Slope Stability Calculations Research Articles

Jolliet Field Thrust Fault Structure and Stratigraphy, Green Canyon Block 184, Offshore Louisiana

ABSTRACT Jolliet Field is believed to be the first development in the offshore U. S. Gulf of Mexico to exploit a major thrust fault structure and, as such, represents a new and potentially important type of deep-water structural play. The field's multiple, stacked reservoirs consist of Pleistocene lowstand gravity flows deposited in upper slope fans. The thrust fault is documented by 3-D seismic interpretation, repeated paleontologic markers, and correlation of up to 3000 feet of repeated pay section. This fault is believed to be the toe thrust of a major gravity slide which was triggered in the Lower Pleistocene when sediments were tilted to a critical angle by a rising salt diapir. Seismic data suggest that the resulting slide surface is approximately cylindrical, connecting a major growth fault on the west side of Green Canyon Block 184 to the Jolliet Field thrust fault. Salt withdrawal in the area produced normal faults, some of which cut the thrust fault, adding structural complexity to the field. In addition to the geologic and geophysical evidence, the structural model is supported by slope stability computer modelling using realistic sediment shear strengths, densities, and pore pressures.

Experience in using the variational method in slope stability calculations

Experience in using the variational method in slope stability calculations

Rapid design assessments from slope stability calculation results : Bromhead, E N; Harris, A J Proc Symposium on Computer Aided Design and Monitoring in Geotechnical Engineering, Bangkok, 3–6 December 1986P284–300. Publ Bangkok: AIT, 1986

Rapid design assessments from slope stability calculation results : Bromhead, E N; Harris, A J Proc Symposium on Computer Aided Design and Monitoring in Geotechnical Engineering, Bangkok, 3–6 December 1986P284–300. Publ Bangkok: AIT, 1986

Jolliet Field Reverse Fault Structure and Stratigraphy: A Deep Water Development Milestone, Green Canyon Block 184, Offshore Louisiana: ABSTRACT

The Jolliet field is believed to be the first development in the offshore U.S. Gulf of Mexico to exploit a major reverse fault trap. With the world's first tension leg well platform (TLWP) set in 1,760 ft (536 m) of water on the upper continental slope, the field has also set a water depth record for a production platform. The field's multiple stacked reservoirs consist of unconsolidated Pleistocene lowstand fan grain flow, debris flow, and turbidite deposits. Regionally, the area is structurally dominated by four major salt diapirs. The field is structurally complicated by an underlying salt ridge, a major syndepositional reverse fault and late normal faults. Reverse fault documentation includes three-dimensional seismic interpretation, repeated paleontological markers, prediction and correlation of up to 3,000 ft (914 m) of repeated pay section as wll as slope stability computer modeling. One well repeated 18 of 23 known reservoir sands in the subthrust. However, syndepositional movement along the fault created an expanded subthrust section relative to the paleohigh of the overthrust section. A structural model is presented, suggesting that the reverse fault developed at the toe of a major salt flank growth fault. The fault was initiated during the lower Pleistocene as themore » sediment slope was diapirically oversteepened. The resultant failure surface was cylindrically constrained by salt at its lateral limits and by higher density Pliocene shale at depth. This model is supported by slope stability computer modeling using realistic sediment strengths, densities, and pore pressure gradients.« less

Analytical method of calculating slope stability

Methods of calculating slope stability in which the equilibrium conditions are not fulfilled can be used only for preliminary calculations if there are no considerable horizontal loads. In this case, it is recommended to use Terzaghi's method, introducing our proposed correction factor to the frictional forces on the failure surface. In critical calculations it is necessary to use methods in which the equilibrium conditions are fulfilled. They give practically the same results. The proposed analytical method makes it possible to calculate stability without dividing the failure mass into vertical elements (“columns”). It seems to us the most simple and accessible of the rigorous methods.

Foundation Design of Anchored Walls, Bay Springs Lock, Mississippi

Bay Springs Lock, the northernmost structure on the Tennessee-Tombigbee Waterway, was designed for a normal lift of 84 ft. As a result of the high walls and the relatively low strength of the foundation rock, deep and extensive excavations for necessarily large gravity wall monoliths would be required, with attendant high costs. To reduce these costs, an alternate design using anchored wall monoliths was proposed. Because this would be the first such design by the U.S. Army Corps of Engineers, a large test excavation and a great deal of subsurface exploration and laboratory testing was warranted. The rock mass would be an integral part of the lock walls; therefore, selection of realistic and reliable rock design parameters was critical. The geotechnical design included the selection of rock mass strengths, as well as the calculation of foundation settlement, bearing capacity and slope stability. Utilizing the developed foundation data, the lock design was completed and the lock constructed such that the monoliths were anchored to the rock mass with 116 tendons that ranged in length from 80 ft to 175 ft.

