Complex Geological Environments Research Articles

Updating Local Anisotropies with Template Matching During Geostatistical Seismic Inversion

Iterative geostatistical seismic inversion methods are widely used to predict petro-elastic rock properties from seismic reflection data. When the model perturbation technique uses two-point geostatistics, these methods struggle to reproduce complex and nonstationary geological environments such as faults, folds and highly variable depositional systems. These limitations are often due to the use of a global variogram model to express the expected spatial continuity pattern of the property of interest. In complex geological environments a global variogram model might be unable to detect local heterogeneities and rapid variations of lithology, and result in nonrealistic geological models. Local heterogeneities might be predicted from the data using seismic attribute analysis, which can be imposed during geostatistical seismic inversion as local anisotropy models. In these approaches, the information about the local spatial continuity patterns is fixed and will guide and condition the entire inversion procedure, which can lead to errors and uncertainty in areas where this approach is not appropriate due to high local uncertainty of geological features, given the poor signal-to-noise ratio of the data or the presence of important geological features below the seismic resolution. This work proposes an iterative geostatistical seismic inversion method which iteratively updates the local spatial continuity models based on the trace-by-trace misfit between observed and predicted seismic data. The update of the local spatial continuity models aims at surpassing the limitations of the seismic inversion methods that use a fixed a priori variogram model. The method is successfully illustrated in a challenging two-dimensional synthetic data set and in a real case application. The results demonstrate the benefit of updating iteratively the imposed local spatial continuity patterns based on the data misfit. The inverted models are capable of better predicting the location of faults and reproducing the continuity of sinuous channels.

Study on heat exchange of groundwater under complex geological conditions in karst area of south China

This paper takes a groundwater source heat pump in the region as the research object and based on field research, experimental tests combined with comparative analysis, the data on its operation is monitored and analyzed in terms of operation, energy saving, and environment. The results show that the cooling temperatures of the test rooms were all below 26°C, the average coefficient of performance of the units was 4.61–4.93 and the average coefficient of performance of the system was 3.08–3.27. In addition, compared to conventional water-cooled chillers, 466 tons of standard coal could be saved in one cooling season, resulting in a reduction of 1,150.8 tons of carbon dioxide emissions, 9.3 tons of sulfur dioxide emissions and 4.7 tons of dust emissions The savings in operating costs are 793,000 RMB. This shows that the groundwater source heat pump has good energy efficiency and economy. The research results obtained in this paper provide a reference for improving energy efficiency and optimizing the operation of the groundwater source heat pump system. It is of great significance to the application of groundwater source heat pump systems in areas with complex geological environments.

Molecular dynamics simulation study on interfacial behaviors of betaines and extended surfactants

The mixed system between different surfactants has characteristic and synergy to reduce the oil/water interfacial tension (IFT). As the reservoir conditions become more and more severe, it is necessary to explore new surfactants suitable for complex geological environments. In this work, we designed the mixed systems between betaine and extended surfactants, and studied the interfacial properties at the decane/water interface by molecular dynamics (MD) simulations and interfacial tension measurements. The effects of betaine structure and oxypropylene (PO) chain length of extended surfactant on the interfacial behaviors were analyzed in detail from the density profile, tilt angle, average rising height of PO unit and radial distribution function. The results showed that the polar part of betaine extended into the water phase and the hydrophobic chain was more upright in the mixed system due to the electrostatic interaction. For the mixed system, the rise height change of the PO unit indicated that the interfacial behavior of short PO chain was controlled by betaine structure, while that of long PO chain was independent of betaine structure because of the poor deformation ability of it. IFT experiments showed that xylyl substituted alkyl sulfobetaine (XSB) mixing with the short PO chain extended surfactant system had a significant synergistic effect to produce ultra-low IFT but had a negative effect with the long PO chain extended surfactant. This work demonstrated that the steric hindrance of betaine and the PO chain length of extended surfactant synergistically affected the interfacial arrangement and IFT of surfactants, which was of significance for improving and designing more effective surfactant flooding systems to enhance oil recovery.

