Search

Confining pressure is an important factor affecting the strength and deformation characteristics of rock mass, it is of great significance to study the mechanical and deformation characteristics of jointed rock mass under confining pressure for the construction of deep underground engineering and the prevention of geological disasters. In order to study the mechanical and deformation characteristics of filled jointed rock under confining pressure, based on the laboratory experiment results of static uniaxial compression of filled jointed rock samples, the Particle Flow Code is used to conduct the numerical simulation. The strength characteristics, failure characteristics and micro-cracks development characteristics of filled jointed rock under different confining pressure levels, different joint inclination angles and different sample sizes are analyzed. The results show that the peak stress and peak strain increase with the increase of confining pressure level, and there is a strong linear relationship between peak stress and confining pressure level. The peak stress and initiation stress decrease first and then increase with the increase of joint inclination angle. With the increase of confining pressure level, the change law of initiation stress of filled jointed rock under different joint inclination angles is different. The confining pressure will prolong the development process of micro-cracks in filled jointed rock, which will make the distribution of micro-cracks more dispersed and the total number of micro-cracks increase. The failure mode changes from splitting failure to shear failure with the increase of confining pressure level. The change of joint inclination angle will seriously affect the failure mode and micro-cracks development characteristics of filled jointed rock.

In the construction project, rock mass is often destroyed from the joint plane, and the jointed rock mass is easy to be eroded by freeze-thaw environment. Therefore, the damage mechanical properties of filled jointed rock mass under freeze-thaw action are very important for construction disaster prevention, engineering safety evaluation and reinforcement. In order to research the effect of the freeze-thaw cycle on the mechanical deterioration properties and damage characteristics of filled jointed rocks, prefabricated filled jointed rock samples are tested with different numbers of freeze-thaw cycles under the temperature range of -20°C~20°C. Then the wave velocity test, static compression test and SHPB impact test are conducted on the rock samples after freeze-thaw. Based on the test results, the change regularity of wave velocity degradation, static compression mechanical properties and dynamic compression mechanical properties of filled jointed rocks under the effect of freeze-thaw cycles were analyzed. The results show that the wave velocity, static compressive strength and dynamic compressive strength of the filled jointed rocks all show a downtrend with the increase of the number of freeze-thaw cycles, and each parameter is positively correlated with the strength of the filling materials. Among them, the decrease in the wave velocity of the rock sample after 30 freeze-thaw cycles is greater than 30%, and the strength loss of the static peak compressive strength exceeds half of its initial strength. The static peak strain rises exponentially with the increase of the number of freeze-thaw cycles while the dynamic peak strain does not show a clear trend. The dynamic peak strain is about 1/10 to 1/5 of the static peak strain. Under the same freeze-thaw action, the lower the strength of filling material, the more serious the damage.

Abstract The prefabricated artificial filled jointed rock specimens are impacted by a self-made drop hammer impact device for many times, and the specimens with different degrees of cumulative damage characteristics are obtained. Then, the static and dynamic compression mechanical properties are studied by using universal testing machine and SHPB device. Through the static compression test, the strength and deformation characteristics of jointed rock specimens after multiple impacts are obtained, and the influence of the damage degree of jointed rock specimens characterized by wave velocity on the compressive strength of filled joints is analysed. Based on the results of SHPB impact test, the dynamic strength and deformation evolution, wave propagation law and energy dissipation law of filled joints after multiple impacts are analysed. During the SHPB test, the impact failure process of rock specimens is recorded by a high-speed camera. The experimental results show that the damage degree of jointed rock samples increases nonlinearly after multiple impacts. The attenuation laws of static strength and dynamic strength of rock samples under the same damage evolution conditions are different. With the increase of impact times, the failure mode of jointed rock samples after damage is simpler and tends to compression failure.

