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

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

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

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.

In the context of urban renewal, how to meet the public's demand for spatial quality in existing underground commercial streets has become an urgent problem to be solved. Corner space, as an important node in the pedestrian system of underground commercial streets, is a key area that affects spatial vitality, walking direction, pedestrian physiology, and psychology. Based on a pedestrian-friendly perspective, the impact of distance, constituent elements, and angles between different underground corners on pedestrian behavior is explored, and an adaptive corner space optimization strategy for (single building) underground commercial streets is proposed using spatial operation methods. The study aims to provide practical application value for optimizing the design of corner spaces in underground commercial streets. The results indicate that: Using obtuse corner angles, appropriate corner spacing, and increasing the boundary area at the corner can effectively enhance the overall vitality of the street and the attractiveness of shops.

For large-section tunnels crossing fault fracture zones, indoor experiments were conducted to study the mechanical and permeability characteristics of the rock specimen. Based on the correlation between rock integrity index and physical and mechanical indicators, the parameters of surrounding rock under different degrees of fragmentation were quantified. Considering the permeability of surrounding rock changes with confining pressure, a three-dimensional numerical model was established to analyze the impact of the engineering characteristics of fractured zone surrounding rock on the tunnel deformation. Through on-site monitoring, the deformation of the tunnel and the stress changes of the support structure are mastered. The results show that: (1) The mechanical properties of the rock specimen in the fractured zone are greatly affected by the water-rock interaction, and the peak stress of the rock specimen in the saturated state is significantly reduced compared to the dry state. (2) The permeability of the rock specimen in the fractured zone decreases in a logarithmic relationship with the increase of confining pressure. When the confining pressure exceeds the crack closure stress, the penetration water pressure of the rock sample approaches. (3) As the integrity index K_v of the rock mass in the fault fracture zone decreases, the maximum settlement of the tunnel arch increases in a logarithmic relationship, and the adverse effect of seepage on tunnel deformation increases. (4) By taking reasonable strengthening support measures and parameters, the tunnel can safely pass through the mileage section of the fault fracture zone, which can be used as a reference for engineering applications.

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

With the development of China's transportation network and the improvement of construction techniques, the construction of numerous high-difficulty tunnels has driven the in-depth advancement of tunnel engineering research. As the primary load-bearing region of the surrounding rock, the range of the pressure arch significantly impacts tunnel stability. Although extensive studies on tunnel pressure (bearing) arches exist, systematic reviews in this field remain scarce. This paper reviews the research progress on pressure arches, tracing their historical development and summarizing research methods and boundary determination criteria. Among these, the inner boundary defined by “tangential stress greater than the original rock stress” and the outer boundary defined by “tangential stress recovering to 110% of the original rock stress” are widely recognized. The formation of the pressure arch is influenced by the interplay of surrounding rock conditions, in-situ stress magnitude, tunnel shape and size, and construction factors. Its evolution process can be categorized into four states: initial pressure arch, separated pressure arch, stable pressure arch, and collapsed pressure arch. The primary goal of construction support is to prevent the occurrence of the collapsed pressure arch state. The relationship between surrounding rock pressure and the range of the pressure arch reveals that the support structure in rock tunnels mainly provides deformation pressure to maintain the stability of the surrounding rock, whereas in soil tunnels, the support structure primarily resists the loose load within the pressure arch. Future research should focus on improving the arch formation mechanism, investigating the distribution of pressure arches in heterogeneous rock masses, and exploring the three-dimensional dynamic morphology of pressure arches.

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

In the straight cut blasting, the empty hole is often used as the auxiliary free surface and the compensation space of the blasting rock, which has an important influence on the blasting effect. Based on the background of a railway tunnel project, this paper studies the empty hole linear cutting blasting through three important means of theoretical analysis and calculation, numerical simulation and field application. With the help of ANSYS / LS-DYNA finite element software, the influence of two key technical parameters of empty holes with different diameters and the spacing between holes on the blasting effect under the action of multi-hole blasting is analyzed. The results show that the final forming effect of the empty hole linear cutting blasting cavity is related to the diameter of the empty hole and the distance between the charging and the empty holes. When the diameter of the empty hole is two times the diameter of the charging hole and the distance between the two is 2.5 times the diameter of the empty hole, the cutting blasting effect is the best. Based on the theoretical analysis and numerical simulation results, the design and application of empty hole linear cutting blasting are carried out on the site. The tunnel face is smooth and smooth, the average linear over-excavation is about 15 cm, and the contour forming quality is high, which verifies the rationality of numerical simulation and blasting scheme. The research results can provide reference for similar tunnel section blasting design.

