It is quite important for the refined design and construction of geotechnical engineering to obtain a certain amount of borehole data and then determine the stratum profile information through geotechnical investigation. However, due to the particularity of the area where some engineering sites are located (existing old urban areas, cultural Relic Protection Building, etc.), there is often a problem that the borehole data is difficult to obtain, which makes the corresponding stratum information determination challenging. To this end, an artificial intelligence (AI) method for stratum information reconstruction is developed based on the fully convolutional network (FCN). The core idea of this method is to use the existing borehole data in the region as a learning sample, analyze and extract the multi-dimensional information features of the sample (vertical stratification, horizontal extension), and then use this information feature as a template to perform probability-based stratum profile information interpolation reconstruction for engineering sites with only a small amount of borehole data. Through the study and reconstruction of the geological survey data of a tunnel project and foundation pit project in the ancient city of Suzhou, it is found that the accuracy of stratum prediction gradually tends to be stable after the number of simulations increases to more than 30 times, and can reach about 90%. This verifies the applicability of the developed AI reconstruction method of stratum information, which will provide an effective choice for the prediction of complex stratum information in related projects.

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.

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.

In order to solve the problems such as long deformation time period, large deformation amount and insufficient support strength of carbonaceous slate tunnel with high ground stress. The viscoelastic constitutive model and large deformation control technique of carbonaceous slate are studied by laboratory experiment, numerical calculation and field test. The results show that: (1) The peak strength of the carbonaceous slate is greatly affected by the bedding inclination, exhibiting a U-shaped trend with increasing inclination, and the strength of the rocks with the bedding inclination of 45° is the weakest. (2) The unsteady Burgers creep constitutive model was constructed, and the creep parameters of the constitutive model were determined according to the triaxial creep test. (3) Six supporting conditions were established by using the creep constitutive model constructed. Considering safety and economy comprehensively, the supporting parameters of the large deformation control test section were defined in case 3 (HW175 steel frame, 0.6 m/pin, 4 m long anchor bolt set at the arch, 6m long anchor bolt set at the side wall, spacing 1.2 m×0.8 (ring × longitudinal)). (4) Through the test section, HW175 steel frame and 4 m arch top + 6 m side wall long anchor rod are used. The average arch top settlement and side wall convergence are 18.1 mm and 79.72 mm, respectively, meeting the purpose of controlling large deformation. The research results can provide reference for similar projects.

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.

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.

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.

The sandy clayey purple soil is susceptible to alterations in particle size distribution due to hydraulic erosion, such as rainfall and fluctuations in reservoir water levels. These changes can affect the soil's strength. To elucidate the strength characteristics of sandy clayey purple soil in the influence of the absence of different particle groups, consolidated drained triaxial shear tests of saturated sandy clayey purple soil with five distinct particle groups were conducted. The fractal dimension was employed to quantify the physical properties of varying particle sizes. The relationship between the strength characteristics of purple soil with different particle groups and the fractal dimension was obtained. The results show that: (1) There is no significant change in the internal friction angle of the soil shear strength index under the missing effect of different grain groups, but the cohesion and fractal dimension show a hyperbolic relationship; the initial tangent modulus of different grain groups is affected by confining pressure and fractal dimension, and there is a quadratic function relationship between parameter n and fractal dimension. Under low confining pressure, the stress-strain relationship of different grain groups is obviously different. With the increase of confining pressure, the stress-strain characteristics tend to be consistent. (2) Based on the Duncan-Chang E-ν model, the nonlinear elastic hyperbolic constitutive model of saturated sandy clayey purple soil under the effect of different particle groups is established by fitting the cohesion-fractal dimension hyperbolic equation, and the validity of the model is verified.

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.

After being disturbed, the regenerated rock mass is prone to looseness and fragmentation, but under the support effect, the regenerated rock mass still has a certain bearing capacity, especially with significant improvement in post peak bearing capacity, which is the foundation for controlling the stability of the regenerated rock mass roadway. To study the bearing characteristics of recycled rock mass and the influence of support on the bearing capacity of recycled rock mass, a four-factor mixed level orthogonal test was designed for uniaxial loading of recycled rock mass. The bearing mechanism of recycled rock mass is analyzed. The significance of anchor spacing, rod diameter, anchor length, and metal mesh on the post peak weakening trend and bearing capacity of recycled rock mass is tested based on orthogonal analysis of variance. The results show that: Under the conditions of no support and partial anchor support, the regenerated rock mass undergoes compression shear failure under uniaxial loading, while some anchor support regenerated rock mass undergoes splitting failure, and the metal mesh constrained regenerated rock mass specimen undergoes plastic sliding failure. The residual strength of the regenerated rock mass after fracture exhibits fluctuating characteristics. The stability of the post peak bearing stage depends on the friction effect of multiple fracture surfaces, and the support reinforcement friction effect resists the sliding and dislocation of the broken block under external loads. The metal mesh has a significant impact on the post peak bearing capacity of the recycled rock mass, while the change in anchor rod parameters only affects the weakening trend of the strength of the recycled rock mass.