Weak Interlayers Research Articles

Investigate the mechanical property of weak interlayers based on micro-RME and AGBM

Investigate the mechanical property of weak interlayers based on micro-RME and AGBM

Experimental investigation on the influence of weak interlayers on sandstone rockburst and associated microcracking mechanism

Weak interlayers (WI) are common in sedimentary rock masses in deep coal mines. The qualitative effect of the WI on rockbursts is widely acknowledged; however, its influence mechanism still needs further investigation. In the present study, true triaxial unloading rockburst tests of sandstone with WI and calcite veins (CV) were conducted to explore their influence mechanisms. To explore the impact of WI, the rockburst stress, failure modes, acoustic emission (AE) parameters (energy, entropy, and b-value), and spatial energy characteristics of AE events were analyzed. The influence of the area ratio of WI and their distribution patterns (centralization and dispersion) on rockburst were further investigated. The results indicate that the rockburst stress (peak of maximum principal stress) decreased by 4 % for every 1 % increase in the sandstone's dispersion WI area ratio (1.9%–9.3 %). Namely, rockburst is more likely to occur when there is appropriate WI distributed in the sandstone because WI exacerbates the microcrack activities and energy release. The CV will reduce the weakening effect of WI on rockburst stress and can enhance the rockburst intensity, especially in samples with dispersion WI. Moreover, the more considerable AE energy is released around CV for the sandstone with dispersion WI. The interface between WI and matrix is prone to rockburst for the sandstone with centralized WI because of the concentrated energy release. The results of this paper can provide a reference for the prevention and control of rockbursts in mine sedimentary rocks containing WI and CV.

Dynamic responses of steep bedding slope-tunnel system under coupled rainfall-seismicity: Shaking table test

The coupling effects of rainfall, earthquake, and complex topographic and geological conditions complicate the dynamic responses and disasters of slope-tunnel systems. For this, the large-scale shaking table tests were carried out to explore the dynamic responses of steep bedding slope-tunnel system under the coupling effect of rainfall and earthquake. Results show that the slope surface and elevation amplification effect exhibit pronounced nonlinear change caused by the tunnel and weak interlayers. When seismic wave propagates to tunnels, the weak interlayers and rock intersecting areas present complex wave field distribution characteristics. The dynamic responses of the slope are influenced by the frequency, amplitude, and direction of seismic waves. The acceleration amplification coefficient initially rises and then falls as increasing seismic frequency, peaking at 20 Hz. Additionally, the seismic damage process of slope is categorized into elastic (2-3 m/s2), elastoplastic (4-5 m/s2) and plastic damage stages (≥ 6.5m/s2). In elastic stage, ΔMPGA (ratio of acceleration amplification factor) increases with increasing seismic intensity, without obvious strain distribution change. In plastic stage, ΔMPGA begins to gradually plummet, and the strain is mainly distributed in the damaged area. The modes of seismic damage in the slope-tunnel system are mainly of tensile failure of the weak interlayer, cracking failure of tunnel lining, formation of persistent cracks on the slope crest and waist, development and outward shearing of the sliding mass, and buckling failure at the slope foot under extrusion of the upper rock body. This study can serve as a reference for predicting the failure modes of tunnel-slope system in strong seismic regions.

Impact of weak interlayer characteristics on the mechanical behavior and failure modes of cemented tailings backfill: A study on thickness, strength, and dip angle

The mechanical properties of cemented tailings backfill (CTB) are crucial for managing ground pressure and sustaining mine productivity. However, multiple fillings often result in weak interlayers (WI) within the backfill, compromising its stability. This study investigates the mechanical behavior and failure modes of composite cemented tailings backfill (CCTB) with different WI characteristics—thickness (ranging from 0 mm to 30 mm), strength (cement-tailings ratio from 1:4 to 1:20), and dip angle (from 0° to 9°)—after 28 days of curing through uniaxial compression tests. Regression and error analysis methods were employed to establish the relationships between WI physical characteristics and CCTB mechanical properties. Additionally, the inherent mechanisms of mechanical strength deterioration in CCTB containing WI were discussed based on experimental and simulation results of CCTB failure modes. The results found that the uniaxial compressive strength (UCS) and elastic modulus (E) of CTB decrease with lower cement content, while the peak strength strain (PSS) increases. Incorporating WIs weakens CCTB, reducing UCS and E, and increasing PSS. Regression analysis combined with error analysis revealed that WI thickness has an exponential relationship with UCS, E, and PSS. As WI thickness increases, reduction coefficients for UCS and E rise significantly, exacerbated by the WI’s diminished strength. The WI’s dip angle significantly affects CCTB’s mechanical behavior, disrupting stress distribution and load transfer, resulting in heightened stress concentrations and structural weakening. COMSOL simulations corroborated these experimental findings, providing deeper insights into stress distribution and failure mechanisms within the CCTB structure. These findings aim to provide a theoretical basis for mitigating the impact of WI characteristics on the stability and load-bearing capacity of CCTB in future mining operations.

