In Situ Testing of Rock Mass
In situ testing is a process used to measure the mechanical behavior of rock mass in in situ or natural conditions (Ural 2006). This type of testing is not only performed to better understand the existing parameters of the natural rock strata, but to also provide valuable insights into the formation conditions, geotechnical characterization, and performance evaluation of the rock mass (Gabriel et al. 2019). In general, in situ testing takes advantage of specialized equipment and probes to monitor rock properties from various orientation, measurement depths, and all across the rock body. In situ testing of rock mass can yield data that can be used to accurately characterize a rock mass for engineering purposes (Das 2019).
In situ tests for rock mass can be classified into two main categories, direct and indirect tests (Ural 2006). Indirect in situ testing involves observing the effects of experimental changes on the rock mass, such as acoustic emissions or ground movements. Direct in situ testing of rock mass gets its data directly from measurements made with rock mass sensors (Fabris 2006). The type of test and tool that is used to perform in situ tests of the rock mass depends on the type of rock and the purpose of the investigation (Xu 2009).
The goal of any in situ testing of a rock mass is to identify the properties of rock that are important for engineering purposes, such as strength, stiffness, permeability, and deformability (Ural 2006). Generally, direct in situ testing involves taking measurements in three principal mechanical properties of rock, namely uniaxial compressive strength (UCS), tensile strength (TS) and shear strength (SS). Other tests, such as ultrasonic pulse velocity (UPV) and seismic wave velocity (SWV) can also be performed to assess the rock mass and form the basis for calculating the other parameters (Xu 2009).
Direct in situ testing is the most reliable method of gathering data from the rock mass (Ural 2006). It is used to measure the properties of rock in their native form and in the geologic environment. Tests are performed with probes, sensors, or other measuring devices that are inserted into or attached directly to the rock mass. Common devices include pressure cells, penetration testers (mechanical or pneumatic), annular shear cells and tie modules. Instrumentation can also be used to study the temporal and spatial properties of the rock mass (Gabriel etal. 2019).
Indirect testing of rock mass can include experiments such as acoustic emission (AE) tests, temperature measurements, thermal stimulation techniques, and borehole radar techniques (Sharma 2009). These techniques can provide important insights into the physical parameters of the rock mass, such as its internal structure, anisotropy and heterogeneity (Sharma 2009).
In situ testing can provide a more accurate picture of rock masses than laboratory tests. It also has many advantages over traditional laboratory methods. As in situ testing can be performed remotely and in real-time, it reduces the need for in-depth sample collection and testing on site (Ural 2006). As well, in situ tests can provide more reliable results because they are collected in the surrounding environments. This can help to better characterize the performance of a rock mass, giving engineers an edge in the engineering analysis in their future endeavors (Ural 2006).
In conclusion, in-situ testing of rock masses offers scientists and engineers a reliable way to assess the mechanical behavior of rock in its native environment. This method of testing provides data on the properties of rock that are important for engineering purposes. It also offers opportunities for understanding the internal structure and geologic characteristics of a rock mass, in addition to testing its anisotropy and heterogeneity. By taking advantage of these properties, engineers can make more informed decisions on the feasibility and safety of construction projects.
