Geometry Of Slip Surface Research Articles

Inferring slip-surface geometry and volume of creeping landslides based on InSAR: A case study in Jinsha River basin

The slip-surface geometry and volume of landslides are fundamental for landslide modeling and mechanism interpretation. The movement of a landslide, which is generally controlled by the slip-surface geometry, can be obtained from interferometric synthetic aperture radar (InSAR) measurements. However, there is a lack of a general approach for inferring the slip-surface geometry and volume of landslides through the InSAR-derived deformation field. Here we developed a geometry-based method to determine the landslide slip-surface geometry and volume using InSAR measurements and applied it to the Jinsha River Basin, a landslide-prone area that poses a significant threat to residents and infrastructure. Through the InSAR-derived displacement, topography, and Google Earth images, 50 creeping landslides were identified in the study area. Based on the displacement field, the landslide slip-surface slope was inverted under the assumption that the landslide displacement was parallel to the slip-surface. Then the two-dimensional slip-surface depths and volumes of selected landslides were inferred using the slip-surface slope. Comparisons with the in-situ data suggest that the results obtained in this study are reliable. The mapped landslides in the study area have depths of approximately 16–160 m along the central axis and volumes ranging from 483,412 to 135,789,944 m3. The derived volume–area relationship and 2D slip-surface depth suggest that deep-seated landslide is a major landslide type in the study area. We conclude that our method can infer the slip-surface geometry of creeping landslides based on InSAR observation and our results have improved the understanding of the landslide mechanisms in the Jinsha River Basin, China.

NURBS Surface-Altering Optimization for Identifying Critical Slip Surfaces in 3D Slopes

The evaluation of slope stability of a three-dimensional slope requires identifying the critical slip surface with the minimum factor of safety, which is a complex optimization problem. Failure to identify the critical slip surface can lead to unconservative conclusions about the stability of a slope. This paper proposes a novel 3D surface-altering optimization method, which iteratively alters the geometry of a 3D slip surface to find the critical slip surface representing the minimum factor of safety in a slope. The geometry of the slip surface is defined via nonuniform rational basis spline (NURBS) curves formed over a plan grid of control points. The proposed method includes a series of five subroutines that apply various forms of transformations to the control points. These subroutines include minimization problems, which determine the optimal transformation parameters for minimizing the obtained factor of safety of the resulting slip surfaces. Given that any geometrically defined slip surface can be approximated using an equivalent series of NURBS control points, the proposed method can be used in efforts to further reduce the global factor of safety first obtained via conventional search methods, such as those involving spherical or ellipsoidal slip surfaces. To demonstrate its effectiveness, the proposed method was applied to further optimize the critical ellipsoidal slip surfaces reported in some numerical examples. Comparing the results with those limited to ellipsoidal slip surfaces, the proposed method was consistently able to identify slip surfaces with significantly lower factors of safety. The postaltered slip surfaces also matched closely with finite element shear strength reduction results. As such, the proposed method is effective in searching for critical slip surfaces and can be used as a final step in the critical surface searching routine.

Performance of two-tiered reinforced-soil retaining walls under strip footing load

In the current study, an attempt was made to investigate the performance of two-tiered mechanically stabilized earth walls (T-TMSEWs) under static footing loading using reduced-scale model tests. For this purpose, twenty-four T-TMSEW models were constructed with three different types of reinforcement (metal strips, geogrid and geostraps) and were loaded using the rotatable and non-rotatable strip footings in different distances to the wall crest. Findings indicated that, although decreasing the reinforcement stiffness and the soil-reinforcement interaction reduces the ultimate bearing capacity of footings, the use of extensible reinforcements with low pull-out capacity and allowing the footing to tilt can be two effective solutions in T-TMSEWs to minimize deformations of backfill surface and connection loads as well as lateral pressures. It was observed that the use of a two-tiered configuration in MSE walls and also reducing tensile stiffness and soil-reinforcement interaction simultaneously, not only lead to change in the slip surface geometry but also prevent the development of deep slip surfaces in the lower tier. On the other hand, increasing the footing distance to the wall crest in the range of reinforced zone was found to be another influential solution to improve the bearing capacity, reduce wall deformations and also minimize lateral pressures.

