Seepage Failure Research Articles

A new method for dynamically estimating long-term seepage failure frequency for high concrete faced rockfill dams

Failure frequency of a dam varies greatly with reservoir water level and time. It is important but difficult to dynamically estimate failure frequency of high concrete faced rockfill dams (CFRDs) merely based on the probabilistic approach due to limited failure cases of high CFRDs. In this study, a new method is developed for dynamically estimating the long-term revolution of seepage failure frequency of high CFRDs by combining an analogical approach with the Bayesian approach. A simple and precise seepage generalized method and a parameter named defect parameter are introduced to provide the basis of comparison between the dam of interest and the accumulated database of high CFRDs. Using the cumulative probability distribution from the database, the correlation between annual seepage failure frequency and defect parameter is established. A high CFRD case in China with an operation history of slab breakage and reinforcement is selected as an example to illustrate the applicability of the new method. It is verified that the variation tendency of safety level of high CFRD is well simulated through the annual seepage failure frequency calculated by the newly proposed method.

Relationship between seepage water volume and total suspended solids of landslide dam failure caused by seepage: an experimental investigation

BackgroundLandslide dams inevitably demonstrate the potential for catastrophic failure with high-risk damage to life and property at the downstream site. Hence, knowledge of the internal stability of dam materials is a key to predicting the seepage failure of landslide dams. In this study, experiments were conducted to examine the relationship between seepage volume and total suspended solids (TSS) of seepage water based on hydro mechanical constrains. Understanding the relationship between the seepage volume and TSS with hydro-mechanical constraints supports the prediction of the seepage failure of landslide dams at the field level.ResultExperiments were conducted with a mixed sample of silica sands. Seepage water was collected from a flume tank with the facility to measure the hydraulic gradient, vertical displacement, and seepage water volume. Grain size affected the life span of the dam. The seepage volume increased with the increase in the percentage of silica sand S4, whereas TSS increased with the increase in the percentage of silica sand S8. With the increase in the dam height, the dam life decreases for low coeficient of uniformity of the grain size distribution. With the increase in the reservoir size, TSS decreased, and the total seepage volume increased.ConclusionDam failure depends on the particle size, dam geometry, inflow rates, reservoir size, hydraulic gradient, and seepage water volume, and TSS of seepage water. The results indicated that with the increase in fine particles, the life span decreases, and TSS increases. With the increase in the flow rate, the dam life span decreases, and the TSS and seepage volume rate increase.The dam height leads to an increase seepage volume with low TSS, where the life span of the dam also depends on the particle size distribution With the increase in the reservoir size, the seepage water volume decreases with low TSS.

Horizontal seepage failure model and experimental study of damaged sidewalls of seams between geotube dam tubes.

The impact of damaged sidewalls at the joints between tubes on dam structures subjected to horizontal seepage is investigated. First, an experimental scheme is designed to test the mode and critical gradient of seepage failure of the soil in the damaged tubes. The effects of various overburden pressures (0, 5, 10, 20, and 30 kPa), hole radii(0.5, 1.0, 1.5, and 2 cm) and soil specimen properties were studied. The test phenomena and the changes in the pore water pressure were used to determine the seepage failure modes and the critical gradients under different conditions. Combined with the modified Terzaghi soil arching theory, a mathematical model was developed for the critical gradient for soil seepage failure. The model fitting curve was in good agreement with the laboratory test results. The critical gradient is independent of the overburden pressure and weakly dependent on the internal friction angle of the soil. The critical gradient increases with the cohesion. For fixed characteristic soil parameters, the critical gradient decreases at a gradually decreasing rate as the radius of the damaged hole increases.

Simulating the Hydraulic Heave Phenomenon with Multiphase Fluid Flows Using CFD-DEM

In geotechnical engineering, the seepage phenomena, especially regarding the hydraulic heave, is one of the most dangerous failure mechanisms related to infrastructural stability. Hence, a fundamental understanding of this occurrence is important for the design and construction of water-retaining structures. In this study, a computational fluid dynamics (CFD) solver was developed and coupled with discrete element method (DEM) software to simulate the seepage failure process for the three phases of soil, water, and air. Specimens were constructed with two layers of gap-graded particles to give different permeability properties in the vertical direction. More significant heave failure was observed for the sample with higher permeability in the upper layer. Special attention was drawn to the particle-scale observations of the internal structure and drag force to study the erosion mechanism. The soil filled with air bubbles produced a higher drag force in the region below the retaining wall and showed a larger loss of fine particles than the saturated soil, particularly in the initial stages. The results indicate that the impact of air bubbles would accelerate the development of the heave or boiling phenomenon and influence the stability of the system at an early stage.

