Stability Of Cut Slopes Research Articles

Assessment of rock slope stability by probabilistic-based Slope Stability Probability Classification method along highway cut slopes in Adilcevaz-Bitlis (Turkey)

Rock slope stability is of great concern along highway routes as stability problems on cut slopes may cause fatal events as well as loss of property. In rock slope engineering, stability evaluations are commonly performed by means of analytical or numerical analyses, principally considering the factor of safety concept. As a matter of fact, the probabilistic assessment of slope stability is progressively getting popularity due to difficulties in assigning the most appropriate values to design parameters in analytical or numerical methods. Additionally, the effect of heterogeneities in rock masses and discontinuities on the analysis results is minimized through the probabilistic concept. In this study, slope stability of high and steep sedimentary rock cut slopes along a state highway in Adilcevaz-Bitlis (Turkey) was evaluated on the basis of probabilistic approach using the Slope Stability Probability Classification (SSPC) system. The probabilistic assessment indicates major slope stability problems because of discontinuity controlled and discontinuity orientation independent mass movements. Almost all studied cut slopes suffer from orientation-independent stability problems with very low stability probabilities. Additionally, the probability of planar and toppling failures is significantly high with respect to the SSPC system. The stability problems along the investigated rock slopes were also verified by field reconnaissance. Remedial measures such as slope re-design and reinforcement at the studied locations should be taken to prevent hazardous events along the highway. On the other hand, the probabilistic approach may be a useful tool during rock slope engineering to overcome numerous uncertainties when probabilistic and analytic results are compared.

Stability of Soil Cutting and Side Slope Based on Stress Route Theory

<p>The stress route analytical method compensates for the limitation of traditional soil slope stability analytical method. Since it disregards the impact of effective stress route on the stress status and anti-shear strength of soil slope, it maps out the soil stress route drawing in the excavation process, and marks the anti-shear strength and shear stress changes under various conditions of soil. It causes the changes of the safety coefficient rules in the excavation of soil slope and affects the excavation stability of soil cutting and side slope. The result reveals: (1) The main analytical method of side slope stability which covers both the limit balance method and finite unit method fails to consider the impact of effective stress route on the existing stress status and anti-shear strength of soil slope; the stress route analytical method is able to overcome this limitation to a certain degree. (2) The stress route theory is adopted for analysis, in which, it can projected the whole stress of typical and most dangerous area of the slope, able to analyse the anti-shear strength of soil in a real-time manner, manage to express the safety coefficient changes in the stress route drawing and provides a selection of a suitable excavation plan by contrast. (3) In the overall excavation, the slope toe suffers from obvious stress concentration which expands to the surrounding areas and inconvenient for the side slope stability in the excavation.</p>

Effect of Extreme Rainfall on Cut Slope Stability: Case Study in Yen Bai City, Viet Nam

This paper addresses the effects of extreme rainfall on the stability of cut slopes in Yen Bai city, Northern Viet Nam. In this area, natural slopes are excavated to create places for infrastructures and buildings. Cut slopes are usually made without proper site investigations; the design is mostly based on experience. In recent years, many slope failures have occurred along these cuts especially in rainy seasons, resulting in properties damaged and loss of lives. To explain the reason that slope failure often happens during rainy seasons, this research analyzed the influence of extreme rainfalls, initial ground conditions, and soil permeability on the changes of pore water pressure within the typical slope, thereafter determining the impact of these changes on the slope stability factor of safety. The extreme rainfalls were selected based on all of the rainfalls triggering landslide events that have occurred over the period from 1960 to 2009. The factor of safety (FS) was calculated using Bishop's simplified method. The results show that when the maximum infiltration capacity of the slope top soil is less than the rainfall intensity, slope failures may occur 14 hours after the rain starts. And when this happens, the rainfall duration is the deciding factor that affects the slope FS values. In short, cut slopes in Yen Bai may be stable in normal conditions after the excavation, but under the influence of tropical rain storms, their stability is always questionable.