Fault-Seg-Net: A method for seismic fault segmentation based on multi-scale feature fusion with imbalanced classification

Fault identification has important geological significance and practical production value. Due to the effects of earth filtering and environmental noise, it is difficult to identify minor faults, and manual fault identification is inefficient. In this study, an end-to-end deep learning semantic segmentation network Fault-Seg-Net is proposed to identify fault on seismic images, which simultaneously learns global semantic features and local detailed features. In Fault-Seg-Net, a multi-scale residual module is designed to expand the receptive field to mine fine-grained fault features from the low-dimensional feature space. Fault-Seg-Attention module is designed to model long-distance dependencies of pixel spatial location to compensate for the spatial continuity loss. In addition, a compound loss is used to guide the model training to handle imbalanced seismic image segmentation tasks. Experimental results on synthetic datasets have verified that Fault-Seg-Net can achieve high Precision (88.6%), Recall (89.2%), Dice (88.8%) and mIoU (81.5%) simultaneously, which is significantly better than traditional image processing methods and deep learning semantic segmentation networks. Experimental results on real large-scale field datasets have verified that Fault-Seg-Net has important practical value and strong robustness. This study provides an effective solution for intelligent seismic fault identification under complex geological environment.

Spreading Magnetic Anomalies Separation of the South China Sea Based on the Nested Elliptical Directional Filters

Spreading magnetic anomalies recorded the paleo-geomagnetic field variation that has great significance in the investigation of the extension process of ocean basins. Interpreting spreading magnetic anomalies under complex geological environments is challenging, especially for marginal sea basins. We proposed nested elliptical directional filters to separate the spreading magnetic anomalies of the South China Sea (SCS). The results show that the spreading magnetic anomalies separated by the nested elliptical directional filters depict the expansion process of the oceanic crust, and the interference magnetic anomalies are effectively suppressed. The separated spreading magnetic anomalies indicate that the expansion process of the SCS is affected by the interactions between the surrounding plates. The spreading magnetic anomalies of the SCS are warped, interrupted, and not strictly parallel. The pattern of the spreading magnetic anomalies reflects multiple ridge jumps during the expansion process and the post-spreading magmatic disturbances. The long-wavelength magnetic anomalies indicate lithospheric fractures and Curie surface variations in the SCS, which are affected by the post-spreading magmatic rejuvenation. The magnetic anomalies of the SCS resulted from the superposition of magnetic anomalies in the ocean crust and the uppermost mantle.

Fracture features of brittle coal under uniaxial and cyclic compression loads

Under the effects of complex geological and stress environments, burst hazards continue to be a major challenge for underground space utilization and deep resources exploration as its occurrence can lead to personnel causalities, equipment damage and structural collapse. Considering the stress path experienced by in-situ coal body, cyclic loading appears in quite various forms for instance shearer cutting, overlying strata breakage, hydro-fracturing and blasting, during tunnel, mining and underground space utilizing process. The stability of the underground coal body subject to periodic loading/unloading stress is extremely important for maintain the function of designed engineering structure for waste storage, safe mining, roadway development, gas recovery, carbon sequestration and so on. The mechanical properties of hard rock subject to cyclic fatigue loads has been intensively investigated by many researchers as the rock burst induced by supercritical loads has long been a safety risk and engineering problems for civil and tunneling engineering under deep overburden. More recently, the mechanical properties of coal samples under cyclic fatigue loads is investigated from the aspect of hysteresis, energy dissipation and irreversible damage as the burst hazards of brittle coal is rising in many countries. However, the crack propagation and fracture pattern of brittle coal need more research to understand the micro mechanism of burst incubation subject to cyclic fatigue loads as brittle coal can store more elastic strain energy and rapidly release the energy when its ultimate strength once reached. This research studied the internal crack status corresponding to different cyclic fatigue loading stage of brittle coal samples. The AE monitoring was applied during the uniaxial and cyclic loading process of brittle coal samples to record the crack intensity of samples at different loading stages. The damage evolution curve corresponding to loading status was then determined. The fracture pattern of coal samples determined by micro-CT scan was observed and discussed. It has been found by this paper that brittle coal of uniaxial compression tests demonstrated sudden failure caused by major splitting fracture while that of cyclic fatigue tests experienced progressive failure with mixture fracture network.

