Rock-soil Mass Research Articles

In-Situ Test and Numerical Simulation of Anchoring Performance of Embedded Rock GFRP Anchor

Compared to traditional steel reinforcement, GFRP anchors demonstrate outstanding mechanical performance and corrosion resistance, and so they are an ideal substitute for steel reinforcement in anti-floating projects. Based on finite element software, a 3D axisymmetric calculation model of GFRP anti-floating anchors in medium-weathered granite was established in this paper. Combined with the in-situ ultimate pull-out tests, the bonding anchoring performance and bearing characteristics between the anchor body, anchoring mortar, and rock–soil mass were analyzed. The research findings indicated that the cohesive bonding elements exhibited a high degree of conformity in defining the interface contact relationship of the GFRP anti-floating anchor anchoring system. The axial force of the GFRP anti-floating anchor body is “attenuated” along the depth direction, and there was a critical value of anchoring length; under the same conditions, the reasonable anchoring length should be 3.5~5.0 m. All the anchors in the in-situ tests exhibited interfacial shear slip failure between the anchor body and the anchor mortar, with an average maximum load of 450 kN, which is consistent with the maximum failure load of the simulated anchors. Compared to a load of 50 kN, the maximum stress of the anchor mortar increased by 50% under a load of 450 kN. The displacement variation of the surrounding rock–soil mass showed a decreasing trend from the inside to the outside and from the top to the bottom. The research results provided valuable references for the optimization design of GFRP anti-floating anchors.

Research on a Space-Time Continuous Sensing System for Overburden Deformation and Failure during Coal Mining.

Underground coal mining can cause the deformation, failure, and collapse of the overlying rock mass of a coal seam. If the mining design, monitoring, early warning, or emergency disposal are improper, in that case, it can often lead to mining disasters such as roof falls, water inrush, surface collapse, and ground fissures, seriously threatening the safety of mine engineering and the geological environment protection in mining areas. To ensure the intrinsic security of the entire coal mining process, aspace-time continuous sensing system of overburden deformation and failure was developed, which breaks through the limitations of traditional monitoring methods that characterize the evolution process of overlying rock deformation and ground subsidence. This paper summarizes the classification of typical overburden deformation and failure modes. It researches the space-time continuous sensing of rock-soil mass above the coal seam based on Distributed Fiber Optic Sensing (DFOS). A multi-range strain optical fiber sensing neural series from micron to meter was developed to achieve synchronous sensing of overburden separation, internal micro-cracks, and large rock mass deformation. The sensing cable-rock mass coupling test verified the reliability of the optical fiber monitoring data. The sensing neural network of overburden deformation was constructed using integrated optical fiber layout technology on the ground and underground. Different sensing nerves' performance and application effects in overburden deformation and failure monitoring were compared and analyzed with field monitoring examples. A physical model was used to carry out the experimental study on the overburden subsidence prediction during coal mining. The results showed that the optical fiber monitoring data were reliable and could be used to predict overburden subsidence. The reliability of the calculation model for overlying rock subsidence based on space-time continuous optical fiber sensing data was verified in the application of mining subsidence evaluation. A systematic review of the shortcomings of current overburden deformation observation technology during coal mining was conducted, and a space-time continuous sensing system for overburden deformation and failure was proposed. This system integrated sensing, transmission, processing, early warning, decision-making, and emergency response. Based on the fusion of multi-parameter sensing, multi-method transmission, multi-algorithm processing, and multi-threshold early warning, the system realized the real-time acquisition of space-time continuous information for the overburden above coal seams. This system utilizes long-term historical monitoring data from the research area for data mining and modeling, realizing the prediction and evaluation of the evolution process of overburden deformation as well as the potential for mining subsidence. This work provides a theoretical reference for the prevention and control of mining disasters and the environmental carrying capacity evaluation of coal development.

