•A damage model based on microseismic data is developed.•Structurally-controlled displacements are predicted in 3D continuum framework.•Geological structures in numerical model can be specifically ...ignored.•Reasonable scope of potential failure region is revealed.
Large displacements controlled by the motion of layered rock strata usually pose a high hazard to the stability of high sidewalls of the underground caverns in bedded rock mass. Timely and accurate prediction of structurally controlled displacement can provide more reasonable guidelines for supporting measures during cavern excavation. In this study, an approach integrating the continuum modeling and microseismic (MS) monitoring data, was proposed to quantitatively predict the structurally controlled displacements in bedded rock masses surrounding large-scale underground caverns. First, a comprehensive method based on the MS data was adopted for judging the fracture type of bedded rock mass, and this method was validated by field surveys. Second, the damage scope of the bedded rock mass caused by each MS event was determined on the basis of fracture types. A damage model based on the MS data was successfully developed to be embedded into three-dimensional continuum modeling. Finally, our proposed method was verified by comparing its predictions with the actual data. Good agreements indicated that the large deformations induced by the rotation of layered rock strata with long deformed length, can be fully predicted using the damage model. Complicated geological structures can even be ignored when establishing the three-dimensional continuum model. The reasonable scope of potential failure region can be revealed by the predicted deformation mode, which verified the damage scope corresponding to each MS event.
Large underground caverns are characterized by high geostress, high sidewalls and complex geological conditions, which make the rock masses suffer a series of failures in the process of excavation. ...The excavation of the large underground powerhouse of the Baihetan Hydropower Station in China is based on the drilling and blasting method with small steps and weak-vibration blasting. To thoroughly understand the mechanism of blasting excavation on the surrounding rock, in situ microseismic (MS) monitoring system was established to analyze the blast-induced microseismicity of the large underground powerhouse of the Baihetan Hydropower Station. The waveform characteristics of blasting events and rock fracturing events are distinguished first. Then, the spatial distribution of density contours of MS events and rock mass seismic deformation induced by blasting excavation are obtained. The results show that the blast-induced risk areas are mainly concentrated in the downstream sidewall of the underground powerhouse. MS monitoring in real time during the excavation process can provide data reference for the dynamic optimization of on-site construction schemes.
•A PD-FEM approach for fast solving static failure problems is proposed.•Solved by assembling the global matrix and adopting the ADR algorithm.•The short-range repulsive force is introduced and the ...coupling force is redefined.•Realizing efficient simulation of excavation process of the underground cavern group.•Compared with pure PD, coupling approach greatly improves the calculation efficiency.
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.
Taking Jiangsu province of China as an example, large-scale underground hydrogen storage (UHS) in salt caverns is proposed to realize peak shaving for wind power. A bedded salt rock, Jintan salt mine ...in Jiangsu, is selected as the potential site for UHS. And the feasibility of UHS in bedded salt rocks is evaluated. Firstly, the regional geological conditions of Jintan salt mine are analyzed. It shows that this mine has good stratigraphic trapping and meets the site-selection requirements for UHS. Then, a numerical simulation model is established to analyze the stability and applicability of the proposed UHS caverns. The tightness of the UHS salt caverns is also investigated. It is indicated that gas tightness can be favorable once the permeability of interlayers is around 10−18 m2 or lower. Finally, it is estimated that the salt caverns for 36.9 TWh-scale UHS of Jiangsu can be mainly provided by salt mine enterprises, but more attention should be paid to the usability of caverns during extraction. This study provides a feasible and economical solution for fulfilling the large-scale UHS in the Jiangsu, as well as for the regions that are rich in both renewable energy and salt resources.
•Large-scale H2 can be stored in salt caverns for peaking regulation of wind energy.•The bedded salt rock of Jintan has favorable geological trapping conditions.•The salt caverns in bedded salt rock satisfy the stability for hydrogen storage.•Interlayers’ permeability is the key to control hydrogen storage tightness.•The mining enterprises can provide most of the cavern volume for hydrogen storage.
The method of Random Forest (RF) was used to classify whether rockburst will happen and the intensity of rockburst in the underground rock projects. Some main control factors of rockburst, such as ...the values of in-situ stresses, uniaxial compressive strength and tensile strength of rock, and the elastic energy index of rock, were selected in the analysis. The traditional indicators were summarized and divided into indexes I and II. Random Forest model and criterion were obtained through training 36 sets of rockburst samples which come from underground rock projects in domestic and abroad. Another 10 samples were tested and evaluated with the model. The evaluated results agree well with the practical records. Comparing the results of support vector machine (SVM) method, and artificial neural network (ANN) method with random forest method, the corresponding misjudgment ratios are 10%, 20%, and 0, respectively. The misjudgment ratio using index I is smaller than that using index II. It is suggested that using the index I and RF model can accurately classify rockburst grade.
•Characteristics of spalling in a large underground cavern have been represented.•A spalling case was entirely recorded in time series by multi measuring ways.•Experimental results expose the ...time-dependent development of spalling performance.•Borehole camera exposes the inner cracking evolution of rock ahead of spalling.
