Wedge Failure Research Articles

Slope Stability Evaluation based on Empirical Methods and it’s Potential Remedy at Lesser Himalayan Zone (A Case Study of Bhalam-Hill Slope, Kaski)

The study area lies in Bhalam, Kaski district nearly 2 km from Batulechour main district road network near Gandarva community residing near Kali Khola river. The study area is comprises of several lithological factors. Field observation, sampling, lab analysis, geological survey with GPS, compass, geological hammer and tape are the main methods utilize to evaluate slope stability and possibility of failure in the study area. From the study it is found that there are few major discontinuities which play vital role in determining slope failure around the study area. The major failure due to discontinuity are planar failure, wedge failure and somewhere block failure. High ground water table approximately 0.06m, steep slope varying from 25° to 60°, improper road cutting, weathering of rock mass are major factor contributing to rock fall and landslide in the study area. The study also shows FOS<1(0.937 and 0.569) at two different places which is most critical and make slope unstable. SMR is calculated on the basis of RMRb, GSI is calculated on the basis of RQD and UCS is calculated on the basis of empirical methods which uses pulse velocity and porosity chart for determining related equation. The calculated value of RMRb, SMR and FOS shows less stability of study area along Bhalam-Batulechour road section near Kali- Khola river with possibility of impact on Bhalam road bridge and two lane road section. There need a corrective measure in slope for sustainable stability in the long run.

Study on calculation method of lateral characteristics of offshore pile near layered soil slope

In actual pile engineering, the laterally loaded offshore pile built near slope is not embedded in uniform clay or sand seabed, but layered soil seabed of different types and properties. For this purpose, a method is proposed to solve the lateral characteristics of offshore pile installed near layered slope in this paper. Based on the interaction force between layered interfaces and the concept of equivalent depth, an equivalent failure wedge model is constructed to evaluate the ultimate soil resistance of each layer of soil. It is assumed that the horizontal subgrade reaction modulus of sand in each layer changes nonlinearly with depth, while the horizontal subgrade reaction modulus of clay in each layer remains unchanged. And the influence of pile diameter and slope effect on the horizontal subgrade reaction modulus is considered. The results obtained in this paper are compared with the field test results and FE results, and the accuracy of the proposed method is verified. The analysis shows that the smaller diameter has the greater impact on the lateral deflection of pile head under the same growth range of diameter. When the pile diameter changes from 1 D to 1.5 D, the lateral deflection of pile head decreases by 42%.

A Qualitative Slope Stability Assessment of Hill Slopes Using Multiple Integrated Approaches Along Bafliaz – Poshiana (Mughal) Road, Jammu and Kashmir

Abstract Transport, communication and socio-economic activities in the hilly areas are completely dependent on the road network. The road network connecting Bafliaz to Shopian town (known as Mughal Road) plays a vital role in the transportation and other activities of the region. It connects the Kashmir Valley with Jammu city and is strategically very important to the country. Almost the entire road length of Mughal Road is vulnerable to landslide incidences and the events of occurrence/recurrence of landslides indicate that the probability of landslide/slope failure is higher along the road cut slopes during the event of antecedent and heavy rainfall and snowfall events. In order to assess the stability of hill slopes, it becomes of utmost importance to understand the failure mechanism along these slopes. In this regard, the slope stability assessment has been carried out by using multiple integrated approaches like the Markland test of kinematic analysis, Geological Strength Index (GSI), Rock mass classification (RMR), and Slope Mass Rating (SMR) at different locations. The type of failure and direction of potential failures for individual slopes have been identified. The obtained results of RMR vary from 23 to 38 after adjustment rating (poor rock mass), SMR from 0 to 54 (very bad to fair rock mass), CSMR from 0 to 53 (very bad to fair rock mass) and the GSI values range from 35 to 45 (poor to fair rock mass). Markland’s test of Kinematic check reveals that planar and wedge failures are the most common phenomenon along the Mughal Road sector.