Research of deformation law about guide rails under the action of mining deformation in mine vertical shaft

To lay a foundation for alleviating the influence of mining shaft deformation (MSD) on the guide rail (GR) and monitoring the shaft deformation state, this paper studies the deformation law and mechanism of the guide rail under the MSD. Firstly, a spring is used to simplify the interaction between the shaft lining and surrounding rock soil mass (SRSM) under MSD, and its stiffness coefficient is deduced by the elastic subgrade reaction method. Secondly, a simplified finite element model is established based on spring element, the stiffness coefficient is calculated by the derivation formula, and its effectiveness is verified. Finally, the deformation law and mechanism of GR are analyzed under different types and degrees of MSD, and the deformation characteristics are studied under the disconnection between the shaft, bunton and guide rail. The results show that the established finite element model can better simulate the interaction between the shaft lining and SRSM, and the calculation efficiency is greatly improved. The guide rail deformation (GRD) has a strong ability to characterize MSD and owns the distinctive feature corresponding to different types and degrees of MSD and the connection state. This research can provide reference and guidance for the shaft deformation monitoring and the maintenance and installation of the GR, and also lays a groundwork for studying operation characteristic of hoisting conveyance under MSD.

Vertical performance of rock-socketed pile group in layered saturated rock-soil mass

This paper studies the vertical performance of rock-socketed pile group embedded in layered saturated rock-soil mass. The three-node bar element is utilized to discretize the pile, and the global stiffness matrix equation of rock-socketed pile group is assembled by the finite element method. Based on the solution for the interaction between a rock-socketed single pile and rock-soil mass, the flexibility matrix equation of rock-soil mass for the pile group is derived by the boundary element method. Combination of the force balance and displacement compatibility conditions for the rigid pile cap leads to the solution of rock-socketed pile group embedded in saturated rock-soil mass. The correctness of the proposed method is examined by comparing the solutions predicted by the present paper with the solutions from existing literature and ABAQUS results. The relevant factors affecting the vertical performance of rock-socketed pile group, such as the socketed length, pile spacing, pile-rock mass modulus ratio, length-diameter ratio and the rock mass stratification, are further discussed

Application of Long-Range Cross-Hole Acoustic Wave Detection Technology in Geotechnical Engineering Detection: Case Studies of Tunnel-Surrounding Rock, Foundation and Subgrade

The adverse geological conditions of soil cave, karst cave and goaf in deep foundation directly affect the safety and economy of geotechnical engineering construction. It is a difficult problem in geotechnical engineering detection to detect the distribution of bad geological conditions efficiently and accurately. Aiming at the problems of short penetrating distance and low resolution of cross-hole acoustic wave detection in rock-soil mass, based on the characteristics of acoustic wave propagation in rock and soil layers and comprehensively utilizing the spark source and data acquisition device, a long-distance cross-hole acoustic wave detection technology is proposed. According to the indoor concrete model test and field tests of geotechnical engineering, the applicability of the long-distance cross-hole acoustic wave detection technology in the detection of geotechnical structure and adverse geological phenomena under complex geological conditions is verified. The results show that acoustic wave CT imaging can accurately detect the cavities in the indoor concrete model test. In addition, the field tests of the grouting effect of tunnel-surrounding rock, high-rise building foundation and subgrade further verify the rapidity, accuracy and intuitiveness of the long-distance cross-hole acoustic wave detection technology. This work provides a reference for eliminating the potential safety problems caused by adverse geological conditions and similar geotechnical engineering investigation.

Damage evolution mechanism of rock-soil mass of bedrock and overburden layer slopes based on shaking table test

Damage evolution mechanism of rock-soil mass of bedrock and overburden layer slopes based on shaking table test

Study on the slope dynamic stability considering the progressive failure of the slip surface under earthquake