An experimental investigation of the mechanical behavior and microstructural features of a volcanic soil (Isparta, Turkey) and stability of cut slopes in this soil

Volcanic soils are widely distributed group of soils, which cover significant parts of the world's surface and include areas occupied by urban settlements, structures and infrastructures, and may create geo-engineering problems. These soils exhibit a distinctive behaviour that is a consequence of their formation history, mineralogy and structure. Some part of the subsoil of a large area surrounding the city of Isparta (western Turkey) mainly consists of volcaniclastic deposits. This paper presents the results of the part of a research programme aiming at geotechnically characterizing the uppermost layer of this volcaniclastic sequence, particularly focusing on its collapse potential, shear behaviour and the influence of microstructure on these behaviours. In addition, its main futures were compared with those of some similar volcanic soils at different parts of the world, and the stability of sub-vertical cuts in this soil was also assessed. The experimental investigation mainly consisted of index and classification tests, double oedometer and direct shear box tests to assess the collapse potential and shear behaviour of the soil, respectively. Matric suction of the samples was also determined for preliminary evaluation of the influence of suction on collapse and shear behaviours of the soil. In addition, thin-section studies, and X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were also conducted to determine mineralogical and microstructural features and to evaluate their influences on the mechanical behaviour of the volcanic soil. The deposit is composed of weakly bonded firm silty sand with an open structure, low unit weight and high porosity, generally unsaturated in-situ. The results of the double oedometer tests suggest that the volcanic soil generally falls in the category of slight collapse potential at normal stresses ranging between 5 and 100kPa, while at normal stresses greater than 100kPa its collapse potential increases and ranges between moderate and moderately severe collapse potential classes. At normal stresses lower than 100kPa, matric suction may have an effect on collapse behaviour. The direct shear box test results indicated that the volcanic soil has two different types of shear strength behaviour represented by bi-linear failure envelopes. In other words, the shear strength parameters of the volcanic soil within a low normal stress range (generally between about 6 and 200kPa) exceed those of determined at higher normal stresses. Since no matric suction was measured during the direct shear box tests, it could not be possible to evaluate the effect of suction on the bi-linear failure envelopes. However, some differences between the suction and degree of bonding of the samples taken from different locations might probably have been contributed to the separation of the bi-linear behaviour at different normal stress levels. The destruction of the bonding (cementation) between the particles is probably more responsible from the bi-linear form of the failure envelope. Comparisons between the SEM micrographs taken from natural and tested specimens revealed that the mechanical behaviour of the volcanic soil is strongly influenced by the bonding material. The results of the stability analyses showed a good agreement with the current situation of the cut slopes observed in the study site and suggested that vertical cut slopes with a height of 14–15m will maintain their stability based on a reasonable factor of safety such as 1.5.

Influence of discontinuities on the stability of cut slopes in weathered meta-sedimentary rocks

The meta-sedimentary rocks along Pos Selim Highway in Perak State, Malaysia showed a gradational weathering profile based on differences particularly in textures, hardness, lateral changes in colour and consistency of material extension. Both large and small scale discontinuities observed in the investigated rocks reduce the physical and mechanical properties of the rocks, and provide slip surfaces for failures. Rock and soil samples were tested using established standards to determine their characteristics and responses under a wide variety of disturbances. Kinematic analyses were also carried out to determine the modes and likely modes of failures.Petrographic analyses revealed associated micro-structures, and the implications of these micro-structures showed shearing components along planes of weakness. From the determined index properties of the tested soil samples, the weathered quartz mica schist is not suitable for structural support. Further study involving unconsolidated undrained direct shear box tests carried out under total stress, revealed a non-uniform response of the rocks to shearing disturbance along discontinuity planes, and the rate and depth of deformation. The shear strength components of the investigated rocks were thereby prescribed in terms of cohesion and friction angle. From the kinematic analyses across this extended cut slope, there are possibilities of wedge and planar failures.

