scholarly journals Pipe–soil interaction model for current-induced pipeline instability on a sloping sandy seabed

2016 ◽  
Vol 53 (11) ◽  
pp. 1822-1830 ◽  
Author(s):  
Fu-Ping Gao ◽  
Ning Wang ◽  
Jinhui Li ◽  
Xi-Ting Han
Keyword(s):  
Limit Equilibrium ◽  
Slope Angle ◽  
Interaction Model ◽  
Earth Pressure ◽  
Model Verification ◽  
Soil Resistance ◽  
Passive Earth Pressure ◽  
Equilibrium Approach ◽  
Full Scale Tests ◽  
Good Agreement

As offshore exploitation moves to deeper waters, ocean currents become the prevailing hydrodynamic loads on pipelines, and at the same time a sloping seabed is always encountered. The prediction of lateral soil resistance is vital in evaluating pipeline on-bottom stability. Unlike previous pipe–soil interaction models used mainly for horizontal seabed conditions, a pipe–soil interaction model for current-induced downslope and upslope instabilities is proposed by using the limit equilibrium approach. The Coulomb’s theory of passive earth pressure for the sloping seabed is incorporated in the derivation. The model verification with existing full-scale tests shows good agreement between the experimental results and predicted ones. Parametric study indicates that the effect of slope angle on pipeline lateral soil resistance is significant in the examined range of slope angle from –15° to 15°. The critical pipeline embedment and corresponding passive pressure decrease approximately linearly with increasing slope angle.

Determination of passive earth pressure coefficients using limit equilibrium approach coupled with the Kötter equation

2015 ◽  
Vol 52 (9) ◽  
pp. 1241-1254 ◽  
Author(s):  
Mrunal A. Patki ◽  
J.N. Mandal ◽  
D.M. Dewaikar
Keyword(s):  
Limit Equilibrium ◽  
Retaining Wall ◽  
Earth Pressure ◽  
Failure Surface ◽  
Passive Earth Pressure ◽  
Pressure Coefficients ◽  
Composite Failure ◽  
Equilibrium Approach ◽  
The Moment

A numerical method is developed to evaluate the passive earth pressure coefficients for an inclined rigid retaining wall resting against a horizontal cohesionless backfill. A composite failure surface comprises a log spiral, and its tangent is assumed in the present study. The unique failure surface is identified based on the limit equilibrium approach coupled with the Kötter equation (published in 1903). Force equilibrium conditions are used to evaluate the magnitude of the passive thrust, whereas the moment equilibrium condition is employed to determine the location of the passive thrust. The distinctive feature of the present study is that no assumption is required to be made regarding the point of application of the passive thrust, which would otherwise be an essential criterion with respect to the several limit equilibrium based investigations available in the literature. The passive earth pressure coefficients, Kpγ, are evaluated for various values of soil frictional angle [Formula: see text], wall frictional angle δ, and wall inclination angle λ, and compared with the existing results.

Coulomb’s solution to seismic passive earth pressure on retaining walls

2013 ◽  
Vol 50 (10) ◽  
pp. 1100-1107 ◽  
Author(s):  
Ming Xiang Peng ◽  
Jing Chen
Keyword(s):  
Limit Equilibrium ◽  
Slope Angle ◽  
Earth Pressure ◽  
Friction Angle ◽  
Retaining Walls ◽  
Cohesionless Soil ◽  
Soil Reaction ◽  
Passive Earth Pressure ◽  
Slip Surfaces ◽  
Seismic Coefficient

The conventional Mononobe–Okabe method is widely used in practice, but is only applicable for calculating total seismic earth pressure of cohesionless soil, not for solving earth pressure distribution. Based on limit equilibrium theory, the backfill is considered to be an ideal elastic–plastic material that obeys the Mohr–Coulomb yield criterion, and a family of slip-lines in the plastic zone is assumed to be a group of straight lines, i.e., planar slip surfaces. Influencing factors including inclination of wall, slope angle of backfill, cohesion and friction angle of soil, adhesion and friction angle between wall and soil, uniform surcharge, and horizontal and vertical seismic coefficients are considered. A more reasonable plastic soil wedge analysis model is established to solve the seismic passive earth pressure on retaining walls, the soil reaction on slip surfaces, and their distributions by using the limit equilibrium method. The geometric and mechanical similarity principle is first proposed by dimensionless analysis. The results show that the total seismic passive earth pressure increases with the algebraic value of the horizontal seismic coefficient, and that it decreases as the algebraic value of the vertical seismic coefficient increases. The present analytical solution is identical to the results in existing literature, and the Mononobe–Okabe method is a special case of this solution.

