Underground Space Research Articles

Numerical analysis of heat and mass transfer in separated ventilation of deeply buried long air intake tunnels

Using earth air tunnel heat exchangers (EATHE) to pre-treat air entering underground space is an effective measure for energy-saving. This paper addresses the scarcity of numerical model for heat and mass transfer in long, separated air intake tunnels by establishing a three-dimensional model that considering condensation, specifically analyzing the heat transfer process in tunnels with separated ventilation earth air tunnel heat exchanger (SV-EATHE). The accuracy of the model was verified by engineering measured data. The heat transfer performance of EATHE and SV-EATHE is compared and analyzed by using the model. The results indicate that the annual heat exchange of SV-EATHE is approximately 80 % of that of EATHE, with the latent heat exchange from March to September accounting for 77.2 % of EATHE's. SV-EATHE significantly reduces condensation in traffic tunnels. Increasing ventilation will correspondingly increase the heat exchange and reduce dehumidification, but the rate of change will gradually decrease. The change in partition wall thickness has an approximately linear relationship with the amount of heat exchange. For every 0.1 m increase in diaphragm wall thickness, the heat exchange in the intake duct in August is reduced by approximately 1500 kWh and the dehumidification is reduced by approximately 0.6 kg/h.

A method for predicting deformation field of deep foundation pit considering spatial effect

Urban underground spaces have experienced significant development and utilization due to the rapid progress of urban construction and continuous advancements in construction technology. The number of foundation-pit projects immediately adjacent to buildings, structures, and pipelines has been increasing. Ensuring the safety of construction and surrounding facilities, it is essential to predict deformation caused by foundation pit excavations. In this study, a simple calculation method was proposed for predicting deformation of an envelope structure and surface settlement caused by deep foundation excavation with spatial effects. Firstly, the principle of minimum potential energy was applied and the lateral displacement equation of the envelope structure was derived, considering spatial deformation effects. Secondly, based on linear elasticity theory, a surface settlement expression was formulated utilizing the plane strain boundary. Finally, the stratigraphic loss method was used to establish a connection between horizontal envelope deformation and surface settlement, allowing for calculations of surface settlement at any position behind the envelope structure. The effectiveness and practicability of the proposed method were demonstrated by comparison of two existing foundation-pit engineering examples.

Enhancing mix proportion design of low carbon concrete for shield segment using a combination of Bayesian optimization-NGBoost and NSGA-III algorithm

The demand for segment concrete increases rapidly with the expansion of urban rail transit and underground space, which may lead to carbon emissions (CE). In the production of segment concrete, using supplement cementitious materials (SCM) can be used to reduce CE instead of cement. However, SCM contents are usually determined by many orthogonal experiments, which are often time-consuming and only consider the limited experimental variables. Therefore, a novel hybrid intelligent algorithm combining Bayesian optimization (BO), natural gradient boosting (NGBoost) and non-dominated sorting genetic algorithm (NSGA)-III is proposed, which overcomes these disadvantages. Firstly, NGBoost model after hyperparameter optimization using BO is used to establish a nonlinear mapping relationship between segment concrete mix proportion and performance, which was used as the fitness function of the non-dominated sorting genetic algorithm (NSGA-III). Secondly, the optimal Pareto solutions were obtained through NSGA-III, and the reasonable range of segment concrete mixing proportion was obtained. Finally, a segment concrete production case was used to verify the effectiveness of the proposed algorithm. The results showed that the proposed hybrid algorithm combining proposed scheme decision strategy can obtain an optimal design scheme for concrete mix proportion. In addition, the comprehensive optimization rate of the obtained optimal scheme compared to the experimental optimal group was 11.5%. Moreover, the amount of phosphorous slag (PS) and granulated blast furnace slag (GBFS) in the optimal scheme was 26%, with a mass ratio of 1:2. Compared to the experimental optimal group, the optimal scheme can reduce the cost and CE per cubic meter by 31.64 yuan and 31.04 kg, respectively. Furthermore, the hybrid algorithm proposed can accurately obtains an optimal amount of SCM, which could be used as a supporting tool to reduce the production cost and CE of segment concrete. Overall, this research contributes to combining machine learning algorithms with actual production processes, which overcomes the data limitations of traditional experiments. It also provides a new intelligent approach and reference cases for the low-carbon design and sustainable development of building materials such as concrete.