地すべり対策杭の挙動と有限要素法による解析

The limit equilibrium method has been used for landslide stability. However, it is difficult to evaluate the quantitative relationship between sliding distance and porewater fluctuation. The slope stability calculation by finite element method combined with joint element is executed to clarify the strain and stress conditions along slip surface, and also to analize the acting stress to steel pile constructed in landslide area. The calculated vesults are relatively good and are in accord with the observed values obtained from actual landslides. In this paper, the approach method of finite element method is discussed.

Consideration of the stress-strain state in calculations of slope stability of earth dams

1. The stability of slopes of earth structures can be estimated directly from solving the appropriate boundary-value problem with modeling of the actual relations between stresses and strains. 2. Even in the simplest cases (a homogeneous “dry” dam under the effect of its own weight and a horizontal seismic load) the proposed method permits refining the surface of sliding and the value of the stability factor obtained by elementary methods. 3. Despite the fact that the VNIIG-Terzaghi method does not take into account the stress-strain state, it provides a comparatively high accuracy. In the investigated example the error in determining the stability factor is 10%. Apparently, in more complex cases for structures being constructed from various types of soils, with consideration of the seepage forces (especially unsteady), with consideration of consolidation in the watertight elements of the dams, and with consideration of their staged construction the divergences can be much greater.

Comparison of observed and calculated slip surface in slope stability calculations. Technical note : Talesnick, M; Baker, R Can Geotech JV21, N4, Nov 1984, P713–719

Comparison of observed and calculated slip surface in slope stability calculations. Technical note : Talesnick, M; Baker, R Can Geotech JV21, N4, Nov 1984, P713–719

Determination of the center of a cylindrical surface of sliding when calculating slope stability

Determination of the center of a cylindrical surface of sliding when calculating slope stability

Stochastic Analysis of Pore Pressure Uncertainty for the Probabilistic Assessment of the Safety of Earth Slopes

A probabilistic slope stability model was developed that includes soil shear strength and pore pressure as random variables. A local estimation technique called the nearest-neighbor method was utilized for simulation of the spatial variability of saturated soil permeability values. The spatial variation in the soil permeability causes a variation in the position of the phreatic surfaces during steady-state seepage flow and, hence, pore pressures. A number of permeability sets were generated and the resulting series of phreatic surfaces were calculated. A series of slope stability computations was made combining the spatial variability of pore pressures and soil strength yielding a probability density function of the factor of safety. The probability of failure was computed from the mean and standard deviation of the factor of safety. The resulting probabilistic model was applied to a hypothetical embankment. In addition, a sensitivity study was performed on the influence of the variability of soil permeability. The results indicated that the variability of soil strength and soil permeability has a large influence on the outcome of the probabilistic analysis and that there is a large discrepancy in the magnitude of the probability of failure if the pore’ pressure uncertainty is excluded from the probabilistic slope stability analysis.

Calculation of slope stability with the use of the hypothesis of cylindrical surfaces of sliding

The proposed probabilistic approach to calculation makes it possible to give a more objective estimate of the stability of earth slopes. Furthermore, in this case it is possible to isolate parameters which have the greatest effect on stability in order to conduct, if necessary, additional experimental investigations to refine them.

Comparison of observed and calculated slip surface in slope stability calculations

This study presents a reanalysis of four documented test embankment failures. Previous analysis of the embankments was done using the simplified Bishop method, for both total and effective stress analyses. The present work makes use of an optimization procedure called SSOPT, which searches a slope for the critical slip surface, without predefining the shape of this surface. This procedure yields reasonable factors of safety and a good estimation of the expected slip surface. This is not always the case for the Bishop-type analyses. Key words: slope stability, slip surface, analysis and observation.

Spatial calculation of slope stability under definite surcharges : Bilz, P; Brodel, C; Reinhardt, K Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981V3, P367–371. Publ Rotterdam: A. A. Balkema, 1981

Proceeding from the fact that too low safety factors contradictory to reality are established by means of procedures covering the plane state for calculating the slope stability in spatially limited failure patterns, a calculation method has been developed which approximately represents the spatial state. The final effects increasing stability are approximately represented by cone sections attached to a circular cylinder section. The procedure is preferably suited for calculating the stability of homogeneous unseeped slopes that are loaded with a limited area on which surcharge is applied (e.g. vehicles, construction machinery or hoisting units). In this contribution, the fundamental statements and assumptions are discussed. Furthermore, diagrams and tables are presented which are summarized in a regulation of the National Building Supervisory Board as a result of comprehensive variational computations by means of a computer program for the above mentioned procedure as an aid for designing. (TRRL)

Horizontal drains to stabilize clay slopes

Five horizontal drains were installed in a natural clay slope and the piezometric heads in the slope were monitored with piezometers. Decreases of piezometric head in the vicinity of the drains were measured and indicated that horizontal drains can be used to improve the stability of clay slopes.Based on the theory of consolidation, estimates were made of the changes of piezometric head within the test slope due to the installation of drains. Good comparisons were obtained between the predicted and the measured values, demonstrating that the method of prediction can be used with confidence for design purposes. The three-dimensional pattern of piezometric levels was averaged to give an equivalent two-dimensional pattern, and this was used in slope stability calculations to determine the improvement in safety factor of the slope.The effectiveness of horizontal drains depends on the spacing and diameter of the drains, and on their location relative to the critical slip zone.The study has shown that installation of horizontal drains is a viable method of improving the stability of certain clay slopes. Keywords: slope, clay, stability, drains, field test, theory.

