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This study scrutinizes the dam behavior during different rates of water level fluctuations via centrifuge model tests and verifies the results by numerical analyses. LVDTs and pore water pressure gauges were installed to scrutinize the settlement and pore water pressure behavior during different rates of water level fluctuation. The centrifuge model test results suggest that the increased rate of water level fluctuation increases the risk of dam failure as drastic variations in pore water pressure and differential settlement were observed. The differential settlement in the upstream and downstream sides of the dam due to water level fluctuation increases the risk of cracking in the dam crest. Also, the dam stability was evaluated by comparing and analyzing the pore pressure and deformation distribution values obtained from the centrifuge model tests with numerical analysis results. Soil-void fluid coupled analyses were performed in the steady and unsteady seepage flow conditions. The analysis results manifest that the increased rate of fluctuation in water level becomes a factor for a rapid increase in the displacement and pore pressure of the dam body, resulting in a reduction in the dam stability. Thus, real-time monitoring of the displacement and pore water pressure during rapid fluctuations in water level, such as heavy rain, is required to ensure dam stability.

Embankment dams are one of the most important geotechnical structures that their failures can lead to disastrous damages. One of the main causes of dam failure is its slope instability. Slope Stability analysis has traditionally been performed using the deterministic approaches. These approaches show the safety of slope only with factor of safety that this factor cannot take into account the uncertainty in soil parameters. Hence, to investigate the impact of uncertainties in soil parameters on slope stability, probabilistic analysis by Monte Carlo Simulation (MCS) method was used in this research. MCS method is a computational algorithm that uses random sampling to compute the results. This method studies the probability of slope failure using the distribution function of soil parameters. Stability analysis of upstream and downstream slopes of Alborz dam in all different design modes was done in both static and quasi-static condition. Probability of failure and reliability index were investigated for critical failure surfaces. Based on the reliability index obtained in different conditions, it can be said that the downstream and upstream slope of the Alborz dam is stable. The results show that although the factor of safety for upstream slope in the state of earthquake loading was enough, but the results derived from probabilistic analysis indicate that the factor of safety is not adequate. Also the upstream slope of the Alborz dam is unstable under high and uncontrolled explosions conditions in steady seepage from different levels under quasi-static terms.

This paper aims to systematically study kinematic characteristics of Wenjiagou rock avalanche triggered by the M8.0 2008 Wenchuan earthquake and one of subsequent debris flows that occurred on August 13, 2010 (8.13 debris flow), using a numerical approach. The kinematic characteristics of the rock avalanche are back-calculated using an energy-based runout model. The erosion process of the subsequent rainfall-induced debris flow is analyzed using a progressive scouring entrainment model incorporated in the energy-based runout model. The results indicate that Wenjiagou rock avalanche traveled farther than most other rock avalanches with a maximum velocity of approximately 73 m/s detected at about 1700 m away from the source zone. The erosion of the 8.13 debris flow mainly occurred right after the dam failure which contributes to more than 97% of the total eroded volume. Besides, four different scenarios, including no blockage of the runoff (scenario I), no dam failure (scenario II), dam failure at the end of precipitation (scenario III), and no erodible material (scenario IV), are supposed to study the effect of the failure of a check dam on the erosion characteristics of the debris flow. The results reveal that the blockage of the channel without failure could reduce 86% of the total volume and the failure of check dams is the main reason for the destructive consequence of the 8.13 debris flow. This paper proposes an approach to explore kinematic characteristics of a rock avalanche and erosion process of the subsequent rainfall-induced debris flows and also innovatively provides a method to indirectly assess mitigation strategies that can be used for the design of mitigation projects.

Concrete gravity dams are generally designed based on the principle that the tension does not occur in any portion of the dam, as concrete is weak in tension. Cracks will occur if concrete is subjected to undesirable tensile stresses. The modeling of crack propagation is of high importance in simulation of dam failure. Koyna concrete gravity dam was chosen for the present study. A seismic study of the dam – reservoir – foundation structure is conducted first by using ANSYS. On the basis of the results obtained, critical zones are identified within which the tensile strength of the concrete exceeds the allowable limits. In these zones cracks have been initiated and are modeled using the Extended Finite Element Method (XFEM). The stress intensity factor (SIF) has been chosen to estimate critical crack length. Further critical crack lengths of each initiated individual cracks are determined to know the structural stability. From the present analysis it was observed that SIF rises with an increase in the length of the crack and it was also observed that the structural failure occurs at the critical crack length of the crack after the fracture toughness of the dam material has been achieved.

f Engineering Sciences Tikrit Journal of Engineering Sciences Hydrodynamic Simulation of Flood Due to Hypothetical Momentary Mosul Dam Failure A B S T R A C T Flood wave simulation due to hypothetical momentary failure of Mosul Dam was carried out by applying the (IBER) hydrodynamic model for the dam storage scenarios (300, 310, 320, 330 and 335) meter above sea level after testing the validity and calibration the model to identify areas that will be inundated between dam site and south Mosul City. Flood waves simulation maps representing borders, water levels and depths were drawn. The inundated areas for between dam site and north Mosul city were determined for the mentioned storage scenarios are (69.14, 114.76, 158.2, 202.5 and 245.6) km2 respectively. The minimum and maximum percentage of the inundated area within Mosul City was also calculated to be (25.6-54.6) % respectively out of the total city area. The maximum flood wave discharges at the failed dam breach and at Mosul City due to the worst dam storage scenario (335) m a.s.l are (781132 and 337138) m3 /s respectively. While the elapsed travel time for maximum discharge reaching Mosul City is (4.18) hours from the initiation of dam failure. The maximum flood depth within Mosul City is (36.7) m occurred after (4.68) hours. Finally, the routing percentage occurred in the maximum flooding discharge (attenuation) between dam site and Mosul City for storage scenario (335) meters is 56.8% while the lag time was (4.03) hours.

