A Heuristic Approach to Predict the Tensile Strength of a Non-Persistent Jointed Brazilian Disc under Diametral Loading

The mechanical response of rock bridges plays a key role in the stability of concrete and rock structures. In particular, the tensile failure of non-persistent discontinuities can result in their coalescence and the failure of rock or concrete engineering structures. The effect of non-persistent joint parameters on rock structures\u27 failure under tensile mode has not been investigated by many researchers yet. Many non-persistent jointed Brazilian concrete discs are tested under diametral loading in this work, to study the influence of joint spacing, joint continuity factor, loading direction with regard to joint angle, and bridge angle on their tensile behavior. Heuristic methods like artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS) and a combination of ANFIS with particle swarm optimization (ANN-PSO) and genetic algorithm (ANFIS-GA) were adopted to explore the relationship between tensile strength and stiffness as the response and non-persistent joint parameters as input parameters. The results revealed that all the applied intelligent methods have the ability to predict tensile strength of non-persistent jointed discs, and their outputs are consistent with laboratory results; however, the ANN approach had the best performance with R2 = 0.966, RMSE = 0.176. In addition, parametric analysis of the proposed model showed that the model is highly sensitive to joint continuity factor and loading direction, while it is sensitive to joint spacing and bridge angle

Support Vector Machines for the Estimation of Specific Charge in Tunnel Blasting

Mine tunnels, short transportation tunnels, and hydro-power plan underground spaces excavations are carried out based on Drilling and Blasting (D&B) method. Determination of specific charge in tunnel D&B, according to the involved parameters, is very significant to present an appropriate D&B design. Suitable explosive charge selection and distribution lead to reduced undesirable effects of D&B such as inappropriate pull rate, over-break, under-break, unauthorized ground vibration, air blast, and fly rock. So far, different models are presented to estimate specific charge in tunnel blasting. In this study, 332 data sets, including geomechanical characteristics, D&B, and specific charge are gathered from 33 tunnels. The data are related to three dams and hydropower plans in Iran (Gotvand, Masjed-Solayman, and Siah-Bishe). Specific charge is modeled in inclined hole cut drilling pattern. In this regard, Support Vector Machine (SVM) algorithm based on polynomial Kernel function is used as a tool for modeling. Rock Quality Designation (RQD) index, Uniaxial Compressive Strength (UCS), tunnel cross-section area, maximum depth of blast hole, and blast hole coupling ratio are considered as independent input variables and the specific charge is considered as a dependent output variable. The modeling results confirm the acceptable performance of SVM in specific charge estimation with minimum error

Numerical Modeling Of Rock Blocks With Nonpersistent Rough Joints Subjected To Uniaxial Compressive And Shear Loadings

Characterizing the mechanical behavior of jointed rocks is important to understand the behavior of structures in rock masses. Jointed rocks can be composed of persistent and nonpersistent joints where the impact of nonpersistent joints requires careful consideration for an accurate rock mass mechanical characterization. Most previous investigations into nonpersistent jointed rocks focused on joints with smooth surfaces, and a few experimental studies focused on nonpersistent rough joints and nothing specific has been reported numerically. Therefore, this study investigated several synthetic jointed rocks with nonpersistent rough joints numerically under uniaxial compressive and shear loadings. The PFC2D-based synthetic rock mass (SRM) approach was adopted to assess the impact of bridge angle (γ) and length (L), joint roughness coefficient (JRC), and normal stress (σn) on the shear strength (τn) and cracking in jointed rocks with nonpersistent rough joints. In addition, the impacts of γ, L, JRC, and joint inclination (θ) on the uniaxial compressive strength (UCS or σcm), elastic modulus (Em), and failure pattern in the jointed blocks were examined numerically. First, several numerical models were developed and verified by the laboratory data, followed by an extensive parametric study to assess the effects of the defined parameters further. The effects of JRC and σn on τn were more pronounced than γ and L due to the formation of interlocking cracks, which could cause significant shear resistance during shear loading. In addition, the numerical results under axial loading revealed that an increase in θ could reduce the deformation modulus and the value of the other parameters, in particular the JRC, could lead to an increase in the strength of jointed samples

Mechanical Behavior of Single-Flawed Cylindrical Specimens Subjected to Axial Loading: A Numerical Investigation

