Utilization Of Underground Space Research Articles

Investigating Urban Underground Space Suitability Evaluation Using Fuzzy C-Mean Clustering Algorithm—A Case Study of Huancui District, Weihai City

The development of underground space resources can alleviate the problems of traffic congestion and land resource tension caused by urbanization, but there are also certain risks in the development of underground space, so the suitability of development needs to be evaluated. This paper takes the geological suitability of underground space resources in Weihai City as the evaluation object, establishes the index system for evaluating the geological suitability of underground space resources development and utilization, determines the criteria for quantifying each factor index, uses the hierarchical analysis method to determine the index weights and applies the fuzzy C-mean clustering algorithm to evaluate the geological suitability of underground space resources development and utilization in the urban area of Weihai City, and achieves excellent results that are more in line with the geological conditions.

Does the scarcity of urban space resources make the quality of underground space planning more sustainable? A case study of 40 urban underground space master plans in China

The international community has reached a consensus on promoting the sustainable development of global cities. As an important and irreversible space resource in a city, the development and utilization of urban underground space should follow the principle of sustainability and emphasize scientific and forward-looking planning. At present, most cities have formulated urban underground space master plans. However, due to the lack of an effective evaluation method, the plan quality is uneven, which directly affects the sustainability of underground space development and utilization. This paper proposes a set of sustainability evaluation framework of underground space planning based on relevant planning standards and plan quality evaluation protocol, and makes a comparative analysis of the 40 urban underground space master plans formulated in China from 2004 to 2020. The research found that the planning documents generally reflected the problem of emphasizing design strategies and engineering technology while neglecting implementation and humanistic care; administrative region, population density, land price and other variables closely related to the scarcity of urban space resources are the main factors affecting the quality of urban underground space planning. The conclusions of this paper can aid planners and researchers to identify the problems and influencing factors of underground space planning related to sustainability, and summarize the methods to improve the quality of underground space planning.

Frequency-Bessel Transform Based Microtremor Survey Method and Its Engineering Application.

The development and utilization of urban underground space depend heavily on an understanding of urban geological conditions. The microtremor survey method is essential in urban geological surveys due to its quickness, convenience, non-destructiveness, and interference resistance. Since only the fundamental dispersion curves of Rayleigh waves can be obtained by utilizing the spatial autocorrelation method, the inversion results have multiple solutions. To improve the accuracy of the microtremor survey, this study employed the frequency-Bessel transform to extract the fundamental and higher modes of dispersion information of Rayleigh waves from the microtremor data array and verified the effectiveness of this method by synthesizing theoretical microtremor signals. Additionally, taking into account the order identification challenges brought on by mode jumps or missing modes in the dispersion curve, this study processed a multi-mode dispersion curve based on the newly proposed inversion objective function coupled with a genetic algorithm to obtain a shallow surface S-wave velocity structure. Compared to the traditional inversion objective function, the new function presented in this study could address mode misidentification more effectively and improved the accuracy of inversion calculations. Finally, the applicability and dependability of the frequency-Bessel-transform-based microtremor survey method were evaluated in a practical engineering case.

Experimental research on the heat transfer characteristics of fluid flowing through rock with intersecting fractures

The research on the seepage and heat transfer characteristics of fluid flowing through fractured rock mass is of great significance to the utilization of geothermal resources. The behaviors and characteristics of heat transfer when fluid flowing through a single fracture channel, two intersecting fractures channels, and three intersecting fractures channels were investigated and compared. Firstly, the calculation formula of convective heat transfer coefficient of water flowing through multi channels was deduced. Then the relationship between the seepage characteristic parameters and the confining pressure during the loading and unloading process was analyzed and discussed. Finally, the heat transfer mechanism of water flowing through rock sample with multi fractures was studied. This work supplements the law and theory of heat transfer when fluid flowing through fracture networks, which is of practical significance to the underground space utilization and geothermal resource exploitation.