3C-3D tunnel seismic reverse time migration imaging: A case study of Pearl River Delta Water Resources Allocation Project

In recent years, tunnel boring machines (TBMs) have been widely used because of their fast construction speed and economical benefits, and the need to obtain geological information ahead of the tunnel to ensure the TBM tunnel construction safety has also arisen. Faced with the complex geological environment, seismic forward-prospecting is the primary method for predicting the unfavorable geological structure in front of the tunnel face. As a crucial step in seismic forward-prospecting method, migration can image geological characteristics and help learn the distribution of unfavorable geology. To achieve all-round imaging of unfavorable geology, we suggested a three-component (3C) three-dimensional (3D) tunnel seismic reverse time migration imaging method. The acoustic wave equation is employed for the forward and backward wavefield extrapolation after the P/S-wave separation to eliminate the imaging artifacts from severe converted waves in tunnels. GPU parallelization is used to accelerate the calculation to further adapt to the rapid excavation of TBMs. The proposed method is validated in two typical numerical models, especially for 3C seismic data that provides all-round geological information to achieve enhanced imaging energy and artifact reduction, which demonstrates the significance of 3C seismic data to migration imaging. This case study was conducted in the Pearl River Delta Water Resources Allocation Project in Guangdong Province, China. The reliability of 3C3D tunnel seismic reverse time migration imaging in field tunnel engineering was investigated. Two consecutive detections were performed, and then the spatial positions of faults and fractures in front of the tunnel face were accurately judged by the combination of the two imaging results. Based on the detection results, the excavation rate was slowed down and the tunnel lining support was increased. The TBM then successfully passed through the risk areas. This case study can serve as a reference for other tunnels with similar concerns regarding the necessity of 3C seismic data and consecutive detections.

Risk Assessment of Oil and Gas Pipeline Based on Vague Set-Weighted Set Pair Analysis Method

This study focuses on a risk assessment method for oil and gas pipelines. Oil and gas pipelines are usually constructed in a complex geological environment and are potentially dangerous. Risk assessment is a key step for their safety management. Therefore, the present paper establishes a risk indicator system as the risk assessment foundation, and we propose a risk assessment method to obtain a quantitative assessment result for the pipeline based on set pair analysis (SPA) theory. For the weight values of each indicator in the assessment process, this paper presents a calculation method based on vague sets theory. Then, a pipeline in the Yanchang oilfield was taken as a case study to verify the feasibility of the method, and the final assessment result was 2.911, which meant the pipeline was relatively safe. The method could also obtain the risk level of each indicator, showing that geological conditions, extreme weather, and public safety awareness were particularly unsafe, and service time, pipeline deformation, ground activity, and operation training were relatively unsafe. It is expected that the risk assessment result could provide a reference for pipeline safety management.

Design of a combined cube of seismic data acquired in areas of complicated relief by use of various seismic source types

The paper gives brief information on the study area with attention focused mainly on complex surface seismic and geological environment, stipulating the use of 3D seismic survey in this area. As the area features complicated relief, the sources and receivers have been chosen individually for each location of the survey. Seismic energy sources generated various seismic oscillations and this complicated the design of combined 3D cube for the whole study area. By use of modeling we have reduced all oscillations to the minimal-phased form. The next stage of processing consisted in use of shifts of time sections for combination of seismic boundaries acquired for various parts of the area: onshore, offshore, swampy areas. Thus, applying the standard procedures it was possible to design combined 3D cube.