Dynamic Response Analysis of Wedge-Shaped Rock Slopes under Harmonic Wave Action

In dynamic disasters involving rock slopes, wedge failures formed by complex structural discontinuities are more predominant, and the dynamic response associated with them remains a classic concern in rock slope engineering. To address this concern, this paper utilized refined modeling to analyze a wedge-shaped rock slope by inputting horizontal harmonics as loads. We conducted dynamic response analyses by varying the inclination of the structural surface on the wedge-shaped rock slope, the axial offset angle, the friction coefficient, and the configuration of the single sliding surface. The results in this paper indicate that for wedge-shaped and single-sliding-surface configurations of rock slopes, with an increase in the structural surface inclination angle, the dynamic response of the sliding body, stress distribution, excellent frequency, and spectrum values all increase. Furthermore, wedge-shaped rock slopes’ dynamic responses are more significant than those of single-sliding-surface rock slopes. For wedge-shaped rock slopes, increases in the axial offset angle and structural surface friction coefficient reduce the dynamic response, excellent frequency, and spectrum values. Meanwhile, within the context of the axial offset angle conditions in wedge-shaped rock slopes, the dynamic response, excellent frequency, and spectrum values are better than the variations in the structural surface friction coefficient. Under the influence of these factors, stress concentration occurs at the sliding fronts of rock slopes.

Slope instabilities and evolution of tectonic geomorphology along the strike of the Main Boundary Thrust zone in the western Himalaya, India

The Main Boundary Thrust (MBT) and Main Boundary Fault (MBF) zones of the southeast Himachal Himalaya are susceptible to various types of mass movement. Several active and in-active landslides are observed along the strike of the MBT. The landslides are mainly controlled by the brecciated and highly fractured nature of the bedrocks, and the intersecting joint sets form wedges. The movements are taking place along the fault planes, fracture planes, and bedding planes; and the types of failure are wedge failure, planar failure, toppling, rock falls, and complex landslides. The various morphotectonic features observed in the study area include fault traces, fault scarps, strath terraces, paleochannels and structurally controlled channels. Fault traces and their associated deformed landforms are the most spectacular tectonic landforms in the area. Along the strike length of the fault traces several linearly arranged sag ponds have formed, in the western segment the fault trace is observed along the MBF and the fault scarp dips south, with a maximum height of about 34 ​m. In the eastern segment the fault trace cut across the MBT, the fault trace is also displaced by transverse faults. Paleochannels and multiple levels of strath and fill terraces collectively indicate the river channel's disequilibrium state concerning the ongoing tectonic activity. The cross-cutting relation and displacement pattern of fault traces indicate later phases of tectonic activity.

Integrated simulation and monitoring to analyze failure mechanism of the anti-dip layered slope with soft and hard rock interbedding

The significant difference between the mechanical properties of soft rock and hard rock results in the complexity of the failure mode of the anti-dip layered slope with soft and hard rock interbedding. In order to reveal the landslide mechanism, taking the north slope of Fushun West Open-pit Mine as an example, this paper analyzed the failure mechanism of different landslides with monitoring and field surveys, and simulated the evolution of landslides. The study indicated that when the green mudstone (hard rock) of the anti-dip slope contains siltized intercalations (soft rock), the existence of weak layers not only aggravates the toppling deformation of anti-dip layered slope with high dip, but also causes the shear failure of anti-dip layered slope with stable low dip. The shear failure including subsidence induced sliding and wedge failure mainly exists in the unloading zone of the slope. Its failure depth and failure time were far less than that of toppling failure. In terms of the development characteristics of deformation, toppling deformation has the long-term and progressive characteristics, but shear failure deformation has the abrupt and transient characteristics. This study has deepened the understanding of such slope landslide mechanism, and can provide reference for similar engineering.

