Steady-state Seepage Research Articles

Judgement of rapid drawdown conditions in slope stability analysis

The rapid drawdown of reservoir may have a significant impact on the stability of adjacent slopes. In order to avoid potential risks, it is important to calculate the change of slope safety factor prior to the reservoir operation. The finite element method is used to analyze the transient seepage during drawdown, and then the pore water pressures are introduced into the stability computation based on limit equilibrium to obtain the transient safety factor. Computations show that for slopes with a specific geometry, the safety factor ratio depends on the parameters K/(Syv) (where K is the permeability coefficient, v is the drawdown speed, and Sy is the specific yield) and c′/(γHtan ϕ′) (where c′ and ϕ′ are the effective cohesion and friction angle, γ is the soil unit weight, and H is the slope height). By considering a wide range of K/(Syv) and c′/(γHtan ϕ′) values and different slope geometries, the percent reduction in critical safety factor of slope during drawdown relative to that during steady-state seepage is obtained. The drawdown condition that causes a large percent reduction in safety factor is judged as a rapid drawdown, and the opposite is a slow drawdown, which does not affect the slope design. This paper presents a series of charts for engineers and designers to judge rapid and slow drawdown conditions. Before the reservoir operation, the appropriate drawdown speed is selected according to the charts to ensure a slow drawdown for adjacent slope, while in the slope stabilization design, only the rapid drawdown stability analysis needs to be performed.

An experimental study on monitoring the phreatic line of an embankment dam based on temperature detection by OFDR

In this study, temperature detection with distributed fibers was used to obtain data for a laboratory model of seepage heat in an embankment dam, and the temperature was monitored using optical frequency domain reflection (OFDR) technology with high temporal and spatial accuracies. First, the temperature field in the infiltrated region of the dam body during the seepage test showed changes similar to that measured by OFDR temperature-sensing fibers. Then the heat transfer characteristics analysis within the embankment dam during seepage was conducted using numerical simulations of heat-flow coupling. Finally, temperature distribution characteristics during steady-state seepage for different water levels were measured, and the relationship between the temperature curve and the phreatic line was obtained. The results demonstrate that accurate temperature detection by OFDR and its high spatial resolution can reflect the characteristics of the temperature field in the seepage model of an embankment dam.

A Theoretical Calculation Method of Ground Settlement Based on a Groundwater Seepage and Drainage Model in Tunnel Engineering

Seepage is ubiquitous during tunneling in areas with high groundwater tables. The ground settlement trough on a single tunnel is well described by Peck’s formula, but it cannot reflect the settlement caused by seepage. In this paper, assuming that the groundwater inside and outside the tunnel is a one-dimensional steady-state seepage condition, the groundwater seepage and drainage model of the tunnel was established. Based on the model and the principle of groundwater dynamics, the seepage flow calculation formula was derived, and the dewatering funnel curve equation of the groundwater level surface of a tunnel aquifer was obtained. A case study of a tunnel project in Gansu Province was carried out, and the influence of seepage on the effective stress of the stratum around the tunnel and the calculation of ground settlement caused by seepage were analyzed. The results show that seepage makes the effective stress of the upper soil layer of the tunnel increase, which leads to an increase in ground deformation; when the groundwater level of the tunnel is greatly lowered, the seepage has a significant influence on the vertical deformation of the stratum.

Retrogressive Failure of Reservoir Rim Sandy Slopes Induced by Steady-State Seepage Condition

Reservoir rim slopes often experience seepage-induced slope instability during rainfall season. The predominant phenomenon observed during monsoons is the establishment of continuous seeping conditions, either steady or unsteady in nature. The infiltrated rainwater seeping toward the drainage basin may induce instability in the slope. This paper presents results from an experimental study conducted to investigate the failure mechanism of a cohesionless soil slope under a steady-state seepage condition. Retrogressive multiple rotational slide type of slope failure occurred during experimentation. It was observed that the failure didn’t occur in one go; instead, it was progressive with time. In usual practice by engineers, while performing numerical simulations for a field problem, the focus is on the formation of failure surface and deformations observed. But, the limitation with such studies is that the movement of the slope surface over a period of time cannot be investigated. It is, therefore, suggested that emphasis should be laid upon the time-dependent analysis as well.