The impact effect can cause structural damage to a transmission tower’s foundation and affect its overall stability. In order to study the influence of the impact effect on the stability of transmission tower foundations, a three-dimensional finite element numerical simulation method was used to investigate the variations in the extent of damage, displacement, and inclination degree of a transmission tower foundation under different impact velocities, impact durations, impactor shapes, and impact locations. The results show that as the impact velocity increases, the damage value of the transmission tower foundation continuously increases, and the damaged area expands. The lateral displacement value increases continuously with the duration of the impact effect, and the variation in lateral displacement follows a linear function distribution. The inclination degree of the transmission tower foundation increases continuously with increased impact duration and can lead to overturning failure. A smaller impact contact area results in a larger compressive damage value for the transmission tower foundation, and different impact contact areas lead to different modes of failure for the transmission tower foundation. The damage value and damaged area of the transmission tower foundation vary with the location of the impact. By comparing the deformation of the transmission tower foundation before and after reinforcement, it is evident that the reinforcement design can significantly improve the deformation resistance and anti-overturning capacity of the transmission tower foundation.

To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage, multiple impact loading tests were performed on the disc marble samples, and then static Brazilian tests were conducted for the damaged samples. Besides, coupling modeling technology of finite difference method (FDM)—discrete element method (DEM) was used to carry out the numerical investigation. The results show that after multiple impacts, more white patches appear on the surface, and some microcracks, macro-fractures as well as pulverized grains are found by optical microscopic. The static tensile strength decreases with the increase of the dynamic damage variable characterized by the ultrasonic wave velocity of sample. The interaction between grains in the damaged sample becomes intense in the subsequent static loading process, causing a relatively large strain. The volume of the fragments falling off around the loading points becomes larger as impact number increases. As the dynamic damage increases, the absorbed energy of sample during the static loading first decreases and then tends to be stable. Both the stress concentration and the breakage of the force chains are the root causes of the degradation of the static tensile strength.

The cutting hills to back ditches (CHBD) project has been widely implemented since urbanization in hilly areas is steadily rising. The stability of the high-filled slope and the problem of foundation settlement deformation has become one of the vital issues for safe construction. This paper focused on the deformation evolution law and stability assessment of the high-filled deposit slope composed of the soil-rock mixture (S-RM) in the CHBD project, in Shiyan City, Hubei Province as examples. First, large-scale direct shear tests of S-RM with different rock block proportions (RBPs) under different various normal stresses were carried out, and its mechanical properties were analyzed. Next, the finite element method was used to simulate the processes of the step-by-step filling, and the deformation evolution law was analyzed. Then, the limited equilibrium method (LEM) was used to obtain the potential sliding surfaces and the corresponding safety factors of the high-filled slope, and the safety of the construction was assessed. Finally, automated monitoring of the step-by-step settlement and deep soil deformation was computerized for the typical locations, and the long-term stability of the high-filled slope was studied. The results demonstrate that the first layer of backfill in the F area contains the largest incremental settlement displacement in the y-direction, whereas the value in the G area occurs at the site of the fill layer close to the slope surface at each filling timestep. The displacement response value steadily declines with the increasing filling depth and horizontal displacement, presenting a clear spatial influence range, with the site of maximum incremental displacement as the center. After filling, the safety factors of the potential sliding surface in the F and G areas are 2.531 and 1.118, respectively, and the slope is in a stable state. The monitoring data show that the deformation mostly takes place within 10 m of the surface. The study’s findings are thought to offer technical and practical knowledge for the slope risks.

Long-term geological storage of carbon dioxide in underground engineering is the most economically viable option for reducing emissions of this greenhouse gas to the atmosphere. Underground engineering projects are often subjected to earthquakes during their lives, thus it is essential to investigate the deformation characteristics of surrounding rock of those underground engineering works subjected to seismic load under different confining pressures. To date, however, there have been notably few studies on the characteristics of rock materials under seismic load and the influences of seismic load on dynamic deformation properties of rock material under different confining pressures remain unclear. Therefore, a numerical study of the dynamic mechanical properties of a rock material (T2y6 marble) under Kobe seismic load with four different maximum stresses and four different confining pressures was conducted. The results show cyclic behavior, strain rate effect and damage are found in the stress-strain curves of the rock under simulated Kobe seismic load. Confining pressure can significantly limit the increases in lateral strain and volumetric strain, thus dilation can occur in the rock when the maximum stress of seismic load is large, and the confining pressure is small. Seismic load with small maximum stress cannot cause severe damage to the rock, but the influence is larger than that of static load. The maximum stress can be treated as a main factor affecting the damage to rock under seismic loads, while the effect of confining pressure thereon is smaller than that of the maximum stress. Furthermore, the relationships between deformation characteristics of the rock under these seismic loads, such as maximum strain, residual strain, plastic internal variable, deformation modulus, and maximum stress are different from that between the deformation characteristics and confining pressure.

