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.

Ensuring that the pressure drop between the model and the original shape is equal is currently a challenge in long tunnel model tests that follow the Reynolds criterion. Therefore, this article proposes to install a throttling port at the air outlet to simulate the extension of the model tunnel length. On a tunnel ventilation model, complete 5 sets of experiments on the area ratio of the throttle opening to obtain the average wind speed, static pressure, and wind speed at the throttle opening; Using this as the boundary condition, the area ratio of the throttling port was further expanded to 9 groups, quantifying the influence of the area ratio on the flow field parameters, and establishing the relationship between the area ratio and the local resistance of the throttling port. The results show that when the area ratio is between 0.108 and 0.192, the calculated equivalent length of the tunnel model increases sharply; When it is less than 0.108, the calculated value of equivalent length diverges with the variation of fan frequency, determining the applicable range of area ratio of the calculation model; Finally, a formula for calculating the equivalent length of tunnels with an area ratio of no less than 0.108 was obtained. This formula greatly broadens the length of the tunnel ventilation model and provides important experimental fluid dynamics references.

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.

The comprehensive management of underground pipelines is a top priority in China's infrastructure construction. Compared to excavation repair technology, trenchless technology has the characteristics of small environmental impact, short construction period, and low comprehensive cost for the repair and renewal of underground pipelines. In this review, the current research on trenchless technology at home and abroad were analyzed, including in situ solidification method, winding method, insertion method, broken pipe method, spraying method, patch method, casing method, robot method, and grouting method. The advantages and disadvantages of trenchless technology and its development and application status at home and abroad were also discussed. Through the analysis of current domestic and international trenchless technology, some suggestions are provided for the development of trenchless technology in China.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

The soil and groundwater in the northwest region of China contain high concentrations of Cl^-, SO₄^2- and Mg²⁺, and the aggressive ions will penetrate into the tunnel lining concrete, seriously threatening the service life of the concrete structure. In this paper, orthogonal tests were used to investigate the effects of water-cement ratio, silica fume mixing amount and fly ash mixing amount on the performance of lining concrete. In order to better simulate the actual environment, five different types of composite salt solutions containing Cl^-, SO₄^2- and Mg²⁺ were prepared, and the optimal combination of factors in the orthogonal test was selected to carry out a study on the change rule of the compressive strength and the chloride concentration in the surface layer after 56 days of erosion, and the micro-analysis of the erosion process was carried out by using Scanning Electron Microscope (SEM) and X-ray diffraction (XRD). The results show that the mechanical properties and anti-chlorine ion erosion performance of lined concrete are best when the water-cement ratio, fly ash dosage, and silica fume dosage are 0.33, 30%, and 8%; when the concrete is under the joint action of Cl^- and SO₄^2-, the expansion of the hydration product calcite destroys its internal structure, which results in the decrease of the compressive strength and the acceleration of the rate of Cl^- invasion; and under the joint action of Cl^- and Mg²⁺, the Mg²⁺ invasion will destroy the alkaline environment inside the concrete, which will also cause the reduction of compressive strength, but its product Mg(OH)₂ will hinder the invasion of Cl^- into the interior of the material. When Cl^-, SO₄^2- and Mg²⁺ act together, Mg²⁺ and SO₄^2- can inhibit the erosion rate of Cl^- to different degrees, respectively, while SO₄^2- and Mg²⁺ exist in a compound effect of mutual inhibition, which makes it possible to effectively reduce the loss of compressive strength of concrete.

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.

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.

