Cavern System Research Articles

Performance Assessment and Optimization of Seepage Control System for Wunonglong Underground Powerhouse Cavern System

Performance Assessment and Optimization of Seepage Control System for Wunonglong Underground Powerhouse Cavern System

Investigation on the failure mechanism of hard rock cavern subjected to adjacent structural plane based on physical model experiments

Structural planes present significant safety challenges in the construction of deep hard rock caverns. However, the influence mechanism of a single dominant adjacent structural plane remains inadequately explored. This study conducted a series of physical model experiments with non-penetrating structural planes positioned adjacent to the cavern under uniaxial step compression, utilizing acoustic emission (AE) and digital image correlation (DIC) to monitor the failure process simultaneously. The results indicate that adjacent structural plane can mitigate stress-induced failure, reducing peak strength and elastic modulus by 10–42% and 13–31%, respectively. In the absence of a structural plane or a non-intersecting plane, stress-induced failure intensifies. Conversely, an intersecting plane contributes to greater crack stability. Precursor AE signals emerge earlier in the combination system. The intact cavern system shows an escalating tensile fracture ratio with loading, whereas the combination systems experience a diminishing tensile fracture ratio. Finally, particle flow code (PFC) simulation revealed that the presence of a single structural plane alters the cavern’s force chains, influencing stress concentration position. This research reveals that the structural plane has the potential to alter the cavern failure mechanism, providing insights into the complex interaction between structural planes and caverns in deep engineering.

RESEARCH OF FORMATIONS INJECTIVITY IN ORDER TO ORGANIZE RESERVOIR PRESSURE MAINTENANCE IN THE CARBONATE FIELDS

In this item, the top-priority is organization of reservoir pressure maintenance system and fields development under natural mode in order to maintain reservoir pressure in carbonate fields. Currently, the fields are being developed in a natural drive, and arranging a system for maintaining reservoir pressure is a top-priority. Carbonate fields are complicated by tectonic faults in the separate blocks and HC production reveals disturbance of the balance in the geological environment. Longtime fluid sampling without reservoir pressure maintenance leads to change of stress fields in formation, which initiates creation of deformations of earth surface. In order to prevent from these events, it is required to maintain reservoir pressure. It is necessary to maintain reservoir pressure to prevent these events from happening. When water is injected, migration occurs through a complex ramified system of cracks, caverns and pore channels. The most permeable in the productive thickness layer are karst intervals and zones of increased fracturing, which serve as the main routes for fluid migration. Considering complication of RPM system organization due to high wellhead pressure, field distance from water sources and possible creation of cavity and carst, conception of carbonate fields development is developed within the frame of item.

Stress distribution and failure characteristics around U-shaped caverns with different height-to-width ratios under biaxial compression

Understanding the stress distribution and failure characteristics around a U-shaped cavern is vital to the stability analysis of rock structures such as tunnels and roadways. In this study, the stress distribution around a U-shaped cavern with different height-to-width (h/w) ratios under biaxial compression was first analyzed based on the complex variable theory. Then, numerical simulations were conducted using PFC2D to study the failure process and energy evolution around a U-shaped cavern with different h/w ratios. Theoretical solution shows that the maximum stress concentration factor occurs at the bottom corner of the U-shaped cavern. With the h/w ratio increasing from 0.75 to 3.0, the stress concentration factor around the sidewall shows a declining trend, while the opposite trend is observed in the vault and floor. Numerical results show that when the maximum principal stress is parallel to the vertical direction, the thin slab buckling occurs in the sidewall of the cavern with low h/w ratios (h/w = 0.75 and 1.0), accompanied by the release of relatively high kinetic energy. Instead, the wedged-shaped slab spalling occurs in the sidewall of the cavern with high h/w ratios (h/w = 1.5, 2.0 and 3.0), which can be considered as a static process. Although the U-shaped cavern with low h/w ratios has higher integrity after failure, more stain energy is accumulated in the remaining surrounding rock, which is likely to cause rockbursts under a higher stress state or dynamic disturbance. When the maximum principal stress is horizontal, the rock slab separates from the cavern floor and presents a reverse trend with the increasing h/w ratio. The above results indicate that the h/w ratio and the direction of maximum principal stress should be considered comprehensively in the design of the support system of U-shaped caverns.

