Construction Of Underground Caverns Research Articles

An Analysis of Two Case Studies on the Construction of Underground Caverns-A Focus on the Tiantai Pumped Storage Station

This paper presents a numerical analysis of two case studies on the construction of underground caverns by FLAC3D, with a specific focus on the Tiantai Pumped Storage Power Station. During the construction period, two main problems, which are crane beam stability and rock support, have been numerically analysed and addressed. The first case study examines the influence of rock wall crane beam support on excavation stability. It has been proven that The reinforcement of connected concrete enhances integrity but may lead to localized cracking. Moreover, over-excavation reinforcement marginally improves anchor safety. The second case study investigates abnormal anchor stress in a powerhouse resulting from excavation. Recommended measures include conducting timely stability evaluations, identifying weakened zones to control rock stress relaxation effects, and establishing effective feedback mechanisms. By enhancing the safety of pumped storage power stations, promoting sustainable energy infrastructure, and improving the design and construction processes of such stations, this research paper aims to contribute to the overall development and success of these projects. In conclusion, the paper has discussed the rock wall crane beam stability and rock support effect, which implement the lack of this type of numerical analysis in underground cavern group construction. Also, it is recommended to accurately determine the rock mass mechanics parameters and timely support the excavated spaces to prevent abnormal increases in anchor stress.

A thermo-hydro-mechanical damage model for lined rock cavern for compressed air energy storage

Large-scale compressed air energy storage (CAES) technology is regarded as an effective way to alleviate the instability of electricity generated from renewable sources such as wind and solar power, which involves the expensive construction of underground caverns to store highly pressurized and high-temperature compressed air. This study documents mechanical behavior and gas permeability of granite under temperature-pressure synchronous cyclic loading, and the response of the surrounding rock to Thermo-Hydro-Mechanical-Damage (THMD) evolution. Firstly, physical experiments were conducted to examine mechanical property and gas permeability evolutions of granite due to temperature-pressure synchronous cyclic loading. Based on these experiments, equations describing the damage evolution of granite were deduced. Subsequently, using these equations in combination with a thermo-hydro-mechanical coupled model of porous media with two-phase fluid flow, a sophisticated computational routine for the thermo-hydro-mechanical-damage analysis of underground gas storage caverns was developed. Lastly, numerical simulations were conducted to study heat transfer, two-phase seepage, and mechanical response of a CAES cavern under operating conditions. Under low to medium pressure and high-temperature synchronous cyclic loading, granite exhibited a significant variation in elastic modulus and compressive strength. Also, its permeability showed a substantial increase due to damage evolution. After two months of operation, prominent heat transfer was observed in the surrounding rock, particularly in the region extending to approximately 10 m from the inner surface of the cavern, exceeding the range of gas leakage diffusion within the cavern. The plastic zone of surrounding rock is distributed above the cavern's roof and below its bottom. Moreover, areas with higher damage are concentrated in the surrounding rock near the cavern's side walls. These findings contributed to our understanding of the behavior of granite in the context of CAES technology and provided valuable insights for the design and operation of gas storage caverns. The development of the THMD model offered a valuable tool for investigating stress and deformation characteristics of the lining and surrounding rock in CAES plants.

Study on the Impact of Different Parameters on Prediction of Crown Deformations in Underground Caverns

Crown deformation is a major concern in the design and construction of underground caverns. It can lead to damage to the cavern structure and surrounding infrastructure and can also pose a safety hazard to workers. This paper studies the factors affecting crown deformation in underground caverns. A parametric study was conducted to investigate the effects of seven parameters on crown deformation: rock mass rating (RMR), uniaxial compressive strength (UCS), Young’s modulus of intact rock (Ei), Poisson’s ratio (υ), tensile strength (σt), angle of internal friction (φ), and cohesion (C). The results of the parametric study showed that the following parameters significantly affected crown deformation: RMR, UCS, Ei, and Φ. A multiple linear regression analysis was conducted to develop a regression equation to predict crown deformation. The coefficient of determination (R2) for the regression equation is 92.92%, which indicates that the equation is a good predictor of crown deformation. The parametric study results and the regression analysis can be used to improve the design and construction of underground caverns. By considering the factors that affect crown deformation, engineers can design more stable caverns that are less likely to experience deformations. The results of the study can be used to improve the design and construction of caverns, making them safer and more sustainable.

