Seepage-stress Coupling Research Articles

Damage and Failure Evolution Mechanism for Coal Pillar Dams Affected by Water Immersion in Underground Reservoirs

In coal mines, underground reservoir systems can increase the availability of water and are an effective technical approach for the protection and utilization of water resources. The stability of coal pillar dams is the key factor in the safety and stability of these underground water storage systems. However, coal pillar dams must operate in complex environments that combine dynamic-static superimposed stress fields and water immersion; moreover, coal pillar dams subjected to both stress and seepage are more susceptible to damage and even collapse. In this study, a seepage-stress coupling model of a coal pillar dam was constructed using the Universal Distinct Element Code (UDEC) simulation software. This model provides a platform for analyzing the characteristics of fracture development in surrounding rock in active mines and the coupled development of crack fields and seepage fields in coal pillar dams. Methods were developed for (1) calculating the water content for the coal pillar dam numerical simulation model and (2) reducing water immersion weakening. The maximum seepage width of a coal pillar dam subjected to water immersion was obtained, and a damage and failure evolution mechanism for coal pillar dams experiencing flooding was developed. The results provide a scientific basis for enhancing the stability control of coal pillar dams and are of great significance for realizing water conservation in coal mines.

Seepage-stress coupled modeling for rainfall induced loess landslide

Although rainfall is rare on the Loess Plateau of western China, landslides occur frequently there in rainy season. Surveys report that landslide hazards always follow heavy rains. In this study, a seepage-stress coupling model for rainfall induced landslide is used to examine an actual disastrous event in Yulin by the end of July, 2017. The effects of rainfall duration, rainfall intensity and soil weakening on slope stability are studied in detail. The results illustrate that the safety factor drops sharply at first and then is gradually declining to below 1.05 during additional two days of heavy rain. With soil strength softening considered, the slope would be more unstable, in which the weakening in soil cohesion is found to be a more sensitive factor.

Research on seepage-stress coupling analyses of shallow buried and dug vertical overlapping tunnels

Research on seepage-stress coupling analyses of shallow buried and dug vertical overlapping tunnels

Research on the creep mechanism of Huangniba landslide in the Three Gorges Reservoir Area of China considering the seepage–stress coupling effect

The impoundment of China’s Three Gorges Reservoir has led to the revival of many old landslides along the bank, and the annual fluctuation in water level of 30 m is likely to affect the creep deformation of these landslides. Through a field investigation of Huangniba landslide in the Three Gorges Reservoir Area, the local deformation signs and field monitoring data were analyzed. It was preliminarily considered that this landslide was currently at the creep stage and the creep rate was affected by the reservoir level variation. In order to carry out further research on the effect of reservoir level variation on the landslide movement, the finite element method was used to establish the seepage–stress coupling model of Huangniba landslide based on the seepage–stress coupling theory and taking into account the creep behavior of landslide material. The model was used to simulate the variation characteristics of the seepage field, stress field, and displacement field in the landslide during 6 years of cycles of reservoir level variation. Based on the numerical simulation results and field monitoring data, the deformation mechanism of the landslide was discussed. Finally, the sensitivity of the parameters in the creep model to the simulation results was discussed. The results show that creep deformation is the main deformation mechanism of Huangniba landslide, and it is obviously affected by the drawdown of the reservoir water level. During drawdown of the reservoir level, the pore water pressure inside the landslide decreases, resulting in an increase in effective creep stress and creep strain rate, thus accelerating creep deformation. The results of this study will provide a reference for the deformation mechanism of such creeping landslides subjecting to reservoir water level fluctuation.

Seepage-stress coupling mechanism for intersections between hydraulic fractures and natural fractures

Most unconventional oil and gas reservoirs contain some natural fractures, which play an essential role during reservoir reconstruction. Given the strong discontinuities in the displacement on both sides of the fracture as well as weak discontinuities in the pore fluid pressure, a novel three-dimensional seepage-stress coupling model using extended finite element method is proposed for fractured reservoirs. This directly coupled scheme for displacement field and stress field avoids the cumbersome process during calculating the fluid pressure in complicated fracture networks and translating into equivalent nodal force. Numerical examples are presented to simulate the fracture propagation pathway during the laboratory experiment on the staged synchronous fracturing of a horizontal well, revealing the deformation response and interaction mechanism between hydraulic fractures and natural fractures at orthotropic and non-orthotropic angles. The results show that due to the stress shadow effects, a non-planar fracture deflecting to wellbore would be formed during the progress of staged synchronous fracturing for a horizontal well. Moreover, the adjacent section to the intersection is opened and the others are closed for orthogonal natural fracture. In contrast, the non-orthogonal natural fracture is activated near the intersection at first and then fully opens as time increases; eventually, it is in the tensile-shear and composite state. In other words, the hydraulic fracture tends to traverse the orthogonal natural fracture and continue to propagate, as it is more easily arrested by the oblique natural fracture and transferred to propagation.

