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ABSTRACT
Unlike sediment soil, residual soil has low cohesion, low friction angle. low bearing capacity and is
not stable. The physical properties of residual soil is mostly determined by its composition such as
grain composition, the grain formation, and mineral composition, rather than its stress history.
Chemical and physical weathering generate specific clay mineral with special structure, and
probably there is cementation process on the soil particle. Besides containing clay minerals such as
illite, kaolinite and montmorillonite, the residual soil contains also hallosyte and hallopane. Those
effects are more important rather than stress history occurred on the soil deposits. Therefore, soil
stabilization of residual soil is different from that on sedimented soil. The purposes of this research is
to improve the shear strength parameters ( cohesion and friction angle) and soil bearing capacity of
residual soil stabilized with ordinary Portland Cement (OPC). The residual soil was taken from
Wonogiri Regency, The province of Mid Java. The soil is red- color due to chemical weathering. The
preliminary experiment that was performed in the Laboratory were water content, specific gravity,
grain size distribution, Atterberg limits, shear strength of the original soil. The oven-dried residual
soil was then mixed with 3, 5, 10, 15 and 20% OPC. The optimum water content was added to the
mix. Then, the blend were cured with 7, 14, 21, 36 and 56 curing period. Each specimen was tested on
the direct shear apparatus to verify the improvement of shear strength and shear strength parameters
of cement stabilized residual soil. To study the improvement of bearing capacity, the methods of
Terzaghi and Meyerhof were used to calculate the bearing capacity of cement stabilized residual soil.
The results indicate that even though residual soil stabilization is different from that of sedimented
soil stabilization , the shear strength parameters , shear strength and bearing capacity of stabilized
residual soil improve with respect to both cement quantity and curing period. In low cement content
and short time of curing, there is no improvement of shear strength and bearing capacity. The
significant improvement can be verified on high binder proportion (15 to 20%) and long curing
period : 56 days of curing. The results of bearing capacity analysis indicate that the bearing capacity
value of Meyerhof method was larger than that of Terzaghi method.