Decrease In Safety Factor Research Articles

Effect of Soil–Water Characteristic Parameters on Saturation Line and Stability of Slope

Rainfall infiltration is the main factor that causes slope instability. To study the effect of hydraulic parameters on the final saturation line and stability of slopes, a numerical slope model is established with a saturated–unsaturated seepage analysis method. Analysis results show the following, (1) When parameter a increases, the effective rainfall duration decreases linearly, and the ultimate safety factor increases gradually; when parameter m increases, the effective rainfall duration increases linearly, and the ultimate safety factor decreases linearly; when parameter n increases, both the effective rainfall duration and the ultimate safety factor decrease first and then remain stable. (2) When the saturated permeability coefficient decreases, the effective rainfall duration presents a crescent trend, and the ultimate safety factor decreases first and then remains the same after rainfall intensity exceeds the saturated permeability coefficient of soil. (3) When rainfall intensity is less than the saturated permeability coefficient of soil, the location of the final saturation line rises as the saturated permeability coefficient decreases and is thus independent of parameters a, m, and n.

Influence of core thickness on stability of downstream slope of earth and rockfill dams under end-of-construction and steady-state-seepage: a comparison

The steepness of the slopes of earth and rockfill dam is governed by stability considerations which in turn are influenced by the strength of the core and shell materials as well as their geometry. An analytical study has been undertaken to evaluate and compare the variation in the factor of safety of the downstream slope of a dam on account of variation in the thickness of vertical core for the two conditions, namely, steady-state seepage condition and end-of-construction condition. A 180-m high earth and rockfill dam section, founded on strong base, having section and slopes similar to a high dam in the northern India was used as a base section for analysis. The study shows that as core thickness increases beyond a critical value, it causes a progressive decrease in the stability of downstream slope. This critical core thickness is observed to lie in the range of 50–150% of dam height for both conditions and a core within this zone does not influence stability of downstream slope. The rate of decrease in factor of safety is also observed to be similar in both conditions. The influence of relative strength of shell to core, height of dam and pore water parameter on critical core thickness is highlighted.

Effects of an increase in reservoir drawdown rate on bank slope stability: A case study at the Three Gorges Reservoir, China

To increase the total power output of the Three Gorges Hydropower Station and generate greater economic benefits, it is necessary to reduce the time required for the water level of the Three Gorges Reservoir to drop, i.e., to increase the rate at which the water level drops. A rapid drop in the reservoir water level might result in a significant change in the reservoir bank environment, which can destabilize landslides that extend into the water, reactivate old landslide masses and form new landslide masses in the reservoir region. A typical slope that extends to the water in the Three Gorges Reservoir region was selected for study. We studied the geologic conditions of a selected landslide mass and developed an expression for the hydrodynamic pressure under the effects of groundwater within the slope area and an expression for the normal stress on a sliding surface under the effect of hydrodynamic pressures. In addition, the evolution of the stability of the slope (submerged to various depths) under the effects of the lowering of the reservoir level is investigated based on a strictly global analysis: (a) safety factor decreases about 14% as the reservoir level drops with rate of 0.6m/d and about 16% with rate of 1.2m/d at the fall of reservoir water level 30.0m; (b) an increase in the drawdown rate of the Three Gorges Reservoir from 0.6m/d to 1.2m/d is unfavourable for the stability of the slope that extends into the water, but the extent of the decrease in safety factors resulting from this increase in rate is not significant.

Numerical Analysis of the Embankment Suffering Heavy Asymmetric Traffic Load

The behavior of the pavement is highly dependent on the deformation and stability of the underlying embankment. To optimize the design of embankment suffering heavy asymmetric traffic load in Shanxi province, China, a series of two-dimensional (2D) numerical analyses were conducted using the finite element software PLAXIS to investigate the deformation and slope stability of the unreinforced, geosynthetic reinforced, and expanded polystyrene (EPS) geofoam reinforced embankments. The results show that the general performance in the geosynthetic reinforced case is thought to be superior compared to that in the EPS geofoam reinforced case taking the slope stability into consideration. As the asymmetric traffic load increases, the embankment deformation increases significantly and obvious decrease of the slope stability safety factor is also observed. Great attention need to be paid to the influence of the heavy asymmetric traffic load.