Failure modes and excavation stability of large-scale columnar jointed rock masses containing interlayer shear weakness zones

The mechanical properties of large-scale columnar jointed rock masses (CJRMs) after excavation would be reduced due to the unloading relaxation, in addition to its influence on the stability of underground caverns . Moreover, the cutting of the interlayer shear weakness zones through the cavern complicates the overall stability of CJRM, and brings challenges to the stability control of project. In view of such problems encountered during the construction of underground caverns, we reconstructed the large-scale CJRMs containing interlayer shear weakness zones to conduct the 3D rock failure process analysis. The numerical models of surge tank caverns during excavation were established and the mechanical properties, failure modes and acoustic emission (AE) characteristics were analyzed. The simulation results indicate that the large-scale columnar joints and C2 interlayer shear weakness zones influence the mechanical properties and failure modes significantly. Three types of damage modes in numerical models containing crush-shear failure along columnar joints, tensile-slip failure along C2 interlayer shear weakness zone and crush failure inside and around caverns were summarized. The concentration zones of tensile stress were found around each cavern and gradually shrunk from sector shape to linear shape. The caverns were divided into two parts along C2 shear weakness zone in the process of X stress loading and two sector damage zones occurring on both horizontal sides of each cavern. In the process of Y stress loading, some crack networks consisting of large-scale columnar joints, intralayer joints and C2 shear weakness zone were formed which led to the complete failure of the numerical models. A new method based on BP neural network was proposed to evaluate the stability of rock mass with large-scale columnar joints and interlayer shear weakness zones. The training results show that the method can distinguish the stability of rock mass well, while its accuracy reaches 97.6%.

Numerical Simulation Analysis Method of the Surrounding Rock and Support Bearing Capacity in Underground Cavern

After the excavation of an underground cavern, how the surrounding rock and the support work together to bear the excavation load is an important prerequisite to correctly analyze the joint force characteristics; effectively play the role of support; and ensure the safety, efficiency, and economy of underground cavern construction. Starting from the elastic-plastic load release characteristics of surrounding rock, this paper proposes a calculation method of the elastic load coefficient of surrounding rock and a graded release method of plastic load, which ensures the actual effect of the synergistic action of the first support and surrounding rock. Based on the elastic-plastic damage evolution characteristics of surrounding rock, a weighted iterative calculation method of elastic-plastic damage is proposed, and an evaluation method of load release ultimate bearing capacity of surrounding rock is determined. By monitoring the change law of rock acoustic wave velocity with surrounding rock damage, the relationship between the wave velocity and the damage coefficient of the surrounding rock in the excavation process is deduced, and it is proposed to determine the latest support time for first support by using the measured rock damage wave velocity. Through the numerical simulation analysis of a diversion tunnel excavation and support, the damage evolution law of the surrounding rock with the release of the excavation load is studied. The ultimate bearing capacity of various surrounding rocks and supporting opportunity is determined. The results demonstrate the validity and practicality of the analysis and calculation methods in this paper, which provide a new idea and analysis method for quantifying the bearing capacity of surrounding rock and determining the support timing in the excavation and support design of underground caverns.

Research on the correction method of the boundary water level of the mountainsides in seepage analysis

The accuracy of the calculation results in seepage analysis is determined largely by the boundary conditions. The construction of underground caverns and reservoir impoundments will inevitably lead to a redistribution of the underground seepage fields and the change in groundwater level. However, commonly used finite-element simulation methods rarely consider the effects of changes in the boundary water level. This study examined the mechanism of the change in groundwater level caused by impoundment. The drainage of underground caverns on the boundary water level of the model on the mountainsides, and the boundary water-level correction method is proposed. By applying simplified engineering examples, the groundwater levels of the boundaries were calculated (impoundment condition). The results show that the distribution of the seepage field before and after the correction is different. Furthermore, the calculation results of the flow rate are exaggerated (drainage condition of the cavern), as the groundwater drawdown at the computation boundary is ignored. The proposed method can correct the water level at the boundary of the model and effectively improve the calculation accuracy of seepage analysis.

