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Sediment scour numerical simulation plays a critical role in the design of water-resistant foundation engineering, and this paper addresses a significant gap in most related studies, which often overlook the transformation of sediment and struggle to identify the actual riverbed obscured by yielding bed and suspended load. To tackle this challenge, a comprehensive sediment model based on the meshless Smoothed Particle Hydrodynamics (SPH) method was developed. Firstly, to enhance computational efficiency and mitigate the high cost of Fluid-Solid Interaction (FSI) between water and sediments, cohesionless sediment grains were modelled as non-Newtonian fluids, with yield strength determined according to a combined strength criterion. Subsequently, sediment transformation and identification were determined based on sediment particle velocity and shear stress, with the seepage force driving yield sediment particle motion at the interface. The effectiveness of this comprehensive sediment model was validated through comparison with three scour experiments. The results show better agreement between the model and experimental data, with a root-mean-square error of less than 2.17% in scour morphology simulation and successful identification of the actual post-scouring bed surface in each case. However, the free surface simulation in this model still exhibits slight error, with a root-mean-square error of less than 8.35%. [ABSTRACT FROM AUTHOR]

Abstract The flow of fluid through the porous matrix of a reservoir rock applies a seepage force to the solid rock matrix. Although the seepage force exerted by fluid flow through the porous matrix of a reservoir rock has a notable influence on rock deformation and failure, its effect on hydraulic fracture (HF) propagation remains ambiguous. Therefore, in this study, we improved a traditional fluid–solid coupling method by incorporating the role of seepage force during the fracturing fluid seepage, using the discrete element method. First, we validated the simulation results of the improved method by comparing them with an analytical solution of the seepage force and published experimental results. Next, we conducted numerical simulations in both homogeneous and heterogeneous sandstone formations to investigate the influence of seepage force on HF propagation. Our results indicate that fluid viscosity has a greater impact on the magnitude and extent of seepage force compared to injection rate, and that lower viscosity and injection rate correspond to shorter hydraulic fracture lengths. Furthermore, seepage force influences the direction of HF propagation, causing HFs to deflect towards the side of the reservoir with weaker cementation and higher permeability.

The flow of fluid through the porous matrix of a reservoir rock applies a seepage force to the solid rock matrix. Although the seepage force exerted by fluid flow through the porous matrix of a reservoir rock has a notable influence on rock deformation and failure, its effect on hydraulic fracture (HF) propagation remains ambiguous. Therefore, in this study, we improved a traditional fluid–solid coupling method by incorporating the role of seepage force during the fracturing fluid seepage, using the discrete element method. First, we validated the simulation results of the improved method by comparing them with an analytical solution of the seepage force and published experimental results. Next, we conducted numerical simulations in both homogeneous and heterogeneous sandstone formations to investigate the influence of seepage force on HF propagation. Our results indicate that fluid viscosity has a greater impact on the magnitude and extent of seepage force compared to injection rate, and that lower viscosity and injection rate correspond to shorter hydraulic fracture lengths. Furthermore, seepage force influences the direction of HF propagation, causing HFs to deflect towards the side of the reservoir with weaker cementation and higher permeability. [ABSTRACT FROM AUTHOR]

The flow of fracturing fluid through rock pores generates a seepage force (SF) that disrupts the existing stress equilibrium and significantly affects rock deformation and failure. Despite its impact, the effect of SF on hydraulic fracture (HF) initiation has yet to be fully understood. In this study, a mechanistic model of SF's impact on fracture initiation was established through analysis of the force balance on a microscopic element. Using the finite difference method, a transient hydro‐mechanical model was developed to simulate fluid seepage‐induced stress distribution and pore pressure variation around a wellbore. Model results were validated through comparison with an analytical solution of pore pressure. The influence of SF on fracture initiation was investigated by conducting simulations with various wellbore pressurization rates and fracturing fluid viscosities. The results showed that fluid viscosity and pressurization rate have a significant impact on fracture initiation pressure (FIP) and SF‐induced circumferential stress. A larger SF‐induced circumferential stress and a lower FIP were observed when the viscosity and pressurization rate were smaller. A higher Biot coefficient results in stronger SF and reduced FIP. The theoretical mechanical model of seepage force established in this paper can provide crucial theoretical support for understanding the mechanism of fracture initiation and propagation, as well as for optimizing the effectiveness of hydraulic fracturing construction. Highlights: The impact of seepage force on rocks is analyzed by establishing a theoretical mechanical model.The mechanism of seepage forces on fracture initiation is studied for the first time.The influence of fluid viscosity and wellbore pressurization rate on fracture initiation is illustrated. [ABSTRACT FROM AUTHOR]