Sealant Performance Test and Stress–Seepage Coupling Model for Tunnel Segment Joints

Although the sealant performance of segment joints has an important influence on the durability of shield tunnels, it is rarely discussed theoretically. In this study, sealant performance tests of segment joints were designed and conducted on the basis of the stress and deformation characteristics of segment joints of a metro tunnel. The sealant performance of segment joints was obtained at different joint openings and dislocation deformations. A stress–seepage coupling model for segment joints was established, and the corresponding coupling equation for contact interface was deduced. The relevant parameters of the coupling equation were determined using the test results. The coupling model was used to analyse the influence of joint opening and dislocation on the sealant performance of joints. The opening and dislocation deformation of segment joints could considerably reduce the sealant critical pressure of the joints. Consequently, the sealant capability of the joints significantly declined, and the seepage flow velocity rapidly increased.

Investigation on the hydraulic fracture propagation of multilayers-commingled fracturing in coal measures

Multilayers-commingled fracturing is the vital step to achieve gas co-exploration in coal measures. Hydraulic fracture is required to penetrate vertically through multilayers in Multilayers-commingled fracturing. However, investigation on the propagation of commingled crack in coal measures which is soft-hard interlaced strata is less studied and not well understood. Therefore, based on the rock seepage-stress coupling effect, a three-dimensional (3D) hydraulic fracture model of multilayers-commingled fracturing in coal strata was established in combination with ABAQUS finite element software. The influence of geological factors and construction factors on the hydraulic cracks expansion in sandstone-coal interbedded reservoirs of X well in Linxing area in China was investigated. We found that the minimum horizontal stress difference is an essential geological factor to contain the vertical extension of commingled fractures; The high elastic modulus of neighboring reservoirs promotes the longitudinal penetration of fractures in the multilayers; The low tensile strength contrast between multiple layers increases the possibility of vertical expansion of combined fractures, while the high permeability of adjacent layers restrains the longitudinal propagation of fractures. The critical displacement of fracturing fluid exists in the combined fracturing process. The commingled cracks breakthrough the stratigraphic interface and penetrate into the adjoining layers when reaching the critical displacement; The high-viscosity of fracturing fluid facilitates the extending behaviors of hydraulic cracks in the vertical direction. The research results provide theoretical guidance for optimization of commingled fracturing layers and design of construction parameters in coal strata.

Stress–Seepage Coupling of Cataclastic Rock Masses Based on Digital Image Technologies

To explore the mechanical properties of cataclastic rock masses and the laws of their permeability changes under hydraulic pressure, cataclastic rock masses in shattered fault zones are sorted according to their particle size. Rubble is sorted under the same conditions to acquire digital images in sections and extract spatial distribution information. Due to significant numerical differences between rocks and pores in pixel functions and image matrices, MATLAB functions are developed for threshold segmentation. Using linear interpolation, three-dimensional digital analysis models are built. Based on these models, interconnected networks of spatial structures and spatial distribution features of stress, seepage and speed are identified for cataclastic rock masses. The seepage flow of cataclastic rock masses is approximated based on the maximum and minimum particle sizes. Additionally, an experimental study is performed with a seepage tester on cataclastic rock masses. According to the results, the impacts of the particle size on seepage differ significantly under different stress conditions. The seepage flow curve determined from the experiment is within the hydraulic pressure flow scope determined based on the maximum and minimum particle sizes. The seepage is in line with Forchheimer’s equations, but sharply contrasts with the theoretical results of Darcy’s law. This simulation method can be used as a reference for studying seepage–stress coupling of cataclastic rock masses.

Study of the Crack Propagation Model Under Seepage–Stress Coupling Based on XFEM

In fractured-vuggy reservoirs, cracks are not only reservoir spaces but also seepage channels. They are more likely to be closed and cracked under the coupling of the seepage field and the stress field. Therefore in this paper fractured-vuggy reservoirs are analyze as the background to study the propagation and closure of cracks under the seepage–stress coupling model. Firstly, the hydraulic model of continuous-discrete medium is established. Secondly, the fracture mechanics method is used to obtain the expression of crack width in the process of propagation and closure with the consideration of the water pressure, and then the propagation and closure criterions are established. On this basis, a numerical simulation method of crack propagation and closure under the seepage–stress coupling model is proposed by using the XFEM, and it is realized in ABAQUS by the secondary development. The calculation of typical cracks shows that: (1) the numerical calculation method established in this study is effective to simulate the propagation and closure of cracks; (2) the direction of crack propagation under Darcy flow is parallel to the vertical stress, and the direction of the crack propagation under the non-Darcy flow is perpendicular to the original fracture. (3) Non-Darcy flow is more likely to cause the whole system to become unstable than the Darcy flow does. This research has great significance for the future experimental researches, theoretical analyses and engineering applications.

