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Volumen 35 (2013): Heft 4 (December 2013)

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Volumen 35 (2013): Heft 2 (June 2013)

Volumen 35 (2013): Heft 1 (March 2013)

Volumen 34 (2012): Heft 4 (December 2012)

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Volumen 34 (2012): Heft 2 (June 2012)

Volumen 34 (2012): Heft 1 (March 2012)

Zeitschriftendaten
Format
Zeitschrift
eISSN
2083-831X
ISSN
0137-6365
Erstveröffentlichung
09 Nov 2012
Erscheinungsweise
4 Hefte pro Jahr
Sprachen
Englisch

Suche

Volumen 38 (2016): Heft 1 (March 2016)

Zeitschriftendaten
Format
Zeitschrift
eISSN
2083-831X
ISSN
0137-6365
Erstveröffentlichung
09 Nov 2012
Erscheinungsweise
4 Hefte pro Jahr
Sprachen
Englisch

Suche

13 Artikel
access type Uneingeschränkter Zugang

Estimation of spatial variability of lignite mine dumping ground soil properties using CPTu results

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 3 - 13

Zusammenfassung

Abstract

The paper deals with application of CPTu test results for the probabilistic modeling of dumping grounds. The statistical measures use results from 42 CPT test points located in the lignite mine dumping ground from the region of Central Europe. Both the tip resistance qc as well as local friction fs are tested. Based on the mean values and standard deviations of measured quantities the specific zones in the dumping site profile are distinguished. For three main zones standard deviations of linearly de-trended functions, distributions of normalized de-trended values for qc and fs are examined. Also the vertical scales of fluctuation for both measured quantities are estimated. The obtained result shows that lignite mine dumping site can be successfully described with the Random Field Theory. Additional use of fs values introduces supplementary statistical information.

Schlüsselwörter

  • Random Field Theory
  • fluctuation scale
  • CPTu testing
  • dumping ground soil
access type Uneingeschränkter Zugang

Numerical analysis of road pavement thermal deformability, based on Biot viscoelastic model of porous medium

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 15 - 22

Zusammenfassung

Abstract

The following study presents numerical calculations for establishing the impact of temperature changes on the process of distortion of bi-phase medium represented using Biot consolidation equations with Kelvin–Voigt rheological skeleton presented, on the example of thermo-consolidation of a pavement of expressway S17. We analyzed the behavior of the expressway under the action of its own weight, dynamic load caused by traffic and temperature gradient. This paper presents the application of the Biot consolidation model with the Kelvin–Voigt skeleton rheological characteristics and the influence of temperature on the deformation process is taken into account. A three-dimensional model of the medium was created describing the thermal consolidation of a porous medium. The 3D geometrical model of the area under investigation was based on data obtained from the land surveying and soil investigation of a 200 m long section of the expressway and its shoulders.

Schlüsselwörter

  • Biot theory
  • thermal consolidation
  • rheological body of Kelvin–Voigt
  • road pavement
access type Uneingeschränkter Zugang

Stability analysis of underground mining openings with complex geometry

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 25 - 32

Zusammenfassung

Abstract

Stability of mining openings requires consideration of a number of factors, such as: geological structure, the geometry of the underground mining workings, mechanical properties of the rock mass, changes in stress caused by the influence of neighbouring workings. Long-term prediction and estimation of workings state can be analysed with the use of numerical methods. Application of 3D numerical modelling in stability estimation of workings with complex geometry was described with the example of Crystal Caves in Wieliczka Salt Mine. Preservation of the Crystal Caves reserve is particularly important in view of their unique character and the protection of adjacent galleries which are a part of tourist attraction included in UNESCO list. A detailed 3D model of Crystal Caves and neighbouring workings was built. Application of FLAC3D modelling techniques enabled indication of the areas which are in danger of stability loss. Moreover, the area in which protective actions should be taken as well as recommendations concerning the convergence monitoring were proposed.

