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

The 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.

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

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

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 utilization scale of underground space in China will continue to grow for a long period of time in the future, which can provide sufficient and stable space and facility support for a variety of emission reduction and sink enhancement technologies, and has great significance to the achievement of the goal of carbon peaking and carbon neutrality. In order to reveal the research hotspots and trend of China's underground space in response to the goal of carbon peaking and carbon neutrality, 944 academic papers published in the CNKI database before Jan., 2024 were used as data samples, and a visual analysis was conducted based on the VOSviewer software to analyze the number of annual publications, the distribution of journals, keywords, and institutions of publications in this field. The results of the study show that the research literature on the response of China's underground space to the goal of carbon peaking and carbon neutrality has shown fluctuating growth, with a significant increase in the number of literature in the past two years; the research content mainly focuses on the low-carbon effect of the subway, carbon utilization and storage in underground, and underground energy storage, etc. The research trend of China's underground space in response to the goal of carbon peaking and carbon neutrality is analyzed from four aspects, namely, spatial compactness, energy diversity, functional integration, and construction phasing.

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.

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.

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.

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.

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.

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.

The space around the proposed excavation in complex environments becomes increasingly limited, the semi-infinite space assumed by the classical earth pressure theory is inconsistent with actual engineering, resulting in a lack of reasonable calculation methods for active earth pressure in excavations with limited soil. Taking the flexible retaining piles and sandy soil of limited soil excavations as the research objects, using the single-row pile cantilever retaining mode and the bottom ends of the retaining piles fixed, four excavations model tests under different soil widths were carried out. To explore the distribution characteristics of active earth pressure and horizontal displacement of retaining piles along the retaining piles. The results show that the horizontal displacement of the retaining structure on each soil width side approximates a triangular displacement pattern, and the earth pressure gradually approximates a D-shaped distribution as the excavation depth increases, with the maximum value appearing at approximately 0.8H depth. The force analysis of the soil differential unit was performed through the limit equilibrium method, and the active earth pressure distribution of the finite soil under the limit state was deduced. Combined with the friction angle development model that considers the influence of displacement, the non-limit active earth pressure distribution and resultant force of the finite soil were deduced. and the height of the point of action. The effectiveness of the calculation method in this paper is verified by comparing the earth pressure test values with the theoretical values in this paper. Through parameter analysis, it was found that the earth pressure is positively related to the aspect ratio and negatively related to the internal friction angle. The critical aspect ratio n_cr = 0.5 to distinguish between finite soil and semi-infinite soil.

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.

Urban land scarcity and increasing student numbers have limited the development of old university campuses. This study proposes a new concept of integrating above-ground and underground space for the study of the renovation design of old university campuses and applies this new concept to the Xueyuan Road Campus of China University of Mining and Technology (Beijing). The study was carried out with a focus on four aspects: functional zoning integration, traffic optimization, emergency evacuation of underground space, and space quality improvement. Adjustment of the functionality and zoning of the campus by analyzing the demolition of some of the existing old buildings, taking into account the surrounding environment and the above and below-ground conditions of the campus after the demolition, to separate pedestrian and motor vehicle traffic on campus. In this design, the large-scale gymnasium is underground beneath the playground where the upper space cannot be opened. An innovative "functional area-secondary safe area-safe area (sunken space)" evacuation system is proposed, and its feasibility was verified using the simulation software. Sunken corridors, sunken courtyards, and skylights were used to solve the problems of lighting in underground spaces. The methodology described in this paper effectively increased the area of various buildings on the campus and significantly improved the quality of the campus space. Our results provide a plan for the renovation of the Xueyuan Road Campus of China University of Mining and Technology (Beijing), and provide an effective method for the renovation of old university campuses.

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.

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 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.

The Burgers mechanical creep model is extensively used in frozen soil engineering for its concise mathematical formulation. The accuracy of this model's calculations significantly depends on the precision with which its parameters are determined. The current practice of using the “trial and error” method to ascertain these parameters often lacks clear physical rationale, thus undermining the model's reliability. This paper presents a study on frozen silty clay under various temperatures and axial pressures, employing uniaxial creep tests to refine the parameter determination process. By integrating the Burgers model with empirical data, the physical significance of its parameters is delineated: the Maxwell elastic shear modulus G_M is derived from the instantaneous strain upon loading, the Maxwell viscosity coefficient H_M is based on the slope of the linear section of the creep curve, the Kelvin elastic shear modulus G_K is ascertained from the intersection of the linear section's extension with the strain axis, and the Kelvin viscosity coefficient H_K is calculated from a specific point on the nonlinear deceleration phase of the creep curve. This approach circumvents the limitations of the traditional trial-and-error method, offering a theoretical foundation for parameter determination that is more scientific, intuitive, and efficient. Comparative analysis of experimental and computational outcomes confirms the Burgers model's efficacy in accurately depicting the attenuation and stable progression phases of frozen soil creep. This validation suggests that the parameter determination method proposed in this study is effective.

