Understanding three-dimensional(3D)in situ stress field is of key importance for estimating the stability of large deep underground cavern groups near valleys.However,the complete 3D in situ stress fields around large...Understanding three-dimensional(3D)in situ stress field is of key importance for estimating the stability of large deep underground cavern groups near valleys.However,the complete 3D in situ stress fields around large deep underground cavern groups are difficult to determine based on in situ stress data from a limited number of measuring points due to the insufficient representativeness and unreliability of such measurements.In this study,an integrated approach for estimating the 3D in situ stress field around a large deep underground cavern group near a valley is developed based on incomplete in situ stress measurements and the stress-induced failures of tunnels excavated prior to the step excavation of the cavern group.This integrated approach is implemented via four interrelated and progressive basic steps,i.e.inference of the regional tectonic stress field direction,analyses of in situ stress characteristics and measurement reliability,regression-based in situ stress field analysis and reliability assessment,and modified in situ stress field analysis and reliability verification.The orientations and magnitudes of the 3D in situ stress field can be analyzed and obtained at a strategic level following these four basic steps.First,the tectonic stress field direction around the cavern group is deduced in accordance with the regional tectonic framework and verified using a regional crustal deformation velocity map.Second,the reliability of the in situ stress measurements is verified based on the locations and depths of stressinduced brittle failures in small tunnels(such as exploratory tunnels and pilot tunnels)within the excavation range of the cavern group.Third,considering the influences of the valley topography and major geological structures,the 3D in situ stress field is regressed using numerical simulation and multiple linear regression techniques based on the in situ stress measurements.Finally,the regressed in situ stress field is further modified and reverified based on the stress-induced brittle failures of small tunnels and the initial excavation of the cavern group.A case study of the Shuangjiangkou underground cavern group demonstrates that the proposed approach is reliable for estimating the 3D in situ stress fields of large deep underground cavern groups near valleys,thus contributing to the optimization of practical excavation and design of mitigating the instability of the surrounding rock masses during step excavations.展开更多
The Jinping I hydropower station is a huge water conservancy project consisting of the highest concrete arch dam to date in the world and a highly complex and large underground powerhouse cavern. It is located on the ...The Jinping I hydropower station is a huge water conservancy project consisting of the highest concrete arch dam to date in the world and a highly complex and large underground powerhouse cavern. It is located on the right bank with extremely high in-situ stress and a few discontinuities observed in surrounding rock masses. The problems of rock mass deformation and failure result in considerable challenges related to project design and construction and have raised a wide range of concerns in the fields of rock mechanics and engineering. During the excavation of underground caverns, high in-situ stress and relatively low rock mass strength in combination with large excavation dimensions lead to large deformation of the surrounding rock mass and support. Existing experiences in excavation and support cannot deal with the large deformation of rock mass effectively, and further studies are needed. In this paper, the geological conditions, layout of caverns, and design of excavation and support are first introduced, and then detailed analyses of deformation and failure characteristics of rocks are presented. Based on this, the mechanisms of deformation and failure are discussed, and the support adjustments for controlling rock large deformation and subsequent excavation procedures are proposed. Finally, the effectiveness of support and excavation adjustments to maintain the stability of the rock mass is verified. The measures for controlling the large deformation of surrounding rocks enrich the practical experiences related to the design and construction of large underground openings, and the construction of caverns in the Jinping I hydropower station provides a good case study of large-scale excavation in highly stressed ground with complex geological structures, as well as a reference case for research on rock mechanics.展开更多
The occurrence of disasters in deep mining engineering has been confirmed to be closely related to the external dynamic disturbances and geological discontinuities.Thus,a combined finite-element method was employed to...The occurrence of disasters in deep mining engineering has been confirmed to be closely related to the external dynamic disturbances and geological discontinuities.Thus,a combined finite-element method was employed to simulate the failure process of an underground cavern,which provided insights into the failure mechanism of deep hard rock affected by factors such as the dynamic stress-wave amplitudes,disturbance direction,and dip angles of the structural plane.The crack-propagation process,stress-field distribution,displacement,velocity of failed rock,and failure zone around the circular cavern were analyzed to identify the dynamic response and failure properties of the underground structures.The simulation results indicate that the dynamic disturbance direction had less influence on the dynamic response