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Stability Charts for Earth Slopes During Rapid Drawdown
Geotechnique
Abstract
Synopsis
Stability charts are presented to facilitate the computation of the factor of safety of earth slopes during rapid drawdown. As the reservoir level is lowered, the factor of safety decreases if it be assumed that no dissipation of pore pressure occurs during drawdown. Pore pressures during drawdown have been estimated by assuming that B is unity and stability calculation for the range of sections and soil parameters commonly encountered in earth dam practice have been carried out using an electronic computer in order to obtain the data given in the charts
Des cartes de stabilité sont présentées pour faciliter le calcul du facteur de sérité des pentes en terre pendant un affaissement rapide. A mesure que le niveau du réservoir baisse, le facteur de sécurité diminue s'il est supposé qu'aucune disparition de la pression interstitielle n'a lieu pendant l'affaissement. L'évaluation de la pression inter-stitielle pendant l'affaissement a ét´ effectu´ en supposant que B est l'unite et les calculs de la stabilité pour la gamme des sections et les parametres relatifs au sol dont l´usaee est habitue1 dans les travaux ayant trait aux barrages en terre ont été exécutés en utilisant une machine á calculer électronique afin d'obtenir les donnés apparaissant sur les cartes.
... Generally, the FS of a dam slope is influenced by both the hydrostatic pressure and the pore water pressure (matrix suction if it is negative) [8,9]. The hydrostatic pressure acting on the surface of the slope contributes to the stability of the slope, which is favorable to dam safety [10,11]. ...
... The Morgenstern-Price method [8] meets the equilibrium requirements of both the force and the moment, and therefore, it is considered to be the strictest LEM. From the equilibrium of moment, a safety factor can be derived as Eq. ...
Water level variations have caused numerous dam slope collapse disasters around the world, illustrating the large influence of water level fluctuations on dam slopes. The required indoor tests were conducted and a numerical model of an actual earth-filled dam was constructed to investigate the influences of the water level fluctuation rate and the hysteresis of the soil–water characteristic curve (SWCC) on the stability of the upstream dam slope. The results revealed that the free surface in the dam body for the desorption SWCC during water level fluctuations was higher than that for the adsorption SWCC, which would be more evident at higher water levels. The safety factor of the upstream dam slope initially decreased and then increased for the most dangerous water level as the water level rose and fell. The water level fluctuation rate mainly influenced the initial section of the safety factor variation curve, while the SWCC hysteresis mainly affected the minimum safety factor of the water level fluctuations. The desorption SWCC is suggested for engineering design. Furthermore, a quick prediction method is proposed to estimate the safety factor of upstream dam slopes with identical structures.
... Currently stability calculation for slopes with cracks are performed with different methods, including limit equilibrium method [7][8][9], numerical simulation way [10][11][12], and limit analysis approach [13][14][15][16]. Among these methods, the limit equilibrium method (LEM) of slices has attracted considerable attention, because of its simplicity and accuracy [7,[17][18][19][20][21][22]. In this method, the ratio of resisting to driving forces on a potential sliding surface is defined as the factor of safety. ...
... Combining Equations (16) to (19), we can get the energy evolution equation of the slope system during progressive failure of the locked section as follows: ...
Progressive failure in rock bridges along pre-existing discontinuities is one of the predominant destruction modes of rock slopes. The monitoring and prediction of the impending progressive failure is of great significance to ensure the stability of the rock structures and the safety of the workers. The deformation and fracture of rocks are complex processes with energy evolution between rocks and the external environment. Regarding the whole slope as a system, an energy evolution equation of rock slope systems during progressive failure was established by an energy method of systemic stability. Then, considering the weakening effect of joints and the locking effect of rock bridges, a method for calculating the safety factor of rock slopes with a locked section was proposed. Finally, the energy evolution equation and the calculation method of safety factor are verified by a case study. The results show that when the energy dissipated in the progressive failure process of rock bridges is less than the energy accumulated by itself, the deformation energy stored in the slope system can make the locked section deform continuously until the damage occurs. The system energy equal to zero can be used as the critical criterion for the dynamic instability of the rock slope with locked section. The accumulated deformation energy in the slope system can promote the development of the cracks in the locked section, and the residual energy in the critical sliding state is finally released in the form of kinetic energy, which is the main reason for the progressive dynamic instability of rock slopes.
... Water saturating the soil is known to generally reduce its shear strength. In non-hydrostatic situations, seepage-induced effects can endanger the safety of previously stable structures, especially in rapid drawdown situations, posing a significant risk to riverside, coastal and near dam slopes [1][2][3]. An important aspect that is often disregarded in most analyses is the spatial variability of the material, which directly impacts the stability of slopes and represents a significant source of uncertainty. ...
Stability analysis of slopes is a fundamental problem of Soil Mechanics. Its main objective consists of evaluating the potential failure of the slope structure under a prescribed loading mode. A major component of the latter refers to the seepage forces induced by pore-pressure gradient, which is known to be responsible of destabilizing effects. This contribution employs a kinematic approach of limit analysis theory to obtain upper-bounds solutions to the stability problem of saturated slopes submitted to rapid water level drawdown. Random fields are used to model the uncertainty surrounding the spatial distribution of soil cohesion, friction angle, and permeability. In the context of effective stress governing the strength capacities of the soil material, it is shown that the seepage forces related to the water flow regime can be considered as external volumetric loads in the assessment of stability. The hydraulic problem governing the water filtration velocity is evaluated by resorting to an analytical variational approach, whose results are validated by comparisons with finite element solutions. The impact of hydraulic-related parameters on stability is first investigated for slopes within a deterministic framework. Subsequently, random fields are considered to take into account the variability related to the spatial distribution of the material properties, which are discretized using the Karhunen-Loève expansion with numerically computed eigenfunctions. The failure probability of slopes is assessed through Monte Carlo simulations. Several analyses have been performed to discuss the influence of the spatial variability of relevant problem parameters.
... The complexity of such problems is the evaluation of the hydrodynamic effect of water and pore pressure during a time-varying process and the exposure to many factors. The development of approaches and methods needed to solve these problems, taking into account pore pressure changes, is addressed in [19][20][21][22][23][24][25]. Studies related to the prediction of changes in seepage conditions, given that seepage boundaries are variable, include numerical methods. ...