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Pre-excavation dewatering treatment before excavation of phreatic aquifer can cause surface settlement. It is of great significance to predict the surface settlement value in advance for practical engineering. The surface settlement value caused by pre-excavation dewatering treatment was solved by theoretical calculation and numerical simulation respectively. In theoretical calculation, the effect of group wells was considered, and the predicted drawdown curve of water level was put forward. The original groundwater level and the predicted drawdown curve were taken as the boundary, and the settlement amount was calculated in different regions. The final settlement amount was obtained after superposition. The PLAXIS 3D modeling was adopted in the numerical simulation, and the well unit was used to simulate the precipitation well. The fluid-structure interactions was used to solve the surrounding surface settlement during the pre-excavation dewatering period, and the variation law of pumping flow and pore pressure under the group well effect was revealed. In order to verify the feasibility of the theoretical calculation method, the calculation results of the design standards and the in-situ data are verified and analyzed. The results show that the theoretical calculation method and the numerical simulation value method can approach the measured value better, and has certain practical value in engineering. [ABSTRACT FROM AUTHOR]

The shield method is commonly employed in the construction of urban subways, and the stability of the excavation surface is extremely important for the safety of tunnel construction. When constructing tunnels in submerged or water-rich strata, the seepage force is a key factor affecting the ultimate support force of excavation faces. Uncertainty of natural geotechnical material hydraulic parameters significantly impacts the seepage force near the face. Based on the classic limit analysis and the random field theory, the principle of effective stress in saturated soil is introduced, and the stochastic numerical limit analysis method considering the influence of pore water pressure is established by combining finite element spatial discretization and second-order cone programming. On this basis, the influence of spatial variability of permeability coefficient on the stability of shield tunnel face in water-rich strata is studied. The results show that the heterogeneity of the permeability coefficient leads to an increase in the pore pressure gradient at the face. The increase in the variation of permeability coefficient and the ratio of vertical to horizontal permeability coefficient significantly increases the support force required to maintain the face stability, and the effect of cross correlation coefficient and autocorrelation distance is relatively small. The present research can provide theoretical guidance for evaluating the face stability of tunnels in water-rich strata.

Fluid penetration into the rock during hydraulic fracturing has been an essential issue in studying the mechanism of fracture initiation, especially the seepage force caused by fluid penetration, which has an important effect on the fracture initiation mechanism around a wellbore. However, in previous studies, the effect of seepage force under unsteady seepage on the fracture initiation mechanism was not considered. In this study, a new seepage model that can predict the variations of pore pressure and seepage force with time around a vertical wellbore for hydraulic fracturing was established by using the method of separation of variables and the Bessel function theory. Then, based on the proposed seepage model, a new circumferential stress calculation model considering the time-dependent effect of seepage force was established. The accuracy and applicability of the seepage model and the mechanical model were verified by comparison with numerical, analytical and experimental results. The time-dependent effect of seepage force on fracture initiation under unsteady seepage was analyzed and discussed. The results show that when the wellbore pressure is constant, the circumferential stress induced by seepage force increases over time, and the possibility of fracture initiation also increases. The higher the hydraulic conductivity, the lower the fluid viscosity and the shorter the time required for tensile failure during hydraulic fracturing. In particular, when the tensile strength of rock is lower, the fracture initiation may occur within the rock mass rather than on the wellbore wall. This study is promising to provide a theoretical basis and practical guidance for further research on fracture initiation in the future. [ABSTRACT FROM AUTHOR]

