The position of fossil fuels as the most important energy for human beings is difficult to change in the short term, but the proposal of the "dual carbon" goal has brought new challenges and opportunities for China's industrial structure upgrading and energy security. Carbon emission reduction technology represented by CO₂ underground storage is an important way to achieve the "dual carbon" strategy. Carbon dioxide geological sequestration technology (CCS) is regarded as a direct and effective means of emission reduction. This technology is to capture the CO₂ originally discharged into the atmosphere and inject it into the closed underground reservoir after treatment, to reduce the emission of CO₂ into the atmosphere and slow down the atmospheric pollution and greenhouse effect. At present, CCS technology has been widely concerned by researchers domestic and overseas. The situation of CO₂ emission reduction in China is very serious, thus, the study of CO₂ geological sequestration is particularly urgent. To carry out further research, this paper reviews the global research status from four aspects: saline aquifer storage, abandoned oil and gas reservoir storage, deep unexploitable coal seam storage, and basalt storage. In addition, the deficiencies in the current research and the problems that need further research are also presented.

The vigorous development of e-commerce has brought great pressure on urban logistics distribution and environmental protection. At present, it is a new idea to let the subway undertake part of the freight function to solve this problem. Based on the operation characteristics and future development trend of urban metro, this paper studies the metro freight transport under the mode of "shared lines but not shared trains". Combined with the operation situation and internal structure of the metro system, through the establishment of a combination model of E-TOPSIS flow screening model, set coverage model, and mixed integer programming, this paper analyzes the metro stations, and selects appropriate stations as freight stations. Finally, the freight transport scheme of urban metro under the mode of "sharing lines but not sharing trains" of metro passenger and freight trains will be realized. Finally, take Tongzhou District of Beijing as an example to carry out simulation and find out the subway stations that can carry out freight transport in Tongzhou District, so as to verify the method of selecting subway freight stations.

Comprehensive and scientifically reasonable planning and design of underground space is the premise for its development and utilization, reviewing the research context of underground space planning and design, predicting its development trend, providing reference for sustainable utilization and high-quality development of underground space. Through the visual analysis method of bibliometrics, the literature of underground space planning and design journals from CNKI and Web of Science database was analyzed, the number of papers, subject categories, main research forces and keywords were processed, then the following conclusions were drawn: the development trend of discipline types is diversified and interdisciplinary. The main research countries/regions are China, and the research institutions are Shanghai Municipal Engineering Research Institute (Group) Co., LTD and Tongji University, etc. Keyword emergence analysis indicates that future research trends will focus on: The improvement of underground space comfort and quality; Green and safe underground space design under the Sustainable Development Goals; Comprehensive planning and layout of three-dimensional and intensive underground space; Digital technology assisted underground space planning and design.

The development and utilization of underground space is an important way to solve many urban problems in China, such as land resource scarcity, dense population, and traffic congestion. However, the current shallow underground space development and utilization methods are difficult to cope with the complex deep land development scenarios in China. Exploring the organizational model of deep land space development is an inevitable need for China's urbanization development in the new era. This article reviews the application scenarios of deep underground space at home and abroad, analyzes the corresponding spatial characteristics and usage needs in various scenarios such as deep mines, deep transportation, deep storage, and deep laboratories through case studies, summarizes and proposes four typical deep underground space network organization modes: point, line, surface, and three-dimensional network. The applicable characteristics and possible application scenarios of the four typical development modes are analyzed, in order to provide reference and reference for the development, construction, and scene design of deep underground space in China.

Deep-buried long tunnel is a key control project in highway construction. Identifying hydrogeological conditions and accurately predicting water inflow are important prerequisites for ensuring construction safety. This paper takes the Tiantoushan tunnel of the third phase project of Shenzhen outer ring expressway as an example, and uses the hydrogeological comprehensive survey method combining hydrogeological surveying and mapping, geophysical prospecting,drilling, hydrogeological test and indoor test to analyze and study the segmentation and classification of tunnel surrounding rock,the division of water-rich sections,and the prediction of water inflow. The tunnel passes through the synclinal axis section,which is a good water storage structure. Geophysical exploration also shows that the water-rich section is concentrated in K84 + 680 ~ K84 + 840. It is predicted that large water gushing will occur during construction. The tunnel section in this range is divided into V-level surrounding rock,which is determined as the main water-conducting rock mass. At the same time, the tunnel is affected by the fracture structure,and the fault zone and wide tensile cracks in the water-rich section will become important water-conducting channels. Furthermore,after obtaining the permeability coefficient of the rock mass in the typical depth section of the tunnel site,the tunnel water inflow is predicted by using the precipitation infiltration coefficient method,the Dupuit theoretical formula and the Goodman empirical formula respectively,indicating that the hydrogeological comprehensive survey method can well evaluate the tunnel water conductivity characteristics and estimate the water inflow.

The multi-arch tunnel without middle drift is the latest development type of the multi-arch tunnel, which can significantly improve the construction efficiency and reduce the project cost. However, there are some disadvantages such as close construction, multiple transformation of the stress system and difficult construction control. Therefore, the mechanical mechanism and failure characteristics of the lining structure of the multi-arch tunnel without middle drift are studied through model tests, combined with typical tunnel disease characteristics and the construction experiences of 65 tunnels, the safety construction countermeasures of the unguided arch tunnel are put forward. The model experiment results show that: The bending moment and axial force values of the right arch waist of the advance hole are both largest and the most unfavorable parts. Therefore, the structural design and construction quality control of the right arch waist and other parts of the advance hole need to be strengthened, and countermeasures of the thirty words principle of "pay attention to geology, strong advance, pre-reinforcement, stable middle wall, first support, short excavation, weak blasting, frequent measurement, tight secondary lining and detail injection" are proposed. The countermeasures in this paper have guiding significance for the design and safe construction of multi-arch tunnel without middle drift.

