Large Underground Caverns Research Articles

Overview of current compressed air energy storage projects and analysis of the potential underground storage capacity in India and the UK

Compressed air energy storage (CAES) is an established and evolving technology for providing large-scale, long-term electricity storage that can aid electrical power systems achieve the goal of decarbonisation. CAES facilities often utilise large underground storage caverns to ensure high capacity systems. This results in the need of locations with suitable geological features to develop a CAES plant. This paper examines recent and ongoing large-scale CAES projects and presents candidate methods of storing high pressure air using underground features. An assessment of the overall potential for CAES in India is presented by examining its geological features and locations with the greatest potential for CAES plants are determined. This is combined with an analysis of the renewable electricity generation potential in India to identify candidate areas for renewable generation and CAES integrated systems. Up to 1.05% of Indian land area is deemed suitable for CAES plant development and if fully utilised would be sufficient to meet the energy storage needs of India, however, practically a very small fraction of the total suitable land that could be developed so other competing energy storage technologies should be considered. Conversely, the UK possesses a very good potential for CAES, enough to greatly exceed necessary energy storage, owing to the abundance of salt beds not present in India. For CAES to garner serious consideration in India, aquifer storage based CAES needs to be demonstrated.

Estimation of the three-dimensional in situ stress field around a large deep underground cavern group near a valley

Abstract 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 stress-induced 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.

Wireless Monitoring–Based Real-Time Analysis and Early-Warning Safety System for Deep and Large Underground Caverns

AbstractLarge-scale underground cavern projects are complicated in terms of construction technology, engineering quality, and safety. Moreover, the timely collection of vital construction informati...

Dynamic Stability Evaluation of Underground Powerhouse Cavern Using Microseismic Monitoring

Construction of any excavation adds to the re-distribution of stresses around abutment and crown. This is stabilised by providing extra reinforcement. When a large underground cavern is excavated, stress re-distribution around abutment is obvious. Underground powerhouse cavern of Tala Hydropower Plant with adverse geological setting is one such cavern which encountered failure of a number of rock-bolts and series of other types of rockmass failure during its construction. It puts a question mark on the long-term stability of this powerhouse. To evaluate the dynamic stability of the rockmass (against induced stresses) around this powerhouse, microseismic monitoring network was installed. Microseismic data has been analysed in terms of static and dynamic parameters to assess the overall cavern stability. Spatio-temporal analysis of microseismic events could identify the potential risk zones which has significant cluster of events. To assess the overall stability due to these induced events, the ratio of transverse wave and longitudinal wave energy of these events was used as an index. It is found that cluster of events had shear failure. These events are basically of small non-damaging type and aid in releasing the built-up induced stresses. The slope of log–log plot of energy versus moment has a very high value. This indicates a stiffer rockmass which adds to its capability to absorb the induced stresses and aid to the overall stability of the region. Analysis reveals that no major seismic events are expected around this rockmass cavern and there is no dynamically unstable region against induced stresses.

Three-Dimensional Mechanical Information Model and Its Application to Large Underground Water-Sealed Storage Caverns for Oil or Gas

This work explores a three-dimensional (3D) mechanical information model for use in the design optimization of large underground water-sealed storage caverns. First, a 3D geological model is built on the basis of the exploration results obtained at the beginning of the exploration stage. Second, a 3D numerical calculation model is established with parameters integrated from various engineering data sources, especially from geophysical explorations and field tests. Finally, the results of the numerical calculation model are used to evaluate the stability and water seal effectiveness of the surrounding rocks. The subsequent analysis of two engineering cases shows the feasibility of the technical method for the design optimization of storage caverns. The method is expected to be improved in the practical construction process in the future.