Cellular automata‐based analysis for seepage failure process of earth‐rock dam

Research on the process and its mechanism of dam failure is a long-term focus in dam engineering field. The reasonable analysis and prediction of dam failure are of great significance to improve the level of dam emergency management and reduce the risk of dam break. A cellular automata (CA)-based approach is introduced to implement the simulation analysis for the process of piping failure and its induced break in earth-rock dam. According to the energy conversation mechanism during the dam body failure, the local effect rule of earth-rock dam failure is presented. Based on the physical and mechanical properties of earth-rock dam, a CA model of earth-rock dam break is built. Some key implementation technologies, which are used to simulate the break process of earth-rock dam, are developed by analyzing the relationship between the generalized energy and the deformation of soil particles. The method simulating the seepage channel formation by the CA model is proposed, and the mechanical criterion on the seepage channel development is given. Lastly, the piping breach of one actual earth-rock dam is taken as an example. Its CA model simulating the process of piping failure is built. The development of breach width, which is induced by the piping failure, is analyzed. The influence of the height of initial seepage channel on the breach width development is estimated.

Numerical Simulation of Seepage and Stability of Tailings Dams: A Case Study in Lixi, China

The purpose of establishing a tailings dam is to safely store tailings to protect the natural environment from damage. Accidents at tailings dams are frequent, however, with serious consequences of not only threats to life and property but also the pollution of the environment. Many tailings dam accidents are caused by seepage failure. In this paper, the object of the case study is the Lixi tailings dam. Three- and two-dimensional finite element models are established. The seepage field of the project under different working conditions is simulated and the position of the phreatic line is obtained. The safety factors under different working conditions are obtained by combining the seepage field with the stable surface. Finally, the influence of different dry and upstream slope ratio on seepage and stability of tailings dam is obtained. The results show that the longer the length of the dry beach, the lower the phreatic line and the greater the safety factor. The higher the upstream slope ratio, the lower the phreatic line and the greater the safety factor.

Analysis of unsteady seepage field and surrounding rock stability of underground cavern excavation

During the cavern excavation, the underground seepage boundaries are constantly changing, and the seepage field is in an unstable state. Meanwhile, most underground caverns are not constructed with grouting curtains and drainage holes during excavation. The caverns are subject to high osmotic pressure, which is prone to water inrush and seepage failure. Based on the Signorini’s type variational inequality, the variable bandwidth iteration method is proposed to effectively simulate the potential overflow boundary in unsteady seepage by loosing restrictions for non-overflow nodes. The advantage of this methods over traditional methods is fast convergence and relatively high accuracy. Subsequently, a simulation method of unsteady seepage field in the cavern excavation process is proposed, and following this we applied the corresponding unsteady seepage load to the surrounding rocks to evaluate the stability of the cavern. The above methods were further applied to the excavation process of Azad hydropower station powerhouse. The results show that during the cavern excavation, the groundwater surface gradually decreases and the flow rate of the cavern generally increases. In addition, although the osmotic load has an adverse effect on the stability of the cavern, the impact is not significant. This research has proofed guiding significance for maintaining stability throughout the underground cavern excavation process.

The variable-mass seepage law of broken porous rock: an experimental study

Induced by tunnel excavation, the particles constantly shift in broken porous rock of faults until failure occurs, which provides channels for water inrush. Therefore, it is essential to investigate the particle migration of broken porous rock. Thus, a visual experimental system of particle migration was developed independently. Further study on the mass loss evolution of broken porous rock induced by seepage failure was performed using physical model tests, and the effect of the grain gradation of broken porous rock was also analyzed. According to the composition and lost characteristics of the samples, the samples were divided into dense-suspension structure and void-skeleton structure. The results indicated that the mass loss of the particles decreased with the increase in the gradation coefficient when the sample had a dense-suspension structure, while there was no significant change in the lost quality with the increase of gradation coefficient when the sample had a void-skeleton structure. Moreover, the time required for water inrush decreased with the increase in the gradation coefficient, which is because the higher the content of the fine particles is, the lower the permeability of the sample. Sample settlement is positively correlated with the lost quality of particles.

