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Global research on the geological particularities of coal‐accumulating environments and the enrichment patterns of coalbed methane (CBM) is still relatively weak. This paper studies the geological characteristics and coal accumulation patterns of Carboniferous‐Permian coal‐bearing seams in the southern Qinshui Basin. The results show that the coal‐bearing strata in the basin represent the offshore marine and continental intercalated coal seam sediments developed. The southern part of the basin is dominated by lacustrine facies, and the delta front sub‐facies is locally developed. The characteristics of coal accumulation environment in the southern Qinshui Basin are characterized by basement properties, fault networks and coal‐bearing sedimentary facies, which collectively control the spatial and temporal distribution characteristics of the coal‐rich belt. The differences in coal accumulation environment in the southern basin affect the tectonic evolution, the thickness of the coal seam roof and floor and the hydrogeological conditions of the coal‐rich area, which further control the CBM enrichment in the Taiyuan‐Shanxi Formation. The aim of this study is to explore the factors of CBM enrichment and gas control mode, so as to enrich and improve the theory and method of CBM exploration, which will also help identify the appropriate underground geological structure environment for carbon sequestration (CCS), reduce greenhouse gas emissions and effectively respond to the challenge of global warming. [ABSTRACT FROM AUTHOR]

Physical and cadastral data management practices for underground facilities are insufficient to represent underground assets' Rights, Restrictions, and Responsibilities (RRRs) and their relationships with the cadastre. For this reason, developing a 3D integrated data (underground and above‐ground) model may be an approach to an effective land management system. This research aims to develop a creative data model by integrating Turkish National Geographic Information System (TUCBS‐AY in Turkish) with international standards (Land Administration Domain Model (LADM) and CityGML) as a holistic approach. The requirements determined for underground facilities using TUCBS‐AY were used. Since the data produced in Turkey were modeled according to the CityGML 2.0 version, the CityGML 2.0 UtilityNetwork version was used in the study to be compatible with the existing Turkish cadastral system. While some classes in the model are generalized, they are expanded using LADM's classes for legal rights and part information. In addition, the CityGML classes have been expanded within the model so that parcels, buildings, and independent sections are represented separately, thus providing the opportunity to represent the underground utilities associated with them, their RRRs, and ownership situations. Requirements for the proposed model were determined based on Turkey's cadastral system and underground data. The main purpose is to manage the legal and physical relations of underground and surface objects at the city scale, compatible with the current Turkish cadastral system, with a holistic approach. The proposed integrated conceptual data model shows how legal rights and ownership of underground structures can be logically represented with a 3D data model. [ABSTRACT FROM AUTHOR]

FOUR FRANKFURT – New high‐rise buildings in Frankfurt am Main On the former Deutsche Bank site in Frankfurt's city centre, an impressive new ensemble of four high‐rise buildings and a shared six‐storey base building with underground car park is being built.The shell of the building is now largely complete and the topping‐out ceremony was held in September 2023. The high‐rise buildings are 233 metres (T1), 178 metres (T2), 125 metres (T3) and 105 metres (T4) high. Office use is planned for the T1 and T4 towers, and residential use and a hotel are planned for T2 and T3. The office space on the top floors of T1 will be the highest in Germany. The inner‐city location poses particular challenges for the project. For example, the excavation pit was constructed using the down method. The different requirements for the use of the towers led to different construction methods for the typical storeys: while the shell of the residential towers was made of in‐situ concrete, prefabricated elements proved to be the optimized construction method for the office towers. The report is divided into three parts. The first part presents the project and provides overviews of the components. The second part deals with the bracing system of the towers, including measures to increase stiffness. Finally, the third part describes special construction methods. [ABSTRACT FROM AUTHOR]

The increasing number of private cars, public transportation vehicles, and pedestrians, as well as the absence of adequate space for these ground amenities, are one of the primary causes of traffic congestion and accidents in the Kathmandu Valley. Investigations have indicated that the Kathmandu Valley has the greatest traffic accidents despite the heavy presence of the government and its agencies there. Most teens and young adults suffer injuries while using motor vehicles. The study's primary objective is to foresee and prevent such complications by planning for sufficient subsurface infrastructure (a cut‐and‐cover rectangular tunnel) for the Kathmandu Valley's transportation network. The overlying pressure, lateral earth pressure, live load, uplift pressure, and live surcharge are some of the forces acting on the tunnel, creating unique stress and moment zones. The tunnel meets the following geometric requirements: (a) Each of the tunnel's two cells has a clear span of 10 m and a clear height of 5.5 m. The side walls, inner walls, top slab, and bottom slab are all 700 mm thick. Soil has built up to a height of 4 m over the tunnel's roof. The analytical method is used in the tunnel segment's analysis. Furthermore, the designed tunnel has been evaluated for stability, considering the deflection and shear resistance. The analysis indicates that the tunnel meets the stability requirements. This implies that the structure is capable of withstanding the applied forces without excessive deflection. Non‐linear dynamic time history analyses of the El Centro earthquake and the Gorkha earthquake were computed. From the El Centro earthquake, the maximum displacement was 23.63 mm at 10.59 s, and from the Gorkha earthquake, the maximum displacement was 16 mm at 0.19 s for the modeled structures. [ABSTRACT FROM AUTHOR]

In the absence of experimental investigations on column members of underground structures, full‐scale column specimens were tested to explore the seismic behavior of shallow‐buried subway stations at various depths. The axial compression ratios of internal column specimens were set as 0.16, 0.33, and 0.40. Both hybrid simulations and quasi‐static tests were performed on the station columns. The hybrid simulations illustrated the drift demands of internal columns, while the load‐carrying capacity and deformation capacity were obtained from the quasi‐static tests. Hybrid simulations at low, moderate, and high‐intensity levels were conducted to study the seismic responses of shallow‐buried rectangular stations. The hybrid simulations suggest that the most severe damage occurred in the station when the axial compression ratio of the tested column reached 0.40. Central columns suffered severe stiffness deterioration under high‐level earthquake excitation, especially in stations at greater depths. Meanwhile, the quasi‐static test results indicate that the ultimate load of the central columns increases with increasing axial compression, but this leads to a significant decrease in the ductility of columns. Besides, the sectional analysis results show that the central columns are prone to tension‐controlled failure, and the safety margin for flexural response deteriorates with an increasing axial compression ratio. The test results indicate that shallow‐buried rectangular stations are susceptible to flexure‐controlled structural failure when their central columns possess a relatively low axial compression ratio and a high shear span‐to‐depth ratio. The failure mechanism of station columns is revealed by both the hybrid simulations and quasi‐static tests, and the findings from the full‐scale tests are beneficial for the practical design of shallow‐buried rectangular stations. [ABSTRACT FROM AUTHOR]

In response to the need for high‐resolution imaging of shallow crustal structure, we present a linear array double‐difference (DD) adjoint tomography method, using DD Rayleigh wave traveltime measurements for enhanced spatial resolution. This method, validated through synthetic experiments, improves velocity anomaly detection with fewer iterations compared to absolute traveltime measurements. Applied to data from four linear seismic arrays in the central Tanlu fault zone (TLFZ) in the eastern China, our approach integrated both DD and absolute difference (AD) of adjoint traveltime measurements. We performed cluster analysis for data quality control, reducing data outliers and increasing reliability, particularly in suppressing cycle skipping for short‐period measurements. The resulting high‐resolution S‐wave velocity profiles in the shallow crust well delineate geological structures, revealing a continuous low‐velocity anomaly beneath the eastern branch of TLFZ. Our comparative analysis with the southern segment of TLFZ further highlights the segmented nature of the fault zone structure. These variations might suggest a dominant influence of deep magmatic processes due to destruction of the North China Craton. Our study links shallow structural features to deeper geodynamic activities, emphasizing the role of TLFZ as a critical tectonic boundary. Plain Language Summary: The Tanlu Fault Zone (TLFZ) in Eastern China, a region crucial for its dense population and economic significance, has historically experienced severe earthquakes. Particularly, the Weifang segment of the central TLFZ, despite its current low seismic activity, raises questions about potential seismic risks. And the weak structures beneath the fault zone can promote earthquake rupture and its associated hazards. To get a clearer picture of the underground structures, we developed an imaging method focusing on the seismic traveltime differences between pairs of stations of linear seismic arrays. We also developed a data screening method for the linear array to reduce the effect of unusual or extreme data points on our analysis. We used this new technique and surface wave data recovered from ambient noise to produce clear images of in the upper crust of the central TLFZ. We found a weak structure beneath the eastern branch of the TLFZ, indicating a higher risk of earthquakes in this region. We compared our results with those from the southern TLFZ and noticed links between the shallow underground features and the deeper dynamic process associated with the destruction of the North China Craton. Key Points: A linear array double‐difference adjoint tomography using ambient noise data is proposed and applied to the central Tanlu fault zone (TLFZ)The refined upper crust Vs models reveal a continuous low‐velocity anomaly beneath the eastern branch of TLFZSeismic velocity variations along the TLFZ indicate the influence of deep magmatic processes resulting from the destruction of the North China Craton [ABSTRACT FROM AUTHOR]

