Search Results (7)

The steep bedding rock slope (SBRS) is easily destabilized under earthquake action, so it is crucial to research the features of this kind of slope’s seismic dynamic reactions in order to prevent and mitigate disasters. Few researchers have examined these slopes from an energy perspective, and the majority of recent research focuses on the displacement and acceleration response patterns of these kinds of slopes under seismic action. This work performed an extended study of a dynamic numerical simulation and systematically analyzed the dynamic response characteristics of this type of slope under earth quake conditions from the standpoint of energy utilizing the Hilbert–Huang transform (HHT) and marginal spectrum (MSP) theory. This was carried out in response to the slope’s shaking table test from our previous work. The findings indicate the following: (1) The ‘elevation effect’ and ‘surface effect’ are clearly seen in the acceleration amplification factor (AAF) of the slope during an earthquake. The selectivity of the slope acceleration’s Fourier spectrum amplification impact indicates that the elevation amplification effect makes the high-frequency peak’s amplitude more noticeable. (2) Although the effect of the weak layer is more pronounced in the high-frequency portion, both the elevation and the weak layer affect the seismic wave’s Hilbert energy. As a result, the weak layer at the top of the slope is usually destroyed first during an earthquake. (3) Prior to the locked segment’s penetration failure at the toe of the SBRS, the Hilbert energy of the high-frequency band of the marginal spectrum at the monitoring point on the top portion of the segment will rise sharply. This suggests that the upper portion of the locked segment has begun to sustain damage. There are antecedents even when there is no penetration failure. Full article

In this study, statistical analysis was conducted to categorize a large number of actual typical cases and analyze the formation conditions of toppling deformation in bedding rock slopes. Based on geological prototypes and similarity theory, a bottom friction test was conducted on the toppling deformable body while considering the excavation process. Based on the deformation and failure phenomena observed in the bottom friction test model, along with the displacement curves at key points, the deformation process in steep bedding rock slopes can be divided into the following five distinct stages: the initial phase, the unloading–rebound phase, the tensile failure phase, the bending creep phase, and the bending–toppling damage phase. To evaluate the stability, a new constitutive model of the nonlinear viscoelastic–plastic rheology of rock masses was developed. This model is based on a nonlinear function derived from analyzing the creep test data of rock masses under fractional loading. Furthermore, a mechanical equilibrium differential equation for rock slabs was formulated to quantitatively describe the aging deformation and failure processes of slopes with delayed instability. Finally, a stability criterion and a quantitative evaluation model for toppling deformation slopes that considered time-varying factors were established. The stability of the model was calculated using a hydropower station slope case, and the results were found to be in good agreement with the actual situation. Full article

The construction of major hydropower projects globally is challenged by slope deformation in reservoir areas. The deformation and failure mechanisms of large rock slopes are complex and poorly understood, making prevention and management extremely challenging. In order to explore the influence mechanism of the water level variation on the deformation of steep toppling bedding rock slopes, this paper takes the right bank slope near the dam area of the Longtou Hydropower Station as an example, and field investigations, deformation monitoring, physical simulation tests and numerical analyses are carried out. It is found that the slope deformation response is obvious under the influence of the reservoir water level variation, which is mainly reflected in the change in the slope groundwater level, rock mechanical parameters and seepage field in the slope body. The toe of the slope produces plastic deformation and maximum displacement. With the increase in the reservoir water level, the plastic zone expands and the displacement increases, which leads to the intensification of the slope deformation. This paper puts forward that the deformation and failure modes of the steep and toppling bedding rock slope caused by water level variation are due to shear dislocation, bending deformation and toppling fracture. This study reveals the influence mechanism of the water level variation on the deformation of steep and toppling bedding rock slopes, which can provide theoretical support for the construction of major hydropower projects. Full article

Steep surrounding rock significantly challenges tunnel stability by affecting the stress distribution and deformation behavior. The angle of dip in surrounding rock greatly influences these factors, heightening the risk of instability along bedding planes, particularly under high ground stress conditions. This paper presents a comprehensive analysis of steep rock strata mechanical properties based on a railway tunnel in Yunnan Province, China. It incorporates long-term field monitoring and various laboratory tests, including point load, triaxial, and loose circle tests. Using experimental data, this study simulated the failure processes of steep surrounding rock and tunnel structures with a custom finite element method (FEM) integrated with the volume of fluid (VOF) approach. The analysis summarized the deformation patterns, investigated the causes of inverted arch deformation and failure, and proposed countermeasures. The findings reveal that increasing the rock dip angle results in greater deformation and accelerated failure rates, with the surrounding rock’s loose zone stabilizing at approximately 8 m once deformation stabilizes. At a surface deformation of 8 cm, the failure zone extends to 6 m; however, this extension occurs more rapidly with higher lateral pressure coefficients. Additionally, failure zones develop more quickly in thin, soft rock on steep slopes compared to uniform rock formations. The rise of the tunnel floor is attributed to the steeply inclined, thin surrounding rock. To enhance bottom structure stiffness, this study recommends incorporating an inverted arch structure and increasing both the number and strength of the anchor bolts. Full article

