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.

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.

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.

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.

Tunnel excavation is actually an unloading process. Due to the influence of unloading stress paths, the parameters of the surrounding rock in the plastic zone of the tunnel are degraded and the mechanical parameters are reduced relative to the unexcavated state. In this paper, a model for calculating the reduced parameters of the surrounding rock in the plastic zone of the tunnel is obtained based on the typical soft rock-mudstone unloading triaxial test of the tunnel by other scholars. Comparing the results with the traditional Fenner formula, it is found that this model is more consistent with the results of excavation and support calculations for soft rock tunnels under high ground stress. The model is solved theoretically using the Euler explicit differential solution algorithm to study the effects of different support forces, cohesive forces, friction angles and deformation moduli on the radius of the tunnel plastic circle and the displacement of the perimeter of the tunnel. The model was developed using FISH language and embedded in FLAC 3D software to calculate the effect of different support timing on the support effect. Finally, the tunnel calculation model is validated based on the field measurement data of Longxi tunnel. The research results can provide a theoretical basis for the design of high ground stress soft rock tunnels.

In order to investigate the stability of the longitudinal inclined tunnel face under the influence of any inclination angle, using the Hoek-Brown strength criterion as an example, considering the influence of the longitudinal inclination angle of the tunnel, using spatial discretization and point generation techniques, the existing 3D active passive failure model of the tunnel face was improved, and the ultimate support pressure of the active passive failure of the inclined tunnel face was solved. A three-dimensional active passive failure model for the inclined tunnel face under the nonlinear Hoek-Brown criterion was established. By comparing and analyzing the calculation results of this model with the numerical simulation results, the rationality of the three-dimensional active passive failure model of the inclined tunnel face under the nonlinear Hoek-Brown criterion established in this paper is verified. The results show that: The maximum error between the three-dimensional active passive failure model of the inclined tunnel face established in this paper and the numerical simulation results under the nonlinear Hoek-Brown criterion is less than 5%, and the fitting effect is good, which is suitable for the stability analysis of the inclined tunnel face. The inclination angle between the tunnel and the horizontal plane caused by any deviation in elevation is an important factor affecting the stability of the tunnel face, and special attention should be paid in practical construction, providing effective theoretical guidance and reference for the safety of shield tunneling similar to tunnel construction.

Now, on the basis of hydrostatic pressure difference of overall stress method, the fluid-solid coupling analysis of saturated slope by strength reduction limit analysis method is realized by adjusting soaking surface and using the action of levitating force, but the changing of pore pressure in the process of strength reduction is not resolved. In this paper, the asynchronous load transfer process on the solid skeleton and free water of soil-rock was explained from the relations of the strength parameters of solid phase (c,φ) and the strength parameters of liquid phase (pore water pressure). The effective stress strength reduction limit analysis method and the approximate determination method of pore pressure increment were advanced, and the pore pressure increment-strength reduction limit analysis method was realized on the basis of hydrostatic pressure difference of overall stress method. The research shows that zero-pore pressure surface increase 0.34~0.44 m(4%~5%)than the safety factors of strength reduction limit analysis method, this is close to the empirical value (0.5 m) that was used in the fluid-solid coupling analysis of saturated slope.