Hydrogen-Driven Microbial Redox Reactions in Deep Geosystems

In the subsurface, biotic and abiotic processes can generate and consume hydrogen. Hydrogen has a low reduction potential and is thus a highly energetic electron donor when involved in sulfate, carbon dioxide or ferric iron reduction. Although known as important drivers for the deep biosphere, the contributions of different processes to hydrogen turnover in different geosystems still are not well understood. In context with the ongoing transformation to renewable energy resources, underground H2 storage (UHS) in deep porous or salt cavern systems came into focus. In situ microbial and geochemical reactions that consume H2 are highly relevant topics in deep biosphere research, and also are still a major uncertainty during UHS. Consequently, we studied the potential microbial hydrogen oxidation rates – combined with the possible production of metabolic products like H2S, acetic acid or CH4 - in formation fluids from natural gas fields and salt caverns, thereby considering the importance of in situ pressure and temperature conditions, fluid chemistry and mineral composition. In addition, more defined experiments were conducted with selected pure cultures representing important metabolic groups of deep biosphere microorganisms. Several original formation fluids showed immediate H2 consumption. Microorganisms oxidized hydrogen at relevant in situ pressure conditions (up to 100 bar) and tolerated dynamically changing pressure and temperature conditions. The microbial hydrogen oxidation rate was strongly dependent on H2 partial pressures and the availability of e.g., sulfate as a terminal electron acceptor. High-throughput sequencing of 16S rRNA gene amplicons indicated hydrogen oxidation by sulfate reducing bacteria to be the presumed process in the studied porous rock reservoir fluids. In addition, hydrogen turnover by methanogenic and acetogenic as well as iron-reducing microorganisms was investigated. Also, the importance of biotic reactions in relation to abiotic hydrogen turnover processes at mineral surfaces will be discussed.

The complexities of complex treatment of a patient with widespread destructive pulmonary tuberculosis against the background of severe pulmonary bullous dystrophy after exogenous exposure to fine particles of coal dust in the anamnesis

An observation from practice is given – a staged surgical treatment of a patient with widespread destructive pulmonary tuberculosis with preXDR MBT against the background of severe bullous lung dystrophy after prolonged exogenous exposure to fine particles of coal dust in the anamnesis. Patient M., 42 years old, smoker, has been working as a loader at a railway station since the age of 20, unloading wagons with bags of coal at high temperatures without using personal protective equipment. He was ill with pulmonary tuberculosis 12 years ago, the original form: infiltrative tuberculosis of the upper lobe of the right lung in the phase of decay and insemination. He was treated with positive dynamics, was removed from the register 10 years ago, the real changes were revealed during a routine examination when applying for a vertebral hernia. According to computed tomography of the chest organs, a picture of fibrous-cavernous tuberculosis of the right lung with a system of polymorphic caverns with multiple foci of dropout in the left lung against the background of pronounced emphysema of both lungs was noted upon admission. He was admitted to the clinic with complaints of shortness of breath at rest (mMRC 3). The patient was selected therapy based on sensitivity data and individual intolerance. The patient underwent EC installation at the mouth of the upper lobe bronchus on the right, successfully, then at the mouth of the bronchus B6, the blocker was coughed up. Against the background of treatment, tuberculomas formed in the left lung. S1-2 resection of the left lung was performed. The patient suffered SARS CoV-2. After that, spontaneous pneumothorax occurred on the left, and therefore the pleural cavity was drained. Against the background of the lack of dynamics, a month after drainage, the patient was taken for revision of the left pleural cavity with suturing of defects, partial pleurectomy and decortication of the left lung. After 3 months, the patient had a bronchoblocker removed from the mouth of the ULB on the right and a combined resection of the right lung (upper lobectomy with S6) was performed, after which, in order to reduce the right hemithorax and reduce the overstretch of the right lung, thoracoplasty was performed with resection of the I-IV ribs on the right. Histological examination confirmed pulmonary tuberculosis against the background of exogenous exposure to fine particles of coal dust (by the type of hypersensitive pneumonitis of chronic course). As a result of treatment, the patient's symptoms of shortness of breath (mMRC 1) decreased, the patient was steadfastly abaculated and returned to a normal lifestyle.