Schlüsselwörter

  • stability analysis of underground workings
  • complex geometry and geological structure
  • 3D numerical modelling
  • Wieliczka Salt Mine
access type Uneingeschränkter Zugang

Stochastic Finite Element Analysis using Polynomial Chaos

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 33 - 43

Zusammenfassung

Abstract

This paper presents a procedure of conducting Stochastic Finite Element Analysis using Polynomial Chaos. It eliminates the need for a large number of Monte Carlo simulations thus reducing computational time and making stochastic analysis of practical problems feasible. This is achieved by polynomial chaos expansion of the displacement field. An example of a plane-strain strip load on a semi-infinite elastic foundation is presented and results of settlement are compared to those obtained from Random Finite Element Analysis. A close matching of the two is observed.

Schlüsselwörter

  • foundation settlements
  • stochastic finite element
  • polynomial chaos
access type Uneingeschränkter Zugang

Large deformation finite element analysis of undrained pile installation

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 45 - 54

Zusammenfassung

Abstract

In this paper, a numerical undrained analysis of pile jacking into the subsoil using Abaqus software suit has been presented. Two different approaches, including traditional Finite Element Method (FEM) and Arbitrary Lagrangian–Eulerian (ALE) formulation, were tested. In the first method, the soil was modelled as a two-phase medium and effective stress analysis was performed. In the second one (ALE), a single-phase medium was assumed and total stress analysis was carried out. The fitting between effective stress parameters and total stress parameters has been presented and both solutions have been compared. The results, discussion and verification of numerical analyzes have been introduced. Possible applications and limitations of large deformation modelling techniques have been explained.

Schlüsselwörter

  • Abaqus
  • Arbitrary Lagrangian–Eulerian
  • ALE
  • FEM
  • Pile jacking
  • Pile installation
  • Undrained analysis
access type Uneingeschränkter Zugang

Magneto-rotatory compressible couple-stress fluid heated from below in porous medium

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 55 - 63

Zusammenfassung

Abstract

The study is aimed at analysing thermal convection in a compressible couple stress fluid in a porous medium in the presence of rotation and magnetic field. After linearizing the relevant equations, the perturbation equations are analysed in terms of normal modes. A dispersion relation governing the effects of rotation, magnetic field, couple stress parameter and medium permeability have been examined. For a stationary convection, the rotation postpones the onset of convection in a couple stress fluid heated from below in a porous medium in the presence of a magnetic field. Whereas, the magnetic field and couple stress postpones and hastens the onset of convection in the presence of rotation and the medium permeability hastens and postpones the onset of convection with conditions on Taylor number. Further the oscillatory modes are introduced due to the presence of rotation and the magnetic field which were non-existent in their absence, and hence the principle of exchange stands valid. The sufficient conditions for nonexistence of over stability are also obtained.

Schlüsselwörter

  • compressible couple-stress fluid
  • thermal convection
  • porous medium
  • rotation
  • magnetic field
access type Uneingeschränkter Zugang

Durability of crystalline phase in concrete microstructure modified by the mineral powders: evaluation by nanoindentation tests

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 65 - 74

Zusammenfassung

Abstract

This paper presents the nanoindentation investigation of the evolution of concrete microstructure modified by the Internal Crystallization Technology mineral powders. The samples under study were retrieved from a fragment of a circular concrete lining of the vertical mine shaft at a depth of approximately 1,000 m. Due to the aggressive environment and exposure to contaminated water, the internal surface of the structure was deteriorated, decreasing its strength significantly. The mineral powders were applied directly on the surface lining. The specimens were investigated one month, three months and one year after the application of the aforementioned substance in order to verify the time dependence of the strengthening processes and durability of the crystalline phase. The microstructural changes of concrete were assessed with the use of nanoindentation technique. The testing procedure involved including the previously cut specimens in the epoxy resin and grinding and polishing in order to reduce the surface roughness. As a result of the nanoindentation tests the hardness as well as Young’s modulus of the material were evaluated. The results were then compared and statistically analyzed. As a consequence, the disintegration time of the crystalline network in the pores of concrete was identified.