Key Technologies and Applications of UAVs in Underground Space: A Review

Key Technologies and Applications of UAVs in Underground Space: A Review

Deep sea mineral resources and underground space as well as infrastructure for sustainable and liveable cities

Deep sea mineral resources and underground space as well as infrastructure for sustainable and liveable cities

Intelligent Analysis of Construction Safety of Large Underground Space Based on Digital Twin

Intelligent Analysis of Construction Safety of Large Underground Space Based on Digital Twin

Enhancing Urban Landscapes through Underground Space Utilization: Public Perceptions

Landscape occupation and green space reduction have decreased livability and hindered the sustainable development of cities. The urban landscape affects the quality of life and physical and mental state of the public, and urban underground space utilization is important for improving the urban landscape. Therefore, underground space utilization must be explored from a public perspective. Referring to typical underground municipal, transportation, and public space projects, an online questionnaire survey of 377 Nanjing residents was performed to construct a structural equation model investigating their perceptions and preferences regarding underground space usage to improve the landscape, focusing on the links between their preferences and opinions. Underground works that provide diverse open spaces were considered to have the most positive impact on the landscape (82.8%). The aesthetic value of the surface landscape (83.5%) and the vitality of historical sites (82.1%) were the most significantly affected, whereas stock underground space had no significant effect on landscape protection. In terms of age, profession, and place of work, the respondents demonstrated heterogeneous preferences. These findings indicate that targeted publicity and public participation are important to strengthen the cooperative utilization of space and realize the potential of the underground space, helping address actual requirements and develop sustainable cities.

Assessment of urban underground spaces inundation during extreme rainfall events.

As urbanization progresses and the impacts of climate change become more pronounced, urban flooding has emerged as a critical challenge for resilient cities, particularly concerning urban underground spaces where flooding can lead to significant loss of life and property. Drawing upon a comprehensive review of global research on underground space flood simulation and evacuation, this paper undertakes the modelling of inundation in a substantial underground area during the extraordinary rainfall event on 7 September 2023, in Shenzhen, China. Specifically, it introduces a two-step method to simulate the coupled surface-underground inundation process with high accuracy. The study simulates the inflow processes in three types of underground spaces: parking lots, metro stations, and underpasses. Utilizing the specific force per unit width evaluation, the research examines how varying flood barrier heights influence evacuation time and inundation risk. Subsequently, the paper proposes corresponding evacuation strategies based on the obtained findings. By highlighting the vulnerability of urban underground spaces to flooding, the study underscores the urgent need for further research in this domain.

Investigating the properties of sprayed insulating cementitious materials with corn cobs

As the mining depth increases, the underground space will face more serious thermal hazards. By using corn cobs, an agricultural waste, to prepare cementitious insulation materials, active insulation layers are constructed by injecting insulation materials into underground spaces using cementitious material spraying techniques. This article designed the ratios of corn cob sprayed cementitious materials and analyzed the changes in the properties of the materials obtained by adding 0–25% of corn cobs. The results of the study showed that the addition of different proportions of corn cobs improved the thermal insulation properties of the material by 6.9%-75.5% as compared to the ordinary mortar material. The mechanical properties became 25.9%-113.6% of the original. When the corn cob is wetted for more than 10 min, the fluidity of the material is sufficient to reach the minimum standard for spraying operations. Considering the comprehensive performance of the material, it is concluded that the wetting time of 30 min, the addition of corn cob 20%, the corn cob particle size of 200 mesh, and the amount of sand doping of 40% are the optimal ratios of the studied corn cob spraying cementitious materials. The study of corn cob lightweight thermal insulation spray cementitious material is of great significance for controlling the ambient temperature in deep underground space, promoting cleaner production and improving the use of environmental resources.

Editorial: Instability mechanisms and disaster prevention of coal and rock in deep underground space

Editorial: Instability mechanisms and disaster prevention of coal and rock in deep underground space

Analysis of geothermal heat recovery from abandoned coal mine water for clean heating and cooling: A case from Shandong, China

Exploiting heat from abandoned mine water using heat pumps is attracting increasing attention worldwide. China has a large number of abandoned coal mines, but there are few applications of geothermal heat recovery from mine water. Here, we report a new case from Shandong, North China. Based on actual geological and underground space structures, numerical analysis is performed to study the flow and heat transfer in the complex connection network among roadways. For given temperature differences on the source side, the underground heat transfer is greatly influenced by flow rates in roadways. Under the acceptable performances and long-term stability of heat pumps, the maximum heat transfer capacity of roadways reaches 697.3 kW at the flow rate of 100 m3/h, with the power per unit length of 151.3 W/m, indicating a promising heat recovery potential. When switching between the extraction and injection well, both fluid directions and the distribution of flow rates in roadways change obviously, thereby affecting the underground heat transfer. Besides dominant flow paths, there exist weak flow paths, which can be identified by numerical analysis, and necessary blocking can be applied to optimize the flow and heat transfer. Excessively long horizontal straight roadways for heat exchange should be avoided.

