SUMMARY
Clay soil is a type of soil that has characteristics, namely low carrying capacity and large swelling and shrinkage, this makes clay soil a poor material for construction work. Civil building construction subgrade shear strength and California Bearing ratio (CBR) value influence the planning of a building. CBR is a comparison between the test load and the Standard Load and is expressed as a percentage. The CBR value was developed to measure the bearing capacity, soil load. The soil stabilization process includes mixing with gypsum material (C2SO4) to obtain the desired gradation so that soil properties become better with calcium levels which bind organic matter soil to clay and also absorb more water which is very useful for strengthening the soil. Testing the California Bearing Ratio (CBR) and direct shear strength of the soil (Direct Shear Test) by adding a different percentage of Gypsum (CaSO4) occurs in the addition of 6% Gypsum in 56 collisions with a value of 48%, in collisions 10 and 25 times the CBR value Optimum occurs in the percentage of 7% gypsum with a value of 27.48% and 28.5%, and the effect of adding gypsum on the cohesion value and the optimum internal friction angle occurs in the addition of 6% lime with a value of 0.017 MPa and 24.93o.