The relationship among the premonitory factors of landslide dam failure caused by seepage: an experimental study

BackgroundA landslide dam always has the potential for catastrophic failure with high risk for life, cost and, property damage at the downstream site. The formation of a landslide dam is a natural process; thus, minimizing the risk due to its failure is important. Landslide dam failure can be categorized into three types: seepage failure, overtopping and slope failure. As described by other researchers, the established premonitory factors of landslide dam failure are hydraulic gradients, seepage and turbidity as well as vertical displacement and inflow into the reservoir.MethodologyThis study only considered seepage failure and used flume experiments to understand it. Three groups of samples which represented fine, medium and coarse particle sizes, respectively, were prepared by Silica sand S4, S5, S6 and S8 of different proportion. These samples were used to conduct the flume experiments of failure and not failure case.ResultFor failure cases, it was found that GI samples have a higher hydraulic gradient and that the seepage water takes time to exit the dam body—however, the seepage water has more TSS. GII samples also had a higher hydraulic gradient, while the flow of seepage water was faster than that of the fine sample with a low TSS. For GIII samples, the hydraulic gradient was very low in comparison with the GI and GII samples. The GIII samples had TSS values that were quite a bit higher than those of the GII samples and lower than those of the GI samples. Experiments on GI samples failed at each attempt; however, the GI samples with kaolinite did not fail and had a higher TSS value. For a GII sample of a non-failed case, the hydraulic gradient was lower than for GI samples and the seepage water flow was faster but the vertical displacement was constant and TSS was on a decreasing order. For a GIII sample, the hydraulic gradient became constant after reaching its initial peak value and TSS was on a decreasing order with an initially increasing vertical displacement that would become constant.ConclusionSeepage failure of a landslide dam can be predicted by understanding the nature of its premonitory factors. These factors behave differently in different particle size samples. The TSS trend line may be the initial factor for checking the stability of a dam crest. A landslide dam with an increasing TSS order will fail and a decreasing order may not fail. Based on all experiments, it can be concluded that the hydraulic gradient has three stages: 1) it starts to increase and reaches a peak value; 2) it starts to decrease from the peak value and reaches a minimum; and 3) it starts to increase again where the seepage water begins to come out and the vertical displacement starts to increase. Dam failures always occur when seepage water comes out with an increasing TSS and an increasing vertical displacement. Repeated experiments on samples having more fine particles show that if a landslide dam is formed by fine particles, then there would be a high chance of its failure. In case of a constant hydraulic gradient, the landslide dam would be stable whenever there is an increasing vertical displacement and presence of TSS. Similarly, in case of a constant vertical displacement and a decreasing TSS, a landslide dam would be stable.

Effects of Upward Seepage on the Resuspension of Consolidated Silty Sediments in the Yellow River Delta

Zhang, S.; Jia, Y.; Lu, F.; Zhang, Y.; Zhang, S., and Peng, Z., 2020. Effects of upward seepage on the resuspension of consolidated silty sediments in the Yellow River Delta. Journal of Coastal Research, 36(2), 372–381. Coconut Creek (Florida), ISSN 0749-0208.Strong seepage flows in coastal zones could significantly change seabed properties, even leading to seepage failure. With respect to the effect of seepage flows on sediment resuspension, available literature has presented conflicting results, indicating that the influence appears to vary for different locations. In the present study, a seepage-scouring, annular flume was designed and employed to evaluate the influence of a sequence of seepage gradients on the resuspension of silts derived from the Yellow River Delta. The experimental results indicated that upward seepage slightly increases the suspended sediment concentration (SSC) level by 4.9–11.1% before the occurrence of seepage failure; however, the occurrence of seepage failure dramatically increases the SSC by at least 64% by pumping massive sediments out of the seabed into the overlying water column. Strong seepage flow and the resultant loss of sediments from the internal seabed are potential mechanisms for the formation of numerous collapse depressions in the Yellow River Delta.

Reliability Analysis for Bypass Seepage Stability of Complex Reinforced Earth-Rockfill Dam with High-Order Practical Stochastic Response Surface Method