Schlüsselwörter

  • nanoindentation
  • concrete
  • Internal Crystallization Technology
  • microstructure
  • durability
access type Uneingeschränkter Zugang

Tunnel support design by comparison of empirical and finite element analysis of the Nahakki tunnel in mohmand agency, pakistan

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 75 - 84

Zusammenfassung

Abstract

The paper analyses the geological conditions of study area, rock mass strength parameters with suitable support structure propositions for the under construction Nahakki tunnel in Mohmand Agency. Geology of study area varies from mica schist to graphitic marble/phyllite to schist. The tunnel ground is classified and divided by the empisical classification systems like Rock mass rating (RMR), Q system (Q), and Geological strength index (GSI). Tunnel support measures are selected based on RMR and Q classification systems. Computer based finite element analysis (FEM) has given yet another dimension to design approach. FEM software Phase2 version 7.017 is used to calculate and compare deformations and stress concentrations around the tunnel, analyze interaction of support systems with excavated rock masses and verify and check the validity of empirically determined excavation and support systems.

Schlüsselwörter

  • rock mass strength parameters
  • rock mass classification
  • FEM analysis
  • Phase2
  • tunnel support design
access type Uneingeschränkter Zugang

Preliminary calculation of irregular triguy mast support

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 85 - 90

Zusammenfassung

Abstract

The instantaneous tangential rigidity (corresponding to the applied horizontal load) of a triguy support with unequal ropes is determined. The differences between the ropes can be due to the different location, both horizontal and vertical, of their anchoring foundations and to the different types of ropes used. The horizontal rigidity of such a support has no general axis of symmetry. Therefore a formula for this rigidity in any direction and a formula for extreme rigidity angles are given in this paper. A notion of the guy’s eigenvalue, standing for the initial tension force above which the guy participates effectively in the support’s rigidity, is introduced. A numerical example is provided.

Schlüsselwörter

  • mast
  • irregular triguy support
  • initial tension values
  • forces in guys
  • numerical example
access type Uneingeschränkter Zugang

Effect of increasing mining rate on longwall coal mining – Western donbass case study

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 91 - 98

Zusammenfassung

Abstract

This paper presents the problems associated with the rapid change of the rock stress-strain state in terms of increasing the rate of coal mining. Parameters of the roof collapse are determined depending on the rate of a longwall advancing under conditions of poor rocks. Statistical data are processed to obtain a general trend concerning the mining rate impact on the roof collapse. The statistical strength theory is applied to explain the increase in mined-out space and the size of hanging roof behind a coal face. Numerical simulation is carried out to determine a critical size of mined-out space that provokes a roof collapse. The area of yielded rocks is outlined using the criterion developed taking into account the rate of longwall advancing. A general regularity is obtained to determine the roof collapse parameters. The developed technics gives a possibility to predict the moment of general roof collapse at the initial stage of longwalling to prevent the negative effect of the rapid stress redistribution provoking joints propagation and intensive gas release. The estimation of the rock stress-strain state considering the rate of mining operations can be useful for tasks related to a new technology implementation. The statistical strength theory and failure criterion applied together provides adequate planning of mining activities and the assessment of natural hazards.

Schlüsselwörter

  • rock
  • stress-strain state
  • mining rate
  • failure criterion
  • roof collapse
access type Uneingeschränkter Zugang

Recovery of microstructure properties: random variability of soil solid thermal conductivity

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 99 - 107

Zusammenfassung

Abstract

In this work, the complex microstructure of the soil solid, at the microscale, is modeled by prescribing the spatial variability of thermal conductivity coefficient to distinct soil separates. We postulate that the variation of thermal conductivity coefficient of each soil separate can be characterized by some probability density functions: fCl(λ), fSi(λ), fSa(λ), for clay, silt and sand separates, respectively. The main goal of the work is to recover/identify these functions with the use of back analysis based on both computational micromechanics and simulated annealing approaches. In other words, the following inverse problem is solved: given the measured overall thermal conductivities of composite soil find the probability density function f(λ) for each soil separate. For that purpose, measured thermal conductivities of 32 soils (of various fabric compositions) at saturation are used. Recovered functions f(λ) are then applied to the computational micromechanics approach; predicted conductivities are in a good agreement with laboratory results.