Hydraulics of Seepage from Trapezoidal Channels

AbstractA tractable analytical solution for steady-state two-dimensional seepage from a trapezoidal channel in a homogeneous, isotropic porous medium of considerable depth is presented. The analysi...

Simulation Parameter Selection and Steady Seepage Analysis of Binary Structure Slope

The selection of calculation parameters for slope excavation support design and the analysis of seepage stability is a significant challenge. This difficulty also hinders the development of slope support engineering. This study examined the right binary structure slope engineering of the K5 + 220–K5 + 770 section of the TJ1A mark of the Jiangkou-Weng’an Highway in Guizhou province. In this study, we propose and use the deep displacement monitoring data and p value test method to check the simulation parameters. Furthermore, the superposition calculation method for steady-state seepage analysis of slope geotechnical structure is proposed. A comparative analysis of the displacement, strain, stress, and safety factor of the slope after the application of pore water pressure was carried out for three slope conditions. The analysis showed that steady-state seepage has a significant effect on the displacement of the slope during the completion of excavation. As a result, a continuous distribution of strain arises on the slope along the interface between the potential sliding surface and the rock–soil layer, and then forms a continuous sliding zone. Additionally, steady-state seepage has a significant effect on the position of the displacement distribution during the initial support of the slope, leading to a significant increase in the extreme value of the shear outlet displacement of the potential slip surface of the slope and in the extreme value of equivalent strain. Finally, steady-state seepage reduces the displacement and equivalent strain upon construction of the secondary slope support. The steady-state seepage has a limited effect on the stress concentration, but reduces the safety factor calculated using the strength reduction method, in all three stages of slope excavation and support. This study enriches the analysis methods for determining the stability of a dual-structure slope during the rainy season, and provides new ideas for the safety and control of slope support projects.

Bayesian Updating of Soil–Water Character Curve Parameters Based on the Monitor Data of a Large-Scale Landslide Model Experiment

It is important to determine the soil–water characteristic curve (SWCC) for analyzing landslide seepage under varying hydrodynamic conditions. However, the SWCC exhibits high uncertainty due to the variability inherent in soil. To this end, a Bayesian updating framework based on the experimental data was developed to investigate the uncertainty of the SWCC parameters in this study. The objectives of this research were to quantify the uncertainty embedded within the SWCC and determine the critical factors affecting an unsaturated soil landslide under hydrodynamic conditions. For this purpose, a large-scale landslide experiment was conducted, and the monitored water content data were collected. Steady-state seepage analysis was carried out using the finite element method (FEM) to simulate the slope behavior during water level change. In the proposed framework, the parameters of the SWCC model were treated as random variables and parameter uncertainties were evaluated using the Bayesian approach based on the Markov chain Monte Carlo (MCMC) method. Observed data from large-scale landslide experiments were used to calculate the posterior information of SWCC parameters. Then, 95% confidence intervals for the model parameters of the SWCC were derived. The results show that the Bayesian updating method is feasible for the monitoring of data of large-scale landslide model experiments. The establishment of an artificial neural network (ANN) surrogate model in the Bayesian updating process can greatly improve the efficiency of Bayesian model updating.

Non-intrusive reliability analysis of unsaturated embankment slopes accounting for spatial variabilities of soil hydraulic and shear strength parameters

Existing reliability analyses of embankment slopes usually considered the spatial variabilities of shear strength parameters and saturated hydraulic conductivity separately. Additionally, the variability in the soil–water characteristic curve (SWCC) was ignored. A non-intrusive approach is proposed for reliability analyses of unsaturated embankment slopes under four different cases on a steady-state seepage analysis. The spatial variabilities of hydraulic parameters (including fitting parameters, a and n, of SWCC and saturated hydraulic conductivity) and shear strength parameters are accounted for simultaneously. To illustrate the proposed approach, a hypothetical embankment under unsaturated seepage is investigated. The soil parameters of the embankment and foundation are modeled as lognormal random fields and lognormal random variables, respectively, to take into account the inherent uncertainties. Parametric sensitivity studies are then performed to account explicitly for the influence of the spatial variation of hydraulic parameters on the reliability of embankment slope stability. The proposed approach can act as a practical and rigorous tool for estimating the reliability of embankment slopes with small levels of probability of failure (i.e., 10−4–10−3). An interesting finding that the probability of failure of the unsaturated embankment slope decreases with the variability of the fitting parameter n of SWCC is observed and explained.