Effect of Area Development on the Stability of Cut Slopes

Many natural slopes were subjected to change in geometry in order to make room for construction of infrastructures. This paper presents stability analysis of a natural slope subjected to cutting to make room for the development of factories in an industrial site. The analysis was performed for the most critical slope section and analysis was made in comparison to the case presented in literature. Data required for slope stability analysis were retrieved from relevant project report. The result shows that the stability of the slope decreases due to slope excavation and stabilization should be done in order to limit further reduction of shear strength due to yielding of soil mass. Analysis using circular failure surface such as Simplified Bishop is simple and is usually suitable for analysis of existing slope where there is no indication of incipient failure. However, pre-defined failure surface in Morgensten Price method is more useful if failure surface could be predicted based on slope assessment or when rectification work has been applied.

Jet grouting: mathematical model to predict soilcrete column diameter - part I

Predicting soilcrete column diameter in jet grouting operations is one of the challenging tasks of engineers. By being able to determine the diameters, number of required columns and their spacing needed for activities such as cut off walls, soil improvement and slope stability activities can be calculated. However, there is no precise method to calculate and design the diameter before the operations. Therefore authors attempt to present a mathematical model using sum of squared–deviations (SSDs) method to estimate the diameter of soilcrete created by triple fluid jet grouting system. To do so, the actual data where soilcrete diameters have been measured, is used to prove and test the mathematical model. The effective jet grouting operational parameters that impact the diameter have been determined according to literature review of previous studies. On the basis of the results of modelling, the presented equation can predict soilcrete diameters with error range of 3–20%.

Assessment of stability problems at southern engineered slopes along Mersin-Tarsus Motorway in Turkey

This paper describes the cut slope stability problems of southern engineered slopes along 57 km long Mersin-Tarsus Motorway. While the northern slopes were slipping during and following construction, the stability problems occurred at southern slopes after heavy rains in December 2001. The most recent slope stability problem took place on chainage at the km 10+800 embankment on 9 April 2009. About 3.62 × 106 m3 soil materials have currently slipped at 60 different location. After the occurrence of slides, different remedial methods (reshaping slopes, soil improvements, etc.) have been applied to stabilize the slipped slopes. The slope stability studies were carried out using back analysis to determine the slope failure mechanisms and to estimate effective shear strength parameters. Pore water pressures increase following intense rainfall events and cause reduced resistance to shear strength at the engineered slopes. In addition, the affects of the static and dynamic parameters to analyse the state of the slope after excavation were investigated and possible remedies to improve the state (toe rockfill and retaining wall) were assessed for motorway slopes through determining the slope stability with water parameter and seismic loading, separately and together. The results of the stability analysis have exhibited that a good drainage system and retaining wall prevents the motorway slope slides.

Cut slope stability evaluation of NH-21 along Nalayan-Gambhrola section, Bilaspur district, Himachal Pradesh, India

In the present work a ready reckon (a handbook used for computation/reference) model for the evaluation of slope instability of road sections, particularly in mountainous terrain, is presented. The integrated approach incorporates different aspects of physical and geotechnical parameters, structural kinematics and the role of different clay minerals constituting the slope-forming materials, aimed at deciphering and understanding the mechanisms that controlled the slope instability. The role of the major sets of discontinuities, derived from stereo plots of structural data, with regard to the total number of unstable slopes present in each segment was considered, and the critical section was determined. The intense monsoon season rainfall in the area not only contributed to weathering of the rock mass, but also increased the water content in the clays that were present, leading to a reduction in the stability of natural slopes. The study revealed that where the slopes displayed relative presence of montmorillonite clays, with significant swelling capacity, failures were more frequent.