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.

Gravel piles are widely used in engineering, and their bearing capacity is an important indicator for evaluating the performance of gravel pile projects. Based on the cavity expansion theory, the calculation formula of bearing capacity of single gravel pile is derived by introducing the extended Lade-Duncan failure criterion, and considering the superimposed effect of stress expansion, the calculation formula of bearing capacity of single gravel pile under square layout scheme is derived. The laboratory scale model test shows that the maximum swelling depth of stone column is about twice the depth of pile diameter, which provides a basis for theoretical calculation. Finally, the proposed calculation method is compared and verified by field tests and existing research results. The results show that: The calculation results of the existing bearing capacity calculation formula of the crushed stone column are conservative, and the bearing capacity obtained by introducing the calculation formula of the extended Lade-Duncan failure criterion is closer to the measured value. This study can provide reference for related engineering and research.

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.

Nowadays, when the country vigorously promotes "high-quality development", the requirements of laboratory environment in various disciplines in universities are gradually improving. In the context of "reducing the development" of Beijing's overall planning policy, the utilization of campus underground space has become one of the indispensable means for the development of universities in Beijing in recent years. Meanwhile, the strong anti-interference of the underground laboratory also shows important advantages. By investigating and analyzing the existing literature of cases of campus underground experimental space at home and abroad, several design principles of underground experimental buildings are summarized. On this basis, combined with the current situation of the location and the function of the peripheral existing buildings, planning and design on the surrounding underground space of the observatory, located in the western part of Tsinghua University campus has been done. Different schemes for the ground entrance form, plane function and streamline organization logic have also been compared, which is hoped to provide reference for the future development of the campus underground experimental space in Tsinghua University.

In order to study the influence of different water content and salt content on the water-salt migration mechanism of Ili salinized loess. The water-salt migration test of saline loess under the action of the freeze-thaw cycle was carried out, and the temperature, moisture, and salt fields and their cohesion change rules were analyzed. The study shows that under the action of freezing and thawing, the temperature field, moisture field and salt field of saline loess show cyclic changes. With the increase of the number of freezing and thawing cycles, the water content of the soil column as a whole is increased, showing a pattern of high water content at the two ends and low water content in the middle. The change of salts in the soil layer under freezing and thawing is consistent with the overall change of moisture, and the salts in each soil layer show a homogeneous distribution before the unfreezing and thawing. Under the effect of temperature potential, the water carries the salts to migrate upward, resulting in higher salinity in the middle and upper part of the soil column. The increase of water content and salinity has a promoting effect on the migration of water and salts. In addition, the increase in water content will have a lubricating effect between the soil particles, resulting in the cohesion of the sample with low water content being greater than that of the sample with high water content. With the increase of salt content, the agglomerates formed by the salt crystals wrapped around the soil particles play the role of skeleton, which makes the cohesion of the specimen with high salt content larger than that of the specimen with low salt content, the value of internal friction angle of salinized loess after freeze-thawing shows a wave distribution.

The triaxial test based on photogrammetry can realize the real-time measurement of the local deformation of the specimen, but the refraction of light leads to the error in the measurement of specimen deformation. The introduction of the refraction correction factor (κ) can not only solve this problem, but also improve the test efficiency. In order to investigate the trend of the refraction correction coefficient in the axial and radial deformation measurements of different specimens, and to analyze the difference between the stress-strain curves measured by applying the refraction correction coefficient and those of the conventional triaxial tests, the photogrammetric-based consolidation and drainage triaxial tests were carried out on red clay and sandy clay, respectively. The results show that: (1) In the axial deformation measurement, the refraction correction coefficients of the different local regions of the red clay and the sandy clay converged to 1, and the refraction amplification effect on the axial deformation measurement of the specimen is negligible; (2) In the radial deformation measurement, the refraction correction coefficients of the red clay and sandy soil are 0.812 and 0.757, respectively. The refraction amplification effect has a greater impact on the radial deformation measurement of the specimen, and the refraction correction coefficients of the different specimens correspond to different refraction correction coefficients; (3) The change trends of the stress-strain curves measured by conventional triaxial and the application of refraction correction coefficient. The stress-strain curves measured by conventional triaxial and by applying the refraction correction coefficient have the same trend, and the bias stress measured by applying the refraction correction coefficient photogrammetry is relatively small in the middle and late stages of the test.

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%.

The traditional algorithm is unable to accurately calculate the ultimate bearing capacity of heavy soil foundation, whereas numerical limit analysis methods can do so precisely. It can be seen that numerical limit analysis can solve geotechnical engineering problems more complex than traditional analytical methods. The incremental load method is used, which applies the principle of failure of engineering materials from quantitative to qualitative changes in stress. As the foundation load gradually increases, the stress on the soil foundation transitions from elastic to plastic, and finally reaches the ultimate failure state, obtaining the corresponding ultimate load value. The ultimate bearing capacity of the foundation under strip foundation load was obtained by combining engineering examples, and compared with the traditional empirical results of Terzaghi, Vesic, and Chen. The results show that the numerical limit analysis method can save 40%, 20%, and similar foundation engineering quantities compared to Terzaghi, Vesic, and Chen empirical methods, respectively. At present, both Terzaghi formula and Vesic formula are applied in practical projects, while Chen formula has not been applied yet.

