Rock Mechanics
Mahan Amirkhani; Mojtaba Bahaaddini; Alireza Kargar; Amin Hekmatnejad
Abstract
The stability of tunnels and underground openings in jointed rock masses is significantly influenced by the development an Excavation Damage Zone (EDZ), where discontinuities alter stress distribution and the fractured propagation zone. In previous studies on EDZ, rock mass is commonly considered as ...
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The stability of tunnels and underground openings in jointed rock masses is significantly influenced by the development an Excavation Damage Zone (EDZ), where discontinuities alter stress distribution and the fractured propagation zone. In previous studies on EDZ, rock mass is commonly considered as a continuum medium, while the joint system can dictate the size of EDZ. This study aims to investigate the EDZ around a tunnel excavated in a jointed rock mass using the Discrete Fracture Network (DFN) and Discrete Element Method (DEM). Three DFN models with different fracture intensities of 0.5, 1.0, and 1.5 m2/m3 were simulated to explore the progressive failure mechanisms and damage evolution around a tunnel. The DFN models were then imported into the DEM code. The area of the plastic zone was considered a representative measure of the EDZ. The influence of joint mechanical properties, including cohesion, friction angle, normal, and shear stiffnesses, was investigated. A dimensionless sensitivity analysis was conducted to evaluate and compare the influence of each parameter. The results show that the joint friction angle is the most influential parameter in all fracture intensities. These insights provide a more precise understanding of joint behaviour and its impact on tunnel stability in different geological settings.
Rock Mechanics
Mohammad Amin HajiMohammadi; Mojtaba Bahaaddini; Mohammad Hossein Khosravi; Hassan Vandyoosefi
Abstract
Discontinuities are known as a primary factor in instability of tunnels and underground excavations. To prevent potential damage and overbreak by underground advancement, it is essential to provide a model, which considers both the geometrical and mechanical characteristics of discontinuities. Discrete ...
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Discontinuities are known as a primary factor in instability of tunnels and underground excavations. To prevent potential damage and overbreak by underground advancement, it is essential to provide a model, which considers both the geometrical and mechanical characteristics of discontinuities. Discrete Fracture Network (DFN) is a conceptual model to represent and analyse the complex system of discontinuities within the rock mass. Combined DFN with analytical or numerical methods can be employed as a scientific tool to analyse generated rock blocks, and their stabilities under different loading conditions. This paper aims to investigate the created overbreak by tunnel advancement in the Alborz tunnel located in the Tehran-North freeway in Iran. First, the geometrical characteristics of discontinuities were surveyed by tunnel advancement in 200 meters. Four major joint sets and a bedding plane were identified and their statistical characteristics were measured. The DFN model was generated and its validity was investigated through a comparison against field data. The average volume of generated blocks in the studied area was measured 0.22 m3. The stability of generated blocks around the opening was kinematically evaluated. The volume of formed blocks around tunnel in the DFN model prone to instability due to static or dynamic loads was estimated 2605 m3 while the measured overbreak in field was 2735 m3. The depth of overbreak in DFN model showed a good agreement with field measurements. The results show that DFN model combined with kinematic stability analysis can provide a scientific tool to investigate geological overbreak in underground excavations.
M. Bahaaddini; M. Serati; M. H. Khosravi; B. Hebblewhite
Abstract
A proper understanding of the shear behaviour of rock joints and discontinuities is yet a remaining challenge in the rock engineering research works owing to the difficulties in quantitatively describing the joint surface roughness both at the field and the laboratory scales. Several instruments and ...
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A proper understanding of the shear behaviour of rock joints and discontinuities is yet a remaining challenge in the rock engineering research works owing to the difficulties in quantitatively describing the joint surface roughness both at the field and the laboratory scales. Several instruments and techniques have been developed over the years for the surface characterisation of joints at the field- and laboratory-scale investigations, amongst which the application of the photogrammetry methods has obtained a growing popularity. This work evaluates the applicability of the photogrammetry techniques for the characterisation of joint surface topography and texture at micro-scales, which has been largely understudied in the literature. Three tensile joint surfaces are digitized using photogrammetry, and the results are compared with those obtained from laser scans with a high 3D accuracy. A comprehensive statistical analysis is then undertaken on the digitized point clouds in order to assess the performance of photogrammetry in surface characterisation. The results of this work show that the height differences between the resulting point clouds from the two adopted techniques (photogrammetry and 3D laser scanning) follow the normal distribution with the mean values close to zero. The statistical analyses illustrate that the measured joint surfaces using the photogrammetry techniques are in good agreement with the laser scanning data, confirming that photogrammetry is a capable method for characterising the joint surface roughness even at micro-scales. Interestingly, the results obtained further indicate that the accuracy and preciseness of the photogrammetry techniques are independent from the joint roughness coefficient but the camera and configuration parameters remarkably control the performance of the measurement.
M. Ghaedi Ghalini; M. Bahaaddini; M. Amiri Hossaini
Abstract
Estimation of the in-situ block size is known as a key parameter in the characterization of the mechanical properties of rock masses. As the in-situ block size cannot be measured directly, several simplified methods have been developed, where the intrinsic variability of the geometrical features of discontinuities ...
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Estimation of the in-situ block size is known as a key parameter in the characterization of the mechanical properties of rock masses. As the in-situ block size cannot be measured directly, several simplified methods have been developed, where the intrinsic variability of the geometrical features of discontinuities are commonly neglected. This work aims to estimate the in-situ block size distribution (IBSD) using the combined photogrammetry and discrete fracture network (DFN) approaches. To this end, four blasting benches in the Golgohar iron mine No. 1, Sirjan, Iran, are considered as the case studies of this research work. The slope faces are surveyed using the photogrammetry method. Then 3D images are prepared from the generated digital terrain models, and the geometrical characteristics of discontinuities are surveyed. The measured geometrical parameters are statistically analysed, and the joint intensity, the statistical distribution of the orientation, and the fracture trace length are determined. The DFN models are generated, and IBSD for each slope face is determined using the multi-dimensional spacing method. In order to evaluate the validity of the generated DFN models, the geological strength index (GSI) as well as the stereographic distribution of discontinuities in the DFN models are compared against the field measurements. A good agreement has been found between the results of the DFN models and the filed measurements. The results of this work show that the combined photogrammetry and DFN techniques provide a robust, safe, and time-efficient methodology for the estimation of IBSD.
Seyed A.R. Kaboli; M. Bahaaddini; Seyed M. Kaboli
Abstract
Traditionally, the earthmoving operations have been developed based on the minimum cost per production criterion. Nowadays, due to the negative impacts of the emissions on the environment, there is an increasing public awareness to reduce the emissions from the earthmoving operations. Different management ...
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Traditionally, the earthmoving operations have been developed based on the minimum cost per production criterion. Nowadays, due to the negative impacts of the emissions on the environment, there is an increasing public awareness to reduce the emissions from the earthmoving operations. Different management strategies can be employed to reduce emissions, amongst other things, which can also result in a reduction in the operational costs. This paper aims to examine the cost and emissions related to the earthmoving equipment from an operational standpoint. The queue theory is used in order to demonstrate that the optimum cost per production fleet size and the optimum emissions per production coincide. The linear and non-linear server utilization functions are employed to present a general optimization proof independent from any specific case study. The findings of this research work provide a better understanding of the relationship between the emissions and cost and how the under-trucking and over-trucking conditions affect the productivity and environmental affairs in the earthmoving operations.
