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Rocks exhibit various mechanical properties under different stress conditions, with changes during unloading having significant implications for geological engineering safety. This study carried out triaxial loading and unloading mechanical tests on sandy slate to investigate its mechanical properties, deformation characteristics, and failure mechanisms at different initial stress levels and stress paths. The results showed that during the unloading process, the deformation modulus (E) of the sandy slate decreased, and the Poisson's ratio (μ) gradually increased. This indicates that significant volume expansion of the rock is the dominant factor in its deformation and failure. The exponential function can be used to describe the evolution of E and μ with confining pressure during unloading. The damage stress of the rock under unloading conditions was lower than that under loading conditions, suggesting that unloading led to an earlier onset of volumetric expansion in the sandy slate. Under conditions where the initial axial stress level approached the damage stress, the mechanical properties were most significantly affected by unloading. Compared to loading conditions, when the initial axial stress level was at 70% of the peak strength, the cohesion (c) decreased by 15.77 to 29.37%, while the internal friction angle (φ) increased by 1.88 to 5.14%. The rock's failure process can be divided into four stages based on the development of microcracks. Unloading during the stages of microcrack initiation and propagation can lead to tensile cracks of varying degrees, resulting in different mechanical properties and failure characteristics under loading and unloading conditions. [ABSTRACT FROM AUTHOR]

Abstract Rocks exhibit various mechanical properties under different stress conditions, with changes during unloading having significant implications for geological engineering safety. This study carried out triaxial loading and unloading mechanical tests on sandy slate to investigate its mechanical properties, deformation characteristics, and failure mechanisms at different initial stress levels and stress paths. The results showed that during the unloading process, the deformation modulus (E) of the sandy slate decreased, and the Poisson's ratio (μ) gradually increased. This indicates that significant volume expansion of the rock is the dominant factor in its deformation and failure. The exponential function can be used to describe the evolution of E and μ with confining pressure during unloading. The damage stress of the rock under unloading conditions was lower than that under loading conditions, suggesting that unloading led to an earlier onset of volumetric expansion in the sandy slate. Under conditions where the initial axial stress level approached the damage stress, the mechanical properties were most significantly affected by unloading. Compared to loading conditions, when the initial axial stress level was at 70% of the peak strength, the cohesion (c) decreased by 15.77 to 29.37%, while the internal friction angle (φ) increased by 1.88 to 5.14%. The rock's failure process can be divided into four stages based on the development of microcracks. Unloading during the stages of microcrack initiation and propagation can lead to tensile cracks of varying degrees, resulting in different mechanical properties and failure characteristics under loading and unloading conditions.

The aim of this study is to investigate the mechanisms and kinematic characteristics of landslides in the southwestern mountainous regions of China. Field surveys and aerial photography were conducted to establish a discrete element method model with calibrated mesomechanical parameters. By considering internal and external triggering factors, a coupled finite difference and discrete element method was used to simulate the deformation, failure mechanism and movement process of slopes as well as to analyse the characteristics of debris movement. The findings revealed that the unique lithological and unfavourable geological structures resulted in an extremely fragmented rock mass, which was the internal cause of landslides. The main external cause was the mining of coal seams beneath the slumped mass, leading to extensive cracks at the trailing edge of the slope and subsequent debris movement. The average velocity of the slumped mass exhibited fluctuation before 3.5 s, followed by a rapid increase at 3.5 s, reaching a maximum speed of approximately 9.5 m/s at 9.8 s. The velocity and displacement of the debris gradually decreased from the bottom to the top in the sliding source area. The maximum displacement of the debris was 1.24 km. The entire landslide process lasted approximately 47 s, with the debris accumulating mostly at the toe of the slope. The research findings provide valuable theoretical support for the prevention and control of geological hazards induced by underground mining activities. [ABSTRACT FROM AUTHOR]

