Deformation and Stability Analysis of Breakwater Structure in Morosari Coast, Demak, Central Java

Abstract

Indonesia is an archipelagic country with the second longest coastline in the world. The problem faced by coastal areas in Indonesia is the erosion, mainly due to the development of ponds, as happened in Morosari Demak. Several segments of breakwaters from concrete blocks have been constructed. But it has not been able to withstand erosion-, even the breakwaters were damaged. This study is aimed to evaluate the stability and deformation of breakwaters that have been built. Evaluations include armoring stability, soil bearing capacity, land subsidence, and consolidation. Two segments of breakwaters constructed in different years, 2011 (A) and 2013 (B), are evaluated by measuring cross-sectional, and elevation. Measurements were made twice at different times. Changes that occurred during that period were compared with the difference between the initial condition (as built drawing) and the condition when the measurement was done. The results indicated that the breakwater have been deformed both horizontally and vertically. The breakwater tends to move northwest by 6.662 and 8.330 cm/year for breakwater A and B consecutively, and go down by 5.976 and 4.982 cm/year. There are two factors caused breakwater deformation, soil consolidation, and armoring. The consolidation rate measured in 2016 was 4.234 and 5.040 cm/year for breakwater A and B consecutively. The 300 kg of existing armoring was unstable, the stable armoring should be 365 kg.