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Geothermal power is being regarded as depending on techniques derived from hydrocarbon production in worldwide current strategy. However, it has artificially been developed far less than its natural potentials due to technical restrictions. This paper introduces the Enhanced Geothermal System based on Excavation (EGS-E), which is an innovative sche...
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... mining in South Africa has accessed into hard orebodies being buried over 4 km deep, and intelligent mine robots are rapidly iterating and evolving. Based on these backgrounds, aiming at solution to the bottleneck of EGS-D, a disruptively innovative geothermal extraction solution based on excavation rather than drilling, i.e., Enhanced Geothermal Systems based on Excavation technology (EGS-E), is proposed, as shown in Figure 1. EGS-E overcomes the shortcomings of the boreholes and fracturing based conventional EGS and provides a new large-scale scheme for developing hot dry rocks. ...
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... using numerical modelling, a section of typical roadway with the circular shape at cross section, which is excavated within high-temperature and high-stress hard rock, was analyzed. During the simulation, a sim- Figure 1. Schematic illustration of the EGS-E conceptual model. ...
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... the tunnel, the partition rupture appears. Figure 10 shows the phenomenon of intermittent compressive stress distributed along radial horizontal direction within the surrounding rock of a tunnel. As shown in Figure 11 is the effects of lateral pressure coefficient Kx on EDZ in the aspects of distribution scale, failure pattern, the maximum plastic strain and the maximum principal stress. ...
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... 10 shows the phenomenon of intermittent compressive stress distributed along radial horizontal direction within the surrounding rock of a tunnel. As shown in Figure 11 is the effects of lateral pressure coefficient Kx on EDZ in the aspects of distribution scale, failure pattern, the maximum plastic strain and the maximum principal stress. It can be seen that Kx has distinct effects on the failure issues of surrounding rock. ...
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... the tunnel, the partition rupture appears. Figure 10 shows the phenomenon of intermittent compressive stress distributed along radial horizontal direction within the surrounding rock of a tunnel. ...
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... shown in Figure 11 is the effects of lateral pressure coefficient K x on EDZ in the aspects of distribution scale, failure pattern, the maximum plastic strain and the maximum principal stress. It can be seen that K x has distinct effects on the failure issues of surrounding rock. ...
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... lateral pressure coefficient of K x = 1.2, greater horizontal stress leads to the shear zones closest to the side walls from where shearing slides continues to propagate until intersect each other and then bend up and down, respectively. As shown in Figure 11 is the effects of lateral pressure coefficient Kx on EDZ in the aspects of distribution scale, failure pattern, the maximum plastic strain and the maximum principal stress. It can be seen that Kx has distinct effects on the failure issues of surrounding rock. ...
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... lateral pressure coefficient of Kx = 1.2, greater horizontal stress leads to the shear zones closest to the side walls from where shearing slides continues to propagate until intersect each other and then bend up and down, respectively. distribution scales failure patterns the maximum plastic shear strain (-) the maximum principal stress (MPa) As shown in Figure 12, there had already been theoretical and laboratory modelled studies on the log-spiral shear-failure sliding curves [55][56][57] surrounding a circular tunnel. Tensile/extensional modes were not evident in these physical model studies, which might be due to weak properties and low level of confinement. ...
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... shown in Figure 12, there had already been theoretical and laboratory modelled studies on the log-spiral shear-failure sliding curves [55][56][57] surrounding a circular tunnel. Tensile/extensional modes were not evident in these physical model studies, which might be due to weak properties and low level of confinement. ...
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... the modelling, the numerical discretization of surrounding rock was kept the same as that in the previous section. As shown in Figure 13, a 10 cm thick thermal insulation liner with its corresponding mesh was appended onto the tunnel wall. It was evenly divided into two blocks along the radial direction and 640 blocks along the circumferential direction. ...
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... the modelling, the numerical discretization of surrounding rock was kept the same as that in the previous section. As shown in Figure 13, a 10 cm thick thermal insulation liner with its corresponding mesh was appended onto the tunnel wall. It was evenly divided into two blocks along the radial direction and 640 blocks along the circumferential direction. ...
