Rock Mechanics
Ehsan Taheri; Reza Mohammadpour; Mohammad Hossein Mokhtarzadeh
Abstract
In recent years, the demand for new trenchless methods has dramatically risen. Pipe jacking is a trenchless method widely used in recent years. Ground deformation is one of the significant parameters that may lead to unrepairable harm to facilities and even people. So, ground deformation analysis is ...
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In recent years, the demand for new trenchless methods has dramatically risen. Pipe jacking is a trenchless method widely used in recent years. Ground deformation is one of the significant parameters that may lead to unrepairable harm to facilities and even people. So, ground deformation analysis is necessary for safety and design reasons. The present study analyzes the factors affecting ground deformation during pipe jacking. This is a descriptive-interventional study. Pipe jacking causes soil displacement in three dimensions (3-D). Therefore, 3-D numerical methods were applied for analysis. In this study, numerical simulation was performed using PLAXIS finite element numerical software, taking the case study into account. The effect of each parameter on the ground deformation pattern was studied in three directions; the uplift and their exact position were then analyzed. It should be noted that displacement analyses were performed in two areas: pipe crown and ground surface. Also, the relation of each parameter was estimated with the ground subsidence. Finally, the effect of each different factor and their sensitivity index were determined using sensitivity analysis. The highest subsidence occurs at the end of the shield due to stress relaxation. Considering the results, it was found that the relationship between the internal friction angle and subsidence is linear and direct. The relationship between the elastic modulus and subsidence is also linear but indirect. The results indicate that the most sensitive factor of ground deformation is the diameter, but the least sensitive factor is the face pressure.
Rock Mechanics
Dariush Mohammadi; Kourosh Shahriar; Parviz Moarefvand; Ebrahim Farrokh
Abstract
The correct design of the cutterhead of a tunnel boring machine (TBM) plays a vital role in the efficient operation of the machine, as the cutterhead structure remains unchanged during the tunneling project. This paper aims to elucidate the fundamental principles in the design of the cutterhead opening ...
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The correct design of the cutterhead of a tunnel boring machine (TBM) plays a vital role in the efficient operation of the machine, as the cutterhead structure remains unchanged during the tunneling project. This paper aims to elucidate the fundamental principles in the design of the cutterhead opening in soft ground based on data obtained from TBM manufacturers. Initially, a comprehensive database of soft ground cutterheads from different TBM manufacturers across various projects and ground conditions was compiled. The most frequently used cutterhead configurations with diameters exceeding 5 meters were categorized into 36 distinct opening configurations based on a radial opening ratio curve and opening patterns per sector. Next, the performance parameters and particle flow characteristics of three Herrenknecht cutterhead designs featuring varying opening configurations in the central and circumference areas were analyzed using the Discrete Element Method (DEM) by considering material parameters for machine and soil and contact parameters between soil particles and soil particles-machine structures. Hertz–Mindlin model was assigned as the contact model for these elements. Additionally, three different cutterheads employed in Tehran metro projects in Iran were identified by monitoring the cutterhead torque and thrust force under same geotechnical conditions and operational parameters. Generally, a higher opening percentage in the central area of the cutterhead indicates good performance during excavation in cohesive soils. However, the higher opening percentage in circumferential areas is a better choice for effective excavated material removal around the cutterhead and tunnel in non-cohesive soils, weathered rocks, mixed and heterogeneous conditions.
Rock Mechanics
Faezeh Barri; Hamid Chakeri; Mohammad Darbor; Hamed Haghkish
Abstract
Excavation with Tunnel Boring Machine (TBM) in urban environments can have risks, such as ground surface settlement. The empty space between the cutterhead and the segment should be filled with suitable grout during the excavation. Nowadays, using grout behind the segment and other fillers fill the empty ...