Discontinuities are inherent components of rock masses and can range from fissures to large faults. Single fissures, the so-called flaws, may affect the mechanical behavior of rock mass, crack initiation, and propagation. In this paper, numerical investigations have been conducted on central-flawed cylindrical specimens subjected to axial loading to investigate the effect of flaw angle (α), length (2a), and aperture (A) on their mechanical behavior and crack development. Particle Flow Code (PFC3D) was adopted to investigate the cracking process of the cylindrical specimens and maximum principal stresses at flaw tips. The numerical models are calibrated and verified using extensive experimental tests. The results show that increasing α, UCS, and E increase while increasing 2a decreases UCS and E, and A does not affect these two parameters. Moreover, numerical simulations reveal that as α rises, the three principal stresses generally fall when 2a = 13 and 26 mm. σ1 and σ3 peak at α = 45°, and σ2 reaches a maximum at α = 30° in models with 2a = 39 mm. The cracking patterns resulting from both methods are highly consistent in that tensile cracks type 1 mainly form at α = 15° to 75°, and tensile cracks type 3 are dominant at other angles. Finally, it is concluded that flaw aperture scarcely affects failure patterns

Tensile Behavior of Layered Rock Disks under Diametral Loading: Experimental and Numerical Investigations

The Tensile Strength and Cracking Behavior of Layered Rocks in a Tensile Stress Field Are One of the Most Significant Characteristics of Rock Masses, Which May Strongly Affect the Stability of Rock Structures. the Study Presented Here Investigated the Effect of Layer Spacing and Inclination Angle on the Indirect Tensile Strength, Crack Development, Failure Pattern, and Contact Force Chain of Layered Disks under Diametral Loading using Experimental and Numerical Investigations. Numerous Experimental Models Made from Plaster Were Examined under Diametral Loading, and a Two-Dimensional Particle Flow Code (PFC2D) Was Adopted for in Depth Simulation of the Failure Process. Both Numerical and Experimental Results Were Found to Be in Great Agreement and Showed that the Increase in the Layer Orientation Up to 15° Results in the Peak in the Tensile Strength Followed by a Decrease. Specimens with the Spacing Ratio (SR) of 0.5 and 0.1 Showed the Highest and Lowest Tensile and Compressive Stresses at the Disk Center, respectively. Moreover, the Numerical Analysis Indicated the Formation of Three Failure Pattern Types: TL, PB, and TL-PB. Tensile Cracks Mainly Formed in the Direction of Diametral Loading, and their Maximum Number Formed at 15° and SR = 0.5. Additionally, the Shear Ones Formed in a Conjugate System and Had Negligible Numbers. the Analysis of the Contact Force Chain Showed that the Layers Do Not Affect the Compressive Force Chain at Α \u3c 45° But at Higher Angles, the Stronger Layers Transfer Compressive Force. However, when Α Ranges from 0° to 30°, Tensile Forces Are Distributed in Stronger Layers, and with an Increase in Α, the Concentration of These Forces in These Layers Diminishes and the Forces Are Reoriented in the Direction of Diametral Loading

Correction To: A Heuristic Approach to Predict the Tensile Strength of a Non-Persistent Jointed Brazilian Disc under Diametral Loading (Bulletin of Engineering Geology and the Environment, (2022), 81, 9, (364), 10.1007/s10064-022-02869-8)

Originally, there is a mistake in the affiliation of the third author. Taghi sherizadeh has just one affiliation as follows: Department of Mining and Nuclear Engineering, Missouri, University of Science and Technology, Rolla, MO 65409, USA The original article has been corrected

A laboratory study on mix design to properly resemble a jointed brittle rock

In this paper attempts have been done to create a mortar with relatively high uniaxial compressive strength (UCS), easy casting, high flexibility, instant hardening, low cost and easy availability. The main use of this material is to physically model the mechanical behavior of jointed rock-like blocks. The effect of four parameters such as joint roughness coefficient (JRC), bridge length (L), bridge angle (γ) and joint inclination (θ) on UCS of non-persistent jointed blocks were studied. For this purpose, 35 cylindrical specimens with a broad range of plaster content (P) and cement content (C) in different ages were tested. In order to increase the strength of blocky specimens, some retarder and lubricant were used. The results showed that using 3 wt. % (Weight percent) lubricant MGAR106 and 0.05 wt. % Retarder decreases water content by 12.5% and increases plaster and cement content of 8.3% and 4.17 % respectively. Consequently, UCS of blocky specimens increased by 284.33%. In order to formulize the effect of P/C content and the age of cylindrical specimens (A) on UCS, Multivariate Non-linear Regression (MNR) and Bayesian Regularized Artificial Neural Network (BRANN) models were deployed. The results showed that BRANN approach can provide more exact predictions of the specimen UCS than MNR model. Moreover, P/C content had more influence on UCS than the specimen age. Finally the UCS tests on blocky specimens indicated that increasing JRC, bridge length and bridge angle increases UCS and it takes its minimum ate joint inclination of 60°. Furthermore, the capability of produced material to model cracking behaviour of jointed blocks was approved