저강도 강우시 절토사면의 흡인력 분포와 안정성에 대한 투수계수의 효과

The authors discuss the effect of hydraulic conductivity on the suction profile and stability of a typical cut-slope subjected to low intensity rainfall. The initial suction value above the ground table in the unsaturated zone is assumed to be 15 kPa. The uncoupled approach of finite element and limit equilibrium method is used to evaluate the stability of the cut-slope at different elapsed times of rainfall. The finite element seepage analysis shows that the soil in the unsaturated zone always remains unsaturated during the course of low intensity rainfall. Furthermore, the slope stability remains practically unchanged so long as the wetting front remains in the unsaturated zone but it decreases noticeably when the wetting front reaches and elevates the ground water table level.

개착사면의 안정성 해석을 위한 횡단면 기법의 활용성 고찰

개착면의 방향성과 규모가 점진적으로 변화되는 개착사면의 안정성을 지반의 암석학적, 구조적 및 역학적 특성을 종합적으로 고려한 횡단면 분석기법을 활용하여 분석하였다. 시추작업을 수행하여 획득한 코어시료를 관찰하여 사면지반의 암석학적 취약성을 조사하였으며, 시추공 내 BIPS 영상을 획득하여 사면 내부의 구조적 특성을 규명하였다. 시추코어 및 코어절리시료를 이용한 암석실험을 통해 사면 지반의 공학적 특성을 분석하였다. 평사투영해석을 수행하여 잠재적인 사면거동 양상과 거동유발 절리들을 분석하였으며, 거동유발 절리들의 트레이스 분포를 개착 형상이 고려된 횡단면상에 도시하였다. 횡단면에 분포된 평면파괴 절리들이 기저면을 형성하는 평면블록들을 절리 트레이스 분포를 고려하여 설정하였다. 횡단면 상에서 심도별 평면블록들의 안정성과 적정 안전율을 유지하기 위하여 요구되는 지보량을 산정하여 최적 사면 설계안 수립에 대한 횡단면 기법의 활용성을 고찰하였다. Stability of cut-slope, the orientation and dimension of which are gradually changed, has been analyzed by employing the cross-section method capable of comprehensibly considering the lithological, structural and mechanical characteristics of slope rock. Lithological fragility is investigated by inspecting the drilled core logs and BIPS image has been taken to delineate the rock structure. Engineering properties of drilled-core including the joint shear strength have been also measured. Potential failure modes of cut-slope and failure-induced joints are identified by performing the stereographic projection analysis. Traces of potential failure-induced joints are drawn on the cross-section which depicts the excavated geometry of cut-slope. Considering the distribution of potential plane failure-induced joint traces blocks of plane failure mode are hypothetically formed. The stabilities and required reinforcements of plane failure blocks located at the different excavation depth have been calculated to confirm the applicability of the cross-section method for the optimum cut-slope design.

Stability analysis and supporting system design of a high-steep cut soil slope on an ancient landslide during highway construction of Tehran–Chalus

The stability of both natural and cut slopes in mountainous areas is a great challenge to highway constructions and operations. This paper presents a successful case study of stability analyses and protection treatments for high-steep cut soil slopes in an ancient landslide zone which was located at Km12+700 to Km15+000 along the Tehran–Chalus highway. This report has three parts. First, geotechnical investigations of in situ direct shear test, SPT tests and laboratory tests were implemented to get the subsurface profiles and the mechanical properties of the soil mass. Second, finite difference analysis was carried out to evaluate the stability of both the natural and cut slopes. Minimum safety factors and potential failure modes of cut slopes were obtained under both static and dynamic conditions. These results indicated that the ancient landslide could not be reactivated under the present climatic and morphological conditions, but there were some potential shallow failures in some cut soil slopes (failure actually occurred during excavation). Protection treatments and reinforcements were thus necessary. Third, the stability of the cut slopes was re-assessed by simplified Bishop limit equilibrium analysis (using Slide 5.0). Some potential failure zones were designed to be protected by back-anchored concrete retaining wall at the slope toe, rock bolts and frame beams on the slope face and planting grass on the slope face. Numerical analysis indicated that these protection measures could stabilize this remedial slope. These practical experiences may be of benefit for similar highway construction projects.

