Rock Mechanics
A. Asgari; A. Ramezanzadeh; Seyed M. E. Jalali; B. Brouard
Abstract
Ensuring the stability and integrity of underground gas storage salt caverns is a very complicated subject due to the non-linear and time-dependent behavior of rock salts under complicated thermal and mechanical loading conditions. For this reason, pressure and temperature fluctuations in the caverns ...
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Ensuring the stability and integrity of underground gas storage salt caverns is a very complicated subject due to the non-linear and time-dependent behavior of rock salts under complicated thermal and mechanical loading conditions. For this reason, pressure and temperature fluctuations in the caverns and their surrounding strata must be integrated into the analysis and the numerical tools that are used for this purpose. LOCAS, a 2D axisymmetric finite-element code, dedicated to the stability analysis of underground salt spaces, was applied to assess the effects of various operating and geometrical parameters on the cavern behavior. In this paper, we aimed to give an overall assessment of the behavior of the salt caverns used for natural gas storage. In this work, some specific loading scenarios were considered first, followed by thorough parametric and sensitivity analyses to reveal the impacts of the geometrical parameters and operational parameters involved on the behavior of salt caverns using the modern stability criteria. The findings showed that the onset of dilation was more likely to happen within the first cavern life cycle when pressure dropped to the minimum level. As for the potential of tension occurrence in the surrounding rock, this is more likely to happen by increasing the number of operation cycles, especially in the upper one-third of the cavern wall. Finally, it was seen that the cavern depth and minimum cavern internal pressure had even more important influences than the others on the salt cavern behavior.
M. Najafi; Seyed M. E. Jalali; F. Sereshki; A. Yarahmadi Bafghi
Abstract
Performing a probabilistic study rather than a determinist one is a relatively easy way to quantify the uncertainty in an engineering design. Due to the complexity and poor accuracy of the statistical moment methods, the Monte Carlo simulation (MCS) method is wildly used in an engineering design. In ...
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Performing a probabilistic study rather than a determinist one is a relatively easy way to quantify the uncertainty in an engineering design. Due to the complexity and poor accuracy of the statistical moment methods, the Monte Carlo simulation (MCS) method is wildly used in an engineering design. In this work, an MCS-based reliability analysis was carried out for the stability of the chain pillars in the Tabas coal mine, located in Iran. For this purpose, the chain pillar strengths were calculated using the Madden formula, the vertical stress on the chain pillars was determined by an empirical method, and a numerical modeling was performed using the FLAC3D software. The results obtained for the probabilistic stability analysis of the chain pillars showed that the failure probability obtained for the designed pillars by applying the MCS method were approximately the same as that obtained by the advanced second moment (ASM) method, and the values obtained varied between 12 and 18 percent.
M. Noroozi; R. Kakaie; Seyed M. E Jalali
Abstract
Fault zones and fault-related fracture systems control the mechanical behaviors and fluid-flow properties of the Earth’s crust. Furthermore, nowadays, modeling is being increasingly used in order to understand the behavior of rock masses, and to determine their characteristics. In this work, fault ...
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Fault zones and fault-related fracture systems control the mechanical behaviors and fluid-flow properties of the Earth’s crust. Furthermore, nowadays, modeling is being increasingly used in order to understand the behavior of rock masses, and to determine their characteristics. In this work, fault zones and fracture patterns are reviewed, and also comprehensive studies are carried out on the fracture geometry and density variations. A model to describe damage zones around the strike-slip faults is developed, in which the range of damage zone styles commonly found around strike-slip fault zones are shown. A computer code, named DFN-FRAC3D, is developed for the two- and three-dimensional stochastic modeling of rock fracture systems in fault zones. In this code, the pre-existing and fault-related fractures are modeled by their respective probability distributions, and the joint density may be varied by the distance from the fault core. This work describes the theoretical basis and the implementation of the code, and provides a case study in the rock fracture modeling to demonstrate the application of the prepared code.
Omid Saeidi; Ahmad Ramezanzadeh; Farhang Sereshki; Seyed Mohammad Esmaeil Jalali
Abstract
This study aims at presenting a numerical model for predicting grout flow and penetration length into the jointed rock mass using Universal Distinct Element Code (UDEC). The numerical model is validated using practical data and analytical method for grouting process. Input data for the modeling, including ...
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This study aims at presenting a numerical model for predicting grout flow and penetration length into the jointed rock mass using Universal Distinct Element Code (UDEC). The numerical model is validated using practical data and analytical method for grouting process. Input data for the modeling, including geomechanical parameters along with grout properties, were obtained from a case study. The effect of rock mass properties such as joint hydraulic aperture, spacing, trace length, orientation and grout properties as yield stress and water to cement, w/c ratio was considered on grout flow rate and penetration length. To illustrate the effect of aforementioned properties, models were constructed with dimensions of 40×20m. A vertical borehole with diameter of 60mm and 10m depth was drilled in a jointed rock media. The results were in a good agreement with analytical method. It was observed that by increasing joint hydraulic aperture, grouting flow increases using a power law function. The optimum grout penetration observed with joint sets intersection of 40°-60° as experienced in practice. With an increase in joint spacing grout penetration increases around borehole when spacing exceeds two meters it decreases, gradually.
S.M.A Hosseini; F Sereshki; M Shariati; S.M.E Jalali; F Crotogino
Abstract
Creep phenomenon in rock engineering plays a key role in development of underground spaces as they must be stable enough for a long period of time. Current research involved designing and manufacturing of a new creep testing machine. The equipment is capable to perform simultaneous light-duty creep tests ...
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Creep phenomenon in rock engineering plays a key role in development of underground spaces as they must be stable enough for a long period of time. Current research involved designing and manufacturing of a new creep testing machine. The equipment is capable to perform simultaneous light-duty creep tests on more than one cylindrical rock samples at a very low cost.To evaluate the equipment’s performance, a series of creep test was performed on salt rock samples and their axial and lateral deformations were measured by dial gauges. Measurements were taken under constant temperature, humidity and sustained loads. The results revealed that the creep rate in lateral direction was far greater than in the axial direction. Another important conclusion was that both axial and lateral creep curves follow the same pattern with an idealized salt rock creep curve. Also, experiments indicated that the steady state creep rate increases with increasing initial stress state. Also, initial stress state showed a great influence on salt primary creep response.