Wedge Failure Analysis and Remedial Measures in Large Unlined Rock Cavern: a Case Study

Wedge Failure Analysis and Remedial Measures in Large Unlined Rock Cavern: a Case Study

Mechanical properties and soil failure process of interface between grouser of tracked mining vehicle and deep-sea sediment

Tracked mining vehicles (TMVs) are key equipment in deep-sea mining systems and can easily slip when walking on soft sediments on the seabed. Thus, it is important to investigate the effect of track parameters and grounding-specific pressure on the shear interaction between mining vehicles and sediment. The sediment was simulated using a mixture of bentonite and water, and a shear test of the track with a single grouser and sediment was conducted. A numerical model of the track–sediment shear test was established, and the shear strength and failure mode of the sediment soil under the track action were examined. The results demonstrate that the peak shear strength of the track–sediment interface increases with an increase in the grounding-specific pressure, gradually increases with an increase in grouser height, and tends to stabilize at a given level of grouser height. Owing to the presence of the grouser, the deep-sea sediment transitions from the elastic state to the plastic state faster than the typical clay during the shear test. The variation law of peak shear strength at the track-sediment interface with the height of track grouser under different grounding-specific pressures was analyzed, and a modified shear stress-displacement relationship model was proposed. Wedge failure is the predominant method of failure for a single-grouser shear sediment soil at various heights. The primary factor affecting the horizontal disturbance range is the grouser height, and the range increases as the grouser height increases; the primary element affecting the vertical disturbance range is the grounding-specific pressure, and the range increases as the grounding-specific pressure increases. The relationship of the grouser height and cohesiveness with the interfacial shear strength was examined and a new shear stress–displacement relationship model that can accurately capture the shear mechanical behavior between the track and sediment under various grouser heights was proposed. In conclusion, the study findings could serve as a guide for the engineering design of a TMV walking system.

Estimation of seismic passive earth pressure coefficients for caissons in c-φ soils with a 3D log-spiral failure wedge

Passive resistance offered by soil to any embedded structure has been of significant interest to researchers since the inception of the concept. The present study deals with the estimation of passive earth pressure coefficients in seismic conditions that will control the passive resistance offered to a caisson embedded in c (cohesion) – φ (friction) soil in presence of surcharge loading. The three-dimensional (3D) geometry of failure wedge (log-spiral in vertical plane and oval in horizontal plane) has been obtained from the results of numerical analysis and past experimental studies. The critical failure surface has been obtained in the presence of all resisting components [unit weight (γ), cohesion (c) and surcharge (q)] by minimizing the passive resistance. Thereafter, seismic passive earth pressure coefficients for cohesion component (Kspc), surcharge component (Kspq) and unit weight component (Kspγ) have been obtained separately corresponding to the critical failure wedge obtained in the previous analysis. Limit equilibrium method of analysis in conjunction with pseudo-static approach has been used to perform the analyses. Charts for a variety of caisson geometry, soil and site condition and seismic condition have been prepared to facilitate prediction of passive resistance in a more economical and reliable manner since unique failure wedge has been considered for all the components instead of separate failure wedge which would be impractical.

Rock slope kinematics analysis by Markland method of the Bener District, Purworejo Regency, Central Java, Indonesia

Bener District, Purworejo Regency, Central Java, Indonesia, located in the Kulon Progo Mountains can be classified as a high-risk area. Many experts and researchers have studied landslides, but there has been little research on rock slope kinematics. In fact, when such a rock slope is unstable and poorly monitored, it has the potential to endanger the community or facilities at the adjacent site. This is why slope kinematics research is required. To complete this study, rock kinematics analysis using the Markland method was performed on six representative slopes. The assessment results show that Kaliwader slope A, Kaliwader slope B, and Argosari slope each tend to collapse with wedge failure, Kaliwader slope D and Wadas slope have the potential for wedge failure and planar slide, but Kaliwader slope C does not. Despite their steep inclination, slopes that are likely to fail are strongly related to the presence of geologic structures, particularly joints, and faults, at the sites. The findings of this study will be helpful in the development of landslide vulnerability zones in the context of disaster mitigation.