The strength of a rock-soil mass shows complex and obvious weakening characteristics under seismic dynamic load. The previous stability analysis methods of a seismic slope do not fully depict the attenuation law of geotechnical materials and cannot truly reflect the stable state of a slope under earthquake action. Based on the theoretical analysis of the progressive failure mechanism and the evolution law of a seismic slope, the adverse effect of progressive failure on slope stability is clarified. According to the progressive failure process of a slope under dynamic load, the strain-softening model and vibration deterioration model are introduced to represent the attenuation law of rock strength parameters, and a calculation method of seismic slope stability coupled with vibration disturbance and progressive failure is proposed. The method considers the strength parameter characteristics of a rock-soil mass in different stages and is combined with the vector sum method to obtain the time-history curve of the slope safety factor under earthquake action, which makes the evaluation result of slope stability more accurate and reliable. The numerical examples show that this method can effectively reflect the dynamic stability of seismic slopes, and solve the problem that the traditional calculation methods are difficult to characterize the strength attenuation characteristics of rock and soil mass. If these characteristics are not considered, the calculation results will be unsafe.

Influence of scour on the vertical response of rock‐socketed piles in layered saturated rock–soil mass

AbstractThe influence of scour on the vertical response of rock‐socketed piles in a layered saturated rock–soil mass is studied through the finite element‐boundary element coupling method. By utilizing the theoretical solution of layered saturated media as the kernel function, the boundary element method (BEM) is used to deduce the boundary integral equations of rock–soil mass. Meanwhile, the pile is modelled with the three‐node bar element and the global stiffness matrix of the pile is assembled by the finite element method (FEM). Then according to the scour type, the flexibility matrix of the foundation is recombined and extended, which is consistent with the stiffness matrix dimension of the pile. In consideration of the force balance and continuity conditions at the pile‐soil‐rock interface, the FEM–BEM coupling equation is established to solve the interaction between layered rock–soil mass and rock‐socketed pile that considers different scour types. A corresponding MATLAB program is compiled to verify the correctness of the present theory by comparisons with the existing literature solutions, field tests and the finite element solutions. The influences of the scour type, scour depth, socketed length as well as pile‐rock mass modulus ratio and rock mass stratification on the vertical response of a rock‐socketed single pile are further discussed through several numerical examples.

Experimental Study on the Evolution Mechanism of Landslide with Retaining Wall Locked Segment

The failure of locked segment-type slopes is often affected by rainfall, earthquake, and other external loads. Rainfall scours the slope and weakens the mechanical properties of rock-soil mass. At the same time, rainfall infiltrates into cracks of slope rock mass. Under the action of in situ stress, hydraulic fracturing leads to the development and expansion of rock cracks, which increases the risk of slope instability. Under seismic force, the slope will be subjected to large horizontal inertial force, resulting in slope instability. In this paper, a self-developed loading device was used to simulate the external loads such as rainfall and earthquake, and the model tests are carried out to study the evolution mechanism of landslide with retaining wall locked segment. Three-dimensional laser scanner, microearth pressure sensors, and high-definition camera are applied for the high-precision monitoring of slope shape, deformation, and stress. Test results show that the retaining wall locked segment has an important control effect on landslide stability. The characteristics of deformation evolution and stress response of landslide with retaining wall locked segment are analyzed and studied by changing the slope shape, earth pressure, and the displacement cloud map. The evolutionary process of landslide with retaining wall locked segment is summarized. Experimental results reveal that as the landslide with retaining wall locked segment is at failure, the upper part of the landslide thrusts and slides and the retaining wall produces a locking effect; the middle part extrudes and uplifts, which is accompanied with shallow sliding; and compression-shear fracture of the locked segment leads to the landslide failure.

Study on Heat Transfer Model and Applicability of Energy Piles in Nanning Basin under Subtropical Climate