Technological innovations in construction of underground caverns in basaltic rocks at Baihetan Hydropower Station on Jinsha River

The two underground powerhouses on the left and right banks of Baihetan Hydropower Station (BHT-HS) are symmetrically arranged inside basaltic rocks in the alpine gorge reach of the lower Jinsha River. Each of them is equipped with 8 sets of 1,000 MW hydraulic turbine generators, with the largest unit capacity, total installed capacity, span of main powerhouse (i.e. 34 m), diameter of dome-shaped tail-regulating chamber (max diameter of 48 m) and scale of underground caverns around the world. Due to complex layout, interaction between caverns and high hollowing rate, the construction process of the underground cavern group is faced many challenges. For example, the cavern excavation is located in the high ground stress area dominated by horizontal tectonic stress; the underlying basalt fractures are well developed, and the rock is hard and brittle, with low crack initiation strength; columnar jointed basalts develop locally; a number of large and weak gently-sloped shear zones develop diagonally cutting the main powerhouse. Following the construction ideology of “understanding, utilization, protection, monitoring, and feedback analysis on the surrounding rock masses during the construction period”, and with the engineering construction procedure of “the excavation, analysis, prediction and inspection of each rock layer”, this paper proposes a set of innovation construction technologies including “advanced pre-control, thin vertical layer, small planar partition, short excavation progress, fine blasting, strong and quick support, short interval monitoring, quick feedback, precise dynamic optimization” to control the internal cracking of the hard and brittle basaltic rocks, discontinuous deformation of staggered zones and spatio-temporal deformation of underground caverns in high geostress. It has promoted the safe and orderly construction of BHT-HS, the technical progress of the construction of hydropower station projects in China, and may also be applicable to the design and construction of similar projects worldwide.

Research on Surrounding Rock Deformation Prediction During Underground Excavation of Hydropower Station Based on Prototype Monitoring

This paper proposes an improved gray model of equal dimensional innovation based on time-varying parameters and the gray characteristics of small sample and poor information of the safety monitoring data during underground cavern construction, so as to predict and judge the deformation of surrounding rocks in underground caverns and to obtain relatively reliable results in the analysis of uncertain systems. Under certain conditions, the improved gray model of equal dimensional innovation based on time-varying parameters can be used to predict the deformation of surrounding rocks during the excavation of underground caverns, thereby providing mathematical analysis tools for safe construction.

Comprehensive safety evaluation method of surrounding rock during underground cavern construction

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 early-warning 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.

Research on Selection Method for the Types and Sites of Underground Repository for Compressed Air Storage

[Introduction] The selection of types and sites of underground repository for compressed air storage is one of the most important issues of large scale compressed air energy storage (CAES) plant planning. [Method] The advantages and disadvantages of 4 types of underground repository for compressed air storage were concluded based on comparison of analyzing literatures published domestic and oversea. The geology characteristics and distribution region of the suitable hard stratum for construction of underground rock cavern were also analyzed. The technology feasibility of rock cavern for compressed air storage was validated by the in-situ experiment results obtained from the first pilot repository for CAES in China. Sites planning method of underground repository for large scale CAES plant was studied taking Guangdong province for example. [Result] Rock caverns built in salt and hard rock stratum are the most feasible types of the underground cavern for CAES plant and hard rock stratum widely exists in most windy and solar energy abundant aera in China. [Conclusion] Wide distribution of the suitiable stratum for underground cavern construction in intermittent energy generation area solves the difficult problem of site selection for large scale CAES plant. Experiment data indicates that good quality of the rock mass is helpful for the solution of key problems such stability and sealing of underground cavern. All in all, it is feasiblity in technology at the present stage in China.