In order to realize the "Double Carbon" strategy, the state is gradually taking measures to reduce the proportion of coal-fired thermal power and increase the use of clean energy such as solar energy and wind energy. In recent years, due to the temporal and spatial uncertainty of renewable energy and the lack of large-scale energy storage facilities, the phenomenon of abandoning wind and power (abandonment of light) is becoming more and more serious. In order to improve the utilization rate of wind and solar energy, it is proposed to use abandoned coal mine goafs as an underground large-scale pumped hydro storage reservoir in areas rich in solar and wind energy to promote the combined use of available energy. The storage capacity of the goaf as a large-scale pumped hydro storage reservoir is analyzed from the aspects of storage capacity, usable capacity and gas-liquid exchange in the goaf. Combined with the characteristics of goaf and related meteorological characteristics of typical abandoned coal mines in China, the energy storage characteristics of underground reservoirs in goaf are analyzed. It has been found that using abandoned coal mine goafs to develop pumped hydro storage plants is technically feasible in wind and solar-rich northwestern and southwestern China.

The green and healthy development of urban underground space is an inevitable requirement to practice the concept of "green water and green mountains are golden mountains and silver mountains" and strive to build a modern harmonious coexistence between man and nature. In view of the current unsystematic and imperfect theoretical system of green construction of underground space in China, the "Three Three" concept of green construction of underground engineering is proposed, that is, in the three stages of planning, design and construction, the three elements of environment, resources and cost are fully considered, and the three basic principles of the principle of cost minimization in the whole life cycle, the goal orientation of "four sections and one environmental protection" and the sustainable development concept of harmonious coexistence of "people, buildings and nature" are followed. In addition, through the investigation of relevant cases and technologies of green construction at home and abroad, the technical system framework of three stages of green planning, green design and green construction of underground projects was systematically built, and the relevant green technology practices were summarized. The concept of green construction of underground engineering and the green construction technology system proposed in this paper can fill the deficiencies of the theory in the field of green construction of underground engineering, with a view to providing some guidance and practical reference for the green construction of underground space in China.

Static blasting technology can be used for weakening and fracturing of underground coal and rock mass. Compared with explosive blasting, it has the advantages of safety, no vibration and no pollution. In order to explore the cracking effect of hard rock weakening and practical engineering application technology of static blasting, through laboratory tests, numerical simulation and field tests, the expansion mechanical parameters of static crushing agent, the crack evolution law and failure range of static crushing agent on specimens under different aperture and hole spacing, and the selection of field hole layout parameters were studied. The results show that the maximum expansion pressure of the static crushing agent can reach 75 MPa, and the reaction process is divided into three stages, initial stage, rapid reaction stage and subsequent slow reaction stage. The crack development direction of the specimen is along the direction of the minimum resistance line, and the crack expansion shape is mostly ‘Y’ shaped. In acoustic emission detection, the cumulative energy increases step by step, and its peak value decreases with the increase of broken hole diameter. The effect of rock breaking and fracturing is better when the pore size of the crushing hole is controlled at 40~50 mm and the row spacing is controlled at 300~500 mm. The research results confirm the feasibility of static blasting scheme for weakening and fracturing of rock strata, which has certain reference value for practical application.

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.

The excavation and support construction of giant underground caverns in large-scale hydropower projects is a key route and a concentrated area of technical difficulties in engineering construction. Improving the excavation and support methods and construction machinery of underground power plants based on the actual geological conditions and working environment on site is an important guarantee for ensuring the safety, quality, efficiency, and green construction of underground caverns. This paper carried out innovative research, development and tackling of key construction methods and technical problems in the construction process of large underground caverns of Wudongde Hydropower Station, which included the excavation and construction of large-span high sidewall, excavation and construction of super large section surge chamber, excavation of small diameter slag chute shaft, support of super large section caverns in unfavorable geological sections, pipe pulling contact grouting construction, penstock assembly in the tunnel, concrete slip form construction of porous deep shaft and large outlet shaft construction, etc. Common key innovative construction methods and technologies from aspects such as process type, fine excavation, support, and equipment innovation technology were summarized. The research results could provide the reference for similar engineering construction.