Stress Patterns and Failure Around Rough Interlocked Fault Surface

AbstractFault zones accumulate stress during interseismic periods and release it by slip along fault surfaces. We explore the effect of fault roughness on stress patterns and failure conditions around interlocked fault surfaces using an analytical approach. Measured slip surface geometry of different fault outcrops parallel to the slip demonstrates surface roughness at outcrop scales generally confined between 0.001L0.5 and 0.01L0.8, where L is the section length. These two power law end‐members are utilized for exploring the influence of scale‐dependent geometrical undulations on stress and failure conditions. Off‐fault static stress pattern is calculated based on perturbation theory. Stress amplification and failure conditions around the surfaces are controlled by the ratio between roughness amplitude to wavelength, and therefore, small power values increase failure associated with short roughness wavelengths, immediately nearby the interface. Increasing both amplitude to wavelength ratio and amplitude heights enhance failure in zones around the interface, but at the same time decreases stress and blocks yielding in other zones. In contrast, failure around faults with smaller amplitude heights initiates at larger external loads, and therefore, more elastic energy is available for slip when failure occurs. Calculations of stress around fractal and nonfractal interfaces indicate that failure nucleation and locations are strongly dependent on the initial surface geometry. We suggest that stress asperities and barriers throughout the seismic cycle can be driven by the geometrical irregularities of the fault surface.

Limit Equilibrium Stability Analysis of Layered Slopes: a Generalized Approach

Traditionally, application of the conventional logarithmic spiral in limit equilibrium (LE) analyses has been limited to homogenous materials. Herein, a modification of the conventional logarithmic spiral LE approach is proposed to account for transitions in soil conditions and provide insight into the internal statics associated with this approach, termed the compound log-spiral (CLS). Comparing both factor of safety (FS) and failure surfaces for a range of frictional strength combinations, the CLS approach demonstrates good agreement with results derived from both generalized, commercially available rigorous LE analyses and finite element analyses. The utility of the CLS method is further demonstrated through an example where the stability of a heavily stratified seacliff is considered. The proposed method satisfies equilibrium at a limit state without resorting to internal statistical assumptions associated with traditional LE approaches. Furthermore, it enables the explicit determination of internal statics, such as inter-slice shear forces, inter-slice normal forces, inter-slice angle, line of thrust, and normal stress distributions, which is a less-than-trivial task for the complex slip surface geometry realized in heterogeneous slope failures. Subsequently, the reasonableness of results could be assessed.

Heterogeneous Coulomb wedges: Influence of fluid pressure, porosity, and application to the Hikurangi subduction margin, New Zealand

AbstractDespite the widespread use of critical Coulomb wedge models, the effects of internal heterogeneities have been largely overlooked. Here we consider how spatial variations in pore pressure and porosity within an accretionary prism affect predictions of shear traction along the base of the prism and the internal slip surface geometry. Compared to Coulomb wedge models that use depth‐averaged parameter values, the basal shear traction will be lower if (i) the pore pressure ratio increases monotonically with depth, (ii) the porosity decreases monotonically with depth, or (iii) the internal friction coefficient decreases monotonically with depth. The first two conditions can be considered first‐order descriptions of many natural settings. To illustrate their effects, we consider two specific functional forms: a linear increase in the pore pressure ratio and an exponential decrease in porosity with depth within the prism. Both cases separately can be completely accounted for by simple modifications to the solution for a homogeneous Coulomb wedge. We show that including heterogeneity in the pore pressure ratio and the porosity, together or separately, can lead to large reductions in the basal shear traction, compared to wedges with relevant depth‐averaged parameters. Finally, we apply our results to the Hikurangi margin at the North Island of New Zealand and show that lateral increases in the pore pressure ratio lead to further reductions in basal shear traction.