Effect of rock mass disturbance on the stability of rock slopes using the Hoek–Brown failure criterion

The process of creating man made or “cut” slopes in rock invariably leads to stress relief within the rock mass which in turn induces a certain degree of fracturing and disturbance. The level of disturbance can be particularly significant when the slope is formed using blasting techniques. However, the effects of this disturbance on the overall rock slope stability have not been investigated thoroughly in the current literature. In order to account for rock mass disturbance during construction, a disturbance factor has been included in the Hoek–Brown failure criterion [1]. This paper uses finite element upper and lower bound limit analyses to estimate rock slope stability based on the Hoek–Brown failure criterion whilst including the effect of rock mass disturbance. A rigorous set of analyses have been performed where the level of disturbance is considered as constant or linearly varying throughout the slope. The results are then compared to a number of reported case histories for verification purposes. From the results of this study, the disturbance factor was found to have significant influence on the rock slope stability assessment, especially for poorer quality rock masses. Hence, cautious engineering judgement must be exercised when estimating the level of disturbance. In addition, utilising stability charts to estimate the stability of cut rock slopes without considering the rock mass disturbance may lead to significant overestimations.

Evaluating cut slope failure by numerical analysis—a case study

Slope failure is very common phenomenon in hilly regions, especially in young techno active mountainous like Himalayas. It is hazardous because of the accompanying progressive movement of the slope-forming material. In order to minimize the landslide effects, slope failure analysis and stabilization requires in depth understanding of the process that governs the behavior of the slope. The present article mainly deals with the analysis of the stability of road cut slopes of Rudraprayag Area, Uttarakhand, India. The area experiences local as well as regional slides every year. Extensive field study was carried out along the road cut slopes. Laboratory experiments were conducted to determine the various Physio-mechanical properties of rock mass. These properties have been used as input parameters for the numerical simulation of slope using FLAC3D (Fast Lagrangian Analysis of Continua) including geological discontinuities. The computed deformations and the stress distribution along the failure surface are compared with the field observations. The study indicates that the overall slope is unstable except at the location E where slope is critically stable. The effects of instability have been thoroughly considered and remedial measures have been recommended.

A simple method to analyze infiltration into unsaturated soil slopes

Assessment of the stability of embankment and cut slopes over the life of a project are critical issues for railway and motorway infrastructure projects. Experience has shown that many slope failures occur during or shortly after rainfall. Analyses show that failure is initiated by the reduction in near surface suction over some critical depth in the slope. A simple method is proposed in this paper to estimate the time needed for a wetting front to develop. The method which is a modification of the traditional Green–Ampt infiltration model assumes that ponding of water cannot occur on soil slopes and as a consequence soil in the wetted zone remains partially saturated at the point of slope failure. It differentiates between cases where the initial suction in the slope is high and the rate of infiltration is controlled by the rainfall intensity (supply controlled) and, situations where the suction is low, and the rate of infiltration is controlled by the infiltration capacity of the soil (demand controlled). When applied to a case history where field measurements of infiltration into a slope were available the new method provided a reasonable approximation of the measured infiltration time.

Evaluation of cut slope stability to prevent creep failure type landslide damage

Evaluation of cut slope stability to prevent creep failure type landslide damage

Geographic Information System (GIS) based stability analysis of rock cut slopes

Road construction is accompanied with the occurrence of the cut slopes. Therefore, when the roads are constructed in mountainous terrain, the number of slopes is increased and the slopes are widely scattered in the regional area. In addition, the stability of rock cut slope is mainly dependent upon geological characteristics such as discontinuities in rock mass. In this study, the regional stability analysis technique based on Geographical Information System (GIS) was developed and applied to practical case, in which the road construction was planned and the planned cut slopes were widely scattered. GIS is the effective tool to deal with the widely scattered and the enormous number of data. Various factors affecting on the slope stability analysis, such as the structural domain, the orientation and dip angle of the cut slopes, and the friction angle of discontinuities, were considered as the input parameters for GIS. By overlaying input data layers and using the developed computer algorithm, the factor of safety (F.S.) values, as an index of slope stability were calculated for each failure mode, which considered for stereographic analysis and limit equilibrium analysis simultaneously. In this research, the factors of safety for each failure mode are evaluated and the minimum factor of safety is also evaluated in the divided small area. In order to verify the developed analysis method, the results of the cut rock slope stability were compared with actual failure modes and locations in the study area. Finally, the stable and economically appropriate cut angle for the planned rock slopes were suggested by using the developed algorithm and applying allowable F.S. value.