The carbon emission and carbon neutrality goal is China's solemn commitment to the effective management of carbon emissions by the international community. The passenger flow intensity management of urban rail transit operating enterprises focuses on the formation mechanism, evolution mechanism, early warning probability, risk management and emergency treatment of large passenger flow in stations. The active prediction of passenger flow can not be realized while Relying on the staff's manual inspection and through the preset monitoring image monitoring of a specific area. Based on AFC big data and intelligent video image recognition processing and analysis principle, a dual-dimension coupling trigger mechanism for subway sudden large passenger flow warning is proposed. The trigger judgment matrix of sudden large passenger flow coupling is constructed, and the early-warning risk probability of sudden large passenger flow is defined hierarchically. Then put forward the passenger flow control response guide. Taking Nanjing Metro intelligent early warning information platform for sudden large passenger flow as an example, the accuracy and operability of early warning mechanism and coupling trigger mechanism is verified.

Shield tunneling method is widely used in subway tunnel construction because of its advantages such as not affecting ground traffic, high mechanization degree and short construction period. However, the problems of cracking and damage caused by uneven rising of segments are often encountered in the construction process of shield method, which affects the normal use of tunnel. However, the research on the mechanism and theoretical calculation of shield tunnel segment floating is relatively rare. In this paper, the floating mechanism of segments in the initial floating stage of shield tunnel is analyzed deeply, and the corresponding theoretical calculation formulas of upward buoyancy/anti-buoyancy and buoyancy are proposed. The theoretical calculation results are compared and analyzed with engineering examples. The results show that: The initial floating of the segment can be divided into two stages: rapid rising and slow rising, in which the rising amount of the rapid rising stage accounts for about 80%~90% of the total rising amount. The theoretical calculation value of the total floating amount is greater than the monitoring value, but the calculation error of the floating amount per ring is relatively stable, the theoretical calculation formula presented in this paper can provide reference for the calculation of the floating amount of the actual segment.

The development of underground transportation based on TOD mode drives the process of underground development of surrounding commercial space, and the connectivity between underground transportation and commercial space has become a link that cannot be ignored. Based on the place theory, this study highly summarizes the spatial composition of the two connected Spaces of Shanghai People's Square Station and Xujiahui Station. Considering the spatial structure and place spirit, field investigation and questionnaire distribution are conducted. Moreover, exploratory factor analysis and SPSS algorithm software are used to find out the strongly related reasons affecting the connectivity quality. By quantifying the subjective factors of pedestrians, five influencing factors are summarized, namely, central place and direction, regional division and shaping, spatial theme culture, spatial interaction, public safety and management, and corresponding optimization method are proposed to provide some reference for the design of underground connected space.

To reduce the vibration intensity of wedge-shape excavation blasting in tunnel, the precisely controlled delay time technology of tunnel V-cut blasting was proposed based on the Mohr-Coulomb strength criterion, the maximum tensile stress, and Anderson superposition theory. Firstly, the mechanism of segmental blasting of V-cut is revealed through theoretical analysis. Secondly, the function of blasting vibration waves was obtained by fitting the Gauss function. Finally, the precise delay time of reducing blasting vibration was obtained by superimposing different delay times with Matlab. The results show that: The stepped V-cut blasting improves the free surface conditions of blasting, and weakens the vibration propagation energy by reducing the amount of blasting charge in a single stage. Based on the Qi Jiazhuang tunnel of National Highway 109, the vibration strength of V-cut blasting was reduced by about 60% when the delay time was 13 ms. The engineering practice showed that the relative error between the theory and the field monitoring data was 13.9%, which verified the validity of the technology.

The popularization and application of underground space utilization and its characteristics puts forward higher requirements for the elaborate demarcation and management of property space of land, and there are many challenges in delimit the three-dimensional property space before land supply. The Qianhai Shenzhen-Hong Kong Modern Service Industry Cooperation Zone has constructed a number of underground space utilization projects and accumulated valuable experience in the demarcation and management of three-dimensional property space. This paper intends to conduct an in-depth analysis of the problems faced by demarcating three-dimensional property space before land supply and its management in the process of underground space development and utilization as well as drawing lessons from typical cases and policy experience of the Qianhai Shenzhen-Hong Kong Modern Service Industry Cooperation Zone, and then put forward improvement suggestions for the elaborate demarcation of three-dimensional property space, the addition of three-dimensional information and graphics to relevant documents or certificates, the verification and management mechanism of three-dimensional parcel, the policy related to three-dimensional property rights and the project implementation mechanism, so as to provides reference for the practice and management of underground space utilization in China.

The hardening strain model with small strain (HSS) can reflect the high nonlinearity of soil modulus at small strain range, which has been widely applied in deformation calculations during pit excavations under complex geological conditions. The appropriate values of model parameters have a significant impact on the computational results. However, the current recommended parameter values have a large range of fluctuations, which brings inconvenience to engineering applications. Therefore, further research is needed on the parameter values of the model. This study analyzes the data characteristics of existing HSS model parameters and introduces the artificial neural network method (ANN). The empirical relationships between the modulus parameters of the HSS model for Shanghai soils and factors such as the initial pore ratio (e) and oedometer modulus (E_s1-2) are established. This allows for the rapid determination of HSS model modulus parameters based on survey reports. Compared with the recommended values, the proposed method for determining the HSS model modulus parameters is closer to the measured value. The study results can provide references for projects in Shanghai.