Rock spalling is one of the most frequent break modes and a serious stability challenge for the supporting design during engineering excavation under high geo-stress and hard rock conditions. The primary objective of this work was the field investigation and experimental testing of basalt spalling in more than 50 cases in a large underground cavern in China. The field characteristics of basalt spalling, including the spatial distribution of events, its micro-surface morphology, the joint effect, the time-dependent relation to the excavation, the spatial distance to the opening face, and the supporting condition, are first presented via detailed statistical investigation. An in situ study of the full spalling process, including the surface development of rock slabbing and inner cracking extension of the surrounding rock, was recorded in a time series via a borehole camera, displacement measurement, and in situ photos. These experimental results exposed the time-dependent development of surface spalling performance and the inner cracking evolution of rock mass ahead of spalling. All of these actual spalling cases in a large underground cavern and the corresponding statistical analysis provided meaningful evidence for the tensile failure mechanism and prevention measures for rock spalling.
Abstract
The surrounding rock stability is a main difficult problem in the hydropower station construction and operation. Taking one hydropower station as object, FLAC 3D numerical simulation ...software was used to calculate the changes in surrounding rock failure zone distribution, surrounding rock strain, and block safety factor before and after supporting. The stability of the surrounding rock after excavation was analyzed and effect of the supporting structure was also evaluated. Finding that: the supporting structure can effectively improve the stability of surrounding rock. After supporting, the failure zone range, the deformation of surrounding rock, and the internal force of the supporting structure all reduced, while the safety factor of the block improved. Due to the effect of bolt, the deformation of the surrounding rock transformed from plastic to elastic, and the rebound zone of the surrounding rock increased, while the plastic and failure zone reduced. The depth of the failure zone on the downstream side is greater than that on the upstream side, and a large number of cracking zones are distributed on the downstream side. At the same time, due to the influence of cracks and geological fracture, the failure of surrounding rock around the main powerhouse is higher than that around the tailgate chamber higher than that in the main transformer chamber. The safety factor of the key blocks distributed around the main transformer chamber and the main power house improved, the sliding form of some blocks transformed from collapse to single-surface sliding.
Dihydrogen (H
2
), commonly named ‘hydrogen’, is increasingly recognised as a clean and reliable energy vector for decarbonisation and defossilisation by various sectors. The global hydrogen demand ...is projected to increase from 70 million tonnes in 2019 to 120 million tonnes by 2024. Hydrogen development should also meet the seventh goal of ‘affordable and clean energy’ of the United Nations. Here we review hydrogen production and life cycle analysis, hydrogen geological storage and hydrogen utilisation. Hydrogen is produced by water electrolysis, steam methane reforming, methane pyrolysis and coal gasification. We compare the environmental impact of hydrogen production routes by life cycle analysis. Hydrogen is used in power systems, transportation, hydrocarbon and ammonia production, and metallugical industries. Overall, combining electrolysis-generated hydrogen with hydrogen storage in underground porous media such as geological reservoirs and salt caverns is well suited for shifting excess off-peak energy to meet dispatchable on-peak demand.
Underground salt caverns are used globally for large-scale energy storage. In the thinly bedded rock salt in China, two butted-well horizontal (TWH) caverns, as alternatives for energy storage, are ...regarded as having better suitability and economy than vertical caverns. However, understandings of the cavern shape development and control methods of TWH-caverns remain insufficient. To overcome these shortcomings with respect to TWH-caverns, we conducted physical simulations of TWH-cavern construction using a high strength steel mold and molded large rock salt specimens. We established a platform for physical simulation of TWH-cavern water-solution construction using the large molded rock salt specimens, so that the construction process is visible and easily observed. Six groups of physical simulations of TWH-cavern construction were designed and implemented. The variables which affect the cavern outline expansion were investigated and compared, including water injection rate, transferring of injection well, oil blanket, and retreating position of the water outlet. Finally the expansion rules of the cavern outline, and different effects when injecting from an inclined well vs. From a vertical well were explored, as well as an attempt of retreating water outlet. This study provides significant guidance for constructing horizontal caverns for energy storage in thinly bedded rock salt.
•Physical simulations of TWHH-cavern were made by using large molded rock salt.•Salt solution mainly appears in the regions where the water outlet is adjacent.•Change to inject water from vertical well can promote to dissolve horizontal region.•Retreating the outlet position is effective to form large and safety TWH-caverns.•TWH-caverns are desirable option for large-scale energy storage in bedded rock salts.
Abstract
Caves have a great archaeological importance: they were used as a dwelling, as a shelter of animals, as an occasional refuge both for funerary and religious purposes. A cave survey is the ...first step towards their exploration. This study describes the San Giorgio cave’s survey that is the object of an archaeological research that concerns both the area above it and the underground environments. The cave, located in the north-west of Sardinia, has an extension of about 140 meters and has a maximum depth (surveyed) of -15 meters. Sixty-two TLS scans were carried out producing 1.5 milliard points. The Poisson surface reconstruction algorithm 3 is used to produce the 3D Model. A 3D model in low resolution can be adopted for aims of public archaeology; however archaeologists should take advantage of all the information available in the original point cloud.
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