Underground Cavern Group Research Articles

Dynamic safety information modeling of underground cavern groups in the entire construction process

The construction of underground cavern groups represents a particularly challenging task in current subsurface engineering due to a multitude of variable and often unknown factors, including diverse geological conditions. This study introduces a four-dimensional spatiotemporal model and formulates a dynamic safety information model for these underground systems. Developed using C# and Python, the model integrates the finite element analysis software ABAQUS and Microsoft SQL Server database. The framework allows for real-time visual management of monitoring data, dynamic coupling of construction phases with safety metrics, and continual updates correlating with construction progress. The theoretical findings offer valuable insights for enhancing the safety and efficiency of underground cavern group construction while also supplying methods for real-time safety feedback and control throughout the construction process.

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.

Failure mechanism of rock masses with complex geological conditions in a large underground cavern: A case study

Reasonable and accurate identification of the failure mechanism of rock masses is of great significance for achieving a comprehensive and thorough understanding of the fracture process in underground caverns under high geostress. Sophisticated microseismic (MS) monitoring was established in underground cavern groups to capture the excavation-induced microfracture signals of intact rock masses and rock masses with weak interlayer zones (WIZs). To clarify the mechanical mechanisms controlling the surrounding rock failure modes, the moment tensor inversion method is adopted to fully reveal the fracture types and focal mechanism solutions (strike, dip and rake) of the rock masses. The spatial distribution of the MS events shows that the excavation-induced microfractures of intact rock masses are concentrated in the working face of underground intersecting chambers. The fracture mechanisms of intact rock masses are dominated by tensile fracturing. Compared with those in intact rock masses, the microfractures induced by excavation in rock masses with WIZ form a strip-like cluster area along the WIZ, and the proportion of shear fractures is significantly higher. The moment tensor method quantitatively reveals the failure mechanism of excavation-induced microseismicity of rock masses with complex geological conditions.

Experimental and numerical study on airflow-dust migration behavior in an underground cavern group construction for cleaner production

A large amount of dust will be generated during the construction of underground cavern group. The understanding of the dust migration in the construction ventilation of the underground cavern group can help to optimize the cavern group’s ventilation design and improve the ventilation scheme of the cavern group’s rationality. In this paper, the effects of dust particle size, dust migration path, initial dust concentration in cavern, tunnel entrance wind speed and air duct outlet wind speed on dust migration were studied by combining a model test and numerical calculation. The results show that in the process of dust ventilation migration, the larger the diameter of the dust particles, the more difficult it is to discharge. The time of dust concentration reducing to 2 mg/m3 has a logarithmic distribution with ventilation conditions. The high-speed airflow from the outlet of the air duct is an important factor affecting the migration of dust. The development of airflow is divided into vortex region, recirculation region, collision region and stability region. Vortex region and collision region have lower wind speed and higher dust concentration, which are the unfavorable positions in the ventilation process. In the actual construction process, shortening the distance of dust migration can make the dust discharge quickly. The amount of dust generated by construction has a significant impact on the peak concentration of dust migration. During the ventilation process, the wind speed at the entrance of the tunnel and at the outlet of the air duct has a significant impact on the migration time of dust, at the same time, the ventilation efficiency should be considered while selecting the wind speed.

Seismic response analysis of the underground cavern group at the Yingliangbao hydropower station to the 2022 Ms 6.8 Luding earthquake

Strong earthquakes can cause damage to underground structures. The Yingliangbao hydropower station, which experienced significant tremors during the 2022 Ms 6.8 Luding earthquake, is located just 10 km from the epicenter. To assess the impact of the earthquake on the stability of the surrounding rock, a combination of field investigation and numerical simulation was conducted. The field investigation revealed displacements ranging from 0 to 6.55 mm in certain areas of the rock, with localized collapses. The numerical simulation showed that the response of the underground cavern rock is closely linked to the acceleration and the frequency of the seismic waves. Displacements and stresses in the rock varied significantly at different seismic wave acceleration. However, there were discrepancies between the numerical calculations and the field monitoring data due to factors such as the neglect of local geological weak surfaces. Despite these differences, the numerical simulation accurately represented the overall response of the site to the earthquake, with the magnitude of the disparities in displacement data being on the millimeter scale. The earthquake also may cause a 2.3 % increase in the size of the plastic zone in the surrounding rock. Additionally, the residual displacement and maximum stress fluctuations in the sidewall of the underground chamber decreased with increasing frequency within a specific range, while the volume of the plastic zone initially decreased and then increased with higher frequencies of the seismic waves.

The criterion for dividing the surrounding rock EDZs of underground caverns based on the energy dissipation degree.