Seismic passive earth pressure coefficients for sands

2001 ◽  
Vol 38 (4) ◽  
pp. 876-881 ◽  
Author(s):  
Jyant Kumar
Keyword(s):  
Limit Equilibrium ◽  
Earth Pressure ◽  
Logarithmic Spiral ◽  
Failure Surface ◽  
Passive Earth Pressure ◽  
Pressure Coefficients ◽  
Straight Line ◽  
Earth Pressures ◽  
Planar Failure ◽  
Seismic Forces

By taking the failure surface as a combination of the arc of a logarithmic spiral and a straight line, passive earth pressure coefficients in the presence of horizontal pseudostatic earthquake body forces have been computed for an inclined wall placed against cohesionless backfill material. The presence of seismic forces induces a considerable reduction in the passive earth resistance. The reduction increases with an increase in the magnitude of the earthquake acceleration. The effect becomes more predominant for loose sands. The obtained results compared well with those reported in the literature using curved failure surfaces. However, the results available in the literature on the basis of a planar failure surface are found to predict comparatively higher passive resistance.Key words: earth pressures, earthquakes, limit equilibrium, plasticity, retaining walls, sands.

scholarly journals Analysis of passive earth pressure modification due to seepage flow effects

2018 ◽  
Vol 55 (5) ◽  
pp. 666-679 ◽  
Author(s):  
Z. Hu ◽  
Z.X. Yang ◽  
S.P. Wilkinson
Keyword(s):  
Limit Equilibrium ◽  
Retaining Wall ◽  
Reaction Force ◽  
Earth Pressure ◽  
Failure Surface ◽  
Friction Angle ◽  
Seepage Flow ◽  
Fourier Series Expansion ◽  
Passive Earth Pressure ◽  
Interface Friction

Using an assumed vertical retaining wall with a drainage system along the soil–structure interface, this paper analyses the effect of anisotropic seepage flow on the development of passive earth pressure. Extremely unfavourable seepage flow inside the backfill, perhaps due to heavy rainfall, will dramatically increase active earth pressure while reducing passive earth pressure, thus increasing the probability of instability of the retaining structure. A trial and error analysis based on limit equilibrium is applied to identify the optimum failure surface. The flow field is computed using Fourier series expansion, and the effective reaction force along the curved failure surface is obtained by solving a modified Kötter equation considering the effect of seepage flow. This approach correlates well with other existing results. For small values of both the internal friction angle and interface friction angle, the failure surface can be appropriately simplified with a planar approximation. A parametric study indicates that the degree of anisotropic seepage flow affects the resulting passive earth pressure. In addition, incremental increases in the effective friction angle and interface friction angle both lead to an increase in passive earth pressure.

Pull-out capacity of single batter piles in sand

1986 ◽  
Vol 23 (3) ◽  
pp. 387-392 ◽  
Author(s):  
A. M. Hanna ◽  
A. Afram
Keyword(s):  
Design Method ◽  
Soil Mechanics ◽  
Earth Pressure ◽  
Axial Loading ◽  
Test Results ◽  
Passive Earth Pressure ◽  
Sand Soil ◽  
Pull Out ◽  
Batter Piles ◽  
Good Agreement

The pull-out capacity of single rigid vertical and batter piles in sand and subjected to axial loading has been investigated. Good agreement was found when test results on instrumented model piles were compared with theoretical estimates. The effect of pile inclination on the pull-out capacity has been explained by means of variable mobilized passive earth pressure on the pile's perimeter. A design method and charts are presented. Key words: pile foundation, pull-out capacity, vertical pile, batter pile, sand–soil mechanics.