Multi-Effects of Tunneling and Basement Excavation on Existing Pile Group

Tunnels and foundation pits are two separate types of excavation that are frequently used in urban settings. Excavating tunnels and foundation pits sequentially around existing pile foundations is becoming more and more prevalent as urban underground space utilization rates increase. The deformation and load transfer mechanisms of the pile group foundation under two asymmetric excavation conditions of “first tunnel, then foundation pit” and “first foundation pit, then tunnel” are studied from the perspective of the relative positions of the tunnel–pile–foundation pit based on the constant gravity model test and 3D numerical simulation. The result shows: The pile settlement of the front pile (closer to the tunnel) caused by the excavation condition of the “first foundation pit-then tunnel” is relatively larger, while the pile settlement of the rear pile (closer to the foundation pit) caused by the excavation condition of “first tunnel-then pit” is larger. The transverse tilting of the pile group caused by the excavation of the “first foundation pit-then tunnel” is relatively larger. For the front pile, the pile tip resistance generated by “first excavation-then tunnel” is about 10% greater than it was before the initial excavation, which is greater than the result of “first tunnel-then foundation pit”. For the rear pile, the pile tip resistance generated by “first excavation-then tunnel” is about 85% greater than it was before the initial excavation, which is smaller than the result of “first tunnel-then foundation pit”. The multiple excavation sequence of “tunnel first-then foundation pit” leads to a larger induced bending moment for the front pile, whereas a larger induced bending moment for the rear pile results from the multiple excavation sequence “first foundation pit-then tunnel”.

Study on strength characteristics of soft and hard rock masses based on thermal-mechanical coupling

For deep resource exploitation and engineering construction, the mechanical properties of soft and hard interbedded rock masses are important factors impacting engineering stability. Simultaneously, the influence of temperature on the strength of deep rock masses poses a significant obstacle to the exploitation of deep resources and the utilization of underground space. In this paper, the particle flow code (PFC2D) is utilized to establish the thermal-mechanical coupling numerical model of soft and hard interbedded rock masses, and then the uniaxial compression response of soft and hard interbedded rock masses following thermal damage is studied. The displacement and contact force produced by applying temperature, as well as the failure strength, strain, and crack development of the specimen after uniaxial compression is analyzed. The findings reveal that: 1) The peak displacement caused by applied temperature increases first and subsequently decreases with the increase of soft rock thickness ratio (Hs/H), whereas the peak displacement increases linearly with increasing temperature. The peak contact force varies in two stages with the increase of the soft rock thickness ratio (Hs/H), and with the same trends. 2) As the soft rock thickness ratio increases (Hs/H), the number of cracks decreases steadily. When the soft rock thickness ratio Hs/H < 0.5, the relationship curve between vertical strain and crack changes in two stages: the stage of crack development along with the stage of vertical strain gradually increases with crack development. When the thickness ratio of soft rock Hs/H > 0.5, the relationship curve changes in three stages: crack development stage, vertical strain increase stage, and vertical strain increase stage with crack development. 3) When the soft rock thickness ratio Hs/H < 0.5, the failure strength gradually decreases as soft rock thickness increases at T = 100°C, 200°C. The failure strength gradually increases as the soft rock thickness increases in general at T = 400°C. Soft rock thickness ratio Hs/H > 0.5, the failure strength increases with the increase of soft rock thickness at T = 300°C, 400°C. At T = 100°C, 200°C, the tendency of the failure strength changes less.

Monetary valuation of the environmental benefits of green building: A case study of China

Reducing negative impacts on the environment is the main benefit of green buildings. However, these benefits are typically evaluated using environmental indicators with different units and implications. Thus, comparisons among different technologies and projects with various benefits are difficult to perform. Moreover, the impact of green building development on economic system is difficult to analyze because of the lack of available data. This study proposes a method of identifying, quantifying and valuing the environmental benefits of green buildings based on the contributions of typical technologies. The environmental benefits are fully identified based on the cause-effect chain associated with changes in environmental endpoints caused by green technologies. Then, a valuation method is proposed, and it consists of the following four steps: quantifying the technical indicators using the application criteria and green technology impacts, quantifying the environmental indicators using available and reliable research data, valuing the environmental benefits using appropriate monetary valuation methods, and calculating the lifecycle benefits using the discounted cash flow method. All projects accredited by the Chinese Assessment Standard of Green Building from 2008 to 2015 were evaluated using the environmental valuation method. The results showed that 75% of typical green technologies could reduce the negative impacts on the environment through different endpoints. The benefit per unit area was valued as ¥ 3138.1 on average. The majority of the benefits (48.36%) were produced by underground space utilization. The public green building produced more environmental value than the residential green building. Overall, the environmental benefits were sufficient to cover the incremental costs of green building. The results obtained by the proposed assessment method provide more comprehensive information to related sectors than the green level standards; moreover, the benefits obtained by different technologies and projects with various environmental impacts can be compared, and important input data can be obtained for analyzing the macroeconomic effects of green building development.