On November 5, 2015, roughly 32 million m3 of iron mine tailings were accidentally released in the collapse of Fundao dam in Minas Gerais, Brazil. Totaling about 61% of the impoundment’s contents, the spilled tailings buried the town of Bento Rodrigues, claiming the lives of 19 villagers, and causing major environmental concerns. This study presents a comprehensive static liquefaction triggering analysis performed on the failing section of the dam prior to its collapse, with the goal to determine its susceptibility to liquefaction under its ultimate loading condition. The method of analysis implemented accounts for variations in mode of shear, anisotropic consolidation, and lateral load transfer along the failure surface normally encountered in the field. The instability line and flow liquefaction concepts are used in conjunction with in-situ test data to estimate liquefaction triggering and post-liquefaction undrained shear strengths for loose saturated tailings in the dam’s section. These are subsequently applied in iterative limit equilibrium analyses to obtain the factors of safety for liquefaction triggering and flow failure. After convergence in this process, the failing dam’s section was found to be susceptible to static liquefaction flow failure with a factor of safety of 0.56.

This paper presents the analysis of an earth dam breaching process which incorporates an analytical erosion model into CFX in ANSYS to calculate the rate of erosion in order to capture the kinematic characteristics of dam breach. Based on the water level and the storage capacity of the reservoir on the upstream side of the dam, the discharge of water over the dam can be calculated. The discharge of water is also used to validate the results from the numerical simulations. The height of the experimental dam during the breaching process is calculated using an empirical relationship based on the water level, the discharge rate, and the width of the breach. A particle-scale progressive scouring entrainment model has been incorporated into CFX in ANSYS to calculate the rate of erosion which is used to simulate the development of the breach. When comparing with field observations, the root-mean-square error (RMSE) between the calculated and measured surface velocities is equal to 0.37 m/s, indicating a discrepancy of 16%, and the RMSE of the calculated and measured discharge is equal to 1.13 m3/s, showing an average discrepancy of 19%. Additionally, the numerical results are validated by comparing the calculated and observed water levels in the breach and the calculated and observed width of the top of the breach. The RMSE between the calculated and observed water levels in the upstream of the dam (hup), the water level in the center of the breach (hc + hd), and the width of the top of the breach (BT) are equal to 0.026 m, 0.095 m, and 0.44 m, respectively, which show average discrepancies of 1%, 4%, and 13%, respectively. This dam break experiment is a unique full-scale experiment for the evaluation of numerical and analytical models. This research shows that the erosion model incorporated into CFX is able to capture the main characteristics of the dam failure process. The incorporation of the erosional model into the dam breach analysis can be used to analyze the failure process of barrier dams.

Dams are massive as well as the expensive hydraulic structure which needs proper attention during designing and construction. Besides earthquakes, seepage and slope instability also cause serious damages which may lead to dam failure. Keeping in view the importance of dam construction and stability, there is a need to work out its stability, seepage, and earthquake analysis very accurately. This study assesses the stability of the existing earthfill Latamber dam located in the Karak region of Pakistan. Rigorous finite element analysis (FEM) tools have been utilized to carry out seepage analysis, and dynamic analysis of the Latamber dam while for the slope stability analysis, limit equilibrium method was adopted. The results indicate that the Latamber dam is secure against seepage and piping failure, slope (upstream and downstream) failure, and dynamic loading, observing no liquefaction.

Seepage control in earthfill dams is a major concern during different phases of dam construction and operation. More than 30% of earthfill dam failures occur due to uncontrolled flow in the dam body and foundation. Seepage control measures, designed and installed at suspected sites of uncontrolled flow, thus play a vital role in stabilizing earthfill dams. However, the actual efficiency of seepage control measures often falls short of expected performance due to soil heterogeneity and changes over time. Assessing the performance of seepage control measures based on monitoring and modeling is necessary to avoid abrupt failures in earthfill dams. In this study, we developed a novel method for quantifying the efficiency of seepage control measures in earthfill dams based on combined seepage modeling and monitoring data. We tested the method by applying it to assess the efficiency of seepage control components at the Doroudzan dam, Iran. The results revealed that the overall efficiency of the dam’s seepage control measures (depending on water level in the reservoir) was 51–70%, based on the magnitude of discharged flow. The efficiency of three major seepage control devices, the chimney drain, cutoff wall, and grouting diaphragm in the left abutment, was 76–82%, 68–74%, and 16–19%, respectively.

Construction seams (joints) are adopted in CVC-RCC combined dams in order to reduce the cracking likelihood of the concrete dam and improve the stress distribution in the dam body. However, the arrangement of construction joints inside a concrete dam body degrades the integrity and the ultimate bearing capacity of the concrete dam. The purpose of this study is to investigate the impact of vertical and horizontal construction seams on the bearing capacity of concrete gravity dams by means of finite element method (FEM) using the software complex “CRACK”. Bureyskaya CVC-RCC combined dam is chosen as a case study. The results of the numerical modelling calculations show that passing from the monolithic dam model to the dam model with weak construction seams, the strength characteristics of the dam tend to decrease progressively. The relationship between the overloading factor and the horizontal displacement of the dam crest is studied and analysed. In addition, the relationship between the overloading factor and the coefficient of dam's anti-slide stability is analysed. Moreover, the results show that the ultimate bearing capacity of the dam with weak construction seams is 25% less than that of the monolithic dam.

Dam models were constructed in an indoor flume to test dam breach failure processes to study the seismic signals induced. A simple dam breach model was also proposed to estimate hydrographs for dam breach floods. The test results showed that when the retrogressive erosion due to seepage of the dam continues, it will eventually reach the crest at the upstream side of the dam, and then trigger overtopping and breaching. The seismic signals corresponding to the failure events during retrogressive erosion and overtopping of the dam models were evaluated. Characteristics of the seismic signals were analyzed by Hilbert–Huang transform. Based on the characteristics of the seismic signals, we found four types of mass movement during the retrogressive erosion process, i.e., the single, intermittent, and successive slides and fall. There were precursor seismic signals found caused by cracking immediately before the sliding events of the dam. Furthermore, the dam breach modeling results coincided well with the test results and the field observations. From the test and modeling results, we confirmed that the overtopping discharge and the lateral sliding masses of the dam are also among the important factors influencing the evolution of the breach. In addition, the widening rate of the breach decreases with decreased discharge. The proposed dam breach model can be a useful tool for dam breach warning and hazard reduction.