Numerical Study on Static and Dynamic Load Response of Temporary Support System for Group Tunnels Excavation

In this study, the static response of the preliminary pilot tunnels excavation to the ground, and the dynamic response of the group cavern system under seismic excitation under the use of the construction of a metro station based on the Pile-Beam-Arch approach are investigated through numerical calculation. The results suggest that the excavation sequences of “top first and then bottom” and “middle first and then both sides” can generate the minimum ground settlement. When the pilot tunnels were excavated, the horizontal PGA (peak ground acceleration) amplification coefficient tends to increase with significant nonlinear characteristics under the excitation of EI Centro wave with a horizontal acceleration of 0.15 g, and the horizontal PGA amplification coefficient reaches the maximum at the ground surface. The effect of horizontal acceleration around the upper pilot tunnels increases. Under the static load, the maximum principal stress of the lining structure after the completion of the pilot tunnels is largely concentrated at the foot of the arch of the pilot tunnel, and the maximum principal stress value is 1.124 MPa. The maximum principal stress is primarily concentrated at the foot of the arch and the foot of the upper and lower guide tunnel under seismic excitation, and the maximum principal stress value is 1.424 MPa. This study reveals that a reasonable excavation sequence can be employed when the pilot tunnels are being excavated to control the settlement. Furthermore, the support of the arch and footing of the pilot tunnels should be enhanced during the seismic design.

New palaeontological evidence suggests an early Middle Pleistocene age for the lower levels of Sun Hole Cave, Cheddar, Somerset, UK

Sun Hole, a small fissure cave on the north side of Cheddar Gorge, Somerset, is best known as the site where late Upper Palaeolithic artefacts are associated with human and other mammal remains that immediately pre-date the Lateglacial interstadial. These remains from the upper levels (Unit I) overlie sediments (Unit II) that are thought to have accumulated during a full glacial period, below which are sediments (Unit III) attributed to an interglacial stage. The extinct land snail Retinella (Lyrodiscus) sp., which in Britain was only known from the Hoxnian Stage, had previously been recovered from Unit III. The interglacial at the base of the sequence was therefore assigned to the Hoxnian Stage (Marine Isotope Stage (MIS) 11, 424–374 kyr). Here we provide additional analyses of samples from Unit III, which as well as containing further Retinella (Lyrodiscus), also yielded a specimen of Monachoides incarnatus, its first record from the British Pleistocene. An associated assemblage of small mammals included a few that are rare in the British Pleistocene, such as birch mouse (Sicista cf. betulina) and garden dormouse (Eliomys quercinus). The vole Lasiopodomys gregaloides and the shrew Sorex (Drepanosorex) savini do not occur as late as the Hoxnian and therefore suggest an older age in the early Middle Pleistocene. The record from Sun Hole therefore has parallels with the well-known sequence from the upper Calcareous Member in the nearby cavern system at Westbury-sub-Mendip.

Nematodes of soft bottoms from the ‘Po’ol Tunich’ cave system, Quintana Roo, Mexico

ABSTRACT The Yucatán Peninsula is a vast karst platform that hosts superficial ecosystems such as sinkholes or underground cave systems. This study aims to give the first nematode species list for and explain their distribution at the Po´ol Tunich cave system. Samplings were carried out from September 2015 to February 2016, at five sampling sites along the cavern system. At each site, two sediment samples were collected with a polyvinylchloride pipe (PVC) corer; sediments were processed by decantation, and meiofauna was collected with a 45 µm sieve. Nematodes were picked manually, mounted on glass slides and identified. At three sites (1, 3 and 5), water temperature and electric conductivity were measured with HOBO data loggers. The nematode fauna was represented by six orders, nine families and 12 genera. Enoplida and Chromadorida have the highest number of species (three each), while Rhabditida and Plectida have two species each. There was only one species of Dorylaimida. Sites with the highest abundance were: 1 (25 organisms) and 2 (24 organisms), with Atrochromadora sp. as the most abundant species, followed by Ironus paludicola, Hoplolaimus tylenchiformis and Dichromadora sp., at five organisms each. The four types of nematode feeding were present, with a predominance of epistrate and deposit feeders, followed by chewers and then suction feeders, and this fact is an indicator of the food resources available in the cave. Our results reveal that nematodes are an important component in the cave fauna, and they exploit the resources available based in detritus. Further efforts are needed to understand the nematode communities associated with subterranean environments.