A Strain-Softening Constitutive Model of Heterogeneous Rock Mass Considering Statistical Damage and Its Application in Numerical Modeling of Deep Roadways

During the construction of underground caverns, the stability of deep underground cavern excavation, which affects the safety and sustainable development of such projects, is a hot issue. First, based on the mechanical properties of surrounding rock in deep tunnels, the strain-softening behavior, damage, and heterogeneity of rock masses are analyzed. Then, a strain-softening model of heterogeneous jointed rock mass that considers statistical damage (SSD) is developed and implemented through FLAC3D simulation software. Finally, the SSD is applied to a deep roadway in the Jinchuan mining area, and a comparative analysis of the computation results of the Mohr–Coulomb (MC) model and the strain-softening (SS) model are carried out. The numerical results are compared with the field-monitoring results, which show that the SSD model simulated the behavior of the surrounding rocks well. The results show that the deformations of the roof and floor are larger, which may serve as a reference for the support pattern of deep roadways.

Engineering Geological and Geotechnical Approaches for the Construction of Powerhouse Cavern of Tehri Pumped Storage Plant (1000 MW) - A Case Study

Construction of underground Cavern in the Himalayan region is full of challenges and uncertainties. Experience has shown that construction in Himalayan regions requires good understanding of geology, adequate site investigations, proper design and selection of suitable construction methodology and technology. The most commonly encountered geological problems during excavation of underground structure in Hydroelectric Projects are, Fault/Thrust/Shear Zones squeezing and swelling, wedge block failure etc. Tehri Pumped Storage Plant (PSP) is located at the left bank of river Bhagirathi in the state of Uttarakhand in Northern India. This case study indicates about the geological challenges faced and their remedial measures during the construction of Tehri PSP Powerhouse Cavern having dimension of 203m x 24m x 58m.3D-geological mapping with 1:100 scales was carried out in excavated central drift of powerhouse to evaluate the rock composition, behavior of rock mass, structural features and further investigation to finalize the layout and orientation. During the investigation Sheared Phyllite with bands of thinly Phyllite Quartzite rock were encountered in the end portion of central drift of powerhouse which had posed a mammoth challenge in designing the powerhouse cavern. Keeping in view the recommendations of geotechnical experts and the design consultants, decision were made to shift the cavern further by 50 m to avoid Sheared Phyllite bands. The shifting of cavern led to the reorientation of structures like control room, service bay and location of units etc. This paper briefly describes the Engineering Geological and Geotechnical set up of powerhouse with proper investigation approaches and excavation sequences highlighting the importance of orientation and Sheared Phyllite Zone.

Early construction cost and time risk assessment and evaluation of large-scale underground cavern construction projects in Singapore

The applicability of the Decision Aids for Tunneling (DAT) as an early construction cost and time predicting tool for large-scale underground cavern construction projects is investigated in this study. For this purpose, three large-scale underground cavern construction projects in Singapore are presented using the proposed framework. The data from Project A, which is already completed, are used to validate the prediction outcomes. The results show that the proposed workflow can well estimate the construction cost and time at the 95% confidence level. The DAT simulation results of the other two projects, which are in the early planning stages, are compared with Project A to assess the accuracy of the predicted cost and time. The results show that the proposed workflow with the DAT as a predictor is a valuable tool in estimating construction cost and time for large-scale underground cavern projects, particularly for feasibility studies.

Deep Fracturing of the Hard Rock Surrounding a Large Underground Cavern Subjected to High Geostress: In Situ Observation and Mechanism Analysis