A Fractional-Order Creep-Damage Model for Carbonaceous Shale Describing Coupled Damage Caused by Rainfall and Blasting

In order to better understand the shear creep behavior of weak interlayers (carbonaceous shale) under the coupling effect of the rainfall dry–wet cycle and blasting vibration, as well as quantitatively characterize the coupled damage of the rainfall dry–wet cycle and blasting vibration, a series of shear creep tests were carried out. The results show that the combined damage of the rainfall dry–wet cycle and blasting vibration greatly intensifies the creep effect of carbonaceous shale, leading to an increase in deceleration creep time, an increase in steady-state creep rate, and a decrease in long-term strength. The coupling damage of the rainfall dry–wet cycle and blasting vibration in carbonaceous shale was quantitatively characterized. Based on the fractional-order theory, a fractional-order creep-damage constitutive model (DNFVP) was established by introducing the Abel dashpot to describe the coupled damage of the rainfall wet–dry cycle and blasting vibration and the nonlinear creep acceleration characteristics. The three-dimensional creep equation of the model was derived. The effectiveness of the DNFVP model was verified through the inversion of model parameters and fitting of experimental data, providing a basis for in-depth research on the long-term stability of high slopes in mines with weak interlayers.

Seismic response investigation of prestressed anchor cable supporting rock slope with weak interlayer in Qinghai-Tibet Plateau, China

Earthquake-induced rock landslides in the eastern mountains of the Tibetan Plateau, especially landslides with weak interlayers pose a significant threat to major construction projects. Prestressed anchor cable is one of the main reinforcement methods of rock slopes. This paper combines shaking table model tests and numerical simulation to study the reinforcement effect and dynamic response characteristics of prestressed anchor cables applied to rock slopes with weak interlayers under strong earthquakes. The research results show that prestressed anchor cables can effectively reinforce slopes with weak interlayers. A small cable inclination, a small spacing and a high prestress are recommended in the seismic reinforcement design of prestressed anchor cable. In addition, the characteristics of slope progressive damage and prestress loss under the earthquake are found by the shaking table test. The results have been applied in hazard prevention and control of rock slopes on the Chengdu-Lanzhou Railway at the eastern Qinghai-Tibet Plateau.

Seismic Response and Mitigation Analysis of a Subway Station in the Site with Weak Interlayers

Challenges related to seismic performance and seismic mitigation are more pronounced in the presence of weak interlayers compared to typical layered soil conditions. This study focuses on a double-layer double-span rectangular frame subway station structure. A coupled static–dynamic finite element analysis model of the soil-structure system is established by using the finite element software ABAQUS/CAE V 6.14. The research investigates the influence of factors such as interlayer thickness, location, and strength on the seismic response of subway station structures. Furthermore, in order to evaluate the effectiveness of FPB in mitigating seismic effects in the weak interlayer ground, two different schemes are proposed in this paper. One is the structure without FPB and the other is the structure with FPB on the top of the central column. The findings reveal that weak interlayers exert a significant influence on the seismic response of subway station structures, especially when these lower-strength weak interlayers are located within the central portion of the subway station structure and exhibit considerable thickness. The FPB on the top of the central column can reduce the overall lateral stiffness of the subway station structure. This, in turn, results in a slight increase in the deformation of sidewall and inter-story displacement angles, accompanied by a marginal exacerbation of sidewall damage. However, the implementation of FPB effectively reduces the deformation of the central column and substantially mitigates the extent of damage to the central column.

