The Influence of Pre-Existing Deformation and Alteration Textures on Rock Strength, Failure Modes and Shear Strength Parameters

Abstract

This study uses the uniaxial compressive strength (UCS), the indirect tensile strength (ITS) and the point load tests (PLT) to determine the strength and deformation behavior of previously deformed and altered tonalite and anorthosite. In general, veined samples show higher strength because the vein material has both cohesive and adhesive properties while fractures have no cohesion, only frictional resistance. This implies that each rock category has to be treated independently and absolute strength predictions are inaccurate. Thus, the conversion factor k is a sample specific parameter and does not have a universal value. The ratio of UCS/ITS appears to be related to the rock strength and can be used to classify rocks based on their strength. The shear strength parameters, the friction angle and the cohesion, cannot be calculated for rocks with pre-existing planes of weakness. Reactivation is favoured only for planes oriented less than 20 • to the maximum stress. For planes oriented between 20 • and 50 • to the maximum stress, failure occurs by a combination of reactivation and newly formed fractures, while for orientations above 50 • , new shear fractures are favoured. This suggest that the Byerlee's law of reactivation operates exclusively for planes oriented ≤10 • to the maximum stress.

Empirical correlation of uniaxial compressive and shear strength of jointed granitic rock

“…Based on the observation, the orientation of samples that have been tested failed along with pre-existing weakness [12]. This condition proved that even though the rock sample looks intact and categorized in weathering grade II, there is an appearance of weakness plane inside it and potentially will form rock joints throughout the weathering process.…”

From Crystals to Crustal‐Scale Seismic Anisotropy: Bridging the Gap Between Rocks and Seismic Studies With Digital Geologic Map Data in Colorado

“…One is that igneous rocks commonly intrude along preexisting foliations (e.g., Brown & Solar, 1998; Hutton, 1988; Mahan et al., 2003; Paterson et al., 1989). Another is that preexisting mechanical heterogeneities influence subsequent deformation as demonstrated in mechanical theory (e.g., Griffith, 1924), laboratory experiments (e.g., Byerlee, 1978; Everall & Sanislav, 2018), and regional geologic studies (e.g., Burchfiel & Davis, 1975; Dunbar & Sawyer, 1988; Nadin & Saleeby, 2010).…”

Structural Control of Ore Deposits: The Role of Pre-Existing Structures on the Formation of Mineralised Vein Systems

“…This cannot be enough for affirming the link between mineralisation and granite activity but strongly argued for this and re-addressed the discussion concerning the characteristics of orogenic and intrusion-related gold deposit (IRGD) [62,63]. (v) Competency contrasts in a volume of rock also appear to be a favourable factor for ore concentration and vein formation [64], as shown herein for the Achmmach tin deposit and Mina Soriana W. In these cases, rheological variation was not due to original lithological differences, but induced during early stages of the mineralisation event itself, by heterogeneous alteration. It has been argued that tin mineralisation could not have formed in the Achmmach domain without earlier development of a tourmaline halo within the monotonous calc-schist.…”