Lateral ultimate bearing capacity of modified suction caisson in uniform and linearly increasing strength undrained clays

AbstractThe modified suction caissons (MSCs) have a cylindrical external skirt surrounding the top of the traditional suction caisson to increase the horizontal bearing capacity. MSCs will be subjected to inclined lateral loadings for anchoring offshore floating facilities, and the maximum lateral bearing capacity will be reached when the loading direction passes through the rotation center of the MSCs to generate horizontal translation in the seabed. This paper proposed an analytical model consisting of a meniscus failure wedge near the mudline and a purely lateral flow‐around mechanism in deeper soil for MSCs moving laterally in clays. The upper‐bound analysis is conducted to obtain the ultimate bearing capacity of MSCs by optimizing only one parameter to approach the critical failure mechanism that offers the minimum energy dissipation. The influences of the external skirt length (L) and radius (R) and adhesion factor (λ) at the caisson‐soil interface on the bearing capacity of MSCs are investigated. The finite element limit analysis (FELA) results are used to verify the rationality of the presented failure mechanisms and upper‐bound predictions. It is proved that the presented upper‐bound analyses can well predict the lateral ultimate bearing capacity of the MSCs with a horizontal translation failure.

Theoretical Evaluation for Soil Thrust of Single-Track System over Clay Slope via Upper Bound Analysis

This study aimed to theoretically evaluate soil thrust on a clay slope as a reaction force associated with the motion of an off-road tracked vehicle. The existing concept of the potential failure modes of a clay block on flat ground has extended to determine the soil thrust of sloped clay ground. Based on the upper-bound limit analysis, the soil thrust under the most critical failure was derived for three potential failure modes: block, triangular-wedge, and trapezoidal-wedge failures. Specifically, the influence of the slope angle, the shear strength of clay, the weight of a vehicle, and the geometry of a track system on the soil thrust was investigated. Only the block and triangular wedge failure modes were able to occur, and the geometry of a single-track system could lead to different failure modes. Under the block failure mode, the soil thrust decreased as the slope became stiff, and the vehicle weight increased. On the other hand, the soil thrust decreased as the slope angle decreased under the triangular-wedge failure mode.

Toward a Plausible Methodology to Assess Rock Slope Instabilities at a Regional Scale

Slope failures along road cuts and highways, occurring due to heavy rainfalls or earthquakes, pose significant threats to people, vehicles, and emergency plans. In the present study, a methodology to assess the stability of rock slopes at a regional scale is proposed using a kinematic analysis and a probabilistic limit equilibrium analysis for plane sliding and wedge failure modes. The workflow adopted is described through its implementation along the main road network of the island of Thasos, located in northern Greece. On-site investigations and measurements along the island’s road network formed the basis of the present study. The results of the kinematic analysis showed that the joint sets, which were identified during the on-site investigations, formed critical intersections that could lead to wedge and plane sliding failures. The on-site measurements and the results of the kinematic analysis were utilized to perform limit equilibrium back-analyses at sites of identified failures due to the water pressure effects to probabilistically estimate the material strength properties of the joints. Subsequently, numerous limit equilibrium analyses were executed within a Monte Carlo simulation framework to produce representative fragility curves of rock slopes against plane sliding and wedge failures along the main road network, due to earthquake loading and water pressures.

Geoenvironmental GIS development to investigate Landslides and Slope Instability along Frontal zone of Central Himalaya

The Frontal Himalayan terrain comprises of Lesser Himalaya and Siwalik Hills; is highly susceptible to landslide disaster due to active tectonics, scrappy geology, steep slope, and reshaping geomorphology. Besides that, hydrological impacts of land use degradation and climate change enhancing the vulnerability of the terrain. Keep in view this; the Dabka watershed, falls in frontal zone of central Himalaya has been selected for case illustration. Geospatial analysis advocates that the areas of the most stressed geo-environment (comprises of very steep slopes above 30°, geology of Lower Krol and Lariakanta formation, geomorphology of moist areas and debris sites and land use of barren land) have high density (5–10 landsides km2) of landslides whereas the areas of least stressed geo-environment (comprises of gentle slopes below 10°, geology of Kailakhan and Siwalik formation, geomorphology of depositional terraces and land use of dense forest) have low density of landslides (2 landsides km2). Out of total 340 landslides in the region, 198 are active landsides whereas 51 and 91 are reactivated and old landsides respectively. Geospatial analysis of landslide areas reveals that across the region total 804.33 ​ha land has been degraded by landslides which account for 11.65% of the total area of the Dabka watershed. The wedge failure analysis suggests that there are 3–4 sets of rock joints across the region and most of the sites are unsafe as their safety factors are less than 1.