This article addresses the reliability and safety of an earth dam in the case of a change in the reservoir water level. The water level must often be reduced to remove water or as a response to an emergency situation in the process of operation of a hydraulic structure. Lower water levels change seepage conditions, such as the surface of depression, values and directions of seepage gradients, seepage rates, and volumetric hydrodynamic loading. Practical hydraulic engineering shows that these changes can have a number of negative consequences. Higher seepage gradients can lead to seepage-triggered deformations in the vicinity of the upstream slope of a structure. Hydrodynamic loads, arising during drawdown, reduce the stability of an upstream slope of a dam and cause its failure. Potential consequences of a drawdown can be evaluated by solving the problem of drawdown seepage for the dam body and base. A numerical solution to this problem is based on the finite element method applied using the PLAXIS 2D software package. Results thus obtained are compared with those obtained using the finite element method in the locally variational formulation. A numerical experiment was conducted to analyze factors affecting the value of the maximum seepage gradient and stability of the earth dam slope. Recommendations were formulated to limit the drawdown parameters and to ensure the safe operation of a structure.
... Evaluating slope stability during water drawdown is expected, as slopes submerged in water tend to experience waterlevel fluctuations. Morgenstern (1963) utilized the limit equilibrium method to investigate changes in the safety factor of soil slopes during rapid drawdown and created safety factor charts for practical use. However, these charts are based on the assumption of 2D saturated soils. ...
The study presents a new hybrid model, called MARS-WOA, which predicts the impact of three-dimensional (3D) and suction-induced effects on soil slope stability. The MARS-WOA model combines the Multivariate Adaptive Regression Spline (MARS) with the Whale Optimization Algorithm (WOA) and applies it to four slope stability datasets. These include 2D and 3D datasets to evaluate the 3D effect in saturated soil slopes and NS (no suction) and WS (with suction) datasets to assess the suction-induced effect in unsaturated soil slopes. The MARS-WOA model demonstrated superior predictive modeling capability and performance compared to two other machine learning models, Support Vector Regression (SVR) and Ensemble Boosting Trees (EBT). This was evidenced by the impressively low Root Mean Squared Error (RMSE ≤ 0.04472) and high R-squared (R² ≥ 0.93) values achieved by the MARS-WOA model across all scenarios. The relative importance analysis indicates that the ratio B/H, representing the 3D effect, moderately influences slope stability design, with a relative importance (RI) value of 15.41%. Similarly, the ratio δαn, which indicates the suction-induced effect, moderately contributes to the slope stability model, with an RI value of 15.73%. These findings suggest that the MARS-WOA model is valuable for soil slope stability analysis and design researchers. The model provides valuable insights into the critical factors affecting slope stability, enabling the creation of more dependable slope designs.
... Although the use of field and laboratory methods have the advantage of investigating influential factors, mechanisms, and establishing empirical equations, they are costly and require a prolonged period to perform and monitor. In lieu of which limit equilibrium methods (LEM), which quantitatively assesses the slope stability conditions in terms of safety factors, have also been developed to assess and analyse slope stability under groundwater effects [20][21][22]. Commercial software based on the LEM, e.g., GeoStudio [23] and Slide [24], represent an important tool to help and guide engineers in solving slope problems. ...
Fluctuating water levels are responsible for many reservoir slope failures. This work develops a novel slope analysis model (Y-slopeW) to evaluate the reservoir slope stability under water–rock coupling effect, based on the combined finite-discrete element method (FDEM). The transient fluid fields under water level fluctuations are first calculated, and then slope stability under water–rock interaction is evaluated in terms of the safety factor using the strength reduction method. Several benchmark tests are proposed to validate the present model. Stability analysis of an ideal slope under reservoir water level fluctuation is analyzed, where the effect of reservoir fluctuation rate and rock permeability coefficient on slope stability are discussed in detail. A practical slope case (Majiagou slope) in the Three Gorges Reservoir area is studied. Results show that the fluctuating reservoir water level plays an important role in slope stability, and a rapid drawdown is the most unfavorable condition to the slope stability. The work detailed herein proposes an efficient tool to better understand the failure mechanism and stability evolution for slopes under water level fluctuation.
... McCullough and Lund determined that a rebound in groundwater pressures can increase the likelihood of slope failure due to a decrease in the effective stress of mine slope walls (McCullough and Lund 2006). Slopes exposed to fluctuations in the waterfront level induce external water loading, changes in pore pressures and erosion, as can be seen in many embankment dam failures (Johansson 2014), and in some cases, slope failure (Jian et al. 2014;Moregenstern 1963). Sources of natural water level fluctuation include tidal water level changes (Li et al. 1997;Raubenheimer et al. 1999) and wind-induced waves (Bakhtyar et al. 2009). ...
Large-scale open-pit mining activities have profound impacts on the surrounding landscape and environment. At the cessation of open-pit mining, the rehabilitation of large void spaces can be achieved by pit-lake filling, where the water body provides a confining pressure on surrounding mine surfaces, reducing both the likelihood of slope failure and the need for ongoing slope maintenance. Although pit-lakes present a range of long-term benefits, the geotechnical performance of mines containing soft soils that are susceptible to creep under increasing loads due to pit-lake filling is seldom considered. From a geotechnical standpoint, creep induced failure is commonly associated with slow, downslope movements, prior to critical slope failure events. In this research, time-dependent slope stability analyses based on creep-sensitive materials are presented for an open-cut mine undergoing pit-lake filling. Numerical simulation provides a mechanism for the assessment of materials exhibiting soft soil creep constitutive behaviour under various loading conditions due to pit-lake filling. The response of mine surfaces is investigated for various filling regimes, highlighting location-dependent deformation rates, pore pressures and slope Factors of Safety for a large Australian open-pit brown coal mine. Results are presented for two separate creep-sensitive materials, identifying the ability to achieve final, stable landforms for a range of long-term pit-lake conditions.
Article Highlights
Time-dependent creep deformation behaviour is investigated for a large Victorian open-pit brown coal mine undergoing pit-lake rehabilitation.
The soft soil creep model is implemented for a large open-pit rehabilitation model, to assess long-lasting creep movements of a specific mine slope.
Mine void filling rates are simulated for a range of rehabilitation scenarios over a 5 to 40 year period, identifying the excess pore water pressure distributions in addition to vertical and horizontal deformations rates.
The long-term behaviour of 8 cross-section profiles is presented, identifying the effect of pit-lake filling for silt and clay interseam materials.
... The researchers showed that even a discharge speed of 10 cm/day can be considered a rapid drawdown in earth-fill dams and can cause failures in the upstream slope. Moregenstern [13] provided stability charts that show the variations in the safety factor with the drawdown level for simple homogeneous slopes. As the reservoir level is lowered, the safety factor decreases provided that no dissipation of the pore pressure occurs during drawdown. ...