A robust assessment of tunnels due to uncertainties present in soil and ground motion properties can affect the dynamic response of these structures. In this paper, a stochastic analysis considering an aleatory variability in shear velocity Vs by performing Monte Carlo simulations and assessing its influence on underground tunnels. To numerically assess the response of the soil‐tunnel system to near‐fault earthquake ground motion, the required computational domain usually spans multiple kilometers including both earthquake fault and the structure. Thus, these simulations are computationally expensive. An efficient alternative method, that is, the Domain Reduction Method (DRM), in which a modular two‐step methodology for reducing the computational costs in the large domain analysis is employed. A 3‐D soil‐tunnel structure interaction is modeled to simulate the response of tunnel subjected to an inclined earthquake fault. The numerical simulation of the soil‐tunnel‐fault system is conducted in an open‐source FE package called Multi‐hazard Analysis for STOchastic time DOmaiN phenomena (MASTODON) based on MOOSE framework. The interactive analyses are carried out for three distinct types of soils based on National Earthquake Hazards Reduction Program (NEHRP) provision, that is, soft, medium, and hard, by generating 130 realizations. The results provide many insights into the influence of local site effects, that is, frequency shift for the peak response and the importance of input ground motion characteristics that govern the response of underground structures. The dynamic response of the structure is very sensitive to the uncertainty in rock material properties, especially, the stiffness of the rock sample and the shear wave velocity. [ABSTRACT FROM AUTHOR]

As urban population increases, integrated underground–aboveground complexes are being constructed at growing paces in major cities. The seismic analysis of such complexes is crucial for the safety and functionality in the threat of potential earthquake disasters. However, fine‐grained numerical modeling and analysis of such large and complex structures are still inefficient due to the consideration of the soil–structure interaction (SSI). To address this challenge, an efficient approach for numerical modeling of large‐scale seismic SSI analysis is presented in this paper to overcome the limitations of existing finite element analysis (FEA) software. Moreover, a multi‐graphic processing unit (GPU) parallel explicit algorithm is implemented for the nonlinear dynamic SSI problems to further increase the computational efficiency. A large underground–aboveground complex project in China is used as an example to demonstrate the capability of the integrated method. The accuracy and reliability of the multi‐GPU parallel explicit finite element algorithm for SSI analysis (GFEA‐SSIA) are verified through a comparative analysis of the linear‐elastic and nonlinear dynamic response of the building calculated by GFEA‐SSIA and common FEA software. Finally, the structural response and structural damage of the underground–aboveground complex are analyzed under multidirectional seismic motions, and the damage distributions of the structures are provided. [ABSTRACT FROM AUTHOR]

Dispersion curve inversion is one of the core contents of Rayleigh wave data processing. However, the dispersion curve inversion has the characteristics of multi‐parameter, multi‐extremum as well as nonlinearity. In the face of Rayleigh wave data processing under complex seismic‐geological conditions, it is difficult to reconstruct an underground structure quickly and accurately apply a single global‐searching non‐linear inversion algorithm. For this reason, we proposed a strategy to invert multi‐order mode Rayleigh wave dispersion curves by combining with grey wolf optimization (GWO) and cuckoo search (CS) algorithms. On the basis of introducing the mechanism of iterative chaotic map with infinite collapses (ICMIC) and the strategy of dimension learning–based hunting (DLH), an improved GWO was developed that was called IDGWO (ICMIC and DLH GWO). After searching the near‐optimal region through IDGWO, the CS with a variable step‐size Lévy flight search mechanism was switched adaptively to complete the final inversion. The correctness of our method was verified by the multi‐order mode dispersion curve inversion of a six‐layer high‐velocity interlayer model. Then it was further applied to the processing of real seismic datasets. The research results show that our method fully utilizes the advantages of each of the two global‐searching non‐linear algorithms after integrating IDGWO and CS, while effectively balancing the ability between global search and local exploitation, further improving the convergence speed and inversion accuracy and having good anti‐noise performance. [ABSTRACT FROM AUTHOR]

This paper presents the design and commissioning of a novel pseudo‐static test apparatus for underground structures that accounts for soil‐structure interaction by simulating the soil with suitably designed springs. The developed apparatus was employed to conduct 1:10 large scale tests on a two‐story three‐span prefabricated subway station structure. Two comparative cyclic load tests were conducted: one involved the developed springs‐structure system; and one involved the structure alone (no springs). The test results demonstrated important differences in the damage location, damage degree, bearing capacity, and deformation capacity of the prefabricated subway station structure under the two loading conditions (i.e., with and without springs). The presence of springs (i.e., soil‐structure interaction) enhanced the lateral collapse resistance of the underground structure and affected the inter‐story displacement ratio (IDR) between the upper and lower layers of the two‐story prefabricated subway station structure. However, it did not affect the deformation coordination of the walls and columns of each layer. A finite element model of the prototype station was also established to conduct dynamic time history analysis simulating the soil‐structure interaction. The results from the dynamic analysis validated the effectiveness of the pseudo‐static test method employing the spring‐structure system. The excellent agreement between the calculated dynamic responses and the responses obtained from the pseudo static tests confirmed the ability of the developed apparatus to conduct seismic tests on complex large‐scale underground structures such as prefabricated subway stations. Thus, this test methodology might be utilized to attain valuable insights into the seismic performance of prefabricated subway stations at a relatively low cost and effort. [ABSTRACT FROM AUTHOR]

Compressive stress generated at collision fronts can propagate over long distances, inducing deformation within the continent's interior. Nevertheless, the factors governing the partitioning of intracontinental deformation remain enigmatic. The Altai Mountains serve as a type‐example of ongoing intracontinental deformation. Here, we investigate the crustal architecture of the Chinese Altai Mountains, using receiver functions obtained from newly deployed dense seismic nodal arrays. The new seismic results reveal distinct crustal features, including (a) a negative polarity discontinuity beneath Chinese Altai Mountains, suggesting a low‐velocity layer; (b) a north‐dipping mid‐crustal structure beneath the suture zone between East Junggar and Chinese Altai, indicating underthrusting of East Junggar's lower crust beneath the Chinese Altai Mountains; (c) a double Moho structure beneath East Junggar, revealing a high‐velocity lower crustal layer. In conjunction with constraints from previous multi‐disciplinary regional studies, the double Moho structures are interpreted as mafic restite from Late Paleozoic magma underplating. The addition of mafic materials can significantly enhance the rheological strength of East Junggar's crust, causing it to function as an indenter that thrust beneath the Chinese Altai Mountains during the subsequent convergence process. As a consequence, significant deformation occurs in the Chinese Altai region, resulting in the emergence of decollements, as evident by the negative polarity discontinuity. The presence of pre‐existing decollements makes the Altai Mountains region more susceptible to deformation, thereby facilitating the concentration of intracontinental deformation. These findings illuminate the evolution history of the Chinese Altai Mountains and highlight the great impacts of ancient tectonics on intracontinental deformation partitioning. Plain Language Summary: The factors that control how deformation is distributed within mountains located within continents are still not fully understood. In this study, we focused on the Altai Mountains to bring clarity to this topic. We used a new kind of seismic data to create images of the underground structures in the East Junggar‐Altai area. By combining information from previous studies in the region, we built a picture of how this area has changed since the Late Paleozoic era. During the Late Paleozoic period, the East Junggar region's crust became stronger due to a process involving molten rock moving upward and hardening beneath it. As a result, it was pushed below the Altai Mountains in a convergence event. This convergence caused extensive changes in the Altai Mountains' crust, creating a weakened section near the surface. The crustal properties and structures formed from ancient tectonic activities during the Paleozoic era have been preserved over time. This has made the Altai Mountains particularly prone to experiencing more recent deformations within the continent. Our findings emphasize how important ancient tectonic events are in determining how deformation is spread within continents. Key Points: High‐resolution images of crustal structures of the East Junggar‐Altai area were obtained from newly deployed dense seismic arraysNew constraints have emerged in the evolutionary history of the Chinese Altai‐East Junggar regions since the Late PaleozoicInherited crustal structures and properties arose from the Paleozoic tectonics govern the partitioning of the intracontinental deformation [ABSTRACT FROM AUTHOR]