Blasting profile evaluation of sand-mud interbedded surrounding rock during the large-span tunnel construction

The sand-mud interbedded surrounding rock contains discontinuities, such as horizontal bedding, joints, weak planes and weak interlayers. Drilling and blasting construction in this kind of surrounding rock is very likely to cause very serious over-/under-excavation phenomenon and excessive damage to surrounding rock, and the contour flatness after smooth blasting of the tunnel is also difficult to be guaranteed, which increases subsequent construction procedures and reduces production efficiency. In order to effectively evaluate the smooth blasting effect of the sand-mud interbedded surrounding rock tunnel, taking a tunnel project in southwest China as the research background, the blasting numerical simulation of the sand-mud interbedded surrounding rock tunnel was carried out using the dynamic analysis program, and the corresponding blasting optimization scheme was obtained. Subsequently, based on fuzzy mathematical theory, the evaluation system of blasting effect of sand-mud interbedded tunnel was established by combining the evaluation criteria of tunnel smooth blasting quality. Immediately afterwards, the weights of each influencing factor index were determined, and the blasting shaping effect of the original blasting scheme and the optimized blasting scheme was evaluated. Finally, the results have shown that the optimized tunnel blasting profile effect was better than the original blasting scheme. The corresponding research results have certain guiding significance for similar tunnel blasting effect evaluation and blasting parameter design.

High quality 3D printing of low-density polyethylene blends considering the softening effect of polyolefin elastomer

Polyethylene (PE) is one of the most widely used thermoplastics in the polyolefin family. Despite its numerous applications in the industry, particularly in packaging, 3D printing with PE has been a significant challenge that has received little attention. The main obstacles to successful 3D printing with PE are high shrinkage, weak adhesion to the print bed, and weak interlayers. This paper addresses this problem by introducing Polyolefin Elastomer (POE) as an additive in the 3D printing process. Three different POE-LDPE compounds with varying LDPE weight percentages (90%, 70%, and 50%) were 3D printed and analyzed for their mechanical and microstructural properties. The POE and LDPE were blended using the melt mixing method, and the resulting POE-LDPE granules were directly used as input for the FDM machine. The 3D-printed samples were then subjected to DMTA, tensile, compression tests, and SEM imaging. The DMTA results showed that the glass transition temperature of all three samples fell within the range of 71°C to 78°C. Increasing the POE content and decreasing the LDPE amount from 90% to 50% led to a decrease in the storage modulus. In terms of the tensile test results, it was observed that reducing the LDPE amount and increasing the POE content had a toughening effect on the samples, improving their formability and elongation from 1566% for POE-90wt% LDPE to 2112% and 2829% for POE-70wt% LDPE and POE-50wt% LDPE respectively. However, the tensile strength decreased with an increase in the POE amount. For POE-90wt% LDPE, the tensile strength was 14.06 MPa, and for POE-90wt% LDPE, it was just below 13.96 MPa. The compression test revealed that the addition of POE weakened the yield strength of the samples. SEM images demonstrated that the printability of the 3D-printed POE-LDPE samples decreased as the LDPE amount decreased and the POE amount increased. The images also revealed single-phase and miscible blends. These findings suggest the potential emergence of a new, affordable, biocompatible, and recyclable raw material for 3D printing.

Time‐dependent analysis and stability evaluation of plane rotary landslides: Insights from a case study

AbstractPlane rotary landslides are characterized by their concealment and challenges in prevention, having caused considerable impacts in recent years. This study aims to elucidate the causative factors behind plane rotary landslides and develop a novel method for assessing their stability through a case. Our focal case, a landslide with weak interlayers, occurred on 1 April 2020, in an open‐pit limestone mine in Sichuan Province, China. The landslide demonstrated distinctive rotational behaviour deviating 45° from the expected direction, presenting a unique case of plane rotary deformation. Employing a multifaceted approach, including geological data analysis, UAV aerial photography, field investigations, laboratory experiments and displacement monitoring, we delved into the deformation and failure mechanisms. Furthermore, A three‐dimensional discrete element method was employed to examine the evolution of the landslide and its relationship with the stable rock mass barrier. The study unravelled the structural alterations of the slope due to mining activities and the degradation of physical and mechanical properties in weak interlayers, which were instrumental in triggering this geological event. The presence of the stable rock mass barrier causes the resultant forces acting on the sliding mass not to pass through its centre of gravity during deformation, thereby generating a moment that induces the rotation. The additional resistance also causes the landslide displacement to transition from being initially dominated by the leading edge to being driven by the trailing edge. This unique displacement pattern serves as a crucial reference for identifying plane rotary landslides.