Taking the underground powerhouse of the Dadu River Shuangjiangkou Hydropower Station as a research object, using single-hole acoustic wave tests to investigate the wave velocity attributes of the unloaded perimeter rock post-cavern excavation under high geostress. This evaluation allows us to pinpoint the extent of the Excavation Damage Zone (EDZ) within the perimeter rock and discern its evolutionary patterns under the influences of stress redistribution and proximity blasting, along with understanding the unique traits of the EDZ across varied regions. By leveraging the finite difference numerical analysis method, we probe into the mechanisms of EDZ formation. This approach exposes the implications of blasting load, transient geostress unloading, and stress redistribution on the EDZ of the surrounding rock under high geostress conditions, considering both individual and concurrent effects of these factors. The findings of this research hold significant theoretical and practical merit, offering crucial technical insights for enhancing the safety evaluations.

The development achievements of sensor technology, Internet of Things, big data, and artificial intelligence have been widely applied in the field of tunnel construction engineering, promoting the development of digital twins for smart tunnel ventilation systems. This study aims to explore the application of digital twins in intelligent ventilation systems for tunneling to achieve accurate regulation of ventilation parameters and enhance safety and efficiency in construction environments. This paper took the fundamental related to establishing the digital twin of construction tunnel ventilation systems and the current situation analysis of intelligent ventilation as the point of penetration. The digital twin framework of an intelligent ventilation system for tunneling with computation-measurement complementary was proposed, which consisted of five modules: physical space, virtual space, data fusion, mechanism model and application services. To effectively implement the digital twin, the research designed the architecture of the intelligent ventilation digital twin management platform and introduced a real-time data-driven multidimensional fusion model to achieve accurate mapping of states and behaviors between the virtual and physical spaces. Based on the proposed theories and methodologies, the study conducted practical application and validation in a real tunnel construction ventilation system. By integrating the developed intelligent ventilation twin model into the construction management platform, successful applications were achieved. Consequently, this study provided a new method for ventilation management in construction tunnels by integrating digital twins into daily ventilation management.

Large deformation of layered rock mass is a common engineering disaster in tunnel construction, especially in high in situ environment. Due to the influence of high stress and bedding structure, the surrounding rock of the tunnel will undergo typical failure modes such as extensive cracking, shearing, and buckling along the bedding planes, resulting in the failure of the support structure, seriously endangering personal safety and restricting the progress of the project. To fully understand the characteristics of large deformation of high stress layered rock masses and guide on-site construction, the current research status at home and abroad was reviewed and summarized from the geological and mechanical characteristics of layered rock masses, the characteristics, mechanisms, grading, and prevention and control of large deformation of layered rock masses. In response to the existing problems and new development trends in the mechanism and prevention of large deformation of high stress layered rock masses, key scientific and technological issues that need to be urgently addressed were discussed.

In order to implement the requirements of the 20th National Congress of the Communist Party of China for building high-quality urbanization with a human centered approach, and to fully utilize underground space to build altitude cold canyon cities into green, low-carbon, ecological, and flexible cities, it is urgent to probe methods for evaluating the potential of urban underground space resources of altitude cold canyon cities and present multidimensional utilization strategies. Taking Ping'an District of Haidong city, a canyon city with high cold, drought, water scarcity, limited land, fragile ecology and frequent natural disasters as an example, with specialized urban geological surveys, field observations and experiments, based on the identification of urban geological conditions of Ping'an District, a new method for evaluating potential of underground space resources in high-cold canyon cities are proposed. The evaluation shows that the potential underground space resources in the mountains on both sides of the Huangshui River Valley in Ping'an District, Haidong City are 597.87× 10⁶m², with a potential underground space resource of 167.58×10⁶m² at the bottom of the river valley;The shallow underground space resources in the urban core area are little potential, and the areas with great potential are mainly distributed in the deep layers at the bottom of the river valley or in the mountains on both sides of the river valley. The utilization strategy of underground space is to make as much use of underground space as possible to leave more surface space for the construction of ecological green spaces, develop underground agriculture to solve the problem of insufficient local agricultural products, and use the deep underground space at the bottom of the Huangshui River Valley to build water storage projects, as well as emergency response projects for urban floods or emergency water source storage facilities. The research results can provide theoretical and methodological guidance for the utilization of underground space in high-cold canyon cities.