The presented article provides a comprehensive study on the stability analysis of earth-fill dams under rapid drawdown and transient flow conditions used to prepare stability analysis charts by conducting coupled finite-element numerical and analytical limit equilibrium procedures. In this regard, the impacts of different rapid drawdown conditions on the safety factor of the Alavian earth-fill dam are determined. The slope stability charts present for both shallow and deep slip surfaces with various permeabilities are verified by ground information obtained with extensive instrumentation on the dam’s site. The results showed that by decreasing the permeability of the core’s material, despite preventing seepage, the instability risk of the upstream slope as a result of rapid drawdown intensifies. Also, as stability charts can be stated, with increasing the slip surface’s depth and decreasing the hydraulic hydration, the reliability decreases, and the sliding surfaces’ sensitivity increases based on the drawdown rates, which have been revealed to be from 0.2 to 0.6, the most critical state for safety factors, showing significant declines.
... Terzaghi [7] 最早通过理论分析的方 法，探讨了库水位缓慢下降和快速下降两种工况下 库岸边坡的稳定性。N. Morgenstern [8] 编制了土质岸 坡稳定性计算表，以预测不同水位下降工况下土质 岸坡的稳定性变化规律。C. Zangerl 等 [9] 的研究表 明，水库滑坡变形速率表现为显著的季节性升降， 与库水位下降有紧密的联系，且在库水位降至最低 时，滑坡运动速率达到峰值。M. ...
... The first group is suitable for impervious materials and neglects the water flow since the dissipation of PWP is much slower than the decrease in the water level. Morgenstern [34] adopted this approach and provided stability charts to estimate the factor of safety during rapid drawdown. Lane and Griffiths [28] developed a chart-based strategy to achieve safe drawdown with 2D Finite Element (FE) undrained analysis. ...
Slope stability in reservoirs depends on time-dependent triggering factors such as fluctuations of the groundwater level and precipitation. This paper assesses the stability of reservoir slopes over time, accounting for the uncertainty of the shear strength and hydraulic parameters. An intelligent surrogate model has been developed to reduce the computational effort. The capability of two machine learning algorithms, namely Support Vector Regression and Extreme Gradient Boosting, is considered to obtain the relationship between geomechanical parameters and the factor of safety. The probability of failure of a hypothetical reservoir slope is estimated employing Monte Carlo simulations for different scenarios of drawdown velocity. A sensitivity analysis is conducted to investigate the influence of the geomechanical parameters, regarded as random variables, on the probability of failure. The results revealed that the coefficient of variation in the effective friction angle and the correlation between effective cohesion and friction angle have the highest impact on the probability of failure. The intelligent surrogate model can predict the factor of safety of reservoir slopes under rapid drawdown with high accuracy and enhanced computational efficiency.
... The stabilizing effect of water on the upstream slope of the embankment is lost, but the pore water pressure may remain high, depending on the permeability of the material during RDD (USBR 2011). Various studies have been carried out to analyze slope failures arising from RDD (Chen and Huang 2011;Alonso and Pinyol 2016;Archard 2016;Duncan, Wright, and Wong 1990;Moregenstern 1963;VandenBerge, Duncan, and Brandon 2013;Pinyol et al. 2011). In most cases, RDD failure occurred after years of operation of embankment structures that had undergone repeated water unloading-reloading cycles; however, none of these previous studies considered the possibility of strain softening of the soil as a result of the cyclic loading of water. ...
Khlong Pa Bon Dam in Thailand underwent the greatest differential drawdown in impounded water in 2014. Unexpected deformation of the upstream slope of the dam was observed on June 27 in the year, after operation for 10 years. The drawdown was hypothesized as the possible cause of the slope deformation. The results from piezometers showed that the upstream slope remained partially undrained after sudden drawdowns. A rapid drawdown analysis confirmed that the movement did not occur due to the sudden drawdown of water in 2014. Back analysis revealed that the shear strength of the embankment slope was near its residual value at the time of failure, which was validated by the movement of inclinometers. Ring shear tests were used to determine the residual shear strength of the failure zone, and the results were validated by the finite element method in ABAQUS. Furthermore, the results of the numerical analysis demonstrated that strain softening was the major cause of the slope movement.
... In the reservoir area, water level fluctuation has significant influence on the stability of bank slopes. Failures of the bank slopes have been frequently reported during the process of water level drawdown (Morgenstern 1963;Song et al. 2018;Miao et al. 2018a, b;Iqbal et al. 2019). The failure mechanism of bank slopes in water drawdown condition has attracted a lot of attention from researchers (e.g., Berilgen 2007;Sica et al. 2019;Siacara et al. 2020). ...
Drawdown of reservoir water level is unfavorable to the bank slope stability due to the large seepage force. In this paper, the siphon drainage method is proposed to decrease the water table as well as the seepage force in the bank slope. The novelty of the siphon drainage used in the bank slope is that it will automatically start working when the drawdown of the reservoir water level occurs. To validate the feasibility of the proposed method, a numerical method which combines GeoStudio and spreadsheet is used to investigate the pore water pressure distribution and evaluate the safety of the bank slope. The “air element method” is adopted in GeoStudio to simulate siphon drains. Chen-Morgenstern generalized equations are modified to consider the hydrostatic force of reservoir water and the suction strength of unsaturated soil. The modified equations are then incorporated in the spreadsheet to calculate the FOS of the bank slopes with siphon drains. The proposed method is illustrated and validated with the Shuping landslide, China. The advantages of the siphon drains are also discussed by comparing with traditional horizontal drains.
... Reservoir water fluctuations and earthquakes constitute the two primary triggers for landslides throughout western China [6,18,19,23,25,30]. The pore water pressure and seepage pressure change gradually with groundwater fluctuations between slopes and reservoirs, thus affecting the stability of the slopes [13,24,28,32]. ...
To investigate the influence of a rapid water drawdown (RWD) on the seismic response characteristics of reservoir rock slopes, numerical dynamic analyses and shaking table tests are conducted on a rock slope containing discontinuities under a RWD using time-frequency analysis from the perspective of spectral and energy propagation characteristics. The results show that a RWD has a magnification effect on the seismic response of a surface slope, which is mainly manifested as the RWD causing the seismic energy of the surface slope to increase significantly. The RWD has a magnification effect on the Fourier spectrum amplitude of the low-order natural frequency band. A time-frequency domain analysis shows that the RWD has an influence on the characteristics of the seismic Hilbert energy spectrum (HES) in the low-frequency band of the surface slope and magnifies the amplitude of the marginal spectrum (MS) in the high-frequency band. In addition, the applicability of the Fourier spectrum, HES and MS in analysing the relationship between the RWD and the slope dynamic response is discussed. An analysis of the seismic HES shows that the RWD has a major impact on the overall dynamic response of the surface slope, while the RWD has a significant impact on the local dynamic response of the surface slope based on the Fourier spectrum and the MS. The influence mechanism of the RWD on the HES and MS of the slope is also discussed. Moreover, the influence of a RWD on the development process of seismic damage to the slope is clarified using an energy-based method.
