Active Earth Thrust Research Articles

Numerical Investigation of Seismic Behaviour for a Flexible Cantilever Retaining Wall with Cohesive Backfill

In the seismic design of flexible cantilever walls retaining cohesive backfill soil, the common practice is to neglect the cohesion effect. Dynamic lateral earth pressure is typically evaluated based on approaches primarily intended for cohesionless soils or through analytical pseudo-static methods. Nevertheless, both experimental and theoretical evidence has demonstrated significant effects due to soil cohesion that are not accounted for by these methods. This study involved finite element modeling (FE) of a flexible cantilever wall with a height of 5.4m, supporting homogeneous cohesive backfill under initial static and seismic loadings. The calculated active earth thrust was then compared with values obtained experimentally and through conventional analytical methods. The obtained results indicate that the presence of soil cohesion significantly reduces seismic demands on flexible cantilever retaining walls, resulting in a substantial reduction of seismic active earth pressures and total seismic thrust by up to 50% and 52%, respectively. It enhances also the overall stability of the system by shifting the point of application of seismic thrust toward the base of the wall, thereby increasing the safety margin. In addition, it significantly decreases the wall displacement at the stem top, with reductions of up to 104% compared with the case involving cohesionless backfill. It was observed that the conventional methods recommended by some seismic regulations largely underestimate seismic active pressure.

New RSM-FEM–Based Active Lateral Earth Thrust Coefficient Determination Method for Inverted T-Type Cantilever Retaining Walls Supporting Narrow Granular Backfill

New RSM-FEM–Based Active Lateral Earth Thrust Coefficient Determination Method for Inverted T-Type Cantilever Retaining Walls Supporting Narrow Granular Backfill

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.

Critical Inclination of Failure Surface and Seismic Active Earth Thrust for a Broken Slope Backfill

This paper presents an analytical approach, based on the limit-equilibrium state, to determine the critical inclination of failure surface and active earth thrust for a cohesive-frictional backfill with a broken slope and a surcharge load at a constant distance from a retaining wall under the seismic condition. A combined analysis using Mononobe-Okabe’s and Culmann’s methods within a trial and error procedure is performed in this study. The influences of several parameters such as wall height, surcharge magnitude, cohesion, and internal friction angle of the backfill, adhesion between the wall-backfill interface, tension cracks, horizontal and vertical seismic acceleration coefficients have been investigated on the critical inclination of failure surface and the active earth thrust. Additionally, the performance of the proposed approach is explored by geotechnical software (Geo5) and two available methods in the literature. All of the results and the detailed comparisons are given in tabular and graphical forms.

Active thrust of sand with anisotropic seepage: A generalized limit equilibrium approach

Estimation of the magnitude and location of the lateral earth thrust on a retaining wall considering seepage flow effects within the backfill is necessary to examine the failures of such walls. In this work, the generalised limit equilibrium approach, based on the method of slices, was used to compute the magnitude and location of active earth thrust on the vertical face of a retaining wall taking into account steady seepage flow in the sand backfill. A drainage system along the backfill and wall interface and an anisotropic permeability characteristic of the backfill was considered for describing the pore pressure distribution within the backfill. Using force equilibrium conditions and an assumption regarding the direction of the interslice forces, the total normal stress distribution along the failure surface and the magnitude of total active earth thrust were determined. Subsequently, the location of the active earth thrust was determined to satisfy the moment equilibrium condition. Both planar and curvilinear failures surfaces were analysed to examine the impact on the solutions. It was confirmed that seepage flow within backfill substantially affects both the magnitude and location of active earth thrust, depending upon the degree of anisotropy.