In the field of shield tunnels, the occurrence of uneven longitudinal settlement in segment linings has presented persistent challenges, including heightened risks of localized damage and water leakage. While the adoption of a secondary lining has been proposed as a viable solution to these issues, the question of how to select an appropriate construction time for the secondary lining, one that enables it to fully harness its load-bearing capacity while optimizing the tunnel’s overall stress and deformation characteristics, continues to be a pressing concern. To address this issue, this study established a three-dimensional longitudinal refined numerical model of double-layer-lined shield tunnel. In addition, the deformation degree of the segment lining was used as a time indicator to define the construction time for the secondary lining. Subsequently, an analysis of the impact of the construction time of the secondary lining on the longitudinal mechanical properties of the double-layer-lined shield tunnel is conducted through an assessment of tunnel longitudinal deformation and structural stress. The research findings indicated that the construction of the secondary lining improved the longitudinal deformation resistance of shield tunnels. Simultaneously, it led to a significant increase in the longitudinal shear forces within the segment lining and a notable reduction in longitudinal bending moments. Moreover, the construction time of the secondary lining played a pivotal role in these alterations. Considering the longitudinal force situations and load-bearing characteristics of the double-layer lining structure, it was determined that the optimal construction time for the secondary lining fell within the range of 20% to 40% of the total construction duration. In this scenario, the deformation and internal forces within the segment lining remained within permissible limits. Additionally, both the segment lining and the secondary lining were able to fully utilize their load-bearing capacities, ensuring the economic and safety aspects of the tunnel.

In recent times, induced joints have been set along the length of subway stations in order to avoid disordered cracking of the main structures occurring due to temperature stress, concrete shrinkage, creep, or uneven foundation settlement. At present, the use of induced joints in subway station structures is mainly based on engineering experience. The seismic response of induced joints has not yet been well explained, much less mastered. In this study, a 3-D numerical model of a subway station incorporating certain sorts of induced joints is established systematically. Then, the seismic response of those induced joints applied in different positions and various forms has been studied under different seismic waves by varying the spectral characteristics and peak acceleration values of the waves. The results show that the horizontal relative sliding displacement of the structures on both sides of an induced joint increases gradually from bottom to top along the structure of the subway station. While the vertical sliding displacements that occur along the section width are larger at both ends of the induced joints than in the middle. What is more, with an increase in seismic intensity, the horizontal relative sliding displacement becomes larger, while the vertical displacement becomes even smaller. In addition, the relative sliding displacement can be reduced by increasing the residual longitudinal reinforcement ratio of the induced joint. Furthermore, it is discovered that the setting of key grooves at the bottom plate of the induced joint section has a certain effect on controlling the horizontal relative sliding displacement, as well as a significant effect on preventing the vertical relative dislocation of the structures on both sides of the induced joint.

As the typical multi-phase geotechnical material, the particle size distribution of the natural soil–rock mixture (S–RM) has a significant impact on the structural and mechanical properties. The coarse grain content used in the laboratory and simulation tests falls short of accurately describing the particle size distribution feature of the entire material. The main subject of this article is the influence of the fractal dimension on mechanical behaviors based on the fractal theory. The double fractal characteristics were principally discussed along with the typical particle size distribution characteristics of the S–RM in the Three Gorges Reservoir and southwest China. The influence of the various fractal dimensions on the mechanical behaviors of S–RM was then investigated using three groups of large–scale triaxial tests, and the responses of the linear and nonlinear strength indexes were analyzed. The results show that the stress–strain curves of S–RM in the hyperbolic shape are visible under various confining pressure, and the nonlinear strength characteristics can be observed. The coarse grain content exhibits a negative correlation to the average fraction dimension. The difference between the coarse and fine grain fraction dimensions becomes considerably more obvious as the coarse grain content increases, which also increases the error when using the average fractal dimension. The voids between the coarse grains cannot be filled with the fine grains as the grain coarseness grows, resulting in a loose structure and a contact frictional effect, which lowers cohesion and raises the peak friction angle.