Deformation monitoring and remote analysis of ultra-deep underground space excavation

The development and utilization of urban underground space is producing many deep foundation pits. On-site monitoring is a key issue to ensure the safety of the foundation excavation, especially the monitoring of the lateral displacement of the structure. The ultra-deep circular foundation excavation project (58.65 m deep, the deepest foundation pit in Shanghai) in the test section of the Suzhou River deep tunnel is one of the most challenging engineering around the world. The distributed optical fiber monitoring technology of Brillouin optical frequency domain analysis (BOFDA) was employed to monitor the lateral displacement of the deep foundation. The monitoring process lasted for 14 months, and a total of 19 times of monitoring was carried out following the progress of the excavation of the foundation pit. This paper introduces the process, methods and precautions of optical fiber monitoring from early installation, equipment debugging to data acquisition, data processing and data analysis. By comparing the fiber monitoring data with the manual monitoring data, the deformation of the deep foundation excavation is analysed. The analysis results not only obtain the deformation law of ultra-deep foundation excavation, but also prove the advantages of optical fiber monitoring in deep foundation excavation. Finally, with the support of the Smart Infrastructure Service System (iS3), the research combines optical fiber monitoring with an information platform. Under the framework of the iS3 platform, an integrated data processing and analysis module for fiber monitoring is developed, and the feasibility of remote real-time collection and analysis of monitoring data is discussed. With the support of the information platform, the monitoring data can be transmitted back to the computer terminal to realize remote monitoring.

Calculation Model for Progressive Residual Surface Subsidence above Mined-Out Areas Based on Logistic Time Function

The exploitation of underground coal resources has stepped up local economic and social development significantly. However, it was inevitable that time-dependent surface settlement would occur above the mined-out voids. Subsidence associated with local geo-mining can last from several months to scores of years and can seriously impact infrastructure, city planning, and underground space utilization. This paper addresses the problems in predicting progressive residual surface subsidence. The subsidence process was divided into three phases: a duration period, a residual subsidence period, and a long-term subsidence period. Then, a novel mathematical model calculating surface progressive residual subsidence was proposed based on the logistic time function. After the duration period, the residual subsidence period was extrapolated according to the threshold of the surface sinking rate. The validation for the proposed model was estimated in light of observed in situ data. The results demonstrate that the logistic time function is an ideal time function reflecting surface subsidence features from downward movement, subsidence rate, and sinking acceleration. The surface residual subsidence coefficient, which plays a crucial role in calculating surface settling, varies directly with model parameters and inversely with time. The influence of the amount of in situ data on predicted values is pronounced. Observation time for surface subsidence must extend beyond the active period. Thus back-calculated parameters with in situ measurement data can be reliable. Conversely, the deviation between predictive values and field-based ones is significant. The conclusions in this study can guide the project design of surface subsidence measurement resulting from longwall coal operation. The study affords insights valuable to land reutilization, city planning, and stabilization estimation of foundation above an abandoned workface.

Feasibility study on using excavated soil and rock to sintering utilization

Urban construction, especially the ongoing large-scale expansion and utilization of underground space, has resulted in massive excavated soil and rock (ESR) from buildings and subways. Therefore, this study aims to explore the technical ways of ESR sintering utilization from the perspective of technology, environment, and policy through qualitative and quantitative methods. The study analyzes the soil properties and distribution of different depths, and the annual production of clay-rich ESR accounts for about 30 million m³ in Shenzhen. More importantly, the comparison between various pollutant concentrations of ESR in Shenzhen and local soil background values showed that the ESR in Shenzhen had no environmental risks. This study can not only provide a scientific basis for ESR as the raw material of sintering but also provide a theoretical basis for the promotion of the pilot of “Zero waste city”.

