In order to investigate the impact of pore and fracture structure on the nonlinear deformation characteristics of rocks during the entire stress-strain process, considering the differences in deformation between pores and the matrix, porous rocks are deconstructed into two components: hard springs and soft springs. The Two-part Hooke's Model (TPHM) and statistical damage theory are introduced. Based on the TPHM, the complete stress-strain relationship of rocks is established, and the porosity evolution equation for the entire stress-strain process of rocks is derived. This model overcomes the limitation of the traditional Two-part Hooke's Model, which is unable to represent the plastic deformation of rocks after yielding. It not only accurately characterizes the nonlinear deformation during the pore compaction stage, plastic yielding, stress drop after peak, and residual stress characteristics in the rock compression process, but also effectively represents the porosity variation during the entire stress-strain process of rocks. Extensive experimental data validation has demonstrated that the theoretical curves of this constitutive model align well with the experimental results, with correlation coefficients consistently exceeding 0.9.

Urban underground logistics system is a complex technology and engineering system developed by the cross integration of modern logistics, transportation, vehicle and underground engineering. Based on the concept of the underground logistics system-pipeline-vehicle collaborative design, a set of cargo vehicle design methods for urban underground pipeline logistics is established. Vehicle technology research and design include vehicle scheme research, vehicle structure and new energy function design, vehicle autonomous driving technology design. This paper designs a special cargo vehicle for pipeline logistics, which is a pipe with inner diameter of 3 800 mm and van with exterior dimension length of 5 000 mm, width of 1 500 mm and height of 2 200 mm. The vehicle has automatic driving, high power, long-distance automatic transportation of goods and wireless charging function when the vehicle is driving in the pipeline. The vehicle design adopts the design concept of green, low-carbon, energy saving and integrated application of more new technological innovations. The technical research and design of cargo vehicle conducted in this paper provides a design scheme of cargo vehicle test sample vehicle and a new vehicle design method of underground pipeline logistics for the implementation of commercial urban underground logistics project.

To explore the influence of coal and rock bedding plane effects on mechanical properties, the micro-mechanical properties of coal and rock with different bedding directions are studied based on nanoindentation tests. By plotting the load-displacement curves of each group of samples, the micro-mechanical parameters of coal and rock with different bedding orientations are obtained and the failure modes of coal and rock are analyzed. Furthermore, the propagation laws of hydraulic fracturing fractures in coal and rock are discussed. The research shows that the microstructure of coal and rock is dense, the bedding structure is clear, and the bedding planes are filled with hard minerals such as quartz, accompanied by a certain amount of natural micro-cracks and developed self-generated pores. Through nanoindentation tests, it is found that the coal and rock samples have obvious anisotropy. The elastic modulus of coal and rock perpendicular to the bedding plane, parallel to the bedding plane, and at an oblique angle to the bedding plane are 5.02 GPa, 4.58 GPa, and 4.92 GPa, respectively, and the hardness is 0.38 GPa, 0.35 GPa, and 0.37 GPa, respectively. The elastic modulus and hardness of coal and rock are consistent with their macroscopic mechanical laws. In terms of the energy dissipation characteristics of failure in different directions, the coal and rock perpendicular to the bedding plane require the largest fracture energy, while the coal and rock parallel to the bedding plane have the smallest fracture energy dissipation. In addition, the fracture toughness is 0.25, 0.22, and 0.23 MPa·m^0.5, respectively. The brittleness coefficient of coal and rock varies with the differences in failure forms in different directions. Based on the nanoindentation test data, the propagation characteristics of fractures under different bedding directions are revealed. Fractures in the direction perpendicular to the bedding plane extend along natural fissures, fractures parallel to the bedding plane mainly develop along the weak bedding plane, and fractures at an oblique angle to the bedding plane are more prone to branching during the deep extension process. The research results provide scientific data support for the engineering application of coal and rock, offer important references for engineering design, construction, monitoring and optimization, and have the potential to improve the safety and economy of engineering, contributing to sustainable development.