scholarly journals Study on Passive Earth Pressure of Retaining Wall in Transversely Isotropic Soil

2020 ◽  
Vol 143 ◽  
pp. 01020
Author(s):  
Tao Chen ◽  
Chao Chen ◽  
Fengting Guan ◽  
Ruoyang Zhou
Keyword(s):  
Limit Equilibrium ◽  
Retaining Wall ◽  
Transverse Isotropy ◽  
Earth Pressure ◽  
Transversely Isotropic ◽  
Least Square Method ◽  
Least Square ◽  
Passive Earth Pressure ◽  
Principal Stress Direction ◽  
Tensor Theory

Based on the fabric tensor theory and the principle of least square method, the method of block processing in the same model to explore the variation of the passive earth pressure of the transversely isotropic soil was used in the study. At the same time, primary displacement application and multiple displacement application were applied to change the angle between the large principal stress direction of the filling and the normal direction of the deposition surface to obtain the new strength parameters ci and φi of each block after the model was divided and additionally analyzing the variation of the anisotropic passive earth pressure. The study shows: 1.Considering the transverse isotropy of the soil and reaching the limit equilibrium, the passive earth pressure of the soil after multiple displacement application is not only smaller than that after primary displacement application but also closed to the theoretical solution of Coulomb’s earth pressure; 2.When the soil is inclined, the anisotropy is significant when compared with the horizontal direction.

Limit equilibrium computation of dynamic passive earth pressure

1995 ◽  
Vol 32 (3) ◽  
pp. 481-487 ◽  
Author(s):  
Ernest E. Morrison Jr. ◽  
Robert M. Ebeling
Keyword(s):  
Limit Equilibrium ◽  
Pressure Coefficient ◽  
Earth Pressure ◽  
Failure Surface ◽  
Friction Angle ◽  
Passive Earth Pressure ◽  
Equilibrium Equations ◽  
Cohesionless Soils ◽  
Earth Pressures ◽  
Earth Pressure Coefficient

Few solution techniques exist for the determination of pseudostatic dynamic passive earth pressures for cohesionless soils. The widely accepted Mononobe–Okabe equation can result in the computing of unconservative values if the wall interface friction angle is greater than half the soil internal friction angle. As an alternate solution, equilibrium equations were formulated assuming a log spiral failure surface, and a research computer program was written to calculate the dynamic passive earth pressure coefficient. The primary purpose of this paper is to present a comparison of results obtained using the Mononobe–Okabe equation with those obtained using the log spiral formulation. Key words : pseudostatic, dynamic, passive earth pressure.

Seismic passive resistance in soils for negative wall friction

2002 ◽  
Vol 39 (4) ◽  
pp. 971-981 ◽  
Author(s):  
Deepankar Choudhury ◽  
K S. Subba Rao
Keyword(s):  
Limit Equilibrium ◽  
Earth Pressure ◽  
Friction Angle ◽  
Wall Friction ◽  
Passive Earth Pressure ◽  
Passive Resistance ◽  
Pressure Coefficients ◽  
Logarithmic Spirals ◽  
Seismic Accelerations ◽  
The Individual

In the presence of pseudo-static seismic forces, passive earth pressure coefficients behind retaining walls were generated using the limit equilibrium method of analysis for the negative wall friction angle case (i.e., the wall moves upwards relative to the backfill) with logarithmic spirals as rupture surfaces. Individual density, surcharge, and cohesion components were computed to obtain the total minimum seismic passive resistance in soils by adding together the individual minimum components. The effect of variation in wall batter angle, ground slope, wall friction angle, soil friction angle, and horizontal and vertical seismic accelerations on seismic passive earth pressures are considered in the analysis. The seismic passive earth pressure coefficients are found to be highly sensitive to the seismic acceleration coefficients both in the horizontal and the vertical directions. The results are presented in graphical and tabular formats.Key words: seismic passive resistance, limit equilibrium, pseudo-static.

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