for the constant in situ stress state,while the failure intensity and damage range around the cavern always exhibited a monotonically increasing trend with an increase in the dynamic load.The crack distribution around the circular cavern exhibited an asymmetric pattern,possibly owing to the stress-wave reflection behavior and attenuation effect along the propagation route.Geological discontinuities significantly affected the stability of nearby caverns subjected to dynamic disturbances,during which the failure intensity exhibited the pattern of an initial increase followed by a decrease with an increase in the dip angle of the structural plane.Additionally,the dynamic disturbance direction led to variations in the crack distribution for specific structural planes and stress states.These results indicate that the failure behavior should be the integrated response of the excavation unloading effect,geological conditions,and external dynamic disturbances.展开更多
The paper gives an insight into the behaviour of large underground caverns which are subjected to blast loads. Caverns are generally constructed in hard rock formation which compels us to use blasting methods for the ...The paper gives an insight into the behaviour of large underground caverns which are subjected to blast loads. Caverns are generally constructed in hard rock formation which compels us to use blasting methods for the excavation works. Comparative study was done between models with intact rock mass and discontinuities to assess the stability of cavern as a result of blast loads. Numerical modelling was performed with 3 dimensional distinct element code(3 DEC) to analyse the performance of cavern walls in terms of displacement and to compute peak particle velocities(PPV) both around the cavern periphery and at surface of models. Results showed that the velocity wave with higher frequency exhibited large displacements around the periphery of cavern. Computation of PPV showed that model with horizontal joint sets showed lower PPV in comparison to model with intact rock mass. PPV values were also analysed on the surface for model consisting vertical joints spaced at 4 m intervals. Comparative study of PPV on surface vertically above the blast location between models with horizontal joints spaced at 4 m and vertical joints at 4 m intervals were conducted. Results depicted higher magnitudes of PPV for model with vertical joints in comparison to model with horizontal joints.展开更多
Regarding excavation-damaged zone (EDZ) around underground opening as non-homogeneous rockmass with spatial deterioration effect on stuffiness and strength, a parametric model of EDZ using radius-displacement-dependen...Regarding excavation-damaged zone (EDZ) around underground opening as non-homogeneous rockmass with spatial deterioration effect on stuffiness and strength, a parametric model of EDZ using radius-displacement-dependent deformation modulus (RDDM) was proposed. Considering the nonlinearity characteristic of deformation and locality otherness of surrounding rock, deterioration parameter field of deformation modulus of rockmass around opening was quantitatively calculated through a given function. Applicability for multi-cavern condition and parameter sensibility of the model was analyzed by numerical experiments using synthetic data. Furthermore, the model was applied to identify EDZ of underground caverns of Pubugou hydropower station by calculating deterioration parameter field. Based on the parametric analysis of spatial effect and geological investigation, it is recognized that large radial deformation of deep fractured rock at the spandrel position and insufficient supporting bolts mainly result in great deformation pressure to act on the shotcrete and cause partial crack and spalling. It is shown that deterioration parameter field along the longitudinal axis of main powerhouse is evidently non-homogeneous in space and distributes exponentially along the radius from the opening. The model provides a simple and convenient way to identify the EDZ in the working state for rapid construction feedback analysis and support optimization of underground cavern from quantitative point of view and also aids in interpreting monitoring displacements and estimating support requirements.展开更多
Underground caverns have important military and civilian uses, but their internal natural radiation may endanger human health, and it is necessary to implement protection. The protective measures taken for an undergro...Underground caverns have important military and civilian uses, but their internal natural radiation may endanger human health, and it is necessary to implement protection. The protective measures taken for an underground cavern in Chongqing have obvious effects. The results show that cleaning the radiation source in the environment and sealing the gap of the hole can re-duce the natural radiation intensity inside the cavern to a certain extent, reducing the ambient temperature can significantly reduce the natural radiation intensity inside the cavern, the use of press-in ventilation can greatly reduce the natural radiation intensity inside the cavern, the cumulative drop can reach 25.63%, and the protective effect is obvious. These protective measures can be used in underground caverns to improve the safety of military and civilian activities.展开更多
