The relationship between the plasticity index, the friction angle and the cohesion of the soils in Jakarta during El Niño and La Niña cycles

Abstract. The Indonesian BMKG (Meteorology , Climatology and Geophysics Agency)'s 2009 study on forecasting an El Niño cycle in the same year in Indonesia was a major step forward in understanding and recognizing the various phenomena and factors that could be behind such an event[1]. This study is based on the measurement of air pressure variations between the various Indonesian waters and the Pacific Ocean, the main source of which is the temperature difference between these different areas .An El Niño or La Niña cycles has impacts that can influence soil conditions, so geotechnical studies are needed to understand how soils behave during such a cycle and to take measures to prevent any risks. C. Kuenzer et al. studied variations in soil moisture during the El Niño and La Niña cycles in 2009, with the aim of finding out whether these events have an impact on soils in the different areas concerned. In our study, we will seek to establish relationships between the various parameters needed to describe soils during El Niño cycles. Indeed, the basic parameters for characterizing the mechanical behavior of soils are mainly related to shear strength. Therefore, we are going to study the soils of West Jakarta during the La Niña and El Niño cycles using a correlative approach, which involves understanding the evolution of properties such as the plasticity index (PI), the water content (wc) and the specific density of solid particles in the soil (Gs), as a function of the mechanical parameters (friction angle and cohesion). Referring to the studies of James et al. in 2023, we will look for a linear correlation between the parameters involved and the accepted correlation coefficient r is that r²>0,7. The relationships retained are the variation of the compression coefficient Cc as a function of the cohesion C governed by Cc = -2,7*C+0,714 ; with a correlation coefficient r²=0,748 , the variation in the angle of friction phi as a function of the cohesion C governed by the equation phi = 48,9*C+3,59.