<![CDATA[Volcanic residual soils in tropical regions exhibit unique engineering behavior that differs significantly from sedimentary soils. These soils often contain amorphous clay minerals such as allophane and halloysite, which contribute to their sensitivity and unusual strength characteristics. Field observations in West Java revealed near-vertical, free-standing cuts up to 12 meters high, indicating apparent cohesion supported by natural cementation and unsaturated conditions. A geotechnical investigation was carried out using standard penetration tests (SPT), cone penetration tests with pore pressure measurement (CPTu), and laboratory tests including Atterberg limits, index properties, and unconsolidated-undrained triaxial tests. Results show that Su values obtained from CPTu are more consistent with laboratory triaxial data, while SPT correlations tend to underestimate strength due to sample disturbance. Furthermore, particle size analyses confirm the gap-graded nature of volcanic residual soils, reflecting differential weathering processes. This study aims to establish representative undrained shear strength parameters of sensitive volcanic residual soils in West Java by integrating field and laboratory investigations. The findings highlight the importance of careful sample handling, the use of less-disturbing in-situ tests, and the selection of appropriate testing methods to obtain reliable soil parameters for engineering design. These findings provide practical implications for the characterization and modeling of sensitive volcanic residual soils in engineering applications.]]>
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