Brittleness is one of the most important mechanical properties in deep rock mass. In order to study the brittle damage evolution mechanism of limestone, the acoustic emission test of limestone under uniaxial compression was carried out, and the relationship between brittleness index and damage variable and b-value was analyzed. The results show that: (1) The ratios of crack closure stress, crack initiation stress and damage stress to peak stress in limestone are 31.3 %, 43.0 % and 85.5 %, respectively. (2) The average brittleness index of limestone is 0.32, and the mean square error is 0.009. With the increase of brittleness index, the damage variable corresponding to the characteristic stress gradually decreases, and the damage variable gradually increases from ‘proportional function’ to ‘concave power function’. The damage acceleration phenomenon exists in the critical failure stage. (3) Under the condition of uniaxial compression, with the increase of brittleness index, the shear failure of limestone decreases and the tensile failure increases, and the brittleness index can better characterize its failure mode. (4) There are four obvious stages in the cumulative ringing count, cumulative energy, cumulative amplitude and time curve of acoustic emission in limestone: slight increase period, quiet period, steep increase period and sharp decrease period. The amplitude of quiet period is less than 80 dB, and the curve shows a step-like upward trend. The larger the brittleness index, the longer the quiet period, the shorter the sharp increase period, and the greater the ratio of the stress corresponding to the b value to the peak stress. (5) The b-value curve shows a trend of rising first and then falling, and the b-value abrupt points are all before the end of the quiet period. These two points can accurately warn the instability and failure of limestone. With the increase of brittleness index, the b-value abrupt point appears later and closer to the peak. The research results provide important reference for surrounding rock stability control and dynamic disaster monitoring and early warning.

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.

The influence of the damage caused by excavation and unloading of soft rock mass on the stress relaxation characteristics of its support reinforcement cannot be ignored. Taking the red layer mudstone as the research object, the uniaxial stress relaxation failure test of unloading damaged mudstone was carried out, and the influence of different strain levels and unloading damage degrees on the relaxation characteristics of mudstone was studied. The results show that: The stress curves of the graded stress relaxation test of the unloading damaged mudstone before and after failure are all incomplete relaxation, and the stress relaxation curve mainly includes two stages: deceleration and stable relaxation, and the relaxation amount and relaxation time at all levels of strain level show a linear increase trend with the increase of the degree of unloading damage. Based on the fractional calculus theory, the R-L fractional order elastic viscous element (F element) is selected, and an elastic viscous time-varying element (FT element) considering the time-varying characteristics of viscosity coefficient is proposed, and then the unloading damage degree factor is introduced, and a fractional order elastic viscous time-varying element (UFT element) considering the initial unloading damage degree is proposed. Finally, the component is introduced into the traditional Burgers model to establish a nonlinear relaxation constitutive model based on fractional order. The comparison and discussion of the calculation values and experimental data of the theoretical constitutive model based on the three fractional order elements shows that the relaxation constitutive model based on UFT elements has higher accuracy, and the theoretical calculation results of the model under different stress levels and unloading damage degrees are consistent with the experimental data, indicating that the relaxation constitutive model can better and accurately describe the relaxation characteristics of unloading damage mudstone.

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.

Mixing soil with a certain amount of binding agent can form artificial cemented soil with remarkable structure, which is widely used in the improvement of natural geomaterials. However, the existence of structure often induces cemented soils to appear more complex mechanical characteristics than remolded soil, and it is necessary to achieve quantitative analysis and reasonable prediction of their mechanical behaviors. This paper focuses on the common mechanical characteristics of cemented soil, the triaxial compression and shear tests of cement-bonded soil with different initial states are carried out, and then the state dependence of its mechanical characteristics is systematically analyzed. Finally, the state-dependent model is used to calculate/predict its mechanical behavior. The research results show that: (1) The peak shear stress ratio of cemented soil is significantly affected by its initial state (void ratio, confining pressure, cementation), while the residual shear stress ratio is less affected by the initial state, indicating that the residual strength can be used as a state-independent mechanical parameter; (2) The isotropic consolidation curves of cemented soil is significantly affected by the initial state (void ratio, cementation), but the damage of structure makes these compression curves gradually converge to that of remolded cemented soil, indicating that the consolidation curve of the remolded cemented soil can be used as the inherent compression curve; (3) The isotropic compression and triaxial shear test results of the above-mentioned cemented soils with different initial states show an encouraging agreement with date by calculation, indicating that the state-dependent constitutive model here can reasonably describe the complex mechanical behavior of cemented soil.