Accurate calculation of the stresses and deformations of tunnels is of great importance for practical engineering applications. In this study, a three-region model for tunnels considering seepage force was established. A new nonlinear strain-softening model is proposed. Then, a unified solution for the stresses and deformations of tunnels is deduced. Through a series of discussions, the effects of seepage force, softening modulus coefficient of cohesion, and initial support resistance on the stress distribution, radii of the post-peak zone, and surface displacement around the tunnel are discussed. Results show that the tangential stresses are always larger than the radial stresses. As the distance from the tunnel center increases, the radial stress continues to increase, while the tangential stress first increases and then decreases. With the increases in seepage force, the radii of the post-peak zone and surface displacement all increase. With the increases in softening modulus coefficient of cohesion, the radii of the post-peak zone increase while the surface displacement decreases. Tunnels with a higher initial support resistance experience lower radii of the post-peak zone and surface displacement. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a work to define four fundamental concepts, namely, buoyant force, submerged unit weight, seepage force, and critical hydraulic gradients, for saturated geomaterials including soils, rocks, and concrete under normal and high pressures using the general effective stress (GES) concept along with Terzaghi's effective stress. In particular, four typical GES expressions are used for this purpose, and their impacts on the definition of the four concepts are compared based on available experimental evidence in the literature. The results suggest that (1) Terzaghi's effective stress can be physically validated in the context of Archimedes' principle for soils under normal conditions; (2) the generalized buoyant force on the unit volume of saturated geomaterials is the product of the unit weight of pore fluid and the GES coefficient tensor; and (3) the generalized seepage force theoretically acts in the direction of pore fluid flow only when the GES coefficient tensor is proportional to the permeability coefficient tensor. These four fundamental concepts have a profound significance for geotechnical applications with GES and thus merit further validation with adequate laboratory and in situ observations. [ABSTRACT FROM AUTHOR]

Sediment incipient motion in shallow water is a major concern for coastal engineers. Wave-induced seepage force has reportedly had an important impact on the sediment incipience. The effect of wave asymmetry and skewness is important for defining nearshore wave motions and the resulting sediment movement, but it has been discounted in most previous studies considering seepage. Using analytical and numerical models, this study examines the influence of two-dimensional nonlinear wave-induced seepage forces on sediment incipient motions in shallow water. A new modified Shields number was derived, which better addresses the problem of seepage. The results indicate that seepage force could stabilize the sand particles by lowering the maximum Shields number by up to 38.0%; in the linear wave cases, the opposite is true. This discrepancy is subject to the nonlinearity and asymmetry of shallow wave motions, as well as the decreasing "suction" force and increasing "injection" force. Besides, disregarding horizontal seepage would greatly underestimate the contribution of seepage to sediment incipient motions, especially in situations with steeper waves or an unsaturated and less permeable seabed. A lower Young's modulus, larger saturation, permeability, and water depth would all considerably decrease the maximum Shields number. • A new modified Shields number considering two-dimensional seepage force is derived. • Seepage reduces maximum Shields number by about 38%, thereby stabilizes the sand particles. • But for unsaturated soil with poor permeability, sand incipience is promoted by a great "suction". • The role of lateral seepage on sand incipience in shallow water is greater than that of linear wave. • The influence factors, such as H / h , H / L , k s , S r and E v are discussed. [ABSTRACT FROM AUTHOR]

Baghdad Metro is a vital project to fulfill the rapidly increased traffic volume requirements. The proposed metro will connect both sides of Baghdad City, passing under the Tigris River. This study is employed finite elements software (PLAXIS 3D) to evaluate the seepage force developed around the sub-river segment during different construction stages and for other water levels of Tigris. The study found that when the water level changes from maximum to minimum, the developed seepage force decreases by (8 to 13%) and (22 to 27%) respectively. The seepage forces were found to be maximum during the excavation stage. The concrete lining process led to a noticeable reduction in seepage forces at all locations. The study also implemented the strength reduction theory to assess the overall stability of the tunnel. The study shows that the overall stability factor was minimum during the concrete lining process. As the water level decreased, the overall stability factor increased by (5% - 8%).

The sand boiling phenomenon occurs downstream of hydraulic structures, and the continuation of this phenomenon could lead to a structural failure. In this paper, by developing a device to simulate sand boiling, experimental tests have been performed to determine the critical hydraulic gradient on various sandy soil. The effect of different parameters was evaluated such as four relative densities (0, 20, 50 and 80%), uniformity coefficient, woven and non-woven geotextiles in both single and double-layer states and the particle size distribution. Based on the results, with increasing the relative density and uniformity coefficient, the sand resistance against the hydraulic failure improved and also in soils with Cu = 1, coarser sands have indicated more resistance to the boiling. In improvement by geotextile, reinforced sands beard more water load than natural sands, and the type and layer number of reinforcements have affected the test results. In addition, a statistical comparison has been performed between the experimental results and the proposed equation by Terzaghi to calculate the critical hydraulic gradient. Finally, by using experimental results, a linear and nonlinear regression model is presented to predict the required seepage force for the hydraulic failure of the specimens. [ABSTRACT FROM AUTHOR]

