فهرست مطالب سید مصلح افتخاری

Mechanized tunneling in hard rock is associated with various challenges and risks, one of which is the penetration rate of Tunnel Boring Machine and the occurrence of grinding and chipping in various conditions. When the strength of the rock is high and the amount of jointing is low, the penetration rate of the machine is reduced and instead of forming rock chips in the tunnel face. In these conditions, which is called grinding, tunneling is associated with wear and high consumption of cutting tools as well as a severe reduction in the efficiency of excavation operations. In this paper, the boundary between grinding and chipping processes is investigated and a criterion for determining the minimum normal force in different geomechanical conditions required to create chipping condition is presented. For this purpose, data related to Kerman Water Tunnel and Southern extension of Tehran Metro Line 6 tunnel are used. In this regard, by comparing the normal forces on the cutting tools and the resulting penetration rate, the threshold for changing conditions from the grinding phenomenon to chipping is determined. The results show that the amount of normal force required to be applied by the disc cutter to the rock mass to excavate under the chipping conditions for rocks with medium, high and very high uniaxial compressive strength are equal to 130, 210 and 225 kN, respectively. Moreover, by examining the data of Metro Line 6, the role of joints in providing the conditions for chips formation was investigated and the result showed that the boundary between grinding and chipping for medium strength rocks can be at RQD=75%. It was also found that with the penetration rate exceeding a certain threshold, a slight increase in normal force causes a significant increase in the penetration rate, which increases efficiency and reduces operating costs.

Mechanized tunneling in rocks is based on fracture propagation and rock fragmentation under disc cutters. Rock chipping is an efficient kind of fragmentation process, while the grinding process may occur under special conditions. The cutter-head penetration is an appropriate parameter involved in order to distinguish between the chipping and grinding processes in rock cutting. In this work, the grinding and chipping processes are investigated in the Uma-Oya water conveyance tunnel in Sri Lanka. The Uma-Oya project is a water transfer, hydropower, and irrigation system in the SE part of the central highland region of Sri-Lanka. From a geological viewpoint, most parts of the tunnel route in the studied section consist of very strong and abrasive metamorphic rocks that potentially are susceptible to grinding occurrence during the boring process under disc cutters. In this work, firstly, data processing is performed in order to identify the boundary between chipping and grinding. Then the chipping and grinding processes are modeled using the practical numerical and artificial intelligent methods. In the numerical modeling stage, we try to make the modeling as realistic as possible. The results obtained from these modeling methods show that for the penetrations less than 3 mm/rev, the grinding process is dominant, and for the penetrations more than 3 mm/rev, rock chipping occurs. Also, in the numerical modeling, no significant fracture expansion is observed in the rock when the penetration is less than 3 mm/rev. Moreover, it can be seen in the numerical modeling of the chipping process that the propagated fractures come together and the chips are created.

Summary:

In this paper, the effect of replacing disc cutters with ripper tools on the performance of a TBM in Tehran Metro Line 6 is investigated by comparing the value of operating parameters of TBM before and after the replacement. The results show that this replacement has a positive impact on the TBM performance.

Improvement of the performance of the TBM machine in tunneling has always been in the spotlight of research and development. The type of cutting tool, which is selected based on the mechanical properties of the formations along the tunnel route, could affect the efficiency and production rate in tunneling. In Tehran Metro Line 6, the consumption of disc cutters increased with decreasing the efficiency of disc cutters, along with increasing the value of thrust and torque. Hence, some of the disc cutters of the TBM were replaced with ripper tools in order to improve the TBM performance.  

Methodology and Approaches:

In this paper, the effect of this replacement on the performance of the TBM is examined by statistical analysis of the field measurements. The value of operational parameters- thrust, torque, and penetration rate of the TBM- in different sections before and after the replacement is investigated.

The statistical analysis shows that the mean value of both thrust and torque as well as their standard deviations after the replacement have considerably decreased in comparison with the figures for before the replacement, while the mean value of penetration rate has been approximately identical in both before and after the replacement of cutting tools. The results show that this replacement of disc cutters with ripper tools in alluvial conditions of Tehran has improved the performance of the TBM machine.