Influence of weak interlayer thickness on mechanical response and failure behavior of rock under true triaxial stress condition

In this study, we meticulously investigate the influence of the thickness of weak interlayer on mechanical response and failure behavior of rock mass near the free surface of tunnel, with the aid of a true triaxial test system. We simulated the true triaxial stress condition of rock mass containing weak interlayer proximate to the excavation boundary, where one face remains free, while others are subjected to loading stress and increasing tangential stress. The experimental results reveal a distinct change in the fracture morphology near the free surface of rock mass as the thickness of weak interlayer increases, concomitant with a gradual decrease in the fractal dimension. With the increase of the thickness of weak interlayer, the failure characteristics of rock mass change from a “binary” to a “unitary” feature, i.e. mixed tension-shear failure near the free surface and shear failure far away from the free surface changes to mixed tension-shear failure that only occurs near the free surface. Moreover, an inverse relationship is observed between the bearing capacity of the rock mass and the thickness of weak interlayer. Conversely, the peak strain in the tangential stress direction increases with the increase of the thickness of weak interlayer, illustrating that the slip shear strain of rock block positioned above the weak interlayer is gradually formed, and governs the strain behavior of rock mass in the tangential stress direction with the increases of the thickness of weak interlayer. By employing the finite-discrete element method (FDEM), we replicated the failure process of surrounding rocks containing weak interlayers near the free surface of tunnel, demonstrating considerable congruity with our physical test results. In light of the failure characteristics of surrounding rocks containing weak interlayers, we advocated a localized area priority reinforcement support strategy, prioritizing regions with weak interlayers. Numerical simulations verified the effectiveness of this approach in controlling fracture proliferation in surrounding rocks and inhibiting the splitting failure of surrounding rocks containing weak interlayers near the free surface of tunnel.

Slope instability mechanism with differential rock mass structure along a fault: a mine landslide from Southwest China

Mine slope stability and mining sustainability are related to the local geological structures, which could change the rock mass structure in deep mining. After 20 years mining in a mudstone mine, western China, the slope structure transforms from anti-dipping structure into a bedding structure by a recently discovered fault (F1), further inducing the two landslides (Landslide #I and Landslide #II). Landslide investigation suggested the residual deposits in Landslide #I first slid over 100 m and overburdened the rear of Landslide #II. The bedding rock with weak interlayers at footwall is separated from the anti-dipping rock at the hanging wall by F1. After excavation, a weak interlayer was exposed and softened by rainfall, resulting in the slip of footwall rock mass and further inducing large scale toppling deformation. The fragmented rock mass sliding along a weak interlayer triggers consequent deformation of adjacent slope, reducing safety reserve of the open mine. The discrete element analysis reveals that the bedding rock mass of footwall slid once the weak interlayer was exposed by mining. And retrogressive deformation transmitted to the hanging wall and induced bending and toppling deformation of anti-dipping rock mass. Mine feasibility assessment should recognize the potential deep geological structures as important in the future.

Analytical solution for the seismic response of a nearly saturated sloping seabed: Weak interlayer

Sloping seabeds often exist in offshore areas with complex structures. It is difficult to accurately analyze the seismic response characteristics of sloping seabeds based on the assumptions used for horizontal seabeds. The degree of saturation in nearly saturated soil notably affects the seismic response of seabeds. Therefore, we developed an analytical solution for the seismic response of a sloping, nearly saturated multilayer seabed. Using this solution, we analyzed the effects of the slope angle and soil saturation degree on the seismic response of the seabed. The results show that the seafloor inclination may has a minor impact on the seismic motion at a specific point, but it has a very significant effect on the overall site. A weak interlayer refers to a layer of material that has lower strength and/or permeability compared to the surrounding soil or rock. This layer can reduce the natural frequency of the seabed and increase the amplitude of long-period seismic components. In addition, the presence of a weak interlayer can lead to increased pore water pressure, decreased effective stress, and increased susceptibility to shear failure. These factors combine to reduce the stability of submarine slopes, highlighting the importance of understanding and managing the effects of weak interlayers in geotechnical engineering and coastal defense projects.