Fluid seepage into rock pores not only generates poroelastic stress but also exerts seepage force on the rock skeleton. However, since the mechanism of the effect of seepage force on the stress field around the wellbore is not clear, conventional methods calculate the stress field only taking into account the poroelastic stress without the coupled effects of seepage force and rock deformation. Based on the theory of porous medium, this paper presents an analytical solution of the circumferential stress field formed by the seepage force around the wellbore and introduces the solution into traditional calculation models to overcome these issues. The numerical study by MATLAB® was used to simulate the stress field around the wellbore. Numerical simulation results show that the seepage force generates a circumferential tensile action and reduces in-situ circumferential compressive stress around the wellbore. Under the effect of seepage force, the effective circumferential stress around the wellbore becomes smaller. When considering seepage force, effective circumferential stress along the θ = 0 direction at the wellbore wall is reduced by about 32% compared with traditional numerical results. In addition, the circumferential stress field formed by the seepage force increases the possibility of rock failure at the well wall. The analytical results indicate that the seepage force should be considered in the stress field calculation around the wellbore, especially in reservoirs with low permeability.

Fluid penetration into the rock during hydraulic fracturing has been an essential issue in studying the mechanism of fracture initiation, especially the seepage force caused by fluid penetration, which has an important effect on the fracture initiation mechanism around a wellbore. However, in previous studies, the effect of seepage force under unsteady seepage on the fracture initiation mechanism was not considered. In this study, a new seepage model that can predict the variations of pore pressure and seepage force with time around a vertical wellbore for hydraulic fracturing was established by using the method of separation of variables and the Bessel function theory. Then, based on the proposed seepage model, a new circumferential stress calculation model considering the time-dependent effect of seepage force was established. The accuracy and applicability of the seepage model and the mechanical model were verified by comparison with numerical, analytical and experimental results. The time-dependent effect of seepage force on fracture initiation under unsteady seepage was analyzed and discussed. The results show that when the wellbore pressure is constant, the circumferential stress induced by seepage force increases over time, and the possibility of fracture initiation also increases. The higher the hydraulic conductivity, the lower the fluid viscosity and the shorter the time required for tensile failure during hydraulic fracturing. In particular, when the tensile strength of rock is lower, the fracture initiation may occur within the rock mass rather than on the wellbore wall. This study is promising to provide a theoretical basis and practical guidance for further research on fracture initiation in the future.

Accurate calculation of the stresses and deformations of tunnels is of great importance for practical engineering applications. In this study, a three-region model for tunnels considering seepage force was established. A new nonlinear strain-softening model is proposed. Then, a unified solution for the stresses and deformations of tunnels is deduced. Through a series of discussions, the effects of seepage force, softening modulus coefficient of cohesion, and initial support resistance on the stress distribution, radii of the post-peak zone, and surface displacement around the tunnel are discussed. Results show that the tangential stresses are always larger than the radial stresses. As the distance from the tunnel center increases, the radial stress continues to increase, while the tangential stress first increases and then decreases. With the increases in seepage force, the radii of the post-peak zone and surface displacement all increase. With the increases in softening modulus coefficient of cohesion, the radii of the post-peak zone increase while the surface displacement decreases. Tunnels with a higher initial support resistance experience lower radii of the post-peak zone and surface displacement.