Hydraulic fracturing is one type of thedam internal erosion leading to concentrated leaks and dam failure. During reservoir impounding,cracks in rock or soil can be initiated and expanded by water pressure. The crack expansionincreasesthe permeability of the soil or rock foundations.A numerical model of crack deformationwas established based on the finite elements methodto study crack characteristics due to hydraulic fracturing pressure.The crack of 1 mm wide and 600 mm long is modeled on 1x1 m of rock mass with the overburden pressure and pore pressure in the crack. The permeability of crack rock with orientations was examined using the equivalent permeability based on crack width due to hydraulic fracturing.The results revealed that crack closure variedwith the elastic modulus of the fillerand the orientation along the crack surface. During reservoir impounding, the crack openingswere related to hydraulic pressure and crack orientation. The model of crack opening indicated that the vertical crack orientation was likely to widen more than the horizontal crack orientation,with crack openings in the range0.003-0.37 mm. The range inrock crack permeability with such crack openings was 5x10-6-1.65 m/s thatagreedwell with the range of field permeability based on the Lugeon test of 1.27x10-4 to 4.96x10-3 m/s. Crack openings due to hydraulic fracturing can be used to predict the rock crack permeability within the hydraulic fracturing area in the dam or its foundation.

A tailing dam accident can cause serious ecological disaster and property loss. Simulation of a tailing dam accident in advance is useful for understanding the tailing flow characteristics and assessing the possible extension of the impact area. In this paper, a three-dimensional (3-D) computational fluid dynamics (CFD) approach was proposed for reasonably and quickly predicting the flow routing and impact area of mud flow from a dam failure across 3-D terrain. The Navier–Stokes equations and the Bingham–Papanastasiou rheology model were employed as the governing equations and the constitutive model, respectively, and solved numerically in the finite volume method (FVM) scheme. The volume-of-fluid (VOF) method was used to track the interface between the tailings and air. The accuracy of the CFD model and the chosen numerical algorithm were validated using an analytical solution of the channel flow problem and a laboratory experiment on the dam-break problem reported in the literature. In each issue, the obtained results were very close to the analytical solutions or experimental values. The proposed approach was then applied to simulate two scenarios of tailing dam failures, one of which was the Feijão tailing dam that failed on 25 January 2019, and the simulated routing coincided well with the in situ investigation. Therefore, the proposed approach does well in simulating the flow phenomenon of tailings after a dam break, and the numerical results can be used for early warning of disasters and emergency response.

During the application of semi-theoretical models to predict peak discharges for breached embankment dams, it is often encountered to be lack of necessary model parameters such as breach height. In order to solve this deficiency and improve the application of the semi-theoretical models for estimating the peak discharge, a mathematical relation is proposed to predict the breach height (Hb) using the water depth above breach bottom (Hw) based on a subset of a composite database (72 historical dam failures). The breach height relation has a high coefficient of determination (R2) when it is applied in the composite database. Using the prediction by the breach height relation as a substitute for the observation, these semi-theoretical models used here produce similar results in terms of both prediction accuracy and uncertainty. Moreover, the dispersion of the flood peak discharge predicted by forecasting models is weakened and the skewness is improved by adopting the breach height relation. Therefore, the application of semi-theoretical models to predict peak discharges can be improved obviously. So, it is found that the breach height using the proposed relation can be a satisfactory substitute when the observed value of Hb is unavailable in a dam failure. Besides, the prediction accuracy will decrease slightly with the increase of database, but the decrease is limited. It should be noted that the proposed breach height relation is only suitable for predicting the height of embankment dam breach in principle.

Slope failure is one of the failure modes of natural dams. Turbid seepage flow is often observed on the downstream slope of a natural dam in the field and indicates the migration of fine particles in the dam. However, the coupling of internal erosion and seepage in natural dams during the impounding process is still unclear. This paper studies fine particles migration in a dam and the slope failure mode in the laboratory. Then, a coupling model was proposed with the fines migration equation, unsaturated seepage flow equation, and local stability analysis equation. In addition to the variation in the permeability coefficient due to fine particles migration, the strength parameters and density of the soil are also changed, which is considered in the model. Based on the conditions of the laboratory tests, simulations were conducted with the coupling model, and some parameters, such as pore pressure, porosity, principle stress, and factor of safety, were analyzed. Meanwhile, the influence of internal erosion and seepage on the stability of dams under different conditions is studied. Furthermore, the influence of some model parameters on the internal structure of the dam and its stability are discussed.

A loess dam is not fully compacted, so there may be a high permeability area in a loess dam. The seepage channel appears inside the dam body, and osmosis damage occurs; these events cause the dam body to be unstable and destroyed. In this paper, the loess dam in the Ansai Area, Yan’an, Shaanxi Province, China, is used as an example monitoring target, and the whole life cycle of the dam is monitored by measuring cracks, liquid level and pore pressure. The timeline regarding multiple instances of damage during the period is used as the basis for subdividing the whole life cycle, and dam damage types are distinguished according to the internal factors and external conditions. By analysing the on-site monitoring data, the dam experienced three obvious types of damage from the onset of monitoring until the dam broke. The triggering factors of the three damage types differ. One factor type is the difference in liquid levels on the two sides of the dam and the seepage channel that is then formed inside the dam. The fine-grained soil in the dam is removed from the seepage channel under the action of hydrodynamic force, the soil at the foot of the dam slope tends to be saturated under the action of osmotic water and the shear strength of the dam slope is reduced. When the soil weight of the upper soil is greater than the shear strength of the soil at the foot of the dam, the first damage type occurs; therefore, it is called “internal erosion damage”. The second type of damage is attributed to the softening of the dam feet under immersion by rainwater, resulting in the dam collapse; it is called “slumping damage”. The third type of damage is due to the infiltration of rainwater through a crack at the top of the dam. The soil at the top of the dam slides along the rainwater intrusion surface, and the width of the dam top is continuously decreased until it completely disappears; therefore, it is called “slippery damage”. On that basis, the loess dam failure modes are proposed due to the difference in hydrodynamic forces on the two sides of the dam and formation of a seepage channel. The fine-grained soil is removed from the seepage channel under the action of hydrodynamic force. The seepage channel is continuously expanded, the soil at the foot of the dam is saturated under the action of seepage water, the soil shear strength is reduced, the dam body becomes unstable and the width of the dam crest is decreased. Under the joint action of infiltration and rainfall, the dam begins the next round of infiltration and erosion and the width of the dam roof continues to decrease. The cycle continues as the width of the dam roof is continuously reduced until overtopping occurs.