In order to meet the requirements of peak carbon dioxide emissions, energy pile systems have been widely used in more and more regions because of their low-carbon, energy-saving, and emission-reducing characteristics. To explore the applicability of the energy pile project in Nanning, which has typical subtropical climate characteristics with warm winters and hot summers, some research work has been carried out in this paper. Firstly, through indoor thermophysical property tests, the geotechnical thermophysical parameters of typical composite strata in this area are obtained. Then a transient heat transfer model of the energy pile is established, which can fully reflect the heat transfer characteristics of the pile and the soil. On this basis, the superposition principle and stepped heat flow theory are used to analyze the temperature recovery characteristics of typical strata in Nanning area under different intermittent operation conditions. The results show that: the rock-soil mass of the typical stratum in Nanning area has good heat transfer characteristics, which is conducive to the promotion of energy pile engineering. The heat transfer model proposed in this paper has higher accuracy than the classical linear heat source model, which can reflect the material characteristics of energy pile system and avoid overestimating or underestimating the temperature field of energy pile system. The operation of energy pile system in a subtropical climate will produce an unbalanced heat load, and corresponding measures need to be taken to achieve the balance of heat load. The research results can provide a reference for energy pile engineering design in different climate regions.

The reactivated mechanism of Aniangzhai ancient landslide in Danba County, China

This study presents a catastrophic landslide that occurred on June 17, 2020, on the left bank of the Xiaojinchuan River in Danba County, Sichuan Province of China. This landslide was a large-scale reactivation of the Aniangzhai ancient landslide. The failure event blocked the Xiaojinchuan River, induced a landslide-outburst flood disaster chain, destroying a 6.6 km-long section of national road G350 and causing significant economic losses. Based on field investigations, unmanned aerial vehicle surveys, and geophysical prospecting, this study unravels the causing factors and reactivates the landslide mechanism. The results suggest that the topography and unconsolidated rock-soil mass are predisposing factors for reactivation. The hourly precipitation within three hours reached 61.80 mm and induced the Meilong debris flow. The debris flow rushed into the Xiaojinchuan River and converted it to flow along the foot of the Aniangzhai ancient landslide. The intense scouring of slope toe caused by the rise of river level is the inducing factor of the landslide. Based on the geometry and geomorphic parameters, the landslide can be divided into four areas: leading edge collapse area, middle bulging area, upstream cracking area, and downstream cracking area. The reactivated Aniangzhai landslide could be determined as a compound landslide involving incipient retrogressive failure and latter progressive slide. Several cracks had developed in the upper part of the slope due to the movement of the landslide, and the four areas of the reactivated landslide mass were still creeping. A detailed monitoring and mitigation measure should be paid to this reactivated deposit.

Model study on backfill grouting in shield tunnels based on fractal theory

Fractal theory demonstrates significant merit in the feature expression of forms of matter in nature. This study uses fractal theory to study the backfill grouting of a shield tunnel. The seepage path was considered as a seepage mesh inserted into the rock-soil mass. For the fractal features of the seepage mesh, the formulas for the diffusion distance and the pressure contribution of grout were derived. The results showed that the diffusion equations of different grout patterns (Newtonian fluid and Bingham fluid) were of a uniform form after calculation, and the equations for the pressure distribution of grout with a change in radius were identical. The diffusion distance of grout increased with increasing grouting time, and there was no indication that the development of diffusion distance tended to be gradual; the downward tendency of the grout diffusion velocity was not moderated. The segment pressure increased with an increase in the diffusion distance. With a constant diffusion distance, a greater grouting pressure produced a greater segment pressure. The favorable performance of grout was attributed to an appropriate mixture ratio. An improper mixture ratio resulted in a smaller reinforcement area in the stratum, which impaired the stability of the shield tunnel.

Dynamic response of rock slope with anti-dip weak interlayer and its influencing factors under seismic actions

The load features of ground motion are mainly reflected by three factors: amplitude, frequency, and duration. The combination of these factors determines the response of rock-soil mass and the structure safety under seismic load. By finite element method, this paper analyzes the influence of the three factors of ground motion on the dynamic response of a slope. The analysis shows that the slope displacement increased with the elevation from the bottom. The anti-dip fault puts the slope in an unfavorable deformation state. Due to the large residual deformation in the fault zone, a large displacement occurred on the slope top. It was also learned that the adjustment of amplitude only leads to proportional growth in the absolute value of the acceleration of the slope. Under the same conditions, the dynamic responses in different parts of the target slope are not greatly affected by the changing amplitude, but depend more on the material and spectral features of the rock-soil mass. The research results provide a reference for the evaluation and prediction of slope seismic stability and the evolution of slope damage under earthquakes with different frequencies, amplitudes, and durations.