... The rapid lowering of U/S water level stability can lead to failure, according to different case studies of natural and artificial slopes. Many authors have dealt with the evaluation of slope stability during rapid drawdowns (Morgenstern, 1963;Lane and Griffiths, 2000;Berilgen, 2007;Pinyol, 2009, 2016;Fattah, M. Y., Omran, H. A., and Hassan, M. A., 2015, 2017, Fattah, M. Y., Al-Labban, S. N. Y., and Salman, F. A., 2014 making use of classical stability analysis, slope stability limit approach or numerical solutions. ...
The present work intends to demonstrate the advantages of considering transient flow regime in the stability analysis of the upstream slope for the rapid drawdown situation of a homogeneous earth dam. Upstream slope stability evaluations were carried out, considering pore pressure and suction from transient flow analysis while simulating rapid drawdown of the reservoir. The evaluations comprised different geometries of the upstream slope (from 1V:1.1H to 1V:2.5H) and heights varying from 10 m to 50 m, as well as several low permeability materials (SM, SM-SC, SC, ML, ML-CL, CL, MH and CH). In addition, equations relating the safety factor to such slopes or dam height were adjusted to the analysis data, in order to define the minimum slope for a certain dam height or the maximum height for a given upstream slope. The results have shown that, considering the transient flow condition, including suction, within the slope stability analysis of the rapid drawdown situation, increases the safety factor in relation to the simplified analysis that is usually adopted. This also results in much steeper slopes (for a safety factor of 1.1) than the ones recommended by the U.S. Bureau of Reclamation (USBR), suggesting the importance of performing transient flow analysis for rapid drawdown situations and considering its results instability analysis.
... Figure 1 shows the collapse of the upstream slope of the Carsington Dam (1984), which occurred due to drawdown conditions. The stability of the slope throughout a reservoir drawdown is affected by many factors, such as rates of drawdown, slope inclinations, and soil characteristics of the earth dam materials (Moregenstern, 1963;Desai, 1977;Viratjandr and Michalowski, 2006 Fathani and Legono (2012), and Sudardja (2012) investigated the impact of lowering on embankment dams' stability using lab experiments, while Berilgen (2007) investigated the safety of submerged slopes subject to reduction of water by utilising a flow program to calculate transient seepage and a coupled program to examine deformation and stability. Lane and Griffiths (2000) and Huang and Jia (2009) (2012) studied the impacts of saturated permeability of embankment soil and the emptiness velocity of the reservoir on the stability of the slopes of an earth fill dam exposed to reservoir drawdown with unsaturated soil characteristics. ...
Sudden drawdowns may cause instability in slopes without adequate levels of protection against failure. In this paper, a numerical approach utilising the finite element method (FEM) was employed to examine the seepage and slope stability of a typical earth fill dam. Finite element software (GEOSTUDIO 2012) was used to carry out both steady-state and transient seepage analyses on Khassa Chai Dam in Iraq to study the seepage and upstream slope stability after various upstream drawdown scenarios. To include water levels during evacuation, variable linear water heads with time were identified as boundary states in the transient seepage analysis. The quantity and direction of water flux, existing gradient, and safety factor were calculated for all scenarios. The results revealed that the stability of the slope during drawdown is highly impacted by how fast its pore water pressure dissipates. The results also showed that a minimum F.S. was achieved within 10 hr in the case of a 1-day water drawdown, with the F.S. reduced by 60.66%; this becomes critical when the water level in the basin drops by about 41.67% of its original height.
... Hence, much effort has been devoted to explore the effects of water drawdown on the slope stability. Morgenstern (1963) investigated the soil slope stability during rapid drawdown and presented stability charts based on the limit equilibrium method (LEM). Lane and Griffiths (2000) investigated the stability of slopes with varying submergence levels and developed a chartbased approach using the finite element method (FEM). ...
... Under such circumstances, the slope stability is severely influenced by internal effects such as pore-water pressure and seepage, and external effects such as surface water pressure of the reservoir. Morgenstern (1963) presented a set of stability charts for slopes during rapid drawdown using the slice method. Later, the use of finite-element techniques to assess the slope stability became prevalent, incorporating the effect of pore pressure (Kim et al. 1999(Kim et al. , 2002Chen et al. 2004) and drawdown (Lane and Griffiths 2000;Gioda and Borgonovo 2004;Berilgen 2007;Xu et al. 2009). ...
The rapid drawdown of reservoirs has an unloading effect and can cause slope deformation and failure. The paper investigates the impact of rapid water drawdown on the reservoir bank slopes, using a case study of the Dahua landslide around the reservoir area of the Dahuaqiao Hydropower Station for illustration. Furthermore, a numerical procedure based on the ABAQUS finite element code has been applied to model the coupled hydro-mechanical process. The analysis was undertaken by integration the shear strength reduction technique and transient unsaturated flow modeling. The numerical results show that the rapid water drawdown generates hydrodynamic pressure, which has a crucial impact on the movement behavior of landslides. Landslide deformation is triggered by the “fore-pulling” of rock mass at the slope toe caused by the water level change. Moreover, the calculated factor of safety decreases by about 10.83 percent as the water level drops at an average speed of 2.1 m/day. Based on the numerical simulation results and field monitoring data, the effectiveness of the numerical simulation has been discussed. The calculated values of the cumulative displacement at the three measuring points are 15.07, 9.08 mm and 5.25 mm, respectively. And the corresponding monitoring displacement values are 16.79 mm, 11.06 mm and 5.75 mm, confirming the numerical simulation’s reasonableness. In addition, this study can provide a case reference for preventing the recurrence of similar incidents.
The stability analysis of a saturated soil slope subjected to seepage flow generated by rapid water level drawdown is investigated in this paper by means of the limit analysis kinematic approach. The analysis takes into account the inherent spatial variability of soil strength and permeability properties. Adopting the framework of effective stresses for formulating the strength failure condition of the saturated porous medium, it is shown that the effect of seepage flow can be accounted for in the stability analysis by means of driving body forces computed from the gradient of pore pressure distribution. The hydraulic boundary value problem governing the water filtration velocity is addressed by resorting to a specific analytical variational approach, whose accuracy is assessed through comparison with finite element solutions. The impact of hydraulic‐related parameters on the slope stability is first investigated within a deterministic framework. In the probabilistic stability analysis, soil cohesion, friction angle, and permeability are modeled as random fields that are numerically generated, making use of the Karhenum–Loéve Expansion. The Monte Carlo simulation method has been employed to evaluate the probability density function of the slope stability factor as well as associated overall failure probability. Numerical analyses have been performed with the aim to investigate the impact of some statistical parameters defining the distributions of strength and permeability on the slope stability conditions. Comparison of the simulation results with available numerical predictions pointed out the ability of the proposed stochastic limit analysis approach to accurately address the slope stability problem.
