Stability Safety Factor Research Articles

Influencing Factors, Design Methods, and Buoyancy Reduction Measures for Basement Anti-Flotation Engineering

Basement anti-flotation design is crucial in modern urban construction. An increase in groundwater buoyancy can cause basement structures to uplift, leading to structural instability or even damage. To ensure the stability and safety of underground structures under various hydrogeological conditions, anti-flotation design must comprehensively consider factors such as construction, design, supervision, structure, and hydrology. During construction, improper dewatering measures or unreasonable construction progress may lead to an abnormal rise in groundwater levels, increasing the risk of anti-flotation. Design considerations must include sufficient safety margins, supervision must fully recognize the impact of groundwater, and the structural dead load must be adequate. Anti-flotation stability verification includes both overall and local anti-flotation, involving the calculation of groundwater buoyancy, structural self-weight, and overburden, and selecting appropriate anti-flotation stability safety factors. The assessment and selection of the anti-flotation design water level are also critical. Common anti-flotation measures include adding counterweights, tension-resistant piles, compression and tension-resistant piles, and hydro-pressure reduction methods, while reinforcement and repair methods include epoxy resin grouting and steel plating reinforcement. Through systematic analysis and comprehensive research, scientific basis and technical support are provided for anti-flotation design, enhancing design efficiency and reliability and ensuring the safety and stability of underground spaces. Future research will develop more accurate calculation methods, improve design standards, and explore new anti-flotation technologies and materials.

Influence Analysis of Material Parameter Uncertainties on the Stability Safety Factor of Concrete Gravity Dams: A Probabilistic Method

Anti-sliding stability safety is a critical issue that must be given sufficient and widespread attention during the entire lifecycle of gravity dams. The calculated anti-sliding stability safety factor (ASS-SF) is usually compared with the allowable value required by the standards in the traditional method, which ignores the influence of material parameter uncertainties and leads to unreasonable safety evaluation results. Therefore, the nonlinear functional relationship between the stability safety factor (SF) and the random variable parameters is constructed based on the response surface equations, and the distribution types of SF sequences calculated by the Monte Carlo sampling are determined, then a probabilistic stability evaluation method for concrete gravity dams is proposed. Engineering application shows that the calculated SF obeys the normal distribution; the minimum guaranteed rate of different sliding paths in a gravity dam is 86.66%, and the guaranteed rate for the overload safety factor (OSF) is 36.00%. The results imply that a guaranteed rate for the allowable value of the ASS-SF should be provided when making the stability safety evaluation of the dams, especially the OSF. The outcome of this research will advance the understanding of stability evaluation of concrete dams, and reduce the potential risk of sliding instability of concrete dams.

2D calculation method on global stability safety factor of diaphragm wall slurry trench based on minimum potential energy principle

In order to limit the phenomenon that the global stability safety factor (GSF) of the diaphragm wall slurry trench calculated by the two-dimensional (2D) wedge method is too small, the 2D calculation model on global instability of trench wall is established by assuming the whole critical failure surface (CFS) is a quarter elliptic cylindrical surface, and the determination method of CFS is given too. In view of the successful application of the minimum potential energy principle in slope stability checking calculation and on the basis of the new model established, the 2D minimum potential energy method for calculating the GSF is proposed according to the minimum potential energy principle. The correctness of the 2D calculation model built and the rationality of the 2D calculation method proposed are verified based on ten engineering cases, and the sensitivity of the GSF to various parameters is analyzed on the basis of six design examples. Finally, the new calculation method is applied to the global stability checking calculation of trench wall in practical engineering, and the result shows the new calculation method given in this paper is still conservative, so the result calculated by the new calculation method is advised to be multiplied by a modification factor of 1.67 in practical application.

