© 2018 by the authors. Licensee MDPI, Basel, Switzerland.Semarang-Demak and other cities along the coast of North Java are vulnerable to land subsidence. The presence of saline groundwater in the coastal region is thought to affect the high subsidence rate, in this case the compressibility of the aquitard layer. We aimed to analyze the effects of groundwater salinity on the compression characteristics of the Semarang-Demak clay using physical analysis. Methods included the determination of groundwater salinity, clay mineralogy and fabrics, and consolidation tests under various salinity conditions. The Semarang-Demak clay is dominated by smectite of high activity, and saline clay exists at the depth of 10 to 35 m. Consolidation tests revealed that the increase insalinity increases the average consolidation rate and hydraulic conductivity up to 42% and 37.5%, respectively. Clay fabric analysis showed that the groundwater salinity modified the interconnectivity of pores by changing the fabric into parallel alignments, facilitating faster porewater dissipation, hence the clay is more readily compressed. These findings are useful for explaining the mechanism of the fast-subsiding coastal plains of North Java.

Clay,Compressibility,Groundwater,Salinity,Semarang-Demak

Acknowledgments: Borehole cores of Semarang-Demak plain were provided by the Research Center for Geotechnology, the Indonesian Institute of Sciences (LIPI) and the Center for Groundwater Resource and Environmental Geology, Indonesian Geological Agency. The support from a P3MI grant (Institut Teknologi Bandung) for field and laboratory work is gratefully acknowledged.

https://doi.org/10.3390/geosciences8040130