Slag and dredged sediment are typical solid waste. In order to expand the utilization of resources, the dredged sediment was modified into early strength flowable soil by using slag and sulfoaluminate cement as curing agent, and it was used for backfilling in municipal pipe ditch engineering. The workability and mechanical properties of flowable soil with different water content and slag replacement ratio were studied after slag partly replaced sulfoaluminate cement. The results show that when the moisture content increases, the fluidity increases and the density decreases, and the change of slag replacement ratio has limited influence on the fluidity and density. The unconfined compressive strength of flowable soil increases with the increase of curing age, but decreases with the increase of moisture content and slag replacement ratio. When the slag replacement ratio is less than 42.9%, the strength can reach more than 100 kPa after curing for 1 day, and the drying-wetting cycle resistance of flowable soil decreases with the increase of slag replacement ratio. When the fluidity is greater than 200 mm, the filling rate of the flowable soil can reach more than 97%, which can be better used for engineering.

Cement-stabilized soil is widely-used to improve mechanical properties of soils in cold regions. For the safety operation and maintenance of geotechnical engineering, it is important to clarify the main control factors of shear strength and the change mechanism of shear characteristics for cement-stabilized soil cured at negative temperatures. In this paper, the shear characteristics of cement-stabilized silty clay were tested under different curing temperatures, cement content, initial water content, and curing age. The influencing factors and variation rules of the shear strength for cement-stabilized silty clay under negative curing temperature were analyzed. The test results show that the shear strength of cement-stabilized soil under negative curing temperature is less than that under positive curing temperature. The pore characteristics of cement-stabilized soil are significantly different under different curing temperatures, which makes the shear failure morphology of cement-stabilized soil shows different degrees of brittleness effect. Besides, initial cement content and initial water content significantly affect the shear strength of cement-stabilized soils, and its shear strength increases with the cement content raised, the optimal initial water content of 16%~20% is the most favorable for the strength growth with cement-stabilized soil. Additionally, the cohesion of cement-stabilized soil increases with the cement content, and firstly increases and then decreases with the initial water content. With the increase of cement content and initial water content, the internal friction angle also firstly increases and then decreases.

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.

To fully exploit the mechanical performance of corrugated steel-concrete composite plate, this paper proposes a prestressed corrugated steel-concrete composite plate structure. Based on the validation of the accuracy of numerical models using experimental results, different types of composite plate were analyzed and compared for their mechanical performance. The loading process and failure mode of the structure were studied to clarify the mechanism of the upper corrugated steel plate and prestressing in the composite plate, in which the combination of the two significantly improved the elastic working range and failure resistance of the composite plates. Additionally, the mechanical properties of prestressed double-layer corrugated steel-concrete (PSCS) composite plates are studied. The results show that: the type of corrugated steel plate, the thickness of core concrete, the spacing of studs and the prestress level have a significant influence on the anti-sliding ability and anti-damage ability of PSCS composite plates, among which the thickness of core concrete and the waveform of corrugated steel plate have a more obvious influence. Appropriate prestress level can better exert the mechanical characteristics of PSCS composite plates. The results of this study provide useful reference and guidance for the design and optimization of prestressed corrugated steel-concrete composite structures.

As the weak part of the force and deformation of the whole ring arch structure, the joint type is the key to the structural design, and its mechanical characteristics are very important for accurate evaluation of the overall bearing performance. In order to evaluate the force performance of the bolted endplate joint and the combined sleeve joint of the high-strength steel pipe grid, the bending test of the local full-length joint was carried out, the changeable law of the failure form, vertical deflection, bearing capacity and stress strain of the two joint components was discussed, and the bending stiffness and bearing capacity of the joints were quantitatively evaluated. The results showed that during the whole loading process, the two kinds of joints showed typical elastic growth stage, plastic development stage, stable bearing stage or residual strength stage. The bolted endplate joint showed a smooth curved failure mode, and the combined sleeve joint showed a broken line failure mode. Compared with the combined sleeve joint, and the ultimate bending moment of the bolted endplate joint was 46.4 kN·m higher than that of the combined sleeve joint, the deflection was reduced by 18.5 mm, and the bending stiffness at initial stage and service stage of the bolted endplate joint were also increased by 1 011 kN·m² and 877 kN·m². The strain response law of the steel tube of the two kinds of joints was basically the same, showing the distribution characteristics of the outer ring being compressed and the inner ring being stretched, and will enter the yield stage first due to the outer compression. The stress of bolted endplate joint was stable during the loading process, the opening deformation of the endplate was small, and the safety factor of bolts was high. The bearing capacity of the combined sleeve joint was weak, the deformation range was large. The research results could provide a certain reference for the joint design and engineering application of steel pipe grid support structure in tunnel engineering.