Slope Stability Analysis of Rockfill Embankments Considering Stress-Dependent Spatial Variability in Friction Angle of Granular Materials

Slope stability is a major safety concern of rockfill embankments. Since rockfills are incohesive materials, only friction angle is considered as a shear strength parameter in the slope stability analysis of rockfill embankments. Recently, it was found that confining pressure can significantly affect the mean value and variance of the friction angle of rockfills. Since the confining pressure spatially varies within a rockfill embankment, the effect of stress-dependent spatial variability in the friction angle of rockfills should be investigated for slope stability evaluation of rockfill embankments. In the framework of the Limit Equilibrium Method (LEM), an approach is proposed for the slope stability analysis of rockfill embankments considering the stress-dependent spatial variability in the friction angle. The safety factors of slope stability are computed with variable values of the friction angle at the bases of slices which are determined by the stress-dependent mean value and variance of the friction angle of rockfills. The slope stability of a homogeneous rockfill embankment is analyzed to illustrate the proposed approach, and a parametric analysis is carried out to explore the effect of variation in the parameters of the variance function of friction angle on slope stability. The illustrative example demonstrates that the stress-dependent spatial variability of friction angle along the slip surface is obvious and is affected by the location of the slip surface and the loading condition. The effects of the stress-dependent spatial variability of the friction angle on the slope stability of high rockfill embankments should be considered.

Dynamic Analysis of Changes in Jambu Riverbed and Banks: Case Study Around Cikuya Bridge

Several cross-sections of the Jambu River, particularly around the Cikuya Bridge, have experienced bank collapse phenomena. This paper interprets the issues related to bank collapse and its impact on the flow capacity of the Jambu River, especially around the Cikuya Bridge. Morphological changes were simulated using a sediment transport model implemented in the Hydrologic Engineering Center's River Analysis System (HEC-RAS) 6.3.1, integrated with the ARS-USDA Bank Stability and Toe Erosion Model (BSTEM). The simulation results indicate that over a period of 10 years, the thalweg elevation (the lowest point of a riverbed) of the Jambu River around the Cikuya Bridge is predicted to experience deposition in 17 cross-sections and erosion in 15 cross-sections. The highest deposition occurs at the cross-section below the Cikuya Bridge, with a thalweg elevation change of 0.59 m. This warrants attention as the storage capacity of the cross-section decreases by 7% from the initial condition. Predictions indicate that bank collapse will occur in 7 cross-sections over the next 10 years. This is attributed to the steep slopes of silt and clay banks, exceeding 45 degrees, and the reduced safety factor of bank stability due to groundwater pressure influenced by river discharge fluctuations and tidal effects reaching the Jambu River. Bank collapse impacts the elevation change of the riverbed and adds load to the sediment transport model from the collapsing cross-sections to the downstream sections. Keywords: Jambu River, Cikuya Bridge, Cilacap, sediment transport, bank stability and toe erosion model

Cut Slope Stability Analysis on Terrain with Slope at Besishahar, Lamjung

Building construction on sloped terrain presents a myriad of challenges that necessitate specialized engineering solutions and careful planning. Though the cut slopes are prone to failure, the increase in urbanization makes construction in such landscape inevitable. The complex topography of this region poses significant scientific and technological challenges, demanding innovative solutions for slope stability analysis and effective mitigation measures. This study incorporates geotechnical and geological study of the Manab Sewa Ashram Site in Besishahar, the cut slope failure analysis using Limit Equilibrium Method and Kinematic failure analysis and suggesting mitigating measure. Three different profiles with critical slopes were selected to represent the overall area for Slope Stability modeling and Kinematic Failure Analysis. The calculation of Factor of Safety for slope stability was done using Slide v.6.020 software under Rocscience package. Since non-engineered cutting of slopes is predominantly existing in the context of Nepal, slope management contributes by majorly focusing on the safety of the structure on or around the slopes.