Closed-Form Solution for Stability of Slurry Trenches

AbstractThis paper presents a variational limit equilibrium closed-form solution for the stability of slurry-supported trenches in cohesive soil, frictional cohesive soil, and cohesionless soil. Study results indicate that the critical slip-surface geometry is either planar or log spiral. The normal stress distribution, which indicates the likely depth of a tension crack at the crest over the slip surface, was also obtained as part of the complete solution and as a function of groundwater-table level. The closed-form solution was used to produce stability charts for a practical range of parameters. The charts can be used to conveniently assess the stability of a given slurry trench for preliminary design. The paper gives two different examples for trenches to illustrate the influence of the slurry level on the trench stability. To introduce the analytical solution, this study is limited to a simple slurry trench problem; however, extension of the present framework to deal with complex problems would be st...

Kinematic Segmentation and Velocity in Earth Flows: A Consequence of Complex Basal-slip Surfaces

We investigated relations between geomorphic structures, movement velocity, and basal-slip surface geometry within individual kinematic domains of two large earth flows in the Apennine Mountains of southern Italy: the “Montaguto” earth flow and the “Mount Pizzuto” earth flow. Our analyses indicated that the earth flows are composed of distinct kinematic zones characterized by specific deformational patterns and longitudinal velocity profiles. Variations in velocity within individual kinematic zones is controlled by the geometry of the basal-slip surface, and, in particular by local variations in slope angle. Slip-surface geometry and slope also seem to control the density of extensional structures in driving earth-flow elements.

Stability analysis of sandy slope considering anisotropy effect in friction angle

This paper aims to investigate the effect of anisotropy of shear strength parameter on the stability of a sandy slope by performing the limit equilibrium analysis. Because of scarcity of mathematical equation for anisotropic friction angle of sand, at first, all results of principal stress rotation tests are processed by artificial neural network and a computational procedure is developed for determining sand friction angle subjected to various loading directions. By implementing this procedure, slope stability analysis is performed in both isotropic and anisotropic conditions. The results indicate that while isotropic slope stability overestimates the factor of safety between 5 and 25% which the deviation is more for flatter slope, the location of critical slip surface is coincident in both conditions. Also in specific slip surface, the parameters of face angle, geometry of slip surface and soil properties relating to anisotropy are the main factors governing the result of anisotropic slope stability.

Influence of slip-surface geometry on earth-flow deformation, Montaguto earth flow, southern Italy

We investigated relations between slip-surface geometry and deformational structures and hydrologic features at the Montaguto earth flow in southern Italy between 1954 and 2010. We used 25 boreholes, 15 static cone-penetration tests, and 22 shallow-seismic profiles to define the geometry of basal- and lateral-slip surfaces; and 9 multitemporal maps to quantify the spatial and temporal distribution of normal faults, thrust faults, back-tilted surfaces, strike-slip faults, flank ridges, folds, ponds, and springs. We infer that the slip surface is a repeating series of steeply sloping surfaces (risers) and gently sloping surfaces (treads). Stretching of earth-flow material created normal faults at risers, and shortening of earth-flow material created thrust faults, back-tilted surfaces, and ponds at treads. Individual pairs of risers and treads formed quasi-discrete kinematic zones within the earth flow that operated in unison to transmit pulses of sediment along the length of the flow. The locations of strike-slip faults, flank ridges, and folds were not controlled by basal-slip surface topography but were instead dependent on earth-flow volume and lateral changes in the direction of the earth-flow travel path. The earth-flow travel path was strongly influenced by inactive earth-flow deposits and pre-earth-flow drainages whose positions were determined by tectonic structures. The implications of our results that may be applicable to other earth flows are that structures with strikes normal to the direction of earth-flow motion (e.g., normal faults and thrust faults) can be used as a guide to the geometry of basal-slip surfaces, but that depths to the slip surface (i.e., the thickness of an earth flow) will vary as sediment pulses are transmitted through a flow.

