Needle penetration tests are used for inferring the uniaxial compressive strength (UCS) of soft rocks particularly in tunnelling through squeezing rocks in Japan. The device can measure the applied load and the penetration depth of the needle of the device. The ratio of applied load to penetration depth is called needle penetration index (NPI). In this study, this device has been used to infer the physico-mechanical properties of soft rocks from Japan, Turkey and Egypt. Various equations are developed to infer the physico-mechanical properties in terms of needle penetration index (NPI) and compared with experimental results. Some additional equations are presented to consider the effect of water content and cycle numbers of freezing-thawing.
The estimations of mechanical properties of intact rocks are essential for the assessment of stability of geo-engineering structures. Furthermore, they require high capacity loading device especially for hard rocks. Some index testing procedures such as Schmidt hammer, eco-tip and ultrasonic tests are available in literature and they are widely used. Some penetration tests are also available in literature and they are widely used in tunnels excavated in soft rocks and bridge foundations on soft rocks . Penetration tests are often carried out to infer the mechanical properties of soils. A similar approach has been also used for inferring the uniaxial compressive strength (UCS) of soft rocks particularly in tunneling through squeezing rocks and bridge foundations on soft rocks in Japan. According to the suggested method developed by JSCE Rock Mechanics Committee  MARUTO Testing Machine Company  produced a simple penetration-testing device for such a purpose and it has been widely used in many engineering projects involving soft rocks in Japan. There are also some applications to infer the properties of rocks in subduction zones such as Nankai Trough.