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• This study presents new analytical closed-form solutions for an underwater tunnel considering the damaged zone. • The solutions are presented for tunnels in elastic–brittle–plastic rock masses with Mohr-Coulomb failure criterion. • The damaged zone is assumed to have cylindrical shape with finite radius. • Three different paths for plasticity evolution including six different states are considered. • It was concluded that the proposed model covers a wide range of tunnel problems. Rock excavation using drill and blast method is commonly used in tunneling world-wide. Drill and blast method has inherent disadvantage of deteriorating surrounding rock mass due to development of a blast-induced damage zone with reduced strength and stiffness parameters and increased permeability. Traditional tunnel analysis adopts same parameters for the entire rock mass, leading to the underestimation of tunnel stability. The blast damage zone with finite thickness is significant in tunnel stability. Tunneling below the groundwater table affects the hydraulic equilibrium. This will, in turn, cause seepage into the tunnel through the pores and discontinuities in the rock masses. The developed seepage force should be considered as an additional body force acting on both damaged and undamaged rock masses. This study presents a new analytical closed-form solution for the determination of stresses, strains, and displacements around a circular deep underwater tunnel with the consideration of the seepage forces and the damaged zone. The solutions are presented for tunnels excavated in pervious elastic–brittle–plastic rock masses with Mohr–Coulomb failure criterion. The damaged zone is assumed to have cylindrical shape with finite radius. The plastic zones may be formed in both damaged and undamaged rock masses, independently. In order to solve the proposed problem, three different paths for plasticity evolution including six different states that can possibly be encountered in the problem are considered. The results indicate that the seepage and the damaged zone have significant effects on the tunnel convergence and the distribution of stresses in the rock mass. [ABSTRACT FROM AUTHOR]

Based on the upper limit theorem of limit analysis and the Hoek-Brown failure criterion and considering the adverse influence of the seepage force, we established a stability analysis method of analyzing the water-resistant rock mass of a karst tunnel face, developed a critical safety thickness criterion for water inrush caused by the instability of the tunnel face, and conducted a sensitivity analysis of the main influencing parameters. We defined the safety coefficient (k) of the tunnel face's resistance to water-inrush instability during the tunnel excavation process and analyzed the dynamic evolution characteristics of the tunnel face's stability during the tunnel construction according to the safety coefficient. We used the method introduced in this paper to calculate the safe thickness of the water-resistant rock mass of the Xiema tunnel face in the first horizontal line of the Chongqing Expressway where it is adjacent to karst cavity 268. We compared these results with the calculation results of a method that did not consider the adverse influence of the karst water seepage force. The results showed that the safety thickness of the water-resistant rock mass calculated using the method proposed in this paper more accurately conformed to the actual situation of the project, which can more effectively ensure the construction safety of the tunnel segment adjacent to the anterior, concealed, high-pressure, water-rich karst cavity. The results of this study hold great significance for improving the predictability and targeted prevention of water-inrush disasters in karst tunnels. [ABSTRACT FROM AUTHOR]

The seepage force is of importance on tunnel face stability. The formulas to determine the seepage force are introduced based on Darcy's Law. The formula of the stability safety factor containing the tunnel face of the seepage force is derived and applied to the actual tunnel engineering using the upper bound limit analysis combining with the strength reduction method. The results show that: as the water level increases, the average seepage force increases, and the safety factor decreases. If the horizontal seepage force is considered only and the vertical seepage force is ignored, the result is unsafe. The stability of the tunnel face can be improved by reducing the excavation height and adopting some reinforcement, such as grouting or rock bolt to increase the cohesion and friction angle of the rock. [ABSTRACT FROM AUTHOR]

The fluctuation of reservoir water levels has significant impact on bank slope stability near a reservoir. Therefore, it is necessary to analyze the stability of bank slopes with reservoir drawdown. In this paper, a novel method combining the seepage force with rigorous limit equilibrium method is proposed to analyze the stability of bank slopes near the reservoir. First, the calculation method of the phreatic surface and the seepage force is developed. Then, six equilibrium equations are established based on the equilibrium conditions of three forces along the coordinate axis and the equilibrium conditions of three moments around the coordinate axes. Finally, a trust–region–reflective iterative algorithm is used to determine the safety factor of bank slopes from these six equations. Moreover, the effects of drawdown speed, the height of the drawdown, permeability coefficient, and the aquifer thickness on bank slope stability are investigated using the proposed method. Two engineering cases of Ataden I landslide and Guanyinping landslide are used to verify the correctness and practicability of the proposed method. [ABSTRACT FROM AUTHOR]