This paper presents the results of the numerical analysis of concrete dam structures which are affected by Alkali Silica Reaction (ASR) and subjected to seismic load. In this research a Chemo-Thermo-Mechanical ASR Finite Element numerical code is developed to model and analyse this phenomenon in concrete dams. It considers the effects of variables such as temperature, non-uniform time-dependent material degradation and 3D stress confinement on ASR evolution. The model is validated by modelling the mechanical response of the Fontana gravity dam and comparing the results with the actual data on macro crack appearance and crest displacement. While the structural behaviour of ASR affected structures under monotonic and quasi-static loading has been extensively investigated over the last decades, limited research has addressed the effect of dynamic loads on structures affected by ASR. The combined effect of old and new cracks under dynamic excitation may cause dam failure. The numerical simulations are used to assess and predict the dynamic stability of the Koyna dam considering fluid-structure interaction and are also used to investigate the evolution of damage associated with inception and development of macro cracks in the dam structure due to the combined effect of the synthetic ASR and realistic seismic loading on the dam. The results show that this combined action can significantly change the dynamic behaviour of typical concrete dams due to concrete material degradation and crack development.

Based on model tests of earthen dam breach due to piping failure, a numerical model was developed. A key difference from previous research is the assumption that the cross-section of the pipe channel is an arch, with a rectangle at the bottom and a semicircle at the top before the collapse of the pipe roof, rather than a rectangular or circular cross-section. A shear stress-based erosion rate formula was utilized, and the arched pipe tunnel was assumed to enlarge along its length and width until the overlying soil could no longer maintain stability. Orifice flow and open channel flow were adopted to calculate the breach flow discharge for pressure and free surface flows, respectively. The collapse of the pipe roof was determined by comparing the weight of the overlying soil and the cohesion of the soil on the two sidewalls of the pipe. After the collapse, overtopping failure dominated, and the limit equilibrium method was adopted to estimate the stability of the breach slope when the water flow overtopped. In addition, incomplete and base erosion, as well as one- and two-sided breaches were taken into account. The USDA-ARS-HERU model test P1, with detailed measured data, was used as a case study, and two artificially filled earthen dam failure cases were studied to verify the model. Feedback analysis demonstrates that the proposed model can provide satisfactory results for modeling the breach flow discharge and breach development process. Sensitivity analysis shows that the soil erodibility and initial piping position significantly affect the prediction of the breach flow discharge. Furthermore, a comparison with a well-known numerical model shows that the proposed model performs better than the NWS BREACH model. Keywords: Earthen dam, Piping failure, Overtopping failure, Breach flow, Numerical modeling, Sensitivity analysis

It has been found that the less care is shown while constructing the water retention structures as compared to the amount of care shown in designing for it. This is more often in earthen embankments, where soil properties need to be controlled within the designed limits. The life and stability of embankments are entirely based on the extent to which the design assumptions are achieved in the field. History shows many failures were due to the lack of quality control during construction. In India every year many water storage structures fail, but very few were reported. Till date, only 37 dam failures in India are reported but not appropriately analyzed. This paper is focused on compiling the Indian dam failure list with relevant data which can be used for developing breach parameters equation. The data are collected from Government reports, articles news reports and magazines. This paper is also focused on developing new empirical equations for breach parameters and peak outflow from the dam failure which suits Indian condition. In developing the regression equation for breach depth, average breach width, peak discharge and failure time, different combinations of control variables is highlighted such as the dam height, reservoir capacity, average dam width, dam type, failure mode and dam erodibility. In this study, we incorporate the dam average thickness as another control variable for finding out the breach parameters and found suitable for breach depth calculation. New equations are proposed to compute the peak outflow rate. Further, these equations are compared with other developed regression equations for breach parameters and peak outflows.

Urban expansion results in a large number of land creation projects in the Chinese Loess Plateau. This has strikingly catalyzed hilltops being cut and valleys or low lands being filled by bulldozed mountain. Meanwhile, a large number of check dams were built into the loess gully to store soil and water. This paper studied a case of check dam failure, which resulted in rapid loess mudflow in a bulldozed mountain area. To investigate kinematic characteristics of the mudflow and trigger mechanism of the dam failure, in situ feature measurements, physical property tests, triaxial tests, and groundwater simulations were carried out. The field investigation revealed that moisture content of the loess in the filled area was very high and that the dam failure was most likely due to groundwater seepage. The VS2DI simulation of the check dam showed that its material was over saturated due to moisture migration in it, which significantly affected its stability. The simulation results are consistent with those of the field investigation. Rapid mobility of the mudflow could be attributed to liquefaction of the loess behind the dams. Meanwhile, the movement velocities calculated from by in situ mud splash height are related to the deposited volume of the mobilized materials at corresponding sites.

In recent years, landslide lake disasters occur frequently in southwest mountainous areas of China. Considering the influence of dam size and discharge channel location, three large-scale field tests were carried out in a natural river to study the failure process and mechanism of non-cohesive soil landslide dam, and the process and mechanism of non-cohesive landslide dam breach were analyzed. The results show that the dam size and discharge channel location have a significant influence on the breach mechanism of the landslide dam. The dam failure process can be divided into three stages: the initiation stage, the development stage and the failure stage. When the discharge channel is located close to the bank, the width of the breach is smaller, and the volume of the residual dam body is larger. The more stable the dam body is, the longer the breach process time is, and the smaller the peak discharge is. This study can provide a scientific reference for the emergency disposal and risk assessment of landslide dam.