Effect of pile driving adjacent to soil slopes on safety factor of specific sliding surface

The effect of pile driving force, plastic zone around the pile tip and anti-sliding action of the pile body on safety factor of sliding surface is investigated by using the stability calculation methods for slopes based on the cavity expansion theory with the consideration of elasto-plasticity of soil. Through a numerical case, change of safety factor in the whole process of the pile driving is analyzed. And the effect of pile diameter, slope angle and distance between pile and slope top on the change of safety factor of slope is discussed. The results show that the pile driving force and the plastic zone at pile top have an adverse effect on slope stability, which leads to a decrease in the safety factor, while the anti-sliding effect of the pile has a positive contribution to the slope stability, especially when the end of pile is below the sliding surface. The safety factor decreases significantly with the increase of the pile diameter, and it significantly increases after the pile end penetrates through the sliding surface. The greater the slope angle, the smaller the safety factor after pile driving. The safety factor drops more slowly with the increase of the distance of the pile away from the slope top, and the effect of the plastic zone on the safety factor also gradually decreases. The pile driving will not affect the stability of the sliding surface when the pile is far from the top of the slope. The results may provide some guiding significance and reference value for the design and construction of static pile driving adjacent to slopes.

English

- This paper examines how rainfall patterns affect the mechanisms of shallow slope failure. Numerical modelling, utilising the commercial software SVFlux and SVSlope, was carried out for a coupled analysis of rainfall-induced slope seepage and instability, with reference to a shallow landslide took place in Jabiru, Northern Territory (NT) Australia in 2007. Rainfall events were varied in terms of pattern in this analysis. The results revealed that slopes are sensitive to rainfall pattern when the rainfall intensity has a high degree of fluctuation at around the same value as that of saturated hydraulic conductivity. Average rainfall intensity at the beginning of a rainfall period plays a primary role in determining the rate of decrease in initial factor of safety (F i ) towards minimum factor of safety (F min ). The effect of rainfall events on the slope instability is attributed to the amount of rainwater infiltration into slope associated with rainfall pattern. Keywords: Rainfall pattern; Fluctuating intensity, Shallow failure mechanism; Slope failure; Rainwater infiltration.

Energetic-particle-driven instabilities and induced fast-ion transport in a reversed field pinch

Multiple bursty energetic-particle (EP) driven modes with fishbone-like structure are observed during 1 MW tangential neutral-beam injection in a reversed field pinch (RFP) device. The distinguishing features of the RFP, including large magnetic shear (tending to add stability) and weak toroidal magnetic field (leading to stronger drive), provide a complementary environment to tokamak and stellarator configurations for exploring basic understanding of EP instabilities. Detailed measurements of the EP mode characteristics and temporal-spatial dynamics reveal their influence on fast ion transport. Density fluctuations exhibit a dynamically evolving, inboard-outboard asymmetric spatial structure that peaks in the core where fast ions reside. The measured mode frequencies are close to the computed shear Alfvén frequency, a feature consistent with continuum modes destabilized by strong drive. The frequency pattern of the dominant mode depends on the fast-ion species. Multiple frequencies occur with deuterium fast ions compared to single frequency for hydrogen fast ions. Furthermore, as the safety factor (q) decreases, the toroidal mode number of the dominant EP mode transits from n=5 to n=6 while retaining the same poloidal mode number m=1. The transition occurs when the m=1, n=5 wave-particle resonance condition cannot be satisfied as the fast-ion safety factor (qfi) decreases. The fast-ion temporal dynamics, measured by a neutral particle analyzer, resemble a classical predator-prey relaxation oscillation. It contains a slow-growth phase arising from the beam fueling followed by a rapid drop when the EP modes peak, indicating that the fluctuation-induced transport maintains a stiff fast-ion density profile. The inferred transport rate is strongly enhanced with the onset of multiple EP modes.

Key Technology for the Structure Design of Mining Metro Station in Rock Strata

Focused on the mining method, the parameters of primary support, and the design method for the interface of metro station and air duct structure, what are encountered during the design of mining station in rock strata. Through the combination of numerical method and theoretical analysis, and the comparison with field measured data, we know that double-side-wall heading method is safe and feasible, design method based on plastic stage can be used for the checking of primary support structure, and the combination of support in advance and closed steel frame can insure the safety of the interface of metro station and air duct structure. Through analysis, the changes of displacement and stress are focused around vault and arch springer, and the decrease and increase of safety factor during construction are also made clear. The study can offer a reference for the similar project in the future.