Stability Analysis of Slope Under Rainfall Infiltration and Optimal Design of Anti-slide Pile

Based on practical slope engineering, analysis model of seepage-stress coupling under continuous rainfall condition was established by Geo-Studio (geotechnical analysis software). The dynamic change process of slope safety factors with time was analyzed. The results show that in the same Infiltration, slope under small intensity but long duration rainfall has lower safety factor and higher risk. In this unfavorable condition, analyzed and optimized the retaining structure of the antislide piles, and puts forward the optimization of landslide treatment scheme and the rainfall instability threshold of the slope. The practical application shows that the treatment effect is obvious. The analysis method is simple and practical, which can provide reference for similar slope engineering analysis and management.

Research on the Effect of Foundation Damage on the Dam Heel Stress of Concrete Gravity Dams

The key part of the stress analysis for the concrete gravity dam is the dam heel where the stress gradient is high. When doing the stress analysis, usually assuming that the bedrock is a homogeneous isotropic elastic body, it does not match with the reality. In this study, using the isotropic damage model and the nonlinear stress-seepage-damage coupling analysis method, taking spillway section 2 of the Three Gorges Dam as an example, regarding the rock mass and dam concrete as isotropic permeable continuous media, the effects of the foundation seepage, damage and stress-seepage coupling on the dam heel stress are analyzed and the following conclusions are obtained: (1) the seepage force is more appropriate when considering the water pressure on dam basin; (2) considering foundation damage and the stress-seepage-damage coupling, the dam heel stress is released the first principal stress and the vertical stress are decreased significantly. The seepage filed around the dam heel is also changed.

Safety Assessment of Buried Pipeline during Pile Driving Vibration in Offshore Engineering

To assess the impact of pile driving on adjacent submarine pipelines during the reconstruction of a pier berth, the local damage model of submarine pipelines is established to explore the safety thresholds of the particle peak velocity and horizontal displacement. The results are analyzed and adjusted by the existing standards and the corresponding literatures. Then, a three-dimensional numerical model is presented to assess the feasibility of the construction of piles by the obtained safety limits, in which the nonlinear behavior of the soil and stress–seepage coupling analysis are considered. After the construction, the safety of submarine pipelines is rechecked by the measured value of the particle peak velocity and horizontal displacement. Meanwhile, the propagation law of vibration, the horizontal displacement of underground soil, and the pore pressure during pile driving are explored. The results indicate that the construction of piles of 2# mooring pier did not cause damage to adjacent submarine pipelines. However, the construction of piles of 1# mooring pier which is nearer may cause damage to submarine pipelines.

Research on borehole stability of shale based on seepage-stress-damage coupling model

In oil drilling, one of the most complicated problems is borehole stability of shale. Based on the theory of continuum damage mechanics, a modified Mohr-Coulomb failure criterion according to plastic damage evolution and the seepage-stress coupling is established. Meanwhile, the damage evolution equation which is based on equivalent plastic strain and the permeability evolution equation of shale are proposed in this paper. The physical model of borehole rock for a well in China western oilfield is set up to analyze the distribution of damage, permeability, stress, plastic strain and displacement. In the calculation process, the influence of rock damage to elastic modulus, cohesion and permeability is involved by writing a subroutine for ABAQUS. The results show that the rock damage evolution has a significant effect to the plastic strain and stress in plastic zone. Different drilling fluid density will produce different damage in its value, range and type. This study improves the theory of mechanical mechanism of borehole collapse and fracture, and provides a reference for the further research of seepage-stress-chemical-damage coupling of wall rock.

Fluid-solid coupling model based on endochronic damage for roller compacted concrete dam

According to the characteristics of thin-layer rolling and pouring construction technology and the complicated mechanical behavior of the roller compacted concrete dam (RCCD) construction interface, a constitutive model of endochronic damage was established based on the endochronic theory and damage mechanics. The proposed model abandons the traditional concept of elastic-plastic yield surface and can better reflect the real behavior of rolled control concrete. Basic equations were proposed for the fluid-solid coupling analysis, and the relationships among the corresponding key physical parameters were also put forward. One three-dimensional finite element method (FEM) program was obtained by studying the FEM type of the seepage-stress coupling intersection of the RCCD. The method was applied to an actual project, and the results show that the fluid-solid interaction influences dam deformation and dam abutment stability, which is in accordance with practice. Therefore, this model provides a new method for revealing the mechanical behavior of RCCD under the coupling field.