The deformation instability of surrounding rock and the collapse of rock blocks are two common failure modes observed during the construction of underground caverns.Therefore,a comprehensive safety evaluation method(C...The deformation instability of surrounding rock and the collapse of rock blocks are two common failure modes observed during the construction of underground caverns.Therefore,a comprehensive safety evaluation method(CSEM)of surrounding rock for application during underground cavern construction is presented in this paper.The method can be used to evaluate the deformation stability of surrounding rock and predict the collapse of rock blocks,rapidly.First,a deformation stability prediction and evaluation method(DSPEM)for rock mass is established.It combines the safety evaluation method based on a deformation statistical analysis and an inverse deformation prediction method using measured deformation data of surrounding rock.This approach possesses the unique characteristics of complementary and mutual verification.In addition,a comprehensive early-warning index system(CWIS)for assessing the deformation stability of surrounding rock is presented.It consists of three types of warning indicators and three levels of warning values.The earlywarning values can be adjusted reasonably by the prediction correction method according to the measured displacements.For the collapse of rock blocks controlled by structural surfaces,a rapid prediction method of rock block collapse(RPMBC)based on the block theory is then presented.Finally,combining the DSPEM,RPMBC,and CWIS,the CSEM of surrounding rock for assessing the safety of cavern construction is established.It can provide technical support for decision making on the safety of surrounding rock during the construction of underground caverns.展开更多
To study the dynamic mechanical properties of tuff under different environmental conditions,the tuff from an ancient quarry in Shepan Island was prepared.The impact damage to the rock was tested using a triaxial dynam...To study the dynamic mechanical properties of tuff under different environmental conditions,the tuff from an ancient quarry in Shepan Island was prepared.The impact damage to the rock was tested using a triaxial dynamic impact mechanical testing system(TDIMTS)with different ground stresses,temperatures,and groundwater pressures.The time-strain relationship,dynamic stress-strain relationship,energy dissipation law,energy-peak strain relationship,and the impact damage pattern of the tuff specimens under impact air pressures were investigated.The TDIMTS experiment on ancient underground rock mass under impact loading was also simulated using the finite element analysis software LS-DYNA based on the Holmquist-Johnson-Cook(HJC)material model.The dynamic failure process,failure pattern and peak stress of tuff specimen were calculated.The simulation results obtained using the above methods were in good agreement with the experimental results.The results of the dynamic experiment show that with the same local stress,groundwater pressure,and temperature,the damage to the tuff specimens caused by blasting and quarrying disturbances gradually increases as the impact pressure increases.Under the same local stress,groundwater pressure,and temperature,the energy required to rupture the tuffs in ancient underground caverns is relatively small if the impact pressure is low accordingly,but as the impact pressure increases,the damage to the tuff caused by quarrying disturbance gradually increases.The damage gradually increases and the degree of damage to the tuff and the strain energy exhibit asymptotic growth when the tuff specimens are subjected to the greater strain energy,increasing the degree of rupturing of the tuff.In addition,the average crushing size decreases with increasing strain energy.By comparing the simulation results with the experimental results,it was found that the HJC model reflected the dynamic impact performance of tuff specimen,and the simulation results showed an evident strain rate effect.These results of this study can offer some guidance and theoretical support for the stability evaluation,protection,and safe operation of the ancient underground caverns in future.展开更多
Engineering design in soft rocks and its stability analysis exerts many challenges to rock engineers. Many engineering works in Turkey’s Cappadocia region must face and tackle the existing sites covered by the soft r...Engineering design in soft rocks and its stability analysis exerts many challenges to rock engineers. Many engineering works in Turkey’s Cappadocia region must face and tackle the existing sites covered by the soft rocks. This study is aimed to examine the stability condition of a typical underground storage cavern(USC) excavated in a soft rock in this region. For this purpose, two-and threedimensional stability analyses of the USCs were performed using the finite element method(FEM).Because of the inherent difficulty in characterizing soft/weak rock masses in the region using traditional classification systems, the stability of a typical USC was evaluated by representing the rock mass condition with two distinct scenarios in FEM analysis.While these structures were unstable according to the 2D analysis conducted in RS2 software in the worstcase scenario, they were stable in the 3D analysis using RS3 software in both scenarios. Besides,feasible cover depths were examined to assess their possible effects on the factor of safety and deformation measurements. It was found that 15 m seems to be an optimal depth for excavating a typical USC in the soft rocks exposed in the region. The 3D FEM results provide valuable information to optimize the future planning and preliminary design of USCs.展开更多