The effect of stress, pressure and temperature on CBM migration with elastic–plastic deformation

The laws relating to changes in permeability in coal reservoirs is central to the simultaneous exploitation of coal and gas. Under the condition of multi–field influences caused by stress, pressure, and temperature, elastic–plastic deformation in the matrix–fracture is complex, which has made it difficult to analyze the coalbed methane (CBM) migration law. The coal matrix is deformed by gas adsorption and thermal expansion. However, deformation in the coal matrix is not equal to fracture deformation, meanwhile, the coal mining process causes obvious plastic deformation. Therefore, in this work, the sensitivity coefficient (Sf) was used to quantify fracture deformation, and the sensitivity coefficient of fracture number to the damage value (ζ) was specified to quantify matrix deformation. Further, a coal reservoir permeability model under elastic–plastic deformation was established. The proposed permeability model was verified by laboratory test data under different boundary conditions. On this premise, the contribution of effective stress and adsorption to permeability was discussed, with the influencing factors of Sf being analyzed, and a sensitivity analysis of Sf and ζ was studied. The results revealed that the permeability model proposed in this work can predict the change law of permeability with elastic–plastic deformation effected by stress, pressure and temperature. The theoretical results from the proposed permeability model were helpful in understanding the law relating to changes in permeability in a complex geological environment during the simultaneous exploitation of coal and gas.

Training astronauts for scientific exploration on planetary surfaces: The ESA PANGAEA programme

Future human missions to the Moon and Mars will require astronauts to perform science-focused surface exploration in complex geological environments. However, the scientific expertise required for these activities is uncommon in the astronaut corps. PANGAEA (Planetary ANalogue Geological and Astrobiological Exercise for Astronauts) is a field training course designed by the European Space Agency (ESA) that addresses the topics of geological and astrobiological planetary exploration. The course intends to impart the essential basic theoretical and practical knowledge of geology and astrobiology, in order to prepare astronauts for advanced mission specific training. Significant focus is given to skills in areas relevant to future missions, such as scientific decision-making, working with a remotely located science team, and efficient documentation. For this reason, although portions of the course are taught in classrooms, developing independent field skills in analogue geological environments is a key part of the training. Classroom and field lessons are tightly interwoven in the course structure with a time separation often of only hours between being introduced to a concept in the classroom and seeing it in the field. The course forms part of the basic and pre-assignment training for European astronauts and is open to trainees from all other agencies. PANGAEA has been running since 2016, with participants including ESA and NASA astronauts, and Roscosmos cosmonauts, as well as mission designers, operations personnel and engineers. The primary field sites selected for the course are Permo-Triassic sedimentary sequences in the Italian Dolomites, impact lithologies in the Ries Crater, Germany, a comprehensive suite of volcanic deposits in Lanzarote, Spain, and anorthosite outcrops in Lofoten, Norway. Each is used as a base to deliver the main learning sessions, respectively: 1) Earth geology, rock recognition and sedimentology on Earth and Mars, 2) Lunar geology and impact cratering, 3) volcanism on Earth, Moon, and Mars, and astrobiology 4) intrusive rocks and lunar primordial crustal evolution. The four sessions are designed to increase trainee autonomy in field geology by including guided or autonomously executed geological traverses and practicing of sampling techniques. Whilst PANGAEA's primary focus is astronaut training, where appropriate and complementary to this training, technologies being developed for future missions are used and tested by the trainees during geological traverses. This provides an opportunity to evaluate the performance of new equipment and software in analogue field environments, whilst also providing trainees with experience using technology that might support future missions.