The Effect of Rainfall Patterns on the Mechanisms of Shallow Slope Failure

Abstract - This paper examines how rainfall patterns affect the mechanisms of shallow slope failure. Numerical modelling, utilising the commercial software SVFlux and SVSlope, was carried out for a coupled analysis of rainfall-induced slope seepage and instability, with reference to a shallow landslide took place in Jabiru, Northern Territory (NT) Australia in 2007. Rainfall events were varied in terms of pattern in this analysis. The results revealed that slopes are sensitive to rainfall pattern when the rainfall intensity has a high degree of fluctuation at around the same value as that of saturated hydraulic conductivity. Average rainfall intensity at the beginning of a rainfall period plays a primary role in determining the rate of decrease in initial factor of safety (Fi) towards minimum factor of safety (Fmin). The effect of rainfall events on the slope instability is attributed to the amount of rainwater infiltration into slope associated with rainfall pattern. Keywords: Rainfall pattern; Fluctuating intensity, Shallow failure mechanism; Slope failure; Rainwater infiltration.

수치해석을 통한 앵커의 긴장력과 사면 안전율의 상관관계 도출

최근 기후변화로 발생하는 이상강우에 의한 지하수위의 상승은 사면보강을 위해 설치한 앵커의 초기 긴장력의 증가를 유발시킬 수 있다. 한편 사면의 국부적 파괴나 낙석 등으로 인한 앵커 두부(head)의 예기치 못한 손상은 긴장력 상실로 이어져 앵커로 보강된 사면의 안정성을 저하시키는 주된 요인이 될 수 있다. 이와 같은 앵커 긴장력의 변화는 사면의 안정성에 매우 직접적으로 영향을 미치지만 현재의 기술은 앵커 긴장력의 존재 유무만을 간단히 확인하거나 단기간의 긴장력 변화를 측정할 수 있는 기술만이 있을 뿐 영구사면과 같이 장기간 앵커의 긴장력 변화와 사면의 안정성에 대한 직접적이고 효과적인 모니터링 방법은 찾아보기 어렵다. 본 연구에서는 장기간의 앵커 긴장력 모니터링이 가능하도록 개발된 광섬유 센서 내장형 텐던을 이용하여 사면의 안정성을 직접 평가할 수 있도록 초기 긴장력 감소 및 증가와 사면 안전율의 상관관계에 대하여 수치해석적 검토를 수행하였다. 앵커가 시공되어 있는 실제 사면의 사례에 대한 한계평형해석 및 3차원 유한요소해석을 실시하여 사면에 설치된 앵커의 긴장력 변화와 사면 안전율(factor of safety) 변화에 대한 검토를 수행한 결과, 지하수위 상승으로 인한 앵커 긴장력의 증가는 사면 안전율의 비선형적 감소를 동반하며 일정 수준 이하의 앵커 긴장력 감소는 선형적 사면 안전율 감소를 동반하는 것으로 나타났다. Main reasons making the slope reinforced with anchors unsafe are rise of ground water table due to heavy rainfall and sudden reduction of initial tensile force due to damage of anchor head. In this research, numerical analysis was carried out to evaluate the safety of slope reinforced by anchors from the monitoring result of tensile force. Limit equilibrium analysis and 3D finite element analysis were carried out to model the sudden reduction of initial tensile force and increase of tensile force due to soil movement, which was caused by rise of ground water table. From the numerical analysis, it was found that the increase of tensile force due to rise of ground water table comes with nonlinear decrease of safety factor and reduction of initial tensile force due to damage of anchor head accompanied with linear decrease of safety factor. From the results, it can be concluded that safety of the slope can be evaluated indirectly by monitoring the tensile force of anchor using FBG sensor embedded tendon.

Influence of filling–drawdown cycles of the Vajont reservoir on Mt. Toc slope stability

In the present work, the 1963 Vajont landslide has been back-analyzed in detail to examine the influence of reservoir operations (filling and drawdown) on Mt. Toc slope stability. The combined seepage–slope stability analyses carried out show that the main destabilizing factor that favored the 1963 Vajont landslide was the reservoir-induced water table that formed as a consequence of rapid seepage inflow within the submerged toe of the slope — decrease in the factor of safety (FOS) up to 12% compared to the initial slope stability condition, i.e., in the absence of the Vajont reservoir. Rainfall would only have been a decisive factor if the initial stability condition of the Mt. Toc slope had already been very close to failure (decrease in FOS caused by heavy or prolonged rainfall is about 3–4%, for the worst case scenario analyzed). The permeability of the shear zone material occurring at the base of the prehistoric Vajont rockslide has been evaluated at 5×10−4m/s, and back-calculated values of the friction angles Φ range from 17.5° to 27.5°. When considering mountain reservoirs, slope failures can occur during both filling and drawdown phases. In the Vajont case, owing to the highly permeable materials of the shear zone, slope stability decreased during filling and increased during drawdown. Another displacement-dependent phenomenon of a mechanical nature – progressive failure of the NE landslide constraint – has to be considered to understand the slope collapse that occurred during the last drawdown (26 September–9 October 1963). The results of the combined seepage–slope stability models indicate that permeability of bank-forming material and filling–drawdown rates of reservoirs can strongly influence slope stability. Slow lowering of the reservoir level is a necessary measure to reduce the occurrence of very dangerous transient negative peaks of FOS.

