This paper presents the results of undrained triaxial and simple shear tests under different stress paths on mixture of Portland cement with clean sand to investigate the effect of principal stress rotations. According to preliminary monotonic tests which revealed that the cement mixture reduces the anisotropy and also improves the mixture mechanical properties compared to compacted sand without cement, it was decided to perform cyclic tests to compare the behavior under repeated loading conditions. Test results in triaxial tests showed that the loose cemented sand is stronger than compacted (dense) sand in cyclic behavior even in more severe loading conditions (larger CSR). Following that, simple shear tests validated the triaxial test results estimating a safe cement content value in practical purposes. Furthermore it clarified the effect of the parameter or rotation of principal stresses on the behavior of cemented sand mixtures.
Low density saturated fine sands are susceptible to failure even under static loads. When subjected to cyclic loads such as earthquake, the pore water pressure rises followed by shear strength loss resulted in initial liquefaction or substantial settlements. One of the improvement methods of loose liquefiable sands from decades ago is injection or mixture of Portland cement (Dupas and Pecker, 1979). Extensive research is available in literature on cement-treated soils, but they are mostly limited to triaxial compression, one-way cyclic and Brazilian tensile tests on cemented sands (e.g. Schnaid et al., 2001; Consoli et al., 2007; Rotta et al., 2003). No study has been reported, however, on the stress reversal or alteration of principal stress directions. This is while in many loading/unloading conditions, such as earthquake excitation in level ground surfaces, the major principal stress may change its direction with respect to vertical and the stress path on the soil element (Yang et al., 2007).