The coupling environment of in-situ stress and gas pressure is among the important factors that can cause coal and gas outbursts and other disasters. Here, an investigation into the deformation and seepage characteristics of raw coal under the coupling environment of in-situ stress and gas pressure was conducted in a laboratory setting, considering the geological conditions of the in-situ stress and gas pressure of the 2+3# coal seam in the Shanmushu Coal Mine. The results show that: Forcing related to gas pressure, in-situ stress, axial strain, radial strain, and deviatoric stress exhibit a linear response in the process of loading axial stress. Poisson's ratio satisfies a quadratic function with increased deviatoric stress, and the permeability and deviatoric stress satisfy an ExpDec1 function. The linear relationship between axial strain, radial strain, and deviatoric stress is satisfied in the process of loading confining pressure, and the Poisson's ratio of coal samples increases with the decreased deviatoric stress, as given by an ExpDec1 function. Before reaching the peak strength, the axial strain and deviatoric stress have a linear relationship while simultaneously loading axial stress and unloading confining pressure, and the radial strain and deviatoric stress are related by a quadratic function relationship. The Poisson's ratio decreases with increasing deviatoric stress, and the elastic modulus increases with the deviatoric stress consistent with an ExpDec1 function. In the subsequent loading and unloading process, the permeability is almost zero before the residual strength appears after failure, and rapidly increases after the residual strength appears.

In order to study the interface properties of loess reinforced with bamboo geogrid, 9 sets of large direct shear tests were conducted to investigate the effects of reinforcement type, grids mesh size and fill compaction on the interfacial properties of reinforced loess, and to analyze the mechanism of their effects. The results show that when the shear displacement is small, the interfacial shear stress increases gradually with the increase of shear displacement and reaches the peak value, and with the further increase of shear displacement, the interfacial shear stress starts to decrease and tends to a stable residual stress; the reinforcing effect of bamboo geogrid increases the cohesion and internal friction angle of the soil, and the enhancement effect is better than that of geogrid. The interface shear strength increases with the increase of fill compaction; there exists an optimal grid mesh size to maximize the interface shear strength. This paper compares the reinforcing effect of bamboo geogrid and geogrid on loess and provides a reference for the engineering application of bamboo reinforced grating on loess.

Subway public space is an important activity place for urban residents, which has the particularity and complexity of space. This paper summarizes and analyses the previous research on the design of urban subway public space in China from the aspects of research perspective and method, design principle and optimization strategy. The results show that: The current research has formed a relatively complete research system, and the research perspectives are diversified, covering the analysis of subway public space elements at the micro level, the special design of space composition at the meso level, and the composite design of macro level and urban space. The research methods are quantified, modelled and visualized. And put forward the prospect of future research, enhance the comprehensive research perspective; introduce the concept of ecological green; deepen the humanized design ; construct a more perfect typed research system and expand the distribution range of research objects ; research methods should promote interdisciplinary integration, improve research paths, and improve the accuracy of data acquisition and analysis.

Tidal induced variations in water levels trigger the redistribution of stress in the seabed strata, impacting the stability of the surrounding rock mass during subsea tunnel excavation. Set the Second Subsea Tunnel in Jiaozhou Bay, Qingdao as engineering background, a multiphase large deformation numerical calculation method, Material Point Method, is employed to analyze the destructive response of the tunnel face's surrounding rock mass under tidal influences. Through a comparison between numerical simulations and on-site monitoring data, the feasibility of the Material Point Method for numerical simulation is validated. By simulating water level changes for 196 groups with varying rock mass grades, the study investigates the distribution and characteristics of seabed settlement, rock mass deformation, and the plastic failure zone. The results indicate that: A decrease in water level amplifies the deformation of the subsea tunnel face during the construction period. The combination of water level changes and unfavorable rock mass parameters is identified as a critical factor leading to instability in the subsea tunnel face, revealing 16 sets of parameter combinations that induce significant deformation instability in the tunnel face.

In view of the problem of fracturing and increasing permeability in deep reservoirs, the high-temperature and high-pressure CO₂ thermal shock fracturing technology has shown great development potential with its green and low carbon, high rock breaking efficiency and low vibration noise characteristics. On the basis of considering the combustion of heat source, heat and mass transfer, transient nonlinear flow and rock damage evolution process, the heat source power is defined by the energy release equation based on the concentration change derived from the experimental phenomena, so as to establish the corresponding numerical model of high-temperature and high-pressure CO₂ thermal shock rock breaking, analyses the influence of rock confining pressure and in-situ stress difference field on the crack propagation law of thermal shock fracturing, and reveal the complex fracture formation mechanism. The results show that: The high-temperature and high-pressure CO₂ thermal shock fracturing process is mainly composed of two stages, namely the dynamic fracturing stage under the action of supercritical CO₂ impact force and the quasi-static stage of high-energy CO₂ gas-driven fracture expansion. The initial in-situ stress can inhibit the expansion of radial fractures within the rock under the impact force to a certain extent. The peak fluid pressure and rock fracturing pressure tend to decrease with the increase of the initial in-situ stress difference, and the peak fluid pressure increases with the increase of rock confining pressure.