An energy calculation parameter named the energy dissipation degree (RUd) is introduced based on the analysis of the energy dissipation mechanism and energy evolution characteristics during conventional triaxial tests of the granite of Shuangjiangkou. The deviatoric stress‒strain curve of rock can be divided into five stages using four stress thresholds (crack closure stress σcc, crack initiation stress σci, damage stress σcd and peak stress σp), which also correspond to the four RUd thresholds (RUdc, RUdi, RUdd and RUdp) on the energy dissipation degree-strain curve. A given stress threshold increases with increasing confining pressure; however, a given RUd threshold is basically stable under different confining pressures. Then, a new criterion for dividing the excavation damaged zones (EDZs) in the rock surrounding underground caverns based on the monotonically increasing characteristics of the energy dissipation degree‒axial strain relationship curve is proposed, and it allows for the classification of the surrounding rock into five types of zones through quantitative analysis of the RUd thresholds. Based on the criterion for dividing the EDZs of the surrounding rock mass of the underground cavern, the EDZs of the surrounding rocks of the underground cavern group of the Shuangjiangkou Hydropower Station are analyzed. The distribution characteristics of the EDZs of the rock surrounding underground caverns obtained by numerical simulation calculations based on RUd are basically the same as those obtained by in situ elastic wave tests. However, the RUd-based method for classifying the EDZs of the surrounding rock has the obvious advantage of being able to probe the boundaries of the undamaged zone (UDZ) of the surrounding rock more explicitly, while the method based on wave velocity testing is not sufficiently explicit. The damage zoning of the surrounding rock based on RUd can provide support design advice for the excavation of the surrounding rock, such as the support method, the length of the free section and anchor section of the prestressing anchor, etc.

Stability Analysis of Surrounding Rock of an Underground Cavern Group and Excavation Scheme Optimization: Based on an Optimized DDARF Method

The surrounding rock stability of an underground cavern group is an important issue in the process of cavern excavation, which has the characteristics of large displacement, discontinuity and uneven deformation, so the calculation and analysis are very complicated. The optimized discontinuous deformation analysis for rock failure method was adopted to analyze the stability of the surrounding rock of a real underground engineering cavern group under different excavation schemes. The cracking process of surrounding rock under different excavation schemes, the depth of crack expansion and the vertical displacement of the arch and bottom floor were obtained, and the following conclusions are drawn: (a) After the completion of the excavation, the stability problems mainly appeared in the surrounding rocks of the arch, left wall, right wall and bottom floor of the main powerhouse, in the surrounding rocks of the arch, left wall and bottom floor of the main transformer chamber and in the surrounding rocks of the arch, right wall and bottom floor of the tailrace surge tank. (b) Fault f2 has an influence on the stability of the surrounding rock of the tailrace surge tank, while fault f1 has no influence on the stability of the cave group. (c) The scheme of simultaneous excavation of three caverns shows the advantages in the crack propagation depth of surrounding rock and vertical displacements of caverns.

Evaluation Methods of Salt Pillar Stability of Salt Cavern Energy Storage

Underground energy storage is essential for the country’s development, and underground salt cavern groups are a productive way to store energy. Safety pillar design is the key to ensuring the safe operation of large salt cavern gas storage groups. Therefore, this paper is based on the salt pillar stability design problem and analyzes three aspects: (1) Three kinds of pillar stability design theories—reliability theory, strain energy theory, and catastrophe theory; (2) Two methods for designing stable pillars—determining pillars through formulas and numerical simulations; (3) The form and influencing factors of salt pillar instability—macro and microform and the main influential factors. From the current research, the major problem is that the design of safety pillars has not been systematic, due to the differences in salt rock in the region, and the engineering of salt pillar design still relies on experience. Finally, the impact of salt pillar width and gas injection and withdrawal on the pillars during the design of the salt cavern is analyzed, and the existing salt pillar theoretical characteristics and development trend are summarized.

A PD-FEM approach for fast solving static failure problems and its engineering application

A method of coupling of peridynamics (PD) and finite element method (FEM) for fast solving static failure problems is proposed. It is based on the force coupling method and adopts interface elements to couple the PD and FE subregions. By assembling the global matrix of the coupling model and using the adaptive dynamic relaxation (ADR) method to solve it, the static solution of elasticity and crack growth problems can be obtained quickly. By introducing short-range repulsive force and re-defining the coupling force, it is not only suitable for simulating tensile failure problems, but also suitable for compression failure problems. Through comparative analysis, the accuracy and effectiveness of this approach are verified. And then the method is successfully applied to simulate the excavation process of an underground cavern group, and the simulation of damage and failure process of engineering rock mass under complex tension–compression conditions has been realized. The stability characteristics of the surrounding rock are revealed by analyzing the damage and deformation evolution laws. It provides an effective numerical simulation method for predicting the excavation damage zone (EDZ) distribution characteristics and deformation law of the surrounding rock during the excavation of an underground cavern group. At the same time, compared with pure PD, the calculation efficiency is greatly improved, which is of great significance for the realization of engineering-scale simulation.

