asis Deb

Failure Process of Brittle Rock Using Smoothed Particle Hydrodynamics

AbstractThis paper presents a numerical procedure based on smoothed particle hydrodynamics (SPH) to analyze the failure process of a rock medium by predicting the initiation of microcracks. The subsequent propagation of cracks has also been analyzed without any special treatment or assumption regarding fracturing process. The procedure for implementing softening elastoplastic model has been discussed in the SPH framework. For failure of a rock specimen under uniaxial compression, the Drucker-Prager yield criterion is used in the elastic-plastic constitutive model by considering associative and nonassociative plastic flow rules. The Rankine maximum tensile failure criterion is implemented to model the tensile failure of a circular rock specimen. The results obtained from this study have been compared with laboratory tests and existing analytical solutions. It is found that the developed procedure has the potential to provide useful information to understand the key physical phenomena that occur in the fail...

Automatic detection and analysis of discontinuity geometry of rock mass from digital images

The inaccessibility of rock exposures is an inherent problem in geotechnical data acquisition that compromises effective geotechnical evaluation. The digital image processing method is a tool that permits a fast, complete, and accurate acquisition of information. Using digital images in photogrammetry, the present study analyzes the discontinuity geometry of rock mass exposures. The study has demonstrated that (a) the transformation function is appropriate for images without any perspective error; (b) the developed system is versatile and can detect both lines as well as curves in multilinear form; (c) the Hough transform algorithm can provide excellent results for rock mass with multiple joint sets having considerable amount of noise; and (d) the beamlets can be classified in an automated manner. The authors recommend the digital face mapping method to characterize rock masses, as it reduces the time spent in the field, thus preserving data integrity. Furthermore, this technique allows for systematic mapping and the building of a permanent and huge database for rock mass characterization.

Numerical Analysis of an Interaction between Hydraulic-Powered Support and Surrounding Rock Strata

AbstractLongwall mining is the only technically proven and well-established mining method used worldwide for extracting coal from deep mines. In this paper, two-dimensional (2D) continuum finite-element models of longwall panels are developed and analyzed to understand the interaction of hydraulic-powered support with surrounding rock strata (i.e., roof, floor, and coal seam). The finite-element models thus developed include the structural components of hydraulic-powered support, the surrounding rock mass, and broken rocks. The study focuses on the evaluation of strata behavior while the coal face is supported by hydraulic-powered supports of different capacities. The results from finite-element models are further analyzed in terms of stress distribution in hydraulic legs, abutment, and roof-to-floor convergence. Statistical relations are developed based on deterministic finite-element results, which provide a good correlation with the field measurements.

Evaluation of the role of a cationic surfactant on the flow characteristics of fly ash slurry.

Transportation of fly ash is a major problem in its efficient disposal. The main problem associated with fly ash transportation is that the particles settle down sooner than desired. The primary objective of this research is that not only the fly ash particles should remain floated till it reaches the end but also settle down after that. In this investigation the role of a drag-reducing cationic surfactant and a counter-ion has been evaluated to achieve the objectives. The experimental results show encouraging trends of surfactant helping fly ash particles to remain water-borne. The material exhibited Newtonian behavior. This paper describes these in term of shear rates, shear stress, temperature, concentration and viscosity. Rheological tests were conducted using Advanced Computerized Rheometer. Zeta potential was measured to test the stability of the colloidal fly ash particles using Malvern Zeta Sizer instrument. Surface tension was also measured to know the drag reduction behavior of the fly ash slurry by using Surface Tensiometer. The test results and flow diagrams were generated using Rheoplus software and are presented in this paper. Surfactant concentration of 0%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5% by weight was mixed with equal amount of counter-ion and the slurry was prepared by adding fly ash with ordinary tap water to achieve the desired solid concentration of 20% (by weight).

Bolt-Grout Interactions in Elastoplastic Rock Mass Using Coupled FEM-FDM Techniques

Numerical procedure based on finite element method (FEM) and finite difference method (FDM) for the analysis of bolt-grout interactions are introduced in this paper. The finite element procedure incorporates elasto-plastic concepts with Hoek and Brown yield criterion and has been applied for rock mass. Bolt-grout interactions are evaluated based on finite difference method and are embedded in the elasto-plastic procedures of FEM. The experimental validation of the proposed FEM-FDM procedures and numerical examples of a bolted tunnel are provided to demonstrate the efficacy of the proposed method for practical applications.

