Weak Structural Planes Research Articles

Comprehensive evaluation of the stability of the left-bank slope at the Baihetan hydropower station in southwest China

The stability of the left-bank slope is a crucial geological engineering problem at the Baihetan hydropower station, China. Due to continuous excavations on the rock slope, different regions of the surrounding rock mass undergo varying degrees of unloading deformation. It is important to assess the stability of the rock slope from a macroscopic viewpoint by investigating its deformation characteristics and mechanisms. Therefore, in this work, microseismic (MS) monitoring was first employed to detect the progressive rock mass damage in the rock slope subjected to excavation, including the initiation, propagation, coalescence, and interaction of rock microfractures. Numerical modeling was subsequently performed to understand the deformation and failure mechanism of the rock slope. Moreover, traditional surveying approaches (i.e., multiple-point extensometers and inclinometers) and field observations were also used to analyze the deformation and failure characteristics of the rock slope. The MS monitoring results showed that spatiotemporal regularities in the evolution of seismic source locations were indicators of deformation failure and potential sliding surfaces. MS event clustering can be used to delineate activated pre-existing geological structures (i.e., LS331 and LS337). The simulation results show that the deformation and failure characteristics of the rock slope are mainly controlled by pre-existing weak structural planes (i.e., the intraformational faulted zones LS3319, LS331, and LS337 and fault F17). These results agree well with the results of geological data and conventional monitoring data. Our study reveals that an integrated approach combining MS monitoring, numerical modeling, traditional surveying, and field observations leads to a better understanding of the behavior of the rock slope under the influence of excavation as well as greater control of the working faces, ensuring safety under complex geological and excavation conditions.

A risk prediction method for water or mud inrush from water-bearing faults in subsea tunnel based on cusp catastrophe model

Constructing a subsea tunnel is exceptionally difficult because of the complex geological conditions involved in the process. Water or mud inrush is a geological hazard that occurs suddenly during the construction of a cross-harbor tunnel, thereby causing major disasters and economic losses. The weak structural planes in a fault zone are the naturally preferred planes for water inrush. It is necessary to analyze the mechanism and to develop a risk prediction method for water or mud inrush from such faults. In order to effectively predict the risk of water or mud inrush during the construction of a subsea tunnel, this paper analyzes the mechanism of water or mud inrush from extensional faults, shear faults and compressive faults based on cusp catastrophe model. The potential function for the risk of water or mud inrush is built, and then the index of water inrush (IP) is obtained based on the equations of equilibrium for the fault surface. Water or mud inrush occurs only when IP > 1. The proposed method of risk prediction is successfully used in Qingdao Kiaochow Bay subsea tunnel to prove its applicability and feasibility.

Long-term stability analysis of the left bank abutment slope at Jinping I hydropower station

The time-dependent behavior of the left bank abutment slope at Jinping I hydropower station has a major influence on the normal operation and long-term safety of the hydropower station. To solve this problem, a geomechanical model containing various faults and weak structural planes is established, and numerical simulation is conducted under normal water load condition using FLAC3D, incorporating creep model proposed based on thermodynamics with internal state variables theory. The creep deformations of the left bank abutment slope are obtained, and the changes of principal stresses and deformations of the dam body are analyzed. The long-term stability of the left bank abutment slope is evaluated according to the integral curves of energy dissipation rate in domain and its derivative with respect to time, and the non-equilibrium evolution rules and the characteristic time can also be determined using these curves. Numerical results show that the left bank abutment slope tends to be stable in a global sense, and the stress concentration is released. It is also indicated that more attention should be paid to some weak regions within the slope in the long-term deformation process.

Numerical Simulation Study on the Detection of Weak Structural Plane of Rock Slope by Using 3D Electrical Resistivity Tomography

The weak structure plane is an important factor affecting the stability of rock slope, and detecting the spatial structure of the weak structural plane is beneficial to analyze the stability of the slope and estimate the quantity of the landslide. Based on 3D electrical resistivity tomography, a model of rock slope with weak structure plane is established, and the characteristics of three-dimensional resistivity imaging of weak structure plane under different ground water conditions are simulated. The results show that the weak structural plane has a better reflection in 3D electrical resistivity tomography; the distribution of weak structural plane of 3D resistivity imaging can be roughly determined under different ground water conditions; the three-dimensional electrical resistivity tomography is feasible in the detection of weak structural plane of rock slope.