Stress-induced cracking performance of hard basalt in a large underground cavern based on multi-information observation

Overcoming the brittle cracking and the corresponding hard rock has become the key bottleneck challenge in the excavation of underground engineering with high geostress. To further understand the onsite cracking’s characteristics and the basic mechanism of hard rock, we carried out a detailed field monitoring action for basalt breaking behaviors in a large underground powerhouse by in situ investigation, digital borehole camera, multi-point deformation measurement, and real-time micro-seismic monitoring. On the basis of our observations, the inner cracking performances of surrounding rock embodied as discontinuous appearance and open of cracks during excavation, and these fractures were often parallel to the outline of the cavern and extended to the inner side because of the subsequent excavation disturbance. Corresponding numerical simulation indicated that the redistribution of rock stress induced local stress concentration and would result in the splitting break of basalt. Field complicated proof indicated that this stress-induced cracking of basalt belonged to the tensile break, and the macroscopic deformation of the surrounding was the result of the accumulation of abundant open deformation of discontinued cracks. This observed achievement can enrich our understanding of the cracking mechanism of hard rock and provide some key cures for optimization design for underground engineering construction under high geostress conditions.

Rock Mass Characterization for the Underground Surge Pool Cavern – A Case Study, India

Abstract Underground surge pool cavern for the storage and lifting of water is being constructed in the part of Telangana State of India. For better rock mass characterization and support design, 3D engineering geological mapping was carried for the heading portion of the surge pool. 3D geologic mapping of heading portion is very important for large underground cavern to know about the cavern behavior during benching down. The direction of the longest axis of the cavern was finalized based on the in-situ hydrofracturing testing inside the deep borehole. The assessment of tunnel quality index ‘Q’ for the exposed granitic rock mass was done based on the information available of the rock joints and their nature, 3D geological mapping and in-situ stress measurement. Roof support and wall support pressure was estimatedbased on Q-values, and in this case applicable for the non-squeezing ground condition. For structural stability of crown and walls, rock support arrangement was recommended based on NMT technology and geological conditions of site, which includes steel fibre reinforced shotcrete, grouting, rock bolt and drainage hole provisions. The capacity of support system is determined to evaluate the efficacy of the proposed support system.

Comprehensive analysis of the surrounding rock mass stability in the underground caverns of Jinping I hydropower station in Southwest China

The geological conditions of the underground caverns in the Jinping I hydropower station are particularly complicated, with high ground stress (the extreme value of the measuring point is 35.7 MPa), complicated deformation and failure mechanisms, and large unloading depth. The large deformation of the surrounding rock mass was beyond current engineering and academic understanding. During the construction period, the deformation and failure mechanisms were complex, and the unloading depth was large. The maximum deformation of the sidewall of the main powerhouse reached 246 mm. The monitoring results of multi-point extensometers basically converged two years after the completion of cavern excavation. Regarding the deformation and failure mechanism of the large underground caverns, the energy dissipation theory that can better describe the complex mechanical response analysis was proposed. The deformation failure mechanism, mechanical behaviour, supporting effect and stability evaluation of the large underground caverns were investigated from the perspectives of excavation unloading and energy dissipation and release. The excavation unloading-induced relaxation characteristics of the surrounding rock mass were analysed using a comprehensive approach incorporating the results of borehole television, acoustic wave testing, multipoint extensometer and numerical simulations. A criterion of the surrounding rock mass delineation incorporating the energy dissipation ratio, acoustic wave testing, wave velocity variation and elastic modulus variation was also proposed. Furthermore, the phenomena and law of deformation and failure of surrounding rock mass in the large underground caverns were revealed. The stability of surrounding rock mass in the underground caverns was evaluated. The related achievements can provide some references for similar deep underground rock engineering.

Dynamic Monitoring and Stability Analysis of Rock-bolted Crane Girder In large Cavern With Layered Surrounding Rock

The large and medium-sized hydropower projects underground cavern group are basically in relatively integrate surrounding rock, so there are few engineering examples in layered surrounding rock with type III surrounding rocks as the main rock, and lack of successful experience. According to rock-bolted crane girder under the layered surrounding rock of a large underground power station, analyzing prototype dynamic monitoring data of the excavation, unloading and load-bearing test .The distribution of the monitoring data conforms to the normal law, and there are no large outliers, under the action of a large number of bolts, rock-bolted crane girder basically forms a good integrity with the layered surrounding rock, and the load-bearing test has no effect on the stress condition and stability condition of surrounding rock.