Numerical Simulation of the Stability of Rock Mass around Large Underground Cavern

Geotechnical problems are complicated to the extent and cannot be expected in other areas since non-uniformities of existing discontinuous, pores in materials and various properties of the components. At present, it is extremely difficult to develop a program for tunnel analysis that considers all complicated factors. However, tunnel analysis has made remarkable growth for the past several years due to the development of numerical analysis method and computer development, given the situation that it was difficult to solve formula of elasticity, viscoelasticity, and plasticity for the dynamic feature of the ground when the constituent laws, yielding conditions of ground materials, geometrical shape and boundary conditions of the structure were simulated in the past. The stability of rock mass around an underground large cavern is the key to the construction of large-scale underground projects. In this paper, the stability analysis was carried out based on those parameters by using 2D FEM RS2 program. The calculated stress and displacements of surrounding rock and rock support by FEM analysis were compared with those allowable values. The pattern of deformation, stress state, and the distribution of plastic areas are analyzed. Finally, the whole stability of surrounding rock mass of underground caverns was evaluated by Rock Science - RS2 software. The calculated axial forces were far below design capacity of rock bolts. The strong rock mass strength and high horizontal to vertical stress ratio enhanced safe working conditions throughout the excavation period. Thus wide span caverns and the system of caverns could be stability excavated sedimentary rock during the underground cavern and the system of caverns excavation by blasting method. The new method provides a reliable way to analyze the stability of the caverns and the system of caverns and also will help to design or optimize the subsequent support. Doi: 10.28991/CEJ-2022-08-01-06 Full Text: PDF

Structures and Settlement Control of Yujingshan High-Speed Railway Tunnel Crossing Massive Rockfill in a Giant Karst Cave

The Yujingshan high-speed railway tunnel crosses a giant cavern system with a 108 × 104 m3 volume chamber and an 18 km long underground river. The massive project, which lasted three years, was eventually awarded the “Overcoming the Challenges” award by the International Tunneling and Underground Space Association (ITA) in 2020. However, since the cave chamber was filled with large-scale rockfill, structural settlement is a non-negligible problem. This paper presents the unique structures of a bridge supporting railway tracks wrapped by tunnel lining and the settlement control of the Yujingshan tunnel crossing massive rockfill in the giant cave. The geological characteristics and design considerations are systematically introduced. A three-dimensional coupling discrete element method (DEM) and finite difference method (FDM) numerical model and 13 months of long-term settlement monitoring were conducted to evaluate the settlement behavior. The results indicate that the morphology of cavern and internal deposits caused the whole rockfill to migrate to the lower left. The tunnel structure consequently developed a significant inclined settlement. The continuous construction load would increase the settlement value by 31.4%. The bottom reinforcement of steel-pipe pile with grouting could effectively inhibit settlement and differential settlement. Considering the simulation results, the tunnel bottom had greater settlement than the limit standard for high-speed railway embankment, which means this special structure form is reasonable for operation. Meanwhile, the monitoring results show that the tunnel bottom settlement in D3K279+891~D3K279+947 had not performed an apparent convergence trend after 13 months. Further structural monitoring and compensation grouting should be actively considered for operation maintenance.

Design of seepage control system around a large-scale underground powerhouse: A case study of Baihetan Hydropower Station

Located at the lower reach of Jinsha River, the Baihetan Hydropower Station is the world’s second largest hydropower station. It consists of a double-curvature arch dam with a maximum height of 289 m and two large-scale underground cavern systems on each side of the bank, which is the largest underground cavern system of hydropower project in the world. The construction site is characteristic of complex geological conditions, and multiple interlayer staggered zones are developed between different strata. Based on the results of on-site packer tests, the interlayer staggered zones generally have a higher hydraulic conductivity than the surrounding rocks, and therefore may act as the potential seepage flow path. Since the underground powerhouse is close to the upstream reservoir and these is a large difference of water level between the upstream and downstream reservoirs, the control of groundwater flow in the surrounding rocks of the underground caverns becomes one of the key technological issues. A large-scale seepage control system including grout curtains and drainage curtains was designed around the underground powerhouses. Besides, the hydraulic conductivity of the interlayer staggered zones was systematically characterized and several anti-seepage tunnels were designed and constructed specifically for the control of seepage flow through the interlayer staggered zones. On this basis, numerical simulation of seepage field was conducted, and the results show that the designed seepage control system is effective in lowering the groundwater level and reducing the amount of seepage around the powerhouse.