At the Baihetan Hydropower Station, the world’s second largest hydroelectric project, reservoir filling began on April 6, 2021. This resulted in a 165-m rise in the reservoir level, leading to potential landslide instability. In this study, we focus on the Shenjiagou landslide, which was exacerbated by the secondary process of water storage at the Baihetan Hydropower Station. We analyzed the deformational features of the landslide before and after impoundment via various data sources, including optical images, field investigations, borehole data, television surveys, interferometric synthetic aperture radar (InSAR), and monitoring data. A cross-wavelet transform was used to analyze the relationship between the reservoir level time series and landslide displacement. The results indicated that the Shenjiagou landslide was an old translational landslide that exhibited continuous deformation prior to the secondary process of water storage. While the reservoir was being filled, the buoyancy effect on the resistant portion decreased the landslide stability, leading to increased deformation, resulting in surface cracks, bank collapses, road damage, and tilted trees. The cross-wavelet transform revealed an in-phase link between the reservoir level time series and landslide displacement. The methods and findings are valuable for understanding the deformational features and processes of landslides in the presence of significant variations in the reservoir level.
Itaipu Binacional é uma usina hidrelétrica localizada no Rio Paraná, entre Brasil e Paraguai. A barragem que forma o reservatório é composta por estruturas de concreto, enrocamento e terra. Após o enchimento do reservatório, em 1984, o nível do lago se manteve com variação média de 1,5 m, entre as cotas 219 m e 220,5 m, cotas de operação da usina, apenas em poucas ocasiões foi reduzido abaixo da cota 219 m. Entre os anos de 2012 e 2015, devido à crise hídrica no sudeste do país, Itaipu passou a operar de maneira atípica a fim de suprir a queda na produção energética de outras usinas, isso fez com que a variação do nível do reservatório aumentasse para 4 m e permanecesse mais tempo em cotas abaixo do nível normal. Nesse mesmo período a instrumentação apontou um recalque de aproximadamente 5 cm em um trecho da Barragem de Terra da Margem Esquerda (BTME). Esse recalque está abaixo dos limites previstos, porém foi considerado atípico já que, desde a construção, os recalques medidos variam de 1 a 2 cm. Neste trabalho foram realizadas simulações para análises de fluxo, estabilidade e recalques no referido trecho, considerando a variação do nível do reservatório no período atípico. As análises permitiram observar o comportamento das poropressões no maciço compactado e fundação, determinar os fatores de segurança críticos para o período nos taludes de montante e jusante e em que momento eles acontecem. As simulações também mostraram que o recalque detectado pela instrumentação não é atribuído ao adensamento primário devido à variação do nível do reservatório.
Cyclic water level fluctuations have been suspected to be the main cause of many reservoir-induced landslides. Rim slope failures are a constant hurdle in the smooth functioning of the hydro-power projects. Understanding of mechanism involved in reservoir-induced landslides, and the assessment of landslide displacement due to water fluctuation is very complex. There is a need for a quick assessment tool for landslide displacement to ensure safe operation of hydro-power plants. In the present article, effect of cyclic fluctuation in reservoir water level on the stability of rim slope has been studied through physical modeling. A small-scale physical slope model test (PSMT) apparatus was developed indigenously and results of tests conducted on 45° modelled soil slope have been discussed. The modelled slope was made using soil samples collected from an actual rim slope situated between Tehri and Koteshwar Dam (India) and was subjected to 30 cycles of water level fluctuations. Total head values and deformations were recorded after every cycle drawdown. Based on the experimental results, a hypothesis on initiation and propagation of reservoir-induced landslides is suggested. A dimensionless term called Spread Index (Si) is defined as the ratio of Spread (horizontal displacement at toe) and Hydro-Fluctuation Belt of the cyclic fluctuation in the reservoir water level. A novel simple approach is proposed based on the spread index to predict displacement of soil rim slopes subjected to cyclic fluctuations as an extended application of the present study. The proposed solution will be helpful for rough estimation of displacements along rim slopes.
This paper introduces a novel closed‐form equation (surrogate model) for approximating the Morgenstern–Price estimate of the factor of safety of homogeneous dry finite slopes with circular failure surfaces. Unlike typically used methods, the proposed equation does not require the definition of a critical failure surface, splitting the soil mass into slices, or the iterative reduction of soil resistance to the limit state. It can be easily programmed into calculators or computers and accurately determines the minimum factor of safety based on the shear strength parameters and slope geometry—meaning that it is ideally suited for integration into reliability calculations. The equation is determined parametrically for various soil parameters and slope geometry using the Morgenstern–Price method and compares favorably with conventional techniques, such as slope stability charts, limit equilibrium, and strength reduction methods (SRM). From a practical perspective, the proposed equation greatly simplifies the analysis of the slope stability as the creation of a numerical model is not required and is suited to use in the feasibility stage of a project, for example, for large linear infrastructure projects with differing slope geometries or in situations where a quick assessment is desired.
حرکت در شیب ها تحت اثر جریان ها، زمینلغزش ها و واژگونی ها پدیده هایی هستند که در شیب های طبیعی و مصنوعی در صورت به وجود آمدن شرایط مناسب به وقوع می پیوندند. به همین منظور برای مقابله و دفع اثرات نامطلوب ناشی از این پدیده ها باید شیب ها به نحوی مطالعه شوند که در مرحله اول از وقوع چنین پدیده هایی در شیب ها جلوگیری کرد و در مرحله دوم در صورت وقوع این پدیده ها بتوان با پیش بینی مناسب اثرات نامطلوب بعد از ریزش را به حداقل ممکن رساند. برای این کار لازم است شیب ها قبل از اینکه ایجاد شوند، با توجه به اطلاعات زمین شناسی منطقه، ژئومکانیک، شرایط آب و هوایی و اطلاعات هیدروژئولوژی منطقه تحلیل پایداری شوند. در منطقه پاهلت بعد از عریض سازی جاده شیبی ایجاد شده که بعد از گذشت چندین سال مواد تشکیلدهنده شیب در اثر زمین لغزش شروع به حرکت کرده و تقریبا وارد جاده شده اند. در این مقاله این پدیده توسط بررسی عکس های هوایی منطقه، تغییرات شرایط آب و هوایی منطقه و همچنین روش های ریاضی تحلیل پایداری شیب تحلیل شده است. در این مقاله کوشش شده روشی مناسب جهت پایدارسازی این شیب ارائه شود.