Application of a discontinuity orientation measurement drilling system to the characterization of an in situ rock mass and the prediction of cut-slope stability

Application of a discontinuity orientation measurement drilling system to the characterization of an in situ rock mass and the prediction of cut-slope stability

Guidelines to prevention of slope failure related disasters in granitic bedrock areas of Malaysia

A variety of slope failures have occurred in the granitic bedrock areas of Malaysia; the more important of which are slump and debris flows that have sometimes led to considerable economic loss and loss of life. These failures have occurred at cut and fill slopes, as well as at natural ground slopes, having a varied vegetation cover ranging from primary and secondary forest to agricultural crops and grass. The failures have mainly involved weathered materials from morphological Zones I and II of the weathering profiles (or rock mass weathering grades 3 to 6) over granitic bedrock. Several factors are responsible for the failures, though the main cause is saturation and loss of negative pore water pressures within slope materials as the failures have mostly occurred during, or following, short periods «3 he) of intense rainfall (when total rainfall >70 mm), or longer periods (>1 day) of continuous rainfall. In order to prevent slope failure related disasters, it is necessary to evaluate the various factors that give rise to the failures. The regional and local topographic settings of any site or area proposed for development needs to be first evaluated in order to allow recognition of the earth materials present and the earthworks that may be necessary. Evaluation of the local topographic setting is particularly important as the location of buildings and other structures needs to be considered with reference to the surrounding terrain. Surface and subsurface drainage patterns at the proposed site and surrounding area should then be evaluated as they influence variations in moisture contents and pore water pressures within slope materials. Stream channels and valleys also directly control the movement of debris flows in hilly to mountainous terrain. The rainfall at the proposed site and surrounding area also needs to be monitored in order to allow recognition of significant rainfall intensities and/or durations that increase the likelihood of slope failures. The vegetation cover at the proposed site and surrounding area also needs to be monitored as changes in this cover can also give rise to variations in moisture contents and pore water pressures within slope materials. The stability of cut and fill slopes associated with earthworks at the proposed site or area should finally be evaluated. Consideration and evaluation of all these factors will serve as guidelines that can prevent slope failure related disasters in the granitic bedrock areas of Malaysia.

Stability of Cut Slopes Against Shallow Failure: Evaluation by Neural Network Model

The discrimination model for road cut slope stability was used to assess 216 cut slope locations on the Chuo Expressway. This model ranks the failure probability of slopes by the rainfall threshold (cumulative precipitation that causes the slope to fail) to identify slopes highly prone to collapse. Because of the complexity (nonlinearity) of the relationship between the factors relating to the cut slope failure and the precipitation that triggers a failure, it has been difficult to correctly evaluate the likelihood of failure for cut slopes. The developed model has overcome that difficulty by involving the neural network as the discrimination technique. The input data included the different factors (topography, soil properties and geology, surface layer status, change in state) in the stability investigation table prepared at the time of road slope inspection, with additional information such as catchment topography. The cut slope data were prepared, referring to a variety of information encompassing the failure history for 30 years after the commencement of service, the rainfall record at the time of failure, the maximum rainfall amount ever recorded, and the data on the status of slope protection around the time of failure. As shown by the discrimination results, the model accuracy (ratio of correct answers to number of slopes evaluated) was as high as approximately 80%, which allowed accurate determination of the amounts of rainfall inducing the failure of different slopes.