Applicability of the needle penetrometer

Abstract

In this study the applicability of the needle penetrometer is investigated. The needle penetrometer is a device which gives an indication of the Uniaxial Compressive Strength(UCS) by pushing a needle in a rock and measuring both the penetration depth and the applied force. More specific; research has been done to different needle types, the upper strength limit of the needle penetrometer, the effect of saturation and the relation between the force and the penetration depth. These limits were tested and found with multiple different needles and on multiple different samples. As far as the needles concerned, the Chenille 22 needle is a very good replacement for the Maruto needle. The upper strength limit of the needle penetrometer depends on the needle that is used and the strength of the rock. The average upper limit is around 10 MPa. The cause of this is that there are deviations at the upper strength limit. These deviations make the results of harder rocks less reliable, such as a non-linear penetration rate when gradually putting more pressure on the needle . Saturated rocks are weaker than their dry counterparts. The last conclusion in this study is that the needle penetrometer isn`t the right tool to acquire the data necessary to conclude anything meaningful about the F/d relation, other than that the relation seems to be linear. Since the spread of the acquired data is too wide.