CPT-SPT correlation of volcanic soils in Kediri, East Java

Abstract

CPT-SPT correlation is one of the most common correlations made in geotechnical practice. Researchers have been proposed such correlations for both cohesive and granular soils. However, correlations for a particular soil, for instance, volcanic soils, are still limited. This paper presents CPT-SPT correlations of volcanic soils in Kediri, East Java. Cone penetration tests, namely piezocone test (CPTu), were conducted sideby- side with Standard Penetration Test (SPT). Seventeen CPTu and SPT data pairs were mainly used to develop qt N and fs N correlations. The qt N correlation results qt/N = 2.15 (qt in kg/cm2) with a coefficient of determination R2 of 0.92. This relationship tends to be similar to the same correlation for clay and silty clay materials. A good agreement is also obtained for the fs N correlation, which resulted in fs/N = 9 (fs in kPa) with an R2 of 0.88. Additionally, a standardized SPT N-value (N60) is estimated using a relationship between soil behavior index (Ic) from the CPTu measurement and SPT N-value, suggested by Lunne et al. (1997) and Robertson (2012). Results show that both relationships give 22 to 49 percent lower predicted values of N60 compared to in-situ N60 values. A new correlation, thus, is proposed for this particular soil type, and a better agreement is obtained.