Using different receptor models to determine the sources of available forms of potentially toxic elements in Rasina District – A case study

Determining the sources of potentially toxic elements (PTEs) in soil is one of the basic postulates for dealing with them properly in the future. In addition to total PTEs, it is extremely important to identify sources of available PTEs, for two reasons: 1. to determine their actual impact on the ecosystem, and 2. to establish whether sufficient levels are present in soil if they are necessary for plant development. In this study, two receptor models were used to determine sources of diethylenetriaminepentaacetic acid (DTPA)-extractable PTEs in soil in Rasina District, Serbia in 2017: Principal Component Analysis (PCA) and Positive Matrix Factorization (PMF). Appropriate PCA was used for total forms and the accuracy of the models in determining sources was tested by comparing them. Based on the results, obtained in quite a complex geological environment, the universality and superiority of the PMF model in so-called diffusion systems, which are more prone to change, was confirmed. The PMF model took geological and anthropogenic sources, characteristic of PCA of total PTEs, into account in equal measure, as well as pedological sources, which are more characteristic of PCA of DTPA-PTEs. The accuracy of the model was also confirmed by the greater number of factors, i.e. 5 in the PMF model compared to 3 in PCA. Based on the obtained results, it is clear that the use of the PMF model is justified when determining sources of individual available PTEs in soil.

Risk uncertainty analysis in shield tunnel projects

Subway shield tunnels usually pass through the complex geological environment of a city. There are many uncertain factors in shield tunnel construction risk, undoubtedly increasing the difficulty of construction safety control. Risk evaluation prior to project construction is necessary for the implementation of tunnel projects and reduces risk levels during construction. However, tunnel risks are uncertain and are characterized by random and fuzzy uncertainty. To account for these two uncertainties in the quantitative transformation of risk qualitative concepts and to improve the evaluation accuracy, in this study a new risk evaluation method based on a two-dimensional cloud model (TDCM) is proposed for shield tunnel projects. First, the risk evaluation criteria are quantified with the harmfulness and the probability of risk as the evaluation dimensions of the two-dimensional cloud, and the conversion relationship between the risk level and the quantitative domain is improved. A risk evaluation index system based on construction accidents and risk types for shield tunnel projects is established. Then, the Delphi method is used to evaluate the probability and harmfulness of the risk, the index weight and numerical characteristics of the two-dimensional cloud model are determined, and a shaped two-dimensional comprehensive cloud of thousands of cloud droplets is generated by a positive cloud generator. Finally, the domain is defined as the overlap between the comprehensive evaluation cloud and the standard cloud at different risk levels, and the contribution of comprehensive evaluation cloud drops to the comprehensive evaluation cloud in each domain is analysed. The risk level of the project is predicted based on the principle of maximum membership degree. The risk evaluation method proposed in this study is applied to two subway shield sections, and the risk level of these projects is accurately predicted. The TDCM evaluation method is compared with the one-dimensional cloud model (ODCM) evaluation method and the fuzzy comprehensive evaluation method (FCEM), and the advantages and applicability of the TDCM evaluation method are discussed.

Study on Characteristics of Overburden Strata Structure above Abandoned Gob of Shallow Seams—A Case Study

To understand the change in overburden structure after coal seam group mining, we investigated the overburden characteristics and bearing capacity of abandoned coal mines in a coal seam group. We provide a theoretical basis for the construction and utilization of a coal mining subsidence area under a complex geological environment. This paper takes the construction project of Zhongtie Huizhi Square in Zhangqiu District, Jinan City, Shandong Province as the engineering background. According to the occurrence conditions of the study area, theoretical analysis, similar simulation, numerical simulation, and engineering practice verification are used. The overburden structure characteristics of abandoned mines in a shallow-buried coal seam group were studied. The results show that the development height of the water-carrying fractured zone after the mining of the 3#, 4#, and 9# coal seams is 17 m, 19.5 m, and 27.1 m, respectively, which shows that the height of water flow in the fractured zone is proportional to the buried depth of the coal seam after coal seam mining. After the model is set aside for three months, the degree of development of the residual fracture in the goaf is analyzed, and the distribution law of residual porosity in the longwall old goaf of a shallow-buried multiple coal seam is obtained. The development rate of residual fissures on both sides of the goaf is between 20.31% and 42.31%. The residual fracture development rate in the middle is relatively small, being between 8.21% and 18.53%. We comprehensively analyzed the characteristics of overlying strata in the abandoned mine under actual stratum conditions, and compared the empirical calculation results, theoretical research, similar simulation, and numerical simulation results in the specification with the engineering practice to prove the reliability of the research.