Fluid seepage into rock pores not only generates poroelastic stress but also exerts seepage force on the rock skeleton. However, since the mechanism of the effect of seepage force on the stress field around the wellbore is not clear, conventional methods calculate the stress field only taking into account the poroelastic stress without the coupled effects of seepage force and rock deformation. Based on the theory of porous medium, this paper presents an analytical solution of the circumferential stress field formed by the seepage force around the wellbore and introduces the solution into traditional calculation models to overcome these issues. The numerical study by MATLAB® was used to simulate the stress field around the wellbore. Numerical simulation results show that the seepage force generates a circumferential tensile action and reduces in-situ circumferential compressive stress around the wellbore. Under the effect of seepage force, the effective circumferential stress around the wellbore becomes smaller. When considering seepage force, effective circumferential stress along the θ = 0 direction at the wellbore wall is reduced by about 32% compared with traditional numerical results. In addition, the circumferential stress field formed by the seepage force increases the possibility of rock failure at the well wall. The analytical results indicate that the seepage force should be considered in the stress field calculation around the wellbore, especially in reservoirs with low permeability. [ABSTRACT FROM AUTHOR]

When a tunnel is excavated below the groundwater table, groundwater flows in through the excavated wall of the tunnel and seepage forces act on it. These forces significantly affect the ground reaction curve, which is defined as the relationship between the internal pressure and radial displacement of the tunnel wall. This study investigates analytical solutions for seepage forces acting on the lining of a circular tunnel under steady-state groundwater flow. Considering the tunnel's construction or service period and boundary conditions, the direction of maximum principal stress changes, and the input stress of the Mohr-Coulomb criterion varies. The stress distribution and yield range of the surrounding soils and linings are studied. The first, second, and third critical inner pressures are defined and evaluated. The influence of the seepage field on the plastic radius, first critical pressure, and stress distribution of the tunnel is analyzed. It is shown that during the construction period, the seepage force promotes the expansion of the yield area, whereas during the service period, the opposite is the case. The first critical pressure increases nearly linearly with the distant water pressure. The radial stress distribution decreases clearly in comparison with that when the seepage force is not considered, and the reduction is more prominent when internal pressure increases. The tangential stress distribution increases clearly compared with that when the seepage force is not considered. [ABSTRACT FROM AUTHOR]

This paper presents a new computational strategy for kinematic upper bound limit analysis in the presence of seepage forces with an improved mesh refinement scheme. In particular, the original adaptive refinement scheme is enhanced with a simple but efficient error-indicator of the nodal plastic dissipation for high-order elements. The proposed refinement criteria facilitate a precise quantitative evaluation of errors in the nodal plastic energy dissipation across each element and ensure that the rate of total refined element number gradually decreases with adaptive step. Adhering to two-dimensional steady state seepage condition, numerical details regarding the calculation of total water head distributions for the seepage field are provided. In a similar manner as treating the unit weight of the soil, the effects of seepage forces are incorporated as body forces in the upper bound formulation. Detailed numerical procedure of the proposed error indicator-based h -adaptive refinement scheme incorporating the inclusion of seepage forces is addressed and implemented in the in-house code. Several benchmark problems, including both homogeneous and non-homogeneous soils, are analyzed to evaluate the excellent performance of the proposed error indicator-based h -adaptive refinement scheme in upper-bound limit analysis and assess the influence of seepage forces on the stability of geostructures through comparison with that for dry condition. [ABSTRACT FROM AUTHOR]

The key issue for construction of subsea tunnels through unfavorable geological conditions is to determine a reasonable reinforcement scheme, while the core problem for the reinforcement design is to accurately evaluate the mechanical behavior of surrounding rock with ground reinforcement. Considering that advanced curtain grouting and full-face grouting are widely used in subsea tunnels, a mechanical model for the subsea tunnel surrounding rock accounting for both ground reinforcement and seepage effect was established. According to the distribution and extent of the plastic zone(s), six potential configurations were appropriately analyzed, which were validated by numerical simulations and analytical solutions for simplified settings from the literature. The sensitivities of the reinforcement parameters were examined, and by taking into account the tunnel radial displacement and the seepage quantity as the main objectives, the multi-objective optimization of the reinforcement parameters was put forward via the stratified sequencing method. Finally, application of the proposed method to the Qingdao Jiaozhou bay subsea tunnel project in China was explained. Research results could provide insightful ideas for the quantitative design of the ground reinforcement of subsea tunnels and may have reference value for their construction safety through unfavorable geological conditions. [ABSTRACT FROM AUTHOR]