A Constitutive Model for the Creep Behavior of Offwhite Marbles

This paper reports an improved constitutive model for the shear creep behavior of offwhite marbles which are selected from slope and underground cavern and contain green schist’s weak structural planes. The shear creep behavior of the samples is characterized using the rheological tests. Based on the experimental measurements on mechanical properties under different normal stress conditions, an improved model is proposed to analyze the experimental results. It is demonstrated from a further discussion that such model can reflect the non-linear creep characteristics of structural planes, and especially, it is suitable for description of the viscoelastic and viscoplastic deformation behavior of structural planes.

Stability analysis of concrete gravity dam on complicated foundation with multiple slide planes

A key problem in gravity dam design is providing enough stability to prevent slide, and the difficulty increases if there are several weak structural planes in the dam foundation. Overload and material weakening were taken into account, and a finite difference strength reserve method with partial safety factors based on the reliability method was developed and used to study the anti-slide stability of a concrete gravity dam on a complicated foundation with multiple slide planes. Possible slide paths were obtained, and the stability of the foundation with possible failure planes was evaluated through analysis of the stress distribution characteristics. The results reveal the mechanism and process of sliding due to weak structural planes and their deformations, and provide a reference for anti-slide stability analysis of gravity dams in complicated geological conditions.

The Elastoplastic Finite Element Analysis for the Deep Anti-Sliding Stability of Gravity Dam by the Method of Overloading

Combined with engineering requirements of the Qingyu reservoir, the ANSYS finite element software was used to establish an elastoplastic gravity dam calculation model which considered the mechanical properties of weak structural plane of rock in the dam foundation. An analysis based on not only the finite element iteration not converging,the plastic zones in dam foundation rock developing to through the foundation and the mutation in horizontal displacement of feature points, but also the discontinuous variation of the distribution of horizontal displacement of dam foundation rock, the dislocation between the above and below of weak layers and the leap of iterations were took as the criterions to get the deep anti-sliding stability safety factor of gravity dam by gradually increasing the load burdened on the upstream face of the dam. This thesis illustrated the principle of the elastoplastic finite element analysis for the deep stability of gravity dam by the method of overloading, demonstrated the feasibility of this method ,expanded the criterions to determine the safety factor and obtains the safety factor of this practical engineering under the elastoplastic overloading method.

Strength Reduction Method for Stability Analysis of Local Discontinuous Rock Mass with Iterative Method of Partitioned Finite Element and Interface Boundary Element

SRM (strength reduction method) with iterative method of PFE (partitioned fnite element) and IBE (interface boundary element) is proposed to solve the safety factor of local discontinuous rock mass. Slope system is divided into several continuous bodies and local discontinuous interface boundaries. Each block is treated as a partition of the system and contacted by discontinuous joints. The displacements of blocks are chosen as basic variables and the rigid displacements in the centroid of blocks are chosen as motion variables. The contact forces on interface boundaries and the rigid displacements to the centroid of each body are chosen as mixed variables and solved iteratively using the interface boundary equations. Flexibility matrix is formed through PFE according to the contact states of nodal pairs and spring flexibility is used to reflect the influence of weak structural plane so that nonlinear iteration is only limited to the possible contact region. With cohesion and friction coefficient reduced gradually, the states of all nodal pairs at the open or slip state for the first time are regarded as failure criterion, which can decrease the effect of subjectivity in determining safety factor. Examples are used to verify the validity of the proposed method.

Constructing a tough shield around the wellbore: Theory and method for lost-circulation control

Abstract According to the mechanism analysis of drilling fluid loss in the formation with low pressure-bearing capacity, three basic theories, including stress cage, plugged zone, and strength ring for wellbore strengthening, were summarized and the corresponding models were established. The application conditions for the three theories and their requirements on the material properties were determined based on the models. Fracture propagation, filtration effect of drilling fluid and depleted formation pressure are the major factors that lead to low formation pressure-bearing capacity. The stress cage theory strengthens the wellbore by establishing the balance between wellbore pressure and formation stress. It is applied in the formation with low-development fracture. It demands that the material has enough compressive strength and reasonable size distribution to sustain certain fracture width and low fracture pressure. The plugged zone theory works by establishing the balance between wellbore pressure and formation pressure. It is suitable in pore and fractured formation and demands that the plugging material has the properties of high surface friction coefficient, resilient deformation, volume fraction and strength to create the synergy effect of rigid granule, fiber and resilient particle. The strength ring theory applies to fracture-vug formation and it requires that the material can cement the weak structural plane or form a high strength body to separate the pressure propagation from wellbore to formation. The effect and guiding significance of the three theories were further confirmed by field applications.

