Abstract
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.
Highlights
The sinking of land surfaces is threatening coastal areas all over the world and affects almost half a billion people living on or near the coast [1]
This study aims to analyze the effects of groundwater salinity on the compressive characteristics of saline clay using physical analysis
We examine the correlation between groundwater salinity and clay consolidation indices and validate the experimental results with a clay fabric analysis, emphasizing the importance of the groundwater salinity effect to the land subsidence mechanisms in the study area and in other North Java cities
Summary
The sinking of land surfaces is threatening coastal areas all over the world and affects almost half a billion people living on or near the coast [1]. More than 150 areas across the world are affected by contemporary land subsidence; most of these areas are located in coastal regions [3], such as Shanghai [4], Hanoi [5], Bangkok [6], and Mekong delta, Vietnam [7]. The high rate of land subsidence in the coastal area is primarily related to the aquifer-aquitard system compaction due to the abstraction of groundwater [2,12,13,14], other factors such as natural compaction could coexist [15,16]. Exploitation of the confined groundwater reduces the piezometric pressure of the aquifer.As the piezometric pressure drops, the total stress of the aquifer-aquitard system remains constant; the effective stress increases
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