Geotechnical structures such as levees, dikes, canals and tailing dams, when subjected to extreme climatic conditions, such as flooding and drawdown, are prone to failure on the upstream and downstream sides due to transient seepage conditions. Therefore, it is imperative to physically replicate such conditions in the actual stress state to understand the performance of these geotechnical structures. Hence, the objective of this paper is to present the performance of an in-flight simulator developed to simulate flooding and drawdown (ISFD) events at enhanced gravities. The working principle, design details, various components of the developed simulator, and calibration at normal (1g) and high gravities are discussed. In the present study, the calibration and performance of the ISFD setup were demonstrated on a model levee section in a 4.5 m radius large beam geotechnical centrifuge facility available at the Indian Institute of Technology Bombay, India. The rate of flooding and drawdown varied from 2.2 m/day to 7 m/day and 1.65 m/day to 4.4 m/day (in prototype dimensions), respectively, obtained with the help of pore-water pressure transducers placed on the upstream and downstream sides of the levee section. A total of three centrifuge model tests were conducted on a scaled-down levee section (with and without internal drainage layers) constructed with silty sand type material to validate the ISFD capabilities. In addition, seepage and slope stability analysis for the centrifuge models was carried out using Plaxis-2D geotechnical software which compared favourably with physically observed tests results.
The drawdown of reservoirs behind dams is an important management strategy (e.g., for removal of aging infrastructure, flushing of sediment), and an opportunity to study erosional processes. A numerical model was developed to examine retrogressive bank erosion across reservoir drawdown scenarios and to evaluate factors controlling the rate, volume, and mechanisms of lateral erosion. Modeled processes included dynamic drawdown of groundwater, sequential slope failures via limit equilibrium analysis, and retrogression considering stress interaction between failing blocks. Field measurements were coupled with Staged, Slow, and Rapid drawdown scenarios. Results highlight the importance of including retrogression as an avenue for lateral erosion, as sequential block failures were found to occur in all scenarios except Slow drawdown. This result indicates that bank stability models without some means of characterizing the evolution of slope failure during drawdown are likely underestimating bank failure rates and volumes. In contrast, dynamic groundwater was not found to be a dominant control for any drawdown scenario. Model results also demonstrate that the drawdown increment is a first‐order control on slope instability via the development of drained or undrained conditions. A majority of failures occurred under undrained conditions. To maximize slope stability, using slow drawdown to activate internal friction under drained conditions is essential. The design of the drawdown rate created a tradeoff between the amount of impact created and when the impact is produced. The study also articulated the need for coupling models and field observations for rapidly changing systems.
Umbrella-shaped anchors, as new stabilizing structures, have been increasingly adopted in engineering practice due to their simple structure, ease of installation, and high load capacity. Reservoir operation, especially during rapid drawdown, affects the long-term stability of reservoir bank slopes as this process affects the stress, seepage and deformation characteristics of the water-level fluctuation (WLF) zone. Thus, the characteristics of the deformation and failure mode of WLF zones reinforced by umbrella-shaped anchors under rapid drawdown conditions are important for the design and construction of anchoring measures. Five slope-anchor scale models based on the Yingpan landslide were established as transparent soil models considering different slope angles and drawdown rates. Displacement, velocity and macroscopic deformation data were obtained using particle image velocimetry (PIV) technology. The results indicated that the deformation process of both reinforced and unreinforced slopes under rapid drawdown conditions could be divided into four phases: initial, shallow sliding, multisliding and stable phases. In the anchor-reinforced models, loss of soil particles occurred when the water level dropped to reach the anchor heads, causing the anchor plates to loosen and slope deformation to accelerate, especially near the lower row of cables. The anchor heads failed first, and progressive slope sliding ensued. Under rapid drawdown conditions, soil liquefaction and subsequent loosening and sliding occurred, generating a far larger zone of accumulation than the zone of collapse. This indicates that soil liquefaction is another important factor of the link between rapid water level drawdown and slope instability causing local collapses. Combining the experimental results and 47 sets of field monitoring data, it could be concluded that the slope stability decreases with increasing slope angle of the WLF zone. This occurs because a higher water level is needed for deformation initiation in the WLF zone in the case of a higher slope angle.
This paper combines transient groundwater analysis with a Random Limit Equilibrium Method (RLEM) to assess the safety of an embankment dam under water level variations. To this end, shear strength parameters, i.e., cohesion and friction angle, are modeled as random variables. The prevailing uncertainties of soil hydraulic characteristics are taken into account by considering multiple deterministic assumptions for the variation of the hydraulic conductivity. An extensive set of random realizations are then generated for the upstream embankment slope under various water levels. Each of the generated realizations is then introduced into the limit equilibrium analysis to determine the non-circular slip surface found using different approximate methods (such as…). The results are then processed to calculate the overall failure probability of the slope. By incorporating time into the limit-state function, the relationship between safety factor, time, and failure probability is established as probability contours to provide a practical tool for slope stability evaluation. A reliability sensitivity analysis is further performed to measure the influence of hydraulic conductivity on the slope failure probability and to find the critical time.
Landslides are closely associated with water level changes (WLCs), especially the macroporous soil slope (MSS). However, the seepage characteristics and instability of macroporous slopes under WLC conditions are scarce. By coupling two Richards' equations, a dual-permeability model was constructed to analyze the effects of WLCs on the seepage and stability of an MSS. Next, the seepage characteristics and local factor of safety (LFS) fields determined via the finite element method were verified by the laboratory and results in the literature. Furthermore, numerical models with or without macropores under the WLC conditions were compared, and the role played by macropores was studied and highlighted via parametric sensitivity analysis. The dual-permeability model could simulate the seepage characteristics of the MSS well under WLC conditions. The results showed that the macropores could substantially accelerate the infiltration rate of water, reducing the LFS of the slope and increasing its instability area by more than 10%. During the rise of water level, increasing the macropore volume fraction (ωf) and the ratio of the permeability coefficient of the macropore domain to the matrix domain (μ) or decreasing the coefficient of water exchange coefficient (αw) would markedly reduce the slope stability. Moreover, when ωf, μ, and αw tended to 0, 1, and infinity, respectively, the seepage characteristics almost resembled those predicted by the single-permeability model. Therefore, when evaluating the slope stability as the reservoir water level rises, the effects of macropores should be considered because it is more in line with the actual situation, and neglecting these effects will overestimate the slope stability, potentially leading to an unconservative design.
Sea level drawdown may lead to the stability decrease and even the failure of coastal clay slopes. Since few attempts have been made to illustrate the impact of sea level drawdown on coastal slope stability considering three-dimensional (3 D) geometry and nonlinear strength, this paper extended 3 D limit analysis approach with nonlinear criterion for slope stability under different sea level drawdown conditions. The least upper bound on stability number was derived by using an optimization procedure. Stability charts were presented and the influences of sea level drawdown on slope stability were illustrated. The drops of sea levels in three cases were found to have different effects on the decreases in slope stability caused by nonlinear parameters. 3 D slope tends to be unstable in the case of rapid drawdown, but it will become stable when the inside water drops after sea level has rapidly decreased. In the case of sea level slow drawdown, slope stability will reduce to minimum and then increase. Effects of sea level drawdowns on slope stability become less significant for slope soils with obvious nonlinear strengths. Certain reinforcement measures can be taken to improve the stability of coastal slopes undergoing sea level rapid drawdown or slow drawdown.