Based on the elastic theory and the seepage flow theory, a new analytical solution with consideration of the seepage force is proposed to determine the external stress on the lining of a circular TBM tunnel. According to this solution, the relationships between the permeability coefficient of rock masses and the maximum allowable drainage flow are studied. The influence of the controlled drainage flow and the elastic modulus of surrounding rocks on the external stress is discussed. Moreover, in order to validate the results obtained from the elastic analytical solution developed in this paper, a comparison between the results obtained from the solution considering the seepage force and that without consideration of the seepage force is performed. [ABSTRACT FROM AUTHOR]

In this study, a finite element method was used to establish a two-dimensional numerical model to solve the problem of the Biot equation describing the poroelastic seabed, and to analyze the seepage force on a buried submarine pipeline under the propagation of a solitary wave. The model provides a solution to the displacement of the poroelastic seabed and the variation of the pore-water pressure. By means of numerical simulation, the effects of Young’s modulus and permeability coefficient of the soil on the pore-water pressure and seepage force are discussed. In the simulation of solitary waves passing through fully buried submarine pipelines, numerical results indicate that the smaller the permeability coefficient in dense sandy bed the greater the vertical force acting on the pipeline, and the smaller the permeability coefficient in loose sand bed the smaller the vertical force acting on the pipeline. In general, when the permeability coefficient is large, the smaller the Young’s modulus the more obvious the influence of the vertical force on the pipeline, and when the permeability coefficient is small, the larger the Young’s modulus the more obvious the influence of the vertical force on the pipeline.

The solutions of stress and displacement of a circular opening excavated in brittle and strain-softening rock mass incorporating rockbolts effectiveness and seepage force are presented in this study. The evolution equation is reconstructed for the strength parameters that incorporate these factors. Based on the evolution equation, an improved numerical method and stepwise procedure are presented which are compatible with the Mohr-Coulomb (M-C) and the generalized Hoek-Brown (H-B) failure criteria, respectively. Then given three interaction mechanisms between rockbolts and surrounding rock, solutions for stress and displacement are proposed in line with the improved numerical method and numerical stepwise procedure. The proposed approach can be reduced to Fahimifar and Soroush’s (Tunn Undergr Space Technol 20:333-343, 2005) solutions for special cases. The proposed method was validated by field monitoring data and FLAC results of Yanzidong tunnel. Examples under the M-C and generalized H-B failure criteria for rock mass are generated through MATLAB programming. Moreover, parametric studies are conducted to highlight the influence of rockbolts effectiveness in combination with seepage force on the stress and displacement of very good, average, and very poor surrounding rock. Results show that in this case, stress confinement is higher and tunnel convergences are lower than the corresponding stresses and displacements obtained in non-reinforced tunnels. Displacement and plastic radius are also higher than those without considering seepage force. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Landslides triggered by rainfall are a major multiple geological hazard on Qin-ba Mountain. Debris landslides in the shallow layer make up a large proportion of all landslides. A flume experiment was conducted to successfully initiate shallow debris landslides using artificial rainfall in Zhouzhi County, Qin-ba Mountain. The results confirmed a strong correlation between the deformation of the slope and pore-water pressure and moisture content. Slope deformation and failure were observed, and a possible mechanism was interpreted based on the experimental results. The primary effects of rainfall on shallow debris landslides on Qin-ba Mountain are the generation of a seepage force and a decrease in the effective stress of the sliding surface as a result of increasing pore-water pressure. The effect of rainfall on the shear strength parameters is inconspicuous, which might be attributed to the relatively high saturation of debris soils under natural conditions. The failure type in Test 1 is considered to be a progressive failure, which is a typical failure mode for homogeneous shallow debris slopes on Qin-ba Mountain, particularly for slopes exposed to artificial excavation. The deformation in Test 2 with higher density, merely taking the form of surface erosion, usually occurs in the regions with the least artificial disturbance. The two deformation types can be primarily attributed to differences in the soil density; the higher density reflected the smaller number and size of inside pores and led to lower soil permeability, which further influenced the distribution of the pore-water pressure, direction of seepage force, and slope deformation. Therefore, higher soil density changed by compaction is beneficial for the stability of shallow debris slopes on Qin-ba Mountain, even with high pore-water pressure. In subsequent work, a series of experiments with various densities should be conducted to explore the dividing point between the two deformation modes, and in addition, tests with larger slope gradients should also be considered. [ABSTRACT FROM AUTHOR]