Discrete element modeling of a rainfall-induced flowslide

The mass movements of flowslides are rarely monitored in field attributed to their sudden failure and rapid movement characteristics. Numerical modeling provides an alternative way to provide an insight into these mechanical behaviors. This paper presents an application of the discrete element method (DEM) for simulating the movement of an actual flowslide using a calibration-based approach. The effect of fluidization was simulated by calibrating the residual friction coefficient at the slip surface. The calibration results showed that the residual friction coefficient played an important role on the travel distance, height and surface of deposits, while the stiffness ratio ks/kn has a negligible effect on the simulation output. The use of the constant residual friction coefficient implies that only the undrained behavior of the flowslide was modeled. This simplification is suitable for the 2D simulation which neglects the lateral spreading effect. The geometry of slip surface has a great influence on the deformation of sliding mass, while the geometry of slip surface significantly affects the velocity of traveling mass.

General Slice Method Based on Rigorous Equilibrium to Solve the Factor of Safety

For a general slice, force and moment equilibrium equations are developed, the recurrence equations of inter-slice force and inter-slice moment are derived, the general formulation based on rigorous equilibrium to solve the factor of safety is studied, hence, the theoretical framework of rigorous method of general slice is developed, rigorous method of vertical slice is a special case of it. Analyzing the applicability of Sarma’s method, two new inter-slice shear force equations are presented based on the compatible relationship among slice’s displacements by leading in the scaling parameter λ and inter-slice force function f(x),hey make the relationship between the inter-slice shear forces and slip surface geometry clear, and indicate that the reduction factor for shear strength along inter-slice boundaries varies from one boundary to the next depending on the geometry of the slices and the slip surface. The rigorous methods of general slice can be developed based on the modified inter-slice shear force equations, they think that the reduction factor for shear strength along inter-slice boundary is different from that for shear strength along slip surface. The example analysis indicates that the proposed new methods work better than Sarma’s method, the reasonable value of safety factor can be obtained by using them. Even if the shape of slice is varied, the proposed new methods can also give consistent values of safety factor and ensure that the iteration is stably convergent.

Meta-Analysis of 301 Slope Failure Calculations. I: Database Description

Since the early part of the twentieth century, two-dimensional limit equilibrium (2DLE) analysis has been the scientific community’s primary means of slope stability calculation. However, it is well established that the input parameters to 2DLE, namely, soil strength and anisotropy, slope geometry, pore water pressures, failure surface geometry, applicable correction factors, and loading conditions are all inherently uncertain. Effective modeling must account for these uncertainties statistically. Unfortunately, most of the key statistical parameters, such as the safety factor statistical distribution and standard deviation (sd), are unknown and must be estimated by the analyst. In response to this growing need for statistical information, a database was established from the literature of 157 different failed slopes and the corresponding published 301 safety factor (SF) calculations. The database, which covered more than five decades of slope stability research, also included a number of the slope stability factors, including analytical method used, stress approach (effective versus total), assumed slip surface geometry, slope type, applied correction factors, and soil Atterberg limits. A temporal analysis found no evidence that SF prediction or deviation had significantly changed. A log (base 10) normal distribution was found to adequately describe the SF data, with a (nontransformed) mean of 1.03 and a (transformed) sd of 0.087, but the pronounced curvature of the residuals indicated significant, unresolved slope factors, further investigated in the companion paper.

