Simple index tests such as penetration tests are available in literature to infer properties of rocks and they are widely used. Particularly the needle penetration test technique is widely used in tunnels excavated in soft rocks. The authors developed a penetration test device which can be also used for medium and high strength rocks. The experimental results indicated that if the nominal strain is defined in terms of penetration displacement divided by rod diameter, the measured responses are independent of rod diameter. This testing technique is applied to various rocks and also to investigate the effect of saturation degree on the properties of soft rocks. In addition to experimental studies, some theoretical and numerical methods are used for how to infer the properties of rocks from the responses measured by this special experimental technique. The developed testing device and experimental results are presented together with those of theoretical and numerical methods. The applicability of the technique in rock engineering is briefly.
The estimations of mechanical properties of intact rocks are generally desired for the assesment of stability of rock structures. They are also important elements of the rock classifications used in empirical assessments of rock masses. Laboratory tests are generally used for this purpose. Nevertheless, they are time consuming due to the sample preparation as well as experimental procedures. Furthermore, they require high capacity loading devices especially for hard rocks. Some penetration tests are available in literature and they are widely used. Among them, the needle penetration test technique is widely used in tunnels excavated in soft rocks. However, there are almost no penetration test technique for medium or high strength rocks. The authors developed a penetration test device utilizing a low capacity loading device and a special rod-like loading platen with a flat-end. This testing technique is applied to various rocks ranging from soft rocks to hard rocks. A theoretical method for interpreting the experimental responses together with the use of numerical methods. This article describes the characteristics of the developed testing device and experimental results together with those of theoretical and numerical methods. It also discusses the applicability of the technique in rock engineering and the potential for further advancement of the method.
The penetration test device utilize a low capacity loading device and a special rod-like loading platen with a flat-end as shown in Figure 1. The device is presently used under laboratory conditions. However it can be easily taken to construction site. The diameter of rod-like platen ranges between 1 to 3 mm. However, experimental results indicates that there are some undesired stress concentrations when the diameter is less than 1mm and the rod-like platen may buckle when For the interpretation of the experimental results, the nominal strain is defined in terms of penetration displacement divided by rod 21 4 diameter. Furthermore, the applied stress is defined by dividing the applied load by the area of the flat-end.