Rockburst is a common dynamic geological hazard in underground engineering. In order to improve the prediction effect of the rockburst grade and the generalization of the prediction model, the Gate Recurrent Unit (GRU) neural network model with excellent memory and strong temporal timing was proposed to predict the rockburst grade. Firstly, based on the characteristics of rockburst genesis and grey correlation analysis, reasonable rockburst prediction indicators were screened, and the data of 137 sets of rockburst samples with existing research results were used as input and output data sets. Then, the optimal hyperparameter and the best prediction effect were through hyperparameter tuning of the model, and the rockburst grade prediction effect of the GRU model was compared with the rockburst grade prediction effect of the RF model, SVM model, CNN model, LSTM model, BP model, Russenes criterion, Wang Yuanhan criterion, Guan Baoshu criterion, brittleness coefficient criterion and elastic energy index criterion to verify the effectiveness of the GRU model, and verify the generalization of the GRU model according to the random sampling analysis of different models. Finally, two engineering examples were used to verify the practicality of the GRU model. The results show that the reasonable prediction indicators of rockburst are tangential stress of surrounding rock σ_θ, stress coefficient σ_θ/σ_c, the ratio of uniaxial compressive strength to uniaxial tensile strength σ_c/σ_t and elastic energy index W_et. According to the result analysis of different prediction methods, the effect of the GRU model in predicting rockburst grade is significantly higher than the above other prediction methods. Moreover, according to the random sampling analysis results of different models, the generalization of the GRU model in predicting rockburst grade is significantly strong. The prediction results of rockburst grade in the two engineering examples are in line with the actual rockburst situation, and the GRU model proposed in this paper is practical.

Excavating tunnels within the influence range of goaf area poses significant technical challenges commonly encountered in underground construction projects. Considering the Baiyunshan Tunnel as the project backdrop, FLAC3D was utilized to analyze the stability of the tunnel under conditions that if the goaf area was filled with water or not. Then optimize the original support plan to suit different conditions. The results show that: Excavating the tunnel without grouting in diverse engineering conditions presented significant safety hazards. Stress concentration occurred at the left end of the goaf, resulting in a wide range of plastic zone above the tunnel and extensive damage to the tunnel. The vertical displacement of the tunnel floor was expected to surpass the prescribed control value that outlined in the pertinent guidelines. The presence of water in the goaf exacerbated the rock softening and damage. High pore water pressure posed a significant risk of water inflow into the tunnel's crown. For the tunnel that underpassed dry goaf area, grouting was carried out within a range of 140° when the distance between the goaf and the tunnel was less than 4.5 meters. Grouting was applied to the entire surrounding area when the distance between the goaf and the tunnel was within the range of 4.5~9 meters. If the distance exceeded 9 meters, grouting was not required to meet safety regulations. During the construction of the tunnel underpassing water-bearing goaf area, it was necessary to extend the grouting range to cover a distance of 4.5~10 meters from the goaf to the tunnel. Other parts of the tunnel could be supported in the same way as the tunnel that underpassed dry goaf area. The field monitoring results indicated that the stability of the tunnel had been ensured.

Large deformation control of soft rock tunnel is an unavoidable technical problem in long-distance water diversion project. The depth of Caijiacun tunnel in Kunming section of Central Yunnan Water Diversion Project is generally large. Also, fault structure and joint fissure are developed as long diagenetic age. During the construction process, the frequent occurrence of large deformations in the soft rock cave section causing intrusion and arch replacement poses a serious threat to the safety, progress, and cost of engineering construction. The large deformation conditions and reasons in the process of tunnel construction are summarized, and taking the upstream section of the 4^# branch as an example to analyze deformation characteristics and the effectiveness of treatment measures using numerical simulation analysis method. On this basis, evaluation criteria of large deformation classification based on strength and strength-stress ratio is proposed. Also, comprehensive treatment guidelines including excavation bench, deformation allowance, advanced support, primary support and bedding layer is established, which effectively solves large deformation problems in subsequent soft rock tunnel sections. The research results can provide experience for tunnel construction under similar geological conditions.

CT scanning and reconstruction provide detailed insights into the internal structure of rocks and enable their quantitative analysis. A critical step in this process involves accurately segmenting different components in the CT images. This study compares and analyzes three deep learning models: the conventional U-Net, the ResUNet enhanced with residual modules, and the ResUNet-TL, which incorporates both residual modules and transfer learning features. Image segmentation using the Weka3D plugin in ImageJ is employed as a baseline for comparison. The analysis reveals that the ResUNet-TL model, leveraging a pre-trained VGG model and deep residual network techniques, outperforms the other models in segmenting complex rock CT images, demonstrating advantages in both accuracy and F1 scores. The ResUNet-TL model is applied to identify fractures in 2D CT images, which are then stacked and reconstructed into a 3D model of the rock sample for quantitative analysis. This approach provides an effective tool for advancing research and applications in rock science.