Meta-Analysis of 301 Slope Failure Calculations. II: Database Analysis

In response to the growing need for statistical information regarding slope stability risk analysis, this work applies inferential analysis to a compiled database of 157 failed slopes and corresponding 301 safety factor (SF) calculations. As presented in the companion paper, this database also includes a number of slope stability factors, including analytical method used, stress approach (effective versus total), assumed slip surface geometry, slope type, applied correction factors, and soil Atterburg limits. Although the SF data were found to be fairly well fit by a lognormal distribution, pronounced curvature of the residuals was observed, likely related to various unaccounted slope factors. In response, inferential statistics are used in this paper to analyze the effects of analytical method, slope type, soil plasticity, and effective versus total stress analysis. ANOVA hypothesis testing indicated significant differences between analytical methods and significant interactions between slope types and pore-water stress approaches. Direct SF calculation methods, such as infinite slope, wedge, and the ordinary method of slices were found to produce SF near 1 as expected, but higher order methods in general, and force methods in particular, predicted safety factors significantly greater than 1. Clay content alone was not a discernible influence on SF calculations. A reduced factor ANOVA model was developed to predict SF, given analytical method (a main effect) and the interactions between analytical method with both slope type and pore-water pressure approach.

Quantitative analysis and visualization of nonplanar fault surfaces using terrestrial laser scanning (LIDAR)--The Arkitsa fault, central Greece, as a case study

Many fault surfaces are noticeably nonplanar, often containing irregular asperities and more regular corrugations and open warping. Terrestrial laser scanning (light detection and ranging, LIDAR) is a powerful and versatile tool that is highly suitable for acquisition of very detailed, precise measurements of slip-surface geometry from well-exposed faults. Quantitative analysis of the LIDAR data, combined with three-dimensional visualization software, allows the spatial variation in various geometrical properties across the fault surface to be clearly shown. Plotting the variation in distance of points from the mean fault plane is an effective way to identify culminations and depressions on the fault surface. Plots showing the spatial variation of surface orientation are useful in highlighting corrugations and warps of different wavelengths, as well as cross faults and fault bifurcations. Analysis of different curvature properties, including normal and Gaussian curvature, provides the best plots for quantitative measurements of the geometry of corrugations and folds. However, curvature analysis is highly scale dependent, so requires careful filtering and smoothing of the data to be able to analyze structures at a given wavelength. Three well-exposed fault panels from the Arkitsa fault zone in central Greece were scanned and analyzed in detail. Each panel is markedly nonplanar, and shows significant variation in surface orientation, with spreads of ~±20°–25° in strike and ±10° in dip. Most of the variation in orientation reflects decimeter- and meter-scale corrugations and longer wavelength warps of the fault panels. Average wavelengths of corrugations measured on two of the panels are 4.04 m and 4.43 m. Whereas the orientations of the three fault surfaces show significant variations, the orientations of fault striae are very similar between the panels, and are tightly clustered within each panel. Fault-slip analysis from each panel shows that the local stress field is consistent with the regional velocity field derived from global positioning system data. The oblique slip lineations observed on the fault panels represent a combination of two contemporaneous strain components: north-northeast–south-southwest extension across the Gulf of Evia and sinistral strike slip along the west-northwest–east-southeast Arkitsa fault zone.

Application of spatial prediction techniques to defining three-dimensional landslide shear surface geometry

This study explores the application of interpolating and non-interpolating spatial prediction algorithms to interpreting shear surface geometries. A number of spatial prediction techniques have been tested, and the most appropriate algorithms for the Downie Slide dataset have been selected based on the root mean squared error (RMSE) determined from cross-validation. Visual assessment of reasonable spatial patterns has allowed for final selection of algorithms that produce geologically realistic results. Through this process, the performance of a number of interpolation algorithms has been tested in terms of accuracy and the development of reasonable spatial patterns. The goal of this study has been: (a) to develop a methodology for interpolating three-dimensional shear surface geometries and (b) to assess which interpolation methods are most appropriate for the interpretation of the Downie Slide basal slip surface geometry, based quantitatively on RMSE and qualitatively on the geological “trueness” of the geometric output.

Experimental analysis of groundwater flow through a landslide slip surface using natural and artificial water chemical tracers

AbstractArtificial and natural tracer tests combined with high accurate electronic distancemeter measurements are conducted on a small landslide with a well known slip surface geometry. Outflow yields and chemical contents are monitored for all the experiment duration and they analyzed to estimate the slip surface hydraulic parameters. The main result is that the slip surface acts as a drain for groundwater flows that evacuates interstitial pressures in the slope and brings the sliding mass to be more stable one. Copyright © 2007 John Wiley & Sons, Ltd.