Toppling is a typical failure mode of a rock slope. The deformation mechanism and sliding mode of a toppled slope are considerably different from those of conventional slopes. The analysis methods and reinforcement strategies for conventional slopes have some limitations in toppled slopes, especially flexural toppled slopes. In this paper, the right bank slope of the Miaowei hydropower plant was taken as a case study. Based on the qualitative understanding, the method of discrete element analysis is used to “reproduce” the deformation and failure of the slope and analyze the mechanism of deformation and failure. Based on the knowledge gained from the discrete element analysis, closed-loop feedback analysis was carried out to design the reinforcement measures. The analysis confirmed that the excavation in the lower part of the slope and heavy rainfall dominate the formation of sliding failure along the toppling-induced fracture zone. With this understanding, strong anchorage on the middle and lower parts of the slope was planned. Meanwhile, more drainage measures were also designed. The slope was relatively stable during excavation, and the effectiveness of the analysis method and design measures was confirmed. The research results can be used to guide the treatment of flexural toppled slopes. [ABSTRACT FROM AUTHOR]

During the construction of the Changning tunnel, large deformation of surrounding rock was induced frequently due to the effects of geological conditions such as weak and broken rock mass, and high ground stress. In this paper, the deformation and failure mechanism were studied using field investigation, rock structure analysis, and physical model test. The surrounding rock is weathered metamorphic sandstone. The SEM observation of rock mass shows that the schistosity structure is obvious, and the structure of rock mass is relatively loose with well-developed pores. The content of clay minerals in the rock is high, and the main components are illite and chlorite. The model test results show that under the original rock stress, the stress and deformation of surrounding rock during excavation showed obvious asymmetry, and the stress of the 3D printed steel arch model gradually changed from tensile stress to compressive stress. In the process of overload, the surrounding rock has obvious slip and spalling, and the spalling mainly occurred in the shear sliding part of the stratum. With the more serious deformation of the steel arch, the stress concentration was obvious. The abnormal temperature area of the surrounding rock gradually expanded with the process of excavation and overload, and the temperature of the rock layer where shear sliding occurs was high. The research results show that the compression bending and shear sliding of rock strata caused by the rock structure and tectonic stress are the main reasons for the large deformation of the Changning tunnel, and reducing the slip deformation of the rock stratum is the key to controlling the deformation of the surrounding rock. [ABSTRACT FROM AUTHOR]

Due to the large differences in physico-mechanical properties of composite strata, jamming, head sinking and other serious consequences occur frequently during tunnel boring machine (TBM) excavation. To analyse the stability of surrounding rocks in composite strata under the disturbance of TBM excavation, a geomechanical model test was carried out based on the Lanzhou water supply project. The evolution patterns and distribution characteristics of the strain, stress, and tunnel deformation and fracturing were analysed. The results showed that during TBM excavation in the horizontal composite formations (with upper soft and lower hard layers and with upper hard and lower soft layers), a significant difference in response to the surrounding rocks can be observed. As the strength ratio of the surrounding rocks decreases, the ratio of the maximum strain of the hard rock mass to that of the relatively soft rock mass gradually decreases. The radial stress of the relatively soft rock mass is smaller than that of the hard rock mass in both types of composite strata, indicating that the weak rock mass in the composite formation results in the difference in the mechanical behaviours of the surrounding rocks. The displacement field of the surrounding rocks obtained by the digital speckle correlation method (DSCM) and the macro-fracture morphology after tunnel excavation visually reflected the deformation difference of the composite rock mass. Finally, some suggestions and measures were provided for TBM excavation in composite strata, such as advance geological forecasting and effective monitoring of weak rock masses.

Incremental sheet forming (ISF) is a promising flexible manufacturing process, which has been tested in sheet forming of various metallic materials. Although ISF-based forming of thermoplastics is relatively new, it has drawn considerable interests and significant progress has been made in recent years. This paper presents a review of concurrent research on the emerging trend of thermoplastic-focused ISF processes. Attention is given to the processing conditions including process setup, process parameters and forming forces. The deformation mechanism and failure behaviour during ISF of thermoplastics are evaluated, which leads to detailed discussions on the formability, effect of different process parameters and the forming quality such as geometric accuracy, surface finish and other consideration factors in ISF of thermoplastics. A comparison of important similarities and differences between ISF of thermoplastic and metallic materials is made. Finally, a brief discussion is provided on the technical challenges and research directions for ISF of thermoplastic materials in the future. [ABSTRACT FROM AUTHOR]