Practical stochastic response surface method (SRSM) using ordinary high-order polynomials with mixed terms to approximate the true limit state function (LSF) is proposed to analyze the reliability of bypass seepage stability of earth-rockfill dam. Firstly, the orders of random variable are determined with a univariate fitting. Secondly, nonessential variables are excluded to identify possible mixed terms. Thirdly, orthogonal table is used to arrange additional samples, and stepwise regression is conducted to achieve a specific high-order response surface polynomial (RSP). Fourthly, Monte Carlo simulation (MCS) is used to calculate the failure probability, and RSP is updated by arranging several additional samplings around the design point. At last, the Bantou complex reinforced earth-rockfill dam was taken as an example. There are 6 random variables, that is, the upper water level and 5 hydraulic conductivities (HCs). The result shows that a third-order RSP can ensure good precision, and the failure probability of bypass seepage stability is3.680×10−5within an acceptable risk range. The HC of concrete cut-off wall and the HC of rockfill are unimportant random variables. Maximum failure probability at the bank slope has positive correlation with the HC of curtain and the upper water level, negative correlation with the HC of alluvial deposits, and less significance with the HC of filled soil. With the increase of coefficient of variation (Cov) of the HC of curtain, the bypass seepage failure probability increases dramatically. Practical SRSM adopts a nonintrusive form. The reliability analysis and the bypass seepage analysis were conducted separately; therefore, it has a high computational efficiency. Compared with the existing SRSM, the RSP of practical SRSM is simpler and the procedure of the reliability analysis is easier. This paper provides a further evidence for readily application of the high-order practical SRSM to engineering.

Seepage failure by heave in sheeted excavation pits constructed in stratified cohesionless soils

In this study, experimental and numerical investigations are performed to clarify the seepage failure by heave in sheeted excavation pits in stratified cohesionless soils in which a relatively permeable soil layer (kupper) lies above a less permeable soil layer (klower) between excavation base and wall tip. It is shown that the evaluation of base stabilities of excavation pits against seepage failure by using Terzaghi and Peck’s approach leads to considerably lower critical potential differences than those obtained from the model tests. On the other hand, a relatively good agreement is achieved between the results of the model tests and the finite element (FE) analyses. Further investigations are performed by using axisymmetric excavation models with various dimensions and ground conditions, and a comparison between the results obtained from Terzaghi and Peck’s approach and finite element analyses is given.

Design for service life of underground space based on water seepage criterion

Ever increased urbanisation in the world has made the underground space a viable alternative to the expanding city space. Underground space usually operates under the water level whereby the water ingress is one of the most detrimental factors affecting its service life and sustainability. But little or no research has been conducted on design for service life of underground space based on the criterion of water seepage. This paper proposes a rational and practical methodology for design of service life of underground space as represented by its lining structures against water seepage. A stochastic model of water seepage depth in concrete lining is developed. The proposed methodology is verified with numerical method for prediction of the probability of failure due to water seepage. The merit of the proposed methodology is that it allows for the randomness and time variation of design variables and also directly relates to the real time in service of underground space. It is found in the paper that the correlation of water seepage depth between two points in time and the concrete constituent materials can significantly affect the probability of water seepage failure. The significance of the proposed methodology is that it can be used as a design guide for service life of underground space based on various design criteria.

A Simplified Approach to Design Jet-Grouted Bottom Sealing Barriers for Deep Excavations in Deep Aquifers

This paper presents a simplified methodology for the design of jet-grouted bottom sealing barriers (temporary water-tightness structures) for deep excavations that was undertaken in deep aquifers. The bottom sealing barriers are usually required to prevent uplift failure against the water head below. Additionally, jet-grouted bottom sealing barriers are never perfect due to the uncertainties of jet grouting columns at the site, so the design must carefully consider the analysis of seepage. For these reasons, the proposed calculation procedure focuses on two different failure mechanisms (i.e., “instability failure” and “seepage failure”) of massive bottom sealing barriers. Subsequently, the design parameters of the jet-grouted bottom sealing barriers (e.g., depth and thickness) for an excavation case were determined while using the proposed design procedure. The field pumping test results show that the water-tightness performance of bottom-sealing barriers performed at site is good, which ensures that the water level inside the excavation can reach the desired level and the groundwater drawdown outside can be minimized. The leakage flow rate of bottom-sealing barriers is lower than the designed maximum allowable seepage when the water level inside stabilizes at the final period of the pumping test.

Use of Quicksand Condition to Assess the Base Stabilities of Sheeted Excavation Pits Against Seepage Failure in Cohesionless Soils

Commonly, the base stabilities of sheeted excavation pits against seepage failure by heave are evaluated by using Terzaghi’s rectangular-shaped failure plane. However, seepage failures usually occur in the corner areas of polygon-shaped excavation pits, where relatively high hydraulic gradients develop as a result of three-dimensional seepage flows. In this study, it is shown by means of numerical analyses and model tests that quicksand condition that requires no three-dimensional failure body can be used to assess the base stabilities of sheeted excavation pits against seepage failure in cohesionless soils. Thereby, uncertainties with respect to the shapes of three-dimensional failure bodies are eliminated.