A new construction method for metro stations in dense urban areas in Shanghai soft ground: Open-cut shafts combined with quasi-rectangular jacking boxes

At present, the metro station constructions in dense urban areas face significant challenges during the rapid urban metro network expansion. The repeating disturbances to city traffic, commerce, and residents' daily life induced by conventional open-cut metro station constructions can no longer be accepted in dense urban areas. To solve these problems, some underground excavation methods, such as enlarging shield tunnels, shallow tunnelling method and pipe-roof mining method, have been attempted, but it is difficult for them to be adapted to the strict limitation of urban space in soft ground. In this paper, the planning, construction, challenges, and relevant key techniques of an innovative type of metro station – open-cut shafts combined with quasi-rectangular jacking boxes (SCJB) were introduced and investigated. The main conclusions are as follows: (1) For the advantages of efficient underground space utilization and little impact on traffic and environment, the SCJB method is recommended for the constructions of metro stations that need to traverse the heavy traffic roads and express-way viaducts. The flexible combinations of open-cut shafts and jacking boxes can form various layouts of underground space to adapt to various complex surrounding environment. (2) Steel-concrete composite lining was designed for jacking boxes considering the transportation convenience and bearing capacity enhancement, and the corresponding earth pressure balanced box jacking machines were developed. (3) By applying thick thixotropic slurry with small filtration loss, the jacking resistance of the large-section box culverts was effectively reduced to 4–6 kPa and the total jacking force was kept at 30,000 kN. (4) By surveying with laser guiding system and performing timely rectifications, the trajectory deviations induced by two large adjacent box jacking were controlled within ±50 mm. The horizontal convergence of east line box segments caused by the west line jacking was controlled within 1.5 mm, through strict trajectory control. The surface settlement induced by the crossing of three box jacking tunnels was effectively controlled within 15 mm. The experiences learnt from this project can provide valuable references for the planning and construction of metro stations in dense urban areas in soft ground.

Strength Characteristics and Failure Mechanism of Granite with Cross Cracks at Different Angles Based on DIC Method

The engineering rock mass is generally composed of the rock matrix and structural plane and is an anisotropic inhomogeneous geological body. Accidents such as roof collapse and well caving caused by joint and fissure expansion occur frequently during tunnel excavation and service, resulting in serious casualties and economic losses. It is of great theoretical significance and engineering value to study the fracture mechanism of the jointed rock mass to ensure the stability of the surrounding rock and the safe and efficient utilization of the urban underground space. To investigate the effects of crossed cracks on mechanical properties and failure characteristics of rock, wire cutting equipment is employed to make rock samples with different crossed cracks, and then acoustic emission system and digital image correlation technique are used to study the fracture process of rock samples under uniaxial compression. It has been found that the strength of rock samples with a single crack is generally larger than that of samples with cross cracks, and the strength changed with the angle of the crack in a “V” shape. When the angle of preexisting crack is 60°, the rock strength reaches the lowest. The primary crack has a more obvious influence on rock strength and is the main controlling factor of rock fracture. The initiation stress of rock samples with a single crack changes more significantly with angle. When the angle of the primary crack is 45°, the rock sample is most prone to crack initiation failure, and the crack initiation stress is only 1/4 to 1/2 of the strength. There are two types of cracks: wing and anti-wing, and the tensile cracks are the main ones. It is revealed that the fracture of cracked rock has significant directional characteristics. For the samples with cross cracks, the primary crack is the main control factor of crack initiation, and the secondary crack has a certain guiding effect on the crack.

Influence of thermal and lighting factors on human perception and work performance in simulated underground environment

The utilization of underground working space in the rapidly developing global economy has broadened the scope of human activities. However, it has also brought new challenges to existing environmental construction strategies. The comfort and performance of the people inside a building are influenced by multiple factors. This study investigates the main factors affecting personnel perception and work performance, such as humidity, heat, and light, to guide the construction of underground working environments. Therefore, an experiment was designed and carried out in an artificial climate chamber to explore the differences in subjective evaluation, physiological parameters, and working performance of personnel under different thermal and lighting environments. The results show that air temperature has a significant effect on most subjective and objective parameters, while lighting has a weak effect. Air temperature and illumination are the two main environmental factors that affect comfort. Regression analysis shows that the recommended air temperature and illumination ranges are 22.0–27.3 °C and 545–1000 lx, respectively. This study also found that the interaction between color temperature and air temperature had significant effects on several evaluation parameters.