Dams are one of the most important hydraulic structures. In view of unrecoverable damages occurring after a dam failure, analyzing a dams’ break is necessary. In this study, a dam located in Iran is considered. According to adjacent tourist and entertainment zones, the breaking of the dam could lead to severe problems for the area and bridges downstream of the river. To investigate the issue, a numerical FORTRAN code based on the 2D finite volume Roe-TVD method on a fixed bed is provided to assess the effects of the dam break. Turbulence terms and dry bed conditions were considered in the code. A numerical wave tank (NWT) with a triangular barrier in the bed was numerically modeled and compared with analytical models to verify the capability of the code. Comparing numerical, experimental and analytical results showed that estimated water level and mass conservation in the numerical model is in good agreement with the experimental data and analytical solutions. The 2D approach used has reduced the cost of computing compared to a 3D approach while obtaining accurate results. The code is finally applied to a full-scale dam-break flood. Six KM of the natural river downstream of the dam, including two bridges, B1 and B2, is considered. Flood flow hydrographs and water level variations at bridges B1 and B2 are presented. The results denoted that bridges B1 and B2 will be flooded after 12 and 21 min, respectively, and are at risk of the potential break. Thus, it is necessary to announce and possibly evacuate the resort area alongside the dam in order to decrease losses.

One of the leading causes of dam failure is internal erosion. The impact of erosion of non-plastic fine particles, known as suffusion, on the soil structure and strength has been studied experimentally. However, influences including sample size have not been thoroughly investigated. Internally unstable gap-graded cohesionless soil samples with various sizes were investigated using an erosion-triaxial apparatus. Samples were subjected to downward inflows of different seepage velocities. The results indicated that the potential for clogging increased with an increase in specimen length, leading to less fine particle erosion. Internal erosion changed the mechanical soil behaviour even after the loss of fines equal to 5% of the overall sample volume. Eroded specimens with similar intergranular void ratios showed similar undrained post-erosion behaviour. However, the magnitude of the post-erosion initial undrained peak shear strength is a function of coarse particle interlocking, residual fine content, and equivalent intergranular contact index. It was also found that the steady state line remained unchanged after erosion of fine particles and the mobilized friction angle at the steady state line is independent of the residual fine content.

Artificial dams are one of the most common hydraulic structures for mitigating debris flow disasters in alpine valley regions. However, performance alteration and failure after successive debris flows can lead to dam failure, releasing large amounts of materials within a very short time; moreover, the contribution of artificial dam failures to debris flows is poorly understood. This study quantitatively analyzed the artificial dam failure effects based on the numerical simulations of the Zhouqu '8.8' debris flow, with three scenarios: all nine dams failed (S1); no dams were ever built (S2); all nine dams remained intact (S3). The results showed that artificial dam failures had a significant amplifying effect on the magnitude of a debris flow. The maximum velocity and flow depth decreased by 20% and 11.2% if all the dams did not collapse; comparison of S1 and S2 showed that discharge and velocity at the front of the debris flow increased by 54.6% and 89%, the bulk density and yield stress increased by 3.3% and 5.7%, due to artificial dam failures. This could increase the destructive capacity of a debris flow and the possibility of a river blockage. A single artificial dam failure could locally amplify the magnitude of debris flow. Overall, on the catchment scale, the magnitude of a debris flow was dominated by topography and channel geometry, which can reduce the amplification effect of dam failures at locations where the channel was curved. However, where the channel was straight and flat, the flow velocity and discharge increased cumulatively by 3 m/s and 637 m3/s due to cascading failure. In addition, a comprehensive scheme combining ecological and engineering measures to mitigate debris flow disasters is discussed. This quantitative study is important and urgent needed to understand the amplification effect of dam failures and to implement debris flow mitigation in alpine valley regions.

Even though Malaysia has no experience of any dam-related failures, the occurrence of a deadly tragedy on October 2013 at Bertam Valley, Cameron Highlands has been triggered as a warning sign that there could be other possible incident. Dam failure such as overtopping flow event and embankment instability which is caused by high intensity and long duration of rainfall to the catchment area. Therefore the objective of this research is to investigate dam stability by indication of current factor of safety (FOS) for selected dams in Malaysia. Kelau dam is selected for this study. Numerical modelling Geostudio software was used for analyzing of seepage and FOS using SEEP/W and SLOPE/W. Result shows that normal water levels in steady-state conditions has an obvious lower FOS compared to the critical water level in steady state. For this study, FOS for Kelau dam have average of 2 and is consider safe.

The final publication is available at Springer via http://dx.doi.org/10.1007/s10230-021-00751-9. The Aznalcóllar dyke failed and released much of its stored, saturated pyritic tailings after a process of progressive failure in the foundation clay. 1.5 Mm3 of tailings and 5.5 Mm3 of acidic water were rapidly discharged from the pond. The paper reviews the main geotechnical aspects that contributed to the development of a sliding surface under the dyke: its downward construction procedure, the brittle nature of the over-consolidated, high plasticity foundation clay, and the prevalent high pore pressures in the clay. The downward construction method created a “wave” of high stress ratios under the advancing toe of the dyke capable of taking the strength from peak to residual values. The brittleness of the foundation clay is very significant because of its high plasticity and the presence of montmorillonite among its mineralogical constituents. The high pore pressures are a consequence of the high density tailings (3.1 g/cc), the low permeability of the clay, and the consolidation process in a dominant upward direction. Also discussed in the paper are the dynamics of the dam failure (displacement, velocity, and acceleration). The geometry of the dyke, in plan view, and its relationship with the direction and dip of the clay layers explains the position of the failure. This paper summarizes the lessons derived from this case history.