The underground water-sealed storage technique is critically important and generally accepted for the national energy strategy in China. Although several small underground water-sealed oil storage caverns have been bu...The underground water-sealed storage technique is critically important and generally accepted for the national energy strategy in China. Although several small underground water-sealed oil storage caverns have been built in China since the 1970s, there is still a lack of experience for large-volume underground storage in complicated geological conditions. The current design concept of water curtain system and the technical instruction for system operation have limitations in maintaining the stability of surrounding rock mass during the construction of the main storage caverns, as well as the long-term stability. Although several large-scale underground oil storage projects are under construction at present in China, the design concepts and construction methods, especially for the water curtain system, are mainly based on the ideal porosity medium flow theory and the experiences gained from the similar projects overseas. The storage projects currently constructed in China have the specific features such as huge scale, large depth, multiple-level arrangement, high seepage pressure, complicated geological conditions, and high in situ stresses, which are the challenging issues for the stability of the storage caverns. Based on years’ experiences obtained from the first large-scale (millions of cubic meters) underground water-sealed oil storage project in China, some design and operation problems related to water curtain system during project construction are discussed. The drawbacks and merits of the water curtain system are also presented. As an example, the conventional concept of “filling joints with water” is widely used in many cases, as a basic concept for the design of the water curtain system, but it is immature. In this paper, the advantages and disadvantages of the conventional concept are pointed out, with respect to the long-term stability as well as the safety of construction of storage caverns. Finally, new concepts and principles for design and construction of the underground water-sealed oil storage caverns are proposed.展开更多
Increasing the allowable gas pressure of underground gas storage(UGS) is one of the most effective methods to increase its working gas capacity. In this context, hydraulic fracturing tests are implemented on the targe...Increasing the allowable gas pressure of underground gas storage(UGS) is one of the most effective methods to increase its working gas capacity. In this context, hydraulic fracturing tests are implemented on the target formation for the UGS construction of Jintan salt caverns, China, in order to obtain the minimum principal in situ stress and the fracture breakdown pressure. Based on the test results, the maximum allowable gas pressure of the Jintan UGS salt cavern is calibrated. To determine the maximum allowable gas pressure, KING-1 and KING-2 caverns are used as examples. A three-dimensional(3D)geomechanical model is established based on the sonar data of the two caverns with respect to the features of the target formation. New criteria for evaluating gas penetration failure and gas seepage are proposed. Results show that the maximum allowable gas pressure of the Jintan UGS salt cavern can be increased from 17 MPa to 18 MPa(i.e. a gradient of about 18 k Pa/m at the casing shoe depth). Based on numerical results, a field test with increasing maximum gas pressure to 18 MPa has been carried out in KING-1 cavern. Microseismic monitoring has been conducted during the test to evaluate the safety of the rock mass around the cavern. Field monitoring data show that KING-1 cavern is safe globally when the maximum gas pressure is increased from 17 MPa to 18 MPa. This shows that the geomechanical model and criteria proposed in this context for evaluating the maximum allowable gas pressure are reliable.展开更多
For better rock mass characterization and support design, 3D engineering geological mapping was carried for the heading portion of the under construction 200.00 m long, 68.75 m high and 20.20 m wide underground additi...For better rock mass characterization and support design, 3D engineering geological mapping was carried for the heading portion of the under construction 200.00 m long, 68.75 m high and 20.20 m wide underground additional surge pool cavern of a Pranahitha-Chevella Sujala Sravanthi lift irrigation scheme package 8, India. To study cavern behavior, 3D geologic mapping of heading portion is very important for large cavern for predicting geologic conditions in benching down up to invert level, planning support system, selecting inclination for best location of supplemental rock bolt and choosing strategic locations for various types of instrumentation. The assessment of Tunnel Quality Index “Q” and Geomechanics classification for the granitic rock mass was done based on the information available of the rock joints and their nature and 3D geological logging. Hoek-Brown parameters were also determined by the statistical analysis of the results of a set of triaxial tests on core samples. On basis of geological characteristics and NMT Q-system chart, support system is recommended which includes rock bolt, steel fibre reinforced shotcrete and grouting. To evaluate the efficacy of the proposed support system, the capacity of support system is determined.展开更多
【目的】明晰地下储气库的热力学过程是压缩空气储能(compressed air energy storage,CAES)电站安全设计与运行调度的重要基础。【方法】现有地下储气库热力学模型在计算热量交换时,存在高压储气阶段热损失偏大和低压储气库阶段补热过...【目的】明晰地下储气库的热力学过程是压缩空气储能(compressed air energy storage,CAES)电站安全设计与运行调度的重要基础。【方法】现有地下储气库热力学模型在计算热量交换时,存在高压储气阶段热损失偏大和低压储气库阶段补热过多的不足。本文在全面分析地下储气库热力学模型理论基础合理性的前提下,先分析储气库热量计算偏差的形成根源;再提出改进模型。【结果】研究结果表明:现有的热力学计算解析模型忽略了CAES地下储气库在运行过程中温度分布的不均匀性,这种温度分布的不均匀导致储气室洞壁与压缩空气之间的对流换热模型失真,导致温度计算结果偏差大。考虑混合对流换热的改进模型二可以较好地解决储气阶段温度计算结果与真实结果之间偏差过大的问题。算例分析证明了改进模型二的合理性。【结论】本文的改进模型二可为CAES地下储气库容积优化设计与效率分析提供计算依据。展开更多
基金This research was funded by the National Science Foundation of China(Grant Nos.U1765206 and 51979268)Innovation Research Group Project of Natural Science Foundation of Hubei Province(Grant No.ZRQT2020000114).