In order to better evaluate the passive instability failure mode of shallow shield tunnel face in sandy soil stratum, the existing three-dimensional calculation model is improved to make the failure area closer to the real soil failure contour. Considering the friction between the upper and lower blocks, the limit support pressure calculation formula is established by using the limit equilibrium method. The finite difference software FLAC^3D is used to construct the numerical model, and the variation law and failure mode of the passive failure support force of the tunnel face are analyzed. The limit support pressure solution obtained by the theoretical model is compared with the solution obtained by numerical simulation and the existing passive failure theoretical model to verify the reliability of the model. The results show that: The proposed theoretical calculation model can meet the limit calculation of passive instability of the tunnel face. The limit equilibrium method is used to calculate the friction between the upper and lower blocks of the model, and it is more reasonable to consider the static friction force. The optimal solution of the logarithmic spiral angle is affected by the internal friction angle. When the internal friction angle increases, the optimal solution of α will become smaller. The passive limit support pressure of the tunnel face of the shallow shield tunnel increases with the increase of the internal friction angle of the soil and decreases with the increase of the tunnel diameter.

Curtain grouting is an important measure for groundwater control in tunneling projects. The water-rich condition is easy to form dynamic water conditions due to the large permeability coefficient of the pebble stratum, which makes it difficult to determine the diffusion radius of the slurry, which will lead to the difficulty in controlling the quality of the curtain. Based on the theory of tortuosity, a model of Newtonian slurry columnar diffusion in pebble strata under dynamic water conditions was established, and the effects of tortuosity, grouting pressure, groundwater pressure, formation porosity, permeability and slurry viscosity on slurry diffusion distance were further analyzed. The results show that the diffusion distance of slurry in the downstream direction is significantly larger than that in the upstream direction under the dynamic water condition, and the tortuosity has a greater influence on the diffusion distance of slurry; The diffusion distance in the upstream direction is more influenced by the grouting pressure, groundwater pressure, permeability and slurry viscosity, and the diffusion distance in the downstream direction is less influenced by the groundwater pressure, and the influence of other factors is the same as that of the downstream flow diffusion distance; Affected by the influence of tortuosity effect, the diffusion distances in the upstream direction and in the downstream direction are less affected by the porosity. The research results can provide theoretical support for designing and constructing grouting curtains in water-rich pebble strata.

Subway freight transportation has problems such as limited transportation attributes, uncertain public recognition, and unclear freight demand. The characteristics of subway freight transportation are summarized and the selection preferences of shippers are investigated. An selection model integrating latent variables and ordered Logit is established and compared with traditional Logit models. The attractiveness of subway freight to shippers of high- and low-value-added goods is evaluated, predicting the probability of shippers choosing subway freight as the share rate of subway freight, and a marginal probability analysis is conducted. The results show that: Compared with the traditional model, the selection model established in this paper has better fitting degree and explanatory power. The probability of the two types of cargo owners choosing to switch to subway freight is higher than the probability of choosing not to transfer. The number of relocations and transportation costs significantly impact high- and low-value freight owners, respectively. Not reloading can increase the probability of high-value-added cargo owners turning to subway freight by 53.01%, and each unit of cost reduction can increase the probability of low-value-added cargo owners turning to subway freight by 23.70%.

When coarse soil particles are under high stress, particle breakage will occur, particle size distribution will change, and finally the compressibility of particles will become larger. In this paper, through one-dimensional compression tests of gypsum and calcareous sand under high stress, the effects of initial particle size and material properties on the yield stress and compression coefficient of samples are explored. The phenomenon of particle breakage during one-dimensional compression of coarse soil particles can be simulated by discrete element software. This paper uses PFC-3D to simulate the process in three dimensions, which not only realizes the visualization of particle breakage, but also explores the influence of initial particle size, friction coefficient between particles, breakage and breakage criteria on the compression characteristics. The test and simulation results show that the yield stress decreases and the compression coefficient increases with the increase of the initial particle size; Both material properties and crushing criteria have different effects on the compression characteristics, while the friction coefficient between particles and crushing conditions have little effect. In the process of experiment and simulation, the particle size changes from the initial uniform distribution to the fractal distribution. PFC-3D can well simulate the particle breakage phenomenon.