Engineering Geological Investigation of Slow Moving Landslide in Jahiyang Village, Salawu, Tasikmalaya Regency

DOI: 10.17014/ijog.v7i1.133An understanding of landslide mechanism is imperative to determine the appropriate mitigation method. The slow moving landslide (creeping) which occurred in Kampung Salawangi, Jahiyang Village, Salawu Subregency, Tasikmalaya had caused economical and environmental losses due to the frequent active movement particularly following rainfall events. Engineering geological investigation and slope stability analysis were carried out in the studied area in order to elucidate the mechanism of the landslide. The engineering geological investigation consists of local topographical mapping, geotechnical drillings, hand borings, cone penetration, and laboratory tests. The slope stability assessment of the recent landslide was conducted by a finite element method. The results of engineering geological data analysis show that the studied area is composed of residual soils of soft to firm sandy silt and loose to compact silty sand and base rock of fresh to weathered volcanic breccias with groundwater level varying between 3 - 16 m. The engineering properties of the residual soils indicate that the sandy silt is of high plasticity and the shear strength properties of the sandy silt and silty sand show low value with effective cohesion of 6.0 - 21.74 kPa and effective friction angle of 12.00 - 25.980. The assessment of slope stability shows that the stability of the studied area is largely influenced by the rise of groundwater level marked by the decrease of safety factor and increase of slope displacement.

Analysis of Three-Dimensional Excavation Slope Stability Subjected to <i>In Situ</i> Stress Based on Strength Reduction FEM

Slope usually lies in an initial stress field, especially in complex three-dimensional stress conditions. When horizontal stress is larger than vertical stress or the two horizontal stresses are not the same, the horizontal in-situ stress has significant effect on the excavation slope stability. To investigate the effects of the original in-situ stresses, the strength reduction method is used to analyze three-dimensional excavation slope, and Mohr-Coulomb yield rule is adopted, the failure criterion based on analysis convergence is suggested. First, the horizontal stress is uniform based on the gravity load, when lateral pressure coefficient increases, the safety factor decreases, and the plastic zones develop from slope to foot foundation. Then the condition of lateral pressure coefficient change is analyzed, slope direction pressure coefficient increases, plastic zone on the slope bottom increases, the safety factor decreases remarkably. Using the same method to analyze that of the lateral pressure coefficient on the slope face direction increases, the slope FS increases little holding the K2 unchanged with the K1 adding. The results show that the slope direction pressure coefficient has more effects on the safety coefficient than that of the axis.

Effect of Antecedent Rainfall Patterns on Rainfall-Induced Slope Failure

Rainfall-induced slope failure occurs in many parts of the world, especially in the tropics. Many rainfall-induced slope failures have been attributed to antecedent rainfalls. Although it has been identified as a cause of rainfall-induced slope failure, the pattern or distribution of the antecedent rainfall has not received adequate attention. In this study, parametric studies were performed by using three typical rainfall patterns, identified by analysis of available rainfall data for Singapore and two different soil types to represent high- and low-conductivity residual soils of Singapore. Antecedent rainfall patterns were applied on soil slopes and a transient seepage analysis was conducted. The computed pore-water pressures were used in stability analyses to calculate the safety factor of the slope. Results indicated that antecedent rainfall affected the stability of both high-conductivity (HC) and low-conductivity (LC) soil slopes. However, the stability of the LC soil slope was more significantly affected than the HC soil slope. Patterns of antecedent rainfall controlled the rate of decrease in factor of safety, the time corresponding to Fs(min) and the value of Fs(min). Delayed rainfall pattern resulted in the lowest minimum factor of safety, Fs(min), for the HC soil slope, and advanced rainfall pattern resulted in the lowest Fs(min) for the LC soil slope.

Observation of confinement degradation of energetic ions due to Alfvén eigenmodes in JT-60U weak shear plasmas

Confinement degradation of energetic ions due to Alfvén eigenmodes (AEs) has been investigated with negative ion based neutral beam injection at ∼370 keV into JT-60U weak shear plasmas. AEs with a rapid frequency sweeping and then saturation as the minimum value of the safety factor decreases have been observed. This frequency behaviour can be explained by the reversed-shear induced AE (RSAE) and the transition from RSAEs to the toroidicity-induced AEs (TAEs). The associated change in the charge exchange neutral particle flux suggests energetic ion transport due to these AEs. The total neutron emission reduction rate in the presence of these AEs is evaluated by calculation using the orbit following Monte-Carlo code taking into account the change in bulk plasmas. The evaluation indicates confinement of energetic ions is degraded due to these AEs. In particular, it is found that the confinement degradation of energetic ions is maximum during the transition from RSAEs to TAEs and the maximum reduction rate (ΔSn/Sn)MAX is estimated to be ∼45%.

