Substructure reinforcement study of Cisomang bridge at Purwakarta-Bandung-Cileunyi toll road, West Java Province, Indonesia

At the end of 2016, significant displacement occurred at P2 pier of Cisomang Bridge at Purwakarta-Bandung-Cileunyi toll road KM 100+700, West Java. The shift of pier is caused by the movement of soil under the substructure that has been indicated since 2012. P2 pier is constructed over clay shale. Clay shale has characteristics when in dry condition, the soil has high shear strength, but when the soil absorbs water or expose in open air, the soil loses its strength. P2 pier displacement results in extreme structural damage, so immediate handling is needed to stop the shifting of the pier. Analysis and reinforcement study are carried out using finite element method. Based on analysis, it is discovered that the existing slope stability safety factor of P2 pier is 1.09, indicating that the soil movement can occur if the clay shale is disrupted. Reinforcement is designed to mitigate the shift of the P2 pier by adding 38 pile foundations to the existing foundation configuration. Each pile has diameter of 1.2 meter with a depth of ±30 meter across the existing slip circle. Reinforcement increases the slope stability safety factor to 1.25, indicating that the P2 pier after reinforcing is in safe condition.