In order to explore the coupling and coordination relationship between underground public spaces and rail transit in the old city center, the principles of coupling and coordination forced from physics are applied to analyze the integration of underground public spaces and rail transit in the city center. A coupling evaluation model and indicator system are constructed from four aspects: scale, form, intensity and equilibrium. Taking into account the phased characteristics of the integrated system in Xinjiekou central area, four time points, namely 2005, 2010, 2014, and 2019, are selected to calculate the coupling degree, which are 0.830 8, 0.896 3, 0.935 1, and 0.892 1, respectively. The coupling degree decreased in 2019, while the coupling coordination degree showed an increasing trend of 0.482, 0.555 6, 0.650 4, and 0.676, respectively.The reason for this trend is that although the early development of rail transit has driven the exploration of the scale and environmental quality of underground public spaces, the improvement of indicators such as the scale and form of the urban rail transit network falls short in the short term, limiting the level of integrated development. Based on this, optimization strategies for the integration of underground public spaces and rail transit in the Xinjiekou central area are proposed.

The friction strength characteristics of gravity anchorages of suspension bridges at the contact surface between concrete and gravel soil have a decisive influence on the slip resistance stability of the anchorages. In order to study the friction strength characteristics of the contact surface between gravel soil and anchor concrete and to determine the friction coefficient of the contact surface, this paper carried out the shear fracture test, shear test, and reciprocating shear test of the contact surface between concrete and gravel soil, analyzed the change rule of the stress-displacement law of the three test phases, and utilized the least-squares method to fit the τ vs. σ relationship curve to obtain the friction coefficient of the contact surface. The result shows that in the shear resistance test, the contact surface showed strain softening phenomenon and pressure embedding effect in the shear damage process, and the depth of pressure embedding ranged from 2 mm to 5 mm; in the shear resistance test and reciprocating shear test, the contact surface did not show significant strain softening phenomenon, and the concrete was mainly sliding horizontally on the contact surface; in the shear section, the shear resistance, and the three phases of reciprocating shear test, the friction coefficient of the contact surface was calculated by the relationship curve between the concrete and the adhesion (c) of the contact surface decreased significantly, and the value of the friction coefficient f decreased at a rate of 1% to 2%, indicating that the occlusion and embedment of the contact surface was weakening; the value of the pure friction strength parameter f (0.48) in the reciprocating shear test was selected as the friction coefficient of the contact surface between concrete and gravel soil.

The subgrade structure of asphalt concrete roads in southern Xinjiang is affected by the coupling environment of water, salt, and temperature in the special saline soil environment in southern Xinjiang, the subgrade structure is damaged under the action of dry-wet cycles and salt-freeze-thaw cycles. The developed water-salt-temperature multi-field coupling test system is used to simulate the unique coupling environmental effects of dry-wet cycles and salt-freeze-thaw cycles in saline soil environment in southern Xinjiang, the damage and failure test of asphalt concrete road subgrade structure samples under the action of salt-freeze-thaw cycles environment is carried out. The results show that the distribution of water and salt in a salt-freeze-thaw cycle has obvious variation characteristics along the height of the subgrade structure, the water and salt in subgrade soil migrate and accumulate from bottom to top under the action of temperature gradient, the stress and strain caused by the change of water and salt phase in subgrade structure under the action of salt-freeze-thaw cycles are the main reasons for the damage and deformation of subgrade structure. By controlling and optimizing the water-salt-temperature environmental factors of road subgrade structure, the migration of water and salt in subgrade structure can be blocked, and the influence of salt-freeze-thaw cycles on subgrade structure can be effectively controlled.