Centrifuge testing and numerical modeling of tunnel face stability considering longitudinal slope angle and steady state seepage in soft clay

Understanding the failure mechanism of a tunnel excavation face under complex hydrogeological conditions is a key challenge for geotechnical engineering. In this study, we investigated the excavation face instability induced by the longitudinal slope angle of the tunnel and steady state seepage flow. First, a fiber Bragg grating (FBG) system suitable for centrifuge model tests was proposed. The test apparatus was enhanced to investigate the influence of longitudinal slope angle on the active limit support pressure. Subsequently, a series of centrifuge model tests and Abaqus numerical simulation analyses were conducted to investigate the progressive failure mechanism of the excavation face. The experimental and numerical simulation results showed that the proposed geotechnical centrifuge FBG test system is fully feasible for multi-parameter monitoring of the centrifuge model. Under the assumptions of homogeneous and isotropic soil and steady state seepage flow, the seepage force in the limit support pressure is independent of the permeability coefficient. Moreover, the active and passive limit support pressures increase and decrease, respectively, with longitudinal slope angle, and the gap between them progressively decreases. Furthermore, under isotropic permeability, the soil internal friction angle, rather than soil cohesion, is responsible for the change in excavation face stability with longitudinal slope angle.

Health monitoring and dynamic analysis of an earth-fill dam at the stage of first impounding: case study—Siahoo dam of Iran

First impounding of the earth-fill dams is considered as one of the most critical stages of these earth structures during their lifespan such that it demands careful monitoring of the dam’s safety. In this study, behavior of Siahoo dam, an earth-fill dam in Iran, is evaluated by numerical modeling at the stage of first impounding to (1) back-analysis and calibration of the numerical model using data of instrumentation measurements, gathered during the dam construction. (2) Determine the optimized plan of the dam’s first impounding so that the dam safety is secured against hydraulic fracturing. (3) Predict the displacements of the dam in the future under seepage and consolidation using the calibrated numerical model. (4) Analyze the dam under seismic loading condition. The material properties were chosen through a two-step procedure based on numerical simulation of laboratory tests in the software and calibration between the stress–strain analysis of the dam and instrumentation measurements at the end of construction stage, so that the real behavior of the dam can be represented. To find the maximum rate of dam’s first impounding in safe condition, a sensitivity analysis was performed assuming eight number of impounding scenarios. Having performed the steady-state seepage analysis, seismic loading was applied using the equivalent linear method and the permanent displacements were predicted using the method of Newmark sliding blocks. Liquefaction analysis was also performed to recognize liquefiable zones of the foundation. Finally, stress redistribution analysis was carried out to estimate the post-earthquake displacements.

Effect of non-liquefiable layer on bearing capacity and settlement of shallow foundations

Liquefaction during earthquake excitations is one of the most important causes of damage imposed on structures. This phenomenon in saturated loose sand deposits increases water pressure and reduces stiffness. An increase in pore-water pressure during excitations can reduce soil shear strength, and consequently, lead to a decrease of the soil bearing capacity and an increase of settlement. In this study, using physical modelling, the effect of the presence of a non-liquefiable layer with different thicknesses on the improvement of the bearing capacity and settlement of shallow foundations has been investigated for both full and partial liquefaction cases. In these experiments, various constant excess pore-water pressure ratios are generated using the steady-state seepage. The tests are carried out in two different groups. The first group is designed for determining the effect of excess pore-water pressure generation on the bearing capacity; the second group is designed for assessing the effect of design safety factor on the settlement of shallow foundations located on non-liquefiable layers with different thicknesses. The presence of non-liquefiable layers causes considerable improvement in the bearing capacity and settlement of shallow foundations, and this issue may be considered in the engineering problems.

Geotechnical Analysis of Teeb Weir Foundation Soil Stability Against Seepage Effects

The steady state seepage analysis is used to compute the factor of safety against piping for Teeb weir in the eastern part of Maysn. Teeb weir is a one of a swarm of hydraulic structures that were suggested and designed to reduce flooding risk in the Teeb area, and to work as a water harvesting system to recharge ground water in the area. The geotechnical engineering map is drawn to analysis the soil properties and estimate the suitability of the soil to support foundation of the weir body and downstream reservoir. SEEP/W software is used to solve the water seepage model underneath the weir foundation. Only the saturated model is selected to compute the factor of safety against vertical piping and to denote the zone of potential piping erosion. The model results show that the stability is critical and that there is a high possibility of failure expected, especially in the downstream zone.

