MEASUREMENT OF THE DRYING SOIL-WATER CHARACTERISTIC CURVE (SWCC) FOR MATRIC SUCTION IN THE RESIDUAL AREA OF SHALE IN CISOMANG, AND APPLICATION OF THE REGRESSION METHOD TO THE SWCC EQUATION OF FREDLUND AND XING (1994)

• Main Author: Anisa Fanani, Maudy
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/83394
• Institution: Institut Teknologi Bandung

The geotechnical phenomenon in the Cisomang area involves unsaturated shale soils that are susceptible to changes in shear strength due to changes in moisture content. In unsaturated soils, the wet-dry cycle can be quantified using soil-water characteristic curve (SWCC). This study measured matric suction to construct the SWCC of shale in Cisomang using the Leong (2002) filter paper method. The filter paper method uses a calibration curve to determine the matric suction value for the moisture content of the filter paper at equilibrium conditions – the time when equilibrium is reached between the filter paper and the shale sample during curing. The generally recognized recommendations for equilibrium time are only mentioned to be more than 7 days for various moisture contents. This study conducted direct laboratory testing to measure the SWCC of drying shale samples at 5.5% and 6.5% moisture content. Laboratory observations revealed that the average relative humidity of Bandung City in January-June of 77.3% could only accommodate a moisture content of approximately 5.45%. Laboratory measurements resulted in an equilibrium time of 28 days for 5.5% and 6.5% moisture content with filter paper moisture content of 4.34% and 4.74%, respectively. The laboratory measurement results were then used as data to update the fitting curve with the Fredlund and Xing (1994) equation. The resulting drying SWCC parameters are: (1) a = 6809.6; m = 2.4; n = 0.5 in gravimetric moisture content, (2) a = 8115.3; m = 2.0; n = 0.5 in volumetric moisture content, (3) a = 9995.1; n = 2.4; m = 0.5 in degree of saturation. The equilibrium time results of the laboratory measurements were verified with the SEEP/W module of the Geostudio application and resulted in an equilibrium time of 18 days for 5.5% moisture content and 16 days for 6.5% moisture content. Optimization of the iteration process to obtain the regression parameters of the Fredlund and Xing (1994) SWCC equation can be done using the gradient descent method with a cost function in the form of SSE (expressed in parameters a, m, n). The calculation process can be done more efficiently because it does not use the brute-force method.