Rock failure analysis using smoothed-particle hydrodynamics

This paper presents a numerical simulation for predicting fracture and failure growth of geomaterial using smoothed-particle hydrodynamics (SPH). The first example deals with slope stability analysis of a chromite mine having friable chromite as the ore body. The ultimate pit may reach up to 144 m below the surface with an ultimate pit angle of 30° for 19 benches. It is require to forecast the stability of the ultimate pit slope for a given material and pit geometry. This paper analyses the stability of this slope by considering Drucker–Prager rock mass medium using the SPH procedure. The second example comprises the fracture growth of a circular rock specimen under diametrically opposite concentrated angular loads. In order to determine the plastic regime of the specimen for a given tensile strength, the Rankine maximum tensile failure criterion is implemented in the SPH framework.

Estimation of blast induced peak particle velocity at underground mine structures originating from neighbouring surface mine

Abstract Surface blasting may cause ground vibration in underground mine workings affecting their structural stability and resulting in loss of coal production. The effects of surface blasting on adjacent underground workings have been studied using peak particle velocity (PPV) measured at various locations in two underground Bord and Pillar mines. Predictor equations of PPV have been developed based on distance D from the source of blasting and charge (explosive quantity) per delay Q. This study finds that the Q0·50 factor, generally used in predictor equations of PPV, may not be applicable when estimating PPV at an underground location. Depending on the number and composition of rock strata through which stress waves are transmitted from the surface to underground, Q0·35 or Q0·26 factors may be appropriate for estimating the scaled distance, which is considered as a measure of PPV. The present paper also compares the results of forecast PPVs using both regression analysis and neural network techniques.

Optical strain for monitoring of concrete failure mechanism with discontinuity

Finite-element-based digital image correlation (FEM-DIC) is one of the most widely used noncontact techniques in the field of experimental mechanics for measurement of deformation/strain. In this paper, the FEM-DIC method is refined by introducing the concept of multilevel extended digital image correlation (X-DIC), which also can capture deformation across discontinuity planes if they exist in images. Using regular and enhanced displacements at each node, strain tensors are estimated by applying the concept of smooth particle hydrodynamics (SPH). Numerical works are carried out to check the accuracy level of the developed algorithm by considering discrete discontinuity on the surface of a sample. Work is further extended to determine displacements and strains developed at the surface of several cubical concrete samples under uniaxial loading conditions. The tests are conducted until fractures are developed in the post-failure region. Using the concept of cumulative effective strain, a parameter is identified, which can be used as a precursor in the object failure process.

An enhanced numerical procedure for modelling fully grouted bolts intersected by rock joint

The stability of underground structure made especially in jointed rock mass is of the utmost important to designer, engineers and operators. Rock bolting is generally being practised to reinforced excavation walls and roofs by minimizing the movement of rock joints. In this study, a numerical procedure has been developed in extended finite element framework (XFEM) to analyze the behaviour of grouted bolt intersected by a joint. A solid finite element intersected by a bolt and a joint along any arbitrary direction is termed as ‘doubly enriched’ element. Nodes of an doubly enriched element have additional degrees of freedom for determining displacements, stresses developed in the bolt rod as well as the displacements jump and traction along the joint. The paper also provides verifications of this procedure by solving two known examples (i) direct shear test performed on a bolted joint sample-experimental verification and (ii) reinforcement of a joint located in the vicinity of a circular tunnel-analytical verification.

Analysis of chock shield pressure using finite element method and face stability index

Abstract The major causes of longwall failure in India are identified to be inadequate selection of powered support, incomplete investigation of geomining conditions, unavailability of spare parts and lack of knowledge for longwall operations. This study focuses on the first and second causes of failures which are to identify and understand the strata behaviour at longwall face. Based on geomining conditions of Indian longwall mines, 324 finite element models were developed to analyse the interaction of surrounding strata with four legged chock shield support, the popular powered support in India. Models thus developed were used to investigate the effect of parameters such as coal type, powered support capacity, elastic modulus, friction angle, thickness of main roof rock and depth of working on longwall face stability in terms of leg pressure, roof to floor convergence and peak abutment pressure. Statistical relations are also developed based on the data generated from finite element models. An index called face stability index (FSI) is also developed for easy estimation of front leg pressure for any longwall panel. Validation of the statistical models is carried out with the monitored shield pressure data collected from two longwall panels.