Rocks that are far removed from caverns or tunnels peripheries and subjected to high geostress may undergo ‘deep fracturing’. Deep fracturing of hard rock can cause serious hazards that cause delays and increase the cost of construction of underground caverns with high sidewalls and large spans (especially when subjected to high geostress). To extensively investigate the mechanism responsible for deep fracturing, and the relationship between fracturing and the excavation & support of caverns, this paper presents a basic procedure for making in situ observations on the deep fracturing process in hard rock. The basic procedure involves predicting the stress concentration zones in the surrounding rocks of caverns induced by excavation using geomechanical techniques. Boreholes are then drilled through these stress concentration zones from pre-existing tunnels (such as auxiliary galleries) toward the caverns before its excavation. Continuous observations of the fracturing of the surrounding rocks are performed during excavation using a borehole camera in the boreholes in order to analyze the evolution of the fracturing process. The deep fracturing observed in a large underground cavern (high sidewalls and large span) in southwest China excavated in basalt under high geostress is also discussed. By continuously observing the hard rock surrounding the arch on the upstream side of the cavern during the excavation of the first three layers, it was observed that the fracturing developed into the surrounding rocks with downward excavation of the cavern. Fracturing was found at distances up to 8–9 m from the cavern periphery during the excavation of Layer III. Also, the cracks propagated along pre-existing joints or at the interfaces between quartz porphyry and the rock matrix. The relationship between deep fracturing of the surrounding rocks and the advance of the cavern working faces was analyzed during excavation of Layer Ib. The results indicate that the extent of the stress relief zone is about 7 m if footage of 3 m is adopted for the rate of advance of the cavern faces. An analysis of the effects of the initial geostress and evolving stress concentration on deep fracturing was also made. It could be concluded that the deep fracturing of the rocks in the upstream side of the cavern is caused by the combined effect of the high initial geostress, the transfer of the stress concentration zone toward the deep surrounding rocks, and the occurrence of discontinuities.

A Real-Time Online Structure-Safety Analysis Approach Consistent with Dynamic Construction Schedule of Underground Caverns

Because of the uncertainties present in geology and construction processes, construction projects in underground cavern groups are typically characterized by high degrees of uncertainty. The real-time safety analysis of underground caverns during construction has been a key technological issue because previous three-dimensional simulations have commonly failed to consider the time-varying changes in construction schedules and geological conditions. Thus, this study couples a construction progress simulation with a real-time dynamic analysis of engineering safety. In this study, a real-time online safety analysis approach based on four-dimensional technology during the construction of underground caverns is introduced, and a dynamic visualization management system of safety information in underground caverns during construction is developed using the OpenGL (Open Graphics Library) Tao Framework and C#, with which integrated management of information related to safety, including geological information, construction progress information, monitoring information, and numerical simulation data, is considered. This study also demonstrates that real-time safety evaluation based on a construction safety information model during the construction of underground caverns is feasible and practical, as shown in a real example in China.

Dat modifications and its application in large-scale cavern construction

The Decision Aids for Tunneling (DAT) have been used world-wide in underground construction projects as a risk assessment tool. However, compared to the linear tunnel construction, underground cavern construction projects involve higher construction risks due to larger sizes and more complex tunnel networks. Therefore, it is useful to examine the capability of the DAT in simulating underground cavern construction with complex networks. This paper discusses the applicability of the modified DAT technique to real construction situation by considering a large scale underground cavern construction. The results show that the overall construction time obtained from the DAT analysis is comparable with the scheduled construction time proposed by the contractor. Time–cost scattergrams for the three partial face excavation scenarios are plotted and a final prediction on the construction time/cost is made. Finally, a parametric study is conducted by increasing the number of simultaneous cavern excavations in order to optimize the resource allocation on the construction site. The overall construction time was found to decrease exponentially with increase in number of simultaneous cavern excavations. The results show that the DAT is a valuable tool in predicting construction parameters and managing resources for underground cavern projects.

Study on Unloading Relaxation Characteristics for Rock Masses under High Geostress

China is rich in hydropower resources that are mainly distributed in the southwest region. The continuous uplifts of Qinghai-Tibet Plateau in the recent hundreds of years result in geomorphologic landscapes of alpine valleys and complex initial geostress field. Constructing large-scale underground cavern groups in such complex geological conditions will lead to some prominent problems. In particular, the unloading and relaxation deformation of rock masses has become one of the key technical problems that restrict the design and construction of underground caverns in southwest China. Based on the engineering practices of hydropower construction in southwest China in recent years and actual engineering geophysical prospecting detection results, typical unloading relaxation characteristics of underground cavern surrounding rock under high geostress are summarized and analyzed. Differences between areas are analyzed and arranged for the rock unloading relaxation area. By reference to the qualitative classification table for the rock mass intactness in the GB 50218-1994 Standard for engineering classification of rock masses, a standard classification methodology for unloading relaxation areas of rock masses under high geostress is initially formed, which is of great significance to the design and construction of underground caverns under high geostress.