Fault reactivations induced by deep excavation can pose significant challenges to underground construction or resource extraction. Laboratory experiments on rock faults demonstrate that unloading‐induced fault reactivations obey the Coulomb failure criterion derived from loading‐induced events. However, the effect of stress path during unloading on the failure criterion and rupture dynamics of fault reactivations remains poorly understood. Here, we present findings from a series of laboratory experiments aimed at elucidating the effect of the unloading path on the failure criterion and rupture dynamics of fault reactivations. We conducted experiments under various stress conditions, examining two cases of unloading paths. In Case I, we unloaded the minimum principal stress, while in Case II, the maximum principal stress was unloaded. Strain gauges and high‐speed photography were employed to capture the transient dynamic rupture process. Our investigations have yielded new insights into the effect of unloading path on the rupture dynamics when the fault is reactivated. In Case I, we observed fault reactivations resembling those loading‐induced events characterized by forward sliding. Conversely, in Case II, fault reactivations associated with stress reversal produce mild reversed sliding with lower stress drop and rupture velocity. Furthermore, we find that there is a remarkable reduction in static friction for reversed sliding, indicating that the failure criterion for fault reactivation is influenced by the stress path. We demonstrate that enhanced stress heterogeneity, caused by stress reversal, serves as a mechanism for reduced static friction. These findings contribute to our understanding of the mechanisms underlying fault reactivations, particularly those involving reversed sliding. Plain Language Summary: It is known that underground excavation, accompanied by stress release, can trigger fault reactivation, resulting in induced earthquakes. Understanding how unloading affects the activation and rupture dynamics of these induced events is crucial. To investigate the role of unloading path, we conducted laboratory experiments to simulate unloading‐induced fault reactivation on analog material containing a fault. Loadings are applied biaxially at the boundary. We observed that unloading the minimum principal stress (i.e., reducing the minimum loading) could reactivate the fault, generating forward sliding resembling loading‐induced rupture events. Conversely, unloading the maximum principal stress (i.e., reducing the maximum loading) induces reversed sliding, featuring smaller stress drop, coseismic slip, and rupture speed compared to forward sliding. Moreover, the static friction coefficient is reduced prior to reversed sliding. We also found that enhanced stress heterogeneity prior to unloading‐induced reversed sliding can account for the difference in static friction coefficient. Therefore, it is necessary to incorporate the effect of loading path into the studies of fault reactivation. Key Points: Rupture process of unloading‐induced fault reactivation is dictated by the initial stress state and stress pathThe static friction of fault is reduced for the unloading‐induced reversed slidingEnhanced stress heterogeneity caused by stress reversal contributes to reduced static friction [ABSTRACT FROM AUTHOR]

The article discusses the Chipperfield extension of the Kunsthaus Zurich, which has made it the largest art museum in Switzerland. The extension was constructed predominantly with in-situ concrete and features a natural stone facade. The building includes an underground connection that connects the new and existing Kunsthaus buildings. The extension is considered groundbreaking in terms of sustainability, as it has reduced primary energy and greenhouse gas emissions. The facade consists of masonry blocks made of natural stone and prefabricated reinforced concrete elements. The building also incorporates state-of-the-art technical installations, such as geothermal energy and photovoltaics. The use of recycled concrete with CO2-reduced cement was prioritized in the construction process. Overall, the extension is a significant addition to the Kunsthaus Zurich and showcases innovative design and construction techniques. [Extracted from the article]

Subsurface dam is a promising engineering technology for groundwater resources development. However, the possible impacts of these dams on the groundwater environment have been a major concern. Here, we used a three‐dimensional (3D), variable‐density, unsaturated‐saturated groundwater flow model to explore how a groundwater‐storage‐type subsurface dam, built in the freshwater domain of an unconfined coastal aquifer, affected groundwater levels and salinity in the downstream area. Model results suggested that, after subsurface dam construction, groundwater levels in the downstream area showed intensified fluctuations in terms of phase advances, greater amplitudes, and higher frequencies following heavy rainfall events. Numerical simulations with variable subsurface dam scenarios indicated that the groundwater level fluctuations were further intensified with a higher crest elevation or a shorter distance from the coast. Moreover, during the recharging period of the subsurface reservoir, sea water in the downstream area intruded landward from its initial location, which can at least temporarily threaten water quality near the coast. A higher dam crest elevation prolonged the duration of sea water intrusion, while a dam positioned closer to the coast induced sea water intrusion with a greater horizontal extent. General implications are discussed with respect to improving assessment methodologies and engineering designs of subsurface dams. [ABSTRACT FROM AUTHOR]

The structural fire safety of tunnels is a highly debated theme at international level. Car accidents in road tunnels, failures on the power lines in railway tunnels [1,2] and electrical related issues of technological installations in underground research infrastructures can lead to trigger a fire. Fire due to cars, trains and combustion of cable insulations can be considerably dangerous. Fire in such infrastructures causes the stress increases and the losses of bearing capacity in the exposed concrete linings. Thus, in presence of a relevant fire risk, both new and existing underground structures need to be assessed. This paper shows the analyses carried out on the cavern UX15 of the ATLAS experiment, located at the Point 1 of the Large Hadron Collider (LHC) of CERN – Meyrin, Switzerland. The structural fire assessment of tunnels requires to model the lining restrain conditions, the related structural resistance and the spalling phenomena. This modelling is done by Finite Element Method (FEM) code taking into account the spalling in advanced thermo‐mechanical analyses. The shell elements have been used due to their relatively conservative temperature distribution predictions, the acceptable accuracy of the displacement estimates, and a reasonable computational burden. [ABSTRACT FROM AUTHOR]

The genus Corydalis, with ca. 530 species, has long been considered taxonomically challenging because of its great variability. Previous molecular analyses, based on a few molecular markers and incomplete taxonomic sampling, were clearly inadequate to delimit sections and subgenera. We have performed phylogenetic analyses of Corydalis and related taxa, using 65 shared protein‐coding plastid genes from 313 accessions (including 280 samples of ca. 226 species of Corydalis) and 152 universal low‐copy nuclear genes from 296 accessions (including 271 samples of Corydalis) covering all 42 previously recognized sections and five independent "series". Phylogenetic trees were inferred using Bayesian Inference and Maximum Likelihood. Eight selected morphological characters were estimated using ancestral state reconstructions. Results include: (i) of the three subgenera of Corydalis, two are fully supported by both the plastid and nuclear data; the third, subg. Cremnocapnos, is weakly supported by plastid DNA only, whereas in the nuclear data the two included sections form successive outgroups to the rest of the genus; (ii) among all 42 sections and five "series", 25 sections and one "series" are resolved as monophyletic in both data sets; (iii) the common ancestor of Corydalis is likely to be a perennial plant with a taproot, yellow flowers with a short saccate spur, linear fruits with recurved fruiting pedicels, and seeds with elaiosomes; (iv) we provide a new classification of Corydalis with four subgenera (of which subg. Bipapillatae is here newly described), 39 sections, 16 of which are consistent with the previous classification, 16 sections have been recircumscribed, one section has been reinstated and six new sections are established. Characters associated with lifespan, underground structures, floral spur, fruit and elaiosomes are important for the recognition of subgenera and sections. These new phylogenetic analyses combined with ancestral character reconstructions uncovered previously unrecognized relationships, and greatly improved our understanding of the evolution of the genus. [ABSTRACT FROM AUTHOR]