This paper aims to explore the deformation and failure mechanism of surrounding rock of small spacing tunnel with super large sections. A geo-mechanical model test was carried out with the Ganggou Tunnel in China as engineering background. Tunnel excavation with and without high strength support were simulated in the experimental test. The effect of high strength support on rock displacement, stress evolution, and mechanical characteristics of support components were analyzed. Afterward, an overloading test was conducted for different overburden depths. Conclusions regarding the deformation and failure mechanism of surrounding rock are developed by comparing with and without high strength support. [ABSTRACT FROM AUTHOR]

• A large-scale model test for metro tunnel crossing the center of land subsidence induced by groundwater exploitation is performed. • The deformation and stress characteristics of metro tunnel under the action of land subsidence is revealed. • The possible deformation and failure modes of metro tunnel induced by land subsidence are identified. • The countermeasure suggestions preventing the tunnel damage caused by land subsidence are proposed. Land subsidence is a geological disaster distributed worldwide, and the large-scale exploitation of confined aquifers is the leading cause. Xi'an is a city with severe land subsidence among inland cities in China, which risks the construction and safe operation of large-scale urban metro projects. To reveal the deformation and failure mechanism of the built metro tunnel under land subsidence induced by groundwater overexploitation, a test device simulating land subsidence was developed and a physical model test was carried out. Combined with numerical simulation, the deformation and stress characteristics of the tunnel lining caused by land subsidence were analyzed. The results show that during land subsidence, the surrounding soil pressure at the top and bottom of the tunnel decreases in the influence area of land subsidence and increases outside. The longitudinal length of metro tunnel affected by land subsidence is 1.25 times the length of the major axis of land subsidence area. The deformation of the tunnel crossing land subsidence area shows a settlement in the middle and upward warping at both ends, and the longitudinal deformation was found to conform to the Gaussian distribution. The tunnel vault in the subsidence area is in compression, and the inverted arch is in tension. The deformation and failure of the tunnel in the land subsidence area are in tensile bending failure mode. The suggestions, including design principles and structural measures, are proposed to alleviate metro tunnel damage induced by land subsidence, providing a significant reference for structural design and safe operation of metro tunnels crossing land subsidence areas. [ABSTRACT FROM AUTHOR]

To solve the support problems of high stress roadways in deep mines, we developed a new 3D U-type confined concrete support system from the conventional U-type steel arch centering. Its core is the U-type confined concrete (UCC) arch centering. With a real scale mechanical test system for the confined concrete arch centering in underground engineering and numerical calculation methods, we studied in depth on the mechanical properties and deformation & failure mechanism of UCC arch centering (UCCAC). The results of the study show the yielding load and the limit load of UCC29 arch centering is 1230 kN and 1310 kN respectively in even pressure loading conditions; and a slight difference between the laboratory test and the numerical simulation on these two is 8.86% and 12.5% respectively. The deformation form of the arch centering is “vault uplifting, legs introverting and the overall shape becomes oval”; and the largest deformation occurs between the middle of the legs and the arch centering springing. The deformation and failure mechanism of arch centering is the partial strength failure causes the entire arch centering to lose its stability. The application on site shows the UCCAC has a superb effect on the surrounding rock control; therefore, the UCCAC is a new effective support for the high stress roadways in deep mines. [ABSTRACT FROM AUTHOR]