Theory and application of rock burst prevention using deep hole high pressure hydraulic fracturing

In order to analyze the mechanism of deep hole high pressure hydraulic fracturing, nonlinear dynamic theory, damage mechanics, elastic-plastic mechanics are used, and the law of crack propagation and stress transfer under two deep hole hydraulic fracturing in tectonic stress areas is studied using seepage-stress coupling models with RFPA simulation software. In addition, the effects of rock burst control are tested using multiple methods, either in the stress field or in the energy field. The research findings show that with two deep holes hydraulic fracturing in tectonic stress areas, the direction of the main crack propagation under shear-tensile stress is parallel to the greatest principal stress direction. High-pressure hydraulic fracturing water seepage can result in the destruction of the coal structure, while also weakening the physical and mechanical properties of coal and rock. Therefore the impact of high stress concentration in hazardous areas will level off, which has an effect on rock burst prevention and control in the region.

Permeability Evolution Laws and Equations during the Course of Deformation and Failure of Brittle Rock

AbstractPermeability tests on limestone and sandstone during the course of deformation and failure are carried out with a servocontrolled testing machine. The permeability evolution of the two kinds of rocks with axial, lateral, and volumetric strains are investigated. The test results show that the permeability has an obvious correlation with the strain. The permeability mechanisms during the course of deformation and failure are discussed. According to the feature variations of permeability and strain of rock specimens, a conceptual model for the permeability evolution with the strain is proposed. The test results of sandstone are used to validate this model, and the relevant permeability-strain equation in the process of deformation and failure is fitted by using the mathematical method. The fitting precision is good. The proposed equation may provide another important control equation for the stress-seepage coupling analysis.

Research on Multiple Holes Grouting of Fractured Rock Mass

Considering the seepage stress coupling of fractured rock mass, the multiple holes grouting problems were simulated to analyse the spread regularity by Universal Distinct Element Code(UDEC).The results show that the correlation between grouting pressure and the diffusion distance is positive, whereas the correlation between ground stress and diffusion distance is negative; With the raising of grouting holes, the diffusion distance is increasing and becoming more uniform in all directions, and the grout pressure and saturation is falling and attenuation amplitude is decreasing along the direction of grout diffusion; With the increasing of fracture aperture, the grout diffusion distance is increasing, and the grout pressure and saturation attenuation amplitude is decreasing along the direction of grout diffusion.

Numerical simulation on fault water-inrush based on fluid-solid coupling theory

About 75% water-inrush accidents in China are caused by geological structure such as faults, therefore, it is necessary to investigate the water-inrush mechanism of faults to provide references for the mining activity above confined water. In this paper, based on the fluid-solid coupling theory, we built the stress-seepage coupling model for rock, then we combined with an example of water-inrush caused by fault, studied the water-inrush mechanism by using the numerical software COMSOL Mutiphysics, analyzed the change rule of shear stress, vertical stress, plastic area and water pressure for stope with a fault, and estimated the water-inrush risk at the different distances between working faces and the fault. The numerical simulation results indicate that: (1) the water-inrush risk will grow as the decrease of the distance between working face and the fault; (2) the failure mode of the rock in floor with fault is shear failure; (3) the rock between water-containing fault and working face failure is the reason for water-inrush.

With FLAC<sup>3D</sup> Simulating Analysis the Rock Stability by Stretching Anchor Cables Reinforce on the Reservoir Dam Abutment

By studying the geological structure and seepage character, in YanJin bridge reservoir region the harmful geological structure had been reinforced with anchor cable. To establish constitutive law and yield-dstroy critertion of anchorage zone, working state of anchor cable was simulated with FLAC software. With two states of no seepage and Stress-seepage coupling in the reservoir, the anchor cables and the state of the dam abutment rock was computed, but the mechanic character of the harmful geological structure and anchor cable was studied. The deformation stability was accurtely appraised in the high slope rock of dam abutment, by comparing with the state of unreinforce rock, analysing the loading effect of the structure face in anchor cables and the stability regular of slope rock . The computing results have the greater practical values for the reservoir work.

A seepage-stress coupled analysis of seabed deformation induced by the decomposition of gas hydrate

The deformation of seabed considering seepage-stress coupling is analysed using finite element method in this study, the effect of the varying pore pressure on stress field is accounted in the analysis, and the impact of reservoir permeability and the well pressure on the decomposition radius is studied. The changes of mechanical parameters due to hydrate decomposition are achieved by using user defined field subroutine. The results show that vertical and horizontal effective stress of soil in the dissociated area increase significantly while gas hydrates are decomposed by depressurisation. The reservoir permeability and well pressure have significant impact on the decomposition radius. The seabed deformation increases non-linearly with the increasing of the gas hydrate decomposition radius. The maximum vertical displacement reaches 18 m and the maximum horizontal displacement reaches 7.5 m.