The damage of a long tunnel is found in parts with an adverse geological structure zone under an earthquake. The phenomenon is normally the consequence of a non-uniform seismic load. Thus, to reveal the mechanism of the phenomenon, the dynamic response of the lining structure in a long tunnel passing through an adverse geological structure zone subjected to a non-uniform seismic load is mainly studied in this paper. Firstly, based on the random ground motion synthesis theory, the non-uniform ground motion acceleration–time history curves that reflect local site effects, such as traveling wave effects and attenuation effects, are generated. Secondly, the behavior of the tunnel with a different adverse geological structure zone (including different inclinations, thicknesses, and lithologies) under non-uniform seismic input is studied. Then, the impact of the different adverse geological structure zone on the internal force and safety factor of the tunnel lining is analyzed. Finally, the failure characteristics of the lining structure in the tunnel crossing through the adverse geological structure zone subjected to a non-uniform seismic load are revealed. The results show that the seismic dynamic responses significantly increase under non-uniform seismic input compared with the results under uniform seismic input, and the dynamic responses distribution along the tunnel axial is distinctly different under non-uniform seismic input. The inclination and thickness of the adverse geological structure zone have a significant influence on the internal force and safety factor of the tunnel lining, while the lithology mainly acts around the adverse geological structure zone. When the inclination angle of the adverse geological structure zone is 45°, a large number of compression-bending cracks appear in the entrance and exit sections of the tunnel, and the tunnel is in the most dangerous state.

Stress wave which is caused either by an explosion in a borehole or by an accidental explosion in a tunnel is supposed to be considered under certain circumstances when it propagates through the surrounding rock masses which contain holes in cylindrical form. Studying the ground motion induced by the cylindrical wave propagation is of practical significance for underground rock engineering and underground energy exploitation. The current study presents a numerical study on the ground motion caused by cylindrical P-wave propagation across a rock mass with a structural plane using a discrete element numerical method, UDEC. Firstly, the accuracy and validity of the cylindrical wave propagation simulation in UDEC and of the induced ground vibration are confirmed by comparison with the theoretical results for a special case that there is no structural plane in a rock mass. Secondly, cylindrical wave propagation across a rock mass with a structural plane is simulated, and then, the particle velocity on the ground surface is subsequently obtained. Finally, parametric researches are carried out on the influence of the monitoring point’s position, the structural plane stiffness, and the frequency of incident wave on the peak particle velocities (PPVs) of the ground vibrations.

The present investigation is concerned with the dynamic seismic response of subway station built in loess site by a series of shaking table tests. Firstly, according to the Bockingham p theorem, the scale ratio is determined and then the model system is designed. Then, based on the geological environment and seismological background of Xi'an, the input ground motions and loading scheme are determined. On the basis of the test data, the acceleration responses of model system, strain response characteristics of the structure, distribution of dynamic soil pressure between loess and structure, the settlement of model ground and the seismic damage mode of model system are analyzed systematically. The results show that the peak accelerations in model soil increase gradually from the bottom to the top of the soil. The peak tensile strains measured at the top and bottom of the center columns are larger than those obtained at the side walls, while the peak tensile strains in the floor slab are the smallest. Moreover, the relationship between structure uplift and soil pressure difference can be fitted by exponential function. [ABSTRACT FROM AUTHOR]

The static and dynamic compression mechanical properties of the prefabricated artificial filled rock joints specimens with different fillings and different joint thicknesses are tested, respectively. Then, the strength, deformation, wave propagation and energy dissipation laws of the filled joints are analyzed. The experimental results show that the static and dynamic compression strength of filled joints increases with the strength of filling materials while decreases with the filling thickness. The deformation characteristics of filled joints under static and dynamic compression are positively correlated with the properties of filling materials and the thickness of filled joints. With the increasing of the filling thickness, the reflection coefficient increases while the transmission coefficient decreases. With the increase of the strength of the fillings, the reflection coefficient decreases while the transmission coefficient increases. The energy dissipation ratio decreases with the increase of the filliing thickness and increases with the increase of the strength of the filling material. [ABSTRACT FROM AUTHOR]