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... term of modelling this procedure, the simulated magnitude and covering area of EDZs were recorded once per physical hour. Figure 14, the radial distributions of temperature across surrounding rock are different with and without installing thermal insulation layer (TIL). Due to the influence of low-temperature airflow inside the tunnel, temperature in surrounding rock continues to descend with ventilating time, and the area of low-temperature disturbance gradually expands. ...
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... the rather small heat conductivity of thermal insulation liner makes it become a barrier. After 300 h Figure 13. The meshing of thermal insulation liner which is quarterly shown as its symmetry. ...
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... term of modelling this procedure, the simulated magnitude and covering area of EDZs were recorded once per physical hour. Figure 14, the radial distributions of temperature across surrounding rock are different with and without installing thermal insulation layer (TIL). Due to the influence of low-temperature airflow inside the tunnel, temperature in surrounding rock continues to descend with ventilating time, and the area of low-temperature disturbance gradually expands. ...
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... 2021, 14, x FOR PEER REVIEW 16 of 20 of ventilation, the lowest temperature of surrounding rock is still as high as 153.0 °C, indicating that the insulation layer (TIL) can effectively mitigate the heat loss from surrounding rock during the process of ventilation. At the end of ventilation cooling, the stress state of surrounding rock along the radial but horizontal direction on the circular tunnel cross-section is exemplified in Figure 15. The falling off of surrounding rock temperature causes additional tensile stress near the tunnel. ...
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... rock in the temperature lowered zone shrinks and is unloaded so the concentration of compressive stress transfers to further zone. At the end of ventilation cooling, the stress state of surrounding rock along the radial but horizontal direction on the circular tunnel cross-section is exemplified in Figure 15. The falling off of surrounding rock temperature causes additional tensile stress near the tunnel. ...
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... rock in the temperature lowered zone shrinks and is unloaded so the concentration of compressive stress transfers to further zone. of ventilation, the lowest temperature of surrounding rock is still as high as 153.0 °C, indicating that the insulation layer (TIL) can effectively mitigate the heat loss from surrounding rock during the process of ventilation. At the end of ventilation cooling, the stress state of surrounding rock along the radial but horizontal direction on the circular tunnel cross-section is exemplified in Figure 15. The falling off of surrounding rock temperature causes additional tensile stress near the tunnel. ...
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... rock in the temperature lowered zone shrinks and is unloaded so the concentration of compressive stress transfers to further zone. Figure 16 shows the scales of EDZs and their evolution process along with ventilation time. With the ventilation time passing by, EDZ d , HDZ d , EDZ a and HDZ a gradually grew. ...
Citations
... Li et al. [27] introduced the Enhanced Geothermal System based on Excavation (EGS-E), as a new method for geothermal energy extraction. The article investigates the initiation and propagation of excavation damaged zones (EDZs) in the EGS-E and the further evolution of surrounding rock stress and EDZs during ventilation by thermal-mechanical coupling. ...
Mining is an essential sector for economic development, as it provides valuable resources that are crucial for modern living.
... It provides a scientific reference for practical engineering design. Due to the complexity of the analytical solution of the actual tunnel temperature field [10,11], it is very important to apply the finite element method to the temperature field analysis of the tunnel and geothermal analysis [12][13][14][15][16]. ...
The distribution of the initial temperature field of a high-rock-temperature tunnel is critical for determining the tunnel line and the construction scheme. This study used model testing, numerical analysis, and field measurement to investigate the initial temperature field distribution of a tunnel with high rock temperatures. A model test system was developed, and the experimental results show that the boundary conditions set by the model are reasonable. The results show that the temperature along the tunnel line is high in the middle and low at both ends. Obviously, the periodic boundary conditions have a significant influence on the temperature field distribution. Then, the corresponding two-dimensional unsteady numerical model is established, and the numerical model is verified by the model test. Next, the numerical model is applied to the actual Jiwoxiga tunnel, which is a high-rock-temperature tunnel. The results show that the maximum ground temperature in the direction of the Jiwoxiga tunnel line is 52.5 °C, the tunnel lengths with ground temperatures above 28 °C account for 96.25% of the total tunnel length, and the tunnel length with a ground temperature above 45 °C comes to nearly 1200 m. In addition, this result is also verified by the field drilling data and field-measured data after excavation. The effectiveness and accuracy of the numerical model are fully demonstrated. This study provides theoretical support for the design and construction of high rock temperature tunnels.