Schlüsselwörter

  • simulated annealing
  • heat transfer
  • homogenization
  • saturated soil
access type Uneingeschränkter Zugang

The influence of normal fault on initial state of stress in rock mass

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 109 - 121

Zusammenfassung

Abstract

Determination of original state of stress in rock mass is a very difficult task for rock mechanics. Yet, original state of stress in rock mass has fundamental influence on secondary state of stress, which occurs in the vicinity of mining headings. This, in turn, is the cause of the occurrence of a number of mining hazards, i.e., seismic events, rock bursts, gas and rock outbursts, falls of roof. From experience, it is known that original state of stress depends a lot on tectonic disturbances, i.e., faults and folds. In the area of faults, a great number of seismic events occur, often of high energies. These seismic events, in many cases, are the cause of rock bursts and damage to the constructions located inside the rock mass and on the surface of the ground. To estimate the influence of fault existence on the disturbance of original state of stress in rock mass, numerical calculations were done by means of Finite Element Method. In the calculations, it was tried to determine the influence of different factors on state of stress, which occurs in the vicinity of a normal fault, i.e., the influence of normal fault inclination, deformability of rock mass, values of friction coefficient on the fault contact. Critical value of friction coefficient was also determined, when mutual dislocation of rock mass part separated by a fault is impossible. The obtained results enabled formulation of a number of conclusions, which are important in the context of seismic events and rock bursts in the area of faults.

Schlüsselwörter

  • underground mining
  • stress field
  • tectonic disturbances
  • fault
  • rock burst
  • seismic events
access type Uneingeschränkter Zugang

Liquefaction mechanism induced by dynamic excitation modeled in Plaxis AE with the use of UBC and MOHR–coulomb constitutive relationships

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 123 - 133

Zusammenfassung

Abstract

Computer Aided Engineering (CAE) is commonly used in modern design of the various types of structures. There are two main issues/aspects that should be consider while using CAE in Geotechnics: the basic theory and material model. The paper deals with a problem of choosing the proper constitutive relationships which according to the authors are equally important in obtaining correct and reasonable results. This problem is illustrated by an example of dynamic calculations of fully saturated non-cohesive soils where liquefaction phenomenon is most likely to occur.

Schlüsselwörter

  • liquefaction
  • constitutive relationships
  • UBC Sand model
  • Mohr–Coulomb model
  • numerical modeling in Plaxis
13 Artikel
access type Uneingeschränkter Zugang

Estimation of spatial variability of lignite mine dumping ground soil properties using CPTu results

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 3 - 13

Zusammenfassung

Abstract

The paper deals with application of CPTu test results for the probabilistic modeling of dumping grounds. The statistical measures use results from 42 CPT test points located in the lignite mine dumping ground from the region of Central Europe. Both the tip resistance qc as well as local friction fs are tested. Based on the mean values and standard deviations of measured quantities the specific zones in the dumping site profile are distinguished. For three main zones standard deviations of linearly de-trended functions, distributions of normalized de-trended values for qc and fs are examined. Also the vertical scales of fluctuation for both measured quantities are estimated. The obtained result shows that lignite mine dumping site can be successfully described with the Random Field Theory. Additional use of fs values introduces supplementary statistical information.

Schlüsselwörter

  • Random Field Theory
  • fluctuation scale
  • CPTu testing
  • dumping ground soil
access type Uneingeschränkter Zugang

Numerical analysis of road pavement thermal deformability, based on Biot viscoelastic model of porous medium

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 15 - 22

Zusammenfassung

Abstract

The following study presents numerical calculations for establishing the impact of temperature changes on the process of distortion of bi-phase medium represented using Biot consolidation equations with Kelvin–Voigt rheological skeleton presented, on the example of thermo-consolidation of a pavement of expressway S17. We analyzed the behavior of the expressway under the action of its own weight, dynamic load caused by traffic and temperature gradient. This paper presents the application of the Biot consolidation model with the Kelvin–Voigt skeleton rheological characteristics and the influence of temperature on the deformation process is taken into account. A three-dimensional model of the medium was created describing the thermal consolidation of a porous medium. The 3D geometrical model of the area under investigation was based on data obtained from the land surveying and soil investigation of a 200 m long section of the expressway and its shoulders.

