LAPINDO MUD BEHAVIOR STABILIZATION USING SAND MIXTURE.

Landfill work is now increasingly needed in the project implementation to improve the carrying capacity and to increase the original soil elevation. Good subgrade stability is able to support the above structural loads and is low in plasticity. The soil that is usually used for landfill is hard soil, red soil, or semi-hard soil. The increasing need of landfill soil, hard or semi-hard soil as materials will eventually decrease in its availability. This research tried to use Lapindo mud as landfill soil so as to reduce the volume of mudflow as well as to be a consideration in carrying out the future infrastructure development. To improve the characteristic quality, stabilization using additional sand mixture was carried out. By adding sand to Lapindo mud, the gradation is tighter so that its density level will be increased. This research used experimental method with Soil Mechanics laboratory test. The laboratory test includes Grain Gradation Analysis, Atterberg Limit,Compaction, CBR Laboratory, Direct Shear, Unconfined, and Free Swelling. The specimens include Lapindo mud from Sidoarjo and sand for building materials. The sand concentration used was10%, 20%, 30%, 40% and 50% of the mud weight. Conclusion: Due to the addition of 40% sand, the liquid limit value of Lapindo mud decreased from 57.33% to 33.33% and the plasticity index decreased from 24.67% to 13.33%. The compaction test results of ɣdmaxincreased from 1,317 gr/cm3to 1,624gr/cm3on the addition of 50% sand. The results of CBR test also increased from 3.65% to 7.59% on the addition of 40% sand. Direct shear test resulted in the increase of inner shear angle from 13.22 degree to 27.92 degree on the addition of 50% sand. Unconfined compression test showed the increase from 0.86 kg/cm2to 1.02 kg/cm2on the addition of 20% sand. While the free swelling test showed a decrease from 2.28% to 1.29% on the addition of 50% sand. Based on the liquid limit value, plasticity index, and swelling result, Lapindo mud in Sidoarjo is classified as high-plasticity soil. Based on the value ofγdmax, qu, inner shear angle and C.B.R, Lapindo mud is categorized as soil with low carrying capacity. After being mixed with 40% sand, Lapindo mud is classified as medium-plasticity soil with good carrying capacity.