文摘Understanding three-dimensional(3D)in situ stress field is of key importance for estimating the stability of large deep underground cavern groups near valleys.However,the complete 3D in situ stress fields around large deep underground cavern groups are difficult to determine based on in situ stress data from a limited number of measuring points due to the insufficient representativeness and unreliability of such measurements.In this study,an integrated approach for estimating the 3D in situ stress field around a large deep underground cavern group near a valley is developed based on incomplete in situ stress measurements and the stress-induced failures of tunnels excavated prior to the step excavation of the cavern group.This integrated approach is implemented via four interrelated and progressive basic steps,i.e.inference of the regional tectonic stress field direction,analyses of in situ stress characteristics and measurement reliability,regression-based in situ stress field analysis and reliability assessment,and modified in situ stress field analysis and reliability verification.The orientations and magnitudes of the 3D in situ stress field can be analyzed and obtained at a strategic level following these four basic steps.First,the tectonic stress field direction around the cavern group is deduced in accordance with the regional tectonic framework and verified using a regional crustal deformation velocity map.Second,the reliability of the in situ stress measurements is verified based on the locations and depths of stressinduced brittle failures in small tunnels(such as exploratory tunnels and pilot tunnels)within the excavation range of the cavern group.Third,considering the influences of the valley topography and major geological structures,the 3D in situ stress field is regressed using numerical simulation and multiple linear regression techniques based on the in situ stress measurements.Finally,the regressed in situ stress field is further modified and reverified based on the stress-induced brittle failures of small tunnels and the initial excavation of the cavern group.A case study of the Shuangjiangkou underground cavern group demonstrates that the proposed approach is reliable for estimating the 3D in situ stress fields of large deep underground cavern groups near valleys,thus contributing to the optimization of practical excavation and design of mitigating the instability of the surrounding rock masses during step excavations.
文摘The Jinping I hydropower station is a huge water conservancy project consisting of the highest concrete arch dam to date in the world and a highly complex and large underground powerhouse cavern. It is located on the right bank with extremely high in-situ stress and a few discontinuities observed in surrounding rock masses. The problems of rock mass deformation and failure result in considerable challenges related to project design and construction and have raised a wide range of concerns in the fields of rock mechanics and engineering. During the excavation of underground caverns, high in-situ stress and relatively low rock mass strength in combination with large excavation dimensions lead to large deformation of the surrounding rock mass and support. Existing experiences in excavation and support cannot deal with the large deformation of rock mass effectively, and further studies are needed. In this paper, the geological conditions, layout of caverns, and design of excavation and support are first introduced, and then detailed analyses of deformation and failure characteristics of rocks are presented. Based on this, the mechanisms of deformation and failure are discussed, and the support adjustments for controlling rock large deformation and subsequent excavation procedures are proposed. Finally, the effectiveness of support and excavation adjustments to maintain the stability of the rock mass is verified. The measures for controlling the large deformation of surrounding rocks enrich the practical experiences related to the design and construction of large underground openings, and the construction of caverns in the Jinping I hydropower station provides a good case study of large-scale excavation in highly stressed ground with complex geological structures, as well as a reference case for research on rock mechanics.
基金The authors would like to acknowledge the financial supports from the National Natural Science Foundation of China(Grant Nos.52004143,51774194)the Open fund for State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines,the China Postdoctoral Science Foundation(No.2020M670781)the NSFC-Shandong Joint fund(Grant No.U1806208).