The construction of utility tunnel plays a significant role in improving the resilience of urban lifelines and intensively utilizing urban three-dimensional space. It is an important infrastructure that serves the city's high-quality development. Based on the practical needs of urban utility tunnel planning and construction, the analytic hierarchy process and expert consultation method were used to clarify the assignment rules and weights of 15 key influencing factors, and build a suitability evaluation system for urban utility tunnel planning and construction. With the help of the spatial analysis and statistical functions of GIS, the suitability of the utility tunnel in the study area was evaluated more scientifically and objectively. The construction scale was optimized using the construction rate of the utility tunnel and the density of the urban utility tunnel construction indicators, reaching a balance of the coverage of the utility tunnel construction with the expenditure on infrastructure construction. This study provides support for regional utility tunnel planning schemes.

In order to investigate the mechanical state of pre-stressed anchors for tunnel support under water-rich ground conditions, an elastoplastic analysis of the tunnel surrounding rock was carried out based on the three-dimensional Hoek-Brown failure criterion, considering the effects of hydraulic coupling and strain softening of the surrounding rock, and considering the pre-stressed anchors as a passive anchor model with anchor pads and non-zero strain at both ends. The numerical calculation method of shear stress distribution and end prestress of prestressing anchor was established by using bond-slip theory. Through the comparison and analysis of the calculation results of relevant engineering cases, the rationality of the calculation method in this study is verified. At the same time, parametric analysis is carried out on the change law of surrounding rock stress and displacement under the influence of different factors by relying on the actual project. The results show that: The maximum values of anchor shaft force, tunnel surface force, and anchor neutral point are well-fitted with the monitoring values of the selected engineering cases. When the anchor shear stress reaches the peak stress of the tunnel wall, the decoupling phenomenon occurs between the anchor and the surrounding rock near the tunnel wall. The actual project reflects that the method of this study can effectively solve the design calculation problem of pre-stressed anchors in the deep tunnel, and the pre-stressed anchors can effectively reduce the surrounding rock deformation after installation. Compared with the passive anchor, its support effect is better. The study results can theoretical guidance for the design of the deep tunnel support under similar engineering geological conditions.

Rockburst has a large impact on the safe mining of underground mines, and accurate and reliable prediction of rockburst is of great significance to safe production. In order to accurately and effectively predict rockburst, firstly, the stress coefficient, brittleness coefficient, elastic energy index, and integrity coefficient are selected as prediction indicators, and the rockburst prediction index system is established. Secondly, based on the hierarchical analysis method (AHP), improved CRITIC method, and the distance function discriminant method for determining the integrated constant weight, the constant weight is dynamically corrected using the variable weight theory. Then, the effectiveness is introduced to modify the principle of maximum posterior probability, and a Bayesian rockburst intensity grade prediction model with variable weight is constructed. Finally, 15 groups of rockburst engineering examples are selected to verify the reliability and compare the accuracy of the model, and the model is used to predict the rockburst in the middle section of the 1 000 m level of Jinchuan No.2 Mine. The research results show that the accuracy of the Bayesian rockburst prediction model with variable weight can reach 93%. The rockburst intensity grade in the middle section of the 1 000 m level of Jinchuan No. 2 Mine is none to slight, and the harm of rockburst is relatively small. The prediction results are in line with the actual situation, which can provide a basis for rockburst prevention and control.

The carbonate sand is the main soil material in the underground space of island reef soil. The shear strength of carbonate sand is studied by direct simple shear tests under constant volume and constant stress conditions on two kinds of carbonate sand with different relative density and by contrast tests on quartz sand with the same particle distribution gradation. The test results show that for the same particle size distribution, carbonate sand has a critical friction angle higher than that of quartz sand, its phase angle and maximum dilation angle lower than that of quartz sand. At the same time, the maximum dilation angle, phase angle and critical friction angle of carbonate sand are affected by particle breakage, of which the maximum dilation angle and critical friction angle decrease with the increase of breakage, while the phase angle increases with the increase of breakage. In this study, the critical friction angle and dilation angle are considered as the "effect angle" of particle breakage. By introducing the relative density that affects particle breakage, a calculation model for the maximum internal friction angle of carbonate sand based on the existing evaluation methods is proposed.

