Perpustakaan Digital ITB

A back analysis of stability of two railway embankments constructed of tropical residual volcanic soils and located at Km.155+500 and Km.156+850 along the railway line from Bandung to Purwakarta has been carried out. Block samples were procured from the foundation outside the toes of the embankment sections and from the body of the embankment at the same locations. Index properties tests were carried out to assess the effect of mixing time and drying on Atterberg limits. Unconfined Compressive Strength (UCS) tests and Consolidated Undrained(CU) triaxial compression tests with pore pressure measurements were performed. Foundation soil taken from Km.156+850, on which an 8m high embankment is founded, was classified as andosol, while the foundation soil found at Km.155+500, underlying a 14m high embankment, was classified as latosol. Both embankment soils investigated were also classified as latosol. Under the UCS test, all soils investigated were found to behave as if they were overconsolidated. In CU tests, shear strength parameters were obtained from undisturbed samples at natural and fully saturated conditions. A back pressure of 190kN/m2 was applied to achieve a fully saturated condition in the laboratory for the latter tests. For all soils investigated, the friction angle was found to decrease with an increase in the degree of saturation, while the cohesion intercept was not found to correlate consistently with increase in the degree of saturation: the cohesion intercept of the andosolic soil did not change, while for latosolic foundation soil, it increased with increase in the degree of saturation. The simplified Bishop method of stability analysis for circular slip surfaces was used to estimate the factor of safety. Various values of pore pressure ratio, ru, were tried in the effective stress analysis. For the values of ru ranging between 0.0 and 0.2, the factor of safety for the 14m embankment underlain by latosolic soil was calculated in the range 1.04 to 1.30, while for the 8m embankment founded over andosolic soil it was in the range 1.95 to 2.30.