The Instability Mechanism of Soil-like Slope under the Action of Acid Corrosion in Open-Pit Copper Mine

Combined with the engineering geological conditions and geological characteristics of soil-like slope in a certain open-pit copper mine, based on the experiments and theoretical analysis, the instability mechanism of soil-like slope under the action of acid mine wastewater is researched. Because the acid wastewater goes into the weak structural plane, reacting with the constitutional materials and fillings in slopes, the react change the microstructure of the rock and soil, and replace, dissolve the components, causing the cohesion and internal friction angle of slope reducing eventually and slope failure.

3D Finite Element Numerical Analysis for Stability Calculation of High Steep Rock Slope

Due to the high steep rock slope stability analysis its complex geological conditions and other factors, its stability calculation has been a technical problems the field of slope engineering, in this paper, 3D finite element calculation software Midas GTS for side slope surface topography and slope internal faults, weak structural plane of complex three-dimensional geological modeling, it overcomes the complex slope geological modeling problem and simulates rainfall, earthquakes and other factors affecting the stability on the slope, calculated results more in line with reality, and the software calculates is in accordance with fact, it provides a useful reference for slope engineering.

Stability Analysis of Steep Bedding Rock Slope with Strength Reduction Method

Stability analysis of steep rock bedding slope with weak structure planes using strength reduction method was simulated in this paper. The post processing function can display the development condition of the plastic zone, which is the criterion for instability of the slope. Analysis with working conditions of natural circumstance, after excavation, and the slope reinforced by anchor shank after excavation were put forward. Failure modes and safety coefficients of the slope proved that weak plane is the main factor controlling slope failure. Simulation results shown that strength reduction method is appropriate in predict the shape and position of the potential failure surface of steep rock bedding slope.

Research on Wellbore Stability in Formation with Anisotropic Strength

As most of sedimentary rocks are anisotropic, it is significant to research the impact of the anisotropy of strength on wellbore stability in drilling engineering. Particularly, in the Kuqa piedmont exploration area, the anisotropy of strength caused by various jointed surfaces, fracture surfaces and fault planes in formation cause the formation of several groups of weak low-intensity planes traversing borehole . These weak planes will become failure earlier than the rock body in the context of strong stress and high pore pressure, causing chipping, breakouts and sticking. If fractures have good permeability and drilling fluid column pressure is greater than pore pressure, loss may occur. The loss pressure would not be controlled by fracturing pressure and horizontal minimum principal stress, but it depends on the relationship between fracture occurrence and triaxial stress state. In the event of loss, the drilling fluid will flow into these weak structural planes, causing the decrease of friction between rocks and increase of wellbore instability. As a result, for strongly anisotropic formation, the collapse pressure and leakage pressure of weak planes are key factors for evaluating well drilling stability. In this study, according to the stability evaluation on the transversely isotropic rock mechanics in Keshen zone of Kuqa piedmont, the impacts of fracture development on wellbore instability is analyzed; relevant suggestions on engineering geology for the special pressure window in strong anisotropic formation are also put forward.

Numerical Investigation on Factors Influencing the Time-Dependent Stability of the Rock Slopes with Weak Structure Planes

Under the combined effects of various external factors, such as temperature, seepage, alternate wetting and drying and so on, the mechanical properties of rock mass are susceptible to be deteriorated, and its strength characteristics are significantly degraded with time. The mesoscopic damage accumulated inside the rock, contributing the rock slope instability with weak structure planes, generate the time-dependent deformation, and eventually lead to the slope failure. Given the time-dependent deformation of the rock, numerical simulations are conducted to investigate the key factors influencing the long-term stability of slopes. Numerical results show that the catastrophic failure time of slopes is linear to its cohesion, and the bigger cohesion and friction angle increase catastrophic failure time, i.e., the stability of rock slope increase. In addition, the configuration of the intact rock bridge can also influence the time-dependent slope stability. Slope height can significantly affect the slope stability and the maximum horizontal displacement. Differences in rock mass storage environment play an important role in the long-term stability of slopes.