The construction lot H41 Sill Gorge–Pfons is one of the biggest construction lots of the Brenner base tunnel and carries out the work on the Austrian side between Austria and Italy. It is situated between the Sill Gorge in Innsbruck and the small mountain village of Pfons. Here, tunnel excavation and inner lining concrete works are carried out based on existing caverns and tunnels made by previous construction lots E41, Sill Gorge and H33 Tulfes–Pfons. The construction lot H41 Sill Gorge–Pfons started in January 2022 with preparation works, and will take 80 months of continuous construction work to complete. All together about 22.5 km of main tubes, 38 bypasses and the remaining parts of the underground Innsbruck emergency station/stop will be excavated by the drill and blast method and by mechanised means (TBM). Additionally, concrete inner lining works will be executed partly alongside the excavation works. In the connection tunnels which are already finished and link the existing Innsbruck bypass with the new Brenner base tunnel, barrier walls are being erected and a new long‐distance water flushing system is being implemented. The limited surface areas in this mountainous region present a huge challenge for logistics and storage as well as on‐site operations for the execution of this complex underground construction lot. [ABSTRACT FROM AUTHOR]

Saving resources and reducing CO2‐emissions by optimizing shoring systems for cut‐and‐cover underground transportation structures The expansion of public transport systems and primarily the expansion of metro networks plays a vital role in the transition of mobility. However, even public transport systems have to pay their share in saving ressources and reducing CO2‐emissions. In particular, cut‐and‐cover underground transportation structures still show considerable reduction potential. In addition to measures at the building material level through cements, reinforcing steel and structural steel with reduced CO2‐footprints or global warming potential (GWP), measures at the design level are also urgently needed: Through engineering‐driven optimization of design, construction methods and construction processes. The starting point for the analysis is a typical subway station as currently planned and built in metropolises like Hamburg, Berlin or Munich. The main contributions to the CO2‐footprint are identified and the potential for improvement is illustrated. Construction pits and temporary shoring systems make large contributions to the GWP. From a systematic analysis of shoring concepts, design ideas for resource‐saving and low‐emission cut‐and‐cover underground structures are derived. [ABSTRACT FROM AUTHOR]

The MRT Orange Line construction works in Bangkok are more complicated than works in earlier projects. As the tunnel alignment passes through the congested urban areas in the city, it either clashes with or passes beneath several existing structures. Underpinning works are then required. Assessment of movement of ground and structure plays an important role in the project. The rebound of piezometric pressure in sand layers that is being developed poses a major point of difficulty in the excavation and underground structure design and construction. Groundwater control measures become a crucial issue in MRT Orange Line project that leads to difficulties in deep MRT station excavations. To control base instability, various methods (e.g., cut‐off wall, staged excavation) are introduced and presented in this article. [ABSTRACT FROM AUTHOR]

The Klang Valley Mass Rapid Transit (KVMRT) project involves the construction of an urban passenger transport system, i.e., Mass Rapid Transit (MRT) system, together with the existing urban rail network, will form the backbone of the public transport system in the Greater Kuala Lumpur/Klang Valley region in Malaysia. The first MRT line implemented is the 47 km Kajang Line, of which 9.5 km is underground tunnels with seven underground stations. Construction of the line began on 8 July 2011 and achieved the full line opening on 17 July 2017. The second MRT line―Putrajaya Line―began fully operations on 16 March 2023, stretches from Sungai Buloh to Serdang and ends at Putrajaya for a length of 57.7 km, of which 13.5 km is underground tunnels with 10 new underground stations. Like all other metro underground stations/tunnels designed as part of the urban city, the KVMRT underground construction faces challenges from a technical (engineering design and construction) as well as social (environmental and land related) point of view. Needless to say, underground construction in Klang Valley is intensified with the inherent geotechnical challenges presented by complex ground conditions ranging from hard granite, heterogeneous Kenny Hill formation and extreme karstic limestone with fully developed weathered profiles to soft recent deposits including alluvium and mine tailing that is under‐consolidated in places due to past mining activities. The development of this large‐scale infrastructure project has not only opened up tremendous works and new frontier for tunnelling and geotechnical engineering in Malaysia, but it also provided a wealth of information of unique geotechnical challenges/accomplishments as well as technology breakthrough and design innovation in underground engineering. This article discusses some aspects of geotechnical challenges and interesting lessons learnt as well as numerous innovations embedded into this highly complex urban underground construction project. [ABSTRACT FROM AUTHOR]

Many years after construction, a number of existing old tunnels and underground structures are deteriorating with time as evidenced by cracks, large deformations, water leakage and so forth, which usually require regular site inspections to record their structural deterioration by taking high‐pixel, high‐overlap images along miles of a tunnel network. For complex underground structures (e.g., long tunnels and large caves), unmanned aerial vehicles (UAVs) may be adaptive in acquiring images at multiple heights and angles with low operational costs. So far, UAV underground structural health monitoring has become mature for open‐air surveying with rapid developments in robotic software and hardware. However, the UAV image acquisition for underground working conditions still faces a number of key challenges. This paper aims to provide an overview of UAV navigation techniques in confined dark spaces for geotechnical engineers, geologists, drone developers and other interdisciplinary researchers & professionals in the structural health monitoring field. It specifies the challenges for UAV application in underground space, mainly including lack of Global Navigation Satellite System (GNSS) signals, poor lighting conditions, weak features and obstacle avoidance and then followed by strategic solutions. For example, in light of poor GNSS signals, the fusion of multi‐sensors (e.g., laser imaging, detection and ranging (LiDAR) and multi‐cameras) can enhance localization accuracy in low‐luminance underground conditions. To address obstacle avoidance, computer vision (CV)‐based navigation algorithms (e.g., deep reinforced learning [DRL]) enable effective navigation in complex 3D spaces, but their adaptability is limited by arithmetic power and pre‐training needs. The review of relevant previous studies concludes that further development for UAVs in underground space inspection may focus on operation in large‐scale geometric inspection environments, obstacle avoidance, features and semantic recognition. [ABSTRACT FROM AUTHOR]

Underground gas storage (UGS) is an important part of the natural gas industry. Its peaking characteristics and storage capacity are critical to national energy supply and energy security. Compared with the mature gas market in Europe, the construction of UGSs in China faces many challenges. This study is expected to provide references for China UGS through a detailed analysis and calculations of the European natural gas market and underground storage. First, the current status and development of the European gas market were summarized. And the situation of primary energy structure, gas utilization, and UGSs construction was compared between the EU and China. Second, the working gas volume of UGSs in Europe was analyzed from the perspective of its relationship with total consumption and peak‐shaving volume. Finally, the simulation and prediction of the working curve of the energy storage facilities and the reasonable ratio of the energy storage to load were solved by the numerical fitting method. Meanwhile, the recommendations for China's natural gas market and UGSs were provided. It is appropriate to set the planning target of China UGS capacity to load at 5% of total consumption and the actual peaking gas volume will be 14.4 billion cubic meters by 2030. [ABSTRACT FROM AUTHOR]