The permanent ground movement caused by earthquake is the main reason for the damage of tunnel structure. The corrugated structure has good large deformation ability, and its application in tunnel support is gradually increasing. However, there are few studies on the mechanical properties of tunnel corrugated plate support under fault dislocation. In this paper, a strike-slip fault simulation device is developed. Based on the similarity ratio theory, loose sand and PVC spiral corrugated pipe are selected to carry out the model test of corrugated plate support for cross-fault tunnel, and the circumferential and axial deformation of spiral corrugated pipe under different dislocation distances is obtained. Then the soil spring coefficient of pipe-soil interaction is determined by the specification. The spiral corrugated pipe with fault dislocation is numerically simulated and compared with the test, and the change of soil spring coefficient is obtained. Finally, the influence of rib stiffness and soil constraint on the supporting performance of tunnel corrugated plate under fault dislocation is studied. The results show that the maximum axial tensile and compressive strain occurs on both sides of the fault. With the rib stiffness increasing to certain value, the deformation of corrugated plate and the maximum ground dislocation distance keep stable. Under the same deformation of corrugated plate, the stronger the soil constraint, the smaller the maximum ground dislocation distance.

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.

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.

In order to realize the unification of the calculation steps and results of the general ring typesetting and the actual deviation calculation of the segment under the tunnel coordinates, the fitting of the segment axis based on the tunnel axis can be carried out accurately and efficiently, and the typesetting technology of the general segmental ring for shield tunnel is optimized. Firstly, the selection of the three-dimensional coordinate system of the tunnel and the representation method of the space attitude of the shield segment are clarified. The calculation method of the true three-dimensional coordinates of the end face center of the typesetting of the general segmental ring for shield tunnel and the positioning method of the starting ring is proposed. According to an example of a shield tunnel project, the research and design software is used for typesetting and fitting. The results show that: The true three-dimensional coordinates of the end face center of the end face of general segmental ring for shield tunnel obtained by this method have a good fitting effect on the tunnel design axis. The center coordinates of the end face of the segment typesetting obtained by fitting can be compared with the actual measurement results, and the construction deviation direction and specific value can be obtained, which can provide quantitative control guidance for subsequent layout and deviation correction. In addition, the research can also realize the trial calculation of segment wedge, thus optimizing the segment design parameters, and providing technical support for the design and construction of shield tunnel, which has great application value.

The technology of geological advance prediction is a necessary means and one of process during tunnel construction, and it is a key technical problem restricting the development of tunnel construction technology. The implementation of seismic wave method for advanced geological prediction of tunnels is a mechanical process. In this paper, we regard the application of seismic wave method as a mechanical trial and assume that the surrounding rock of the tunnel is a two-phase medium including solid and gas (pore). By analyzing the stress-strain relationship of the surrounding rock caused by the artificial seismic wave, the continuous equations of the incident, refraction and transmission of the seismic wave at the reflecting surface are obtained. According to the relationship between the wave impedance, the reflection coefficient and the dynamic stress of the surrounding rock, the expression of the relationship between the pressure gradient of the surrounding rock and the amplitude and frequency at different times is derived. The stress gradient of surrounding rock is regarded as one of the important indexes to evaluate the geological disaster. On this basis, a method of seismic wave advances geological prediction based on the stress information of surrounding rock is formed. Through the field seismic wave test, the stress information of surrounding rock can well express the change of geological lithology, which is proved to be accurate and reasonable and has important application value.