Актуальность. Мониторинг деформаций грунтовых дамб хвостохранилищ - это важный элемент в обеспечении промышленной безопасности. Результатом деформационного мониторинга являются зафиксированные смещения поверхности дамб или отдельных марок деформационной сети. Однако не все фиксируемые смещения являются опасными. В данной работе обосновано разделение фиксируемых смещений на деформации склонов, представляющее опасность прорывов, и оседания вследствие сжатия нижерасположенного массива горных пород, не представляющие опасности. Целью работы является определение характера механического воздействия заполняемого резервуара хвостохранилища на ограждающую дамбу и окружающую земную поверхность на примере одного из хвостохранилищ. Примененный подход в оценке деформирования грунтовых дамб базируется на соотношениях между наблюдаемыми смещениями, характеристиками объекта и интенсивностью складирования отходов. При этом принципиально важно, что нет зависимости между предлагаемой обработкой измерений и методами определения смещений. Методы. Измерение и обработка результатов осуществлялись при помощи геодезических методов - геометрического нивелирования и ГНСС позиционирования. Анализ результатов производился с помощью статистических и геостатистических методов. Результаты и выводы. Установлено, что в течение восьми серий измерений преобладающим типом смещений являются оседания. Анализ измерений показал, что горизонтальные смещения пунктов наблюдательной станции находятся на уровне погрешности измерений. Распределение оседаний марок дамбы хвостохранилища, характер деформирования головной плотины, а также отсутствие значимых горизонтальных смещений позволяют заключить, что тело дамбы находится в устойчивом состоянии, а фиксируемые оседания - проявление деформации естественного массива в основании гидросооружения под нагрузкой веса складируемых хвостов. Relevance. Monitoring of earth-filled tailings dams deformation is an important element of industrial safety. The result of deformation monitoring is the defined displacement of dam surface or individual marks of the deformation network. However, not all displacements are dangerous. In this paper, the author justified the separation of displacements into slope deformations, which is a risk of dam failure, and subsidence due to compression of the underlying rock mass that are not dangerous. The purpose of the research is to assess the mechanical effect of the storing tailings on the surrounding earth-filled dam and the underlying rock mass; determine the prevailing nature of the observed deformation marks displacements - the dam ground layer sliding or subsidence of the earth's surface under the influence of the mass of stored mining waste. Research methods are geostatistical analysis of vertical and horizontal displacements of the deformation network marks. The displacements of the deformation marks were determined using GNSS measurements and leveling. Conclusions. It is established that the predominant type of displacements is subsidence. Horizontal displacements are equal to the level of measurement error. Investigation have shown that the observed displacements are not a result of the sliding of the earth-filled dam's material, but subsidence caused by compression of the rock mass under the influence of the weight of the tailings.

Landslide dam failure may be triggered by heavy rainfall or earthquake and may fail due to seepage or piping because of the asymmetric compaction. Hence, they have the potential to result in serious natural hazards. Rapid assessment of this phenomenon requires the application of investigation and monitoring techniques providing information on the ongoing failure process. To this aim, a downscaled model of a natural dam landslide was reconstructed in a simulation facility (the ‘Landslide Simulator’) located in the Lecco Campus of Politecnico di Milano university, Italy. The failure of the dam was induced by artificial rainfall. A sensor network was setup to record observations during the simulation experiment, including geotechnical, geophysical, and imaging/ranging sensors. This paper focuses on the analysis of deformation measurement and other changes over time, which were observed in the recorded image sequences and 3D point clouds to analyze and predict the failure of the dam. Results showed that water seepage may play a dominant role in the dam failure process, which is anticipated by a sharp increase of strain in the dam body. Furthermore, image processing techniques may help scientists to calibrate numerical models to improve their quality and reliability.

Dam-break flood simulation can evaluate the impact of a dam break, and is significant in conducting risk analyses, creating emergency plans, and mitigating calamities. In this study, the dam-break flood evolution process in the downstream areas of Minzhi Reservoir in Shenzhen, China, was investigated using a two-dimensional shallow-water model. The two-dimensional shallow-water model was utilized for solving two-dimensional shallow water equations for free-surface flow using the finite volume method. A refined grid with an unstructured mesh of triangular cells constrained by building walls was constructed in this model to represent urban structures. The dam-break flood hydrograph and the process of the expansion of the flood under different failure conditions were determined by adopting two breach mechanisms, namely, the instantaneous and gradual dam break mechanisms. The results indicated that the peak flow of the instantaneous dam break was relatively large at the beginning of the dam break. The peak flow in the case of the gradual dam break was comparatively small when seepage failure deformation occurred near the upper part of the dam. The inundation information obtained during the evolution of the dam-break flood, including information regarding the regularity of the flood evolution, distribution of the maximum water depth, and variation of the depth and velocity with time, were also analyzed.

When drawing up a feasibility study of designing estimates for the repair of a bridge across the Kunka River of the M-12 Stryi-Ternopil-Kropyvnytskyi-Znamianka motorway section (via Vinnytsia) due to the proximity of a number of reservoirs formed by obsolete dams with increased pressure and a high probability of damage to the bridge from the formation and passage of a breakthrough wave, the problem of developing measures to ensure security moving through bridge arose. To simulate and analyze the parameters of the breakthrough wave in the bridge area, the available cartographic data with bottom surface marks and the determination of the coastal zone at the level of the maximum supported horizon were processed. The magnitude of the bridge opening was calculated and the total overflow through the bridge was estimated. It allowed making conclusions regarding the structural solutions of the bridge structure. The results of the development of the site calculating model and its use for calculating the costs, velocities and flood zones are presented in the form of initial data. The final values of the flow velocity of the breakthrough wave near the supports, frontal and end slopes of the bridge bulk dam, splash marks, the need to erect protective structures on the pressure slope of the dam were determined using mathematical modeling of the dam failure. Also, recommendations on the necessary layout and structural protective measures of the motorway and bridge were developed.

The present study focuses on the breaching process and failure of barrier dams due to overtopping. In this work, a series of centrifugal model tests is presented to examine the failure mechanisms of landslide dams. Based on the experimental results, failure process and mechanism of barrier dam due to overtopping are analyzed and further verified by simulating the experimental overtopping failure process. The results indicate that the barrier dam will develop during the entire process of overtopping in the width direction, whereas the breach will cease to develop at an early stage in the depth direction because of the large particles that accumulate on the downstream slope. Moreover, headcut erosion can be clearly observed in the first two stages of overtopping, and coarsening on the downstream slope occurs in the last stage of overtopping. Thus, the bottom part of the barrier dam can survive after dam breaching and full dam failure becomes relatively rare for a barrier dam. Furthermore, the remaining breach would be smaller than that of a homogeneous cohesive dam under the same conditions.