文摘The occurrence of disasters in deep mining engineering has been confirmed to be closely related to the external dynamic disturbances and geological discontinuities.Thus,a combined finite-element method was employed to simulate the failure process of an underground cavern,which provided insights into the failure mechanism of deep hard rock affected by factors such as the dynamic stress-wave amplitudes,disturbance direction,and dip angles of the structural plane.The crack-propagation process,stress-field distribution,displacement,velocity of failed rock,and failure zone around the circular cavern were analyzed to identify the dynamic response and failure properties of the underground structures.The simulation results indicate that the dynamic disturbance direction had less influence on the dynamic response for the constant in situ stress state,while the failure intensity and damage range around the cavern always exhibited a monotonically increasing trend with an increase in the dynamic load.The crack distribution around the circular cavern exhibited an asymmetric pattern,possibly owing to the stress-wave reflection behavior and attenuation effect along the propagation route.Geological discontinuities significantly affected the stability of nearby caverns subjected to dynamic disturbances,during which the failure intensity exhibited the pattern of an initial increase followed by a decrease with an increase in the dip angle of the structural plane.Additionally,the dynamic disturbance direction led to variations in the crack distribution for specific structural planes and stress states.These results indicate that the failure behavior should be the integrated response of the excavation unloading effect,geological conditions,and external dynamic disturbances.
文摘The paper gives an insight into the behaviour of large underground caverns which are subjected to blast loads. Caverns are generally constructed in hard rock formation which compels us to use blasting methods for the excavation works. Comparative study was done between models with intact rock mass and discontinuities to assess the stability of cavern as a result of blast loads. Numerical modelling was performed with 3 dimensional distinct element code(3 DEC) to analyse the performance of cavern walls in terms of displacement and to compute peak particle velocities(PPV) both around the cavern periphery and at surface of models. Results showed that the velocity wave with higher frequency exhibited large displacements around the periphery of cavern. Computation of PPV showed that model with horizontal joint sets showed lower PPV in comparison to model with intact rock mass. PPV values were also analysed on the surface for model consisting vertical joints spaced at 4 m intervals. Comparative study of PPV on surface vertically above the blast location between models with horizontal joints spaced at 4 m and vertical joints at 4 m intervals were conducted. Results depicted higher magnitudes of PPV for model with vertical joints in comparison to model with horizontal joints.
基金Project(2010CB732005) supported by the National Basic Research Program of ChinaProjects(51279136, 51209164) supported by the National Natural Science Foundation of China
文摘Regarding excavation-damaged zone (EDZ) around underground opening as non-homogeneous rockmass with spatial deterioration effect on stuffiness and strength, a parametric model of EDZ using radius-displacement-dependent deformation modulus (RDDM) was proposed. Considering the nonlinearity characteristic of deformation and locality otherness of surrounding rock, deterioration parameter field of deformation modulus of rockmass around opening was quantitatively calculated through a given function. Applicability for multi-cavern condition and parameter sensibility of the model was analyzed by numerical experiments using synthetic data. Furthermore, the model was applied to identify EDZ of underground caverns of Pubugou hydropower station by calculating deterioration parameter field. Based on the parametric analysis of spatial effect and geological investigation, it is recognized that large radial deformation of deep fractured rock at the spandrel position and insufficient supporting bolts mainly result in great deformation pressure to act on the shotcrete and cause partial crack and spalling. It is shown that deterioration parameter field along the longitudinal axis of main powerhouse is evidently non-homogeneous in space and distributes exponentially along the radius from the opening. The model provides a simple and convenient way to identify the EDZ in the working state for rapid construction feedback analysis and support optimization of underground cavern from quantitative point of view and also aids in interpreting monitoring displacements and estimating support requirements.
文摘Underground caverns have important military and civilian uses, but their internal natural radiation may endanger human health, and it is necessary to implement protection. The protective measures taken for an underground cavern in Chongqing have obvious effects. The results show that cleaning the radiation source in the environment and sealing the gap of the hole can re-duce the natural radiation intensity inside the cavern to a certain extent, reducing the ambient temperature can significantly reduce the natural radiation intensity inside the cavern, the use of press-in ventilation can greatly reduce the natural radiation intensity inside the cavern, the cumulative drop can reach 25.63%, and the protective effect is obvious. These protective measures can be used in underground caverns to improve the safety of military and civilian activities.
基金The research presented in this paper was supported by the National Nature Science Foundation of China(Grant Nos.51739006 and U1765204).
