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.

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.

A large number of different inclinations of tectonic fracture exist for the Sichuan-Tibet Railway along the tunnel peripheral rock, and often in the high ground temperature and high stress coupling environment. In order to study the influence of fracture inclination on the unloading failure characteristics of hard rock under high temperature and high stress coupling, this paper analyzes the unloading rupture characteristics of granite specimens of a tunnel of Sichuan-Tibet Railway under 50 ℃ real-time temperature field through unloading test by adopting indoor test and numerical simulation method. The results show that: the unloading strength decreases with the increase of fracture inclination angle, when the fracture inclination angle is 0°, the unloading strength of the specimen under the 50 ℃ real-time temperature field is obviously smaller than the unloading strength at room temperature; the fracture specimen under the unloading condition has strong tensile damage characteristics, and the dilatancy phenomenon of the specimen under the 50 ℃ real-time temperature field is more obvious when the fracture inclination angle is 30°; When the fracture inclination angle is 0°, a penetrating fracture through the center of the pre-fracture is generated; under the real-time temperature field of 50 ℃, the larger the fracture inclination angle is, the more dispersed microcracks are developed in the unloading process of the specimen, and the smaller the inclination angle is of the pre-fracture, the earlier the accelerated point of fracture development occurs.

Microwave radiation, as an emerging rock-breaking technology, shows promising applications in assisting mechanical rock fragmentation. To explore the damage mechanisms of microwave radiation on quartz sandstone, this study investigates the variations in uniaxial compressive strength, wave velocity, and macro-microscopic damage characteristics of quartz sandstone under different microwave powers and exposure times. The results indicate that with increasing microwave power and exposure time, the uniaxial compressive strength and elastic modulus exhibit a decreasing trend, while peak strain gradually increases. Both P-wave and S-wave velocities show an overall decline. The damage factor shows an upward trend, and the longer the radiation time, the greater the increase in the damage factor. As microwave power and exposure time increase, the degree of quartz sandstone fragmentation significantly intensifies, resulting in smaller and more numerous fragments. The failure mode shifts from a single shear failure to shear and cleavage along fragile planes. SEM images and fractal dimension (D-value) results indicate that as microwave exposure time increases, the number, length, width, and depth of internal cracks in specimens show an increasing trend, evolving from initial single cracks to superimposed fractures.

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.

To solve the problems of waste accumulation and deep and narrow backfilling of foundation pit in the construction process, by adding polycarboxylate superplasticizer (PCE), cement, phosphogypsum (PG) and water glass (WG), the engineering residue is improved into fluid solidified soil for foundation pit backfill. The effects of various admixtures on the fluidity, strength and drying shrinkage of the improved fluid solidified soil were studied through laboratory mobility test, unconfined compressive strength test, drying shrinkage test and microscopic test, and the improvement mechanism was analyzed. The results show that: The flow property of the material can be greatly improved by adding PCE, but the flow rate decreases rapidly with the increase of cement content. PG can make the sample obtain higher strength in the later stage, while water glass can improve the early performance and drying shrinkage property of the sample. With the incorporation of cement, PG and water glass, various hydration products fill the pores in the soil, and the internal structure of the soil becomes more dense. In addition, the feasibility of using fluid solidified soil as backfill for foundation pit is verified by selecting test section for field backfill. This paper can provide reference for improving the performance of fluid solidified soil and the design of mix ratio.

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.

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.

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.