Rock mass quality prediction on tunnel faces with incomplete multi-source dataset via tree-augmented naive Bayesian network

Rock mass quality serves as a vital index for predicting the stability and safety status of rock tunnel faces. In tunneling practice, the rock mass quality is often assessed via a combination of qualitative and quantitative parameters. However, due to the harsh on-site construction conditions, it is rather difficult to obtain some of the evaluation parameters which are essential for the rock mass quality prediction. In this study, a novel improved Swin Transformer is proposed to detect, segment, and quantify rock mass characteristic parameters such as water leakage, fractures, weak interlayers. The site experiment results demonstrate that the improved Swin Transformer achieves optimal segmentation results and achieving accuracies of 92%, 81%, and 86% for water leakage, fractures, and weak interlayers, respectively. A multi-source rock tunnel face characteristic (RTFC) dataset includes 11 parameters for predicting rock mass quality is established. Considering the limitations in predictive performance of incomplete evaluation parameters exist in this dataset, a novel tree-augmented naive Bayesian network (BN) is proposed to address the challenge of the incomplete dataset and achieved a prediction accuracy of 88%. In comparison with other commonly used Machine Learning models the proposed BN-based approach proved an improved performance on predicting the rock mass quality with the incomplete dataset. By utilizing the established BN, a further sensitivity analysis is conducted to quantitatively evaluate the importance of the various parameters, results indicate that the rock strength and fractures parameter exert the most significant influence on rock mass quality.

The Effect of Excavation Disturbance on the Stability of Bedding Cataclastic Rock Mass High Slope Containing Multimuddy Interlayers

In China, slope engineering occasionally faces landslides in rocky slopes containing muddy interlayers, primarily triggered by excavation activities. These incidents lead to considerable human casualties and substantial economic losses. However, existing studies predominantly concentrate on the excavation-induced impacts on the stability of rocky slopes characterized by single-layered soft and weak interlayers. Conversely, reports on how excavation influences the stability of bedding cataclastic rock mass high slope containing multimuddy interlayers remain notably absent in the literature. Moreover, unloading due to excavation can swiftly compromise the mechanical integrity and overall quality of the rock mass, consequently impacting the stability of slopes postexcavation. Therefore, this paper modeled the unstable slope excavated at a waste incineration power plant in Yuxi, Yunnan, using the finite element strength reduction method. This approach was employed to comprehensively simulate the entire process of artificial multilevel excavation in a bedding cataclastic rock mass high slope containing multimuddy interlayers. This study investigated the impact of multilevel artificial excavation on slope stability by thoroughly considering factors including alterations in slope morphology, unloading effects, and the degradation of geotechnical parameters. The research yielded the subsequent conclusions. Multimuddy interlayers were the key to the slope’s instability. For slopes subjected to such multilevel excavation, efforts were made to minimize the exposure of muddy interlayers. Slopes above exposed muddy interlayers did not require additional support, while those below needed prioritized reinforcement. The likely instability mode of the actual slope was local destabilization leading to landslides. Furthermore, when using numerical simulation methods to study the impact of excavation disturbances on the stability of such slopes, it was necessary to consider the deterioration of geotechnical parameters to obtain results more reflective of actual conditions. These research findings provided valuable theoretical and empirical support for studies on similar excavated slopes.

Meshless numerical manifold method with novel subspace tracking and CSS locating techniques for slope stability analysis

The meshless numerical manifold method (MNMM) inherits the advantages of handling continuous and discontinuous problems uniformly, improving interpolation precision, and avoiding linear dependence issues. This paper refines the MNMM method for slope stability analysis to overcome the dependence and sensitivity of the strength reduction method of the finite element method on the number of finite element meshes and the algorithm for solving the nonlinear equations when calculating slopes with soft and weak interlayers. First, the strength reduction method (SRM) was incorporated into MNMM to create the numerical model called MNMM-SRM. Based on the MNMM-SRM, a complementary Mohr-Coulomb (M−C) control equation compliant with Koiter's rule of multi-yielding surfaces was established. In the principal stress space, the subspace tracking method was used to track the eigenvalues and eigenvectors of the stress tensor, thereby addressing the corner problem of M−C multi-yield surfaces. Combining the k-means clustering algorithm with wavelet transformation and employing the slope's total nodal displacement field as an input variable, an intelligent and efficient critical slip surface (CSS) automatic extraction method was developed. Three typical cases were used to validate the accuracy of the numerical model. This numerical model has a wide range of potential applications in slope stability research.