Research on dynamic inverse method of surrounding rock mechanical parameters of large underground caverns in excavation

Rock mechanical parameters are important factors to affect the stability of surrounding rock in underground engineering. With the development of underground cavern excavation progress, the mechanical parameters of rock mass will change significantly. In order to reflect the change of parameters during excavation in real time based on uniform design and optimization algorithm technology, dynamic inverse method of surrounding rock parameters during excavation of underground caverns is carried out. Considering the location, elevation and period of excavation, the parameters inversion are divided into excavation sections and staged. Verified by actual engineering, the calculated displacement values of the inversion agree well with the measured.

Experimental Study of Mechanical Behavior of Interlayer Staggered Zone under Cyclic Loading and Unloading Condition

AbstractThe unloading and reloading of geostress during the excavation of large underground caverns tends to bring about large deformation and failure problems of rock masses with interlayer stagge...

Dynamic analysis of rock mass deformation in large underground caverns considering microseismic data

The underground powerhouse of a hydropower project is one of the most significant structures that will be permanently in use. Large scale excavation induced rock mass damage may pose a threat to the stability of the underground powerhouse. In the present study, a microseismic (MS) monitoring system was established to capture microcracks induced by excavation of the underground powerhouse caverns at the Houziyan hydropower station. Based on tempo-spatial characteristics of the MS events, the relation between MS activities and field construction was analyzed and the main damage regions were revealed. A damage-driven model considering the effect of MS source sizes is adopted for dynamic analysis of rock mass deformation of the underground caverns. The rock mass damage is simulated by a micro-mechanics-based constitutive model described by the fracture density determined by the MS source radius. A numerical model of a typical profile of the underground powerhouse was established. The MS data monitored in each bench excavation period of the underground powerhouse caverns was imported to the numerical model for dynamic analysis of deformation. The results showed that the effect of rock damage played a significant role in the rock mass deformation of the underground powerhouse during each bench excavation. The displacements of rock mass considering MS data obtained from the numerical analysis can provide better predictions for real conditions on site.

Superconducting Detector Magnets Baseline Designs for Particle Physics Experiments at the Future Circular Collider

In early 2014 a design study started at CERN for a Future Circular Collider. A new tunnel with a circumference of about 100 km for the collider magnets is foreseen as well as new general-purpose particle detectors to probe electron-positron (e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ), electron-hadron (eh), and hadron-hadron (hh) collisions, housed in large underground caverns. In the last four years baseline designs for the various detector magnets were developed. For the FCC-ee detector two magnet variants were defined: a 7.6-m bore and 7.9-m-long classical 2 T solenoid with 600 MJ stored energy, surrounding the calorimeters, and also a very challenging 4-m bore, 6-m-long, some 100-mm-thick ultrathin and radiation transparent 2 T solenoid with a stored energy of some 170 MJ, that surrounds only the inner tracker of the detectors. For the FCC-eh detector, the detector solenoid is combined with forward and backward dipole magnets required to guide the electron beam in and out of the collision point. This detector requires a 3.5 T solenoid, 2.6-m free bore and 9.2-m length with about 230 MJ of stored energy. Most demanding is the FCC-hh detector with a 14 GJ stored energy magnet system comprising three series connected solenoids, requiring 4 T in the main solenoid with 10-m free bore and a length of 20 m, in line with two 3.2 T forward solenoids with 5.1-m free bore and 4-m length. A quite challenging series of detector magnets is proposed, that needs to be further engineered in the coming years. The superconductor technology though is essentially the same in all the solenoids proposed: conductors comprising Rutherford type cables made of NbTi/Cu strands, stabilized by nickel doped pure aluminum and structurally reinforced with a high yield strength aluminum alloy. The cold masses are conduction cooled through helium cooling pipes welded to their outer support cylinder. The designs of the various baseline magnets as well as their engineering are presented.