In recent years, the frequent occurrence of extreme weather conditions, coupled with intensified human activities, has led to frequent fluctuations in groundwater levels in the northwest region, exerting significant impacts on stabilized soils. This paper explores the utilization of fly ash and steel slag as raw materials, activated by an alkaline sodium silicate solution, to form a high-strength geopolymer gel material for the stabilization of loess soil. Through unconfined compressive strength tests, direct shear tests, scanning electron microscopy (SEM) examinations, and X-ray diffraction (XRD) analyses, the mechanical properties and microstructure changes of the stabilized soil after wet-dry cycles were investigated. The results indicate that: The degree of wetness during wet-dry cycles is a crucial factor contributing to the degradation of stabilized soil, with an increase in degradation observed as the wetness level rises. Notably, the incorporation of geopolymers effectively mitigates this degradation process. The cohesion of the stabilized soil exhibits a linear and continuous deterioration with an increasing number of cycles. A geopolymer-stabilized soil with a 20% additive content demonstrates superior resistance to wet-dry stability. After 15 cycles, both the internal friction angle of the untreated soil and the stabilized soil decrease within the first 7 wet-dry cycles but show a flattened trend subsequently. SEM and XRD analyses reveal that, in the early stages of wet-dry cycling, a small amount of unreacted steel slag and fly ash are present in the stabilized soil. These materials undergo further hydration reactions to form C-S-H and C-A-S-H cementitious compounds, which fill the voids between soil particles and thereby reduce the extent of degradation during the stabilization process.

Salt crystallization causes a decrease in compressive performance and microstructral damage of lime cured sulfate soil. A series of tests, including unconfined compressive strength test, SEM observation, and EDS test, were conducted on lime stabilized soil with a salt content of 0.3% to 5% to study the relationships between salt content, compressive strength, and microstructure indicators. The results show that: (1) The compressive strength of the soil first increases and then decreases with the increase of salt content, and the strength of stabilized soil with salt content of 1.5% reaches its maximum. (2) When the salt content is less than 1.5%, the shape of soil particles tends to be an ellipse, and the soil structure becomes compact. After the salt content is more than 1.5%, the shape of soil particles tends to be a circle, leading to the instability of the soil structure. (3) For soil with low salt content, some salt particles fill the soil pores and play a role as soil skeleton, improving the strength of the soil. But the salt content is more than 1.5%, and salt swelling plays a dominant role, weakening the structural stability of the soil. Therefore, lime can be used to stabilize the soil with a salt content less than 1.5% to meet the requirements of oil and gas pipeline foundation engineering. Saline soil with a salt content above 1.5% cannot be directly used in engineering, and special research should be conducted.

When tunnels are built in super deep soft rock, due to high geo-stress and weak surrounding rock, large deformation disasters often occur in tunnels. The middle pilot tunnel stress release technology is used to release part of the crustal stress, which can transform the high-ground stress field in the surrounding rock into the low-ground stress field, reduce the stress of the surrounding rock on the support structure when the main tunnel is expanded, thus reducing the tunnel deformation and ensuring the safety of the support structure. Therefore, relying on the Haba Snow Mountain Large Deformation Tunnel in the Lixiang section of the Yunnan Tibet Railway, literature research, numerical simulation, and on-site tests are used to study the tunnel deformation, initial support structure stress, and distribution of the loose zone of the surrounding rock under different advance distance conditions of the middle pilot tunnel. Finally, a reasonable advance distance for the middle pilot tunnel was proposed, and its application effect was analyzed through on-site monitoring. The results show that when the leading distance of the middle pilot tunnel is twice the diameter of the middle pilot tunnel, the deformation and plastic zone of the tunnel and surrounding rock are relatively small, and the stress on the support structure is relatively reasonable. Moreover, the average deformation of the tunnel measured on site can be reduced by 44.52%. The initial support structure reduces the surrounding rock pressure, steel stress, and shotcrete stress by an average of 32%, 35%, and 31%.

To achieve the goal of utilizing the underground space of abandoned mines for military purposes, this paper uses the Flac3D software to simulate and study the feasibility of expanding abandoned mine tunnels into ammunition storage facilities in terms of stability. First, based on the distribution of the tunnels in the abandoned mine, and then combining the burial depth of the ammunition storage, the safe adjacent distance, and specific cross-sectional parameters and other quantitative indicators, the specific layout of eight ammunition storage facilities was determined. Subsequently, after three-dimensional modeling, the stability of the surrounding rock in a certain mining area was simulated after undergoing the entire mining process, including development, extraction, and backfilling, in its abandoned state. This determined the feasibility of expanding the ammunition storage facilities in terms of stability for a certain mining area. Finally, through further refined modeling of the ammunition storage facilities, the stability of the expanded eight ammunition storage facilities was simulated and analyzed, and the following conclusions were drawn: there is only a small area of tensile stress concentration on the surface but no destruction, most of the underground tunnels have very good stability, and local damage is mainly concentrated in the arch top and floor of the tunnels; the eight ammunition storage facilities expanded with these cross-sectional parameters can basically ensure overall stability.