Three-dimensional calculation method on local slurry wall stability of diaphragm wall trench based on minimum potential energy principle

Because the soft weak soil layer rich in confined groundwater is prone to local instability and failure in the construction of diaphragm wall trenches, in order to check the local slurry wall stability in the construction of diaphragm wall trenches, a new three-dimensional (3D) calculation method on the local stability safety factor (LSF) of slurry walls is proposed based on the minimum potential energy principle. After the new method is applied to two engineering cases, the value of the LSF solved is 0.82 for engineering case 1, and the values of the LSF solved are 0.84 and 1.05 when the phreatic water levels are 2 and 4.5 m, respectively, for engineering case 2. These results are very close to the calculation results in the existing references, so the rationality of the new method is verified. Then the sensitivity of the LSFs obtained from the new method to various parameters has been analyzed and clarified on the basis of ten design examples. Finally, the new method is used to check the local slurry wall stability in the construction of diaphragm wall trenches for a practical project, and the obtained values of the LSF for three concerned weak soil layers are 1.37, 1.19, and 0.82, respectively. These results are in agreement with the actual situation in the construction site. This reveals that both the 3D model established and the 3D calculation method proposed in this paper are suitable for application in practical projects.

The method for determining the safety factor of rock mass stability

The article is devoted to determining the safety factor of rock mass stability by measuring the intensity of electromagnetic pulses in the rock mass that are derived from natural stresses within the massif as well as additional applied loads imposed on it. The rock mass stability is evaluated according to the parameters of the electromagnetic pulses. The distinctiveness of this lies method in the preliminary determination of a frequency range corresponding to a specified depth within the mining massif, facilitating the calculation of the stability reserve coefficient. Explosive events resulting from the detonation of geological formations serve as external influences for instrumental measurements of the mass. The approach entails the measurement of electromagnetic pulses and the time required for these impulses to decay from post-explosion levels to the background electromagnetic pulses level. The stability reserve coefficient of the mass is subsequently determined through an equation accounting for the internal friction angle of the geological formations, the maximum electromagnetic pulses amplitude induced by the explosion, and the duration of decay until the background electromagnetic pulses level is reached.

A modified Prandtl upper-bound solution of basal stability for narrow-deep excavations in undrained clay

In recent years, the construction of narrow-deep excavations has been steadily developing. Narrow-deep excavations exhibit a clear size effect in the basal heave stability analysis. However, the classical Prandtl mechanism ignores the size effect and influence of the inserted depth of wall penetration. Based on this, a modified Prandtl failure mechanism that considers the above factors was proposed in this study. Subsequently, a practical equation was derived to simplify the analysis process and obtain the safety factor against basal heave. The upper-bound solution provides a convenient and concise method for basal heave stability analysis of narrow excavations in undrained clay, and its feasibility was verified by comparing it with the results obtained by finite element limit analysis. The results showed that the proposed failure mechanism can provide a better upper-bound solution for the safety factor of the basal stability of narrow excavations than the classical Prandtl failure mechanism.

Effect of geomembrane liner on landfill stability under long-term loading: interfacial shear test and numerical simulation.

Clay liners have been widely used in landfill engineering. However, large-scale clay excavation causes secondary environmental damage. This study investigates the feasibility of replacing clay liners with high-density polyethylene (HDPE) geomembranes with different specifications and parameters. Laboratory interface shear tests between municipal solid waste (MSW) samples of different ages and geomembranes were conducted to study the influence of landfill age on interface shear strength. Finite element method was adopted to compare the long-term stability of landfills with HDPE geomembrane versus clay as intermediate liner. The interfacial shear test results show that the cohesion of MSW increases in a short term and then decreases with landfill age. The internal friction angle exhibits an increasing trend with advancing age, however, the rate of its increment declines withage.The rough accuracy of the film surface can increase the interfacial shear strength between MSW. The simulation results show that, unlike clay-lined landfills, the sliding surface of geomembrane-lined landfills is discontinuous at the lining interface, which can delay the penetration of slip surfaces and block the formation of slip zone in the landfill. In addition, the maximum displacement of landfills with geomembrane is 10% lower than that with clay, and the absolute displacement of slope toe decreases with the increase of roughness at the interface of geomembrane. Compared with clay-lined landfills, the overall stability safety factor increased by 18.5-30%. This study provides references for landfill design and on-site stability evaluation, contributing to enhanced long-term stability.