Medium-steep bedding rock slopes (MBRSs) are generally considered relatively stable, because the dip angle of the rock layers (45–55°) is larger than the slope angle (40–45°). However, the stability of MBRSs was significantly impacted during the 1933 Diexi earthquake, leading to slope instability. Field investigations revealed that no continuous sliding surface was recognized in the failure slopes. Instead, the source areas of landslides present a “reverse steps” feature, where the step surfaces are perpendicular to the bedding surface, and their normal directions point towards the crest of the slopes. These orientations of “reverse steps” differ significantly from those of steps formed under static conditions, which makes it difficult to explain the phenomenon using traditional failure mechanism of the slope. Therefore, a large-scale shaking table test was conducted to replicate the deformation and failure processes of MBRSs under seismic action. The test revealed the elevation amplification effect, where the amplification factors of the acceleration increased with increasing elevation. As the amplitude of the input seismic wave increased, the acceleration amplification factor initially rose and subsequently decreased with the increase in the shear strain of the rock mass. The dynamic response of the slope under Z-direction seismic waves is stronger than that under X-direction seismic waves. The deformation and failure were mainly concentrated in the upper part of the slope, which was in good agreement with the field observations. Based on these findings, the deformation and failure mechanism of MBRSs was analyzed by considering both the spatial relationship between the seismogenic fault and the slope, and the propagation characteristics of seismic waves along the slope. The seismic failure mode of MBRSs in the study area was characterized as flexural–tensile failure. This work can provide a reference for post-earthquake disaster investigation, as well as disaster prevention and mitigation, in seismically active regions. Full article

Due to the diverse types of sedimentary source supply systems, the research on the distribution patterns of fine-grained sedimentary rocks in rifted lake basins is relatively underdeveloped. The authors of this article selected the lower third member of the Shahejie Formation (${\mathrm{E}\mathrm{s}}_3^{\mathrm{L}}$) in Zhanhua Sag as a research object. Using rock core, thin section, and other data, we analyzed rock types and genesis mechanisms, identified the spatiotemporal distribution patterns of facies within the sag, and established a fine-grained depositional model for the rifted lake basin. Five lithofacies were identified, revealing the differential distribution patterns of fine-grained sedimentary rocks in the region. The northern steep slope zone and the deep depression zone are characterized by the deposition of gravity flow-formed terrestrial layered-pebbly mudstone and gravity flow-formed mixed-source pebbly mudstone, respectively. In the central lake basin zone, mixed-source laminated mudstone with vertical rhythmic interlayers has developed. In the southern gentle slope zone, biologically cemented endogenic irregularly bedded algal limestone and chemically precipitated endogenic laminated limestone have developed. The characteristics of strong northern and weak southern terrestrial inputs in the study area control the differential distribution of lithofacies, and based on this, a fine-grained rock depositional model for the rifted lake basin was established. Full article

Collapsing valley glaciers leaving their bed to rush down a flat hill slope at the speed of a racing car are so far rare events. They have only been reported for the Kolkaglacier (Caucasus) in 2002 and the two glaciers in the Aru mountain range (Tibet) that failed in 2016. Both events have been studied in detail using satellite data and modeling to learn more about the reasons for and processes related to such events. This study reports about a series of so far undocumented glacier collapses that occurred in the Amney Machen mountain range (eastern Tibet) in 2004, 2007, and 2016. All three collapses were associated with a glacier surge, but from 1987 to 1995, the glacier surged without collapsing. The later surges and collapses were likely triggered by a progressing slope instability that released large amounts of ice and rock to the lower glacier tongue, distorting its dynamic stability. The surges and collapses might continue in the future as more ice and rock is available to fall on the glacier. It has been speculated that the development is a direct response to regional temperature increase that destabilized the surrounding hanging glaciers. However, the specific properties of the steep rock slopes and the glacier bed might also have played a role. Full article