Stochastic kinematic analysis of rock slope failure angle based on multi algorithm optimization, a case study of the proposed bridge project

ABSTRACT Due to the randomness and complexity of the discontinuity distribution, it is always complicated to analyse the three-dimensional stability problem of discontinuity-controlled rock slope in the field of engineering geology. Specifically, when restricted by poor sampling conditions, the discontinuity data obtained are very limited. To solve this problem, we propose a stochastic kinematic method to estimate the slope failure angle based on limited data. Taking the high-steep rock slope on the right bank of a proposed bridge as an example, the stochastic kinematic method based on multiple algorithms (Monte Carlo simulation, Latin hypercube, and Bayesian estimation) is used to analyse the failure angles of potentially unstable blocks in two modes of plane and wedge failure. After statistical optimisation, the slope failure angles are determined to be 65.69° (plane failure) and 58.65° (wedge failure); this approach is more objective than the empirical formula method and can be used as the basis for judging the slope stability. The method proposed in this study fully considers the randomness of discontinuity distribution and combination, and can use limited sample data to realise failure angle analysis and stability judgement. The result is important as a reference of significance for engineering construction and disaster prevention.

Seismic passive earth pressure resistance for caisson in layered soil using modified pseudo‐dynamic approach

AbstractThe determination of seismic passive earth pressure resistance is of utmost importance during the analysis of geotechnical structures. In the present study, seismic passive earth pressure coefficient for caisson embedded in n‐layered soil is computed using modified pseudo‐dynamic method. Limit equilibrium method of analysis considering poly‐planar failure wedge has been adopted in the study and parametric variation of geometry of failure wedge has also been studied. The current study proposes formulation for variation of horizontal and vertical seismic acceleration profile with depth through various layers and studies the effect of number of layers, relative depths of various layers and relative soil friction angle in those layers, soil‐wall friction angle, horizontal and vertical seismic acceleration coefficients and normalized width of caisson. The study has been extended for submerged soil and the effect of excess pore pressure has been investigated. The results of the present study have been compared with previous theoretical studies and found to be in good agreement. It is observed that the extent of failure wedge formed in front of caisson increases with increasing soil friction angle, soil‐wall friction angle, horizontal seismic acceleration coefficient and width of caisson.

3D Discrete Fracture Network Modelling from UAV Imagery Coupled with Tracer Tests to Assess Fracture Conductivity in an Unstable Rock Slope: Implications for Rockfall Phenomena

The stability of a rock slope is strongly influenced by the pattern of groundwater flow through the fracture system, which may lead to an increase in the water pressure in partly open joints and the consequent decrease in the rock wall strength. The comprehension of the fracture pattern is a challenging but vital aspect in engineering geology since the fractures’ spatial distribution, connectivity, and aperture guide both the water movement and flow quantity within the rock volume. In the literature, the most accepted methods to hydraulically characterise fractured rocks in situ are the single borehole packer test, the high-resolution flow meters for fractures, and the artificial tracer tests performed in boreholes. However, due to the high cost a borehole requires and the general absence of wells along coastal cliffs, these methods may not be appropriate in rockfall-prone areas. In this study, an unsaturated rocky cliff, strongly affected by rockfalls, was investigated by combining kinematic analysis, Discrete Fracture Network (DFN) modelling, and artificial tracer tests. The DFN model and potential rock block failure mechanisms were derived from high-resolution 3D virtual outcrop models via the Structure from Motion (SfM) photogrammetry technique. An artificial tracer was injected using a double ring infiltrometer atop the recharge zone of the slope to determine the infiltration rate and validate the DFN results. The DFN and tracer test methods are frequently used at different spatial scales and for different disciplines. However, the integration of digital photogrammetry, DFN, and tracer tests may represent a new step in rockfall and landslide studies. This approach made possible the identification of groundwater flow patterns within the fracture system and revealed about a 10-day tracer transit time from the injection area and the monitored slope, with similar conductivity values gathered from both the DFN and tracer test. Planar and wedge failures with volumes ranging from 0.1 and 1 m3 are the most probable failure mechanisms in the areas. The results were consistent with the delay between the intense rainfall and the slope failures previously documented in the study area and with their mechanisms.