A Virtual Planning Method for Spatial Pose and Performance Fusion Advancement of Mining and Transportation Equipment in Complex Geological Environment

A Virtual Planning Method for Spatial Pose and Performance Fusion Advancement of Mining and Transportation Equipment in Complex Geological Environment

Geo-mechanical model test on the water inrush induced by zonal disintegration of deep tunnel under hydro-mechanical coupling

With the increase of burial depth, complex geological environments such as high in-situ stress and high seepage pressure will inevitably affect the generation of zonal disintegration and may induce water inrush disasters during the excavation of the deep tunnel. A true three-dimensional geo-mechanical model test is conducted to study the mechanism of water inrush induced by zonal disintegration under hydro-mechanical coupling. The distribution and variation of different physical information during excavation, including displacement, stress and seepage pressure, are comprehensively analyzed. Test results reveal that zonal disintegration may induce water inrush when the tunnel is excavated under the coupling action of high stress and high seepage pressure. The excavation disturbance causes the stress in the rock mass to be oscillating. As a result, rupture and non-rupture zones appear alternately around the tunnel. With the increase of seepage pressure, the rock mass in non-rupture zone, which acts as the water barrier, is damaged and connects with rupture zone to form a water inrush channel. Eventually, high-pressure water pours into the tunnel to form a water inrush disaster. The reproduction of this special phenomenon will provide an important test basis for further theoretical and numerical studies.

A Geotechnical Perspective on a Complex Geological Environment in a High-Speed Railway Tunnel Excavation (A Case Study from Türkiye)

The T26 tunnel was designed within the scope of the Ankara-Istanbul high-speed railway in accordance with the speed of 250 km/h. Some serious problems and excessive deformations were encountered during the excavation works. The deformations in the tunnel caused subsidence on the surface and the Tunnel Boring Machine (TBM) became stuck; therefore, tunnel excavation works were suspended. Design works for re-excavation in the T26 tunnel and extracting of the TBM were carried out and the tunnel was re-designed by the New Austrian Tunneling Method (NATM) system. The main purposes of the present study are to describe the problems encountered during the T26 tunnel and to discuss the sources of the problems. The advantages and disadvantages of TBM and NATM methods for the tunnel having difficult ground conditions were discussed. Critical points needing to be considered for the tunnels excavated with TBM through weak ground conditions and the effect of the TBM selection process were discussed. Considering the complex geological and geotechnical structure of the tunnel route, it is possible to say that the T26 case is an interesting case for tunnel engineering. Along the tunnel route, landslides, high seismic activity, groundwater conditions, and extremely weak rock mass features coexist. Therefore, the tunnel route is a very complex environment. However, due to the geometric limitations of the high-speed railways, relocation of the route is not possible. The experiences gained from tunnel excavations under difficult conditions are capable of bringing new horizons to future tunneling studies.

Strength Characteristics and In Situ Stress Measurement of Rock Cores from a Large Section Underground Station: A Case Study