Aiming at the problem of excessive floating of segments when shield tunneling in full section weathered surrounding rock strata firstly, the initial setting time of the slurry was tested by the inverted cup method under different additive dosage (strengthening dry powder (Material A), liquid activator (Material B)), and the synchronous two-component grout with controllable initial setting time and satisfactory pumping performance was prepared. Secondly, the finite element model of segment floating was established, considering the nonlinearity of axial tension and circumferential shear stiffness of the ring joints. The model can be used to consider the gradual accumulation effect of floating displacement during shield tunneling, and the influence of synchronous two-component grout on the floating of shield tail segment in stable surrounding rock stratum was obtained. Finally, the developed synchronous two-component grout was applied to a shield tunnel project in Guangzhou, and the effect of controlling segment floating is verified, which greatly reduces the leakage of segment joint with excellent segment assembly quality. The results show that: (1) 1% Material A and 1.5% Material B are mixed evenly with the single grout mortar in the shield tail grouting pipe and injected into the shield tail gap, which can effectively reduce the floating displacement of the segment up to 79%. (2) The floating displacement gradually increases with the increase of the distance from the shield tail and tends to be stable. The stable position is about 10.5 m (7 rings) from the shield tail. The maximum floating displacement is about 23 mm. (3) The use of the new synchronous two-component grout also effectively reduces the number of leakage points of the segments. The reduction is up to 59%, which greatly reduces the construction cost of plugging grouting due to leakage and has good economic benefits.

Pile foundations are commonly employed as load-bearing structures in loess regions. This study sought to investigate the bearing capacity characteristics of cyclic uplift piles in the northwest region by conducting on-site model tests. These tests examined the axial displacement and lateral friction performance of uplift piles under three different working conditions and varying cyclic loads. The findings revealed that the axial displacement at the pile top during pile failure under cyclic loading was merely 30% of that observed under conventional loading. There exists a significant relationship between the axial displacement at the pile top and the bearing capacity of the pile foundation. During the loading-unloading process, the pile-soil interaction leads to yield as the number of cycles increases, signifying repeated shear between the pile and soil. While the decline in frictional resistance strength of each layer in conventional pile foundation tests typically manifests during the ultimate load stage, this weakening is observed during the cyclic process prior to reaching the ultimate load in cyclic loading conditions. These insights can inform the application of pile foundations.

Large-diameter shield tunnels have been widely used in various river crossing traffic projects, and the problem of segments upward moving is prominent. Based on the Jinan Yellow River tunnel project, the middle section and the receiving section of the Yellow River were selected for on-site monitoring of segments upward moving, respectively. Combined with the indoor grout proportioning test, a comparative analysis of the law of segments upward moving of large diameter slurry shield tunnel in different test sections and the effect of treatment measures was conducted. The results show that when the large-diameter shield tunnel at the powdery clay formation is driven in the section with a buried depth of 2.5D and water pressure of 0.4 MPa, the process from the completion of segment assembly to uplift stability can be roughly divided into four stages: initial deformation stage (floating accounts for 22%), rapid floating stage (floating accounts for 55%), gentle floating stage (floating accounts for 28%) and slow settlement stage (settlement accounts for 5%); In the section with a buried depth of 1.6D and water pressure of 0.2 MPa, the percentage of segment elevation increments in each stage differed by 3%, 8%, -14%, and 3%, and the uplift period was extended by 2 times; The best time to control the segment uplift is within 10 hours of starting synchronous grouting and the comprehensive measures adopted in the project can effectively control segment uplift. Only grouting in the vault area has the most obvious control effect on segment uplift.