A micro-disturbance support technique using MJS waterproof wall set drilling and grouting piles has been designed to tackle the challenge of difficult excavation and support of deep foundation pits in narrow and confined spaces. Employing the Plaxis 3D finite element analysis software, a 3D numerical calculation model was established based on the third phase of the deep foundation pit project of the Hai'an railway station expansion project in order to optimize the impact of the MJS waterproof wall on the deformation of the pile foundation of adjacent existing buildings under various working conditions, including grouting pressure, grouting range, pile diameter, and construction sequence. The results indicate that the horizontal deformation displacement at the depth of existing pile foundations increases linearly with the MJS pile grout pressure coefficient; the deformation effect on adjacent existing pile foundations decreases along the pile depth direction with the reduction in MJS pile grout range; the deformation displacement of existing pile foundations changes non-linearly with the MJS pile diameter; considering the effect of different construction sequences of multiple piles, the symmetric construction method from the middle to both sides has the least cumulative deformation on the nearby existing pile foundation, which can provide experience for the excavation and support of the foundation pit in similar narrow and confined spaces.

Air-raid shelter is an important component of the underground space in Chongqing city. During the Anti-Japanese War period, they served as shelters for military and civilian production and life, enhancing the overall protection capacity of the city and providing effective protection for the war. Nowadays, there are problems with insufficient space utilization and unclear design concepts in the reuse of air raid shelters in the urban areas of Chongqing during the Anti-Japanese War. Therefore, specialized research on the adaptive reuse of air defense shelters in the urban areas of Chongqing during the Anti-Japanese War period is conducted. Based on relevant theories of adaptive reuse, firstly, by transforming and reusing the original functions and spaces of air defense shelters, the old functions is continued, the old functions is integrated with the new functions to expand the new functions. Secondly, the existing wartime air defense voids should be designed for adaptive reuse by expressing regional characteristics, optimizing internal spatial forms, showcasing ecological landscapes, upgrading functional efficiency, and enhancing safety performance, in order to improve and extend the efficiency and lifespan of wartime air defense voids. Finally, based on the unique regional characteristics of wartime air defense shelters, a diversified integration plan, a combination of civil defense functions and disaster prevention and rescue, and an adaptive reuse design strategy that integrates military and civilian functions are proposed, in order to better leverage the cultural and socio-economic benefits of air defense shelters in the Chongqing urban area during the Anti-Japanese War in the context of peace and war integration.

In the high altitude cold area, tunnel disease is a serious threat to road safety. In this paper, a large number of monitoring data obtained from field experiments are used to study the climatic characteristics and temporal and spatial distribution of temperature field in a tunnel in a cold area of high altitude on the Qinghai-Tibet Plateau. The coupling frost heave model of hydraulic-thermal-mechanical is established, and the hydraulic-thermal-mechanical numerical simulation is carried out by using the coefficient type partial differential equation and the solid mechanics model in COMSOL mathematical module. The accuracy of the model was verified by the monitoring data. On this basis, the hydraulic-thermal-mechanical distribution characteristics of the tunnel project in the cold region were studied. The results show that there is a strong correlation between the outside air temperature and the tunnel temperature, and the closer to the entrance, the stronger the response between the two. The influence of air temperature on the radial temperature field of tunnel is mainly reflected in the lining and shallow surrounding rock, and the influence on the temperature of deep surrounding rock is small and relatively lagging. In the cold season, the ice content at the invert of the tunnel and the secondary lining stress at the side wall of the tunnel reach the maximum. In addition, the interaction between meteorological elements, lining and surrounding rock is the main cause of freezing damage at tunnel entrance in high altitude cold area. The research results are helpful to better understand the mechanism of hydraulic-thermal-mechanical action of tunnels in cold areas of high altitude, and provide scientific basis and reference for the design and maintenance of tunnel engineering in cold areas.

Long-term settlement is one of the significant factors affecting the longitudinal structure safety of shield tunnel during operation. In order to more accurately predict the long-term settlement development of shield tunnel during operation, relying on deep learning algorithms, this paper proposes a long-term settlement prediction method of shield tunnel based on empirical mode decomposition and multi-layer long short-term memory artificial neural network (EMD-Multi-layer LSTM). The proposed method is designed to achieve the long-term settlement prediction of shield tunnel during operation through four key steps, namely data pre-processing, empirical mode decomposition, prediction model construction and result reconstruction, and has been successfully applied to the long-term settlement prediction analysis of multiple monitoring points in Shanghai Metro Line 10. The results indicate that: (1) Compared with the benchmark algorithms like traditional LSTM and Support Vector Machine (SVM), the model proposed in this study can more effectively predict the dynamic development of the shield tunnel's long-term settlement during operation. The generalization ability of the model is significantly improved, and the prediction accuracy of the long-term settlement is excellent, of which the maximum absolute prediction error can be controlled within 1.3 mm. (2) Meanwhile, the applicability performance analysis shows that the EMD-Multi-layer LSTM prediction model established in this paper has excellent applicability and the prediction results are always reliable under different circumstances. In general, the prediction method proposed in this study provides a new solution for the long-term settlement prediction of shield tunnel during operation, and relevant research can provide early warning and guidance for the maintenance of shield tunnel during operation.