文摘The deformation instability of surrounding rock and the collapse of rock blocks are two common failure modes observed during the construction of underground caverns.Therefore,a comprehensive safety evaluation method(CSEM)of surrounding rock for application during underground cavern construction is presented in this paper.The method can be used to evaluate the deformation stability of surrounding rock and predict the collapse of rock blocks,rapidly.First,a deformation stability prediction and evaluation method(DSPEM)for rock mass is established.It combines the safety evaluation method based on a deformation statistical analysis and an inverse deformation prediction method using measured deformation data of surrounding rock.This approach possesses the unique characteristics of complementary and mutual verification.In addition,a comprehensive early-warning index system(CWIS)for assessing the deformation stability of surrounding rock is presented.It consists of three types of warning indicators and three levels of warning values.The earlywarning values can be adjusted reasonably by the prediction correction method according to the measured displacements.For the collapse of rock blocks controlled by structural surfaces,a rapid prediction method of rock block collapse(RPMBC)based on the block theory is then presented.Finally,combining the DSPEM,RPMBC,and CWIS,the CSEM of surrounding rock for assessing the safety of cavern construction is established.It can provide technical support for decision making on the safety of surrounding rock during the construction of underground caverns.
基金financial supports for this research project by the National Natural Science Foundation of China(No.41602308)supported by Zhejiang Provincial Natural Science Foundation of China under Grant No.LY20E080005.
文摘To study the dynamic mechanical properties of tuff under different environmental conditions,the tuff from an ancient quarry in Shepan Island was prepared.The impact damage to the rock was tested using a triaxial dynamic impact mechanical testing system(TDIMTS)with different ground stresses,temperatures,and groundwater pressures.The time-strain relationship,dynamic stress-strain relationship,energy dissipation law,energy-peak strain relationship,and the impact damage pattern of the tuff specimens under impact air pressures were investigated.The TDIMTS experiment on ancient underground rock mass under impact loading was also simulated using the finite element analysis software LS-DYNA based on the Holmquist-Johnson-Cook(HJC)material model.The dynamic failure process,failure pattern and peak stress of tuff specimen were calculated.The simulation results obtained using the above methods were in good agreement with the experimental results.The results of the dynamic experiment show that with the same local stress,groundwater pressure,and temperature,the damage to the tuff specimens caused by blasting and quarrying disturbances gradually increases as the impact pressure increases.Under the same local stress,groundwater pressure,and temperature,the energy required to rupture the tuffs in ancient underground caverns is relatively small if the impact pressure is low accordingly,but as the impact pressure increases,the damage to the tuff caused by quarrying disturbance gradually increases.The damage gradually increases and the degree of damage to the tuff and the strain energy exhibit asymptotic growth when the tuff specimens are subjected to the greater strain energy,increasing the degree of rupturing of the tuff.In addition,the average crushing size decreases with increasing strain energy.By comparing the simulation results with the experimental results,it was found that the HJC model reflected the dynamic impact performance of tuff specimen,and the simulation results showed an evident strain rate effect.These results of this study can offer some guidance and theoretical support for the stability evaluation,protection,and safe operation of the ancient underground caverns in future.
文摘Engineering design in soft rocks and its stability analysis exerts many challenges to rock engineers. Many engineering works in Turkey’s Cappadocia region must face and tackle the existing sites covered by the soft rocks. This study is aimed to examine the stability condition of a typical underground storage cavern(USC) excavated in a soft rock in this region. For this purpose, two-and threedimensional stability analyses of the USCs were performed using the finite element method(FEM).Because of the inherent difficulty in characterizing soft/weak rock masses in the region using traditional classification systems, the stability of a typical USC was evaluated by representing the rock mass condition with two distinct scenarios in FEM analysis.While these structures were unstable according to the 2D analysis conducted in RS2 software in the worstcase scenario, they were stable in the 3D analysis using RS3 software in both scenarios. Besides,feasible cover depths were examined to assess their possible effects on the factor of safety and deformation measurements. It was found that 15 m seems to be an optimal depth for excavating a typical USC in the soft rocks exposed in the region. The 3D FEM results provide valuable information to optimize the future planning and preliminary design of USCs.