Empirical Correlation for Viscoelastic and Viscoplastic Behaviour of Rock Surfaces under Different Normal Stress Conditions

Abstract This paper reports an improved constitutive model for the shear creep behaviour of offwhite marbles which are selected from slope or underground cavern and contain greenschist's weak structural planes. The shear creep behaviour of the samples is characterized by rheological tests. Based on the experimental measurements on mechanical properties under different normal stress conditions, an improved model is proposed to analyze the experimental results. It is demonstrated from a further discussion that such model can reflect the non-linear creep characteristics of structural planes, and especially, it is suitable for description of the viscoelastic and viscoplastic deformation behaviour of structural planes.

Analysis of Slope Stability Containing Weak Layers

In order to search for the control factors of slope stability containing weak layers, combining with the methods of the finite element and the limit equilibrium to simulate the slope stability problems. From the numerical simulation results, the stress field distribution and displacement field distribution internal the slope could be got. According to the finite element analysis results and the safety factor of slope stability got with the limit equilibrium method, evaluate the slope stability. By the simulation analysis of slope which contains a number of weak structural surfaces, the conclusion we got is that the existence of weak structural plane like weak layers and faults are the main factors of slope instability.

Interface stress element method and its application in analysis of anti-sliding stability of gravity dam

The rigid body limit equilibrium method (LEM) and the nonlinear finite element method (NFEM) are often used in the analysis of anti-sliding stability of gravity dam. But LEM cannot reflect the process of progressive instability and mechanical mechanism on failure for rock mass while NFEM is difficult to use to solve the displacement discontinuity of weak structural plane. Combining the research with Xiangjiaba Hydropower Station project, the analysis of anti-sliding stability for segment 12# of the dam has been carried out using interface stress element method (ISEM). The results can reflect the most dangerous location, the scope and distribution of failure zone in weak structural plane, and present the process of progressive failure in dam foundation as well as the safety coefficient of possible sliding body. These achievements provide an important technical reference for dam foundation treatment measures. The computational results show that ISEM can naturally describe discontinuous deformation of rock mass such as dislocation, openness and sliding. Besides, this method is characterized by good adaptability, convenient calculation and high compatibility, thus it is regarded as an effective way to make an analysis of anti-sliding stability of gravity dam

A Structural Failure Model for the Rock Mass with a Discontinuous Weak Structural Plane

A structural failure model is presented for the rock mass with a discontinuous weak structural plane. The present model takes into account the effect of weakening of both deformation and strength parameters. And it can degenerates into classical Mohr-Coulomb model or Jaeger model according to corresponding conditions. The numerical tests by Particle Flow Code demonstrate that the capability and performance of the proposed model in capturing behaviors of the mass rock.

Anti-sliding stability of a gravity dam on complicated foundation with multiple structural planes

Anti-sliding stability of a dam foundation is one key problem that affects engineering safety. High gravity dams are typically built on complicated foundations, and maintaining their stabilities can be very challenging due to the formation of natural sliding paths from multiple weak structure planes. This paper presents two geomechanical model tests to study the stabilities of a foundation before and after reinforcement. By testing the original foundation, the resultant test results demonstrate that the stability safety factor is low and the associated weak structural planes are control factors therein. Subsequently, a sensibility analysis is performed to study the impacts of weak structural planes on foundation stability. Some reinforcement measures have been adopted accordingly, and the stability of the reinforced foundation is further studied in another model test. The second test indicates that the reinforcement effect is satisfactory in that, after reinforcement, the working performance and stability of the investigated foundation are greatly improved. These research results provide an important scientific basis for the evaluation of safety and reinforcement effectiveness in a gravity dam project.

A Constitutive Model for the Creep Behavior of Offwhite Marbles

AbstractThis paper reports an improved constitutive model for the shear creep behavior of offwhite marbles which are selected from slope and underground cavern and contain green schist’s weak structural planes. The shear creep behavior of the samples is characterized using the rheological tests. Based on the experimental measurements on mechanical properties under different normal stress conditions, an improved model is proposed to analyze the experimental results. It is demonstrated from a further discussion that such model can reflect the non-linear creep characteristics of structural planes, and especially, it is suitable for description of the viscoelastic and viscoplastic deformation behavior of structural planes.