• The failure mode and deformation characteristics of segmented utility tunnel are analyzed. • The relationship between the failure mode and intersection angles is analyzed. • The deformation of utility tunnel is calculated based on the holding effect of stratum. Ground fissures are a special urban geological disaster within the city of Xi'an. The differential settlement between strata can cause ground cracking and severely threatens the safe construction and operation of underground engineering. This study establishes a 3D-FDM calculation model of different intersection relationships between the segmented utility tunnel and the ground fissures using Flac 3D software. The influence of the intersection angles on the deformation and failure characteristics of the structure was analyzed. The results show that the segmented utility tunnel presents with the deformation characteristic of three-dimensional movement under the action of the ground fissures. The deformation between structures is primarily vertical dislocation, horizontal tension, and compression, indicating that the structure may be subjected to a bending-torsion failure. The vertical settlement of the roof of the utility tunnel shows the deformation characteristics of three broken lines. The third and fourth structures have a significant differential settlement, showing a negative correlation with the intersection angle. The segmented measures can eliminate the void area at the bottom of the hanging wall in the utility tunnel; however, when the intersection angle is ≤30°, the contact pressure at the bottom is close to 0, indicating that the intersection angle has a significant impact on the formation of the void areas. In addition, the calculation method of the vertical settlement of the segmented utility tunnel crossing the ground fissure zone is also proposed. It has proven to be effective in calculating the vertical deformation of the structure. This study provides scientific guidance for constructing utility tunnels within ground fissure development areas. [ABSTRACT FROM AUTHOR]

The deep roadway with thick top coal is a typical roadway difficult to support in deep mining project, and resolving this sophisticated problem to control the stability of surrounding rock is of great significance in safety production of coal mines. In order to explore the surrounding rock deformation and failure mechanisms of such deep roadways, with Zhaolou coal mine in Juye mining area of China as the engineering background, a large-scale geomechanical model test was carried out. The displacement and stress evolution laws of surrounding rock supported by the pressure relief anchor box beam system were researched. Meanwhile, the related results validate and analyze main failure characteristics and mechanisms of the surrounding rock by comparing with field test. [ABSTRACT FROM AUTHOR]

• The induced factors of the Baige landslide are comprehensively investigated. • The Baige landslide is caused by deep-seated gravitational slope deformation. • River downcutting is a prerequisite for the evolution of the Baige landslide. • Earthquake contributes to accelerating the development of the Baige landslide. On October 11 and November 3, 2018, two successive landslides happened at the same location near Baige Village in Tibet of China and dammed the Jinsha River twice. The induced factors and formation mechanism of the Baige landslide are still being questioned. In this paper, high-resolution topographic data, multi-temporal remote sensing images (including the unmanned aerial vehicle (UAV) 3D image, remote sensing, and Geographical Information Systems (GIS) techniques), rainfall data, seismic records, comprehensive field investigations, and numerical simulations are used to identify the main characteristics, the induced factors, and the formation mechanism of the event. The results show that deep-seated gravitational slope deformations play an important role in the evolution process of the Baige landslide; river downcutting is a prerequisite for the progressive evolution of the gravitational slope deformation behavior of the Baige landslide, whereas earthquake plays a catalytic role in the development of the gravitational slope deformation of the Baige landslide. The Baige landslide would be a typical case study for understanding the formation mechanism of large-scale landslides along the Jinsha River. [ABSTRACT FROM AUTHOR]

The quasi-static tensile behavior of tungsten/glass composites containing 40–50 vol% tungsten at elevated temperatures in the range of 550–750 °C was investigated. Results show that the composites present absolute brittleness at temperatures up to 650 °C while exhibit brittle-to-ductile transition in the temperature range of 650–700 °C and super-plasticity at 750 °C due to the decreasing viscosity of glass matrix. The strength of the composites declines with the increase of tungsten content at temperatures lower than 650 °C and increases with increasing the volume fraction of tungsten at 750 °C. In the temperatures between 650 and 700 °C, 55BH/45W exhibits the highest strength while 60BH/40W presents the lowest one. The elongations of the composites reduce with increasing tungsten content at 750 °C because of the amount of W/W and W/G interfaces increasing. In addition, the effects of temperature and tungsten content on the deformation and fracture mechanism of the composite were analyzed. • Increasing temperatures leads to the brittle-ductile-transition of the composites. • The composites show the super-plasticity at 750°C with elongations more than 100%. • The elongations of the composites decrease with tungsten content increasing. • The deformation and failure occurred in glass matrix at elevated temperatures. • The fracture mode of the materials at 750°C changed into a mixed mode as tungsten content increasing. [ABSTRACT FROM AUTHOR]