Mechanical reaming and pressure-relief can accurately reduce the stress concentration of shallow surrounding rock mass, which is of great significance to effectively solve the problem of decreasing stability of roadway surrounding rock caused by dense large-diameter drilling and pressure relief. Based on the engineering practice of the 3106 working face of a mine, ABAQUS finite element simulation software was used to compare and analyze the changes of vertical stress, displacement, and plastic zone of surrounding rock after pressure relief by large-diameter drilling and mechanical reaming, and study the mechanism of pressure relief by mechanical reaming. The results show that: After mechanical reaming, the peak stress of the surrounding rock decreases by 14.89%, the stress of the relief section decreases by 13% on average, and the peak stress shifts back by 1.25 m. The displacement at the roof of the roadway decreases by 28.67%, and the average displacement at the top, middle, and bottom of the roadway slope decreases by 98.71%, 97.27%, and 90.63%, respectively. The proportion of plastic strain zone is reduced to 12.92%, and the plastic zone between the adjacent holes around the mechanical reaming is connected to play a coupling pressure relief role. After field application, the mechanical reaming reduces the maximum microseismic energy by 63.11%, the pressure relief effect is good, and the impact risk of the working face in the test range is eliminated.

Pile-anchor (-strut) retaining structure is widely used in deep foundation pit, and the elastic foundation beam method is a common method to simulate and analyze the deformation and stress changes in the construction process of this kind of support of foundation pit. However, when applying this method for analysis, it is necessary to first divide a soldier pile into several segments at the braces for each construction stage, and then re-derive the corresponding undetermined parameter equations by using the continuous conditions of displacement and force balance conditions at the junction of the segments, resulting in difficulty to form a unified calculation formula and complication in the analysis method. In order to solve the above problems, by using δ-function to represent the concentrated force of brace on the soldier pile and re-solving the deflection equation of the soldier pile, a unified calculation formula is derived which applies to pit with strutted or anchored retaining structures, arbitrary number braces and case of excavation or brace setting. The new method not only avoids the subdivision of the soldier pile, but also forms a simple and unified calculation method. The numerical results of the method proposed in this article have only slight differences from the segmented method, indicating that the method is feasible.

The clay shock method is gradually introduced as auxiliary construction in the shield tunnel that crosses the existing structures. The rheological properties of the clay shock slurry have an important influence on the backfilling injection construction of mid-shield. The hydration mechanismand rheological properties of the slurry are investigated based on the analysis of the material composition of the clay shock slurry. The RVDV-1T rotational viscometer with stepless speed regulation was used to carry out the rheological test. The applicability of the commonly used shear-thinning rheological model to characterize the rheological properties of the clay shock slurries was studied. The effects of stirring time, stirring rate, hydration time, and water-powder ratio on the rheological properties of the clay shock slurries were analyzed. The permeability and diffusion of the clay slurry in the stratum were investigated based on the actual project. The research results are as follows. (1) The Bingham model is more suitable for characterizing the rheological properties of the clay shock slurries. (2) The apparent viscosity and yield stress of clay shock slurry initially increase and then decrease with increasing stirring time and stirring rate. They also increase with increasing hydration time and decrease with increasing water-powder ratio of component A. (3) The soil in the infiltration zone is affected by the injection of the clay slurry, resulting in cohesive effect and an increase in strength. (4) The penetration diffusion distance of the slurry in the sand and round gravel strata is between 5 and 10 cm. The apparent viscosity and the yield stress of the slurry have a strong negative correlation with the diffusion distance. The permeability coefficient and the porosity of the stratum correlate positively with the diffusion distance. The research results provide reference for the engineering application of the clay shock method.

Aiming at the existing blasting seismic wave stress calculation formula mainly considers the source parameters and ignores the influence of the propagation medium, using the method of magnitude analysis, the blasting seismic wave stress equation of the rock body is deduced, and the theoretical calculation model of the critical vibration velocity of the rock body yielding is established by combining with the DP yielding criterion. The results show that: The magnitude of positive stress is positively correlated with the vibration velocity and the mechanical parameters of the medium. When the vibration velocity is certain, the smaller the elastic modulus is, the more obvious the change of positive stress in the medium is; when the elastic modulus is certain, the larger the vibration velocity is, the more obvious the change of positive stress in the medium is; compared with the empirical formulas, the theoretical model of the positive stress in blast seismic wave has a wider scope of application, and it can simulate the propagation of seismic waves in different medium materials and seismic wave conditions more accurately; based on the DP yield criterion, the blast seismic wave stress equation is adopted Based on the DP yield criterion, the blasting seismic wave stress equation is used to accurately predict the critical vibration velocity of different media materials when they reach yield.