The behavior of groundwater and subsurface fluid on underground space utilization

The behavior of groundwater and subsurface fluid on underground space utilization

Three-dimensional high-precision assessment of mountainous urban underground space resources: A case study in Chongqing, China

Urban underground space resource (UUSR) assessment can facilitate the planning of underground space development and utilization in highly populated urban areas. Typically, UUSR assessment involves dividing the assessment area, determining the assessment index, establishing the assessment model, integrating the assessment data, and calculating the results. A method for streamlining the three-dimensional (3D) high-precision UUSR assessment process was proposed, aiming at the mountainous cities. Assessment indexes suitable for the mountainous UUSR were determined, and a variable weighting model was constructed to enhance the credibility of the assessment results. Multi-source assessment data were compressed and stored using a chain run-length encoding data structure, which can be queried to obtain the attributes of the assessment cells. In addition, a 3D assessment system was developed to automate the assessment process using distributed computing. Finally, taking Chongqing City as a case study, the assessment was conducted over a surface area of approximately 19.4 km2 and to a depth of 50 m. The study area was divided into 9.72 × 108 assessment cells, with the dimension of 1 m × 1 m × 1 m. The results show that the 3D high-precision UUSR assessment successfully reported the construction risks at the urban scale. The construction risks of a 15-km underground rail transit line can be analyzed, thereby providing decision-making support for underground space development and transit line layout.

A Suitability Evaluation Method of Urban Underground Space Based on Rough Set Theory and Conditional Entropy: A Case Study in Wuhan Changjiang New Town

In order to make full use of underground space resources and reasonably determine the development function and scale, it is important to evaluate the suitability evaluation of urban underground space (UUS). The development and utilization of underground space is affected by many factors, such as topography, geomorphology, geotechnical characteristics, hydrogeology and so on. Taking the starting area of Changjiang New Town in Wuhan as a case study, this paper introduces the rough set theory and conditional entropy and establishes a suitability evaluation model of UUS. Rough set theory is used to construct a decision information table, preprocess sample data and classify the knowledge base, while conditional entropy is employed to calculate the attributes’ own and relative importance. Then, the fuzzy comprehensive evaluation method, the most unfavorable grade discrimination method and the exclusive method are used to evaluate the model, and the partition map of regional underground space development suitability is obtained. In this method, any prior knowledge and additional information will not be needed except the sample data, and the obtained weights are more objective and reasonable. The results show that the overall suitability of underground space development and utilization in the starting area of Wuhan Changjiang New Town is good.

Permeability evolution of fractured granite after exposure to different high-temperature treatments

A detailed understanding of permeability in fractured granite after exposure to high-temperature treatments under different confining pressures is critical for deep resource exploitation and underground space utilization. Along with the mechanical behaviour deterioration resulting from geologic and engineering effects, thermal stress leads to a permeability variation. In this research, uniaxial compression tests are performed on granite after exposure to a high-temperature treatment, and water flow experiments are then conducted on the fractured granite. A non-Darcy approach is used to analyse the permeability. When the temperature increases from 200 to 600 °C, changes in the microstructures are observed using scanning electron microscopy, new cracks generate along with the coalescence of original cracks, and the uniaxial compression strength and Young's modulus decrease rapidly. As the temperature increases, the permeability experiences three stages: decrease slowly, increase rapidly, and increase slowly. An exponential function fits the relationship between temperature and permeability well as the temperature is higher than 400 °C. When the confining pressure increases at a certain temperature, the decreasing rate of permeability at a higher confining pressure is smaller than that at a lower confining pressure, and it becomes more difficult for the seepage channels to close. As the confining pressure increases from 2 to 4 MPa at room temperature, the permeability decreases from 1.58 × 10–16 to 4.18 × 10–17 m2, decreasing by 73.54%. The decreasing rate is 16.39% as the confining pressure increases from 6 to 8 MPa.

