that the soil specimen densities be controlled in order to isolate the influence of water content. If certain void ratio remains constant for all specimens tested the only variable affecting the shear strength is the suction stress. Compacted specimens with fixed values of void ratio but different water content percentages were used to analyze the influence of degree of saturation on the soil behavior. It is worth mentioning that if the specimens are compacted at the same void ratios but with different water contents not only the degree of saturation is a variable but also the internal structure of the soil which is dependent on the amount of water use for compaction. These changes in structures can also affect the shear strength of the soil, but they can be considered also a consequence of the changes in the suction stress. According to Mitchell (1997), soil structure can be defined as the combined effect of fabric, composition, and interparticle forces. Nevertheless, Mitchell (1997) mentioned that the mechanical properties of soils are influenced by the soil type, the structure type, and the stresses, and soil structure and interparticle forces are included in our definition of suction stress. On the other hand, the resulting fabric, after the compaction process is done, will be affected by the energy of compaction and the degree of saturation, but
1 INTRODUCTION
A series of shear strength tests were performed on six different types of soils at controlled densities and degrees of saturation. Testing included fullysaturated triaxial and unconfined compression tests at different degrees of saturation. Since the specimens were prepared at the same densities, and using the same soil type, the most important variable affecting the shear strength of these soils and in its undrained strength parameters, is the change in suction stress. Baltodano-Goulding (2006) performed direct shear testing and tensile strength testing on unsaturated F-40, F-55, and F-75 Ottawa Sand with three different particle sizes to isolate the effects of changes in the degree of saturation on the shear strength on those types of soils. It was concluded that for this particular kind of soil the effect of the changes in matric suction resulting from varying the degree of saturation were minimal. So it could be inferred that for similar granular soils changes in shear strength parameter related to water content might be minimal too, due to the small ranges of matric suction that these soils can developed.