Weathered granitic soil is widely distributed in south China, which is fissure-rich and water-weakened. In such a special soil, bearing capacity of the commonly used slurry displacement (SD) pile is significantly lessened, while as a new technology, the continuous flight auger (CFA) pile performs superiorly, and even exceed the empirical value range for dry-drilling pile in design code. To reveal the bearing characteristics and mechanism of CFA pile in weathered granitic soil, a series of static load tests and optic fiber-based measurement on the CFA piles were performed in Huangpu District, Guangzhou. The test results show that the ultimate bearing capacity of CFA pile was twice of that of SD pile with the same dimensions, and was positively correlated to pile diameter and pile length. Size effect was not observed in the diameter range of 600 mm to 800 mm. By incorporating the ultraweak Fiber Bragg Grating sensing technique, the shaft resistance was found to follow the unimodal distribution, with the peak driven deeper from GRS to CDG by the increasing load. Ultimate shaft resistances in GRS and CDG were estimated as 128 kPa and 154 kPa, respectively, both exceeding the empirical value ranges in Guangdong/industrial pile design code. The ultimate base resistance in CDG was estimated as 3 080 kPa, double of the empirical value. Based on the soil profile excavated in the field and the CT scan image of undisturbed GRS sample, is attributed to that the associated installation method, where the pumping out of concrete and the withdraw of drill stem are executed synchronously, prohibits the development of fissure water and the resultant deterioration of the soil-pile interface. The bearing capacity of the pile type is better than that of mud pile and other dry working pile.

A microbially induced calcium carbonate precipitation (MICP) grouting reinforcement system was designed and used to perform model tests on MICP reinforced siliceous sea sand under natural seawater conditions. The test results indicated that sand column Φ25×50 cm in natural seawater environment could be solidified by MICP technology, and the sand column was hard. The non-destructive ultrasonic testing revealed that the middle part of the sand column had the highest density after reinforcement, followed by the lower part, and the upper part was the smallest, and the average values of their axial direction wave velocity were 2.993 km/s, 2.877 km/s, and 2.867 km/s, respectively. The average unconfined compressive strength of the sand column core sample was 13.72 MPa, which was 44.88% higher than that of the material size. The average dry density of the sand column was 1.82 g/cm³, which was 18.18% higher compared to the loose sand sample. The permeability coefficient of the sand column was 4.48E-04 cm/s, two orders of magnitude lower than the original specimen. The deposits formed by MICP technology consisted of cubic and columnar calcite, and needle clusters and irregularly flocculent magnesium calcite. Mineral crystals were mainly distributed on the surface of sand particles and between particles, thus playing a cementation role. This study provides a theoretical basis and empirical data to support the improvement of marine loose sandy foundation soils using MICP.

In order to explore the stress state of high-fill culvert under load reduction, the expression of vertical earth pressure on slab culverts under load reduction condition was derived based on the conception of minor principal stress arch and combined with the Marston theory. Physical and mechanical properties of filling, culvert sizes, height of the fill have been considered in the formula. The results show: the vertical stress above the culvert structure is transferred to the soil outside the structure by soil arching effect under load reduction condition, which reduces culvert pressures. The influence range of soil arching effect on the stress in the external soil column is about 0.5 times of the structure width. Vertical earth pressure of structure is distributed evenly along the structure width direction. The soil arching effect is unconspicuous when the filling height on the top of tunnel is less than structure height. When the filling height on the top of tunnel is greater than structure height, the effect of load reduction measures is obvious. And the higher the filling height is, the more significant the load reduction effect is. The vertical earth pressure on culvert increased approximately linearly with the increment of fill height, but the growth rate is slowly. The formula shows certain accuracy and applicability by comparison with field measured values and numerical simulations.

The rapid development of higher education has led to the increasingly tense development of land in colleges and universities, the shortage of accommodation and living space resources for teachers and students, and the development and utilization of underground space has gradually become the top priority in the construction of colleges and universities. This paper clarifies the motivation for the development of underground space in colleges and universities, collates the types and development modes of underground space, compiles the characteristics of underground space in colleges and universities both at home and abroad, and analyses it in the case of a college in Southwest China to predict the trend of the development of underground space in colleges and universities campuses. The study shows that: the development of underground space in colleges and universities needs to pay attention to the continuation of the era, emphasise the synergy of the landscape, strengthen the function of a single underground space, improve the depth of space, create an underground complex with the composite function of "learning-living-communicating", strengthen the connection of multiple points, and take into account the synergy of the whole, and take the underground space of the college campus as a construction whole for planning and designing. A construction whole for planning and design, at the same time, pays attention to the combination of static and dynamic traffic in the development of underground space, to create intelligent underground space, in order to build intensive and high-quality underground space on college campuses. It is only through the construction of intensive and high-quality underground space on college campuses that we can add bricks and mortar to the progress and development of colleges and universities.

A tunnel is affected by the poor geology of the weak fracture zone. During TBM tunneling, problems such as poor self-stability of surrounding rock, easy collapse, and accumulation of slag accumulation occur, resulting in the shield being locked or the cutter head being stuck. To get the TBM out of trouble, the small pilot tunnel construction technology is proposed to carry out new technology of the small pilot tunnel construction from the top of the TBM shield, and the method of long-distance horizontal reinforcement of the bad geology in front of the tunnel face and the cleaning of the slag around the cutter head and shield body is carried out so that the TBM can be smoothly promoted. Under the condition of long and large fault fracture zones, the half-section method construction technology of upper-section excavation and TBM tunneling is proposed to solve the risk of frequent TBM jamming and tunnel collapse. The results show that the construction technology of a small pilot tunnel has the advantages of reducing the risk of jamming, realizing the horizontal advance reinforcement of surrounding rock in front of TBM, shortening the construction period, saving cost and construction.