Analysis of a Complex Flexural Toppling Failure of Large Underground Caverns in Layered Rock Masses

Flexural toppling failure is one of the most common instabilities in large underground caverns and occurs when the steeply inclined rock layers form a small angle to the cavern axis. This study investigates a typical flexural toppling failure in the underground powerhouse at the Wudongde hydropower station, Southwest China, using in situ tests and numerical tools. The characteristics of flexural toppling failure in the large underground caverns were initially analysed by field observations and conventional testing methods, including the use of multipoint extensometers, acoustic wave tests and borehole television images. A high-resolution microseismic monitoring system was installed in the right main powerhouse to reveal new and important insights into the mechanisms of typical failures that occur in bedded rock masses. The fracturing processes of the rock mass associated with the flexural toppling failure were analysed based on microseismic monitoring data, and the development of flexural toppling failure was related to shear failure. Then, the discrete element method was used to further investigate the effect of geological planes on the formation of flexural toppling failure. Finally, the complex mechanism of flexural toppling failure was evaluated by incorporating field observations, in situ monitoring and numerical modelling. An effective method of preventing this type of failure in underground caverns was analysed. The results can improve our understanding of flexural toppling failure in the underground caverns of the Wudongde hydropower station, and the proposed method can be adopted to study similar large underground caverns.

The failure mechanism and construction practice of large underground caverns in steeply dipping layered rock masses

The stability of large underground caverns in steeply dipping layered rock masses is not only affected by the engineering geological characteristics of surrounding rock masses, but also by the excavation sequences and reinforcement measures. Certain places around the periphery of underground openings, such as the high sidewalls, would exhibit significant displacement increases and various failure patterns if the excavation and support were not properly designed. These issues can, according to the basic principles of structurally-controlled concept, be largely attributed to the mechanical properties of bedding planes and other discontinuities. In order to clarify the possible mechanisms behind these failures and to realize the dynamic adjustment of construction, a thorough investigation was conducted to the underground caverns of the Wudongde hydropower station throughout the excavation process. The geological conditions and mechanical properties of the rock masses in the study area were first introduced in detail. Four examples were then presented following the overall logic from geological background to failure mechanism and finally to reinforcement practice. The first example focused on the local wedge-type instability analyses, including the collection of necessary information, the identification of potential blocks, as well as the determination strategies for the factors of safety. The second example illustrated typical tensile failure mode of steeply inclined strata induced by large-scale excavation. The sudden normal unloading of bedding planes led to observable fractures along these weaknesses and considerable increases in sidewall displacements. Large quantities of extra reinforcements had to be installed to control further development of fractured range of the upstream sidewall. The third example highlighted the long-range influence of excavations on the stability of downstream roof, where multistage displacement increase and shotcrete cracking took place as a result of stress concentration and strata buckling, possibly also of the local unfavorable discontinuities. The last example was related to the failure mode of combined discontinuities on the surfaces of piers between two pits. Lessons learned from these examples mainly involve what the mechanical behaviors of the steeply dipping layered rock masses in different places after excavation will be like, and to what extent these behaviors could be predicted or anticipated, which then put emphasis on the importance of geological investigations, and how the optimization of excavation sequence and bench height as well as the timely installation of regular supports could effectively reduce the risks of instability.

Stability of large underground caverns excavated in layered rock masses with steep dip angles: a case study

The Wudongde Hydropower Station is constructed in layered strata that typically have steep dip angles. These features, together with the folds and faults that have developed in the strata, directly threaten the stability of the underground powerhouse. In this work, the behavior of the surrounding rocks under the original support measures is detailed in terms of rock mass deformation, anchor bolt stress, and extent of the excavation-disturbed zone, as obtained from safety monitoring and field testing. The characteristics of deformation and cracking of the surrounding rocks were also interpreted. To enhance rock mass stability, the support design and construction process were optimized and the positions liable to cracking treated. The efficiency of suggested scheme is verified by subsequent safety monitoring data and field testing. Then, a transversely-isotropic elastoplastic constitutive model for the layered rock masses was established. Numerical simulations are performed during the construction process to provide reference for decision making. The calculated deformations are in good agreement with the monitored values and they tended to be more stable. The plastic zones of the surrounding rocks fall within the range controllable using cables. Thus, the proposed measures are necessary and ensure sufficient stability. Finally, the mechanisms for the deformation and cracking of the surrounding rocks during the construction process are discussed. The work described aims to deepen our understanding of the mechanical properties of layered rock masses with steep dip angles and to improve the design philosophy.

