Seepage Failure Research Articles

An Experimental Study on the Seepage Failure of Sandy Soil Over Confining Pressure

To study the properties of the base of sandy soil and internal erosion of dam body, we designed equipment for the experiment of seepage failure that was able to measure the confining pressure, changes of water head and amount of quicksand. In results, the amount of quick sand, differential head and flow velocity reduced with increase of confining pressure in the seepage failure experiment. In addition, the incident of erosion, differential head and critical velocity reduced with the increase of maximum particle diameter of sandy soil. In conclusion, the study showed the correlation of flow velocity of seepage failure with differential head and maximum particle diameter. Keywords: Seepage Failure, Internal Erosion, Quicksand, Sandy Soil, Confining Pressure

Application of CFD-DEM to investigate seepage characteristics of landslide dam materials

A coupled computational fluid dynamics and discrete element method was presented to quantitatively investigate the seepage characteristics of fine and coarse materials relevant to landslide dam. The numerical model was verified by comparing the calculated seepage parameters, critical hydraulic gradient and failure mode with the corresponding tests. The microcosmic mechanisms of the seepage failure were studied by considering seepage field, force chain, and particle trajectory. The failure mode of fine-grained soils was flowing soil because the effective stress was close to zero. However, for coarse-grained soils, the failure mode was piping that resulted from the presence of some effective stress.

Experimental studies on sand plug formation in suction caisson during extraction

ABSTRACTA series of model tests were conducted on Perspex-made suction caissons in saturated dense marine sand to study the sand plug formation during extraction. Suction caissons were extracted by pullout loading or by pumping air into the suction caisson. Effects of the pullout rates, aspect ratios and loading ways (monotonic or sustained) on the pullout capacity, and plug formation were investigated. It was found that the ultimate pullout capacity of the suction caisson increases with increasing the pullout rate. The sand plug formation under the pullout loading is significantly influenced by the pullout rate and the loading way. When the suction caisson is extracted at a relatively slow rate, the general sand boiling through the sand plug along the inner caisson wall occurs. On the contrary, the local sand boiling will occur at the bottom of the suction caisson subjected to a rapid monotonic loading or a sustained loading. Test results of the suction caisson extracted by pumping air into the caisson show that the pressure in the suction caisson almost follows a linear relationship with the upward displacement. The maximum pressures for suction caissons with aspect ratios of 1.0 and 2.0 during extraction by pumping air into the caisson are 1.70 and 2.27 times the maximum suction required to penetrate the suction caisson into sand. It was found that the sand plug moves downward during extraction by pumping air into the caisson and the variation in the sand plug height is mainly caused by the outflow of the sand particles from the inside of the suction caisson to the outside. When the suction caisson model is extracted under the pullout rate of 2 mm/s (0.28 mm/s for the prototype), the hydraulic gradient along the suction caisson wall increases to the maximum value with increasing the penetration depth and then reduces to zero. On the contrary, when extracted under the pullout rate of 10 mm/s (1.4 mm/s for the prototype), the hydraulic gradient along the suction caisson wall increases with increasing the pullout displacement. When extracted by pumping air into the caisson, the hydraulic gradient reaches the critical value, and at the same time, the seepage failure occurs around the suction caisson tip.

Numerical modeling and verification of grouting with mold bag treatment on seepage failure in foundation excavation

This article presents a numerical modeling and verification on a new grouting technique, called mold bag prestress reinforcing method, which was successfully used for grouting control on seepage failure during a foundation pit excavation project. A numerical model is established based on finite element method to simulate the prestrss reinforcing and grouting process. The displacement and stress field during grouting process are calculated. Based on the calculation results, the rationale of the pretress method is clearly illustrated and the reinforcing mechanism is revealed. Results show that the horizontal displacements on the monitoring lines parallel to the mold bag are distributed in a parabola shape, and the prestress method effectively improves the mechanical properties of the soil. The influence of multimold bag interaction is also analyzed. The impermeability of the interior areas between two mold bags can be further improved due to a combining effect. The numerical results are compared with the actual excavation results of the foundation project. After grouting treatment, the water inflow amount reduced from 94 m3/h to 4 m3/h, which means more than 96% water inflow was successfully reduced. It is concluded that the numerical model can successfully simulate the process of prestress method and reveal the reinforcing mechanism.