Integrated ground penetrating radar, electrical resistivity tomography and multichannel analysis of surface waves for detecting near‐surface caverns at Duqm area, Sultanate of Oman

ABSTRACTCaverns in hard limestone form natural karstic features. Surveying, detecting, and managing caverns are valuable as they provide an accurate and reliable understanding of the geohazards that caverns represent. With the construction of the highway network in Duqm (Duqm Port, Sultanate of Oman), near‐surface stability problem (caverns) appeared. Three geophysical tools – ground penetrating radar, electrical resistivity tomography, and multichannel analysis of surface waves – were utilized to delineate the subsurface cavities beneath an area of 10,000 m2 (200 m × 50 m). Based on interpretation of the results of two‐dimensional and three‐dimensional ground penetrating radar, electrical resistivity tomography and multichannel analysis of surface waves, the caverns are found to extend in the N–S direction. The results show two cavern systems of varying thicknesses. The caverns are separated at the top, but at some locations they become an one‐unit cavern system, especially in the northerly direction. The cavern system is not completely hollow; at some locations, they are filled with materials of different physical properties than the host rock. The depth of the cavern system varies between 0 and 5.2 m. The caverns are found only within the limestone rock unit. There is no evidence of caverns within the shale rock unit. The results from the three methods show good agreement in terms of depth and dimensions of the detected caverns.

Historical storage cellars in Budapest

The Kőbánya district of Budapest is situated on the eastern margins of the Hungarian capital city. Beneath Kőbánya there is an extensive limestone layer, in which tunnels and passages have been made, ‍some of which appear to date from the 13th century. In the 19th century, the limestone caverns of Budapest-Kőbánya were used for the refrigeration of perishable goods in large quantities. The caverns‍ represent one of Budapest’s historical industrial landmarks, although their architectural history has not been documented in full. This article analyses the architectural development of these evidently low-tech‍ facilities, while also exploring their significant role in the city’s urbanisation. The technical functions and structure of the system of caverns may be useful as a resource for society in the future when the supply‍ of fossil fuels runs out. The effectiveness of the caverns as places for refrigeration can be demonstrated through climatic calculations. The cavern system has significant energy capabilities, given that there is a‍constant air temperature throughout the year. The vast amount of geothermal energy could be used to cool heat pumps or heat exchangers. The results of measurements taken in preparation for this article are‍ presented.

Semmering Base Tunnel – Design and construction of the shaft head caverns under difficult conditions

AbstractIn contract SBT1.1 of the Semmering Base Tunnel, the single‐track main tunnels are being driven from the portal in Gloggnitz and from a temporary intermediate starting point in Göstritz. The temporary intermediate starting point in Göstritz is being constructed in order to reduce the risk to the tunnel construction time for the Graßberg‐Schlagl fault system. During the construction phase, the contractor developed optimisations of the planned logistics concept for the intermediate access point in Göstritz, which led to a redesign of the shaft head cavern system. Shortly before the excavation of the shaft head cavern, an unexpected and geotechnically relevant fault zone was encountered in the access tunnel. In order to investigate the geological situation in the area of the shaft head, extensive additional investigation measures were carried out. Due to the updated geological forecast, the layout of the shaft head cavern and the support concept had to be changed. Thanks to the measures taken, the shaft head cavern system cold be successfully excavate without any damage to the support.

Gloggnitz contract after completion of the intermediate access at Göstritz

AbstractThe intermediate construction access at Göstritz was planned based on the results of a comprehensive geological investigation programme. The intermediate access minimises the risk of the excavation of the Semmering Base Tunnel through the Grassberg‐Schlagl fault system, which is located in the Otterstock area in Lower Austria. The site consists of an approx. 1000 m long access tunnel, a complex system of shaft head caverns, two shafts with a depth of about 250 m down to the level of the tunnel as well as a system of shaft bottom caverns for the four tunnel drives in the directions of Gloggnitz and Mürzzuschlag. During the construction of the access tunnel, a new shaft head layout was proposed by the contractor in form of value engineering to optimize further construction operation, and the optimized layout was adopted to the contract. At the end of the access tunnel, it turned out that the shaft head cavern system could neither be constructed in the original layout as tendered nor in the newly revised layout due to a geological fault zone, which had not been predicted despite extensive geological investigation in advance. Consequently, ÖBB, designer and contractor worked intensively to find a new feasible design to enable further construction of the cavern system, avoid a standstill of tunnelling works and comply with all approvals.