Schlüsselwörter

  • Biot theory
  • thermal consolidation
  • rheological body of Kelvin–Voigt
  • road pavement
access type Uneingeschränkter Zugang

Stability analysis of underground mining openings with complex geometry

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 25 - 32

Zusammenfassung

Abstract

Stability of mining openings requires consideration of a number of factors, such as: geological structure, the geometry of the underground mining workings, mechanical properties of the rock mass, changes in stress caused by the influence of neighbouring workings. Long-term prediction and estimation of workings state can be analysed with the use of numerical methods. Application of 3D numerical modelling in stability estimation of workings with complex geometry was described with the example of Crystal Caves in Wieliczka Salt Mine. Preservation of the Crystal Caves reserve is particularly important in view of their unique character and the protection of adjacent galleries which are a part of tourist attraction included in UNESCO list. A detailed 3D model of Crystal Caves and neighbouring workings was built. Application of FLAC3D modelling techniques enabled indication of the areas which are in danger of stability loss. Moreover, the area in which protective actions should be taken as well as recommendations concerning the convergence monitoring were proposed.

Schlüsselwörter

  • stability analysis of underground workings
  • complex geometry and geological structure
  • 3D numerical modelling
  • Wieliczka Salt Mine
access type Uneingeschränkter Zugang

Stochastic Finite Element Analysis using Polynomial Chaos

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 33 - 43

Zusammenfassung

Abstract

This paper presents a procedure of conducting Stochastic Finite Element Analysis using Polynomial Chaos. It eliminates the need for a large number of Monte Carlo simulations thus reducing computational time and making stochastic analysis of practical problems feasible. This is achieved by polynomial chaos expansion of the displacement field. An example of a plane-strain strip load on a semi-infinite elastic foundation is presented and results of settlement are compared to those obtained from Random Finite Element Analysis. A close matching of the two is observed.

Schlüsselwörter

  • foundation settlements
  • stochastic finite element
  • polynomial chaos
access type Uneingeschränkter Zugang

Large deformation finite element analysis of undrained pile installation

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 45 - 54

Zusammenfassung

Abstract

In this paper, a numerical undrained analysis of pile jacking into the subsoil using Abaqus software suit has been presented. Two different approaches, including traditional Finite Element Method (FEM) and Arbitrary Lagrangian–Eulerian (ALE) formulation, were tested. In the first method, the soil was modelled as a two-phase medium and effective stress analysis was performed. In the second one (ALE), a single-phase medium was assumed and total stress analysis was carried out. The fitting between effective stress parameters and total stress parameters has been presented and both solutions have been compared. The results, discussion and verification of numerical analyzes have been introduced. Possible applications and limitations of large deformation modelling techniques have been explained.

Schlüsselwörter

  • Abaqus
  • Arbitrary Lagrangian–Eulerian
  • ALE
  • FEM
  • Pile jacking
  • Pile installation
  • Undrained analysis
access type Uneingeschränkter Zugang

Magneto-rotatory compressible couple-stress fluid heated from below in porous medium

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 55 - 63

Zusammenfassung

Abstract

The study is aimed at analysing thermal convection in a compressible couple stress fluid in a porous medium in the presence of rotation and magnetic field. After linearizing the relevant equations, the perturbation equations are analysed in terms of normal modes. A dispersion relation governing the effects of rotation, magnetic field, couple stress parameter and medium permeability have been examined. For a stationary convection, the rotation postpones the onset of convection in a couple stress fluid heated from below in a porous medium in the presence of a magnetic field. Whereas, the magnetic field and couple stress postpones and hastens the onset of convection in the presence of rotation and the medium permeability hastens and postpones the onset of convection with conditions on Taylor number. Further the oscillatory modes are introduced due to the presence of rotation and the magnetic field which were non-existent in their absence, and hence the principle of exchange stands valid. The sufficient conditions for nonexistence of over stability are also obtained.