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Excavation with Tunnel Boring Machine (TBM) in urban environments can have risks, such as ground surface settlement. The empty space between the cutterhead and the segment should be filled with suitable grout during the excavation. Nowadays, using grout behind the segment and other fillers fill the empty space behind the segment and reduce the amount of ground surface settlement. Undoubtedly, using a grout with appropriate mechanical behavior can be a suitable substitute for excavated soil in mechanized tunneling. In this research, the mechanical behavior of the grout behind the segment during injection into the space between the soil and the segment and its mixture with the soil is studied. Also, the effect of mechanical properties of grout mixed with soil on the ground surface settlement is investigated using numerical modeling. The components of two-component grout of this study comprises Sufian type 2 cement with 28-day strength of 44 MPa and density of 3050 kg/m3, Salafchegan bentonite with density of 2132 kg/m3 and precipitator of liquid sodium silicate with density of the solution 1500 kg/m3. The results of the laboratory studies indicated that mixing the grout and soil increases the mechanical properties of grout significantly. Increasing the soil in the mixture of soil and grout up to 40% increases the uniaxial compressive strength up to 300%, the elasticity of modulus up to 156% and the cohesion of the mixture up to 100%. On the other hand, based on the results of numerical modeling, the proper injection pressure can significantly reduce the ground surface settlement. Increasing the injection pressure from 0 to 120 kPa has a 17% influence on the reduction of ground surface settlement.
Rock Mechanics
Sadegh Amoun; Hamid Chakeri
Abstract
This study is an attempt to design and manufacture a tunnel boring machine (TBM) simulator to better understand the interaction between soil and cutting tools, due to the lack of an accepted method for this issue. In this paper, Sahand Soil Abrasion Test (SSAT) is introduced, which is built by the Sahand ...
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This study is an attempt to design and manufacture a tunnel boring machine (TBM) simulator to better understand the interaction between soil and cutting tools, due to the lack of an accepted method for this issue. In this paper, Sahand Soil Abrasion Test (SSAT) is introduced, which is built by the Sahand University of Technology. The experimental and real results of tool wear are presented. The results firstly demonstrate that the cutting tools wear in the coarse-grained soils can be less than in the fine-grained ones in the real conditions. However, in the soils with fine grains higher than 10%, the wear of cuttings tools increase in the laboratory condition when grading parameters increase. In soils with fine grains less than 10%, the wear of tools decreases by increasing the grading parameters. Also the results reveal that the coefficient of gradation depend on the amount of silt and clay in the soil samples. The investigations show that sorting is another good criterion for investigating the power of soil abrasively. Furthermore, it indicates that the cutting tools wear increases when the moisture content of the soil structure in the dense condition approaches the optimal moisture content. Finally, the results indicate that the wear and torque of the cutterhead could be reduced by 58% and 34%, respectively, when the excavated materials have the appropriate conditioning.
Rock Mechanics
Ali Kazempour Osalou; Sayfoddin Moosazadeh; Ali Nouri Qarahasanlou; Mohammad-Reza Baghban Golpasand
Abstract
Nowadays, tunnel excavation plays a major role in the development of countries. Due to the complex and challenging ground conditions, a comprehensive study and analysis must be done before, during, and after the excavation of tunnels. Hence, the importance of study and evaluation of ground settlement ...
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Nowadays, tunnel excavation plays a major role in the development of countries. Due to the complex and challenging ground conditions, a comprehensive study and analysis must be done before, during, and after the excavation of tunnels. Hence, the importance of study and evaluation of ground settlement is dramatically increased since many tunnel projects are performed in urban areas, where there are plenty of constructions, buildings, and facilities. For this reason, the control and prediction of ground settlement is one of the complicated topics in the field of risk engineering. Therefore, in this paper, the proportional hazard model (PHM) is used to analyze and study the ground settlement induced by Tabriz Metro Line 2 (TML2) tunneling. The PHM method is a semi-parametric regression method that can enter environmental conditions or factors affecting settlement probability. These influential factors are used as risk factors in the analysis. After establishing a database for a case study and using a proportional hazard model for surface settlement analysis, and then by evaluating the effect of environmental conditions on the ground surface settlement, it has been found that the risk factors of grouting pressure behind the segment, the ratio of tunnel depth to groundwater level, and drained cohesion strength at a significant level of 5% have a direct effect on the probability of settlement. The results also showed that the effect of grout injection pressure on ground subsidence is more than other parameters, and with increasing injection pressure, the probability of exceeding safe subsidence values decreases. In addition, it has been found that increasing the risk factor for the ratio of tunnel depth to groundwater level reduces the probability of exceeding the safe ground settlement. Finally, increasing the number of risk factors for drained cohesion strength increases the probability of exceeding safe settlement.