In this study, analytical solutions for tide-induced pore pressure, seepage force and water inflow into a subaqueous drained tunnel are developed. The results are compared with numerical solutions from a commercial software. The effects of the soil permeability, shear modulus, lining thickness and buried depth of the tunnel on tide-induced pore pressure, seepage force and water inflow are discussed. Larger tide-induced pore pressure and seepage force are obtained for smaller tunnel depth and higher soil permeability. The phase lags of the maximal tide-induced pore pressure at different depths are determined and investigated. [ABSTRACT FROM AUTHOR]

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The key issue for construction of subsea tunnels through unfavorable geological conditions is to determine a reasonable reinforcement scheme, while the core problem for the reinforcement design is to accurately evaluate the mechanical behavior of surrounding rock with ground reinforcement. Considering that advanced curtain grouting and full-face grouting are widely used in subsea tunnels, a mechanical model for the subsea tunnel surrounding rock accounting for both ground reinforcement and seepage effect was established. According to the distribution and extent of the plastic zone(s), six potential configurations were appropriately analyzed, which were validated by numerical simulations and analytical solutions for simplified settings from the literature. The sensitivities of the reinforcement parameters were examined, and by taking into account the tunnel radial displacement and the seepage quantity as the main objectives, the multi-objective optimization of the reinforcement parameters was put forward via the stratified sequencing method. Finally, application of the proposed method to the Qingdao Jiaozhou bay subsea tunnel project in China was explained. Research results could provide insightful ideas for the quantitative design of the ground reinforcement of subsea tunnels and may have reference value for their construction safety through unfavorable geological conditions.

Hie stability prediction of shallow buried tunnels is one of tire most difficult tasks in civil engineering. The aim of this work is to predict the state of collapse in shallow tunnel in layered soils by employing non-associated flow rule and nonlinear failure criterion within the framework of upper bound theorem. Particular emphasis is first given to consider the effects of dilation on the collapse mechanism of shallow tunnel. Furthennore, the seepage forces and surface settlement are considered to analyze the influence of different dilation coefficients on the collapse shape. Two different curve functions which describe two different soil layers are obtained by virtual work equations under tire variational principle. Tire distinct characteristics of falling blocks up and down the water level are discussed in the present work. According to tire numerical results, the potential collapse range decreases with the increase of the dilation coefficient, hr layered soils, both of the single layer's dilation coefficient and two layers' dilation coefficients increase, the range of the potential collapse block reduces. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) stability of a slope subjected to seepage forces is studied in this work in light of the kinematic approach of limit analysis. The widely used horn model for 3D stability of slopes is presented and discretized for the first time. To compute the seepage forces developed in a slope, 3D numerical calculations are used to solve the seepage-flow problem. The discretization makes it possible to calculate the seepage force acting on each element of the discretized horn mechanism by using the numerical results. The safety factors obtained by the proposed approach agree well with those given by numerical calculations. The influence of soil properties, 3D slope geometry, and anisotropic permeability is discussed in this work. Numerical results show that the 3D effect is important for B/H ratios lower than 10.0, beyond which the two-dimensional (2D) plane-strain analysis can be used for a 3D slope, and that a larger horizontal permeability with respect to the vertical one is a favorable factor for the slope stability. [ABSTRACT FROM AUTHOR]

This paper focuses on the influence of intermediate principal stress and seepage force on visco-elasto-plastic solution of surrounding rock. By assuming that the surrounding rock satisfies the 3-D Hoek–Brown failure criterion and Hohai model, the stress, displacement and long-term deformation of tunnel are obtained. For elasto-plastic surrounding rock, an analytical approach was presented. For strain-softening surrounding rock, the potential plastic zone was subdivided into a finite number of concentric annuli and a numerical model was presented. Thus, based on 3-D Hoek–Brown failure criterion and Hohai model, the nonlinear visco-elasto-plastic models considering the intermediate principal stress and seepage force were proposed for elasto-plastic and strain-softening surrounding rock. The accuracy of the proposed approaches was validated with the published results in which the intermediate principal stress was not considered. Comparisons illustrate that the influence of seepage force on 3-D Hoek–Brown failure criterion is greater than that on generalised Hoek–Brown failure criterion. Taking the safety factor as 1.5, the proposed model is applied in predicting the long-term deformation of Hebian Tunnel, the deformation is calculated to be 8.0 cm which is 33.3% smaller than the designed value. [ABSTRACT FROM PUBLISHER]