Reasonable Paths of Construction Ventilation for Large-Scale Underground Cavern Groups in Winter and Summer

Forced ventilation or newly built vertical shafts are mainly used to solve ventilation problems in large underground cavern groups. However, it is impossible to increase air supply due to the size restriction of the construction roadway, resulting in ventilation deterioration. Based on construction of the Jinzhou underground oil storage project, we proposed both a summer ventilation scheme and winter ventilation scheme, after upper layer excavation of the cavern is completed and connected with the shaft. A three-dimensional numerical model validated with field test data was performed to investigate air velocity and CO concentration. Fan position optimization and the influence of temperature difference on natural ventilation were discussed. The results show that CO concentration in the working area of the cavern can basically drop to a safe value of 30 mg/m3 in air inlet and exhaust schemes after 10 min of ventilation. Since there is inevitably a back-flow in the winter ventilation scheme, it is necessary to ensure that airflow is always moving towards the shaft. Optimal placement of the axial flow fan at the shaft bottom is on the central axis of the cavern, 5 m away from the shaft. The greater the temperature difference, the better the natural ventilation effect of the shaft. The natural ventilation effect of the shaft as an outlet in winter, is better than that of the shaft as an inlet in summer.

Excavation Optimization and Stability Analysis for Large Underground Caverns Under High Geostress: A Case Study of the Chinese Laxiwa Project

In situ investigations and detailed laboratory tests indicated that the granite at the Laxiwa hydraulic station is a typical hard rock, with high compressive strength and elasto-brittle failure modes, such as spalling and slabbing, and that the underground caverns are prone to brittle failure. Thus, an intelligent optimization method for cavern excavation was developed to improve the underground engineering’s stability during its construction. This artificial intelligence method utilized the advantages of both the particle swarm optimization algorithm, which is capable of global optimization, and the support vector machine algorithm, which is capable of highly nonlinear mapping. The corresponding numerical analysis indicated that this optimization of excavation sequencing can considerably reduce both the total volume of the damage zone and the brittle failure of the surrounding rock. Furthermore, the measured deformations, the depth of the tested excavation damage zone, and the exposed in situ failures resulting from the applied excavation scheme were similar to the results predicted by the numerical simulation of the cavern excavation.

Continuum and Discontinuum Analysis of Rock Caverns

Over the last decades, constructions of large underground rock caverns are experiencing a rapid development across the globe. However design and construction of these structures is a complex and challenging task, specifically with limitations of limited investigations data and presence of many uncertainties. Rock mass parameters along with joint configuration such as persistence, spacing and strength of the joints are the main factors which significantly modify stresses and displacements in the vicinity of the openings. Thus, a detailed cavern stability assessment based on field data collection from the excavated cavern’s face is critically important. This paper discusses continuum and discontinuum modelling of underground rock caverns based on case study of crude oil storage project located on southern coast of India. Critical points of observation for these two types of analysis are reviewed in reference to results of the case study. Data obtained from geotechnical monitoring of underground rock cavern is also compared and discussed with the results obtained from both continuum and discontinuum analysis for better understanding of the same. The results obtained from this study indicate that inclusion of discontinuities in rock mass for numerical modelling captures essential instability conditions around the cavern while continuum representation gives a more idealised illustration of the instability. Observed displacement values in most of the cases lie in between the calculated displacement values of continuum and discontinuum analysis.

A numerical modelling approach to assess the behaviour of underground cavern subjected to blast loads

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 (3DEC) 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.