Study on the influence of branch slope on smoke movement mechanism in bifurcated tunnel fire under natural ventilation

In order to investigate the impact mechanism of branch slope on fire smoke in underground bifurcation spaces, a series of small-scale fire experiments were conducted. This study measured relevant data under natural ventilation conditions for four different branch slopes and six fire power levels, focusing on the highest ceiling temperature in the tunnel and the attenuation pattern of ceiling temperatures along the longitudinal direction in both the main and branch tunnels. It also analyzed the temperature field, velocity field, and pressure field at the bifurcation. The results indicate that a decrease in branch slope leads to an increase in the highest temperature in the main tunnel, primarily due to the enhanced chimney effect that intensifies the entrainment of smoke and accelerates the flow of fire smoke. A modified model for the highest temperature, considering the influence of branch slope, was proposed. Branch slope has a certain impact on the longitudinal temperature attenuation of the tunnel ceiling, with a relatively weaker effect on the main tunnel. Based on empirical formulas, a formula for longitudinal temperature attenuation involving slope, including both the main and branch tunnels, was developed. Fire smoke accelerates at the bifurcation point, a phenomenon that intensifies with an increase in the slope of the branch tunnel. The research in this paper provides a reference for fire safety issues in bifurcated tunnel structures.

Study on the fracture propagation of ground fissures with syn-depositional structure in Fenwei Basin, China

In Fenwei Basin, most of the tectonic ground fissures show characteristics of growth faults on the section. They continue to destroy the engineering properties of soil at different depths. This has introduced significant security risks to the construction processes of deep underground spaces. However, there are few studies have been conducted on syn-depositional ground fissures. Therefore, in this study, a physical simulation test was used to study the fracture propagation of syn-depositional ground fissures. The characteristics of sections and surface fractures were analyzed. The engineering properties of model soil were divided into bad and poor areas. The syn-depositional ground fissure fracture propagation process was divided into five phases. The results show that soil profile exhibited a composite Y-shaped fracture morphology. Syn-deposition affects the fracture angle and healing state of fractures. The soil strain and surface displacement were positively correlated with the number of deposition layers. The conclusions of this study provide a theoretical geological basis and practical engineering significance for design of deep underground space structures.

Optimisation of Synchronous Grouting Mix Ratio for Shield Tunnels

During shield construction in underground spaces, synchronous grouting slurry is poured between the surrounding rock and tunnel lining to ensure stability. For synchronous grouting slurries, few studies have investigated the relationship between the rheological parameters and physical properties, grout-segregation mechanism, and anti-segregation performance. Therefore, we explored the relationships between the slurry rheological parameters, segregation rate, and bleeding rate. Cement, sand, fly ash, and bentonite were used to prepare the slurry, and the effects of different polycarboxylate water-reducing agents and dispersible latex powder dosages were studied. The rheological parameters of 16 groups of uniformly designed slurries were tested, and the data were fit using the Herschel–Bulkley model. The optimal mix ratio lowered the slurry segregation rate, and its rheological behaviour was consistent with the Herschel–Bulkley fluid characteristics. High-yield-shear-stress synchronous grouting slurries with high and low viscosity coefficients were less likely to bleed and segregate, respectively. The optimised slurry fluidity, 3 h bleeding rate, 24 h bleeding rate, segregation rate, coagulation time, and 28 days compressive strength were 257.5 mm, 0.71%, 0.36%, 3.1%, 6.7 h, and 2.61 MPa, respectively, which meet the requirements of a synchronous grouting slurry of shield tunnels for sufficiently preventing soil disturbance and deformation in areas surrounding underground construction sites.