文摘The underground water-sealed storage technique is critically important and generally accepted for the national energy strategy in China. Although several small underground water-sealed oil storage caverns have been built in China since the 1970s, there is still a lack of experience for large-volume underground storage in complicated geological conditions. The current design concept of water curtain system and the technical instruction for system operation have limitations in maintaining the stability of surrounding rock mass during the construction of the main storage caverns, as well as the long-term stability. Although several large-scale underground oil storage projects are under construction at present in China, the design concepts and construction methods, especially for the water curtain system, are mainly based on the ideal porosity medium flow theory and the experiences gained from the similar projects overseas. The storage projects currently constructed in China have the specific features such as huge scale, large depth, multiple-level arrangement, high seepage pressure, complicated geological conditions, and high in situ stresses, which are the challenging issues for the stability of the storage caverns. Based on years’ experiences obtained from the first large-scale (millions of cubic meters) underground water-sealed oil storage project in China, some design and operation problems related to water curtain system during project construction are discussed. The drawbacks and merits of the water curtain system are also presented. As an example, the conventional concept of “filling joints with water” is widely used in many cases, as a basic concept for the design of the water curtain system, but it is immature. In this paper, the advantages and disadvantages of the conventional concept are pointed out, with respect to the long-term stability as well as the safety of construction of storage caverns. Finally, new concepts and principles for design and construction of the underground water-sealed oil storage caverns are proposed.
基金financial supports of National Natural Science Foundation of China (Grant No. 41502296)Youth Innovation Promotion Association, Chinese Academy of Sciences (CAS) (Grant No. 2016296)+1 种基金National Natural Science Foundation of China Innovative Research Team (Grant No. 51621006)Natural Science Foundation for Innovation Group of Hubei Province, China (Grant No. 2016CFA014)
文摘Increasing the allowable gas pressure of underground gas storage(UGS) is one of the most effective methods to increase its working gas capacity. In this context, hydraulic fracturing tests are implemented on the target formation for the UGS construction of Jintan salt caverns, China, in order to obtain the minimum principal in situ stress and the fracture breakdown pressure. Based on the test results, the maximum allowable gas pressure of the Jintan UGS salt cavern is calibrated. To determine the maximum allowable gas pressure, KING-1 and KING-2 caverns are used as examples. A three-dimensional(3D)geomechanical model is established based on the sonar data of the two caverns with respect to the features of the target formation. New criteria for evaluating gas penetration failure and gas seepage are proposed. Results show that the maximum allowable gas pressure of the Jintan UGS salt cavern can be increased from 17 MPa to 18 MPa(i.e. a gradient of about 18 k Pa/m at the casing shoe depth). Based on numerical results, a field test with increasing maximum gas pressure to 18 MPa has been carried out in KING-1 cavern. Microseismic monitoring has been conducted during the test to evaluate the safety of the rock mass around the cavern. Field monitoring data show that KING-1 cavern is safe globally when the maximum gas pressure is increased from 17 MPa to 18 MPa. This shows that the geomechanical model and criteria proposed in this context for evaluating the maximum allowable gas pressure are reliable.
文摘For better rock mass characterization and support design, 3D engineering geological mapping was carried for the heading portion of the under construction 200.00 m long, 68.75 m high and 20.20 m wide underground additional surge pool cavern of a Pranahitha-Chevella Sujala Sravanthi lift irrigation scheme package 8, India. To study cavern behavior, 3D geologic mapping of heading portion is very important for large cavern for predicting geologic conditions in benching down up to invert level, planning support system, selecting inclination for best location of supplemental rock bolt and choosing strategic locations for various types of instrumentation. The assessment of Tunnel Quality Index “Q” and Geomechanics classification for the granitic rock mass was done based on the information available of the rock joints and their nature and 3D geological logging. Hoek-Brown parameters were also determined by the statistical analysis of the results of a set of triaxial tests on core samples. On basis of geological characteristics and NMT Q-system chart, support system is recommended which includes rock bolt, steel fibre reinforced shotcrete and grouting. To evaluate the efficacy of the proposed support system, the capacity of support system is determined.
文摘【目的】明晰地下储气库的热力学过程是压缩空气储能(compressed air energy storage,CAES)电站安全设计与运行调度的重要基础。【方法】现有地下储气库热力学模型在计算热量交换时,存在高压储气阶段热损失偏大和低压储气库阶段补热过多的不足。本文在全面分析地下储气库热力学模型理论基础合理性的前提下,先分析储气库热量计算偏差的形成根源;再提出改进模型。【结果】研究结果表明:现有的热力学计算解析模型忽略了CAES地下储气库在运行过程中温度分布的不均匀性,这种温度分布的不均匀导致储气室洞壁与压缩空气之间的对流换热模型失真,导致温度计算结果偏差大。考虑混合对流换热的改进模型二可以较好地解决储气阶段温度计算结果与真实结果之间偏差过大的问题。算例分析证明了改进模型二的合理性。【结论】本文的改进模型二可为CAES地下储气库容积优化设计与效率分析提供计算依据。