First report of long term measurements of the MGGL laboratory in the Mátra mountain range

Matra Gravitational and Geophysical Laboratory (MGGL) was established near Gyöngyösoroszi, Hungary in 2015, in the cavern system of an unused ore mine. The laboratory is located 88 m below the surface, with the aim of measuring and analysing the advantages of the underground installation’s third generation gravitational wave detectors. Specialized instruments have been installed to measure seismic, infrasound and electromagnetic noise, and the variation of the cosmic muon flux. In the preliminary (RUN-0) test period, March–August 2016, data collection was accomplished. In this paper we describe the research potential of the MGGL, list the installed equipment and summarize the experimental results of RUN-0. Here we report on the RUN-0 data, that prepares the systematic and synchronized data collection of the next run period.

Performance assessment of an underground gas storage cavern using water-shed scale groundwater flow modeling with large grid spacing

In this study, we simulated the water-shed scale groundwater flow near an underground LPG storage cavern system to assess its performance. To consider the effects of the storage cavern system on groundwater flow with large grid spacing, we proposed a mathematical model of a head-dependent flux boundary condition for a storage cavern system. Then, we examined its applicability by comparing the simulation results from assigning head-dependent flux boundary conditions, to those from assigning constant head boundary conditions for a hypothetical storage cavern system. Then, we applied this new simulation to the performance assessment of a real underground LPG storage cavern system. The results show that the influence of a storage cavern system on groundwater flow can be modeled in a 3-D water-shed scale with large cells by applying the proposed head-dependent flux boundary condition. The proposed model for a head-dependent flux boundary condition was used for performance assessment of the storage cavern systems and discussion of future works for their performance.

Inverse modelling of groundwater flow around a large-scale underground cavern system considering the excavation-induced hydraulic conductivity variation

This study proposed an inverse modelling procedure for evaluating the anisotropic hydraulic conductivity and its variation induced by excavation in fractured rocks by integrating a strain-dependent hydraulic conductivity model. The time-series measurements of both hydraulic head and discharge were used to construct the objective function for improving the reliability, which was solved with a combined method of orthogonal design, transient groundwater flow modelling, artificial neural network and genetic algorithm-based optimization for reducing the computational cost. The proposed methodology proves its effectiveness by successful inverse modelling of the groundwater flow around the underground caverns at the Jinping-I Hydropower Station.

Comparison of compressed air energy storage process in aquifers and caverns based on the Huntorf CAES plant

CAESA (compressed air energy storage in aquifers) attracts more and more attention as the increase need of large scale energy storage. The compassion of CAESA and CAESC (compressed air energy storage in caverns) can help on understanding the performance of CAESA, since there is no on running CAESA project. In order to investigate the detail thermodynamic process, integrated wellbore-reservoir (cavern or aquifer) simulations of CAES (compressed air energy storage) are carried out based on parameters of the Huntorf CAES plant. Reasonable matches between monitored data and simulated results are obtained for the Huntorf cavern systems in the wellbore and cavern regions. In this study, the hydrodynamic and thermodynamic behaviors of CAES in cavern and aquifer systems are investigated, such as pressure and temperature distribution and variation in both the wellbore and cavern regions of the CAES systems. Performances of CAESA are investigated with numerical models and compared with the performances of CAESC. The comparisons of CAESC and CAESA indicate that the pressure variation in CAESA shows a wider variation range than that in CAESC, while the temperature shows a smooth variation due to the large grain specific heat of the grains in the porous media. The simulation results confirm that the CAES can be achieved in aquifers, and further that the performance of energy storage in aquifers can be similar to or better than CAESC, if the aquifers have appropriate reservoir properties, which means the gas bubble can be well developed in an aquifer with such properties and the aquifer should have closed or semi-closed boundaries. The impacts of gas-bubble volume, formation permeability, and aquifer boundary permeability on storage efficiency are investigated and the simulation results indicate that the increase of gas bubble volume and permeability can improve the efficiency, but the effect is not significant. The gas bubble boundary permeability has a small effect on the energy efficiency of the sustainable daily cycle but can significantly affect total sustainable cycle times. The analysis of thermodynamic behaviors in CAESA suggests that more attention should be paid to the heat storage, reservoir properties and two-phase flow processes.