A method for active seismic earth thrusts of granular backfill acting on cantilever retaining walls

The failure mechanism plays an important role in the active seismic earth thrusts acting on cantilever retaining walls. Cantilever retaining walls can be classified as having a long heel or a short heel based on the intersection between the stem of the retaining wall and the failure surface. In the literature, different seismic earth thrust calculation methods have been suggested considering the long heel or the short heel cases. However, no unique study has been done that is applicable to walls with either a long heel or a short heel. The aim of this study is to suggest a new active seismic earth thrust calculation method for granular soils which is applicable to retaining walls with either a short heel or a long heel using a pseudo-static approach. Three different earth thrusts are considered to be acting on three different parts of a wall backface. Each thrust is derived in terms of the parameters defining the wall geometry, the soil properties and the seismic activity. The thrust coefficients are determined by maximizing the sum of the horizontal components of the earth thrusts. An algorithm is developed and coded for this aim. The results of the suggested method are compared with those of other conventional methods and an experimental study.

Active Earth Thrust Considering Tension Crack, Pore-water Pressure and Soil Nonlinearity

The presences of tension cracks and pore-water pressure will reduce the stability of a soil-wall system. This study develops a kinematical approach to analyze how the active earth thrust is influenced by tension cracks and pore-water pressure, using the powerlaw nonlinear yield criterion. Although many cracks may be present in the backfill, this paper only involves one crack which leads to the most unfavorable effect. The influence of pore-water pressure is also considered using the concept of pore-water pressure coefficient. The power-law yield criterion is adopted characterize the soil strength, and the generalized tangential technique is introduced to realize the transition to the conventional linear problem. An objective function for the active earth thrust is derived from the equilibrium of rates of work and energy. Numerical results are determined from a maximization programming. By comparing with the available solution, the presented solution is validated. The results show that the presence of cracks has an unfavorable influence of increasing the active earth thrust, and this effect is even more obvious when the impact of seepage pressure is considered.

Structures of pedestrian underpasses and overpasses under seismic conditions

In this article, on the basis of analyzing damages of pedestrian passes during earthquakes that caused injuries or death of people, structural designs of these structures in order to enhance their stability are elaborated, and actions for reduction of their damageability degree are proposed. The essence of the invention lies in the fact that operation of arched ceilings is in reduction of reinforcement ratio, enhancement of dynamic stiffness, and reduction of seismically active earth thrust due to reduction of thrust force. The proposed structure operates in compression, which allows diminishing the thickness of concrete, due to which inertial seismic forces are reducing. In this structure, foundation is combined with the floor and transmits the thrust force from wall panels to the arched floor. Strategically, arched structures are better than beam structures, as their sections are mainly operating for off-center compression; at that, stretching forces caused by bending moments are insignificant, whereas bending moments occurring in beam structures cause essential stretching.

Analytical solution for active earth pressure of c–φ soil considering arching effect

ABSTRACTThe current study was undertaken to study the effect of soil arching on active earth pressure distribution in retaining walls with c–φ backfill. An analytical approach is presented to develop a general solution considering the effects of surcharge, backfill soil cohesion and slip surface inclination. The magnitude and height of the application of lateral active force is also derived. The results from the proposed equation corresponded to the measured results from a full-scale test, shows non-linear pressure distribution with zero pressure at wall base and less pressure in deeper heights compared to Coulomb’s method. According to the results of parametric analysis, the proposed equation predicts the active earth thrust nearly equal to that of the Coulomb’s equation, however, the surcharge-induced soil pressure is obtained approximately 50% greater than the conventional equation. Moreover, the height of application of active thrust is located at the height of 0.4H from the wall base. These indicate that using the Coulomb’s active equation for retaining walls design, is not in the safe side.

Estimation of Active Earth Pressure on a Translating Rigid Retaining Wall Considering Soil Arching Effect

By analysing the actual catenary arch of minor principal stresses under Rankine rupture surface, a new coefficient of lateral active earth pressure is proposed. And based on the limit equilibrium theory, new formulas of lateral active earth pressure on translating rigid retaining structures is derived, considering effects of soil arch and stress on rupture surface as well as surcharge stress. Further, the effects of the parameters (i.e., backfill internal friction angle, wall-soil friction angle, wall height and surcharge stress) on active earth pressure and its coefficient, active earth thrust and height of its application are investigated. In addition, the comparisons between the proposed methods by this study and others as well as existing test data, show that the predictions by this study are better accordant with results of the model test.

