Soil has a very important role in building construction. Soil consists of mineral and
organic particles such as sand, clay, mud, gravel, and other materials. The rapidly
growing contruction industry requires a more comprehensive approach to the use
of land as a contruction material. To overcome various problems that arise, it is
important to understand soil characteristics and construction techniques correctly,
one of which is by increasing soil stability through soil improvement techniques.
Soil improvement using additional materials such as coconut shell charcoal ash is
expected to increase the stability of clay soil in the village of Tanjung Sari,
Kawunganten, Cilacap, Central Java, where roads frequently experience
damage/collapse. Physical tests and mechanical test including direct shear strength
tests will be carried out to see the impact of adding coconut shell charcoal ash on
the stability of the clay soil. This research used a mixture of coconut shell charcoal
ash with percentages of 0%, 5%, 10%, and 15% with curing for 7 days. The test
results showed that the coconut shell charcoal ash mixture increased the shear
strength of clay soil. The largest increase occurred at a mixture percentage of 15%
with a shear stress value of 38,65 kPa, shear angle of 27,62º, normal stress of 23,44
kPa, and cohesion of 26,38 kPa. This research shows the potential for a mixture of
coconut shell charcoal ash to increase the shear strength of clay soil.