Three-Dimensional Quality Assessment of Urban Underground Space Resource Based on Multiple Geological Environmental Factors

With the rapid advancement of urbanization, the development and utilization of urban underground space resource (UUSR) has become one of the dominant features. However, in certain areas, the development of UUSR may cause disasters and accidents, such as ground collapse, settlements, and tunnel water gushing. Geological environmental factors (GEFs) are recognized as the fundamental constraining factor of UUSR development. In this paper, quality based on GEFs is defined to assess the development difficulty degree of UUSR. A 3D assessment framework is proposed based on 3D geological modelling and the interval continuous mathematical model (ICMM). The subjective and objective joint weight method of analytic hierarchy process and entropy weight method (AHP–EWM) is utilized to determine the weight of each indicator. The quality index (QI) of each spatial node of the 3D geological model is calculated by the ICMM mathematical model. A case study conducted in the Jiangbei New District of Nanjing, China, serves as a demonstration of the UUSR assessment. The results clearly illustrate the 3D distribution characteristics of the quality in the study area, offering valuable insights for future 3D urban underground space planning.

Bio-inspired mobile robot design and autonomous exploration strategy for underground special space

PurposeTo make the robot that have real autonomous ability is always the goal of mobile robot research. For mobile robots, simultaneous localization and mapping (SLAM) research is no longer satisfied with enabling robots to build maps by remote control, more needs will focus on the autonomous exploration of unknown areas, which refer to the low light, complex spatial features and a series of unstructured environment, lick underground special space (dark and multiintersection). This study aims to propose a novel robot structure with mapping and autonomous exploration algorithms. The experiment proves the detection ability of the robot.Design/methodology/approachA small bio-inspired mobile robot suitable for underground special space (dark and multiintersection) is designed, and the control system is set up based on STM32 and Jetson Nano. The robot is equipped with double laser sensor and Ackerman chassis structure, which can adapt to the practical requirements of exploration in underground special space. Based on the graph optimization SLAM method, an optimization method for map construction is proposed. The Iterative Closest Point (ICP) algorithm is used to match two frames of laser to recalculate the relative pose of the robot, which improves the sensor utilization rate of the robot in underground space and also increase the synchronous positioning accuracy. Moreover, based on boundary cells and rapidly-exploring random tree (RRT) algorithm, a new Bio-RRT method for robot autonomous exploration is proposed in addition.FindingsAccording to the experimental results, it can be seen that the upgraded SLAM method proposed in this paper achieves better results in map construction. At the same time, the algorithm presents good real-time performance as well as high accuracy and strong maintainability, particularly it can update the map continuously with the passing of time and ensure the positioning accuracy in the process of map updating. The Bio-RRT method fused with the firing excitation mechanism of boundary cells has a more purposeful random tree growth. The number of random tree expansion nodes is less, and the amount of information to be processed is reduced, which leads to the path planning time shorter and the efficiency higher. In addition, the target bias makes the random tree grow directly toward the target point with a certain probability, and the obtained path nodes are basically distributed on or on both sides of the line between the initial point and the target point, which makes the path length shorter and reduces the moving cost of the mobile robot. The final experimental results demonstrate that the proposed upgraded SLAM and Bio-RRT methods can better complete the underground special space exploration task.Originality/valueBased on the background of robot autonomous exploration in underground special space, a new bio-inspired mobile robot structure with mapping and autonomous exploration algorithm is proposed in this paper. The robot structure is constructed, and the perceptual unit, control unit, driving unit and communication unit are described in detail. The robot can satisfy the practical requirements of exploring the underground dark and multiintersection space. Then, the upgraded graph optimization laser SLAM algorithm and interframe matching optimization method are proposed in this paper. The Bio-RRT independent exploration method is finally proposed, which takes shorter time in equally open space and the search strategy for multiintersection space is more efficient. The experimental results demonstrate that the proposed upgrade SLAM and Bio-RRT methods can better complete the underground space exploration task.

