Publisher's Note: Introducing Rock Mechanics Letters

Rough joints are prevalent in natural rock masses, and their shear mechanical properties are crucial for ensuring the safety and stability of these masses. Existing studies often neglect the contribution of various joint asperities to shear stress resistance. This study addresses this gap by eluci-dating the local shear mechanisms of different asperities in rough joints throughout the shear process. This was achieved through a combination of quantitative and qualitative analyses using the Discrete Element Method (DEM). Initially, Barton's ten standard roughness joint profiles were dig-itized, and rough joints were modeled using the Modified Smooth Joint Model (MSJM). Direct shear tests on joint specimens under constant nor-mal stress were performed using servo-controlled methods. Subsequently, the shear stress behavior was analyzed in relation to the test results. The failure modes of the joint specimens were examined in detail using crack tracking and force chain analysis. The study also explored the relation-ship between the number of cracks and shear stress. Additionally, variations in average stress across ten different segments of joints during shear were monitored using the measuring circle function. The shear resistance contributions of local joint segments were quantitatively assessed using three stress indices: maximum stress, upper limit of maximum stress, and the distribution range of maximum stress. The Joint Roughness Coeffi-cient (JRC) of joints was found to correlate well with these indices. Overall, the progressive failure of local joint segments was analyzed both qual-itatively and quantitatively. The study confirmed that the local shear mechanisms of different joint segments during the shear process are distinct.

A rock mass in-situ rotary cutting test system (RMIRCS) was developed to estimate the mechanical properties (i.e. compressive strength and elastic modulus) of rock masses. The pressure-on-bit and torque-on-bit of the RMIRCS were investigated in detail over a wide range of revolution speed and penetration rate. A simple experimental model is proposed to describe the qualitative relationships between rotary cutting test data and mechanical parameters. The existence of a linear constraint between pressure-on-bit and torque-on-bit and the depth of rotary cutting exhibits good agreement with the proposed model. The mechanical properties obtained from the quasi-static compression tests were in agreement with those of the RMIRCS at lower revolutions rate of 300 rpm and 350 rpm, which suggests that the developed RMIRCS is valid. Furthermore, the experimental test results on rock mass demonstrated that the mechanical properties of rock masses are revolutions speed-dependent and drilling rate-dependent.

Dimension stone and terrazzo are quarried rocks following specific dimensions, generally huge in tonnage than ore minerals. Dimension stone and Terrazo resource development opportunities in the Tigray Region, Ethiopia, are studied regarding their potential to make dimension and terrazzo, geology and deposit nature, physio-mechanical properties, rock petrography, and opportunity for exploitation. The granite and marble are quarried as dimension stones and they meet the quality parameters of the rocks, which include, being durable, easy to quarry, work, cut, and polish. It was conducted through the integration of new geological descriptions, interpretation of thin sections, and physico-mechanical tests. Both surface and quarry rock samples were used for the study. 15 from granite and 15 from marble deposits in total 30 samples were used for petrographic analysis and physico-mechanical tests. Based on petrographic and physicomechanical results, granite is harder than marble this may be due to silicates being less dissolved than carbonates. The accessory minerals in both granite and marble deposits limit the quality of the deposits as being impurities. The integrated results indicate that the marble and granite deposits in the area are good in quality and quantity. In addition, they are geologically widespread, technologically do not need sophisticated technology and economically they do not need huge investment and have less effect upon the environment. Diamond wire saws and diamond belt saws separated the dimension stone, which are oblate to curved in shape with 1m width. In the area, investment has been at a relatively low stage more investment will significantly increase production of the dimension stone for local usage, export, and economic growth of the region.

The block caving is one of the most commonly used methods in underground mining of massive, low/high grades, and deep deposits. As a result of undercutting, caving occurs and propagates toward the upper part of the ore block. It is essential to predict the height of caved ore and its volume based on shape of the caved zone to make an economic decision. This paper describes the mechanism of height of the caving zone development. Consequently, four new mathematical models (prismatic, parabolic, cubic, and hemispheric) are proposed to estimate the height of this caving zone. The results are compared with the existing approaches. The proposed methods have proven that the height of caving zone has a linear relationship with the uniaxial tensile and compressive strengths and the height of undercut as well. Also, the height of the caving zone has a negative exponential relationship with unit weight of undercut roof materials and its expansion factor. The Height of the caving zone of the prismatic model is 1.5 times higher than the parabolic model and 1.3 times higher than the hemispheric model. The cubic model estimates the lowest height of the caving zone (0.3 times the height estimated by the prismatic model). The average height of the caving zone, taking the average unit weight of 27 KN/m3 into account, is about 69.4 times the tensile strength, 5.8 times the uniaxial compressive strength of the rock mass, and 18.8 times the height of the undercut.