3-D direct numerical model for failure of non-cohesive granular soils with upward seepage flow

The paper reports the application of a 3-D direct particle–fluid simulation model to the seepage failure of granular soils. The goal of this study is to numerically capture the process of the failure which is induced by the seepage flow from the micromechanical aspects with no macroscopic assumptions. In order to accomplish this goal, non-cohesive granular assemblies with an upward seepage flow and a variety of pressure gradients are investigated. The motion and the collision of the soil particles are calculated by a soft sphere model, such as the discrete element method, and the flow of the pore fluid is directly solved at a smaller scale than the diameter of the soil particles by the lattice Boltzmann method. By coupling these methods, the interaction between the soil particles and the seepage flow is also considered. As a result of the series of analyses, the numerically predicted value for the critical hydraulic gradient is found to be in good agreement with the theoretical value. In addition, the rapid change in the flow pattern around the critical hydraulic gradient can be microscopically captured. By observing the evolution of the force chains inside the soils, it is demonstrated that the failure process of the contact networks can also be reproduced by the simulation model presented here.

Evaluating the Mesostructural Changes of Laboratory Created Soil-Rock Mixtures Using a Seepage Test Based on NMR Technology

Abstract Soil-rock mixtures (S-RMs) have great potential as a material for use in hydropower engineering. However, seepage can change the porosity and structure of such mixtures, which can in turn threaten hydropower engineering structures. The objective of this study was to understand the mesostructural changes in S-RMs when S-RMs undergo seepage failure. Laboratory seepage tests were performed using a custom-made seepage instrument under different hydraulic gradients, i.e., 0, 20, 24, 27, and 30, and under a constant critical hydraulic gradient (30) for different lengths of time, i.e., 15 min, 30 min, 60 min, 120 min, and 180 min. Nuclear magnetic resonance (NMR) can directly determine the physical properties of S-RMs, such as the pore distribution, porosity, and permeability. The results of the NMR tests reveal that the pores in the S-RMs are well developed. As the hydraulic gradient and time increase, the pores are expanded by the hydraulic pressure, and the connectivity of the pores increases. The structure and cohesion of the S-RM can be damaged by hydraulic pressure. When the hydraulic gradient is equal to the critical hydraulic gradient, the S-RM experiences erosion or seepage failure, and these phenomena become increasingly obvious with time. A relatively strong correlation exists between porosity and permeability. Movable fluid porosity contributes considerably more to permeability than does irreducible porosity.

Numerical Analysis on Seepage in the deep overburden CFRD

There are many problems in the construction of hydraulic structures on deep overburden because of its complex foundation structure and poor geological condition. Seepage failure is one of the main problems. The Combination of the seepage control system of the face rockfill dam and the deep overburden can effectively control the seepage of construction of the concrete face rockfill dam on the deep overburden. Widely used anti-seepage measures are horizontal blanket, waterproof wall, curtain grouting and so on, but the method, technique and its effect of seepage control still have many problems thus need further study. Due to the above considerations, Three-dimensional seepage field numerical analysis based on practical engineering case is conducted to study the seepage prevention effect under different seepage prevention methods, which is of great significance to the development of dam technology and the development of hydropower resources in China.

The Mechanism and Numerical Simulation Analysis of Water Bursting in Filling Karst Tunnel

In order to investigate the mechanism and the process of water bursting in filling karst tunnel, based on the geological defect of karst water bursting formations, the instability model of filling karst conduit is built. There are the seepage failure of permeable media, the sliding instability of impermeable media and the seepage and sliding instability of low-permeable media. The corresponding instability criterions of these models are obtained by deriving their mechanics formulas. Based on the karst water bursting in Fenshuiao tunnel project, the mechanism and numerical simulation analysis of its water bursting process are analyzed. The safety factor of filling of karst conduit is 0.502 which indicates that filling of karst conduit is instable. This analysis result is in accord with the actual situation of water bursting. The process of karst water bursting is simulated by Fast Lagrangian Analysis of Continua (FLAC3D) which shows the whole process of water bursting in karst conduit.