Earth Pressure behind a Retaining Wall under Linearly Varying Geotechnical Parameters

Objectives: The present study discuss estimation of active and passive earth pressure behind a smooth vertical retaining wall with horizontal backfill under linearly varying geotechnical properties, i.e., cohesion (c), angle of internal friction (φ) and unit weight (γ) of backfill vary linearly with depth.It is noted that the earth pressure behind the retaining wall is nonlinear and its variation can be established through regression analysis that follows 2nd order polynomial in the form of pa = -az2+bz+c; where z is the depth below the backfill surface, a, b & c are constants. Methods/Statistical Analysis: Regression analysis incorporating least square error approach option is available in Microsoft excel in data analysis tool pack. The total amount of thrust (active or passive ) estimated through non-linear distribution of earth pressure behind retaining wall is compared with the corresponding values computed through most widely used Rankine’s earth pressure theory in which average values of geotechnical parameters are taken. Findings: It is noted that there is 5-7% reduction in the active earth thrust although not much reduction is achieved in the moment. In passive case, the increase in passive thrust is almost 20%. Application/Improvements: Consideration of non-linear earth pressure distribution is useful in situations where base width of the retaining wall is controlled with respect to base shear. It will ultimately lead to reduction in the total cost of construction of the retaining wall and will help in achieving economy when the length of the retaining wall is large.

Generalized Seismic Active Thrust on a Retaining Wall with Submerged Backfill Using a Modified Pseudodynamic Method

The appropriate estimation of seismic earth pressures acting on retaining walls supporting submerged backfill is an important area of research in earthquake geotechnical engineering. There is a scarcity of research work on retaining walls with submerged soil under seismic conditions in the literature. In this paper, closed-form generalized solutions for computing seismic active earth thrust and its distribution on nonvertical rigid retaining walls with fully submerged backfill are proposed using the modified pseudodynamic approach. The seismic analysis of retaining walls was carried out with a planar rupture surface in viscoelastic submerged backfill. The proposed modified pseudodynamic analysis satisfied the zero-stress-boundary condition on a free surface and considered the standing shear and primary waves, soil damping, amplification in the backfill, and an excess pore-pressure ratio in the backfill. A detailed parametric study was performed to gain an understanding of the effects of different parameters, including the horizontal seismic acceleration coefficient, excess pore-water-pressure ratio, period of lateral shaking, damping ratio, wall inclination, and soil-friction and wall-friction angles. A comparison of the present study results and the existing analytical and experimental studies resulted in good agreement.

Phasing issues in the seismic response of yielding, gravity-type earth retaining walls – Overview and results from a FEM study

An overview of past and recent developments on the subject of seismic earth pressures on yielding, gravity-type walls, retaining cohesionless backfill, is first presented, focusing on available data on the issue of phase difference that develops between the peak values of wall inertia and seismic earth thrust increment. The results of a FEM parametric study are next presented regarding the dependence on the resulting dynamic earth thrust reduction – acting on the time of peak wall inertia – on backfill rigidity, wall height, and shaking characteristics. The reliability of the numerical analyses was verified by modeling centrifuge tests reported by Nakamura [24] and successfully comparing measured vs. computed behavior. The results of the parametric analyses indicate that the seismic active earth thrust, acting on the wall at the time of maximum wall inertia, is significantly reduced (compared to its peak value) with increasing shaking intensity of backfill, increasing wall displacements, increasing wall height, and decreasing backfill rigidity. No systematic dependence on the ratio of input motion frequency to the natural frequency of the backfill (f/f1) was observed. The above findings: (1) verify earlier experimental and numerical results, (2) explain the reported lack of damage to retaining walls under strong ground shaking, and (3) indicate the need for revising the pertinent provisions of current seismic codes. Graphs summarizing the results of the numerical analyses are presented which may be used as a guide for selecting the magnitude of seismic active earth thrust that needs to be taken into account in the design of the examined type of earth retaining walls.

