Large Underground Caverns Research Articles

The effect of pegmatite veins on fracture behaviors of granite in a deep large underground cavern

The effect of pegmatite veins on fracture behaviors of granite in a deep large underground cavern

True triaxial modeling test of high-sidewall underground caverns subjected to dynamic disturbances

Seismicity resulting from the near- or in-field fault activation significantly affects the stability of large-scale underground caverns that are operating under high-stress conditions. A comprehensive scientific assessment of the operational safety of such caverns requires an in-depth understanding of the response characteristics of the rock mass subjected to dynamic disturbances. To address this issue, we conducted true triaxial modeling tests and dynamic numerical simulations on large underground caverns to investigate the impact of static stress levels, dynamic load parameters, and input directions on the response characteristics of the surrounding rock mass. The findings reveal that: (1) When subjected to identical incident stress waves and static loads, the surrounding rock mass exhibits the greatest stress response during horizontal incidence. When the incident direction is fixed, the mechanical response is more pronounced at the cavern wall parallel to the direction of dynamic loading. (2) A high initial static stress level specifically enhances the impact of dynamic loading. (3) The response of the surrounding rock mass is directly linked to the amplitude of the incident stress wave. High amplitude results in tensile damage in regions experiencing tensile stress concentration under static loading and shear damage in regions experiencing compressive stress concentration. These results have significant implications for the evaluation and prevention of dynamic disasters in the surrounding rock of underground caverns experiencing dynamic disturbances.

Probabilistic evaluation method for the stability of large underground cavern considering the uncertainty of rock mass mechanical parameters: A case study of Baihetan underground powerhouse project

For deep large underground cavern projects under complex geological conditions, the determination of rock mass mechanical parameters and stability analysis is fraught with a great deal of uncertainty. This paper proposes a set of methods for estimating rock mass mechanical parameters and probabilistic stability assessment suitable for construction characteristics of large underground caverns. On the one hand, according to the Hoek-Brown criterion and Monte Carlo simulation, a dynamic estimation method for rock mass mechanical parameters is proposed by using Rock Mass Rating (RMR), the uniaxial compressive strength (UCS) of intact rock, and the material constant (mb) as input parameters. On the other hand, considering the uncertainty of rock mass mechanical parameters, a probabilistic evaluation method applicable to the unloading response characteristics of rock mass (including displacement and fracturing zones) around the large cavern is put forward, combining the point estimation method and numerical simulation. The proposed methods were applied to an underground powerhouse, with an excavation span of 34 m and height of 88.7 m, at the Baihetan hydropower station in the southwest of China. Based on extensive field investigations and tests, the probability distributions of key rock mass mechanical parameters were obtained. Furthermore, the high sensitivity of input parameters in the H-B criterion for estimating rock mass mechanical parameters were revealed. Through dynamic simulation, the probability distributions of the displacement and fracturing zones in surrounding rock during the layer-by-layer excavation of the cavern were presented. Comprehensive on-site tests showed that the simulated results were in basic agreement with the actual unloading response behavior during the cavern excavation, validating the correctness and applicability of the proposed methods. The study provides a relatively comprehensive approach for estimating rock mass mechanical parameters and stability evaluation in similar underground engineering projects, and also has guiding significance for predicting and preventing engineering rock mass hazards.

Global stability coefficient of large underground caverns under static loading and earthquake wave condition

Global stability coefficient of large underground caverns under static loading and earthquake wave condition

Overview of the carbon capture and storage opportunities in Oman

This work presents an overview of the surface and subsurface carbon capture and storage (CCS) opportunities, and their associated risks, in Oman. Oman's stratigraphy encompasses various rock sequences that can be harnessed for CCS purposes. The ultramafic rocks of the Samail Ophiolite have long been researched for their ability to permanently sequestrate CO 2 near the surface, whilst the well-studied subsurface sequences also offer storage opportunities for CO 2 , particularly in deeply buried clastic and carbonate saline aquifers. Structural and stratigraphic traps could hold potential for carbon disposal. Producing hydrocarbon fields can also be considered for CCS, either to enhance hydrocarbon production from existing reservoirs or by utilizing deep traps for disposal. Oman's Late Proterozoic to Cambrian evaporites could be utilized to create large underground salt caverns for storing hydrogen and, a less attractive option, CO 2 . In this work, the identified CCS opportunities are ranked based on different criteria. Using injected CO 2 to enhance hydrocarbon recovery by providing additional reservoir pressure support, using depleted hydrocarbon fields for CO 2 storage and the injection of CO 2 in deep clastic saline aquifers rank among the main opportunities for CCS in Oman.