In order to explore a more safe and effective slope rockfall protection structure, this study is based on the numerical calculation of SPH-FEM coupled dynamics and the 1∶10 geometric similarity indoor model test, aiming at the vibration reduction mechanism of the "sand-foamed rubber" composite cushion shed tunnel. The results show, when the falling rock is impacted at the speed of 20 m/s, the peak stress of the central unit of the roof abdomen can reach 2.89 MPa, which exceeds the ultimate tensile strength of C30 concrete by 2.01 MPa. After adding 0.2, 0.4, 0.6, 0.8, and 1.0 m foam rubber cushion, the peak stress of the central unit is 2.36, 1.12, 0.79, 0.65, and 0.58 MPa, which is 18.34%, 61.25%, 72.66%, 77.51%, and 79.93% lower than that of the pure sand cushion. Add 2, 4 and 6 cm thick rubber cushion at the longitudinal measuring point P1 on the roof belly of the shed during the test, and the peak strain is 50.57 με. It dropped to 27.17, 15.22 and 10.36 με respectively. The decrease was 46.27%, 69.90% and 79.51%. For the transverse test position T1 of the roof abdomen, the peak strain under the composite cushion condition is 48.47 με to 26.54, 17.29, 13.59 με. The composite cushion can significantly reduce the impact energy of rockfall and the stress level of the roof. The model test and numerical calculation results are basically consistent. The suitable thickness for on-site setting of foam rubber under this working condition is 0.4~0.6 m. The research results can provide reference and reference for relevant protective engineering design.

In order to verify the suitability and correctness of plane test and curved surface test in studying the frictional mechanical characteristics of pipe jacking in rock stratum under complex contact conditions, large-scale rock direct shear test was used to study the shear frictional characteristics between plane sandstone and new curved sandstone and concrete pipe under seven kinds of complex contact conditions. On this basis, the mechanical effects of pipe jacking under low contact height and variable contact conditions were numerically analyzed. The results show that the difference of the shape of the specimen results in the great difference of the effective friction angle between the plane test and the curved test. In numerical analysis, it is more reasonable to uniformly set the contact range of pipe jacking to 1/2 contact than 1/3 contact. By comparing the jacking force error of 1/2 contact condition in two types of tests, it can be saw that the average jacking force error based on the result of curved surface friction test is smaller than that of plane test. Finally, it is concluded that the curved surface test has better adaptability in the relationship between test conditions and the quantitative accuracy of test results.

Energy piles realize the integration of shallow geothermal energy development and underground engineering structure, and broaden the use function and application field of pile foundation, so they have been widely used, and at the same time promote the development of energy pile analysis theory. The load transfer method has been applied to the calculation and analysis of energy piles due to its advantages of simple calculation and practicality, but the thermo-mechanical load transfer analysis method still has the disadvantages that the calculation results are difficult to converge and do not accurately reflect the actual loading at the top of the pile. The reasons for the pile top error were analyzed, and the iterative method for eliminating the unbalanced force at the pile top of energy piles was established based on the load transfer displacement coordination algorithm of energy piles, so that the calculation results could accurately reflect the actual loading conditions at the pile top, which made the analysis of the thermo-mechanical coupled bearing performance of energy piles more accurate. Combined with the field test, the feasibility of the iterative method for eliminating the unbalanced force at the top of the pile is verified, and the calculation results show that the method can well reflect the effect of the combined load-temperature action on the bearing performance of energy piles.

The open grouting of bridge cast-in-place piles is difficult to control the grouting area, grouting pressure and grouting amount. The stability of grouting effect is poor and the bearing capacity of single pile fluctuates greatly. In order to improve the reliability of post grouting of pile foundation, a new type of composite post grouting technology at pile bottom is proposed. By installing hollow annular steel plate capsules at pile bottom, the soil at pile end is strengthened through the composite inside and outside of the capsule. To reveal the improvement effect on the bearing capacity of pile foundation, composite post-grouting operation of two test piles was conducted at S340 overpass bridge project of Fenshi Expressway under construction. The dynamic changes of grouting pressure, grouting volume and pile top displacement during grouting were analyzed, and the grouting effect was tested by elastic wave CT. Then, the vertical static load tests of pile foundation were carried out under post-grouting and non-grouting conditions. The results show that the composite post-grouting at the pile bottom can effectively eliminate the sediment at the pile bottom and form an expansion pile end. The bearing capacity of the pile foundation is increased by 34.1%. The pile end resistance enhancement coefficient is 1.70, and the pile side friction enhancement coefficient is 1.32~1.37 within the influence range of the slurry.

To study the detection and evaluation methods for the effectiveness of karst cave grouting treatment, this article conducted on-site drilling core detection and high-density electrical method indoor model test research on the karst grouting treatment section of a certain project. This article first tested and analyzed the grouting effect of the karst cave in the treatment section through drilling and coring, and found that the grouting treatment effect of the karst cave in the section was relatively good; Then, combining digital modeling and 3D printing, the construction of a karst cave model was achieved, providing a reference for indoor karst model experiments; Finally, based on the evaluation method of high-density electrical method for detecting the effectiveness of karst grouting under different slurry filling conditions was deeply studied through indoor model experiments. The results indicate that the apparent resistivity value at the location of the karst cave after grouting will decrease to a certain extent compared to before grouting, and the area of high resistivity anomaly will decrease; As the amount of grouting in the karst cave increases, the time for the apparent resistivity image to reach stability at the grouting site of the karst cave is correspondingly prolonged. Usually, when the karst cave is completely filled with cement slurry, the apparent resistivity image will reach stability 7 days after grouting. This study provides a certain reference for optimizing the detection and evaluation methods of karst grouting effectiveness.