Optimization of Multiple Seepage Piping Parameters to Maximize the Critical Hydraulic Gradient in Bimsoils

Seepage failure in the form of piping can strongly influence the stability of block-in-matrix-soils (bimsoils), as well as weaken and affect the performance of bimsoil structures. The multiple-factor evaluation and optimization play a crucial role in controlling the seepage failure in bimsoil. The aim of this study is to improve the ability to control the piping seepage failure in bimsoil. In this work, the response surface method (RSM) was employed to evaluate and optimize the multiple piping parameters to maximize the critical hydraulic gradient (CHG), in combination with experimental modeling based on a self-developed servo-controlled flow-erosion-stress coupled testing system. All of the studied specimens with rock block percentage (RBP) of 30%, 50%, and 70% were produced as a cylindrical shape (50 mm diameter and 100 mm height) by compaction tests. Four uncertain parameters, such as RBP, soil matrix density, confining pressure, and block morphology were used to fit an optimal response of the CHG. The sensitivity analysis reveals the influential order of the studied factors to CHG. It is found that RBP is the most sensitive factor, the CHG decreases with the increase of RBP, and CHG increases with the increase of confining pressure, soil matrix density, and block angularity.

Experimental study on distributed optical fiber-based approach monitoring saturation line in levee engineering

Seepage is one of key factors which affect the levee engineering safety. The seepage danger without timely detection and rapid response may likely lead to severe accidents such as seepage failure, slope instability, and even levee break. More than 90 percent of levee break events are caused by the seepage. It is very important for seepage behavior identification to determine accurately saturation line in levee engineering. Furthermore, the location of saturation line has a major impact on slope stability in levee engineering. Considering the structure characteristics and service condition of levee engineering, the distributed optical fiber sensing technology is introduced to implement the real-time observation of saturation line in levee engineering. The distributed optical fiber temperature sensor system (DTS)-based monitoring principle of saturation line in levee engineering is investigated. An experimental platform, which consists of DTS, heating system, water-supply system, auxiliary analysis system and levee model, is designed and constructed. The monitoring experiment of saturation line in levee model is implemented on this platform. According to the experimental results, the numerical relationship between moisture content and thermal conductivity in porous medium is identified. A line heat source-based distributed optical fiber method obtaining the thermal conductivity in porous medium is developed. A DTS-based approach is proposed to monitor the saturation line in levee engineering. The embedment pattern of optical fiber for monitoring saturation line is presented.

Multiple failure modes-based practical calculation model on comprehensive risk for levee structure

Risk calculation of levee in the complex environment has significant theoretical values and practical meanings. As there still exists problems in present risk calculation models, a simple and efficient calculation model of the comprehensive levee risk is needed to be established. This paper studies the comprehensive risk calculation model of levee with multiple failure modes based on the analysis of levee instability and seepage failure. Firstly, coupling calculation of the seepage field and stress field is made using the finite element method, and safety factor of levee slope and critical failure hydraulic gradient of levee foundation are determined according to the strength reduction and piping theory. Then, particle swarm optimization is applied to conduct a comparative study on potential impact factors of levee stability and seepage, thus to determine explicit expressions for instability of levee body and seepage failure of levee foundation. Finally, Monte Carlo method is introduced to simulate the levee structure stochastically and calculated the comprehensive levee risk. Calculation results of the example show that the risk calculation method proposed in this paper has higher computational efficiency and can provide references for the decision of levee reinforcement.