Numerical simulation of seepage failure by upward flow considering internal erosion

Numerical simulation of seepage failure by upward flow considering internal erosion

Experimental study on bed pressure around geotextile mattress with sloping plate.

A geotextile mattress with sloping curtain is a newly proposed countermeasure against river and estuarine scour. In previous laboratory experiments, a geotextile mattress with sloping curtain was capable of protecting the bed downstream from scour and stimulating sediment deposition on both sides. However, the seepage scour under its geotextile mattress is inadequately researched at present. In this study, the Geotextile Mattress with Sloping Plate (GMSP) is proposed based on the simplification of the geotextile mattress with sloping curtain with the construction feasibility considered. A series of experiments was conducted to investigate the pressure distribution around the GMSP and the averaged seepage hydraulic gradient beneath its mattress. The results indicate remarkable pressure difference on two sides of the GMSP. The minimum bed pressure appears about 1.3 times the plate height downstream to the GMSP. The averaged seepage hydraulic gradient beneath the mattress increases with the sloping angle increasing from 35° to 60° in general. The averaged hydraulic gradient also ascends as the relative plate height increases, but reduces as the opening ratio increases at opening ratios greater than 0.143. The safety boundary for the averaged hydraulic gradient under the geotextile mattress of the GMSP could get much smaller than the critical hydraulic gradient of piping and can easily be overwhelmed. This phenomenon can mainly be attributed to the discontinuous contact between the mattress and the seabed. A suggestion for the parametric design of the GMSP is to extend the width of the mattress to reduce the risk of seepage failure.

Dual criterion-based dynamic evaluation approach for dike safety

Seepage failure and slope instability in dike engineering are the most common dangerous cases which can easily lead to the break accident. The two dangerous cases have remarkable features such as complex causes, many influencing factors and strong uncertainty. The advantages in the safety factor method and the reliability analysis method are integrated. A dual criterion, which combines the certain index (safety factor) with the uncertain index (reliability), is proposed to evaluate the seepage and stability safety of dike engineering. The dynamic determination approach for the safety status of dike engineering and the corresponding dangerous water level threshold is developed. A representative section of one actual dike engineering is taken as an example. The seepage and stability safety of dike section is analyzed. The more comprehensive and objective evaluation results on service safety status and development trend are obtained. The determined threshold of dangerous water level, which can ensure the service safety of dike engineering, is very helpful to guide the scientific management of dike engineering.

A case study of water inrush incident through fault zone in China and the corresponding treatment measures

In 2010, a water inrush accident through a fault with a high flow rate occurred at Tianzhuang coal mine in Jining, Shandong Province, China, which was subject to the fault excavation. Grouting is an important treatment method before and after water inrush accidents. In this paper, the evolution of this water inrush accident is studied, and the effective treatment method is presented. The obtained results indicate that groundwater from Ordovician limestone aquifer 28.5 m below the floor flowed into the roadway through the fault zone. Results also show that this water inrush through the fault zone can be divided into a flow rate steady increase phase, a rapidly increase phase, a decrease phase, and a steady phase. The first two phases resulted from permeability increase of the fault, which was caused by seepage failure, and water level of the aquifer led to last two phases. Additionally, grouting using the ground borehole successfully controlled this water inrush accident, and it is proven to be a valid method.

Experiment and numerical simulation on seepage failure of sand caused by leakage of underground water pipe

Underground water pipe leakage accident is a serious threat to the city road and people's life safety, the internal mechanism is necessary to carry out related study. In this paper, numerical simulation technology and model test device was used for researching on the effect of different factors on the seepage failure of sand. The research shows that the evolutionary process of sand seepage failure induced by underground water pipe leakage can be divided into three stages: unfluidized stage stable cavity stage and fluidized stage. At the initial stage, the pressure distribution at different height reaches a peak with the increment of water pressure and flow rate. When the water pressure and flow rate is beyond the peak, cavity would occur at leakage hole. Under the action of seepage force, the cavity would dissipate at the surface of soil, and the distribution of fluidized bed pressure would maintain a stable state. Moreover, the smaller the leakage diameter, the greater the critical water pressure is. In a numerical test of a wedge angle of 62 degrees, F (upward drag force) is equal to the W (weight of wedge), which indicates the cavity reaches a force balance. The wedge with an angle of 62 degrees is significant to the sample model used in numerical simulation.