Based on the field process test of the south anchorage foundation of Zhangjinggao Yangtze River Bridge, the key technology in the construction of ultra deep special-shaped grid joint diaphragm wall was innovated and verified. The results show that: The combined construction process of trench cutter and hydraulic grab can ensure the verticality of the ultrasonic irregular groove section and the stability of the groove wall by reasonable setting construction sequence, introducing virtual collision detection technology for slot segments based on composite detection methods and extended guide frame and strengthening mud performance control and other control measures, the verticality and stability of ultra deep special-shaped panel trench can be ensured. The inclinometer and three-dimensional hydraulic jack are used to adjust the posture of the rigid joint, and the guide device is used to assist the rigid joint to enter the trench, so that the precision can be measured and controlled during the installation of the rigid joint. Intelligent synchronous welding technology can effectively control welding deformation and optimize welding quality. The relative position relationship between rigid joints and reinforcement cages can be effectively controlled on the basis of matching fabrication of reinforcement cages, supplemented by verticality monitoring means. The special wall brushing device is used to clean up the sludge at the row inserted reinforcement, and the synchronous pouring platform is used to realize the synchronous pouring of each compartment of the rigid joint, which is conducive to the improvement of the pouring quality and the structural safety control of the joint. The concrete bypass channel can be blocked with anti flowing water tape, which can effectively prevent the concrete from polluting the rebar at the joint and ensure the strength and integrity of the diaphragm wall. Later excavation tests have verified that the construction control measures proposed in this article can effectively ensure the quality of the diaphragm wall and the bearing capacity of the joints.

The formation mechanism of rock disintegration phenomenon of surrounding rock in deep rock mass tunnels has always been highly controversial. The article explores this issue theoretically from the perspective of stress wave propagation. A physical model of stress wave propagation in the surrounding rock of a semi-circular tunnel was established. The wave equation of the surrounding rock area was solved, and the amplitude distribution of stress waves in the surrounding rock area of the tunnel showed a characteristic of wave attenuation. The innovative proposal was made for the width and theoretical depth of the fracture zone in the surrounding rock area of the tunnel. Taking Dingji Mine as the object, the theoretical calculation of the central radius of the surrounding rock partition was carried out and compared with the measured results. Most of the partition radii were in good agreement. The research results of this article have a certain promoting effect on the theory of zoning and fracturing of surrounding rock in tunnels.

In order to reasonably predict the surface settlement caused by the construction of large-diameter slurry shield, this paper conducts regression analysis on the actual measured data in the field and studies the adaptability of Peck's formula in the prediction of settlement of large-diameter slurry shield, while introducing the correction factor α for the maximum surface settlement and the correction factor β for the width of the settlement trough to correct Peck's formula. The results show that: There is a significant difference between the measured settlement value of large diameter slurry shield tunneling in upper soft and lower hard composite strata and the predicted settlement value of Peck formula after linear regression. When the value of α is distributed between 0.1 and 0.5 and the value of β is distributed between 0.5 and 1.0, it can better reflect the surface settlement deformation of large diameter slurry shield in the upper soft and lower hard strata. By comparing and analyzing the correction coefficients of settlement trough for small diameter and large diameter shield tunnels, it can be seen that the variation range of the correction coefficient of settlement trough increases with the increase of the excavation cross-sectional area and the difference in soil properties of the excavation surface. The research results can expand the application scope of the Peck formula and provide a reference for the design and construction of large diameter shield tunnels.

In order to provide reference data for the fire protection design of corrugated steel utility tunnels, the damage and deformation laws of a corrugated steel utility tunnel under fire were studied. Based on FDS software, the fire dynamic model of the power compartment of the circular corrugated steel utility tunnel was established, and the temperature evolution of the compartment in the case when the fire extinguishing system fails was obtained. The results show that when the cable fire occurs, the fire spreads upward rapidly, and the maximum temperature can reach 1 000 ℃. And the fire can last for 20~ 25 min. On this basis, the general finite element software ABAQUS is used to establish the thermal-mechanical coupled model of corrugated steel utility tunnel. The temperature boundary obtained by FDS simulation is input, and the influence of temperature on various material properties of corrugated steel is considered comprehensively. The structural mechanical properties of corrugated steel utility tunnel under fire are simulated. The results show that the temperature of corrugated steel increases rapidly, and the elastic modulus and strength decrease accordingly. When the fire continues to burn for 4 ~ 5 min, the corner of the inner ground and the middle partition wall of the power compartment of the utility tunnel will yield first. At about 7 minutes, the bearing capacity of the steel structure decreases rapidly, and then the deformation of the steel structure developed rapidly until it was completely destroyed Especially, the horizontal displacement of the tunnel waist was large. Along with the yield failure of lining structure, the pavement above the utility tunnel also appears large settlement displacement.