CO2 foam to enhance geological storage capacity in hydrocarbon reservoirs

Geological CO2 storage is an emerging topic in energy and environmental community, which is, as a commonly-accepted sense, considered a powerful approach to mitigate the global carbon emissions during the transition to net-zero. The geological media initially considered cover the saline aquifers, oil and gas reservoirs, coal beds, and potentially basalts. Up to now only the first two choices have been proven to be the most capable storage sites and successfully implemented at pilot/commercial scales. Here, novel strategies were proposed for the first time, by synthesizing and utilizing new high-dryness CO2 foam, to enhance geological CO2 storage capacity in oil and gas reservoirs. As a major storage site, the oil and gas reservoirs ranked only second to the saline aquifer, due to their huge underground spaces, and more importantly, spontaneous economic benefits by injecting CO2 for geological storage. However, at any development stage, particularly late stage with high water cut, CO2 injection usually tends to cause gas channeling and therefore result in low-efficient storage. In this paper, a series of dynamic evaluation experiments are carried out to investigate the effect of newly-synthesized high-dryness CO2 foam in oil and gas reservoirs. A comprehensive set of parameters, including the fluid production volume, rate, efficiency, pressure, porous media weight, water cut, mobility reduction factor, oil-gas-water ternary phase saturation, etc., are specifically analyzed. The lab results show that when the foam quality is 85 %, the oil recovery performance and gas phase saturation reach their highest values, of 82.68 % and 75.36 %, respectively; meanwhile, the water consumption is at the lowest level, 43.88 g/mol, for the CO2 storage in oil and gas reservoirs. This indicates the synthesized high-dryness CO2 foam, attributed to its superb stability, modifies the mobility ratio, suppresses the viscous fingering, and finally results in higher oil recovery and more CO2 storage. Similar work has been done for the reservoirs with permeabilities from high to low levels. The study provides experimental evidences that suggest benefits from applying CO2 flooding in oil and gas reservoirs.

An underground drip water monitoring network to characterize rainfall recharge of groundwater at different geologies, environments, and climates across Australia

Abstract. Understanding when and why groundwater recharge occurs is of fundamental importance for the sustainable use of this essential freshwater resource for humans and ecosystems. However, accurately capturing this component of the water balance is widely acknowledged to be a major challenge. Direct physical measurements identifying when groundwater recharge is occurring are possible by utilizing a sensor network of hydrological loggers deployed in underground spaces located in the vadose zone. Through measurements of water percolating into these spaces from above, we can record the potential groundwater recharge process in action. By using automated sensors, it is possible to precisely determine when recharge occurs (which event, month, or season and for which climate condition). Combined with daily rainfall data, it is possible to quantify the “rainfall recharge threshold”, the amount of rainfall needed to generate groundwater recharge, and its temporal and spatial variability. Australia's National Groundwater Recharge Observing System (NGROS) provides the first dedicated sensor network for observing groundwater recharge at an event scale across a wide range of geologies, environments, and climate types representing a wide range of Australian hydroclimates. Utilizing tunnels, mines, caves, and other subsurface spaces located in the vadose zone, the sensors effectively record “deep drainage”, water that can move beyond the shallow subsurface and root zone to generate groundwater recharge. The NGROS has the temporal resolution to capture individual recharge events, with multiple sensors deployed at each site to constrain the heterogeneity of recharge between different flow paths, and to quantify (including uncertainty bounds) rainfall recharge thresholds. Established in 2022, the network is described here together with examples of data being generated.

Cluster analysis of underground space in the core area of new districts from the perspective of urban morphology

Extensive underground space development worldwide has significantly contributed to the sustainability of social, ecological, and economic growth. In view of the tendency towards haphazard urban sprawling during the development of new areas in China, underground spaces have been increasingly utilized to create sustainable and resilient urban built environments. However, insufficient attention has been paid to their morphological characteristics, resulting in a lack of sustainable and resilient underground space morphological planning and design techniques. To bridge this gap, we established a computational morphology indicator system pertaining to underground spaces, considering land use, spatial distribution, and street networks. We selected 20 underground spaces in well-developed core areas of new districts in China. Hierarchical cluster analysis was adopted to investigate the morphological features of underground spaces. Additionally, the typology of underground space morphology and the corresponding characteristics were systematically summarized to facilitate decision-making for different patterns of underground space planning.

Evaluating efficiency of metro-led urban underground public space: a case study in Shanghai

Metro-led urban underground public space (UUPS) are among the most common and important types of underground and public spaces. The need to measure metro-led UUPS performance and improve urban planning and public services has facilitated the development of various evaluation methods. However, the essential performance aspects of efficiency and effectiveness are rarely balanced. Most methods focus on evaluating effectiveness while neglecting the cost incurred. This study proposed two sets of efficiency indicators of cost (input) and effectiveness (output) separately and used data envelopment analysis (DEA) to analyze the relative efficiency of 20 metro-led UUPS in Shanghai, China. The results indicated that the UUPS of People’s Square, Hanzhong Road, and Huamu Road were the most efficient. Whereas, the South Shanghai Railway Station UUPS and other five cases were neither technically efficient nor scale efficient; a waste of space volume was observed in half of the inefficient cases. Through comparisons of the results with previous studies, it was determined that different conclusions could be drawn when considering efficiency. Moreover, the evaluation framework based on the DEA method proposed in study paper can provide a comprehensive and holistic approach to guide metro-led UUPS planning optimization.