Recent studies on the frequency‐Bessel transform (F‐J) method demonstrate the ability of the array‐based method to extract higher‐mode surface wave dispersion curves from ambient noise, which provides a new opportunity to reveal more accurate underground structures. However, problems with the subarray selection for three‐dimensional imaging remain. On the one hand, we need the subarray to be large enough such that the F‐J method can capture high‐quality dispersion curves, and on the other hand, we want the subarray to be small enough to maintain a sufficient horizontal resolution. To solve this problem, we propose a strategy that randomly and repeatedly partitions the subarray based on Voronoi diagrams. We call this the FJ‐VoroTomo method. The FJ‐VoroTomo method does not require tedious parameter tuning and can measure high‐quality dispersion while maintaining horizontal resolution. More importantly, this method can quantitatively analyze the uncertainty of the measured dispersion curves. In this work, we use the noise cross‐correlation functions from the LArge‐n Seismic Survey in Oklahoma array as an example to demonstrate the dispersion and its uncertainty obtained by the FJ‐VoroTomo method and evaluate the three‐dimensional S wave velocity structure beneath this dense array. We hope that by using this strategy, the multimodal surface wave method can be more feasible in dense arrays that are currently widely used. Plain Language Summary: Surface wave dispersion imaging is one of the most widely used tools for detecting underground structure. Usually, seismologists invert shear wave velocity structures from the fundamental surface wave dispersion curves. In addition to the fundamental dispersion curves, the recently developed frequency‐Bessel transform (F‐J) method extracts higher‐mode surface wave dispersion curves, which could provide additional constraints to the underground structures. However, limited by the dozens of stations required by this method, it is necessary to partition the study area into different subarrays for three‐dimensional structure imaging. If the subarray is too small, the quality of the dispersion extraction is often unsatisfactory. However, if the subarray is too large, it is difficult to obtain the underground inhomogeneous feature. To overcome the subarray selection challenge, we propose the FJ‐VoroTomo method of randomly repeated partition based on Voronoi diagrams. This method does not need tedious parameter tuning for array partitioning and can achieve the advantages of both smaller and larger subarray selections. And this method can effectively evaluate the uncertainty of the dispersion curve measurement. In this work, we applied this method to the LArge‐n Seismic Survey in Oklahoma array and compared the results to that of the traditional subarray partitions. Key Points: We propose the FJ‐VoroTomo method to achieve the 3‐D structure imaging with the array‐based multimodal dispersion inversionThis method does not require tedious parameter tuning and can take the advantages of smaller and larger subarray selectionsThis method can effectively evaluate the uncertainty of the observed dispersion curves which can be propagated into inversion [ABSTRACT FROM AUTHOR]

Clay rocks are multiphase porous media whose complex structure is characterised by heterogeneity and possible anisotropy on a wide range of scales. The mesoscopic scale plays a particular role in deformation mechanisms under mechanical loading by cracking. The behaviour of rocks at mesoscale is characterised by the material and morphological (shape and size) properties of its components and their interactions. The accurate reproduction and influence of these mesoscale characteristics on the material behaviour and damage at large scale remain a complex issue. This question becomes crucial when investigating the underground stability during excavation works such as tunnels. In this numerical multi‐scale study, the mesostructure characteristics are embedded in a Representative Elementary Area (REA) in a 2D configuration. A double‐scale numerical framework, with finite element resolution at both scales (FE2) and computational homogenisation, is considered. The influence of the mesostructural characteristics of a heterogeneous rock and the effect of different inter‐granular properties on their macroscopic behaviour, are examined. Additionally, a predictive strategy which is based on the connection between the failure modes of the REA and the failure mechanisms of the macroscale structure is also presented. This study investigates the effect of the mesocracking on the shear banding in a rock specimen during laboratory biaxial shear test and the development of the Excavation Damaged Zone (EDZ) around tunnels. The objective of this work is to explain the failure mechanisms observed up to the engineering scale of underground structures through the morphological and material small‐scale characteristics of the REA. [ABSTRACT FROM AUTHOR]

The underground building environment plays an increasingly important role in the construction of modern cities. To deal with possible fires, collapses, and so on, in underground building space, it is a general trend to use rescue robots to replace humans. This paper proposes a dual‐robot system solution for search and rescue in an underground building environment. To speed up rescue and search, the two robots focus on different tasks. However, the environmental perception information and location of them are shared. The primary robot is used to quickly explore the environment in a wide range, identify objects, cross difficult obstacles, and so on. The secondary robot is responsible for grabbing, carrying items, clearing obstacles, and so on. In response to the difficulty of rescue caused by unknown scenes, the Lidar, inertial measurement unit and multiview cameras are integrated for large‐scale 3D environment mapping. The depth camera detects the objects to be rescued and locate them on the map. A six‐degree‐of‐freedom manipulator with a two‐finger gripper is equipped to open doors and clear roadblocks during the rescue. To solve the problem of severe signal attenuation caused by reinforced concrete walls, corners and long‐distance transmission, a wireless multinode networking solution is adopted. In the case of a weak wireless signal, the primary robot uses autonomous exploration for environmental perception. Experimental results show the robots' system has high reliability in over‐the‐horizon maneuvering, teleoperation of the door opening and grasping, object searching, and environmental perception, and can be well applied to underground search and rescue. [ABSTRACT FROM AUTHOR]

India is well on its way to create a world‐class Mass Rapid Transport system environment as an integral part of community infrastructure development. Mumbai Metro Line 3 is one such project being constructed in Mumbai city. It comprises 33.5 km‐long underground metro corridor running along Colaba to Bandra to Santacruz Electronic Export Processing Zone. It includes 27 stations (26 underground and 1 at grade), depot and associated twin‐tube tunnel. Mumbai Metro Rail Corporation Ltd., an affiliate organisation of Mumbai Metropolitan Region Development Authority, is responsible for the implementation of the project. Excavation and tunnelling works posed significant challenges as they cross densely inhabited zones of Mumbai. There were several buildings which were old and in delicate condition, many of which were heritage structures. In Mumbai – being a coastal city – the water table is almost at ground level which added to complications. There were several utilities, many of which were lifeline utilities, which could not be diverted or even closed, thus requiring support during excavation. Likewise, ensuring traffic movement with minimal disruptions with enormous excavation works for the project required several innovative solutions. Other criticalities included low overburden to the existing flyovers and to the air traffic control tower as well as saving a 100 year‐old banyan tree. [ABSTRACT FROM AUTHOR]

The new Ontario Line is one of four priority transit projects announced by the province of Ontario in 2019 for the Greater Toronto Area (GTA). It will be a 15.6 km stand‐alone rapid transit line that will run through the city from Exhibition/Ontario Place in the southwest, through the heart of downtown Toronto, all the way to the Ontario Science Centre in the northeast. Over half of the route (9 km) is planned to run underground through new tunnels, with the remainder running along elevated and at‐grade rail corridor sections of track. Fifteen new stations are proposed, whereby eight are planned as deep underground structures. Most of these underground stations will be built in the downtown core, with numerous connections to the broader transit network of the GTA, including GO Transit rail services, the Toronto Transit Commission's (TTC) existing subway Lines 1 and 2, the Line 5 (Eglinton Crosstown LRT) currently under construction, as well as numerous bus and streetcar routes. The expected project benefits of Ontario Line are as follows: A faster and more reliable access to rapid transit system with more than 227,500 people living within walking distance to the new line.Reduction in crowding of existing Line 1 subway.Up to 47,000 jobs accessible by transit in 45 min or less for Toronto residents.Economic and community growth along the future transit line and significant reduction in traffic congestion and greenhouse gases by providing alternative transportation options. The Ontario Line is currently being delivered through a number of contracts with different procurement approaches. [ABSTRACT FROM AUTHOR]

In 2013, the Austrian Society for Geomechanics published the Guideline for the Geotechnical Design of Underground Structures with TBM Excavation. The Guideline contains general procedures for the geotechnical design and construction. In the design phase, the first steps are evaluating different ground conditions by classifying different ground types, different ground behaviours, their categorization into ground behaviour types, and the determination of construction measures derived from the ground behaviour. On this basis the expected system behaviour in each system sector of the tunnel boring machine (TBM) is predicted and described in detail to enable comparison in the construction phase. In the construction phase, geotechnical relevant ground parameters as well as observations regarding the actual system behaviour are recorded and compared with the assumptions of the design. The geotechnical design is updated continuously based on the encountered ground conditions and geotechnical observations. The improved quality of the geotechnical model allows an optimization of the construction while meeting all safety and environmental requirements. In the first part of the article, the general procedures of the guideline are described and parameters to describe the system behaviour in each system sector adequately are listed. In the second part of the article, the implementation of the guideline during design and construction at the Semmering Basetunnel in Austria is described. [ABSTRACT FROM AUTHOR]