A finite-element upper-bound procedure is presented to assess the stability of a soil slope under reservoir drawdown and rainfall conditions. In order to overcome the scientific challenge of generating a kinematically admissible velocity field, discretizing the problem of interest into finite elements is carried out for this specific purpose, and based on which the upper bound formulation of slope safety factor is derived. The slope stability analysis is transformed to the optimization of a linear programming model under four constraint conditions, by virtue of an interior-point algorithm. Steady-state and transient water flows are discussed. Based on the soil–water characteristic curve (SWCC), matric suction above the phreatic surface is considered so as to provide a reliable assessment for unsaturated slope stability. True cohesion of soils and apparent cohesion stemmed from matric suction are combined to describe the shear strength of unsaturated soils. After validating the robustness of the proposed procedure by limit equilibrium and FEM, it is further applied to evaluate the slope stability under (rapid, general, slow) reservoir drawdown and rainfall conditions.
Three-dimensional upper-bound analysis of rock slopes subjected to seepage flows is a classical problem in geotechnical engineering. However, it is difficult to obtain a rigorous upper-bound solution of the safety factor of slopes when seepage flows are involved. In order to address this problem, the three-dimensional (3D) hydraulic head distributions inside a slope under steady state hydraulic conditions are solved numerically. The obtained numerical hydraulic head distributions are further employed to compute the seepage forces applying to the 3D discretized rotational failure mechanism to assess the stability of a rock slope. The Hoek-Brown yield criterion is employed to characterize the failure of rock masses. The generalized tangential technique is employed to formulate the problem as a classical optimization problem. The particle swarm optimization algorithm combined with the Nelder-Mead simplex algorithm is used to search for the best solutions of slope safety factor. The proposed approach is validated by comparing with 2D plane strain analysis results in the literature. Parametric analysis shows that the safety factor increases as mi or GSI increases, but decreases with the increase of the slope angle β and B/H. It is also found that the 3D influence is significant for B/H smaller than 10, beyond which it becomes negligible. The computational results in the form of design tables are presented for practical use in rock engineering.
The rapid drawdown of reservoir may have a significant impact on the stability of adjacent slopes. In order to avoid potential risks, it is important to calculate the change of slope safety factor prior to the reservoir operation. The finite element method is used to analyze the transient seepage during drawdown, and then the pore water pressures are introduced into the stability computation based on limit equilibrium to obtain the transient safety factor. Computations show that for slopes with a specific geometry, the safety factor ratio depends on the parameters K/(Syv) (where K is the permeability coefficient, v is the drawdown speed, and Sy is the specific yield) and c′/(γHtan ϕ′) (where c′ and ϕ′ are the effective cohesion and friction angle, γ is the soil unit weight, and H is the slope height). By considering a wide range of K/(Syv) and c′/(γHtan ϕ′) values and different slope geometries, the percent reduction in critical safety factor of slope during drawdown relative to that during steady-state seepage is obtained. The drawdown condition that causes a large percent reduction in safety factor is judged as a rapid drawdown, and the opposite is a slow drawdown, which does not affect the slope design. This paper presents a series of charts for engineers and designers to judge rapid and slow drawdown conditions. Before the reservoir operation, the appropriate drawdown speed is selected according to the charts to ensure a slow drawdown for adjacent slope, while in the slope stabilization design, only the rapid drawdown stability analysis needs to be performed.
Reservoir filling and water level variations are important factors that induce slope failures near the reservoir banks. Once a landslide occurs, a tsunami might form which can result in a far greater disaster. This study provides insight and a method for analyzing the disaster chain of a landslide near the reservoir water by taking a slope near the bank of A’lagou reservoir in Xinjiang, China, as an example. The instability mechanisms of the slope are studied based on the field investigation and numerical analysis. The results show that there are two factors that increase the process of slope instability: the rock structure of the slope, which is an important internal factor, and the reservoir filling, especially the rapid drawdown which is an important external factor. Then, a numerical simulation that is based on SPH-DEM coupling method is used to evaluate the landslide tsunami process. The quantitative analysis of the tsunami indicates the initial wave height is about 22 m, the tsunami run-up on the opposite slope is about 44 m high, the maximum overtopping flow is about 1.35×104 m3/s, the maximum velocity is about 9 m/s, the maximum overtopping depth is about 7 m, and the erosive velocity on the downstream slope of the dam is > 20m/s. The results of this study will be useful for preventing and mitigating landslide hazards in reservoirs.
The levee stretch near Dataran Bandar Baharu was a part of the Kerian River Flood Mitigation Project (Phase 3) in Kedah to address frequent flooding problems at the area. It has been facing recurring levee failure despite several repair attempts in the past. As the research area was subjected to water level fluctuations, a numerical model using SEEP/W was analysed to study the effect of drawdown and seepage on the failed levee. Variables considered in this study include soil permeability, groundwater table and time dependent river water levels on the upstream side of the levee. The transient analysis carried out indicated that the levee was susceptible to failure due to the relatively high phreatic line within the levee during drawdown and a seepage face occurrence on the upstream side of the levee.
Infrastructure embankment failures due to flooding have been recorded in many countries. The consequences of flood-induced embankment failures have mainly been limited to infrastructure downtime; however, failures have caused fatalities and include multiple near-miss events. Here we review the types of flood which cause transportation embankment failure and the associated types of failure, processes which cause failure, and the potential for lasting slope weakening after flooding. Four types of flood which cause transport embankment failure are identified; offset head, overtopping, basal floods at slope toes and floods above slopes. Failure is caused by flood-specific processes including rapid drawdown, sliding, scour and internal erosion in addition to the development of destabilisation from effective normal stress decrease and saturation loading. Existing destabilisation modelling tends to focus on single flood events which cause failure, with limited consideration of repeat flooding and the long-term degradation of embankment strength which may occur following rainfall and flooding. Although there is a well-developed understanding of generic landslide development, we suggest that that there has been limited consideration of the destabilising effects caused by dynamic conditions which develop during repeat flooding. Furthermore, while the effects of live traffic loading from high speed trains during flooding have previously been considered and shown to cause destabilisation, such previous work is found to be limited to specific embankment structures which are not representative of the wider rail network and considerable uncertainty exists for older earthworks. We conclude this review by identifying future research priorities to help improve prediction and mitigation of flood-induced embankment instability.
