The reloading mechanical properties of the surrounding rock in an underground energy storage cavern are crucial for determining the safety of underground energy storage projects. This study conducted triaxial loading and unloading tests on mudstone, as well as reloading tests on unloaded damaged mudstone. By employing testing and analysis techniques such as nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), the research investigated the impact of unloading effects on the reloading mechanical properties of mudstone and revealed the deterioration mechanisms of reloading damaged mudstone. The results indicate that the fractal dimension ultimately decreases as confining pressure increases, and the confining pressure's control over internal micro-cracks in the mudstone becomes more pronounced. With increasing unloading damage, small-size micro-pores inside the mudstone samples develop into medium-sized pores, resulting in a higher internal porosity. The greater the initial unloading damage, the larger the reduction in reloading strength of the mudstone. The degree of unloading damage progressively affects the failure mode of rock samples, transitioning from shear failure to shear-tensile failure, and eventually to tensile-shear failure with increasing unloading damage. A correlation between unloading damage degree, porosity, and reloading strength has been established, bridging the gap between microstructural damage and macro-strength deterioration in unloaded damaged mudstone. This finding provides a reference for delineating unloading damage zones and predicting reloading strength within unloading areas.

The soil in the northwest loess irrigation area has been affected by the dual effects of dry-wet cycling and salt pollution, leading to significant deterioration of the loess properties in this region. Taking Q₃ loess contaminated by Na₂SO₄ as the research object, direct shear tests and scanning electron microscopy (SEM) are used to analyse the changes in mechanical properties and microstructure characteristics after different numbers of dry-wet cycles. The results show that: Under the dual effects of dry-wet cycling and salt pollution, the strength of the loess deteriorates significantly, and the microstructure changes significantly. Among them, the cohesion shows obvious deterioration, with a decline rate of up to 38.24% to 51.4%. With the increase of salt pollution and dry-wet cycling times, the proportion of individual particles in the loess body increases significantly, and the aggregates begin to disintegrate; Na₂SO₄ repeatedly crystallizes and dissolves during dry-wet cycling, thereby exerting a combined effect of salt swelling and salt erosion on the soil; among the two effects, the destructive effect of dry-wet cycling on the soil structure is greater than that of salt pollution. The research results provide an effective reference for engineering activities and pollution control in loess areas.

With the rapid development of infrastructure such as railways, highways, and water conservancy and hydropower projects in the western region of China, a number of extremely complex geological conditions and highly challenging ultra-deep buried tunnels have emerged. These developments place higher demands on the collection, analysis, and application of tunnel geological information. Geological information transparency technology plays a crucial role in ensuring safety, controlling costs, and optimizing construction progress, serving as key technical support for the smooth execution of ultra-deep buried tunnel projects. This paper systematically reviews the current development status of geological information detection technologies, covering remote sensing survey technology, geophysical exploration technology, and directional drilling technology in the pre-construction phase, as well as advanced geological forecasting technology during construction. The application scope and development directions of various technologies are analyzed. The paper also reviews the research status of multi-source geological information fusion technology and 3D geological modeling technology, detailing their progress and challenges in predicting geological conditions, model building, and applications. Finally, this paper looks ahead to the overall development of geological information transparency technology for tunnels: First, establishing a five-dimensional integrated detection system encompassing "space-air-ground-borehole-tunnel" to improve detection accuracy; second, developing intelligent geological monitoring technologies and equipment; and third, based on multi-source data fusion, constructing 3D geological models and applying virtual reality technology to achieve dynamic geological information visualization, thus enhancing the safety and efficiency of tunnel construction.

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.

To address the challenge of structural deterioration caused by frequent cracking in the lining structures of deep-buried hydraulic tunnels in high-altitude areas, the enhancement of concrete's mechanical properties is investigated through the addition of fibers and determines the optimal fiber content for practical engineering application. Firstly, tests on the tensile, compressive, and flexural mechanical properties of basalt fiber-reinforced concrete (BFRC) with varying fiber contents were conducted, the variation patterns of concrete's tensile, compressive, and flexural mechanical properties under different volumetric fiber contents were obtained. Subsequently, a mesoscopic numerical model of fiber-reinforced concrete that truly reflects the microstructural factors such as aggregate shape, gradation, aspect ratio, fiber distribution, and initial defects was established. By comparing the mesoscopic numerical model with indoor axial tension test results, the mechanism of fiber reinforcement on the tensile strength of concrete was revealed. Finally, the optimal fiber content was analyzed. The results indicate that: Compared to the plain concrete, a fiber volume content of 0.2% is optimal, with the axial tensile strength, split tensile strength, and flexural strength of BFRC increased by 12.81%, 14.79%, and 21.26%, respectively. The error between the tensile strength of the fiber concrete predicted by the established mesoscopic numerical model and the indoor test results for plain (fiber) concrete is 4.24% (5.26%), and the model can accurately reflect the failure development process and macroscopic mechanical behavior of fiber-reinforced concrete specimens. The findings of this study can provide a reference for the design and application of basalt fiber-reinforced concrete structures.

At present, the construction of large-span and super-large-span subway tunnels is increasing. Temporary support is often designed to reduce the span in the construction of those tunnels. However, temporary support needs to be removed before secondary lining is constructed due to the spatial overlap between them. The removal of temporary support is the weak situation, because the original stress balance of the structure will be broken. Improper construction can easily cause safety accidents such as tunnel collapse. In view of the lack of systematic research on the structural mechanical response and safety of the super-large-span tunnel constructed by the double-layer initial support arch-cover method at home and abroad, this paper takes the four-line parallel tunnel of Huahua section of Guangzhou Metro Line 11 as the basis project. Through the combination of theoretical analysis and numerical calculation, the mechanical response and safety of the structure during the dismantling of the tunnel are analyzed from both horizontal and vertical aspects. Finally, a scientific, reasonable, safe, efficient and rapid dismantling scheme was determined, and successfully passed the inspection of on-site construction. The results show that it is feasible to dismantle the super-large-span tunnel in urban soft stratum by using the scheme of 'first edge and then middle, and symmetrical demolition in cross direction, first three demolition and one demolition, and then one demolition and one demolition in longitudinal direction', which can provide reference and guidance for subsequent 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.

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.

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 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.