In order to study the failure mechanism of barrier dam overtopping, centrifugal model tests of dam failure were conducted in this research. A calculation method of rectangular weir flow in the centrifugal field was derived. The process and mechanism of barrier dam overtopping were intensively analyzed. They were further verified by the breach flow curve and the development curve of the breach top width acquired from model tests. Results showed that the barrier dam breach developed during the entire process of overtopping in the width direction. The development of the barrier dam breach in the depth direction, however, ceased at an earlier time on account of the large particles accumulated in the downstream slope. Moreover, coarsening in the downstream slope could be clearly observed in the last stage of overtopping. Thus, it was concluded that the bottom part of the barrier dam could survive after dam breaching and that a full dam failure is relatively rare for a barrier dam. Furthermore, the size of the remaining breach would be less than that of a homogeneous earth dam under the same conditions.

Background Landslide 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. Result Experiments 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. Conclusion Dam 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.

This article discusses the results of experimental studies of the breakthrough wave in the lower pool of a hydroelectric complex after an emergency partial instantaneous failure of the dam across the width.

Prediction of peak discharge of floods has attracted great attention for researchers and engineers. In present study, nine typical nonlinear mathematical models are established based on database of 40 historical dam failures. The first eight models that were developed with a series of regression analyses are purely empirical, while the last one is a semi-analytical approach that was derived from an analytical solution of dam-break floods in a trapezoidal channel. Water depth above breach invert (Hw), volume of water stored above breach invert (Vw), embankment length (El), and average embankment width (Ew) are used as independent variables to develop empirical formulas of estimating the peak outflow from breached embankment dams. It is indicated from the multiple regression analysis that a function using the former two variables (i.e., Hw and Vw) produce considerably more accurate results than that using latter two variables (i.e., El and Ew). It is shown that the semi-analytical approach works best in terms of both prediction accuracy and uncertainty, and the established empirical models produce considerably reasonable results except the model only using El. Moreover, present models have been compared with other models available in literature for estimating peak discharge.

Measuring the surface velocity and breach outflow discharge is a challenge in earth dam-break experiments. To solve this problem, large-scale particle image velocimetry (LS-PIV), a non-intrusive approach to measuring surface velocities, was applied in earth dam-break experiments. In this paper, two dam-break experiments were conducted in a large flume, and LS-PIV was used to measure the surface flow velocities of the dam breach. The flume was 50 m long, 4 m wide and 2 m high, and an idealized, non-cohesive, homogeneous earthen dam was placed in the middle of the flume. Three pressure sensors were used to measure the water depth over time. In addition, three high-speed digital cameras and two industrial cameras were used to record the dam breach process. The measured velocities were applied to evaluate the breach outflow discharge. Acceptable agreement was obtained between the discharges estimated with the LS-PIV and water level change methods. The surface velocity field was also obtained, and a dam crest cross section was selected to analyze the process of surface velocity change. Moreover, a convenient and simple formula was introduced to rapidly estimate breach discharge at the dam crest cross section. Finally, based on the Manning formula and surface velocity, the shear stress of the breach bottom was computed and discussed. The findings of this paper validate the accuracy and reliability of the LS-PIV technique for dam-break experiments and suggest that it is a reliable and advantageous technology for dam failure experiments.

The disastrous impact of a tailings dam failure is more far-reaching than that of a water retention dam failure. This paper analyzes the movement characteristics of mudflow during a tailings dam failure using physical models based on the Wadugou tailings impoundment. The physical models were built according to the similarity laws to investigate an overtopping dam failure under natural conditions and when additional protective measures were used. Based on the experimental results, the dam breach size, the breach flow discharge, flow velocity, downstream inundated area, and tailings deposition volume are all reduced by preferably protecting and maintaining the tailings dam embankment to mitigate the destructive effects of a potential dam failure. Finally, the time required for safe evacuation for the Wadugou tailings impoundment area is given.

Bolivar Dam, located in eastern Ohio, is an embankment dam constructed by the U.S. Army Corps of Engineers in 1937 as part of the Muskingum River Basin Project for flood control. As a result of seepage concerns observed at the dam during several flood events over the life of the project, seepage reduction measures, including a partial-depth seepage barrier wall through the embankment and a grout curtain in the left abutment, were designed and constructed. These dam safety modifications were constructed between 2014 and 2016. During flood events, Bolivar Dam experiences excessive seepage through the glacial outwash foundation as well as through a network of open joints within the left bedrock abutment. Seepage in the bedrock abutment could erode/scour the dam embankment at the bedrock contact, potentially leading to dam failure. To lower this potential risk of dam failure in the left abutment, a grout curtain was constructed between the new seepage barrier wall and an existing grout curtain across the emergency spillway. The new grout curtain is designed to impede groundwater seepage, resulting in reduced groundwater velocity/energy downstream of the grout curtain, thereby decreasing its potential to scour or transport fine-grained embankment material. The double-line grout curtain is approximately 65 ft (19.8 m) deep and 400 ft (121.9 m) long and was completed in November 2015 as part of a major dam safety modification project. Two thin limestone units encountered during drilling proved to be problematic and posed various challenges during construction. It was common during drilling to lose water circulation within the vicinity of these limestone units, which then required the use of downstaged grouting methods. The majority of the grout volume for the project was placed within these downstaged intervals. This article presents the risk-informed decisions that were made during both design and construction of the grout curtain and includes various lessons that were learned during this process.

In this study, Material Point Method (MPM) is improved to simulate coseismic slope stability and liquefaction-induced embankment failure under earthquake loading. First, by using elastic or elastoplastic models, topographic amplification and different slope failure modes are analyzed considering the effects of slope geometry, soil properties and excitation frequencies etc. The MPM model is then applied to predict a cascading slope failure process, including triggering, shear band formation, runoff and final deposition. Finally, a fully nonlinear bounding surface soil model is implemented in the two-phase soil-water coupled MPM framework to investigate the liquefaction mechanism and associated dam failure using two case histories. The numerical results are generally comparable with the post-failure profiles obtained from field investigation, which highlight the advantage of MPM in handling liquefaction-induced large deformation. The MPM shows great promise to quantitatively assess risk and consequence associated with seismic slope failure and soil liquefaction, thereby, advance the performance-based engineering design and analysis.