Research on image recognition method of rock and soil porous media based on dithering algorithm

Rock-soil mass is a kind of material with complex internal structure, and its macro-mechanical response and failure process are influenced by internal microscopic composition and structure. Based on the research results of digital image technology in quantitative aspects of internal structure of rock and soil, a method for segmentation of rock and soil pore images based on dithering algorithm and statistical method for multiple parameters of pores is proposed in this paper. The result of verification shows that the pore recognition method proposed in this paper is reliable, can obtain the pore distribution and related parameters quickly and effectively, which has certain academic value and research significance.

Stability Monitoring and Analysis of High and Steep Slope of a Hydropower Station

Slope deformation and failure are major challenges for hydropower station engineering. Taking the left bank slope at the exit of the flood discharge tunnel of the Wudongde Hydropower Station in China as an example, the deformation mechanism of the high-steep rock slope was studied. The height of the slope is about 200 m, which is affected by slope excavation, rainfall, and atomized rain. The results of multipoint displacement meters, surface deformation monitoring, and anchoring stress meters showed that the deformation and deformation rate of the slope have increased dramatically. Through the comprehensive analysis of the slope, it is found that the overall lithology of the slope is poor, the excavation disturbance causes the redistribution of the stress in the slope, and the excavation surface is relatively steep, which provides space for the deformation of the slope rock mass. Unloading relaxation leads to a large number of new fissures in the slope rock mass. These new fissures and fault fracture zones provide convenient conditions for rainfall and atomized rain infiltration. The rainwater infiltrated along the slope surface, formed the seepage field in the slope body, and weakened the rock-soil mass parameters. Meanwhile, saturated runoff is formed on the slope, causing large deformation of the slope rock mass. However, the migration of water in the slope has a time effect, and its influence on the stability of the slope also has a time effect. It is difficult for traditional monitoring methods to monitor the resulting changes in internal sliding force of the slope. Therefore, a remote monitoring and early warning system for landslide anchor cable force was introduced to monitor the slope stability changes caused by the impact of water flow and rainfall infiltration, which provided a reasonable and scientific reference for subsequent slope construction.

A Theoretical Calculation Method of the Unsupported Span for the Shallow Tunnel in the Soft Stratum

During the construction of the tunnel in soft stratum, it is often found that the unsupported span is too large, resulting in instability of the tunnel face and collapse of the vault. However, the unsupported span was often selected according to the experience of engineers in the actual construction process, which was lack of the theoretical basis. Therefore, based on the calculation model of the surrounding rock pressure of shallow buried tunnel, this paper analyzed the stability of the tunnel face and the vault and then obtained the calculation formula of the unsupported span of the shallow buried tunnel in soft rock stratum. It was pointed out that the unsupported span is not determined by the arch crown stability or the tunnel face stability alone, but by both. The rationality of the formula was verified by a centrifugal test and an engineering case. The analysis and discussion showed that the unsupported span is sensitive to the cohesion and internal friction angle of the rock‐soil mass, especially the cohesion. The unsupported span of the shallow buried tunnel in the soft rock stratum is a linear function of the support pressure. The support pressure has a more significant contribution to the increase of the unsupported span by the centre cross diaphragm (CRD) method, and the unsupported span increases linearly with the increase of the support pressure. The research results provide a theoretical reference for the determination of the unsupported span for the shallow tunnel in the soft stratum.