Stability analysis of roadbed under flood scouring

Soil roadbed along the river suffers from water erosion at the bottom and collapse at the top under flood scouring, which leads to the suspension of upper pavement slab. In order to ensure the safety of soil roadbed along the river, this study explored the development mechanism of soil roadbed damage by flood in actual cases, and proposed the evolution process of instability under roadbed scouring. The stability law of roadbed along the river under flood scouring was analyzed, and the stability safety factor was corrected to analyze the sensitivity of water depth, flow rate, river bending angle and stability safety factor K in working conditions. The sensitivity of width and height of soil roadbed after flood scouring to water depth, flow velocity, river bending angle was investigated. Moreover, numerical simulation was carried out to determine the displacement nephogram and maximum shear stress nephogram of soil roadbed along the river under the conditions of road surface and roadbed load, vehicle loading or constant change of water depth. By comparing the above theories and engineering cases, the water damage mechanism of soil roadbed along the river was further verified.

Numerical study of creep in soil anchor walls - a case study

ABSTRACT One of the fundamental unknowns in geotechnical engineering, particularly in the design and analysis of retaining walls, is creep. Traditional design approaches for anchored walls often specify a certain prestressing force in the anchors while allowing minimal wall displacement. Unfortunately, the long-term effects of creep are frequently overlooked. Over time, creep leads to increasing displacement in anchored walls, changing the loads acting on stabilizing elements and diminishing the factor of safety for excavation stability. While past research has predominantly focused on short-term behaviour in anchored and nailed walls, only limited attention has been devoted to their long-term behaviour. This study addresses the existing gap by collecting data related to the long-term behaviour of anchored walls in an excavation project. Utilizing two-dimensional finite element numerical modelling, using plane-strain analyses, the study predicts the behaviour of these walls both at the end of the excavation and five years after its completion. Long-term behaviour modelling employs a history matching approach to determine creep variables. Subsequently, the study investigates horizontal wall displacements and changes in loads within the anchors over a five-year period. Through a comparison of modelling results with field measurements, the study demonstrates the model validation in forecasting horizontal displacements at various locations and changes in loads on the anchors over time. Furthermore, the proposed method for long-term deformation calculations of excavation walls enables the anticipation of when horizontal wall displacements may surpass allowable limits. This research concludes with an examination of the evolving trends in anchor loads over time, substantiated by a combination of measurements and numerical modelling.

Numerical Analysis of the Effect of Crude Oil Pollution on Vertical Clay Trenches

ABSTRACT The presence of oil contamination causes changes in mechanical properties of clayey soil trenches with low liquid limits (CL) such as stress-strain behavior, rupture plain position, plastic zone, and strain energy for soil trenches compared with uncontaminated soils. These changes usually lead to a lower factor of safety against failure and expansion of the plastic zone. The effects of crude oil contamination on the soil shear strength were evaluated by direct shear and plate load tests for various clays and sandy soils. In this research, a numerical finite element modeling in ABAQUS software was used to estimate the effect of oil contamination in the range of 0 to 16% (0%–4%–8%–12%–16%) on the stability safety factor of vertical clayey trenches with heights of 3 m, 4 m, 5 m, and 6 m, and the results were compared with results of a limit state analysis. The findings of the limit equilibrium method show that adding 4% of oil contamination to a clayey trench will decrease 62% of its critical depth. Also, the numerical analysis results show that adding oil contamination in the range of 0 to 16% to the clayey soil will increase the maximum displacements of the trenches to five times their clean state.