Analysis of Structural Characteristics of Underground Cavern Group by Simulating All Cavern Excavation

The traditional Three‐dimensional (3D) model for stability analysis of a large underground cavern group only includes the main powerhouse, the main transformer chamber, the tailrace surge tank, the main electrical wire hall, and part of the diversion tunnel and tailwater tunnel. Other caverns excavation are not taken into consideration, which is inconsistent with the actual project. In this study, a 3D Finite Element Method (FEM) model, including all the cavities, and a 3D simplified model containing only part of the cavities were established based on the actual underground cavern group project. We study the structural characteristics of the cavern group during excavation via 3D nonlinear FEM. At the same time, three numerical calculation schemes are designed for comparison. The results show that the simulated distributions of the stress field, deformation field, and plastic zone of the two numerical models are similar, but the magnitudes of the 3D FEM model, which considers all caverns are generally higher than the simplified model. The difference between the two simulated horizontal displacements of the main powerhouse reaches 53.72%. Therefore, from the perspective of engineering safety and actual construction, it is advisable to adopt the 3D FEM model, including all the cavities, when conducting a simulation analysis of the underground cavern group.

Inversion of the 3D in situ stress field in a complex valley area around the underground cavern group of the Yingliangbao Hydropower Station

The inversion of three-dimensional in situ stress fields in complex river valleys is of great significance for evaluating the excavation stability of deep underground caverns. Based on known in situ stress measurements, it is a major method for obtaining the geostress of the engineering area through the inversion geostress of the whole area with the application of geo-mathematical mechanics. However, the inversion results are often limited by the geological structure and heterogeneous alterated rock, as well as the measurement data reliability. A three-dimensional nonlinear neural network inversion was combined with a simulation of stratigraphic denudation by stages, tectonic compression, and alteration degree in the fault structure. The model was then applied to an underground cavern group of the Yingliangbao Hydropower Station. Comparative analysis showed that the inversion results were in reasonable accordance with the measured in situ stress values. Moreover, the reliability of the three-dimensional in situ stress field obtained using this method was further verified from the stress-induced failure during the cavern excavation. This technique is helpful for optimizing the design of subsequent excavation and reduces the potential instability of surrounding rock during a layered excavation.

Dangerous Rockfall Protection Technology Research on High Slopes of Large-Scale Underground Cavern Group Outlets of a Hydropower Station

In the construction of hydropower projects in southwestern China, the powerhouse, diversion tunnel, tailrace tunnel, access tunnel, and other structures are often located underground in cavern groups. The high slopes of the outlets of these large cavern groups are often characterized by steep terrain, high elevation, and frequent rockfalls, which seriously threaten the safety of construction and operation personnel. Therefore, it is urgent to carry out research on protection technology for dangerous rockfalls on underground excavation outlet slopes. In this paper, Uncrewed Aerial Vehicle (UAV) survey technology is applied. First, large-scale three-dimensional (3D) terrain data is collected by a UAV, then a Digital Orthophoto Map (DOM) and Digital Elevation Model (DEM) of the slope are obtained, and a 3D visualization is constructed. Meanwhile, an orthophoto image for detailed UAV route planning is generated. Second, according to the 3D visualization, a preliminary judgment of potentially dangerous rockfall areas is made by the engineers, and the UAV track planning for these areas is carried out. Third, refined low-altitude aerial photography is carried out on the dangerous areas according to the results of the UAV trajectory planning, and high-precision pictures are obtained. Based on the rock joints, fissures, and configurations displayed in these pictures, the areas with the most likely rockfall risks are further determined. Finally, 3D rockfall simulation software is used for rockfall simulation analysis. Comparing the rockfall interception rates and the distribution probability of rockfalls in each area under different protective net schemes, the final protective net plan is determined. The research results are applied to the design of a dangerous rockfall protection scheme on a natural slope at the outlet of a large underground hydropower station on the Dadu River, which provide a scientific basis for the setting of the protective net. The researches results can be used as reference for similar projects and provide a new idea for the design of dangerous rockfall protection measures on high slope tunnel outlets.

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.