Prediction of representative deformation modulus of longwall panel roof rock strata using Mamdani fuzzy system

Deformation modulus is the important parameter in stability analysis of tunnels, dams and mining structures. In this paper, two predictive models including Mamdani fuzzy system (MFS) and multivariable regression analysis (MVRA) were developed to predict deformation modulus based on data obtained from dilatometer tests carried out in Bakhtiary dam site and additional data collected from longwall coal mines. Models inputs were considered to be rock quality designation, overburden height, weathering, unconfined compressive strength, bedding inclination to core axis, joint roughness coefficient and fill thickness. To control the models performance, calculating indices such as root mean square error (RMSE), variance account for (VAF) and determination coefficient (R2) were used. The MFS results show the significant prediction accuracy along with high performance compared to MVRA results. Finally, the sensitivity analysis of MFS results shows that the most and the least effective parameters on deformation modulus are weathering and overburden height, respectively. Keywords: Deformation modulus, Dilatometer test, Mamdani fuzzy system, Multivariable regression analysi

The Evolution of Dynamic Energy during Drop Hammer Testing of Brazilian Disk with Non-Persistent Joints: An Extensive Experimental Investigation

Rock mass is well known as a discontinuous, heterogeneous, and anisotropic material. The behavior and strength of rock mass is heavily controlled by the condition and orientation of discontinuities (faults, joints, bedding planes) and discontinuity sets. Under dynamic loading conditions, rock bridges along non-persistent discontinuity planes may crack, and a fully persistent discontinuity may form, potentially affecting the stability of a rock structure. The study of the dynamic behavior of rock discontinuities has critical implications for civil engineering, the mining industry, and any other areas where rock mass is utilized as a structural foundation in areas prone to dynamic loading conditions, such as those formed during earthquake events. In this paper, cement-mortar-based Brazilian disks containing open, non-persistent joints were constructed and subjected to impact loading to investigate their impact energy behavior. The effect of some parameters, such as joint continuity factor (the relationship between joint length and rock bridge length), bridge angle, joint spacing, joint orientation, and impact angle were investigated to estimate the required Dynamic Energy for Crack Initiation (DECI), Dynamic Energy for Crack Coalescence (DECC) and failure pattern of specimens. The results of the experiments revealed an increasingly continuous joint reduces the DECI and DECC, while larger joint spacings past the middle value of those experimented increase the DECI and DECC. The bridge angle and loading direction do not affect DECI, but by increasing bridge angle DECC decreases, and it increases by increasing loading direction angle. Finally, an optimization analysis was conducted which showed that joint spacing and joint continuity factors significantly affects DECI, and joint continuity factor and loading direction have significant effect on DECC

Compressive Strength of Flawed Cylindrical Specimens Subjected to Axial Loading

Discontinuities are known to have a significant impact on the engineering characteristics of the rock masses, governing their potential failure pattern, increasing their deformation, and reducing their strength. In particular, the impact of non-persistent joints on the strength and failure mechanism of rock mass needs to be investigated further. The impact of different flaw geometrical characteristics such as flaw inclination, flaw length, flaw aperture, and flaw filling on uniaxial compressive strength of specimens has not been investigated thoroughly. In this paper, a series of uniaxial compression tests were conducted on cylindrical specimens containing an open central flaw. The effect of different parameters such as flaw inclination, flaw length, flaw aperture, and filling on the uniaxial compressive strength of specimens have been investigated through laboratory experiments. Response Surface Methodology (RSM) is adopted to analyze the impact of flaw parameters on the compressive strength of the constructed samples. The results of the experiments show that flaw inclination and flaw length have a significant impact on the peak strength of the samples, meaning that strength increases by growing of flaw angle and decreases by increasing of flaw length. In addition, at a low flaw length, aperture affects the UCS significantly, while by increasing flaw length, its effect decreases dramatically, and strength drops at a flaw inclination of 45 degrees. Conversely, at a higher flaw length, by increasing flaw inclination, the UCS increases constantly. It also has been observed that changing the flaw aperture had no important effect on the peak strength