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.

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.

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 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.

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.

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 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 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 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.

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.

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.

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.

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.

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.

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 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.

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.

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.

Inadequate lining thickness and debonding are very common in operating tunnel vaults, which may cause local cracking and falling blocks in the lining and threaten tunnel operation safety if not rectified in time. By means of data research, numerical calculation and field application, the hazards of such defects and their remediation measures were studied. The study shows that: the severity of insufficient lining thickness and debonding is graded by 2.0 m and 6.0 m in longitudinal and circular directions; When the lining defect range is small, the lining thickness change has less effect on the lining stress. When the lining defect range is larger than 4 m² and the lining thickness is less than 40% of the design thickness, it will cause sudden change of lining stress; When the single size of defects in longitudinal and circular directions is larger than 2 m, the circular dimension is more likely than the longitudinal. When the longitudinal and circumferential single size of defects is larger than 2 m, the circumferential size is more likely to cause the change of lining stress than the longitudinal size; Combined with the grading of lining defects and lining thickness, three remediation schemes of filling and grouting, window repair and lining set are proposed; Based on the actual application of the project, the correctness of the grading of defects and the feasibility and effectiveness of the remediation scheme are verified, which can provide some guidance and reference for the remediation of insufficient tunnel lining thickness and dehollowing.

Confining pressure is one of the main factors affecting rock mechanical properties. In order to study the effect and mechanism of confining pressure effect on the strength and brittleness characteristics of granite, this paper takes Sejilashan granite as the research object, carries out indoor triaxial compression tests under different confining pressure conditions, obtains the variation rule of strength parameters such as failure form and peak stress, and constructs a triaxial constitutive model considering the confining pressure effect within the framework of unified strength theory. Based on the total stress-strain curve, an evaluation index of rock brittleness characterized by fracture energy was established to determine the quantitative relationship between confining pressure and rock brittleness. On this basis, RPFA software is used to simulate the whole process of failure and acoustic emission evolution characteristics of granite under different confining pressures, so as to reveal the damage evolution mechanism of granite. The results show that the confining pressure can effectively limit the formation and propagation of microcracks in granite, and then significantly improve the macroscopic strength and deformation properties of granite. The triaxial constitutive model and brittleness evaluation index established in this paper can effectively reflect the law of confining pressure effect on rock strength characteristics and brittleness.

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.

Experimental studies show that the dynamic size effect is opposite to the static size effect of rock strength, but the intrinsic micro-dynamic mechanism of the dynamic size effect of rocks has not been clarified yet. In this paper, sandstone sample is selected as the research object, and based on the wing-crack model of rock, the crack motion equation and loading equation of sample are jointly calculated, the mechanism of rock specimen size on strength under dynamic loading, namely the dynamic size effect of rock strength is analyzed. The results show that: Under the same dynamic loading rate, with the larger the specimen size, more time is required for crack coalescence, and the applied stress at the moment of the specimen failure (dynamic strength) is greater, the dynamic size effect is more evident, and the rock dynamic strength increases with strain rate approximately in a power law; The critical strain rate range at a definite size range of specimen of rock is obtained by numerical calculation, and the static size effect takes the dominant position when the strain rate is below the critical strain rate, while the dynamic size effect dominates when the strain rate is above the critical strain rate, and the critical strain rate decreases with the increase of specimen size; The critical size of the specimen decreases with the increase of the strain rate.

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.

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.

In order to study the problem of fire evacuation in different architectural spatial forms of underground commercial streets, three sets of simulation experimental models of fire smoke and personnel evacuation were constructed. After model investigation and statistical calculation, the fire load density, heat release rate and other data were obtained, and fire and evacuation simulations are carried out through Pyrosim and Pathfinder. The impact of different typical spaces on the spread of fire smoke and evacuation of personnel was compared. The results show that since the propagation rate of fire smoke in different typical spaces is different, and the direction of fire smoke spread is basically consistent with the direction of personnel evacuation, with the spread of fire smoke in a typical space is faster, the safe evacuation time of personnel is shorter. Therefore, the safe evacuation effect of personnel from fire sources in different typical spaces is different, from high to low: corridor space, hall-type space, and intersection space. According to the simulation results, the unfavorable factors affecting the evacuation efficiency are analyzed, and a targeted underground commercial street design optimization strategy is proposed.

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.

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.

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.

When the tunnel passes through the fracture zone of the high-temperature hot spring fault, construction personnel will encounter a challenging environment characterized by high temperature and humidity. The construction process involving drilling and blasting is complex, leading to high labor intensity. Regrettably, existing research has overlooked the impact of high-humidity environments on tunnel personnel. To ensure the safety and well-being of construction workers in such conditions, this study establishes revised labor intensity grades for tunnel construction personnel operating in high-temperature, high-humidity environments. Additionally, it develops a human body predicted heat stress correction model based on changes in energy metabolic rates. Furthermore, recommendations are provided regarding safe continuous working times for tunnel construction personnel under these conditions. Field tests were conducted within a hot tunnel environment to validate these findings. Results indicate that when temperatures exceed 30 ℃ and humidity surpasses 70%, labor intensity levels for tunnel construction personnel increase by approximately one grade for every 4 ℃ rise in temperature or 10% increase in relative humidity. When temperatures exceed 38 ℃ with relative humidity exceeding 90%, or when temperatures exceed 40 ℃ with relative humidity over 70%, operations should be halted by construction personnel as per safety guidelines. Notably, field test results demonstrate that the error margin of the human heat stress correction model remains below 5%.