Analysis the Concentrations of Toxic and Harmful Gases in Ventilation of Underground Caverns

For ventilation of underground cavern construction, analysis and research the state of motion of the gas in the ideal state and ventilation processes derived the formula of the concentration changes during the construction ventilation toxic and harmful gas diffusion reveals the variation of the diffusion of toxic gases, and engineering examples to verify the theoretical analysis. At the same time, simulation analysis the concentration changing curve of toxic and harmful gas, obtained the ventilation of cavern under different ventilation. The results show that ventilation mode of a constant amount has some shortages in energy efficiency.

Information and communications technology for the construction of underground powerhouse cavern in the Kyogoku hydropower project

This paper presents the outline of observational construction scheme employed for underground cavern construction, and of the Information and Communications Technology (ICT) as a technological tool to facilitate the observational construction. The Hokkaido Electric Power Co., Inc. has been conducting a Hydropower Project in Kyogoku, on the Pepenai and Bihinai tributaries of the Shiribetsu River in Hokkaido, Japan. The Kyogoku Hydropower Plant is the first pumped-storage hydroelectric power plant that was built by the Power Co. It will output a maximum power of 600 MW, with an effective head of 369 m and a maximum water usage rate of 190.5 m 3 /s. The power plant is housed in a large underground cavern of which the dimension is 45.8 m high, 24.0 m wide, and 141.0 m deep. Its total excavated volume is 116,000 m 3 and the maximum cross-sectional area amounts to 1000 m 2 . The geology in the vicinity of cavern belongs to a so-called “Green Tuff” region of the Miocene period, primarily composed of tuff breccia. The geology presents considerable challenges, including a distribution of tuff blocks and two major fault zones with a low uniaxial compressive strength, presumably due to faulting and hydrothermal alteration. Therefore, observational construction method was applied to the project in conjunction with other ICT-solutions, and the actual rock response during excavation was examined in order to ensure the optimum structural support for the cavern and construction safety.

Integrated investigation of seawater intrusion around oil storage caverns in a coastal fractured aquifer using hydrogeochemical and isotopic data

► We analyzed seawater intrusion into oil storage cavern facilities. ► PCA and isotope analysis were used to find the origin of salinization. ► Ion mixing ratio and isotope analysis were used to find the seawater mixing ratio. ► Seawater was one of the major sources of salinity with other possible sources. ► Hydrogeological heterogeneity causes local difference in seawater mixing ratio. Seawater intrusion can be activated by the construction of underground caverns which act as groundwater sinks near a coastal area. In an environment complicated with such artificial structures, seawater intrusion is not simple and thus needs to be evaluated by means of multiple analytical approaches. This study uses geochemical and isotopic indicators to assess the characteristics of salinized seepage into an underground oil storage cavern in Yeosu, Korea. Cl − /Br − ratios, principal component analysis (PCA) of chemical data, and stable isotope data were used to determine the origin and the extent of salinization. Indications of seawater intrusion into the cavern through fractured bedrocks were observed; however, it was highly probable that another source may have contributed to the observed salinity. The PCA results revealed that the seepage water chemistry was predominantly affected both by seawater mixing and cement material dissolution. The maximum seawater mixing ratio in the seepage water was estimated on the basis of the Cl − –Br − mixing ratio and the Cl − –δ 18 O relation, with the results showing considerable variation ranging from less than 1% to as high as 14%, depending on the cavern location. The spatial variations in the chemical characteristics and in mixing ratios are believed to have resulted from the hydrogeological heterogeneity of the study site, as caused by both fractured aquifer and the cavern facilities.