Calculation of active earth pressure on external corners with equal length on both sides in excavation engineering

Taking the external corner with equal lengths as the research object, two failure modes of the equilateral external corner are established, and the active earth pressure calculation formula of the equilateral external corner in the limit state is further deduced when the external angle is 90°. The comparison between the theoretical calculation results and Midas/GTS simulation results shows that when the ratio of the side length B to the depth H is large, the sliding wedge failure will occur at the external corner, and the active earth pressure of the external corner in the range of wedge-shaped slider will not change with the change of size B. When the ratio of the side length B to the depth H is small, the displaced soil is composed of two parts, and the earth pressure varies with the change of size B. In this paper, the magnitude and distribution law of the active earth pressure obtained by the horizontal micro-layered limit equilibrium analysis method is similar to the three-dimensional simulation value of the Midas/GTS software, which can prove the feasibility and rationality of the theoretical calculation.

Numerical investigation and estimation of active earth thrust on gravity retaining walls under seismic excitation

Earthquakes can create severe damage to retaining structures. A numerical study is carried out to understand the seismically induced active earth pressure force on free-standing gravity retaining walls. Dynamic behavior in terms of acceleration amplification/deamplification, deformation mechanism, and earth pressure force are examined. Further, the influence of input peak ground acceleration (PGA), retaining wall height, Young's modulus of the wall, relative density of soil, and soil-structure interaction on total active earth pressure force (Pae) are investigated. The results show that Pae decreases until PGA value is around 0.55 g and later increases for higher values. The primary cause for this response is the loss of wall-soil interaction due to the overturning effect, which dominates until PGA approaches 0.55 g. Also, the generation of failure wedges causes an increase in Pae after 0.55 g. Sensitivity analysis concludes that Pae is highly sensitive to PGA, wall height, and soil-structure interaction. Based on regression analysis, an equation is proposed for the total active thrust. Later, the accuracy of the equation is confirmed by comparing it with the response of FE analysis and established study. This study contributes to developing an equation that is anticipated to provide total active thrust at the initial design stage under comparable work environment.

Development and Application of Methodology for Quantification of Overbreaks in Hard Rock Tunnel Construction

A methodology for determining overbreaks in hard rock tunnel construction using the drill-and-blast technique is presented in this paper. The methodology was developed for and applied to crystalline medium- to thick-bedded limestone, but it can be used in any jointed hard rock mass. Overbreaks are inevitable in hard rock tunnelling in a low-confinement environment (shallow tunnels up to several hundred meters deep) as a result of wedge failures along unfavourably oriented discontinuities caused by blasting. It is widely accepted in engineering practise that overbreaks will be inevitable even if smooth contour blasting is applied. If not controlled, overbreaks can result in extreme financial and time costs; and determining, predicting, and mitigating them is the key to successful tunnel construction in hard rock. Technological overbreaks, which are caused by the inappropriate use of drill-and-blast excavation, are not easily distinguished from the inevitable overbreaks dictated by the geological conditions with which they interfere and overlap. A methodology was developed with the aim of distinguishing the two causes of overbreaks, which can be applied in any phase of tunnel construction for evaluation or mitigation. The analysis of key inputs, including geological face mapping, shear strength tests along discontinuities of the rock mass, and their spatial orientation relative to tunnel advancement and survey overbreak measurements, is presented in this paper. Due to the stochastic and statistical nature of the problem, a probabilistic concept was also applied as part of the method so that the probability of failure around unprotected tunnel sections could be determined. The so-called stability criterion is introduced to distinguish between stable and unstable sections in terms of the probabilistic safety factor. The quantification of overbreaks, including the threshold value distinguishing technological from geological overbreaks, is proposed. The application of the methodology, demonstrated on an 8.1 km long section of a 12 km long pressure tunnel in hard rock, is presented in the paper.