Study of Natural Ventilation Potential and Performance for the Undergroun Utility Corridor Using Numerical Method

The utilization of urban underground space is a strategic choice to solve land space shortage, traffic congestion and environmental pollution. The underground corridor serves as both commercial and entertainment spaces. Proper natural ventilation system is believed to combine the advantages of good indoor air environment and high energy efficiency. In the present study, field experiments and numerical simulation are performed to compare the natural ventilation performance in the underground utility corridor under different layout of gates and skylights during the transitional season. The results show that the overall Richardson number is calculated to analyze the dominant driving force of the corridor. Second, it has been found that the arrangement of skylights and asymmetric gates can well promote natural ventilation in the corridor. The air exchange rate of the corridor with asymmetrical outlet is 10% higher than that with symmetrical outlet under the conditions in this study. Third, the wind speed at the openings in the middle of the corridor is higher than that of other openings in the corridor with skylights.

Application of active-source surface waves in urban underground space detection: a case study of Rongcheng County, Hebei, China

Active-source surface wave exploration is advantageous because it has high imaging accuracy, is not affected by high-speed layers and has a low cost. It has unique advantages in the investigation of shallow surface structures. For the development and utilization of urban underground space, there are two important parameters in the shallow surface, namely, shear wave velocity (vs.) and site predominant period, which determine the elevation and aseismic grade of the building design. The traditional method mainly obtains the above two parameters through the testing and measurement of drilling samples. However, this method is extremely expensive and time consuming. Therefore, this paper uses the multichannel surface wave acquisition method to extract the fundamental dispersion curve of the single shot data using the phase shift method and obtains the vs. characteristics in the uppermost 40 m by inversion. According to the vs. profile, the following two conclusions were obtained. First, the study area can be roughly divided into 5 layers, among which the layers 0-8 m, 14-20 m, and 20-30 m are low-velocity layers, corresponding to miscellaneous fill, a water-bearing sand layer and a sand layer. Therefore, the vs. is relatively low, and the layers at 8-14 m and 30-40 m are high-velocity layers that are mainly composed of clay, with a relatively better compactness and relatively high vs. values. In addition, the low-speed anomaly suddenly appears in the high-speed area at 20-40 m. Combining this with geological data suggests that it is an ancient river channel. Second, according to the vs. value, the V_se(equivalent shear wave velocity) was calculated. The construction site soil is classified as Category III, with good engineering geological conditions. In addition, according to vs., we calculate the site predominant period to be 0.56-0.77 s. Therefore, in the overall structural design of foundation engineering, the natural vibration period of the structure should be strictly controlled to avoid the predominant period of the site.

Quantitative Analysis of the Microstructures of Deep Silty Clay Subjected to Two Freezing–Thawing Cycles under Subway Vibration Loading

The bypass of subway tunnels in soft soil areas is usually constructed by the artificial freezing method due to the waterproof property and high strength of frozen soil. The thawing settlement and deformation of silty clay under subway vibration loading is becoming a major issue. The Shanghai subway lines cross vertically and horizontally, of which the deepest station reaches 33.1 m. With the rapid development and utilization of underground space, the depth of subway excavation will become increasingly deeper. Under subway vibration loading, the dynamic characteristics and microstructures of deep clay should be investigated. In this paper, a series of scanning electron microscopy (SEM) tests and mercury intrusion porosimetry (MIP) tests were carried out to study the microscopic parameters of deep silty clay subjected to two freezing–thawing cycles under cyclic loading. The freezing–thawing soil produced higher axial strain than that of the unfrozen soil with the same loading. After freeze–thaw cycling, the soil particles show the phenomenon of agglomeration. As the pore diameter increases, the pore shape coefficient decreases gradually from 0.45 to 0.85. Under similar vibration loading, the anisotropy of the frozen–thawed clay increases as the freezing temperature decreases. The fractal dimension obtained by SEM tests is between 1.25 and 1.33. There is an approximate linear relationship between the axial strain and the fractal dimension. In MIP tests, there exists a bottleneck effect in the process of mercury intrusion. The pore volume and pore diameter of the freezing–thawing soil increase with decreasing freezing temperatures and freezing–thawing cycles, respectively. The thermal fractal model is applicable to the fractal characteristics of silty clay. The results can provide a reference for the design and construction of deep-buried subway tunnels in soft soil areas.