Excavation response and reinforcement practice of large underground caverns within high-stress hard rock masses: The case of Shuangjiangkou hydropower Station, China

The construction of large-scale underground caverns poses numerous challenges due to their massive scale and high complexity. Among them, stability has always been a major concern during the construction process of large underground caverns within high-stress hard rock masses. It is not only influenced by the geological background of the project but also by the engineering activities during construction. This study takes the construction of the Shuangjiangkou (SJK) hydropower station as a case study and combines field investigations to summarize engineering issues and solutions under high geostress in three aspects. Firstly, it focuses on estimating and modifying the in-situ stress field of the underground caverns in the deep-cut valley area using limited geostress testing data and the observed failure phenomena in the pilot tunnel. Secondly, it discusses the typical failure phenomena of caverns under high geostress, including global stress-induced failures and local vein-controlled failures, as well as the corresponding failure mechanisms and treatment measures. Finally, it addresses the special failure phenomena occurring in the protective layer of the rock-anchored beam and optimizes the excavation scheme based on the observed failure patterns. The research results and solutions provided in this study, based on the case of the SJK hydropower station, are expected to serve as a reference for subsequent construction of large underground caverns within high-stress hard rock masses.

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 Study on Seawater Intrusion Law and Countermeasures within Island Underground Water-Sealed Oil Storage Caverns

Underground water-sealed oil storage caverns constructed in island environments is a promising approach for expanding oil storage caverns. However, few researchers have studied the risks of seawater intrusion and the distribution characteristics of intrusion interfaces in large underground water-sealed oil storage caverns in island environments. In this paper, we established a visualized physical simulation platform to investigate the characteristics and control measures of seawater intrusion in single fracture of rock masses within island underground water-sealed oil storage caverns. In addition, the effects of the excavation of caverns, the distance between the cavern and coast, fracture width, seawater level, oil storage stage, water curtain, and water injection pressure were evaluated. The results show that excavation of oil storage caverns carries the risk of seawater intrusion. Specifically, reducing the distance between the oil storage caverns and the coast, increasing the fracture width, and raising the seawater level all contribute to accelerated seawater intrusion into the caverns. However, the vertical water curtain can effectively inhibit seawater intrusion, and increasing the injection pressure of vertical water curtain can avoid the risk of seawater intrusion into the caverns. The research results provide an experimental basis for the study of seawater intrusion in underground oil storage caverns in island environments.

Stability analysis of jointed rock mass in large underground caverns based on multi-scale analysis method

Random defects at different scales are the crucial cause of damage evolution and cascade transfer in rocks. For a large-scale underground cavern, the rock mesoscopic heterogeneity and macroscopic random joints are inevitable factors of rock stability, which needs to be further studied. In this study, a multi-scale analysis method for the stability of jointed rock mass in large underground caverns is proposed. The statistical damage theory is used to describe the mesoscopic heterogeneous rock damage. Monte Carlo simulation and measured joint geometric information are combined to reconstruct the macroscopic random joint network of rock mass. The integrated analysis of mesoscopic heterogeneity of rock and the macroscopic response of random jointed rock mass is performed by Rock Failure Process Analysis (RFPA) system. The research shows that the existence of joint affects the failure mode of rock mass and strengthens the heterogeneity. The representative elementary volume (REV) of jointed rock mass and its equivalent mechanical parameters are determined and used in the stability analysis of a large-scale underground cavern project. Results show a good agreement with the in-situ monitoring deformation of surrounding rock mass, which verifies the effectiveness of the rock mass multi-scale analysis method.