The operation of dams at times requires a sudden decrease in the existing reservoir level. This abrupt change in the upstream water level, known as rapid drawdown, results in the development of unbalanced forces and occasionally causes catastrophic failure of the upstream shell. The drawdown-induced slope stability analyses are typically performed assuming that geomaterials used to build the dam exhibit isotropic permeability; even though, in reality, the geomaterials mostly exhibit anisotropic properties. The principal objective of this study is to comprehend the impact of anisotropic permeability on the drawdown-induced stability analysis of earthen dams and assess the impact of erroneously assuming isotropic permeability properties for numerical analyses. The influence of dam geometry, rate of drawdown, and depth of reservoir water before drawdown were also studied. The results of this research study highlight that the assumption of isotropic permeability inevitably leads to erroneous estimation of deformations incurred during drawdown. The extent of error was observed to increase with an increase in the dam slope and drawdown velocity.
This paper presents a series of computational tools for quick estimation of factors of safety and critical circular failure surface location for embankments. The embankments are assumed to be made of homogeneous frictional-cohesive dry soils, obeying a linear Mohr-Coulomb shear strength criterion. Cases of a firm horizon that the failure surface cannot cut through are considered to exist at the base of the embankment or at great depth. The latter case corresponds to the case of a slope in homogeneous soil. Dimensionless functions defining the factor of safety and position of the critical failure surface are constructed using the Bishop method of slices in the commercial limit equilibrium software SLIDE. Results are implemented in a computer spreadsheet that is made available for free downloading. Formulas for quick evaluation of factors of safety are also presented. The effect of the cohesion and friction angle of the soil and the position of the firm horizon on the resulting factors of safety and depth of the failure surface are discussed. An application example solved with the proposed tools and with the shear strength reduction technique implemented in the commercial software FLAC is presented. Although the tools provided in this paper have been developed for teaching basic slope stability analysis in an undergraduate soil mechanics course, the tools could be useful when performing preliminary estimates of factors of safety of embankments in actual geotechnical design practice.
The paper focuses on the rapid drawdown of earth dams in the hypothesis that a prompt reservoir lowering is
needed soon after a strong earthquake. The interest on such a topic comes from the fact that in Italy and
worldwide there are many large dams placed very close to active faults. In this case, the dam may be asked to
face the earthquake first and the rapid drawdown later to face an emergency state. The problem has been
numerically investigated with reference to a zoned earth dam (Campolattaro Dam) placed in a highly seismic
area of Southern Italy. To solve the overall boundary value problem, encompassing several stages of the dam
lifetime, a 2D finite difference model has been solved through the FLAC2D code, implementing a coupled
transient seepage formulation, which accounts for partial saturation of the soil during the drawdown stage.
Unlike past literature studies, in which the drawdown stage was modelled without accounting for the past
loading history of the dam, in the performed simulation the drawdown stage was placed at the end of a quite real
sequence of events, encompassing the embankment construction, the reservoir impounding, and earthquake
scenarios compatible with the dam site seismic hazard. The performed analyses pointed out that a seismic stage
previously experienced by the dam could further contribute to decreasing dam stability during the drawdown
especially during the first stages of reservoir lowering. In addition, the faster the drawdown, the smaller the dam
safety factor against stability (FOS) with more prominent effects of the initial (pre-drawdown) soil conditions.
In this paper, the effect of soil material parameters including soil specific weight (γ), cohesion (C), angle of internal friction (), and geometric parameter of slope including angle with the horizontal (β) for a constant slope height (H) on factor of safety (Fs) was investigated. Fs was considered in two scenarios: (1) slope with dry condition, and (2) with steady-state saturated condition that comprises water level drawdown circumstances. In addition, the type of slip circle was also investigated. For this purpose, the SLOPE/W software as a subgroup of Geo-Studio software was implemented. Results showed that decreasing of water table level and omitting the hydrostatic pressure on the slope consequently would result in safety factor decrement. Comparison of the plane and circular failure surfaces showed that plane failure method produced good results for near-vertical slopes only. Determination of slip type showed that for state (30° < β < 45°), the three types of failure circles (toe, slope or midpoint circle) may occur. For state (45° < β < 60°), two modes of failure may occur: midpoint circle and toe circle. For state (β > 60°), the mode of failure circle is only toe circle. Linear and nonlinear regression equations were obtained for estimation of slope safety factor.
An improved version of the solid–liquid coupled material point method (MPM) is proposed to simulate ground collapses with fluidization involving transition processes from soil structures to flowing mixture. A water-saturated soil is assumed based on porous media theory, and the physical quantities of the soil and water phases are assigned to two separate sets of particles (material points). The main contribution of this study is the introduction of the fractional step projection method for the time discretization of the momentum equation of the water phase on the assumption of incompressibility. Thanks to this, the proposed solid–liquid coupled MPM is capable of suppressing the pressure oscillations caused by the weak incompressibility of water, which is commonly assumed in the previous studies, and of representing the wide range of behavior of the soil–water mixture at relatively low computational cost. Also, B-spline basis functions are utilized for the spatial discretization to suppress the cell-crossing errors caused by particles crossing element (cell) boundaries. Several numerical tests are conducted to examine the performance of the proposed method that inherits the beneficial features of MPM and demonstrate the capability of reproducing a model experiment of wave collision to sandpile that exhibits the water flow-induced fluidization process of soil involving scouring, transportation and sedimentation.
With the development of economy, more and more buildings are constructed on both sides of rivers. The rapid drawdown of water level may induce the change of groundwater seepage in the river bank, thus affecting the stability of buildings on the bank. In this study, the right bank of Qinhuai river with its ancillary building from the Dinghuai Gate to the Qingliang Gate in Nanjing City is analyzed to reveal the failure mechanism and coupled failure mode of slope and building adjacent to water. The soil-water coupled SPH program considering the interaction between soil and structure has been proposed. Then this model is used to study the evolutionary deformation mechanism of slope and building under the rapid drawdown of water level. The results indicate that the potential slip surface of slope and the asymmetrical distribution of plastic zone in the foundation of building become more obvious under the rapid drawdown of water level. Besides, the differential settlement of building induced by the rapid drawdown causes the building tilt. When the sliding surface of the slope passes the building, the differential settlement will become larger. This study is conducive to reveal the coupled failure mechanism of slope and building and also to provide scientific basis for the prevention of such disasters.
On the character of seepage waters and their effect on the stability of earth embank-ments Disaster Prevention Research Inst The stability of earth dams
- K Akai
- Kyoto
- Japan
- D J Bazett
AKAI, K., 1958. " On the character of seepage waters and their effect on the stability of earth embank-ments. " Bull. No. 24, Disaster Prevention Research Inst., Kyoto, Japan. BAZETT, D. J., 1960. Discussion in Proc. Conf. Pore-Pressure, p. 134, Butterworths, London. BISHOP, A. W., 1952. " The stability of earth dams. "