A plastic flow model for the Acquara–Vadoncello landslide in Senerchia, Southern Italy

A previously developed model for stress and velocity fields in two-dimensional Coulomb plastic materials under self-weight and pore pressure predicts that long, shallow landslides develop slip surfaces that manifest themselves as normal faults and normal fault scarps at the surface in areas of extending flow and as thrust faults and thrust fault scarps at the surface in areas of compressive flow. We have applied this model to describe the geometry of slip surfaces and ground stresses developed during the 1995 reactivation of the Acquara–Vadoncello landslide in Senerchia, southern Italy. This landslide is a long and shallow slide in which regions of compressive and extending flow are clearly identified. Slip surfaces in the main scarp region of the landslide have been reconstructed using surface surveys and subsurface borehole logging and inclinometer observations made during retrogression of the main scarp. Two of the four inferred main scarp slip surfaces are best constrained by field data. Slip surfaces in the toe region are reconstructed in the same way and three of the five inferred slip surfaces are similarly constrained. The location of the basal shear surface of the landslide is inferred from borehole logging and borehole inclinometry. Extensive data on material properties, landslide geometries, and pore pressures collected for the Acquara–Vadoncello landslide give values for cohesion, friction angle, and unit weight, plus average basal shear-surface slopes, and pore-pressures required for modelling slip surfaces and stress fields. Results obtained from the landslide-flow model and the field data show that predicted slip surface shapes are consistent with inferred slip surface shapes in both the extending flow main scarp region and in the compressive flow toe region of the Acquara–Vadoncello landslide. Also predicted stress distributions are found to explain deformation features seen in the toe and main scarp regions of the landslide.

Contribution of multi-temporal remote sensing images to characterize landslide slip surface ‒ Application to the La Clapière landslide (France)

Abstract. Landslide activity is partly controlled by the geometry of the slip surface. This activity is traduced at the surface by displacements and topographic variations. Consequently, multi-temporal remote sensing images can be used in order to characterize the geometry of landslide slip surface and its spatial and temporal evolution. Differential Digital Elevation Models (DEMs) are obtained by subtracting two DEMs of different years. A method of multi-temporal images correlation allows to generate displacement maps that can be interpreted in terms of velocity and direction of movements. These data are then used to characterize qualitatively the geometry of the slip surface of the la Clapière landslide (French Southern Alps). Distribution of displacement vectors and of topographic variations are in accordance with a curved slip surface, characterizing a preferential rotational behaviour of this landslide. On the other hand, a spatial and temporal evolution of the geometry of the slip surface is pointed out. Indeed, a propagation of the slip surface under the Iglière bar, in the W part of the landslide, is suspected and can be linked to the acceleration of the landslide in 1987. This study shows the high potential of multi-temporal remote sensing images for slip surface characterization. Although this method could not replace in situ investigations, it can really help to well distribute geophysical profiles or boreholes on unstable areas.

Interslice Shear Forces in Slope Stability Analyses—A New Approach—

A procedure for limit equilibrium slope analysis based on a realistic consideration of the mobilized interslice shear forces is presented in this paper. This new approach ensures that solutions are kinematically admissible and the possibility of convergence problems, often associated with numerical solutions, is minimized. The proposed approach recognizes the importance of slip surface geometry in estimating interslice shear forces whether vertical or non-vertical slices are used in a limit equilibrium analysis. Illustrative examples are presented and the results shown to be reasonable. The calculated factors of safety based on the new method compare very well with values based on recognized methods of analysis. Yet the method is more direct and enables a proper visualization of the transfer of mobilized normal and shear forces through a sloping soil mass above a potential slip surface. The method also gives consistent results with non-vertical slices even if the shape of non-vertical slices is varied.