Real-time arrival picking of rock microfracture signals based on convolutional-recurrent neural network and its engineering application

Accurately picking P- and S-wave arrivals of microseismic (MS) signals in real-time directly influences the early warning of rock mass failure. A common contradiction between accuracy and computation exists in the current arrival picking methods. Thus, a real-time arrival picking method of MS signals is constructed based on a convolutional-recurrent neural network (CRNN). This method fully utilizes the advantages of convolutional layers and gated recurrent units (GRU) in extracting short- and long-term features, in order to create a precise and lightweight arrival picking structure. Then, the synthetic signals with field noises are used to evaluate the hyperparameters of the CRNN model and obtain an optimal CRNN model. The actual operation on various devices indicates that compared with the U-Net method, the CRNN method achieves faster arrival picking with less performance consumption. An application of large underground caverns in the Yebatan hydropower station (YBT) project shows that compared with the short-term average/long-term average (STA/LTA), Akaike information criterion (AIC) and U-Net methods, the CRNN method has the highest accuracy within four sampling points, which is 87.44% for P-wave and 91.29% for S-wave, respectively. The sum of mean absolute errors (MAESUM) of the CRNN method is 4.22 sampling points, which is lower than that of the other methods. Among the four methods, the MS sources location calculated based on the CRNN method shows the best consistency with the actual failure, which occurs at the junction of the shaft and the second gallery. Thus, the proposed method can pick up P- and S-arrival accurately and rapidly, providing a reference for rock failure analysis and evaluation in engineering applications.

The Deformation Law of a Soft-Rock Cavern by Step Excavation in a Pumped Storage Power Station

The surrounding rock stability of large underground caverns in a pumped storage power station is one of the most crucial problems in hydropower project design and construction. In the construction of hydropower projects in Southwest China, many underground soft-rock caverns in are excavated. Influenced by the high sidewall, high ground stress, large burial depth, and hydrodynamic pressure action, the deformation of the cavern is special, especially in terms of its soft-rock distribution. At present, most research of underground engineering on soft-rock stability focuses on small-scale tunnel excavations in homogeneous geological conditions, with limited studies on the large-scale excavation of deeply buried underground powerhouses in complex geological structures, featuring extensive soft-rock-layer exposure on the cavern wall. Therefore, it is particularly important to investigate the excavation method of and support measures for soft-rock caverns under complex geological conditions. Based on laboratory rock mechanics testing (petrographic analysis, uniaxial compressive strength tests, shear tests, and triaxial compression creep tests) and the distribution characteristics of the surrounding soft-rock layer of the proposed underground powerhouse, obtained from the survey, we discuss the excavation and support measurements. These include the influence of support measures on the deformation of the underground excavated cavern considering the inclination of rock layers, the impact of the excavation under supported conditions on the deformation of the underground cavern, and the correlation between the lining thickness and stress variation within the lining.

Numerical back analysis method of three-dimensional in situ stress fields considering complex surface topography and variable collinearity

Numerical back analysis based on incomplete in situ stress measurements is widely used to estimate the three-dimensional (3D) in situ stress fields of large deep underground caverns. However, the variable collinearity caused by complex geological environments has rarely been considered. This paper proposes a numerical back analysis method for 3D in situ stress fields based on stepwise regression (BSSR). In BSSR, the collinearity between independent variables is associated with the surface topography, and insignificant variables caused by variable collinearity are eliminated through stepwise regression. BSSR was applied to the underground powerhouse of a hydropower station for validation, and the results showed that it can reliably estimate the 3D in situ stress field despite the complex geological environments. Multidimensional mathematical models of in situ stress fields were established with the improved predictive ability and clear physical meaning, which can quantify the contributions of six geological actions and three stress sources. The findings of this study can help with understanding the formation mechanism of in situ stress fields for large, deep underground caverns in complex geological environments and provide a useful reference for optimizing excavation schemes and support designs.

Accurate Identification of Broken Rock Mass Structure and Its Application in Stability Analysis of Underground Caverns Surrounding Rock

In view of the broken rock mass in the surrounding rock of large underground caverns, the 3D distribution model of the joints is obtained through the on-site investigation of the joints and the digital imaging technology, and the image processing software. Based on the analysis of the mutual cutting degree of the joints and the geometric shape of the block, the concepts and calculation methods of the degree of fragmentation and the degree of bite are proposed, and the degree of rock mass fragmentation is quantitatively described. Furthermore, the multi-factor analysis method is used to establish the quality evaluation method and the standard of broken rock mass based on the degree of rock fragmentation and the degree of bite, and the failure mode and safety criterion of broken rock mass of surrounding rock are proposed. Applying the discrete element numerical analysis method, the mechanical parameters of different broken rock masses are obtained. The reinforcement analysis of the surrounding rock of different broken rock masses shows that the degree of fragmentation, the degree of bite, and the classification of surrounding rock proposed in this paper can implement precise reinforcement measures for the surrounding rock of different broken rock masses, as it provides an important theoretical basis for the surrounding rock safety of large underground caverns in the broken rock mass and has wide applicability.