Stability analysis for excavation in frictional soils based on upper bound method

This paper adopted both the numerical and analytical methods to investigate the excavation stability against base heave failure. The finite element limit analysis method (OPTUM) was firstly employed to calculate the safety factor of the excavation stability against base heave failure, and the failure mechanism of the excavation was obtained. Based on the analysis and observation of the numerical results, a rigid block rotational failure mechanism was proposed, and the analytical formula of the safety factor of the excavation was developed through the upper bound method of limit analysis. In order to verify the rationality of the proposed failure mechanism, the analytical formula of the safety factor and the failure pattern of excavation were compared with the numerical results and the existing classical failure mechanism. Furthermore, the influences of soil and excavation conditions on the excavation stability were analyzed and discussed. Finally, a rigid block rotational failure mechanism under stratified stratum conditions was also proposed to consider effects of the complex soil conditions on the excavation stability. The results show that the proposed rigid block rotational failure mechanism provides a more critical safety factor calculation result for actual engineering examples and obtains a more continuous and smooth failure surface, which can serve as an alternative for the analytical method of excavation stability.

Shallow stability of soil slope with frame protection considering rainwater seepage: A calculation method

This paper introduces an integrated calculation method for analyzing the impact of frame protection engineering on the safety factor of shallow stability for soil slopes. The calculation method is based on the infinite long slope model, but it produces superior results by comprehensively taking into account the anti-sliding effect of the shallow slope sliding body. It combines the tension zone at the upper edge, the main sliding zone in the middle section, and the compression zone at the lower edge, while considering the anti-sliding force system of the frame protection structure and its contact surface with the soil. By converting the three-dimensional force system into a two-dimensional plane problem, an approximate calculation method for the shallow stability analysis of soil slopes with frame protection under rainfall seepage was established and numerically verified using the finite element method. The analysis indicates that the safety factor of the slope decreases significantly when seepage force is considered. As the length of the main sliding zone increases, the safety factor gradually decreases and approaches the result of the infinite long slope model. When the length decreases to zero, the safety factor gradually increases and approaches the result of the circular slip model. The use of frame protection significantly improves slope stability under rainfall seepage, and the safety factor increases with the number and embedded depth of the frame structure.

Spline Search for Slip Surfaces in 3D Slopes

A novel method involving the transformation of spline surfaces is introduced to search for the critical slip surface in a three-dimensional (3D) slope, which corresponds to the minimum limit equilibrium method factor of safety for overall slope stability. A slipping surface in a slope can be represented as the intersection of any continuous geometrical entity with the slope topography, over which the mass of sliding soil is discretized to solve for the factor of safety satisfying given equilibrium conditions. Traditionally, many researchers have searched for a critical ellipsoidal or spherical surface, or surfaces formed using other simple shapes. However, the critical slip surface in complicated cases, for example, a landslide, is seldom purely ellipsoidal or spherical, which leads to overestimations of the true factor of safety in a slope. To provide greater flexibility for transforming the shape of the slip surfaces during a global search, the geometry representing the slip surface is assumed to be in the form of a nonuniform rational basis spline (NURBS) surface in this paper. The proposed method involves varying the parameters of a parametric exponential function, which spawns control points within its domain to create NURBS surfaces. The parameters in the exponential function are varied to transform the slipping surface using a metaheuristic search algorithm, such as particle swarm optimization. A major advantage of the proposed method is that the final spline surface in the search is formulated such that it can then be locally optimized using surface altering optimization methods by adjusting the locations of its control points.

Static and Pseudo Static Analysis of Embankment Slope Stability of Bener Dam, Purworejo Regency, Central Java

The Bener Dam is considered as one of the largest rock-fill dams in Indonesia. This dam will impact the inundation area of three main villages in the Wonosobo and Purworejo regency. Since this zoned embankment dam consists of rock-fill and the core material, the stability of the dam slope has to be done to ensure that the dam is stable against any failures including the seismic effects. Moreover, the seismic coefficient in the study area in the seismic analysis of the large dam slope is needed to be used in the analysis which is not yet done from the previous studies. This paper presents the analysis of the embankment slope stability of the Bener dam under static condition and pseudo static condition. The analysis takes into account the end stage of construction, the steady-state stage, and rapid drawdown stage. The results of utilizing the Finite Element Method to analyse the slope stability demonstrates that the dam embankment slopes are stable under static and seismic stress conditions in all the reservoir condition stages. After applying the seismic loading, the result of safety factor of slope stability is reduced while the rapid drawdown stage has the lowest safety factor.