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%.

As a new type of material for tunnel shotcrete support, steel fiber shotcrete has better tensile, crack resistance, and durability. To study its impact on bearing capacity and cracking when used for tunnel support, a safety analysis method for steel fiber shotcrete structures was established. This analysis method detects whether the steel fiber sprayed concrete component cracks under load based on the size of the steel fiber sprayed concrete component. If it does not crack, the component size is reasonable; If cracking occurs, it is necessary to calculate the actual crack width to determine whether it meets the requirements of safety regulations. According to the analysis process, engineering verification was conducted on three types of support types of steel fiber shotcrete for Class III surrounding rock, namely Type I, Type II, and Class IV surrounding rock. The results showed that the thicker the steel fiber shotcrete for the same level of surrounding rock, the less likely it is to crack, and the higher its safety. The greater the load on different levels of the surrounding rock, the easier it is for steel fiber sprayed concrete of the same thickness to crack and the wider the crack width after cracking. At the same time, the theoretical calculation results are basically consistent with the on-site test results, verifying the practicality and effectiveness of the safety analysis method for steel fiber-sprayed concrete structures.

With the increasing development and utilization of urban underground space, it is inevitable to excavate around the urban operational tunnels. The excavation and unloading of the foundation pit above the tunnel has a great influence on the formation of the pressure arch of the existing tunnel. Based on previous studies, three unloading ratio models for excavation of foundation pits are summarized, and a method for judging the inner and outer boundaries of the pressure arch is provided. The effect of excavation and unloading of foundation pit on the formation of pressure arch of underlying tunnel is studied by numerical simulation. The results show that: The tunnel vault rock and soil are subjected to the combined effect of the lateral pressure of the rock and soil on both sides of the foundation pit above. Compared with the one-dimensional unloading ratio N₁, the correlation between the two-dimensional unloading ratio N₂ and the boundary of the pressure arch is more significant. Based on the analysis of the impact of foundation pit excavation on the formation of the pressure arch of the underlying tunnel, the engineering impact zones of foundation pit excavation and unloading are proposed, which are divided into general impact zone, secondary impact zone, significant impact zone and strong impact zone. When the excavation width L of the foundation pit is not greater than D and the excavation depth h of the foundation pit is less than 0.15 H, it is regarded as the general influence area; When the excavation width L is not greater than D and the excavation depth h is between 0.15 H and 0.225 H, it is regarded as a significant influence area; When the excavation width L of the foundation pit is greater than D and its two-dimensional unloading ratio N₂ is less than 0.33, it is regarded as a secondary affected area; when the two-dimensional unloading ratio N₂ of foundation pit excavation is not less than 0.33, it is regarded as a strong influence area.

Taking the transfer hall project of a subway station as an example, FLAC^3D numerical simulation software was used to analyze and summarize the influence law of the excavation of the deep excavation of the upper span on the deformation of the underpass three-dimensional cross tunnel with different spatial distances and distribution forms. Combined with the field monitoring data and the mutual verification of the numerical simulation results, the results showed that: (1) The effect of excavation unloading on the structural deformation of the tunnel is mainly manifested as vertical displacement, and its deformation is closely related to the spatial position of the foundation pit and the unloading amount of the rock-soil mass of the foundation pit; (2) The monitoring data of the whole construction cycle of the left and right tunnels of Line 1 are in good agreement with the numerical simulation results, which verifies the accuracy of the judgment of the influence of the numerical calculation method on construction activities; (3) The vertical displacement of the cascade tunnel coupled with multiple stress states is significantly affected by superposition effect, and the maximum vertical displacement is located in the area with many influencing factors, and the maximum vertical displacement is 34.84 mm; (4) Tunnels with shallow burial depth are more sensitive to construction disturbance than those with deep burial depth. The deformation dispersion at different locations is stronger, and the deformation has certain integrity and coordination.

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.

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.

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.

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.