Summary In this paper, a novel method based on a semi-ring support has been developed and proposed to facilitate TBM passing the station and restarting the excavation. The results show that the proposed method can be safely used. Introduction Crossing of station is one of the most challenging problems in construction of metro lines. Given the difficulties and problems of using the push frame in the TBM passing station and restarting excavation, this study presents a method based on the use of segmental rings that has been developed for use in underground stations. Methodology and Approaches In this method, in order to create a support for applying the force of TBM thrust, a different pattern of the installation of the incomplete rings has been used so that in addition to utilizing the advantages of using the semi-ring support in such a way that any complete ring is not installed in the space of the station. The proposed pattern is such that three floor segments are used to a distance of about 5 to 6 rings to the end of station; so that TBM will pass through the length of the station. Thereafter, in a few rings, the number of segments increases to 4 and then 5 segments per ring until the cutter head reaches the end of the station. From this stage, the tunnel excavation continues with the installation of the semi-rings of 5 and 6 segments, until the boring machine is completely inserted into the tunnel so that the first complete ring is installed at the beginning of the tunnel. Results and Conclusions The results show that excavation can begin using the 5 and 6 segments, but semi-ring of 6 segments is somewhat superior to 5 segments. The proposed model has been evaluated at some stations of line 6 of Tehran metro and the results show that, in addition to the effectiveness of this method, any over-the-counter deviation has not occurred. Therefore, the proposed method can be safely used.

Since all mining projects are subjected to uncertainty, risk analysis of these projects is essential. It is also possible to know the exact amount of minable reserve, due to its location in the underground and the operating limitations, when the entire reserve is extracted. Therefore, the effective parameters in the technical and economic evaluation of mining projects are highly diverse and all of them are subject to wide variations with respect to the quantitative and qualitative dimensions of the data. This process is caused by causes beyond human control, and sometimes, no matter how much it costs, full information is not possible. Hence, in all mining projects, in calculating income and expenditure figures and therefore economic calculations, they have to take into account the margin of confidence and are required to calculate risk. It would make more logical to consider the probabilistic changes of effective parameters in the economic analysis of mining projects. And taking into account the least and most likely occurrence of each row. When one of the most important issues with uncertainty is the price of metal, then uncertainty in the ultimate pit limit determination is raised. Since metal price prediction is uncertain, chaos theory and fractal geometry can be used to predict metal price. In this study, chaos theory and fractal geometry have been used to estimate the metal price correctly, since the metal price changes follow fractal and chaotic behavior. Therefore, if a correct estimate of the metal price is obtained, the ultimate pit limit will be close to reality and based on that the optimal pit limit can be obtained, which according to the principles of sustainable development leads to the metal mining at a lower price and the ultimate pit limit is more sustainable and has better environmental protection.

Existence of rock fracture is very important in evaluating the penetration rate (PR) of TBM in fractured rock masses. In previous research works, the influence of geometrical properties of a joint set such as joint spacing and orientation on PR has been investigated. Since the actual rock mass is geometrically complex, the hybrid Discrete Fracture Network- Distinct Element Method (DFN-DEM)which is used a closer conceptual modelto the reality (DFN) and facilitated a powerful numerical method (DEM) is used for numerical modeling of PR of TBM in fractured rocks. The DFN models is based on stochastic representation of fracture systems, using the probability density function (PDF) of fracture parameters (e.g. orientation, length) formulated according to field mapping results and generated by Monte Carlo method. Using a number of DFN-DEM models for predicting the penetration rate of TBM, a probabilistic numerical modeling is established. Numerical modeling results show that the PDF of positive incremental chipping area follows the normal distribution with the mean value of 46%. The Probabilistic Cumulative Distribution Function (PCDF) of results shows that the positive incremental chipping areas are greater than 20% and 33% when 95% and 80% are respectively considered.

Performance analysis and accurate prediction of Penetration Rate (PR) of a TBM have been the ultimate goals of many research works. A reliable prediction of a TBM performance is necessary in budget control and also time schedule planning in underground excavation projects. Evaluating the optimum operational parameters of machine using Artificial Neural Networks (ANN) method is the main objective of this research work which has not been estimated and reported in previous studies in this field of study.