Blow-filled soil with high water content has poor engineering characteristics such as low strength, high water content and structural instability, etc. A new type of curing agent researched in-house was used to cure the blow-filled soil in the Binhai area of Tianjin, to achieve the properties of lightweight and high strength. In order to investigate the factors affecting the strength of blow-fill cured soil, the blow-fill cured soil was subjected to unconfined compression test, triaxial shear test and microstructure test. The results show that: The unconfined compressive strength of blow-fill cured lightweight soil is positively correlated with its density; The alkaline environment and salt content are favourable to the strength of blow-fill cured lightweight soil when the pH value is less than 11.4 and the salt content is lower than 1%, and the strength growth of cured soil is inhibited when the salt content is higher than this limit, respectively. When the salt content and pH value are low, the soil shows strain softening phenomenon, and the cohesion and internal friction angle of blow-fill cured lightweight soil gradually increase with the increase of salt content and pH value. The change mechanism of the strength of blow-fill cured lightweight soil with density, salt content and pH is explained from the microscopic level by nitrogen adsorption test and SEM scanning electron microscope test. The research results can provide a theoretical basis and reference for engineering practice.

The stabilization of slurry properties in slurry shield tunneling is the key to form a slightly permeable filter cake on the excavation surface and to effectively balance the soil-water pressure in the ground. The deterioration of slurry properties due to seawater intrusion is mainly caused by the high salt concentration, especially the concentration of divalent cations such as Ca²⁺, Mg²⁺, etc. To address the issue of the deteriorating slurry properties due to seawater, study on the effects of adding sodium carbonate, ethylenediaminetetraacetic acid (EDTA), and xanthan gum were conducted to a slurry with bentonite to seawater ratio of 3 ∶ 50. Variations in slurry density, Marshall's funnel viscosity and 2 h bleeding rate were measured. The experimental results indicate that: The addition of sodium carbonate increased the slurry density, while EDTA and xanthan gum alone have minimal impact on the slurry properties. However, when EDTA and xanthan gum were added with a ratio of 10 ∶ 1, the 2 h bleeding rate of the slurry decreased by 50%. The characteristic particle size d₈₅ of the particles in the slurry and their zeta potential test results showed that the stability of the slurry and its colloidal properties were less relevant. The complex addition of EDTA and xanthan gum significantly improved the stability of the slurry, because EDTA chelated divalent cations in the seawater, which restored the thickening capacity of xanthan gum. The results are important guidelines for the development of cation-resistant thickeners to enhance the stability of seawater slurries.

The artificial ground freezing method is widely used in underground engineering due to its environmental friendliness, safety, and reliability. This study is conducted based on the connection passage of a section of the Fuzhou metro. Field measurement data and numerical simulation are used to investigate the coupled evolution of temperature and displacement fields of the frozen curtain during the freezing-excavation process. The study results indicate that: A staggered freezing method on both sides was chosen to reduce the strong frost heave impact caused by large-volume freezing. Upon completion of freezing, the surface displacements on the left and right sides were 64.51 mm and 76.72 mm, respectively. Upon completion of the freezing process, the surface displacements on the left and right sides were 64.12 mm and 73.84 mm, respectively. During the excavation, the maximum convergence displacement of the frozen curtain was 1.52 mm, and the maximum displacement convergence rate was 0.082 mm/d, both well below control values. Under varying support timing conditions, deformation and displacement of the frozen curtain increased with extended support timing. The average vertical displacement change at each monitoring point is less than 0.03 mm/d. Increasing the excavation step length from 1.5 m to 2.5 m resulted in the frozen curtain's bottom heave and top settlement increasing by 1.16 times and 5.56 times, respectively. Vertical displacement changes were greater when the excavation step length was between 1.5 m and 2.0 m compared to when it was between 2.0 m and 2.5 m. These findings can be a reference for future freezing-excavation projects of ultra-long subway connecting passages.

At present, the actual pollutant emissions under slag removal stage have not been fully considered in the ventilation of tunnel construction, greatly increasing the required air volume for tunnel construction and causing huge energy waste. On-site testing of CO concentration and wind speed was conducted based on a certain tunnel, the changes in CO concentration over time under different processes were studied, and the effects of engineering vehicle emissions and fan air supply on the distribution of CO concentration and wind speed in the tunnel were analyzed. The results show that: The CO concentration on the palm face remained basically unchanged within 25 minutes after blasting, about 200 mg/m³; During the slag removal stage, the CO concentration on the palm surface decreases linearly and reaches the standard limit (30 mg/m³) after 90 minutes of ventilation; The actual required air volume for tunnel construction during the slag removal stage is much lower than the standard requirements. As the supply air volume increases, the CO concentration in the return air section decreases exponentially. Based on the research results, an empirical calculation formula for CO concentration in highway tunnel construction ventilation is proposed, which takes into account the coupling effects of CO emissions and supply air volume.