Schlüsselwörter

  • compressible couple-stress fluid
  • thermal convection
  • porous medium
  • rotation
  • magnetic field
access type Uneingeschränkter Zugang

Durability of crystalline phase in concrete microstructure modified by the mineral powders: evaluation by nanoindentation tests

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 65 - 74

Zusammenfassung

Abstract

This paper presents the nanoindentation investigation of the evolution of concrete microstructure modified by the Internal Crystallization Technology mineral powders. The samples under study were retrieved from a fragment of a circular concrete lining of the vertical mine shaft at a depth of approximately 1,000 m. Due to the aggressive environment and exposure to contaminated water, the internal surface of the structure was deteriorated, decreasing its strength significantly. The mineral powders were applied directly on the surface lining. The specimens were investigated one month, three months and one year after the application of the aforementioned substance in order to verify the time dependence of the strengthening processes and durability of the crystalline phase. The microstructural changes of concrete were assessed with the use of nanoindentation technique. The testing procedure involved including the previously cut specimens in the epoxy resin and grinding and polishing in order to reduce the surface roughness. As a result of the nanoindentation tests the hardness as well as Young’s modulus of the material were evaluated. The results were then compared and statistically analyzed. As a consequence, the disintegration time of the crystalline network in the pores of concrete was identified.

Schlüsselwörter

  • nanoindentation
  • concrete
  • Internal Crystallization Technology
  • microstructure
  • durability
access type Uneingeschränkter Zugang

Tunnel support design by comparison of empirical and finite element analysis of the Nahakki tunnel in mohmand agency, pakistan

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 75 - 84

Zusammenfassung

Abstract

The paper analyses the geological conditions of study area, rock mass strength parameters with suitable support structure propositions for the under construction Nahakki tunnel in Mohmand Agency. Geology of study area varies from mica schist to graphitic marble/phyllite to schist. The tunnel ground is classified and divided by the empisical classification systems like Rock mass rating (RMR), Q system (Q), and Geological strength index (GSI). Tunnel support measures are selected based on RMR and Q classification systems. Computer based finite element analysis (FEM) has given yet another dimension to design approach. FEM software Phase2 version 7.017 is used to calculate and compare deformations and stress concentrations around the tunnel, analyze interaction of support systems with excavated rock masses and verify and check the validity of empirically determined excavation and support systems.

Schlüsselwörter

  • rock mass strength parameters
  • rock mass classification
  • FEM analysis
  • Phase2
  • tunnel support design
access type Uneingeschränkter Zugang

Preliminary calculation of irregular triguy mast support

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 85 - 90

Zusammenfassung

Abstract

The instantaneous tangential rigidity (corresponding to the applied horizontal load) of a triguy support with unequal ropes is determined. The differences between the ropes can be due to the different location, both horizontal and vertical, of their anchoring foundations and to the different types of ropes used. The horizontal rigidity of such a support has no general axis of symmetry. Therefore a formula for this rigidity in any direction and a formula for extreme rigidity angles are given in this paper. A notion of the guy’s eigenvalue, standing for the initial tension force above which the guy participates effectively in the support’s rigidity, is introduced. A numerical example is provided.

Schlüsselwörter

  • mast
  • irregular triguy support
  • initial tension values
  • forces in guys
  • numerical example
access type Uneingeschränkter Zugang

Effect of increasing mining rate on longwall coal mining – Western donbass case study

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 91 - 98

Zusammenfassung

Abstract

This paper presents the problems associated with the rapid change of the rock stress-strain state in terms of increasing the rate of coal mining. Parameters of the roof collapse are determined depending on the rate of a longwall advancing under conditions of poor rocks. Statistical data are processed to obtain a general trend concerning the mining rate impact on the roof collapse. The statistical strength theory is applied to explain the increase in mined-out space and the size of hanging roof behind a coal face. Numerical simulation is carried out to determine a critical size of mined-out space that provokes a roof collapse. The area of yielded rocks is outlined using the criterion developed taking into account the rate of longwall advancing. A general regularity is obtained to determine the roof collapse parameters. The developed technics gives a possibility to predict the moment of general roof collapse at the initial stage of longwalling to prevent the negative effect of the rapid stress redistribution provoking joints propagation and intensive gas release. The estimation of the rock stress-strain state considering the rate of mining operations can be useful for tasks related to a new technology implementation. The statistical strength theory and failure criterion applied together provides adequate planning of mining activities and the assessment of natural hazards.