Numerical simulation of mechanical and fracture behavior of composite rock containing weak interlayers

Numerical simulation of mechanical and fracture behavior of composite rock containing weak interlayers

A Review of the Evolution Characteristics and Argillization of Clay Interbeds in Rockslides

Weak interlayers in rockslides often become the controlling factor for slope deformation due to their poor physical properties and tendency to undergo argillization. Achieving a comprehensive understanding of the weak interlayers will help us comprehend the mechanism of rock slope failure and protect people’s property. Some weak interlayers will develop into clay interbeds after tectonic activity and long-term groundwater action. A comprehensive review of clay interbeds includes a discussion on the formation conditions, the governing factors of the argillization process, and the investigation methods. The clay minerals in clay interbeds, illite, montmorillonite, and Kaolinite, play a major role in the acceleration of the argillization process. The argillization process can be observed through scanning technology and investigated using nonlinear dynamics, statistics, and numerical modeling methods, which may result in limitations for extracting parameters. It is necessary to conclude a unified evaluation standard to find the basic commonness during the argillization process of clay interbeds. It would be a future trend to establish the quantitative relationships among the mechanical strength, micro-structure and content of clay minerals of the clay interbeds during the argillization process.

Study on filling mining technology for gently inclined thin to medium thick phosphorus deposits

This study is grounded in research conducted at the Kunyang Phosphate Mine No. 2, a Chinese open-pit phosphate mining enterprise owned by the Yunnan Phosphate Group Co., Ltd. Due to the small inclination angle and the presence of weak interlayers in the middle of the gently inclined thin to medium thick phosphate ore layer, mining such ore bodies cannot rely on self weight migration, making roof management difficult and mining costs high technical challenges. The methods utilized on-site research, engineering comparisons, and theoretical analysis experiments to address the gently inclined phosphorus deposits. Based on the actual technical and economic conditions of current phosphorus mines, the advantages, disadvantages, and practical conditions of upward horizontal layered filling mining method, upward horizontal layered drift filling mining method, and pseudo inclined segmented strip filling mining method are compared. Priority should be given to using the pseudo inclined segmented strip method as the main method for mining, supplemented by the upward horizontal layered filling method in the panel area. And theoretical calculation methods were applied to obtain various numerical values of the filling capacity of the 2 million t/a mine filling test section, providing technical support for the mining design and equipment selection of the filling test system. The relevant research results can provide guidance for the selection of mining methods for gently inclined thin to medium thick phosphate deposits with an average inclination angle of 15°. The theoretical calculation method used can provide technical guidance for the filling system and filling equipment.

Prediction analysis of slope stability due to soft and weak interlayers based on partial least squares method

Abstract In this paper, based on sampling and analysis of a large number of soft and weak sandwich slope data, several factors that have a great influence on slope stability are established, and a predictive analysis model describing the stability of soft and weak sandwich slopes is established by using the now more advanced partial least squares method. Then, for the traditional partial least squares method that is not suitable for the non-linear stability coefficient of the weak sandwich to slope stability prediction, the recursive partial least squares method with forgetting factor is proposed for the weak sandwich to slope stability prediction analysis to solve the problem of stability prediction lag. Finally, based on elastic mechanics, elastic fracture mechanics and unsaturated soil mechanics, the structure of soft and weak interlayers on slopes and their stability strength are studied, and the performance of MATLAB-based partial least squares method for slope stability prediction analysis is verified by designing orthogonal experiments. The results show that the predicted values do not differ much from the results of finite element calculation, the absolute errors are all less than 0.15, and there are 5 absolute non-differences less than 0.1, accounting for 62.5% of the total number of predicted groups. The relative errors were less than 6%. This study shows that the partial least squares method can deal with the nonlinear mapping relationship between slope stability and influencing factors well and can make more accurate and objective prediction results on the stability of slopes.