Seepage Piping Evolution Characteristics in Bimsoils -An Experimental Study

Piping is a kind of seepage failure mode that commonly occurs under the influence of seepage force in soil materials. Many studies have been done to study the characteristics of piping for soil materials, however, the initiation and development mechanism of piping in bimsoils is poorly understood. In this work, an experimental program was set for investigating the evolution process of piping, in a self-developed servo-controlled flow–erosion–stress coupled testing system. All the studied samples with rock block percentage (RBP) of 30%, 40%, 50%, 60%, and 70%, were produced as a cylindrical shape(50 mm diameter and 100 mm height) by compaction tests with different hammer strike counts to roughly insure the same void ratio. The results show that the amount of rock blocks in bimsoil samples significantly influenced the initiation and development of piping. Furthermore, the stress state has a crucial influence on the critical hydraulic gradient, seepage velocity, permeability, erosion, and migration of soil particles. Moreover, interactions among soil matrix, rock blocks, and rock–soil interfaces control the seepage stability of the bimsoil sample.

Particle Flow Code Method-Based Meso-scale Identification for Seepage Failure of Soil Levee

The long-term action of internal and external factors leads constantly to seepage failures of soil levee engineering such as soil flow failure and piping failure. It is very disadvantageous to the service safety of levee engineering. Most of disastrous accidents are induced directly or indirectly by seepage. It has been known that the water–soil interaction with particle migration determines the occurrence and development of seepage failure. In this paper, a particle flow code (PFC)-based approach is introduced to implement the numerical simulation for seepage behavior in soil levee and investigate the meso-scale seepage failures. Firstly, according to the granular properties and particle migration characteristics of soil levee, an implementation process is presented to construct the meso-scale soil particle model and analyze the levee failure. Then, considering the coupling action of soil and water, a numerical method combining PFC with computation fluid dynamics is developed to simulate the seepage failure of soil levee. The corresponding criteria on seepage failures of soil levee are given. Lastly, one actual levee engineering is taken as an example. The movements of soil and water in the soil flow and piping processes are investigated with meso-scale soil particle model of selected levee. The meso-scale mechanism of seepage failures is analyzed, and the seepage stability is evaluated. It is indicated that the proposed PFC-based approach can fulfill the real-time observation for the movement status of soil particles and water during seepage failure of soil levee. The seepage stability identification with the introduced meso-scale criteria shows good agreement with the experimental result.

Study on Mechanism of Concentrated Leakage Accesses Formed Due to Current Scouring in Weak Structure Plane

Weak structure plane is high in plasticity and low in strength, which provides the necessary condition for deforming rock mass and forming concentrated leakage accesses and seepage failure under the effect of groundwater in the long term. Seepage stability of weak structure plane has always been an important engineering geological and hydrogeological problem of water conservancy and hydropower project. At present, their understanding of the mechanism of seepage failure still exist many unsolved problems. Since they rarely studied the concentrated leakage accesses formed due to the weak structure of bedrock before, this article will discuss seepage and deformation problems in weak structure plane. It mainly discusses the current scouring development mechanism of weak structure plane and critical flow velocity and corresponding fissure width when soil particles start at different positions. Finally, it introduces living examples like concentrated leakage accesses formed due to weak structure plane, which means weak structure planes of bedrock can form concentrated leakage accesses under appropriate geological conditions.

Numerical simulation of backward erosion piping in heterogeneous fields

AbstractBackward erosion piping (BEP) is one of the major causes of seepage failures in levees. Seepage fields dictate the BEP behaviors and are influenced by the heterogeneity of soil properties. To investigate the effects of the heterogeneity on the seepage failures, we develop a numerical algorithm and conduct simulations to study BEP progressions in geologic media with spatially stochastic parameters. Specifically, the void ratio e, the hydraulic conductivity k, and the ratio of the particle contents r of the media are represented as the stochastic variables. They are characterized by means and variances, the spatial correlation structures, and the cross correlation between variables. Results of the simulations reveal that the heterogeneity accelerates the development of preferential flow paths, which profoundly increase the likelihood of seepage failures. To account for unknown heterogeneity, we define the probability of the seepage instability (PI) to evaluate the failure potential of a given site. Using Monte‐Carlo simulation (MCS), we demonstrate that the PI value is significantly influenced by the mean and the variance of ln k and its spatial correlation scales. But the other parameters, such as means and variances of e and r, and their cross correlation, have minor impacts. Based on PI analyses, we introduce a risk rating system to classify the field into different regions according to risk levels. This rating system is useful for seepage failures prevention and assists decision making when BEP occurs.

