Cyclic Behavior of K0-Consolidated Soft Clay under Stress Paths with Different Major Principal Stress Directions

The combined effect of pre-existing cracks and pores on the damage evolution behaviour and mechanical properties of rocklike materials under uniaxial compression was numerically studied. Simulations of cracks and pores alone showed that increasing crack length and pore diameter decrease uniaxial compressive strength (UCS) and elastic modulus. Subsequent simulations considered two types of combinations of pre-existing cracks and pores – two cracks either side of a centric pore, and two pores either side of a centric crack – and the distance between cracks and pores was changed. In the case of two cracks at either side of the pore, UCS increased only slightly when the distance between the cracks and pore was increased. This was attributed to the more profound effect of the presence of the pore on UCS, and was confirmed by the progressive crack development characteristics and the major principal stress distribution patterns, which showed that the cracks initiated from the tips of the two pre-existing cracks made little or no contribution to the ultimate macroscopic failure. In contrast, models with two pores at either side of a centric crack showed a marked dependency of UCS on the distance between the pores and the crack. Cracks propagating from pre-existing pores made a greater contribution to the ultimate macroscopic failure when the pores were close to the centric crack and the effect gradually diminished with increasing space between pre-existing pores and the centric crack. Major principal stress distributions showed an asymmetric mobilisation of compressive stresses at the right and left sides of the two pores, favouring macroscopic shear failure when they were close to the centric crack which had led to a lower UCS. Overall, this study presents some critical insights into crack-pore interaction behaviour and the resulting mechanical response of rocklike materials to assist with the design of rock structures.

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Factors Influencing Ore Recovery and Unplanned Dilution in Sublevel Open Stopes. Case study of Shaft No.4 at Konkola Mine, Zambia

Current World Environment ◽

10.12944/cwe.15.special-issue1.03 ◽

2020 ◽

Vol Special Issue (1) ◽

Author(s):

Kalunga Ngoma ◽

Victor Mutambo

Keyword(s):

Numerical Modelling ◽

Principal Stress ◽

Underground Mining ◽

Poisson Ratio ◽

High Stress ◽

Geological Strength Index ◽

Total Displacement ◽

Ground Conditions ◽

Geological Discontinuities ◽

Major Principal Stress

Konkola Copper Mine’s Number 4 Shaft is a trackless underground mine applying sublevel open stoping (SLOS) mining method. Number 4 shaft wants to increase ore production from 1 million metric tonnes per annum to 3 million metric tonnes per annum in the next 5 years but ore recovery is 70% or less and dilution is 20% or more. In order to achieve the desired annual target of 3 million metric tonnes ore recovery should be increased from70% to (≥85%) and dilution should be reduced from 20% to (≤10%). Despite being one of the most used underground mining methods, the current SLOS has a challenge of high unplanned dilution. This paper reviews and evaluates parameters that influence recovery and unplanned dilution in sublevel open stopes and applies numerical modelling using PHASE2 software to establish the influence of stress environment on unplanned dilution at the mine. The input parameters for numerical modelling were: Uniaxial Compressive strength (UCS=170MPa), Geological Strength Index (GSI) =55, Young’s Modulus (E) =26000MPa, Hoek-Brown constant (s) =0.0067, Hoek-Brown constant (mi) =20 and Poisson ratio (v) =0.2 major principal stress (σ1) 39MPa, intermediate stress (σ2= 18MPa) and the minor principal stress (σ3= 15MPa). Results obtained from review of mine production records indicate that the main factors that influence unplanned dilution at Number 4 shaft are: poor ground conditions, lack of compliance to recommended stope designs, poor drilling and blasting practices, presence of geological discontinuities, adopted mining sequence of extracting high ore grade first that leads to creation of high stress blocks within the orebody and delayed mucking practice. Results obtained from PHASE 2D model indicate that total displacement of 90mm is recorded in the hangingwall hence influencing stope wall instability that leads to increased unplanned dilution. After stope extraction, it was observed that 60MPa of induced stress developed at the top right corner and 45-50 MPa at the crown pillar and right bottom corner of the stope.

