Rehabilitation and Protection of Bridge Against Landslides: Case Histories at Semarang Ungaran Bridge

Semarang Ungaran highway is geologically located on Miocene clay, which is well-known as clayshale. This material degraded easily upon exposure to air and water. Of particular interest is the bridge between Semarang City and Ungaran which was severely distorted due to ground movement. The bridge consisted of 10 spans with 421.5 m long. It was then found out that bigger and older landslides had been the reason for the whole movement on the bridge. The reactivation of the landslides could be due to high rain intensity and construction activities, however, there was no sign of the movement before the completion of the bridge. Back analysis for the bridge was attempted to estimate the forces on the structural members of the bridge including the foundation. Bored piles have been used under each pier and the abutment and ground anchors have been constructed to protect the slopes. Inclinometers were installed both in soils as well as embedded into the bored piles. The results of inclinometers were used to interpret the shear and bending moments in the piles then the residual strength can be back calculated.