A field investigation was conducted on the temperature distribution of the high-temperature tunnel environment during the construction period, and a three-dimensional numerical model for single-head ventilation of the high-temperature tunnel during the construction period was established after quantifying the heat source based on the construction conditions. After verifying the reliability of the numerical model, a study was conducted on the distribution characteristics of tunnel temperature and optimization of ventilation parameters. The results show that: (1) The environmental temperature distribution along the tunnel can be divided into two sections. Within the first 20 meters from the heading face, there is a sudden increase followed by a decreasing trend, while from 20 meters beyond the heading face to the tunnel entrance, there is a trend of initial increase, followed by a decrease, and then a continuous increase with decreasing inlet air temperature or increasing airflow; (2) Decreasing inlet air temperature leads to a linear decrease in the peak environmental temperature within the tunnel, while increasing airflow results in a quadratic decrease in the peak environmental temperature, indicating that inlet air temperature has a more significant impact on the peak environmental temperature within the tunnel compared to airflow; (3) Utilizing a multivariate function, we established a predictive model for tunnel environmental temperature considering the coupling effects of airflow and inlet air temperature. The model suggests that when the inlet air temperature is ≤15 ℃, an airflow rate of >40 m³/s is sufficient to meet the construction requirements for the tunnel environment. However, when the inlet air temperature exceeds 20 ℃, additional cooling measures are necessary.

Research on frozen geotechnical material is focused on guaranteeing the security of civil engineering and preventing of geological hazards in cold regions. The acoustic emission (AE) tests of the ice, ice-rock mixture, frozen soil, and frozen soil-rock mixture samples were carried out under Brazilian splitting conditions. The characteristics of crack evolution, acoustic emission energy and, b-value were discussed. The results show that: (1) The cracks in the ice-rock mixture and frozen soil-rock mixture are more tortuous than those in ice and frozen soil. (2) The crack in the ice-rock mixture is mainly distributed inside the ice near the ice-rock interface. Moreover, the tensile strength and acoustic emission energy of the ice-rock mixture are larger than that of ice. (3) The crack of frozen soil-rock mixture is composed of frozen soil crack and soil-rock interface crack. The frozen soil-rock interface is the weakest part inside the frozen soil-rock mixture, which leads to the acoustic emission energy of the frozen soil-rock mixture is smaller than that of frozen soil. (4)The acoustic emission energy peak of ice and ice-rock mixture being consistent with the leading peak and shows an obvious single peak pattern. Nevertheless, in the case of frozen soil and frozen soil-rock mixture, the acoustic emission energy peak lags behind the loading peak and display a multi-peak feature. (5) The b-values of all the samples decrease with the increasing loading in the pre-peak region, and then show an increasing trend with the decreasing loading in the post-peak region. Furthermore, the amplitude of the b-value of frozen soil-rock mixture is larger than that of others. It can be postulated that the alternating crack growth of soil and interface cracks triggers the different acoustic emission energy.

The tensile strength of soil is significantly lower thanits compressive and shear strengths, leading to its frequent neglect in theoretical and experimental research. This paper provides a comprehensive review of both direct and indirect methods for measuring soil tensile strength, comparing and analyzing the advantages and disadvantages of existing testing techniques. Our findings indicate the following: (1) The uniaxial tensile strength of soil can be categorized into vertical and horizontal methods based on the direction of applied force. The vertical method's accuracy is compromised by the weight of the soil sample above the failure plane. (2) Common methods for securing soil samples include bonding, anchoring, friction, and clamping, with clamping proving to be more convenient and practical than the other techniques. We recommend optimizing the horizontal uniaxial tensile test due to several issues, such as soil sample loss during preparation and demolding, uneven stress distribution across the tensile section, inapplicability to large-aggregate gravelly soils, cumbersome sample fixation, and challenges in minimizing friction between the soil sample and the testing platform.

In order to study the distribution features of sinking resistance of caisson in soft clay area, taking the open caisson of a comprehensive pipe gallery in Ningbo as the research object, the basic soil experiments of open caisson were carried out. The results show that the basic mechanical parameters of soft soil were obtained through direct shear test and conventional triaxial test; The sinking process of the open caisson is monitored in real time, the stress mechanism of the sinking process of the open caisson is deeply analyzed, and the distribution laws of shaft wall side friction and blade foot end resistance at different depths of the open caisson are obtained. At last, based on the test data, when the open caisson foundation sinks through the silt soil layer is put forward σ_f0 changes with the sinking depth, and the corresponding empirical formula is fitted. The test results show that the lateral resistance of the caisson has not yet reached the maximum value during the sinking process, and the lateral resistance of the caisson relative to the two sides is not the same. The research results can be used to provide a reference for the same kind projects.

With the rapid development of urban underground space in China, the implementation of detailed planning for underground space has become an important issue in planning management. However, due to unclear responsibilities, insufficient technical support, and weak regulation enforcement, it is difficult for the planning to be implemented smoothly. Therefore, a "clarifying responsibilities, strengthening technology, refining regulation" framework and approaches are proposed to improve the implementability of underground space detailed planning. Regarding clarifying responsibilities, subjects should be identified based on project attributes and coordination mechanisms should be established. Regarding strengthening technology, emphasis should be placed on preliminary technical demonstration and economic benefit analysis. Regarding refining regulation, reasonable arrangement of implementation timeline, differentiation between rigid and flexible elements, and strengthening constraints in land supply should be adopted. Finally, the applicability of this method is illustrated by a case study of the Qianhai Shenzhen-Hong Kong Modern Service Industry Cooperation Zone. The proposed approaches to improve implementability of underground space planning can provide scientific basis for underground space planning in China and help optimize planning content and improve enforceability and applicability.