841213 Probabilistic modeling of tailings embankment designs. Volume 3. User's manual for probabilistic slope stability computer program, PROBISH : Anderson, L R; Bowles, D S; Canfield, R V; Sharp, K D US Bureau of Mines reportOFR161(5)-82, Jan 1982, 66P

841213 Probabilistic modeling of tailings embankment designs. Volume 3. User's manual for probabilistic slope stability computer program, PROBISH : Anderson, L R; Bowles, D S; Canfield, R V; Sharp, K D US Bureau of Mines reportOFR161(5)-82, Jan 1982, 66P

Seepage regime of the hydraulic-fill dam of the mingechaur hydropower development

1. The anomalies of the seepage regime of the Mingechaur hydraulic-fill dam established during on-site observations are not related to intensification of the seepage flow and at present do not pose a danger for operation of the structure within the normal pool level of the reservoir, 83.0 m, which is also indicated by the temporal constancy of the seepage discharge being intercepted by the toe drain. The static calculations of slope stability under various most unfavorable operating conditions and an investigation of its earthquake resistance show a safe condition of the dam. 2. To judge from the results of investigating the soils of the core zone in the upper part, the Mingechaur hydraulic-fill dam in its current condition should be regarded not as a core-wall dam but as a gravel-sand dam with a lean central zone. About 10 such hydraulicfill dams, although of smaller height, have been constructed in the Soviet Union (Plyavinyas, Dubossary, Kaunas, etc.). 3. The presence of layers of increased permeability in the upper part of the core zone and the very high values of the permeability coefficient (up to 50 m/day) within the coreless “cap” of the dam (above elevation 84.0 m) give rise to the probability of a substantial increase of seepage discharge in the case of raising the level above the normal at reservoir elevations within 83.00–85.50, which can cause overfilling of the drainage system. At the same time we cannot preclude the possibility of the occurrence of contact erosion on the crest of the core zone under these operating conditions. With consideration of the aforesaid, it is recommended to take the elevation of the maximum water level with some margin equal to 83.50 m (the design specified 85.50 m). 4. To ensure safe operating conditions of the Mingechaur hydropower development at the designed maximum operating level above the elevation of the normal reservoir level of 83.0 m, it is required to strengthen the upper part of the core zone and “cap” by creating a watertight barrier. The design of the barrier should be selected on the basis of a technical and economic comparison of possible variants.

The effect of discontinuity persistence on rock slope stability

Discontinuity persistence has a major effect on rock mass resistance (strength) but, as direct mapping of discontinuities internal to a rock mass is not possible, persistence is a difficult parameter to measure. As a result, the conservative approach of assuming full persistence is often taken. In this paper a method is developed for relating rock mass stability and hence persistence to the geometry and spatial variability of discontinuities. The method is applied to slope stability calculations in which the probability of failure is related to discontinuity data, as obtained in joint surveys. The complete method makes use of dynamic programming and simulation, but a closed form expression satisfactory for most purposes is also presented.

Slope stability analysis of riverbanks

Practical considerations for the use of subsurface exploratory data and material strength data in slope stability calculations for estimating the factor of safety along potential slip surfaces in natural slopes are described and illustrated with a sample problem. An alternative form of the slope stability equations for the method of slices, using the limit equilibrium method and satisfying complete statics on each slice, is presented for plane problems. The shortcomings inherent in commonly available computer programs for the analysis of slope stability problems are discussed. Means to overcome some of the limitations are indicated and illustrated with a sample problem. It is suggested that the general purpose computer programs for slope stability analysis should use the complete form of the slope stability equations. The alternative form of the equations and the discussion of their solution are valid for slope stability analysis of natural slopes and embankment dams. Keywords: stability analysis, slope stability, riverbanks, lake banks, natural slopes, soil mechanics, embankments.

Use of the probabilistic method of calculating stability when designing rock slopes

1. At present rock slopes are usually designed on the basis of the most unfavorable (of those possible) arrangement of potential shear joints in the investigated mass and without consideration of the probability of the presence of joints of such orientation in it. 2. A new method is proposed here for calculating the stability of rock slopes based on the use of a statistical probabilistic method of processing the measurements of orientations of potential shear joints and taking as the criterion of stability of slopes their reliability value. 3. The practical use of the method when designing the rock slopes of foundation pits of the Southern Ukraine power complex showed the advantages and prospects of the probabilistic approach to estimation of the stability of masses. In particular, use of the method made it possible to design some steeper slopes, which as a whole for the complex will permit avoiding additional excavation of tens of thousands (potentially as much as 160,000) of cubic meters of rock. 4. The results of calculating slope stability for various values of the hydrostatic pressure indicate the need for special investigations (e.g., on an electrohydrodynamic analogue) to determine the shape of the line of seepage in masses and the expediency of refining this line during excavation works.