Chongqing is a mountain city in western China with a complex geological environment, which brings many difficulties to the construction of large sections of underground projects. In order to avoid serious problems in the construction of Guobo Station with large sections, intensive coring and laboratory tests were carried out to obtain the rock mass properties in detail. The boreholes reveal that the lithology of the rock mass in the project area consists mainly of mudstone and a small area of sandstone. The uniaxial compressive strength (UCS) and the Brazilian tensile strength (BTS) of mudstone are highly scattered, which are 4.43~42.43 MPa and 0.66~4.30 Mpa, respectively, but they all show a lognormal distribution. The average UCS of sandstone is 65.31 MPa, and the BTS is 3.06 MPa. Meanwhile, the softening coefficients of mudstone and sandstone are 0.33 and 0.73, which indicate that the water content has a great influence on the mechanical properties of the rock. For the in situ stress field, the relationship between the three principal stresses is as follows: the maximum horizontal principal stress > minimum horizontal principal stress > vertical principal stress, and the lateral pressure coefficient is 2.11~5.71. Based on the present experimental results, it is proposed that the potential risks of excavation include: (1) bias pressure (2) high in situ stress; (3) surrounding rock deterioration.

A parallel adaptive finite-element approach for 3-D realistic controlled-source electromagnetic problems using hierarchical tetrahedral grids

SUMMARY To effectively and efficiently interpret or invert controlled-source electromagnetic (CSEM) data which are recorded in areas with the kind of complex geological environments and arbitrary topography that are typical, 3-D CSEM forward modelling software that can quickly solve large-scale problems, provide accurate electromagnetic responses for complex geo-electrical models and can be easily incorporated into inversion algorithms are required. We have developed a parallel goal-oriented adaptive mesh refinement finite-element approach for frequency-domain 3-D CSEM forward modelling with hierarchical tetrahedral grids that can offer accurate electromagnetic responses for large-scale complex models and that can efficiently serve for inversion. The approach uses the goal-oriented adaptive vector finite element method to solve the total electric field vector equation. The geo-electrical model is discretized by unstructured tetrahedral grids which can deal with complex underground geological models with arbitrary surface topography. Different from previous adaptive finite element software working on unstructured tetrahedral grids, we have utilized a novel mesh refinement technique named the longest edge bisection method to generate hierarchically refined grids. As the refined grids are nested into the coarse grids, the refinement technique can precisely map the electrical parameters of inversion grids onto the forward modelling grids so that the extra numerical errors generated by the inconsistency of electrical parameters between inversion grids and forward modelling grids are eliminated. In addition, we use the parallel domain-decomposition technique to further accelerate the computations, and the flexible generalized minimum residual solver (FGMRES) with an auxiliary Maxwell solver pre-conditioner to solve the final large-scale system of linear equations. In the end, we validate the performance of the proposed scheme using two synthetic models and one realistic model. We demonstrate that accurate electromagnetic fields can be obtained by comparison with the analytic solutions and that the code is highly scalable for large-scale problems with millions or even hundreds of millions of unknowns. For the synthetic 3-D model and the realistic model with complex geometry, our solutions match well with the results calculated by an existing 3-D CSEM forward modelling code. Both synthetic and realistic examples demonstrate that our newly developed code is an effective, efficient forward modelling engine for interpreting CSEM field data acquired in areas of complex geology and topography.

Destruction Characteristics and Control Countermeasure of Shaft Surrounding Rock Mass in Complex Geological Environment

Increasing construction depth, changeable failure formations, and redistributed stress conditions inevitably make the mechanical response of mining shaft rock mass complicated. The design method and construction technology of deep shaft need to be perfected urgently. We studied the stability and control method of a main shaft from −930 m located in a deep gold mine. It is concluded that the surrounding rock of the shaft faces conditions including non-high-stressed, high-stressed, and possible instabilities. The failure types include structural plane-controlled failure, deep stress induced failure, rock burst, low confining pressure shear failure, spalling, and frequent conversion of multiple failure. The damages of the surrounding rock mass at −930~−1500 m displayed “ear-shaped” damage, with damage ranges of less than 2.5 m. The shaft temporary reinforcement adopted bolt mResh beam support, in which the length of the bolt was 2.5~3 m, and the row spacing was 1.5 m. The steel type and diameter were determined by the on-site bolt pull test. This temporary support countermeasure plays an important role in preventing shaft deformation and is worth promoting in similar mines.