The bank slope of hydropower project inevitably encounter unloading effect in operation, and the periodic rise and fall of water level will further degrade the structure of some rock mass on the bank slope, which is easy to breed landslide and seriously threaten people's life and property safety. Therefore, it is necessary to study the unloading mechanical characteristics of jointed sandstone under the water pressure circulation. In this paper, the sandstone of typical bank slope in the Three Gorges Reservoir area is taken as the test object, and the unloading mechanical properties of sandstone with cross joints of different angles are designed and tested under the circulating water pressure. The result shows that the strength of the cross-jointed rock samples is mainly affected by the inclination angle of the main joint α. As α increases from 0° to 90°, the peak strength increases successively. Under the same main joint inclination angle, the peak strength decreases first and then increases when the secondary joint inclination angle β comes from 0° to 90°, and the overall change amplitude is small. The elastic modulus and deformation modulus increase with the increase of α, and decrease first and then increase with the increase of β. The axial and circumferential strain increases with the number of water pressure cycles, and the increasing velocity first increases and then decreases. The increment of axial strain and circumferential strain is maximum at α=60° and minimum at 90°. The deterioration degree of elasticity and deformation modulus of the samples at α=60° is the largest, and the deterioration of the samples at α=60° is the most obvious due to water pressure circulation.

To explore the mechanical properties and damage evolution law of bedded slate under a triaxial compression load. The slate with apparent bedding structural plane is a composite rock mass formed by a series of connections of common plane closing element and shear deformation element of rock block containing microscopic defects. Considering the influence of closure of bedding structural plane and shear slip deformation on axial deformation of bedding rock specimen, the damage constitutive model of bedding slate under triaxial compression load is given, and the accuracy of the damage constitutive model is verified by triaxial compression test. The results show that the establishment of the damage constitutive model can accurately describe the compaction section and elastic section of the stress-strain curve of bedding slate ;When the bedding dip angle changes from 0° to 90°, the strength and deformation capacity of the bedding slate show a U-shaped distribution as a whole, and the minimum value appears at 60°; With the increase of dip angle, the failure type develops from tensile-shear composite failure to shear-slip failure, and it is splitting tensile failure at 90°; The damage evolution curve shows an overall S-shaped distribution law.

To enhance the accuracy of karst collapse risk prediction, 457 historical collapse points in the Zhongliangshan area of Chongqing City were used as the basic data. Combined with the fuzzy analytic hierarchy process and information value method, karst collapse susceptibility zones were delineated, and the accuracy of these zones was verified using a receiver operating characteristic (ROC) curve based on evenly distributed non-collapse points selected considering the density of collapse points. A threshold equation for early effective rainfall volume and rainfall duration (P_EE-D) was established using recent historical data from 57 rainfall-induced karst collapse points. This equation, along with susceptibility zones, was used to construct a heuristic matrix risk prediction model. By fitting the probability of collapse with the intensity and duration of rainfall, continuous probability values for rainfall-induced karst collapse were obtained and coupled with susceptibility zones to construct a continuous probability prediction model. These two karst collapse prediction models were validated using four recent rainfall-induced collapse events from 2021 to 2022. The results show that: (1) The area under the ROC curve (AUC value) obtained using non-collapse points selected at different multiples of the number of collapse points exceeded 0.95, indicating a high accuracy of the delineated susceptibility zones; (2) A logistic regression model for continuous probability of rainfall-induced karst collapse in the Zhongliangshan area was established, with a goodness-of-fit of 0.9135 compared to the discrete probability results obtained from the critical rainfall threshold model; (3) Both prediction models yielded similar risk level predictions for the four recent collapse events. However, the area classified as extremely high risk by the heuristic matrix risk prediction model was significantly larger than that by the continuous probability prediction model, indicating a conservative bias in its predictions. The heuristic matrix risk prediction model is easy to implement, while the continuous probability prediction model offers higher accuracy and spatial resolution.

In order to improve the granite residual soil to meet the needs of embankment filling, considering the characteristics of calcium lignosulfonate, the test of improving granite residual soil with calcium lignosulfonate was designed and carried out. The macroscopic physical and mechanical test, indoor model test and microscopic test were carried out to systematically analyze whether calcium lignosulfonate could meet the needs of embankment filling and the improvement mechanism. The results show that: (1) The addition of calcium lignosulfonate effectively improves the road performance of granite residual soil. The content of calcium lignosulfonate reaches the best at 4.00%. Compared with before improvement, the liquid limit is reduced by 32.28%, the plastic limit is reduced by 40.06%, the optimum moisture content is reduced by 18.63%, and the bearing ratio is increased by 567.09%. (2) The incorporation of calcium lignosulfonate significantly improved the mechanical properties of granite residual soil. The compressive strength of the solidified body increased by 61.12%~126.11%, the internal friction angle increased by 13.08%~37.74%, and the cohesion increased by 108.50%~379.86% under the dosage of 2.00%~8.00%. (3) There are two main aspects of the enhancement mechanism of calcium lignosulfonate modified granite residual soil. On the one hand, after the hydrolysis of calcium lignosulfonate, it can undergo protonation reaction to form lignin polymer, which can cement the soil and improve the mechanical properties. On the other hand, the calcium ions hydrolyzed from calcium lignosulfonate form a typical carbonate cementing material CaMg (CO₃)₂ through ion exchange reaction, and the carbonate cementing strength is higher than that of clay minerals.