Coefficients of active earth pressure with seepage effect

A calculation method for the active earth pressure on the possibly inclined face of a retaining wall provided with a drainage system along the soil–structure interface is presented. The soil is cohesionless and fully saturated to the ground surface. This situation may arise during heavy rainstorms. To solve the problem, the water seepage through the soil is first analyzed using a numerical procedure based on the boundary element method. Then, the obtained pore-water pressure is used in a Coulomb-type formulation, which supposes a plane failure surface inside the backfill when the wall movement is enough to put the soil mass in the active state. The formulation provides coefficients of active pressure with seepage effect which can be used to evaluate the active earth thrust on walls of any height. A series of charts with values of the coefficients of active earth pressure with seepage calculated for selected values of the soil internal friction angle, the wall–soil friction angle, and the wall face inclination is presented.

Analytical active earth thrust on cantilever walls with short heel

The use of Rankine’s method is inappropriate for calculating active thrusts in cantilever retaining walls with a short heel because the thrust wedge is interrupted by the wall backface. The use of Coulomb’s approach is preferable, but at present only numerical solutions have been proposed to solve the problem. This paper presents an analytical solution, based on Coulomb’s approach, for evaluating the active thrust on cantilever walls with a short heel subjected to homogeneous backfill with a regular topographic profile and without pore pressure. The solution is given by an algorithm where two equations, one quadratic and the other cubic, are solved in turn, in an iterative procedure that converges rapidly. The distribution of lateral pressure and the position of the point of application of the thrust are also given in analytical terms.

Discussion of "Active earth thrust by backfills subject to a line surcharge"

Silvestri 1223 The author has to be commended for obtaining an elegant solution to the problem of the Coulomb active thrust exerted by a cohesionless backfill and a vertical line load. This discusser has been using a slightly different approach for several years. The active thrust is firstly obtained in the absence of the line load. In such a case, the active thrust Fca (maximum value) is generally found by means of the wellknown Coulomb equation

Reply to the discussion by V. Silvestri on "Active earth thrust by backfills subject to a line surcharge"

Reply to the discussion by V. Silvestri on "Active earth thrust by backfills subject to a line surcharge"

Lateral Earth Pressure due to Backfill Subject to a Strip of Surcharge

The evaluation of the active earth thrust of backfill, on which a surcharge strip acts, is generally made using a hybrid approach where a thrust increment due to the surcharge strip is calculated using elasticity theory and added to the thrust calculated in absence of the surcharge strip and in failure condition of the thrust wedge. This paper gives a coherent solution to the problem, based entirely on Coulomb’s approach. It presents the analytical solution of the active thrust and of the position of the application point of the thrust.

A Coulomb-type solution for active earth thrust with seepage

A Coulomb-type general solution for active earth pressure on the vertical face of a retaining wall with a drainage system along the soil–structure interface is presented. The soil is cohesionless and fully saturated to the ground horizontal surface. This condition may happen during heavy rainfall and is the most critical, when the active pressure reaches its peak value. In order to solve the problem, a theoretical, closed-form solution for the water seepage through the soil is first developed. This is used in a Coulomb-type formulation, which supposes a plane failure surface inside the backfill when the wall movement is enough to put the soil mass in the active state. The formulation provides Coulomb-like coefficients of active pressure, which solve the problem in a generic way. Comparison with published results obtained by hand calculation shows very good agreement. A table with values of the coefficients of active earth pressure with seepage calculated for selected values of the soil internal friction angle and of the wall–soil friction angle is presented.

Active earth thrust by backfills subject to a line surcharge

The current analytical solution for the thrust computation when a line of vertical surcharge acts on the backfill behind a wall assumes the soils to be simultaneously elastic, for calculating part of the thrust, and in the active state of failure, for calculating the remaining part of the thrust. This paper gives a coherent analytical solution based on Coulomb's approach. The position of the active thrust is also given in a simple analytical form and compared with the approximate solution of Terzaghi.Key words: active earth force, cantilever walls, lateral pressure, active condition.