The handling of a tunnel construction project poses great challenges for all those involved. Variables that cannot be clearly quantified can arise during the entire process of the project. The subsoil in tunnelling is one of these parameters which is difficult to forecast. The geological and hydrogeological conditions must be assessed during the planning phase with the help of exploratory measures and from the experience from projects that have already been built. During the execution work, deviations from the documents on which the target determination is based occur in almost all underground construction projects. These changes can either cause a change in the construction process and/or lead to a different construction time in relation to the calculated duration. Based on this initial situation, the development of an innovative contract and remuneration model for machine tunnelling appears to be important. The main focus of the model is to generate a transparent and comprehensible method of how the remuneration‐worthy portion can be calculated in the case of a different construction time in mechanised tunnelling. In order to ensure this transparency and traceability of the system to be developed, the data records that can be digitally recorded during the tunnelling work are used as a fundamental basis for the created model. [ABSTRACT FROM AUTHOR]

Prevention of earthquake disaster is critical in the densely populated Kanto Basin, Japan, because of the presence of thick sediments that amplify strong ground motion. For this, a high‐resolution three‐dimensional S‐wave velocity model is essential to understand the complex amplification of strong ground motion. We constructed a three‐dimensional S‐wave velocity model using the joint inversion of multimodal dispersion curves of Rayleigh and Love waves. Inclusion of higher modes significantly improved the accuracy and precision of the surface‐wave inversion by more than 50% compared to using only fundamental mode. Our proposed model revealed a low‐velocity anomaly of sediments toward the east and a curved velocity contour of the basement rock, thereby better explaining the observed complex surface‐wave dispersion curves that have been unexplained in past homogeneous multilayered models. Estimated S‐wave velocity model better reflected subsurface heterogeneity, providing vital information for hazard assessment in a metropolitan area where huge earthquakes are expected. Plain Language Summary: The Kanto Basin where the capital of Japan is located comprises large‐scale thick soft sediments which amplify seismic waves. Constructing an accurate underground structure model is important to reveal the propagation properties of seismic waves, and provide better hazard assessment. We constructed a highly accurate and precise underground structure model by using surface waves. Usually, only fundamental tone of surface waves is used to estimate underground structure model. In this study, we separated fundamental and over tones of surface waves, and jointed speed information of both tones to estimate underground structure model. Inclusion of overtones of surface waves significantly improved the accuracy and precision by more than 50%. Our proposed model better explains observed surface‐wave properties that previous models have not been able to explain. Our high‐precision underground structure model better reflected subsurface shapes, providing vital information for hazard assessment in a metropolitan area where huge earthquakes are expected. Key Points: A three‐dimensional S‐wave velocity model was estimated by joint inversion of multimodal Rayleigh and Love wavesInclusion of higher modes significantly improved the accuracy and precision of the inverted solutions by at least 50% in the simulation testEstimated model better explains observed surface‐wave properties that previous model has not been able to explain [ABSTRACT FROM AUTHOR]

Qanat is an ancient underground structure to abstract groundwater without the need for external energy. A recognized world heritage, Qanat has enabled civilization in arid and semi‐arid regions that lack perennial surface water resources. These important structures, however, have faced significant challenges in recent decades due to increasing anthropogenic pressures. This study uses remote sensing to investigate land‐use changes and the loss of 15,983 Qanat shafts in the Mashhad plain, northeast of Iran, during the past six decades. This entails obtaining a rare aerial imagery from 1961, as well as recent satellite imagery, over a region with the highest density of Qanats in Iran, the birthplace of Qanat. Results showed that only 5.59% of the Qanat shafts in 1961 remained intact in 2021. The most prominent Qanat‐impacting land‐use changes were agriculture and urban areas, that accounted for 42.93 and 31.81% Qanat shaft destruction in the study area, respectively. This study also showed that groundwater table decline, demographic changes, and reduction in the appeal of working in the Qanat maintenance and construction industry among the new generation are existential threats to Qanats, and may result in the demise of these ancient structures in the future. Findings of this study can be used for urban planning in arid and semi‐arid areas with the aim of protecting these historic water structures. Article impact statement: Qanats are historical, sustainable groundwater abstraction infrastructure that face an existential threat from anthropogenic pressures. [ABSTRACT FROM AUTHOR]

The UK net‐zero target requires the integration of significant renewable energy resources into the electrical grid. This, together with the projected growth in electricity demand imposes practical challenges on the power transfer capability of existing transmission feeders. For environmental and planning reasons, construction of new overhead lines is problematic, and where possible upgrading of existing substations and lines is preferred. This paper investigates the feasibility of transforming an existing three‐phase (3Φ) double‐circuit 400 kV line into a six‐phase (6Φ) feeder for a simulated future GB scenario. Results indicate a 6Φ feeder, operating at a 'phase‐adjacent phase' voltage of 400 kV can effectively solve the constraints of boundaries in transmission networks. When considering the various operating contingencies, associated with an important UK network boundary and its expected near‐future winter‐peak power transfer requirements, the thermal overload issues are mitigated by transforming a feeder from 3Φ to 6Φ. The paper demonstrates upgrading to 6Φ technology is a potential solution to certain future boundary constraints and in these cases avoids the need to build new underground or overhead AC/DC lines. [ABSTRACT FROM AUTHOR]

In situ stress and groundwater have important effects on the deformation and stability of deep underground rock masses. Therefore, it is extremely important to study the mechanical properties and permeability evolutionary processes of rocks under hydromechanical (HM) coupling. The purpose of this study was to investigate the mechanical properties and permeability evolution of sandstone using triaxial compression tests under different confining and seepage pressures. The test results show that the confining pressure can increase the strength of sandstone, whereas the seepage pressure has the opposite effect. The initial and maximum permeabilities were positively correlated with seepage pressure and negatively correlated with confining pressure. The confining and seepage pressures had little effect on the change in initial permeability. As a common parameter of acoustic emission (AE), cumulative AE counts can intuitively reflect the permeability evolutionary process in the sandstone failure process. A permeability evolutionary early warning model for the sandstone failure process under HM coupling is proposed. The results are helpful for understanding the influence of in situ stress and seepage pressure on deep sandstone and the permeability evolutionary mechanism, and they can be used to provide early warning of water inrush disasters in deep underground structures. [ABSTRACT FROM AUTHOR]

CERN (Conseil Européen pour la Recherche Nucléaire) is the world's largest research centre for high‐energy and particle physics. The research infrastructure contributed to the greatest successes in the field of experimental physics. A new, approximatively 91 km long subsurface infrastructure connected to the existing particle accelerator complex is being conceived in the frame of the Future Circular Collider. It would serve a global community of researchers with two subsequently operated particle colliders until the end of the 21st century. Even at an early stage of such a project, comprehensive investigations have to be carried out into the nature of the subsoil in order to find an optimal utilisation strategy for the excavated material in accordance with the national and international regulations in order to promote the recycling of excavated tunnel material in terms of resource conservation and the improvement of the sustainability of underground construction projects. [ABSTRACT FROM AUTHOR]

Sustainability is a guiding principle for political, economic and ecological action, which in companies, societies and countries all over the world, is based on the following three pillars: ecology, economy and social aspects. With the associated worldwide efforts to reduce emissions, this topic has also arrived in the construction industry in general and thus in tunnel construction in particular. In addition to the actual planning, construction, use and maintenance of mined structures, tunnel builders certainly have a special role to play, since the creation of underground structures relieves overground structures and can also change living space for the better. However, the influences and impact must always be considered in the overall context of all three pillars of sustainability – and in our fast‐paced times, this requires a considerable change in mindset as well as a clear change and expansion of the assessment standards. The following article draws a current picture of "sustainable tunnelling" on the basis of four sub‐sections that describe selected tasks and approaches from the perspective of operators, planners, the construction industry and science as a basis for discussion. [ABSTRACT FROM AUTHOR]