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Rotation of the principal stress directions due to earthquake faulting and its seismological implications

Bulletin of the Seismological Society of America ◽

10.1785/bssa0850051513 ◽

1995 ◽

Vol 85 (5) ◽

pp. 1513-1517

Author(s):

Z.-M. Yin ◽

G. C. Rogers

Keyword(s):

Shear Stress ◽

Normal Stress ◽

Principal Stress ◽

Stress Drop ◽

Rotation Angle ◽

Overburden Pressure ◽

Rupture Area ◽

Earthquake Faulting ◽

Stress Directions ◽

Before And After

Abstract Earthquake faulting results in stress drop over the rupture area. Because the stress drop is only in the shear stress and there is no or little stress drop in the normal stress on the fault, the principal stress directions must rotate to adapt such a change of the state of stress. Using two constraints, i.e., the normal stress on the fault and the vertical stress (the overburden pressure), which do not change before and after the earthquake, we derive simple expressions for the rotation angle in the σ1 axis. For a dip-slip earthquake, the rotation angle is only a function of the stress-drop ratio (defined as the ratio of the stress drop to the initial shear stress) and the angle between the σ1 axis and the fault plane, but for a strike-slip earthquake the rotation angle is also a function of the stress ratio. Depending on the faulting regimes, the σ1 axis can either rotate toward the direction of fault normal or rotate away from the direction of fault normal. The rotation of the stress field has several important seismological implications. It may play a significant role in the generation of heterogeneous stresses and in the occurrence and distribution of aftershocks. The rotation angle can be used to estimate the stress-drop ratio, which has been a long-lasting topic of debate in seismology.

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Stress Path Tests with Controlled Rotation of Principal Stress Directions

Laboratory Shear Strength of Soil ◽

10.1520/stp28768s ◽

2009 ◽

pp. 516-516-25 ◽

Cited By ~ 17

Author(s):

JRF Arthur ◽

S Bekenstein ◽

JT Germaine ◽

CC Ladd

Keyword(s):

Principal Stress ◽

Stress Path ◽

Stress Directions

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Expected principal stress directions under multiaxial random loading. Part I: theoretical aspects of the weight function method

International Journal of Fatigue ◽

10.1016/s0142-1123(98)00046-2 ◽

1999 ◽

Vol 21 (1) ◽

pp. 83-88 ◽

Cited By ~ 57

Author(s):

Andrea Carpinteri ◽

Ewald Macha ◽

Roberto Brighenti ◽

Andrea Spagnoli

Keyword(s):

Weight Function ◽

Principal Stress ◽

Function Method ◽

Random Loading ◽

Weight Function Method ◽

Stress Directions

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Design of a defence hole system for a shear-loaded plate

The Journal of Strain Analysis for Engineering Design ◽

10.1243/030932403770735872 ◽

2003 ◽

Vol 38 (6) ◽

pp. 507-517 ◽

Cited By ~ 9

Author(s):

S. N Akour ◽

J. F Nayfeh ◽

D. W Nicholson

Keyword(s):

Finite Element Analysis ◽

Principal Stress ◽

Pure Shear ◽

Optimization Method ◽

Optimum Size ◽

Stress Concentrations ◽

Element Analysis ◽

Search Optimization ◽

Stress Directions ◽

Circular Holes

Stress concentrations associated with circular holes in pure shear-loaded plates can be reduced by up to 13.5 per cent by introducing elliptical auxiliary holes along the principal stress directions. These holes are introduced in the areas of low stresses near the main circular hole in order to smooth the principal stress trajectories. A systematic study based on univariate search optimization method is undertaken by using finite element analysis (FEA) to determine the optimum size and location for an auxiliary defence hole system. The results are validated using RGB (red-green-blue) photoelasticity.

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