Rock Mechanics
Ghorban Khandouzi; Mohammad Hossein Khosravi
Abstract
Granular materials used in engineering structures tend to experience arching under different geotechnical factors. Arching is a factor of load transfer from the destroyed zone to stable areas in these structures. Soil arching plays an important role in stress redistribution, settlement, and load on supports ...
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Granular materials used in engineering structures tend to experience arching under different geotechnical factors. Arching is a factor of load transfer from the destroyed zone to stable areas in these structures. Soil arching plays an important role in stress redistribution, settlement, and load on supports in tunneling. This paper reviews the effect of various parameters on the development of soil arching and formation of expansion and contraction zones around the tunnel. A comprehensive literature review, analysis of new published papers, and investigations were conducted to study the effects of various parameters on soil arching. The results were obtained by studying the formation of shear bands, deformed zones, and their development. The achieved results of investigations show that soil arching and ground deformation around tunnels in sandy grounds are complex phenomena that require careful consideration during tunnel construction. Also the results reveal that despite the arching zone, a loosened zone with non-linear slip surfaces forms above the tunnel. With the onset of tunnel convergence, initial non-linear sliding surfaces appear, and the arching area forms above the tunnel. When tunnel convergence increases, a stable arch forms inside the arching zone, and a de-stressed area as a loosened zone is created under the stable arch. Understanding of soil arching, ground deformation, and the stable arch formed inside the arching zone around tunnels in sandy grounds is very important for the engineers evaluating stress redistribution and load on tunnel supports. Also understanding these issues can help the designers and practitioners make informed decisions during tunnel construction.
Rock Mechanics
Taha Ansari; Hamid Chakeri; Mohammad Darbor; sadegh Amoun; Hadi Shakeri
Abstract
There is no acceptable method for investigating the tool wear phenomenon in soft grounds. In this article, first, a new equipment made at Sahand University of Technology is introduced, which is used for simulation of TBM tunneling mechanism. Next, the effect of various soil grading parameters such as ...
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There is no acceptable method for investigating the tool wear phenomenon in soft grounds. In this article, first, a new equipment made at Sahand University of Technology is introduced, which is used for simulation of TBM tunneling mechanism. Next, the effect of various soil grading parameters such as D10, D30, and D60 (which indicate the corresponding diameters on the soil grading diagram where 10, 30, and 60% of the grains are smaller than these values, respectively), coefficient of gradation, uniformity coefficient, sorting coefficient and effective size on the cutting tools wear. The initial studies show that in soils with fine grains greater than 10%, by increase in the values of D10, D30, D60, and effective size, the tool wear increases. However, in soils with fine grains less than 10%, by increase in the above-mentioned parameters, the soil abrasiveness reduces. Also in soils with more than 10% fine grains, by increase in the coefficient of gradation value, the soil abrasiveness reduces. But in soils with fine grains less than 10%, by increase in the value of this parameter, the tool wear increases. The results of experiments show that sorting coefficient could be a good criterion for investigating the soil abrasiveness.
Rock Mechanics
Alireza Afradi; Arash Ebrahimabadi; Mansour Hedayatzadeh
Abstract
Tunnel Boring Machines (TBMs) are extensively used to excavate underground spaces in civil and tunneling projects. An accurate evaluation of their penetration rate is the key factor for the TBM performance prediction. In this study, artificial intelligence methods are used to predict the TBM penetration ...
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Tunnel Boring Machines (TBMs) are extensively used to excavate underground spaces in civil and tunneling projects. An accurate evaluation of their penetration rate is the key factor for the TBM performance prediction. In this study, artificial intelligence methods are used to predict the TBM penetration rate in excavation operations in the Kerman tunnel and the Gavoshan water conveyance tunnels. The aim of this paper is to show the application of the Multivariate Linear Regression (MLR), Artificial Neural Network (ANN), and Support Vector Machine (SVM) for the TBM penetration rate prediction. The penetration rate parameter is considered as a dependent variable, and the Rock Quality Designation (RQD), Brazilian Tensile Strength (BTS), Uniaxial Compressive Strength (UCS), Density (D), Joint Angle (JA), Joint Spacing (JS), and Poisson's Ratio are considered as independent variables. The obtained results by the several proposed methods indicated a high accuracy between the predicted and measured penetration rates, but the support vector machine yields more precise and realistic outcomes.