Research on values of safety factor coordination under random supply

This research evaluates how supply uncertainty and safety factors affect a supply channel. Under deterministic demand, lead time variability at the retailer increases in the lead time variability at the warehouse and decrease in the warehouse's safety factor. Moreover, the greater the safety factor is, the smaller effect of supply uncertainty at warehouse on supply uncertainty at the retailer is. Meanwhile, this paper makes an optimisation of the safety factor and finds the optimal numerical solution. It is shown that optimisation and coordination of safety factors lead to inventory cost savings at two sites, especially under great supply uncertainty.

Does substrate quality influence take‐off decisions in Common Starlings?

1. An instrumented perch was used to measure the reaction forces during take‐off of starlings from perches of three thicknesses. There was no significant decrease in reaction force with decreasing perch thickness; however, over the range of perch sizes there was a 10‐fold decrease in safety factor and a 400‐fold increase in the energy of deflection of the thinnest perch. 2. The implications of these results are that birds do not change their take‐off strategy when faced with perches of variable thickness and that, as a result, leaps from thin perches are very much less efficient than those from thicker perches. Birds appear not to adjust their leaping behaviour to minimize the risk of substrate failure during take‐offs.

Stability and range of motion of Insall-Burstein condylar prostheses: A computer simulation study

The Insall-Burstein Posterior Stabilized Prosthesis (Zimmer, Warsaw, IN) uses an articulation between a femoral cam and tibial spine to provide anteroposterior stability to the knee. Dislocation can occur if the femoral cam translocates anteriorly and over the tibial spine. A computer model was used to examine the effects of design changes made between the Insall-Burstein I (IB I), Insall-Burstein II (IB II), and revised Insall-Burstein II (IB II R) knees. The effects of these design changes were determined from their influence on knee stability and maximum obtainable knee flexion. Knee stability was characterized by a dislocation safety factor, defined as the vertical distance from the top of the tibial spine to the bottom of the femoral cam. Our analysis showed that the dislocation safety factor is greatest at approximately 70° of knee flexion for all IB knees. As knee flexion is increased from this angle, the dislocation safety factor decreases, reducing knee stability. The simulations highlighted a trade-off between improving knee flexion and improving knee stability. The geometry of the IB II knee allowed greater knee flexion. The maximum flexion achieved with the IB II knee was 125° compared with 115° and 117° for the IB I and IB II R knees, respectively. However, the simulations indicate that the IB I and IB II R knees are less likely to dislocate because they have greater dislocation safety factors than the IB II knees.

Tree dimensions: Maximizing the rate of height growth in dense stands.

To determine the effect of tree dimensions on the rate of height growth a model was constructed relating tree weight to total height and R, the ratio of crown weight to trunk weight. The model is based on the assumption that the trunk buckling safety factor is constant. If trees also maintain a constant R as they grow then the rate of height growth is maximized by R=0.17. In addition, the height growth rate increases as the buckling safety factor decreases. These predictions of optimal form for height growth are appropriate for shade intolerant, successional species growing in dense stands. Dimensional measurements of self thinning Populus tremuloides indicate near optimal dimensions for height growth. Trees ranging from 7 to 19 m in height had trunks which were only 50% thicker than the minimum required to prevent them from buckling under their own weight, and had a mean R of 0.13. This ratio of crown weight to trunk weight is significantly lower than the optimal value, but the predicted height growth rate for R=0.13 is 99% of that predicted for R=0.17.

Centrifugal Modelling of Riverbank Failure

Pilot tests were first performed on kaolin models, and then further tests were carried out on models made from undisturbed block samples taken from the site. The investigation described was limited to a study of the individual and combined effects on the riverbank stability of dredging of the riverbed, flooding and drawdown, and heightening of the retaining wall. Although no visual collapse occurred in the block samples under field conditions, measuring techniques developed at Cambridge University enabled the study of the displacements and strains within the models, leading to identification of the failure surface. The fact that the model slope mechanism of progressive failure, and stability analyses carried out on the preceding surface, using laboratory obtained strength parameters, show that this mechanism leads to a decrease in safety factor from 1.2 to 0.9. It is concluded that although progressive failure may not be able to develop fully in the centrifuge, the failure surface may be identified using special measuring techniques.