SEISMIC STABILITY OF CEMENT TREATED GROUND BY TILTING AND DYNAMIC SHAKING TABLE TESTS

MASAKI KITAZUME, KIMITOSHI HAYANO AND HIDEO HASHIZUME

ABSTRACT: A series of tilting tests and shaking table tests with a geotechnical centrifuge apparatus to determine the dynamic active earth pressure of cement treated clay ground by investigating the seismic stability of cement treated clay ground having an unsupported vertical slope. In the tilting tests, the horizontal seismic inertia force was simulated statically by tilting the whole model ground in accordance with the horizontal seismic coefficient k_h. The tilted model ground was subjected to monotonically increasing centrifugal acceleration until it failed due to the enhanced self-weight. In the shaking table tests, on the other hand, the model ground was subjected to dynamic excitations under a high centrifugal acceleration field. The magnitude of the dynamic excitation was increased stepwise until the model ground failed. It was found from the both test results that the model ground failed with a combination of a vertical tensile crack and a straight shear failure plane, which was much different from the failure phenomenon of sandy or clayey ground. It was also found that the conventional pseudo-static limit equilibrium method such as Mononobe-Okabe's earth pressure theory was not able to evaluate the critical height and the failure zone of the model ground accurately. Based on the model test results, a modified pseudo-static limit equilibrium method incorporating the tensile force along the crack plane was proposed in this study. In the method, the critical height and the failure zone of the cement treated ground were influenced by the strength ratio of the tensile strength to the compressive strength of the treated soil. It was found that the proposed method with a suitable strength ratio was able to predict the tilting test results with fairly high accuracy. Also, the proposed seemed to be able to reasonably explain the shaking test results if the dynamic response acceleration of the model ground was carefully taken into account. Dynamic active earth pressure of cement treated clay ground was also discussed in which the importance of incorporating the failure pattern was emphasized.

Key words: centrifuge model test, failure, limit equilibrium method, seismic response, shaking table test, shear strength, soil stabilization, tensile strength, (tilting test) (IGC: D10/E8)