Though widespread in disaster-prone areas, debris flow dams have unique characteristics in their formation and failure. An accurate description of their failure is the prerequisite to predict the dam-break floods, although little has been done in this research area. This paper describes the longitudinal evolution processes of a debris flow dam with 15 different grain-size distributions through flume tests, and put forward the formula of the downcutting rate for the whole process of overtopping failure. Results have shown that, according to the longitudinal evolution characteristics of the debris flow dam failure, the breach process can be divided into three stages: the formation of a retrogressive scarp, the erosion of the retrogressive scarp, and its decline stage. When the dam overtops and breaches, the downcutting rate for the whole evolution process can be expressed as E = k v sin(0.85 + θ)3, where E is the erosion rate, v and θ are the flow velocity and the longitudinal slope of the breach respectively, and k is the erosion rate coefficient. The larger the value of the erosion rate coefficient k is, the faster the erosion rate E is. The minimum correlation coefficient R2 between the calculated and the measured erosion rates is 0.73. In addition, the relationship among erosion rate coefficient k, grain-size distribution parameters μ, and Dc is also proposed, and the correlation coefficient R2 reaches 0.965. The results provide an important theoretical basis for the prediction of debris flow dam-break floods, which can facilitate evidence-based decision-making in disaster prevention and mitigation.

A cellular automaton for the study of the progressive failure of rockfill dams caused by overtopping flows is presented. The celebrated Bak, Tang and Wiesenfeld’s model, proposed in 1987 to reproduce sand avalanches on the surface of a sand heap is adapted to a rockfill dam with an impervious central core that is subjected to extreme throughflow caused by overtopping flow or by failure of the watertightness of the core, or the dam foundation. The downstream rockfill shoulder is represented by a set of cells whose states (elevation and submergence) evolve according to a set of fixed transition rules. These rules, which are affected by the instantaneous throughflow, are based on widely used hydraulic and geotechnical approaches to mass sliding and particle dragging mechanisms. The CA model has been validated with laboratory experiments performed on a U-shaped channel. Albeit the apparent simplicity of the underlying formulation, this model not only sheds light on a complex phenomenon but also provides a way for quantifying the overtopping throughflow needed to threaten the central core or upstream face, which can lead to a catastrophic failure.

Landslide dams often fail shortly after the formation, resulting in huge risks to the downstream residents and properties. Fast and accurate forecasting of the breaching process and discharge hydrograph is important for a decision making to mitigate the damages. Morphological data indicate that the longitudinal length of most landslide dams is much larger than their transverse length. Additionally, headward erosion is more intense in landslide dams than manmade dams during the overtopping failure process. However, most existing models neglect this phenomenon. The objective of this study is to build up a dam-break model considering the headward erosion process, assuming that the change rate of downstream slope-angle is consistent with the rate of breach vertical erosion. And a dam-break numerical model to simulate the overtopping failure process of landslide dams considering the headward erosion was developed based on the theories of hydraulics, hydrology, soil mechanics, sediment dynamics, and etc. Nevertheless, the breach final bottom elevation, which can only be measured after the dam failure, is directly applied in currently available dam break models. To overcome this problem and for the prediction purpose of a newly formed landslide dam, we proposed an empirical model to estimate the breach final bottom elevations of high, medium and low erodibility landslide dams based on the statistical analysis of worldwide landslide dam failure cases collected recently. To verify the effectiveness of proposed dam-break numerical model, the ‘11.03′ Baige landslide dam which locates at the border of Tibet Autonomous Region and Sichuan province was selected as a case study. Results of this study show that the relative errors in the simulated peak discharge, time to the peak, and the total flood volume are 1.59%, 3.50% and 0.53%, respectively, which meet the accuracy requirements of hydrological forecasting. The relative error in the prediction of breach final bottom elevation is 4.28%, which indicates that the accuracy of the simulation is satisfactory. Finally, a sensitivity analysis indicates that the downstream slope affects the prediction of the breach and flood hydrograph significantly, and the excavation of diversion channel is an effective measure to reduce the peak discharge of dam overtopping failure.

Dam failure has been the subject of many hydraulic engineering studies due to its complicated physics with many uncertainties involved and the potential to cause many losses of lives and economical losses. A primary source of uncertainties in many dam failure analyses refers to prediction of the reservoir’s outflow hydrograph, which is studied in the present investigation. This paper presents an experimental study on instantaneous dam failure flood under different reservoir’s capacities and lengths in which the side slopes change within a range of 30°–90°. Thus, several outflow hydrographs are calculated and compared. The results reveal the role of the side slopes on dam break flood wave, such that lower side slope creates more catastrophic outflow. The reservoir capacity and length are also recognized to be important factors, such that they do affect peak discharge and time to peak of the outflow hydrograph. Finally, the paper presents two simple relations for peak discharge and maximum water level estimation at any downstream location.

In the strong seismic zone of Western China, many high concrete face rockfill dams (CFRDs) have been built or designed, and some of these high dams are located in the near-fault region. A near-fault earthquake has relatively long velocity and displacement pulse periods, and a dynamic directivity effect could result in dam failure. However, there are few seismic analysis of high CFRDs considering pulse-like effect. Therefore, it is necessary to investigate the dynamic response of high CFRDs in the near-fault area. In this study, 16 ground motions are selected including 8 pulse-like motions with rupture forward directivity effects and 8 non-pulse motions. The rockfill materials are described using a generalized plasticity model, while a plastic damage model that considers stiffness degradation and strain softening is used to simulate the face slabs. Furthermore, the interfaces between the face slabs and cushions are modeled using interface elements that follow a generalized plasticity model to describe the relative sliding between slab and rockfill. The numerical analysis results indicate that although the near-fault pulse-like ground motion has a moderate impact on the dam acceleration, it has a remarkable impact on the residual deformation of dam and concrete slab damage, especially for the dam crest. The seismic response of the dam increases with an increasing ratio of the peak ground velocity to the peak ground acceleration (PGV/PGA). In addition, even with the similar Arias intensity, the residual deformation of the dam under pulse-like records is larger than those under non-pulse ones. The pulse-like ground motion often generates a high input energy which will cause large deformation of concrete face slab in a short period of time. Therefore, when a CFRD is constructed in the vicinity of an earthquake, the effects of the pulse-like ground motion should be investigated to comprehensively evaluate the seismic safety of the dam.