DEVELOPMENT OF PORE WATER PRESSURE AND DISPLACEMENT IN LIQUEFACTION OF STRATIFIED SAND WITH A CAPPING LAYER

Abstract

The 2018 Palu earthquake (Mw 7.5) caused extensive damage due to liquefaction of saturated sand deposits, even in areas with gentle slopes The presence of a capping layer overlying loose sand deposits is suspected to have exacerbated liquefaction conditions. This study aims to analyze the influence of such a capping layer on excess pore water pressure and lateral displacement in stratified sand. Laboratory tests were conducted using a shaking table. The soil model was prepared in an acrylic box measuring 150×40×50 cm with configurations of dense sand (DS), loose sand (LS), and medium sand (MS). These configurations were tested both with and without a silt capping layer. The shaking table harmonic motion input with an amplitude of 2cm and a frequency of 1.4Hz. The Pore water pressure transducers were installed to monitor the development of pore water pressure ratio (Ru) during dynamic loading. This mechanism is relevant to field liquefaction cases, such as the 2018 Palu event, where a low-permeability layer intensified pore-pressure buildup and prolonged deformation. The results show that the presence of a capping layer significantly affected soil response. Test with a capping layer exhibited faster, higher, and longer-lasting increases in Ru, (persisting for >80 seconds. In addition, lateral displacement in the model with a capping layer was significantly larger (±4.6cm) than in the model without one (<0.89 cm). These findings indicate that a capping layer not only accelerates and prolongs liquefaction by impeding the dissipation of pore water pressure but also amplifies the magnitude of lateral displacement.