Before refracturing, due to the long-term injection and production of old wells, the distribution of regional formation pressure shows non-uniform variations. It is urgent to coupling consider this non-uniform stress evolution in the subsequent refracturing. For this purpose, taking the Chang-6 reservoir in the W block of Changqing Oilfield as an example, an in-situ stress evolution model under long-term injection and production of vertical wells is established using the Fast Lagrangian Analysis of Continua. The simulated stress field is then imported into a hydrofracture numerical model based on the discrete lattice method for modeling fracture propagation of refracturing, achieving an integrated simulation of in-situ stress evolution and hydraulic fracturing evolution. The results show that: (1) After the production of well WJ, the pore pressure around this well decreases by about 4 MPa, and the two horizontal principal stresses experience a similar synchronous reduction, but the decreasing magnitude is only about 2.5 MPa. This indicates that production will result in a decrease in the total stress but an increase in the effective stress. (2) Hydraulic fractures tend to propagate towards the depleted area preferentially. The engineering measures, such as slowly injecting fluid or shutting in before refracturing to increase the formation pressure in the depleted area, are recommended on site, thereby avoiding or reducing refracturing fractures extending into these areas. (3) As the injection time increases, the primary growth of refracturing fractures transitions from area expansion to width expansion, indicating that a short-duration, high-volume refracturing should be adopted. On the one hand, maximizing reservoir transformation can be achieved in a short time, on the other hand, increasing the injection rate can promote the even expansion of multiple fractures.

The underground caverns has the advantages of safe concealment, environmental protection, and land saving. However, due to its enclosed space, pollutants are easily accumulated during construction. Consequently, improving the operation efficiency of the ventilation system and reducing energy consumption during the construction period are the keys to ensuring the safety of personnel and the normal operation of equipment. Taking an underground cavern project as the object, a theoretical calculation is used to determine the frequency conversion control strategy of the cavern fan, and numerical simulation (Fluent) is used to analyze the concentration changes of benzene and dust pollutants in the underground cavern before and after frequency conversion under the pressure ventilation condition, the field environmental quality monitoring data are compared and validated. The results show that: the concentration of pollutants on the longitudinal section of each cavern before and after continuous ventilation frequency conversion increases gradually and then stabilizes. The gradual conservation of pollutant generation and emission rates, with pollutant concentrations at breathing height below the limit values, verifies the effectiveness of the variable frequency strategy. In the construction site, the ventilation dynamic control system is established to realize the variable air volume control. When the axial flow fan maintains an energy-saving rate of around 25% and the jet fan maintains an energy-saving rate of over 60%, the pollutant concentration in the cavern remains within the limit range. This not only ensures the safety of construction personnel but also reduces energy consumption. The study can provide reference for the ventilation frequency conversion design of multi-face construction in underground caverns.

Based on the actual project, a three-dimensional simulation model is constructed to study the deformation and stress characteristics of the special-shaped soil-rock foundation pit excavation of the suspended pile. By adopting bar demolition method, a strength redundancy expression method based on the ultimate bearing capacity of the inner support is proposed, and two inner support importance evaluation indexes of the associated bar and the correlation coefficient are proposed. The findings indicate: (1) Deformation of special-shaped soil-rock foundation pit with the suspended pile mainly concentrates in the upper soil layers, the position of the positive angle and the middle of the longest side of the foundation pit., achieving a peak value of 17.02 mm. This deformation is linked to the geometric composition and stiffness distribution of the support system itself. Notably, the upper deformation of the supporting structure at the positive corner of the foundation pit is larger, and the influence range is about 2 times that at the negative corner; (2) The strength redundancy based on ultimate bearing capacity can comprehensively and quantitatively evaluate the redundancy of deep foundation pits, where the associated bar can pinpoint which component would be most affected after damage occurs, while the correlation coefficient can, to some extent, reflect critical components within support structures; (3) The redundancy of the inner support based on the ultimate bearing capacity is related to its own load and the arrangement of adjacent support bars. The minimum is 4.18. The associated bar are mainly concentrated in the adjacent bars. In the design of the correlation coefficient, should be optimized to decrease the correlation coefficient of the bar and improve the overall reliability of the support structure.