Development of rod penetration test to measure shear strength of cohesive soil

Abstract

A rod penetrometer was designed and fabricated. In the laboratory the penetration test was performed by this rod penetrometer. From the test results correlations were developed between undrained shear strength and rod penetration for 16 mm and 25 mm diameter rod. In the laboratory, remoulded clay soil samples were prepared at various moisture contents in the range of 20% to 30%. The relation between undrained shear strength and rod penetration is linear for the whole range of water content (20-30%). From 20 to 25% moisture content, the relation is linear with steep slope. From 25 to 30% moisture content, the relation is linear with milder slope. The reason of different slopes before and after at around 25% water content is unkown. Shear strength decreases, in general, with the increase of water content and liquidity index. However, before and after 25% moisture content the slope of the relation is different. The calibration curve which was developed in this study for the portable static rod penetrometer was verified in the field and the verification result was quite satisfactory.