At present, many integration construction problems such as the disconnection of integrated development of urban rail stations and surrounding areas, insufficient integration of stations and cities, insufficient accessibility, and low comprehensive benefits are becoming more and more prominent, and at the same time, the mechanism for supervising and implementing the assessment of urban rail stations is not yet perfect. Based on the framework of urban rail station assessment system, this paper established an integrated assessment index system for urban rail stations from eight dimensions, including land function, traffic organisation, spatial environment, commercial vitality, economic benefits, safety resilience, underground space and implementation effectiveness, and took 32 rail stations in Beijing as the objects of study, and carried out the assessment and classification of the rail stations in different radial scales by using entropy Weight-TOPSIS method. Evaluation and classification of different radiation scales of rail stations were carried out by using entropy Weight-TOPSIS method. The results show that there are spatial differences in the influencing factors of rail station integration construction in different radiation scales of rail stations, and the assessment results are divided into four categories by using K-means clustering, and classification optimisation suggestions are put forward.

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.

In order to study the crack-resistance performance of fiber-reinforced composite (FRP) reinforced tunnel cracked lining, based on the peridynamics theory, a peridynamics simulation method for FRP reinforced concrete structures is established by introducing the interface weakening criteria. Four-point bending tests of FRP reinforced concrete beams are conducted to verify the simulation method. The problem of FRP reinforced tunnel cracked lining is modeled and analyzed to explore the influence of FRP reinforcement width and layers on the reinforcement performance of various cracked linings. The results indicate that: Interfacial debonding is the main failure mode of FRP reinforced cracked lining. The width and number of layers of FRP reinforcement are positively correlated with the reinforcement performance. Nevertheless, when the reinforcement width exceeds 2/3 of the arch bottom and the number of layers exceeds 2, the structural reinforcement performance does not significantly improve. In addition, the distribution and depth of cracks have a significant impact on the reinforcement performance of FRP, and the reinforcement effect of mid-span cracks is significantly better than that of eccentric cracks. Moreover, when the height ratio of mid span cracks is 1/5, the global damage index of FRP reinforcement lining decreases by 40.3%, significantly improving the crack resistance performance of the structure.

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.

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.

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.

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.

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.

Rock anchorage is a new type anchorage structure of suspension bridge with complex stress mechanisms. In order to study the deformation characteristics and bearing capacity of the suspension bridge rock anchorage, the 1∶10 scaled model tests on site are carried out based on the Xihoumen Rail-cum-Road Bridge rock anchorage project. By sequentially conducting tests on 1.2P prestressing condition loading, 1P design load condition loading, and overload condition loading, the deformation distribution law of the rock anchorage under various working conditions are analyzed and the bearing characteristics of the rock anchorage are studied. According to the research, the deformation of rock anchorage mainly occurs in the two rock anchorage bodies and the rock mass area between them under various working conditions. And the deformation distribution curve is characterized by a bimodal shape centered on the rock mass between the anchorages.Under the design load condition, the maximum deformation of the actual bridge rock anchorage is 4.17 mm. Moreover, and the safety stability coefficient of the actual bridge rock anchorage is 11. Both deformation and safety stability coefficient of the suspension bridge anchorage are meet the requirements of the specifications. The research results may provide the experimental basis for the safety evaluation of the rock anchorage of the Xihoumen Rail-cum-Road Bridge, and also provide the technical reference for the research and application of rock anchorage related issues.

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.

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.

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.

Tunnels crossing fault zones are common in railway engineering, water conservancy engineering and highway engineering. Engineering geological disasters induced by crossing fault fracture zones account for more than 50% of the total number of tunnel disasters in China. Ensuring the safety and stability of tunnels crossing fault zones is the top priority in the development of tunnel engineering in China. Based on the engineering background of Tabaiyi Tunnel, this paper explores the effective support measures of surrounding rock under the influence of fault fracture zone. In order to solve the problem of large deformation of soft rock in Tabaiyi Tunnel, this paper first explores the main controlling factors of large deformation by carrying out on-site point load test, in-situ stress test and indoor mineral composition analysis test. Then, according to the deformation mechanism of Tabaiyi Tunnel, a high pre-tightening force and long-short NPR anchor net support scheme is proposed. According to the excavation compensation theory, the high pre-tightening force of NPR anchor cable is used to compensate the stress of tunnel surrounding rock. Through numerical simulation and field monitoring, it is shown that the tunnel can effectively reduce the large deformation of surrounding rock under the influence of fault fracture zone under the high pre-tightening force and long-short NPR anchor net support scheme. The research results can provide reference for tunnel support crossing fault zone.