In order to study the enhancement effect of different annular joint structures on the longitudinal stiffness of shield tunnel, the influences of section diameter on the longitudinal tension and compression, longitudinal shear and longitudinal bending stiffness of tunnel are calculated by equivalent continuous model. The longitudinal stiffness enhancement measures are related to the annular joint structure of segment. Additionally, the mechanical properties of nine annular joint structures are deeply explored by numerical simulation, and the annular joint structure with the best effect of enhancing the tunnel longitudinal stiffness is obtained by comparison. The results show that the diameter has little effect on the longitudinal tension and compression and longitudinal bending stiffness, but has a great influence on the longitudinal shear stiffness. The stiffness enhancement measures of the circumferential joint can significantly reduce the displacement of the segment and improve the tunnel longitudinal stiffness. The enhancement effect is: oblique bolt > bend bolt, positioning tenon > shear pin > concave tenon; at the same time, both the bolt type and the longitudinal stiffness enhancement measures have a great influence on the maximum shear stress of the bolt.The shear stress of the bolt is significantly influenced by the bolt type at vertical load and is significantly influenced by the longitudinal stiffness enhancement measures at horizontal load. Combining economy and effectiveness, when the joint bolt is a curved bolt, setting the positioning tenon is a relatively better choice.

Underground space evaluation is a crucial step in developing underground spaces. Over the past two decades, several Chinese cities have conducted underground space suitability evaluations on different scales. However, due to unclear evaluation semantics, disparities in geological conditions, and technical personnel, these cities have used different evaluation indicators and methods for the evaluation process, which has restricted the promotion and application of the evaluation results. This paper proposes a system theory-based approach to evaluate the geological suitability for underground space development. It suggests that the evaluation of the system's ability to maintain a relative balance under external disturbances is critical, and it identifies specific evaluation elements and contents to address this objective. The paper focuses on the key issues of hierarchy organization, grain selection in the evaluation index system, method selection, optimization, and verification of the evaluation index system, which ultimately leads to the construction of a set of evaluation method procedures. The practice of Jiangdong New District in Haikou validates the method of dividing the first criterion layer into "restriction level, security level, cost level" and calculating weight by "composite iterative entropy weight method". This approach, which reflects the guidance of professional knowledge and the objectivity and differentiation of data, can provide guidance for the geological suitability evaluation of underground space development in coastal plain cities in China.

With the increase in the number of urban rail transit users for commuting purposes, the rapidly changing and large-scale short-term rapid increase passenger flow in rail transit stations during peak hours makes it difficult for transfer stations to safely, stably and effectively accommodate passenger flow and meet the needs of transferring. The characteristics of passenger flow and its effect on stations were analyzed through field research and simulation by Anylogic. Based on prefabricated, assembled, foldable and other transformation technologies or equipment, the spatial transformation in the field of space and facilities is proposed. The research establishes the relevance between transformation application scenarios and technologies and measures, and explores the application of space variability in dynamically optimizing the transfer space in underground rail transit stations. The results can provide reference for the optimal design of existing urban rail transit stations in the future.

In order to address the problem of the influence of multi-field coupling in high-ground stress areas on the rupture range of deep-seated surrounding rocks, a mechanical analysis model of the plastic zone of surrounding rocks under multi-field coupling is established based on the double-shear unified strength theory, and a formula for calculating the radius of the plastic zone of surrounding rocks in deeply buried tunnels under the action of heat-force coupling is proposed. On this basis, the rupture zone radius calculation formula for the rupture of surrounding rocks in deeply buried tunnels under the action of heat-force coupling is further proposed. Combined with the analysis of engineering examples, it can be seen that, under the action of heat-force coupling, the error of the fracture radius of the surrounding rock zoning calculated based on the double-shear unified strength theory is less than 8.9%, which proves the reasonableness and feasibility of the calculation method proposed in this paper. The research results provide a theoretical basis for the analysis of the stability of the surrounding rock under the influence of high ground stress and high ground temperature and also provide a new method and means to quantitatively describe the phenomenon of zonal rupture.

In order to reveal the rock breaking mechanism of hydraulic fracturing, a set of indoor rock hydraulic fracturing physical simulation system was established by using a true triaxial loading system, acoustic emission instrument and high pressure piston pump, which can study the rock breaking mechanism of hydraulic fracturing. Based on the Griffith strength criterion, the critical water pressure and the location of rock fracture initiation are established. The experimental results are as follows: When the water pressure is far below the critical pressure, the acoustic emission characteristics of sandstone are more obvious in the rising period of water pressure, and the acoustic emission characteristics of sandstone are quiet in the maintaining period of water pressure, and the signal is that the primarily closed microfractures of sandstone are pressed open; When the water pressure is close to the critical pressure, the impact number, amplitude and energy of acoustic emission of sandstone increase in the rising period and maintaining a period of water pressure, and the signal is the expansion and coalescence of new fissures caused by sandstone fracture; The direction of fracture initiation and propagation is perpendicular to the direction of the minimum principal stress, and the primary fractures control the direction of fracture initiation and propagation. The research results provide a reference for the hydraulic fracturing treatment of coal mine fine sandstone thick main roof.