Schlüsselwörter

  • rock
  • stress-strain state
  • mining rate
  • failure criterion
  • roof collapse
access type Uneingeschränkter Zugang

Recovery of microstructure properties: random variability of soil solid thermal conductivity

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 99 - 107

Zusammenfassung

Abstract

In this work, the complex microstructure of the soil solid, at the microscale, is modeled by prescribing the spatial variability of thermal conductivity coefficient to distinct soil separates. We postulate that the variation of thermal conductivity coefficient of each soil separate can be characterized by some probability density functions: fCl(λ), fSi(λ), fSa(λ), for clay, silt and sand separates, respectively. The main goal of the work is to recover/identify these functions with the use of back analysis based on both computational micromechanics and simulated annealing approaches. In other words, the following inverse problem is solved: given the measured overall thermal conductivities of composite soil find the probability density function f(λ) for each soil separate. For that purpose, measured thermal conductivities of 32 soils (of various fabric compositions) at saturation are used. Recovered functions f(λ) are then applied to the computational micromechanics approach; predicted conductivities are in a good agreement with laboratory results.

Schlüsselwörter

  • simulated annealing
  • heat transfer
  • homogenization
  • saturated soil
access type Uneingeschränkter Zugang

The influence of normal fault on initial state of stress in rock mass

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 109 - 121

Zusammenfassung

Abstract

Determination of original state of stress in rock mass is a very difficult task for rock mechanics. Yet, original state of stress in rock mass has fundamental influence on secondary state of stress, which occurs in the vicinity of mining headings. This, in turn, is the cause of the occurrence of a number of mining hazards, i.e., seismic events, rock bursts, gas and rock outbursts, falls of roof. From experience, it is known that original state of stress depends a lot on tectonic disturbances, i.e., faults and folds. In the area of faults, a great number of seismic events occur, often of high energies. These seismic events, in many cases, are the cause of rock bursts and damage to the constructions located inside the rock mass and on the surface of the ground. To estimate the influence of fault existence on the disturbance of original state of stress in rock mass, numerical calculations were done by means of Finite Element Method. In the calculations, it was tried to determine the influence of different factors on state of stress, which occurs in the vicinity of a normal fault, i.e., the influence of normal fault inclination, deformability of rock mass, values of friction coefficient on the fault contact. Critical value of friction coefficient was also determined, when mutual dislocation of rock mass part separated by a fault is impossible. The obtained results enabled formulation of a number of conclusions, which are important in the context of seismic events and rock bursts in the area of faults.

Schlüsselwörter

  • underground mining
  • stress field
  • tectonic disturbances
  • fault
  • rock burst
  • seismic events
access type Uneingeschränkter Zugang

Liquefaction mechanism induced by dynamic excitation modeled in Plaxis AE with the use of UBC and MOHR–coulomb constitutive relationships

Online veröffentlicht: 18 Apr 2016
Seitenbereich: 123 - 133

Zusammenfassung

Abstract

Computer Aided Engineering (CAE) is commonly used in modern design of the various types of structures. There are two main issues/aspects that should be consider while using CAE in Geotechnics: the basic theory and material model. The paper deals with a problem of choosing the proper constitutive relationships which according to the authors are equally important in obtaining correct and reasonable results. This problem is illustrated by an example of dynamic calculations of fully saturated non-cohesive soils where liquefaction phenomenon is most likely to occur.

Schlüsselwörter

  • liquefaction
  • constitutive relationships
  • UBC Sand model
  • Mohr–Coulomb model
  • numerical modeling in Plaxis

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