Investigation and numerical modeling of the overloading-induced catastrophic rockslide avalanche in Baige, Tibet, China

After the first high-position landslide occurred in Baige Village, a second slide originated from the crown of the first landslide on November 3. The approximately 1.6 million m3 second slide moved rapidly and applied an impact load on the upper part of the residual mass of the first landslide, resulting in a 6.6 million m3 entrainment volume. The sliding mass rushed into the Jinsha River and blocked the channel again, causing catastrophic flooding which destroyed numerous roadbeds, bridges, and a large number of residential houses in Sichuan and Yunnan provinces. Based on field investigations and simulation results by dynamic discrete element method (DEM), after the first landslide, the blocks formed by the trailing edge of the landslide became unstable and slid, continuously and dynamically loading and accumulating on the upper part of the first debris deposit, which rested in the grooved terrain of the slope, leading to the instability of the residual slope’s rock–soil mass and the initiation of a debris avalanche. With a peak velocity of 62 m/s, the debris avalanche slid rapidly to the location of the first slide deposit. Due to the topographic effect, it was transformed into a diffused debris avalanche, which scattered and accumulated, exhibiting the typical characteristics of a rapid long-runout landslide. Then, the calculated velocity value by DEM was also compared with those using other dynamic modeling approaches (e.g., sled model and rheological model). The DEM was proven producing a reasonable velocity variation pattern, and thus, it is suitable for the simulation of the entire movement process of high-position rockslides similar to the second Baige landslide.

Mechanical deformation mechanism and verification of sections at junctions of light and dark tunnel in a mountain area

Projects involving junctions of light and dark tunnel in mountainous areas are complex engineering problems that combine tunnel structure, slope rock-soil mass and protection projects. Such junctions suffer from a complex and changeable load. The stress and deformation of the junction varies under different conditions. Thus, it is a major source of inconvenience for construction and monitoring operations. In this paper, according to the load conditions at a junction of light and dark tunnel, we divide the junction hole into thrust, compression, and combined thrust-compression types. Three types of structures were simulated by numerical analysis, and we explored the structural deformation and stress of these types of tunnel under different condition. Thus, in any construction process, the mechanical deformation mechanism and the weak point in the structure should be worked out. Based on the weak parts, some monitoring points were installed, and four fields for monitoring were chosen. The monitoring results show that the actual deformation, stress and structural failure location are basically consistent with the numerical simulation results. The deformation mechanism of light and dark tunnel junction obtained can provide the basis for selecting the treatment measures and controlling the structural deformation. Furthermore, the results can also be used as a reference for similar engineering design, construction and site monitoring projects.

Simulation study of the void space gas effect on slope instability triggered by an earthquake

This study aims at exploring the void space gas effect of earthquake-triggered slope instability and providing a new method for studying the formation mechanism of earthquake-triggered landslides. We analysed the basic characteristics, kinematic characteristics, initiation mechanisms and physical mechanical parameters of the Daguangbao landslide, generalized a landslide prototype, and established a geological model and performed simulation tests. Based on the seismic wave propagation theory of rock-soil mass, rock fracture mechanics and the effective stress principle, we found that the void space gas effect is due to the occurrence of excess void space gas pressure when the dynamic response of seismic loads impacts the void space gas in weak intercalated layers of the slope. The excess void space gas pressure generated by the vibration (earthquake) damages the rock mass around the void space with a certain regularity. The model test results show that the effective shear strength of the rock mass can be reduced by 4.4% to 21.6% due to the void space gas effect.

Application of transparent soil model tests to study the soil-rock interfacial sliding mechanism

When transparent soil technology is used to study the displacement of a slope, the internal deformation of the slope can be visualized. We studied the sliding mechanism of the soil-rock slope by using transparent soil technology and considering the influence of the rock mass Barton joint roughness coefficient, angle of the soil mass, angle of the rock mass and soil thickness factors on slope stability. We obtained the deformation characteristics of the soil and rock slope with particle image velocimetry and the laser speckle technique. The test analysis shows that the slope sliding can be divided into three parts: displacements at the top, the middle, and the bottom of the slope; the decrease in the rock mass Barton joint roughness coefficient, and the increase in soil thickness, angles of the rock mass and soil mass lead to larger sliding displacements. Furthermore, we analyzed the different angles between the rock mass and soil thickness. The test result shows that the displacement of slope increases with larger angle of the rock mass. Conclusively, all these results can help to explain the soil-rock interfacial sliding mechanism.