... In tunnel excavation within a geothermally rich area, the change in temperature after excavation greatly influences the stress distribution and mechanical properties of the surrounding rock [5][6][7][8]. In recent years, many studies have focused on the effect of high temperature on rock damage; however, relatively few studies have focused on the influence of temperature on rockbursts [9][10][11]. ...
To further understand the stress evolution and rockburst occurrence mechanism in geothermally rich areas in the Sichuan–Tibet railway project, this work presents a theoretical study of the influence of temperature change on the failure of rock, conducts numerical studies of the temperature and stress evolution in the surrounding rock during high-temperature tunnel excavation, and further studies the possibility of rockbursts under high in situ stress and high-temperature conditions. Rockbursts occur frequently at the junction of a face and tunnel wall, and ventilation and cooling of tunnels reduce the stress and sometimes reduce the possibility of rockbursts. Continuous cooling leads to a larger tensile stress and the possibility of failure of wall rock. In addition, the influence of the convection heat transfer coefficient, in situ stress and fault effect on the stress distribution and possibility of rockbursts are also discussed in detail. The results are beneficial for the prevention and control of rockbursts in high in situ stress and geothermally rich areas.
In order to solve the problem of designing the thermal insulation layer for high geothermal tunnels, this paper studies the nature of thermal insulation materials and the structure of the thermal insulation layer. Based on the mechanisms of heat transfer from the cylinder wall and the flat plate, combined with the physical and thermophysical properties of the materials tested, the selection of thermal insulating materials for high geothermal tunnels as well as the layout were analyzed. The results of the study showed that polyurethane materials proved to be a better overall insulation material, with better water resistance and lower thermal conductivity, as well as better compressive strength. The flat plate heat transfer model can be used to predict the temperature distribution of the lining structure, which simplifies heat transfer calculations and analysis. This paper proposed a new insulation design solution using polyurethane-corrugated steel insulation lining with a double layer deployment. Numerical simulation results show that the thermal insulation design scheme can effectively reduce the temperature of the lining structure, which is beneficial to improve the thermal performance of the lining structure. The results of the study may provide new ideas for the design of heat-insulating structures for high geothermal tunnels.
This work aims to cope with the increasingly complex geological conditions in the process of traffic tunnel construction in China, improve the stability of tunnel construction, and reduce the probability of collapse, water gushing and other hazards in the construction process. The instability and deformation mechanism of tunnel surrounding rock is explored based on the theoretical knowledge of support vector machine (SVM), fuzzy reasoning, and Q classification method, and combined with the characteristics of tunnel surrounding rock in China. Moreover, a classification model via SVM and fuzzy reasoning is constructed for tunnel surrounding rock, followed by the outline of the shortcomings of tunnel surrounding rock classification in China. Then, the corresponding optimization method is put forward according to Q classification method. Finally, simulation experiments are conducted on arch collapse surrounding rock to evaluate the deformation stability. Experimental results demonstrate that the unstable area of tunnel surrounding rock increases with the increase in tunnel span, and the supporting treatment area required by the tunnel is also greatly enlarged. With the increase in span, the settlement value of vault increases continuously, and the increase rate varies with the hardness of surrounding rock. Moreover, the influence of the change of structural plane spacing of surrounding rock on the stability of surrounding rock gradually reduces. The influence of surrounding rock with larger hardness is more significant than that of surrounding rock with smaller hardness. Furthermore, there is a corresponding relationship between the hardness of rock and the rebound value. Besides, through the comparison between the actual surrounding rock test and the surrounding rock grade, there is no significantly corresponding relationship between the rebound value and the surrounding rock grade. Therefore, the rebound instrument can be used as an auxiliary tool for determining the surrounding rock grade. The research conclusion is that the classification optimization method of tunnel surrounding rock reported here facilitates the classification speed of tunnel surrounding rock.