Mechanisms of slope instability induced by two-hole oversized tunnels with small clearances underneath

The double-tunnels crossing potential landslides are gradually developing towards smaller clearances and larger cross-sections. The disturbance of the tunnel construction is very likely to cause slope instability, tunnel damage, and other natural disasters. In the paper, model tests and numerical analysis are applied to investigate the instability mechanism of landslides caused by double-tunnels with oversized sections orthogonally beneath, based on the Shaoxin High-Speed Hanshankou Tunnel. The mechanism of tunnel-induced landslides is obtained and the stability factor of safety is modified by strength reduction and parametric analysis. The results indicate the following: The superimposed effect of double-hole excavation and the disturbance of surrounding rock caused by super-large cross-section excavation are the two main reasons for the landslide in Hanshankou Tunnel. The degree of influence of various factors on the stability of the tunnel-landslide mass is: section size > buried depth > clear distance > construction method > support parameters. It is recommended to use the formula F=α1α2α3Fst to modify the slope stability safety factor.

Analysis of the Hydromechanical Properties of Compact Sandstone and Engineering Application

The paper proposes a method to simulate the mechanical behavior of compact rock considering hydromechanics by combining physical experiments and numerical analysis. The effectiveness of the constructed method is validated by the comparison between the numerical and physical results of triaxial shear experiments on sandstone in seepage conditions. Based on the validated method, the stability of underground water-sealed oil and gas storage caverns in surrounding compact sandstone during excavation is analyzed. The main findings are as follows: The intrinsic permeability of compact sandstone has a power function relationship with the porosity; the combination of the porous media elastic model and the modified Drucker–Prager plasticity model can preciously represent the mechanical properties of compact sandstone; the proposed method can accurately replicate the hydromechanical response of compact sandstone in seepage conditions; the effects of hydromechanical effects have significant impacts on the stability of surround compact sandstone during the excavation of underground water sealed oil and gas storage caverns, which causes the obvious increase in stress, deformation and plastic deformation zones of the surrounding compact sandstone and remarkable decrease in the stability safety factor.

Analysis of Deformation Formation Causes and Reinforcement Disposal Effects in Deep Excavated Expansive Soil Canal Slope: Case Study

Deeply excavated expansive soil canal slopes can have instability risks during operations. The deformation mechanism is analyzed using internal and external factors, such as engineering geology, hydrogeology, rainfall, and groundwater levels in the middle expansive soil canal slope in the central line of the South-to-North Water Diversion Project, Taocha District, Nanyang City, Henan Province, China. The stability of the canal slope and the effect of the reinforcement and disposal measures are evaluated with a geological survey, manual inspection of the defects, safety monitoring data analysis, hidden danger geophysical detection, and stability numerical simulation. The following conclusions are drawn: (1) the surface-refilled cement-treated soil failed to isolate the water vapor exchange between the expansive soil and the atmosphere; and (2) the stagnant water in the upper layer is replenished by precipitation, leading to the increase in the groundwater level during the rainy season and the decrease in the groundwater level during the dry season. Shear creep deformation occurs along the fissure of the second to fourth grade canal slopes. The potential sliding surface consists of a gentle dip angle leading edge and a steep dip angle trailing edge. The arrangement of the antisliding piles on the water-passing section and the crack surface distribution had an effect, and the potential shear outlet is in the first grade berm, the deformed body is still developing, and the trailing edge is not apparent. The potential failure mode of the slope is deep sliding, and the current safety factor is 1.002. A combination of groundwater discharge and micropile reinforcement is required to improve the stability of the canal slope. After the drainage and reinforcement are implemented, the slope’s deep antislide stability safety factor increases to 1.462, which met the safety requirements. The results could provide a reference for the operation management and reinforcement governance of similar projects.