A study to determine the location of perforated drainpipe in a levee for controlling the seepage line

Levees are facilities constructed along river to protect floodplains against flooding. However, levee failures are also possible if seepage reaches landside surface of the levee. The seepage on the surface of the landside slope can be prevented by efficient design of levee drainage systems. This study aims to show the seepage control potential on levees by installation of perforated drainpipes, which was verified through hydraulic experiments. Scenarios were performed with four different water stages at riverside. For each scenario, the piezometric heads located at the bottom of the experimental levee were measured. The results of the hydraulic experiments showed that the precise positioning of perforated drainpipes is vital since it greatly affects the amount of seepage in the levee. The SEEP/W model that was calibrated and verified with the experiment results was used to suggest appropriate installation location range of the perforated drainpipe. From the numerical simulation, as the central location of perforated drainpipe is closer to landside levee toe horizontally and to foundation surface vertically, the safety of levee was increased from the seepage failure.

Model tests on installation and extraction of suction caissons in dense sand

ABSTRACTA series of model tests were performed on steel- and Perspex-made suction caissons in saturated dense marine sand to explore installation and extraction behaviors. The extractions of the caisson were conducted by applying monotonic loading or by pumping water into the caisson. Responses of suction caissons to pullout rates, aspect ratios, and extraction manners were examined. Test results show that a cone-shaped subsidence region occurs around the suction caisson during the suction-assisted installation. The pullout bearing capacity of the suction caisson in sand is dominated by the loading rate and the loading manner. For the suction caisson subjected to monotonic loading, the maximum bearing capacity is reached at the pullout rate of about 20.0 mm/s. The mobilized vertical displacement corresponding to the pullout capacity increases with increasing the pullout rate. The passive suction beneath the suction caisson lid reaches the maximum value when the pullout bearing capacity is mobilized. In addition, during the suction caisson extracted by pumping water into the caisson, the maximum pore water pressure in the caisson is obtained under the displacement of approximately 0.04 times the caisson diameter. The absolute values of the maximum pore water pressures for the suction caissons approximately equal those of the maximum vertical resistances at the monotonic pullout rate of 5 mm/s. When the vertical displacements of the suction caissons with the aspect ratio of 1.0 and 2.0 reach 0.92 and 1.77 times the caisson diameter, respectively, the seepage failure occurs around the caissons. Using a scaling method, the test results can be used to predict the time length required for the prototype suction caisson to be extracted from the seabed.

Safety Factors against Seepage Failure of Soil within a Cofferdam and Effect of Upstream Residual Soil

Safety Factors against Seepage Failure of Soil within a Cofferdam and Effect of Upstream Residual Soil

Effects of Soil Improvement on Stability against Seepage Failure of 2D Soil within a Cofferdam

Effects of Soil Improvement on Stability against Seepage Failure of 2D Soil within a Cofferdam

Numerical analysis on seepage failures of dike due to water level-up and rainfall using a water–soil-coupled smoothed particle hydrodynamics model

For seepage failures of dike due to water level-up and rainfall, surface infiltration and strength change induced by suction reduction are important factors; thus, numerical analysis should consider the coupling of water and soil, as well as the effect of saturation to obtain more precise failure mechanism. Based on the advanced smoothed particle hydrodynamics (SPH) method, this work proposed a two-phase-coupled SPH model in coordination with a novel constitutive model for unsaturated soils. Then, a triaxial compression test is simulated to check the applicability of the SPH method on the soil phase. After that, the failure test of a dike due to water level-up is discretized and simulated, from which the seepage process, the distribution of maximum shear strain, the slip surface, and pore water pressure are obtained. The two-phase-coupled SPH model is also applied to a slope failure test of heavy rainfall, and the results are compared to the model test. Finally, a dike failure test due to rainfall is analyzed using the proposed SPH model to reproduce the surface infiltration and suction reduction. The proposed SPH model provides several insights of seepage failures and can be a helpful tool for the analysis of dike failures induced by water level-up and rainfall.