West Link (Swedish: Västlänken) is one of the biggest infrastructure projects in Sweden building an in total 8 km double‐track railway tunnel in Gothenburg, which is currently under construction. "E05 Korsvägen" is a construction lot which is part of the West Link project with the Swedish transport authority Trafikverket as the client. The works were awarded to the Joint Venture (JV) West Link Contractors consisting of Wayss & Freytag Ingenieurbau AG and NCC. A special contract model with a design and build part combined with a regular bill of quantities comprises building an underground double‐track railway tunnel with a length of 3.2 km and the new Korsvägen station. This sub‐project includes three drill and blast sections and three open excavation sections. All three construction pits will be executed in challenging soft ground conditions. The JV is confronted with high environmental demands and special requirements for the blasting works in the urban area of Gothenburg. [ABSTRACT FROM AUTHOR]

Tunnel construction is not immune to the climate crisis – here too there is an urgent need to improve the carbon footprint. The production of concrete and consumption of cement cause climate‐damaging CO2 emissions. A tunnel with a 10 m diameter, for example, generates around 10 t of CO2 per linear metre. The main priority is thus to reduce the amount of concrete and steel reinforcement used and to select low‐carbon cements and binders, as well as employing single‐shell construction methods suited to the requirements of the construction project. We need to consider practical approaches to reducing concrete volumes which go beyond structural requirements. CO2 reduction in tunnelling starts with the design and approval process, so financial incentives must be built into award criteria and construction contracts. This article aims to highlight ideas which in future will play an increasingly important role in the design of underground construction works than is currently the case. Although many well‐established work practices and design details in underground construction are based on decades of experience and are bound by normative and contractual framework conditions, it is now time to re‐examine the facts and consider new ideas that reflect the need to reduce CO2 in concrete construction. [ABSTRACT FROM AUTHOR]

Tunnelling and underground construction is a material‐intensive undertaking that involves the use of large quantities of concrete. Analyses of the life‐cycle assessment of a new tunnel show that the carbon footprint is largely determined by cement and concrete consumption. Optimising the quantity used, composition and properties of this construction material is thus crucial to reducing ''grey'' emissions – CO2 emissions arising from the construction phase. While strength and durability requirements along with exposure classes are clearly set out in directives and tender specifications, CO2 emissions per cubic metre of concrete are not currently considered a relevant criterion when it comes to project design, award and implementation. And this, despite the fact that the current state of knowledge and research shows that substantially lower‐carbon concretes could be used than is generally the case today. A paradigm shift is required to achieve the goal of carbon neutrality in the construction industry. This paper shows how CO2 emissions per cubic metre of concrete can be declared and reduced in tunnel construction, and how concrete recipes can be formulated using climate‐friendly materials, while maintaining the required strengths and durability properties. Using the design approaches outlined here, it is possible to increase clinker efficiency and reduce CO2 intensity without adversely affecting the structure and its functionality. [ABSTRACT FROM AUTHOR]

The Rudolf‐Fettweis hydropower plant, owned and operated by EnBW Energie Baden‐Württemberg AG, is situated in the Murg valley in the Northern Black Forest. The construction of a new underground Lower Basin is planned to upgrade the existing hydropower station. The in‐situ rock mass consists of Forbach Granite with local weakness zones, as encountered in the boreholes. Considering the extent of the project area, a 3D geological prediction model was used to allow a better interpretation of the spatial relationships of weakness zones in the rock mass and to optimize the orientation of the underground caverns. Adverse effects for the public were counteracted at a very early stage, so that the project received a high level of public acceptance. The present paper describes the current state of the project. [ABSTRACT FROM AUTHOR]

Various methods have been developed in recent decades to predict hazards associated with karst voids in underground construction. Common to all these methods is that the predicted range of water inflow is often insufficient for the purpose of implementing the planned construction works. This is usually due to an incomplete knowledge of the karst conduit system within a project area, making it difficult to predict the position and characteristics of karst voids. The method presented in this paper permits a robust prediction of karst water inflow. It is based on a combination of stochastically generated, pseudo‐genetic karst conduit systems and hydraulic modelling of the hydrogeological conditions using a Monte Carlo approach. This approach facilitates a plausible estimation of the expected range of karst‐induced water inflows and also enables the probability of encountering a karst voids. to be determined. The predictions allow for differentiated treatment of the hazards associated with karst water during the construction and operation phase of underground structures. In concrete terms, this relates to the planning and implementation of exploratory measures and ground‐improvement measures, the design of the dewatering system and its monitoring during the construction and operation phase. [ABSTRACT FROM AUTHOR]

When it comes to underground structures, water ingress from the surrounding formations leads to several environmental, economic and sustainability issues. To obtain the sealing, the grouting of rock fractures is done. Today, in the grouting operations, which are commonly conducted in almost all the tunnel and subsurface infrastructure projects, the pressure applied is static. This type of applied pressure might be suitable for the large fracture apertures > 100 μm, but it has been acknowledged that it is difficult to obtain sufficient penetration through smaller apertures, where filtration of cement particles starts to occur. Research is already done to overcome this issue by applying dynamic grouting pressure instead of static. It was proved that this approach erodes the formed filter cakes and improves grout penetrability in fractures below 100 μm. This research focuses on low‐frequency rectangular pressure impulse as an alternative to other methods. The goal is to improve grout spread in micro‐fractures (especially in apertures < 70 μm). During the investigation, a prototype dynamic injection equipment was built and tested under laboratory conditions. The 4 m variable aperture long slot (VALS) was used in the experiments to simulate rock fractures. The test showed better grout penetrability using dynamic pressure approach. At the current time of writing this article, preparation works are done for field test of prototype equipment at SKB Hard Rock Laboratory (HRL) at Äspö, Sweden. [ABSTRACT FROM AUTHOR]

We propose a resolution‐enhancement method based on the non‐local similarity of the seismic profile. Because of the similarity in underground structures, the seismic data have similar event structures in different regions. We introduce the similarity as prior information to enhance the resolution of seismic data. The similarity, as a regularization term for enhancing the resolution, can improve the stability of the solution. The non‐local similarity constraint is usually implemented based on nuclear norm minimization. We use the L1–L2 norm instead of the L1 norm in the nuclear norm, which will obtain a more accurate approximation of low rank. Compared with the deconvolution algorithm based on the L2 norm, we use non‐local similarity as a constraint term. The proposed method can enhance the resolution with a low signal‐to‐noise ratio, suppress random noise and improve lateral continuity. The synthetic and field data prove the superiority of the proposed method for low signal‐to‐noise ratio data. [ABSTRACT FROM AUTHOR]