Accidents frequently occur in the operation and maintenance of urban underground utility tunnels. To quantify the operation and maintenance risks of utility tunnels and analyze the key risk factors, a risk assessment method for the operation and maintenance of urban underground utility tunnels based on fault tree and fuzzy Bayesian network was proposed. A fault tree was constructed based on comprehensive consideration of the risk factors of tunnel, and it was mapped to a Bayesian network. Then, the risk factor status was classified based on ALARP criteria, fuzzy number and fuzzy subset were used to calculate the probability of occurrence of bottom events, Maximum Likelihood Estimation was used to solve the conditional probability of intermediate events, and a Bayesian network model was constructed for operation and maintenance risk of utility tunnels to assess the operation and maintenance risk of urban underground utility tunnels accurately. The results show that the probability for the assessed risk level of utility tunnels’ operation and maintenance process is High is 28%, which was close to the risk threshold of 30%. Therefore, it is necessary to control the risks of the utility tunnels timely. This method can scientifically and reasonably evaluate the risk level and determine the key factors, and can be used as a decision-making tool for the safety assurance and management of the utility tunnels’ operation and maintenance.

The water absorption and softening and volume expansion characteristics of the red mudstone are prone to cause the phenomenon of slurry mud and uneven settlement of the roadbed and other diseases, so it should be improved when used as highway roadbed filler. In this paper, fly ash was chosen as an improver to analyze the compositional composition and ionic content of red-bedded mudstone and fly ash through indoor X-ray diffraction tests, chemical composition tests and easily soluble salts. The physical and mechanical properties of the specimens before and after improvement were analyzed by unconfined compressive strength tests, indoor variable head penetration tests and consolidation tests. The effects of different fly ash admixtures on the shear stress-strain gauge shear strength of the modified specimens were investigated by conventional triaxial UU tests; the effects of the age of maintenance on the shear strength parameters of the modified tests when the fly ash admixture was 10% were analyzed. The results show that the red mudstone in the area is a low liquid-limit clay with the highest SO₄^2- ion content and alkaline pH in its labile salt solution. In triaxial shear test, both modified and unmodified specimens showed plastic damage, and both the amount and age of fly ash admixture of the specimens contributed to the increase of shear strength of the specimens, and the increase of cohesion was much larger than the internal friction angle. The cohesive force of the specimens at the age of 28 d with 10% fly ash was 37.9% and 6.9% higher than that of the unmodified unmaintained specimens and 10% unmaintained specimens, respectively, and the internal friction angle increased by 1.2° and 0.7°. The hydrostatic experiments of the specimens all verified the reliability of the fly ash improvement.

The cutterhead is prone to mud cake problems when the shield is tunneling in the cohesive stratum. In severe cases, the cutterhead is blocked to reduce the shield tunneling efficiency and affect construction safety.During the process of the slag adhering to the cutter head, it is accompanied by the solidation and hardening of the mud cake. To find out the influencing factors of consolidation and hardening of mud cake in shield cutterhead, laboratory tests are carried out by using a self-made cutter head tunneling simulation device. The relationship between soil properties, temperature, cutterhead earth pressure, and consolidation and hardening characteristics of mud cake is studied. The experiment of soil conditioning is carried out to explore the influence of different soil conditioners on the degree of consolidation and hardening of mud cake. The results show that the water content and cone penetration depth of mud cake can characterize the consolidation and hardening characteristics of mud cake. The properties of the soil have the greatest influence on the degree of consolidation and hardening of the mud cake formed by the cutterhead after excavation, followed by the temperature, and the cutterhead earth pressure has stratigraphic differences on the degree of consolidation and hardening of the mud cake. The foam agent has an obvious effect on the consolidation and hardening of pure clay and sand-containing clay cake, while the dispersant only has an obvious effect on pure clay.

To calculate the ultimate bearing capacity of pile foundation in karst areas, a simplified analysis model is proposed, which fully considers the influence of the distance between the pile and the karst cave on the bearing capacity of pile foundation. Based on the upper bound limit analysis, the corresponding assumed failure mode is proposed. The triangular rigid block is used to discrete the failure mode, and the external force power and internal energy dissipation rate are calculated. Taking the ultimate bearing capacity of pile foundation as the objective function, the problem is transformed into a mathematical optimization model, which is solved by the MATLAB software. To verify the correctness of the present method, the calculation results of the present analysis are compared with those from the upper bound finite element limit analysis. Finally, the influence of material parameters and geometric parameters on the ultimate bearing capacity of pile foundation is analyzed. The parameter analysis shows that with the increasing distance between the pile and the karst cave, the influence of the karst cave on the bearing capacity of the pile tip becomes smaller and smaller. When the distance between the pile and the karst cave exceeds a certain value, the ultimate bearing capacity of the pile tip will not be affected by the karst cave.

With the continuous development of cities, the convenience of rail transit as a public infrastructure is increasingly prominent. The emergency evacuation capability of underground stations in subway areas is of great significance for the safe, normal, and low-risk operation of urban rail transit. Subway stations are key nodes in rail transit, and due to their mostly underground location, the safe evacuation after an accident during operation is more difficult. In order to develop a more scientific and reasonable subway emergency evacuation plan, this paper conducts an in-depth analysis of relevant research on emergency evacuation in underground stations in domestic and foreign subway areas and summarizes the main influencing factors of emergency evacuation in underground stations. Due to the multi-disciplinary and multi-disciplinary issues involved in evacuation in underground spaces, the paper discusses and summarizes the aspects of personnel behavior, subway station facilities, and subway station disasters. By comparing the research on emergency evacuation in subway stations by different scholars at home and abroad, combined with the three elements of human, machine, and environment, this paper proposes existing research problems and solution strategies, which have good reference value for the formulation of emergency plans for underground stations in subway areas in the future.