A study on hollow effect and safety design of deep crossing caverns under blasting vibration

Due to the spatial complexity of deep underground cavern group, the safety of crossing caverns during blasting excavation is attracting more and more attention. This article presents a systematic study on the effect of blasting excavation on the crossing caverns and surrounding rocks, based on the firsthand data from the main powerhouse and pressure pipelines of Baihetan Hydroelectric Power Station in China. Through the on-site blasting test and numerical simulation on the powerhouse, the vibration velocity and dynamic stress of surrounding rock under different blasting sources and different maximum explosive quantities are analyzed, the dynamic response characteristics of blasting vibration on the straight sidewalls and the opening of crossing caverns are obtained, and a modified formula for calculating the maximum explosive quantities that consider hollow effect is proposed. The study shows that, the blasting vibration velocity of the powerhouse is highest in the axial direction, followed by the transverse and vertical direction. The peak particle velocity (PPV) generally decreases with the increase of distance to the explosion center, whereas the hollow amplification effect at the openings of pressure pipelines is prominent (can be as high as 41.8% for this case). When the blasting zone is from 1.25 times of the cavern diameter in front of the pressure pipeline to the opening of caverns, the influence of hollow effect on the vibration of pressure pipeline is significant. The worst blasting location is the wall footing of the pressure pipeline that facing the blasting. The maximum vibration velocity, maximum tensile stress, and maximum shear stress on the opening mainly locate at the arch footing, the middle of straight sidewall, and the baseplate. In addition, the maximum tensile stress ratio was greater than the maximum shear stress ratio, indicating that the opening of the crossing cavern is more susceptible to tensile failure. The modified formula considering hollow effect is successfully applied in the blasting design of this project, which can provide experiences and references for the design and construction of similar deep-buried crossing caverns.

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.

Comparative study on tunnel blast-induced vibration for the underground cavern group

Seismic wave induced by blasting excavation of tunnel may exert adverse effects to the surrounding rock. To study the different characteristics and attenuation of blast-induced vibration in the blasting tunnel and adjacent tunnel, field blasting tests are carried out to record velocity–time histories during blasting in Wanhua Underground Gas Storage. The characteristics and attenuation of vibration velocity and energy are presented based on the field data. And the dynamic finite-element model is established to further study the vibration attenuation law. Results demonstrate that PPV and vibration energy of the adjacent tunnel is greater than that in the blasting tunnel and attenuates more readily when monitoring points are near the blasting area. The dominant frequencies of the adjacent tunnel are higher than that in the blasting tunnel at three orthogonal directions. Adopting vibration energy as the evaluation index of seismic intensity, the fitting formula has favorable prediction accuracy, which will provide more accurate guidance for controlling the adverse effects of tunnel blasting.

Comprehensive Evaluation of Sensitivity of Surrounding Rock Parameters for Underground Powerhouse Experience Support

At present, the design and construction of underground powerhouse support are still in the experimental stage. Moreover, before the construction of the underground cavern group, the mechanical parameters of the surrounding rock mass cannot be accurately obtained. During the implementation process, these reasons may cause adjustments to the construction and design plans. To comprehensively evaluate the sensitivity of surrounding rock parameters, we used the multi-indicators, which have certain guiding significance for the accurate acquisition of surrounding rock parameters and the adjustment of empirical support schemes. This study combines the initial geological conditions of the underground powerhouse caverns of the hydropower station and the support scheme. We selected the key position deformation of the lining and the cable stress as the evaluation indicators. The elastic modulus, Poisson’s ratio, friction angle, and cohesion are the influencing factors for the comprehensive evaluation of sensitivity. The results show that the elastic modulus is a highly sensitive parameter for the empirical support scheme, the friction angle is a middling sensitive parameter, and the Poisson’s ratio is a low-sensitivity parameter. Moreover, it is reported that sensitivity is related to the selection of indicators.

Simulation analysis and effect evaluation of excavation and support of underground cavern group

According to the main construction procedures of underground caverns, an analysis model for the excavation of a certain pumping station underground cavern group was established, and its excavation and support process are dynamically simulated. The calculation schemes of unsupport and support are compared with indicators such as plastic zone, bolt axial force and displacement field distribution. The analysis results show that after the support, the plastic zone distribution and deformation characteristics of the rock around the cave are greatly improved. The bolt axial force also meets the requirements, indicating that the support parameters and support methods are reasonable. The supporting effect has been well simulated and realized.

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.

Leading-edge Technologies in Hydropower Development in China

After the implementation of the Reform and Opening-up Policy for a period of 40 years, the exploitation of China’s hydropower resources developed significantly. Through vast amounts of scientific and technological research and construction practices, China has accumulated abundant engineering experience with respect to the construction technologies required for 300-meter-high concrete arch dams, 200-meter-high roller-compacted concrete gravity dams, 200-meter-high concrete face rockfill dams, and 250-meter-high earth core rockfill dams, large-flow discharge and energy dissipation, huge underground cavern group constructions, complicated foundation treatments for high earth and rockfill dams and high and steep slope reinforcements. These series of technologies have now reached an international leading level. In the near future, these technical improvements will likely have broader application prospects and make greater contributions toward hydropower development both in China and across the world.