Empirical Green Functions (EGFs) obtained from ambient noise cross‐correlation are important for imaging and monitoring underground structures. The EGFs on the Island of Hawai'i in different years are similar at low frequencies (0.1–0.4 Hz), but very different at high frequencies (0.4–1.0 Hz): Only the EGFs after the 2018 Kı̄lauea eruption show clear P waves. Grid search reveals a strong noise source near the Kı̄lauea summit before the eruption, which contaminated the EGFs but became silent after the eruption. Modeling of the P waves identifies the direct arrival and post‐critical reflections from two velocity discontinuities at 4.7 and 7.2 km depth beneath the island, which we interpret as the base of volcanic edifices and deposits and the boundary between basaltic dikes and gabbros, respectively. The P waves in EGFs could provide valuable high‐resolution constraints for monitoring deep magmatic changes and imaging the volcano structures. Plain Language Summary: Modern seismometers can record not only the ground shaking produced by earthquakes, but also the ground vibrations produced by ocean waves and magma motions. Although these small vibrations appear to be noise, they carry information about the underground structures. Because ground vibrations are dominated by waves propagating along the Earth's surface, it has been difficult to observe body waves, which propagate in the interior of the Earth, from these small vibrations, especially in volcanic regions. In this study, we found that body waves can be extracted from ambient vibrations only after the 2018 Kı̄lauea eruption on the Island of Hawai'i, where tremors caused by the magma and/or hydrothermal activities masked the body wave signals before the eruption and the volcano became quieter afterward. The body wave signals include the direct arrival and those reflected off wave speed boundaries at different depth beneath the island. The new signals could be useful to monitor magmatic activities and study the structures of the Island of Hawai'i. Additionally, the study emphasizes the importance of conducting seismic observations after volcano eruptions. Key Points: Direct and post‐critically reflected P waves in ambient noise cross‐correlation on Hawai'i are visible only after the 2018 Kı̄lauea eruptionA strong noise source near the Kı̄lauea summit contaminated the ambient noise cross‐correlation before its 2018 eruptionThe post‐critically reflected P waves reveal two middle crust velocity discontinuities at about 4.7 and 7.2 km beneath Hawai'i [ABSTRACT FROM AUTHOR]

We consider a Bayesian multi‐model fault slip estimation (BMMFSE), which incorporates many candidates of the underground structure (Earth structure and plate boundary geometry) model characterized by a prior probability density function (PDF). The technique is used to study long‐term slow slip events (L‐SSEs) that occurred beneath the Bungo Channel, southwest Japan, in around 2010 and 2018. We here focus on the two advantages of BMMFSE: First, it allows for estimating slip distribution without introducing relatively strong prior information such as smoothing constraints, by combining a fully Bayesian inference and better consideration of model uncertainty to avoid overfitting. Second, the posterior PDF for the underground structure is also obtained during the fault slip estimation, which can be used as priors for the estimation of slip distribution for recurring events. The estimated slip distribution obtained using BMMFSE agreed better with the distribution of deep tectonic tremors at the down‐dip side of the main rupture area than those based on stronger prior constraints when the corresponding Coulomb failure stress changes are compared. This finding suggests a mechanical relationship between the L‐SSE and the synchronized tremors. The use of the posterior PDF of the underground structure estimated for the 2010 L‐SSE as prior PDF for the 2018 event resulted in more consistent estimation with the data, indicated by a smaller value of an information criterion. Plain Language Summary: This study attempts to accurately estimate the slow motion between two plates, which does not produce seismic waves and is known as slow slip events (SSEs), targeting those occurred in southwest Japan. This was accomplished by analyzing satellite data of ground movement during the SSEs using a novel approach called the Bayesian multi‐model fault slip estimation (BMMFSE) framework, which considers multiple candidates of assumptions for Earth structures. BMMFSE stabilizes the analysis and removes artifacts from the estimation results which are otherwise introduced because of the choice of a wrong Earth model. These advantages were validated by comparing the estimation results obtained based on previous approaches that do not consider multiple Earth models. The result of BMMFSE exhibited spatial distributions of motion between plates that are more consistent with other slow earthquakes which occurred synchronously in the nearby fault. In addition, BMMFSE improved the consistency of the estimates with the data by taking over the model uncertainty in the sequential analysis of repeated SSEs. Key Points: Fault slip distributions for slow slip events (SSE) at southwest Japan were estimated considering the uncertainty of underground structureThe mechanical relationship between the SSEs and synchronized tectonic tremors are better justified than in previous studiesInformation criterion indicates that estimates for recurring SSEs taking over model uncertainty result in better consistency with the data [ABSTRACT FROM AUTHOR]

We propose a new three‐dimensional anisotropic inversion scheme for magnetotelluric (MT) data. In this method, the earth is discretized into unstructured tetrahedral grids that can fit complex structures well, such as the earth topography and coastline. We use a 3 × 3 tensor to describe the anisotropic conductivity in the governing equation for MT inversions that can be simplified to three principal conductivities and three rotation angles. The edge‐based finite‐element (FE) method is adopted to do the forward and adjoint modeling to compute full impedance and sensitivity. To make the inversion flexible in the restoration of anisotropic and isotropic structures tendentiously, we add an additional regularization in the objective function, with its weight controlled by a distribution function. Before solving the inverse problem using L‐BFGS optimization, we add upper‐bound and lower‐bound constraints to the parameters to suppress the solution space. Four synthetic experiments are designed to test the resolvability and resolution for the six anisotropic parameters in the inversion. The results show that our inversion method can well recover the resistivity in the principal x and y directions and the strike angle γ. Finally, we apply our inversion algorithm to the USArray MT data with the aim to reveal anisotropic structure under Oregon State. Plain Language Summary: Magnetotelluric (MT) is a method of imaging underground structures using the natural electromagnetic field observed on the ground. The conventional interpretation of MT data is based on assumption that the earth is isotropic, i.e., the resistivity is same in all directions. However, in many regions of the earth, the resistivity exists difference in different directions, which is called anisotropy. The inversion methods based on isotropic assumption cannot accurately image the widely existing anisotropic structures underground. Therefore, we propose a three‐dimensional inversion method of MT data considering the anisotropy of earth. In this method, the earth model is spatially discretized by unstructured tetrahedral grid, and the vector finite‐element (FE) method is used to calculate the MT data and its sensitivity to underground media. In order to save computational memory, the limited memory BFGS method is adopted to realize the final inversion. Through the tests of several typical models, we prove the reliability of the proposed method, and analyze the resolvability of six anisotropic parameters. Finally, the newly proposed anisotropic inversion algorithm is used to process the MT data of USArray and the result reveals a possible anisotropic structure under Oregon State. Key Points: We propose a new three‐dimensional inversion method of magnetotelluric (MT) data for arbitrarily anisotropic earth using unstructured tetrahedral gridsResolvability and resolution of six anisotropic parameters are analyzed via numerical experiments on synthetic dataThe new scheme is successfully applied to USArray MT data set and the result reveals a possible anisotropic structure under Oregon State [ABSTRACT FROM AUTHOR]

Future missions to Mars will undoubtedly be directed toward sedimentary terrains in search for evidence of past life and geologic history. Astronauts will need to find shelter from harsh surface conditions. Natural underground voids provide a readily adaptable habitat for crews to shelter from radiation. Naturally formed caves would be desirable habitat sites, but thick deposits of limestone or other soluble rocks in which karst topography would form have not been identified by current observations. Alcoves, arched recess in steep escarpments, should be widely distributed across the planet and provide an adaptable shelter for astronauts operating on the surface of Mars. Alcoves provide a more stable thermal environment, a reduced radiation environment, shielding from macro‐ and micro‐meteorite impacts, and protection from atmospheric disturbances. Plain Language Summary: Future Mars explorers will face a hostile environment that includes high radiation, extreme temperatures, and high windstorms. Establishing safe living quarters for prolonged stays presents problems like those of early man on Earth. The choices are whether to bring a suitable structure; to build a structure; or to find and adapt underground facilities. Of these choices, finding natural shelters requires less transported materials and less expenditure of energy than surface shelters. Lava tunnels may be useful, but future explorers will require safe quarters in the areas of Mars where sedimentary rocks are common, which will be important exploration targets to determine the geologic history of Mars. Caves in sediments on Mars may be difficult to find, but alcoves may be present. Unlike caves, alcoves have large openings at the surface in rock escarpments. Early humans used alcoves as natural shelters. Even as construction techniques developed, structures were placed within alcoves for additional protection. The Mesa Verde alcoves and pueblos in Colorado are examples of the adaptation of terrestrial alcoves for protected sites. Similarly, future astronauts to Mars could adapt shelters within alcoves as bases for operation. The earliest shelter could be as simple as a sealed tent containing a suitable atmosphere and pressure erected in an alcove. Key Points: Sedimentary rocks on Mars will be a high‐priority target for astronauts as they will reveal much of the geologic historyAlcoves provide potential habitats for future explorers on MarsAlcoves provide protected environments and possible water sources for primitive lifeforms on Mars [ABSTRACT FROM AUTHOR]