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.

At present, the pile spacing of micro-pile and micro-pile combination anti-skid structure is generally determined by engineering experience, which greatly affects the anti-skid performance. To solve this problem, the axis of the soil arch between piles is assumed to be parabola. Then, the maximum pile spacing formula is given under the control condition that the soil at the arch crown or arch foot reaches the limit state. The rationality is verified by comparing it with the model test results. On this basis, considering the interaction between soil arches between piles and soil arches among pile groups, a simplified calculation model of pile spacing of the structure is established and applied to a simplified engineering example. The results obtained are compared with the numerical simulation results, and the rationality is verified. The calculation model of pile spacing established in this paper can provide a theoretical basis for the pile location of the micropile group.

Through model tests based on digital image correlation technology and discrete element numerical simulation method (PFC), the influence of thread setting, the relative density of sand, loading conditions on the uplift bearing capacity, and deformation characteristics of the screw-shaft pile are studied. The test results are used to calibrate the micro parameters of the discrete element program. The simulation results are used to analyze the load sharing characteristics, the influence of pile type parameters on the bearing capacity and the sliding surface of the soil around the pile. The results show that: The uplift force-displacement curves of pile foundation present softening characteristics, and the 0.05D failure criterion is applicable to the determination of the ultimate bearing capacity of the uplift pile. The setting of the screw threads increases the bearing capacity of the pile by 37%, the load sharing ratio of the threaded section is close to 70%, and the shaft section is twice that of the compression condition. The uplift bearing capacity decreases with the increase of thread pitch. H/D=1.00 is a reasonable parameter under this condition. The improvement of the relative density of sand makes the uplift bearing capacity of screw-shaft pile and straight rod pile increase by 19.4% and 26% respectively, while the influence of displacement mode of soil around the uplift pile is limited. The maximum influence range of soil around the screw-shaft pile is about 4D, while that of straight rod pile is about 2D.

The triaxial compression tests of raw coal under different confining pressures were carried out by the industrial CT scanning system of coal and rock under load to investigate the mechanical properties and damage characteristics of raw coal under different confining pressures, the CT scanning information of the whole process of destabilization and damage of raw coal was obtained by combining with its own CT scanning system, and the evolution law of crack propagation of raw coal under different confining pressures was analyzed. The results show that: (1) With the increase of confining pressure, the overall bias stress-strain curve shifts to the right, the peak strength increases linearly, while the peak strain and elastic modulus both increase as a quadratic function, and the peak strength increases by the largest amount; (2) Based on the CT scan images, the fracture evolution characteristics inside the coal sample can be divided into four stages: fracture pressure density slowly decreasing stage, fracture sprouting stable development stage, fracture rapid increase stage, fracture expansion through stage, and with the increase of confining pressure, the fracture density gradually decreases; (3) Under triaxial loading, the damage of raw coal is mainly in the form of shear damage, with the size of the breaking angle ranging from 20° to 40°, and with the increase of confining pressure, the breaking angle increases as a quadratic function. The research results have certain reference significance for underground roadway, stope support design, surrounding rock stability judgment and mine disaster and accident prevention.

When tunneling progresses into the geothermal areas, the high-temperature environment threatens the quality of engineering structures and the health of workers, reduces the work efficiency of staff, or impacts the normal operation of mechanical and electronic equipment. Therefore, it is significantly important to understand the heat transfer characteristics of geothermal construction tunnels for cost-effective heat-hazard-prevention measures. Based on the understanding of the thermal characteristics of geothermal construction tunnel, a method of heat-hazard prevention based on fuzzy comprehensive evaluation of heat hazards is proposed. Firstly, considering the factors of geothermal, construction conditions, subjective and objective construction workers, fuzzy comprehensive evaluations of heat hazards for different stages of tunnel excavation are carried out. Then, corresponding heat hazard prevention measures are formulated according to the heat hazard evaluation results. Finally, heat hazard evaluations and heat hazard prevention measures are constantly updated and iterative throughout construction period. While ensuring the cooling and prevention of heat hazards, the cost of heat hazard prevention measures is reduced, as well as the consumption of energy and resources, that makes the whole process of geothermal tunnel construction safe and economical.

Microwave-assisted rock breaking is a new rock breaking method proposed in recent years. To explore the feasibility of this method in assisting PDC bits to break hard-to-drill formations, a PDC cutter-rock interaction model considering the effects of microwave heating has been developed based on the bond particle model (BPM) built in discrete element software PFC. The effects of different microwave irradiation conditions on the cutting and rock breaking of PDC cutter were studied. The results show that under the same microwave irradiation time and low power, the cutting rock breaking mode is dominated by the extrusion and scraping of PDC cutter. With the increase of microwave power, the thermal cracks in rock gradually increase, and the damage effect of microwave on rock dominates the failure mode of rock in the cutting process. When the microwave loss power reaches 3.51 kW and the irradiation time is 90 seconds, the average cutting force and specific work of rock breaking are 56.77% and 73.9% lower than those of conventional cutting, respectively. The larger the microwave loss power is, the longer the irradiation time is, and the higher the rock breaking efficiency is. Microwave irradiation can reduce the fluctuation of cutting force and make the change of cutting force more gentle, which is helpful to improve the working life of PDC cutter.