Experimental Study on Mechanical Properties of Deeply Buried Granite During Layered Excavation of Large Underground Caverns

Experimental Study on Mechanical Properties of Deeply Buried Granite During Layered Excavation of Large Underground Caverns

Microseismicity and focal mechanism of blasting-induced block falling of intersecting chamber of large underground cavern under high geostress

Microseismicity and focal mechanism of blasting-induced block falling of intersecting chamber of large underground cavern under high geostress

Equivalent Constitutive Model for Jointed Rock Masses and Its Application in Large Underground Caverns

Equivalent Constitutive Model for Jointed Rock Masses and Its Application in Large Underground Caverns

Rock Stress Measurement Methods in Rock Mechanics—A Brief Overview

The current brief review paper on rock stress measurement methods is very crucial factors in mining, civil infrastructure, geothermal energy, nuclear underground disposal, large underground oil storage caverns, etc as well as in geology and geophysical area. Measurement of in situ rock stress is a very challenging and difficult quantity and not possible to measure directly. Measure the deformation or displacements or hydraulic factors by perturbing the rock and converting the measured quantity into rock stress. There are two main categories for measuring methods: direct and indirect methods. The most common methods of direct in situ stress techniques are briefly described including advantages, disadvantages and limitations. Moreover, authors included the application of Artificial Intelligence (AI) for rock stress measurement methods.

Physical overloading test for 3D printed caverns: Failure performance and supporting effect

Excavation of a large underground cavern often induces the unstable behavior of the surrounding rock due to intensive stress redistribution; thus, reasonable supporting measurements are necessary. A new 3D print-based physical overloading test method is presented for exposing the failure performance of caverns and the reinforcing effect of supported structures. Taking the Yingliangbao underground caverns as an engineering background, a physical model and supporting elements for the cavern groups are manufactured first by 3D printing (3DP) technology, including a multi-cavern 3DP sand model, 3DP polymer lining and metal bolt. Further overloading tests for the printed physical models are carried out, and the progressive failure performances are exposed, including crack extension, model loading evolution, local strain development, etc., which indicate that shear failure often appears on the mid-wall. Moreover, the overloading test for the supported cavern model also quantitatively reveals the reinforcing role of the 3DP polymer lining and metal bolt, such as increasing the bearing capacity by more than 10%. A corresponding numerical back analysis is further applied to certify the progressive failure process of multiple caverns under overloading conditions, which provides some cures for the supported bolt position and depth in multiple caverns. This method can enrich the physical model test and guide the support design for underground engineering construction.

Bayesian Estimation of Rock Mechanical Parameter and Stability Analysis for a Large Underground Cavern

Bayesian Estimation of Rock Mechanical Parameter and Stability Analysis for a Large Underground Cavern

Study on the stability of rock mass around large underground cavern based on numerical analysis: A case study in the Cai Mep project

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 over the past several years due to the development of numerical analysis methods and computer development, given the situation that it was difficult to solve the 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. Actual problems have been successfully analyzed in addition to simple analysis and more reasonable design and construction management materials have been obtained. The stability of rock mass around an underground large cavern is the key to the construction of large-scale underground projects which have to divide into different parts stages. Rock bolt and shotcrete are important means to ensure the stability of the underground cavern. The objective of the paper is to evaluate the stability of a large cavern in the Cai Mep project in Ba Ria- Vung Tau by numerical method. The results from numerical simulations show that the stability of rock support of the cavern is in fair agreement with the original design calculation. The maximum displacement of rock mass surrounding caverns, maximum compressive stress and tensile stress in shotcrete, and the maximum axial force of rock bolt obtained by Rocscience -RS2- Phase2 software are the main parameters in the stability assessment.