An Analytical Continuous Upper Bound Limit Analysis of Pore Water Effect on the Tail Stability of Underwater Shield Tunnels during Construction

An analytical continuous upper bound limit analysis is developed to analyse the effects of seepage on the transverse stability of underwater shield tunnels. The approach is based on an analytical continuous upper bound limit analysis method for cohesive-frictional soils. It employs the complex variables solution of the displacement field due to tunnel deformation and movement, and the analytical solution of the pore water pressure field for steady state seepage due to pore water influx at the tunnel perimeter. The most critical slip line position and the minimum required tunnel support pressure are determined by using a particle swarm optimization scheme for various generic situations. The method is verified via finite element simulation and comparison with the solution from using rigid block upper bound limit analysis. The parametric analysis revealed among other things that both the infimum of the necessary tunnel support pressure and the most critical plastic zone increase when the hydraulic head at the ground surface increases, but decrease when the tunnel influx increases due to the fact that pore water pressure at the tunnel perimeter decreases with the tunnel influx.

Three dimension deformation analysis of Jatigede Dam

In large dams, the reservoir water level will become a large hydrostatic pressure and reduce the effective stress due to the effect of seepage on the dam body. The total stress that occurs can cause deformation in the dam body to exceed the allowable deformation. Therefore, it is necessary to evaluate the deformation of the dam to know the stability of the dam. This research aimed to analyze the deformation of the dam in a steady-state seepage condition. The reservoir water level was modeled on minimum, normal, and flooded water levels. The deformation was analyzed using the three-dimension finite element method. Deformation analysis results show that the deformation increased when the reservoir water level increased. Significant deformation increase occurred in x-direction deformation i.e. 0.27 m at minimum water level, 0.55 m at normal water level and 0.55 m at flooded water level. The deformation obtained from the analysis still required the maximum deformation criteria of 2 m, which is half of the freeboard.

Productivity Testing and Analysis of Low Permeability and Thick Layer of N Gas Field

For a better guidance of production, a combination of drill stem testing (DST), regional statistical method and pseudo steady-state seepage theory model was used to analyze the productivity of N gas reservoir in light of the complex geological features of the low-permeability thick-layer. Firstly, the DST method was used to test the N gas reservoir. And then the binomial pseudo-pressure method, binomial pressure square method and exponential method were used to interpret the test data of DST of this formation. Finally, the binomial pseudo-pressure interpretation method was used and the results showed that only the productivity of H3b layer was successfully tested of the four. The H3a, H4b and H5a layers are ultra-low pore and permeability gas reservoirs and the productivity of these layers can’t be explained by the available data due to the short testing time and a non-stationary state of testing pressure and quantity, resulting in the failure of the test. The productivity of the main layers were estimated and forecasted by the regional statistical method and the theoretical model of pseudo steady-state seepage, taking the arithmetic average value of the regional statistical method and the theoretical formula as the final value of absolute open flow rates(AOF). The final calculation results are as follows: the AOF of main gas layers H3a, H3b, H4b and H5a in N gas field is 31.30×104m3/d, 388.92×104m3/d, 20.82×104m3/d and 30.80×104m3/d, respectively. This method may sheds light on verifying and calculating the productivity of gas wells and determining the reasonable production allocation of gas wells.

Assessment of steady-state seepage through dams with nonsymmetric boundary conditions: analytical approach.

In this study, new analytical solutions were developed for 2D and 3D steady-state water seepage through dams with nonsymmetric boundary conditions. The nonsymmetric boundary conditions for the 2D cases were created with different unit step functions on a part and/or parts of the right boundary of dam plane. Six cases were investigated in 2D, where a constant hydraulic head is applied at the left boundary of the dam plane and rectangular, ramp, triangular, trapezoidal, tunnel, and piecewise rectangular distributions of hydraulic head are applied at the right boundary of the dam plane. Then, a 3D case with a constant hydraulic head at the upstream and a linearly distributed hydraulic head at the downstream of the dam was investigated. Subsequently, the performance of proposed analytical solutions was examined by comparison with numerical finite difference modeling. The results demonstrate reasonable accuracy of the developed equations. The developed analytical solutions can be utilized as a benchmark to verify numerical models with similar boundary conditions.

Effects of micro- to meso-features on the permeability of fissured clays

This paper discusses the relation of the coefficient of saturated permeability in a given direction, ki, with the void ratio, e, for fissured and unfissured clays, wherein ki characterises the hydraulics of the equivalent uniform porous model. The ki–e data for the fissured clays are compared with what is observed for unfissured clays, either natural or reconstituted. For each clay, the ki–e data result from laboratory investigation and are related to the fissuring identity of the clay, classified through a fissuring characterisation chart. Through this procedure, the study provides an initial rational insight of the variability of the ki–e law with both the micro- and the meso-scale clay features. Fissuring is shown to cause meso-scale non-uniformities of the flow patterns, which may cause a variation between the ki for steady-state seepage and that controlling transient seepage. In general, fissuring increases the clay permeability with respect to the same clay if unfissured and also with respect to the same clay when reconstituted. Also, the study sheds light on the difference between the ki–e law holding during compression and that during swelling for both unfissured and fissured clays, showing that such difference is more important for fissured clays.

A mathematical model for a steady-state seepage flow of groundwater under a reinforced concrete dam

A numerical technique is applied to solve a biharmonic equation problem of a steady-state seepage flow of water through a thin layer of soil, under an impermeable dam. Due to the existence of a point boundary singularity and particular boundary conditions in the problem of the present study, the biharmonic equation is selected to be the governing equation. The potential function of the problem is approximated by the leading terms of the local asymptotic solution expansion. These terms are also used to weight the governing biharmonic equation in the Galerkin sense. Implementing Green’s theorem twice, the discretized equations are reduced to boundary integrals. The system of linear equations is completed by weakly enforcing the Dirichlet boundary conditions by means of Lagrange multipliers. The values of the latter are calculated together with the singular coefficients. The numerical results obtained with the method, indicate high accuracy and very fast convergence with the number of singular functions and the number of Lagrange multipliers. The volume of water per unit time q flowing through the soil in the horizontal direction, under the dam, which is directly proportional to the directional derivative of the potential function, is approximated by the derivatives of the leading terms of the local asymptotic solution expansion. Values of q and the corresponding discharge velocity, obtained with the method, compare favourably with the values given by FEM and soil Mechanics theory. The favourable numerical behaviour of this numerical technique, which in the bibliography is known as singular function boundary integral method (SFBIM), can be exploited in numerous ways. Combining the SFBIM with standard schemes, such as the FEM, appears to be an interesting extension of the method for future work, aiming at enforcing the strengths of the SFBIM in problems with boundary singularities.

Reliability-Based Slope Stability Analysis of Durgawati Earthen Dam Considering Steady and Transient State Seepage Conditions Using MARS and RVM

In this study, reliability analysis of slope failure of Durgawati earthen embankment has been performed using two different methods specifically multivariate adaptive regression splines (MARS) and relevance vector machine (RVM). Reliability index $$(\beta )$$ is calculated using both MARS and RVM under steady-state and transient-state seepage conditions. The analyses are performed for two different sections CH 21.0 and CH 22.0 at RD 640.09 m and RD 670.57 m, respectively. The Durgawati dam is situated in Kaimur district of Bihar, India. The FOS values of Durgawati earthen dam is calculated for using modified Bishop’s method for different seepage conditions, i.e., steady state and transient state. The seepage and slope failure analysis of Durgawati earthen dam is performed using SEEP-W and SLOPE-W modules of Geo-Studio 2007 software. The FOS values are calculated for these conditions for different realizations of the material parameters $$(c,\varphi ,\gamma )$$. After that, MARS and RVM have been applied to estimate the reliability index $$(\beta )$$ for the estimated FOS values for different realizations over the body of the dam. The computed reliability index $$(\beta )$$ under different situations indicates that the performance of the dam is satisfactory.

Stochastic Analysis of Rainfall-Induced Slope Instability and Steady-State Seepage Flow Using Random Finite-Element Method

Stochastic Analysis of Rainfall-Induced Slope Instability and Steady-State Seepage Flow Using Random Finite-Element Method