Pressure Of Backfill Research Articles

Active failure mechanisms and earth pressure of narrow backfill behind retaining structures

Through a series of model tests accomplished by particle image velocimetry analyses, this study presents the visualisation of the displacement field of narrow soil behind retaining structures under translational mode. The progressive development of failure mechanisms and active earth pressure are measured in the process of tests. Finite-element limit analyses are additionally carried out to investigate and verify the ultimate failure mechanism and active earth pressure acting on retaining structures. Furthermore, this study carried out analyses on the development of failure mechanisms and active earth pressure with different aspect ratios, inclinations of the existing structure and backfill surface surcharge. A reasonable agreement was observed between experimental and numerical results. With an increase in backfill spacing, the failure mechanism of backfill turns from reflective shear bands into a single shear band, and the earth pressure exerted on the retaining structure increases.

Evolution law and mechanism analysis of strength for backfill under different stress and drainage conditions

In recent years, with the improvement of construction safety requirements in deep well mining, the backfill mining method has been widely used. However, the strength of paste filling acquired in quarry often surpasses the design strength determined in laboratory settings. In view of the problems that indoor conditions cannot restore deep mining environment, and the mechanism of coupling effect under multiple fields is unclear. This paper has carried out relevant research work through theoretical analysis and indoor experiments. First of all, after completing the preparatory experiments, this paper analyzed the strength difference of backfill under different curing stress and drainage conditions, and studies the influence of different curing conditions on the strength. Secondly, MPS-6 and 5TE sensors were used to monitor the electrical conductivity, pore water pressure, porosity and other parameters of backfill during the stress-drainage curing process, and changes of parameters during curing process were analyzed. Finally, the relationship among relevant parameters and strength properties of paste backfill was analyzed, as to clarify the influence mechanism of stress-drainage curing conditions on the strength formation for paste backfill. Research shows that both stress-undrained and stress-drained conditions can effectively increase the strength of backfill. Under stress-drainage conditions, the internal porosity of backfill will decrease, and the pore water pressure of backfill will first increase slightly and then continue to decrease. Under this condition, the electrical conductivity of backfill will first increase and then continue to decrease. The entire research has important positive significance for reducing mining costs, optimizing mining processes, and developing mining technology.

Study on active earth pressure of narrow backfill of balance weight retaining wall under translational displacement mode

The balance weight retaining wall is a kind of gravity retaining wall. However, the theoretical results of the earth pressure are relatively few. The failure modes of backfill soil under different factors such as width to depth ratio of fill soil and rock inclination angle were studied by finite element limit analysis. Based on differential element methods and wedge limit equilibrium method, the active earth pressure calculation formula of balance weight retaining wall under translational displacement mode was derived. According to the parameter analysis, the interface friction resistance escalates alongside the rise in the boundary friction angle. The active earth pressure resultant force of the retaining wall increases with the increase of the width to depth ratio of filling, and decreases with the increase of the friction angle of filling. The design of counterweight retaining wall can benefit from the scientific basis and technical reference offered by the research findings.

Nonlinear description of active earth pressure for finite backfill based on principal stress trajectory method subjected to steady unsaturated seepage

To simplify calculations, soil cohesion, horizontal shear stress, and unsaturated properties have usually been neglected in previous earth pressure analytical methods. This negligence has certain theoretical flaws and does not conform to the actual situation. Especially for finite backfill, which often occurs, it is worth continuing to expand research in this field to seek a more rigorous solution. This work presents an analytical framework for estimating the active earth pressure of finite backfill on inclined retaining walls under steady unsaturated seepage conditions. The extended Mohr–Coulomb failure criterion expresses soil shear strength, and a unified effective stress method considering the suction stress is adopted. For a classic failure model, a calculation method using curved differential elements is established based on the principal stress trajectory. The proposed method fully considers soil cohesion, arching effect, and unsaturated properties. Relative to the existing test and theoretical results, the rationality of this method is verified. The sensitivities of relevant parameters are discussed based on different assumed soil types. The results show that seepage significantly affects the lateral earth pressure. The earth pressure distributions vary greatly under different unsaturated types for various soils. The results can provide a reference for the selection of engineering backfill.

Passive Earth Pressure on the Retaining Wall of Limited-width Backfill Based on Curvilinearly Layered

This study presents a new method to calculate the passive earth pressure on the rigid retaining wall of non-cohesive limited-width backfill. The proposed method considers the non-cohesive backfill behind the wall as the research object. It was assumed that under the translational mode of the retaining wall, the fracture surface was the plane passing through the heel of the wall and that the principal stress trajectory of the backfill was arc-shaped. The backfill was divided into several arc thin-layer elements by layering along the principal stress trajectory. The non-uniformity of stress distribution on the upper and lower surfaces of the elements was considered. The proposed method was validated with the data obtained from the model tests found in the literature. The results showed that compared with the common horizontal element layering method, the arc thin-layer element method can accurately consider the complex stress acting on the element and better reflect the variation law of the passive earth pressure on the retaining wall. The passive earth pressure of limited-width backfill presented a non-linear distribution along the height of the wall and increased with an increase in soil depth. With an increase in the aspect ratio of soil or a decrease in the internal friction angle, the resultant force of the passive earth pressure gradually decreased while the height of the action point of the resultant force gradually increased. When calculating the passive earth pressure on the retaining wall of limited-width backfill, the critical aspect ratio of limited-width to semi-infinite width was 3.

Slip-Line Solution to Earth Pressure of Narrow Backfill against Retaining Walls on Yielding Foundations

When a retaining wall is adjacent to a natural slope, the overturning of the wall is usually caused by a yielding foundation. At the point of overturning, the narrow backfill behind the wall has reached the active limit state. However, in previous studies, the foundation conditions of the retaining wall were not fully considered when the earth pressure on the retaining wall with the narrow backfill was calculated. To comprehensively consider the stress state of the retaining wall, the finite-element limit analysis method was employed to study the failure mode of a retaining wall adjacent to a natural slope. The simulation results indicate that the sliding surface starts from the wall heel, with one side developing at the surface of the natural slope and the other developing in the ground in front of the wall. Based on this failure mechanism, a slip-line computational model for the retaining wall was established. When the slip-line solution was compared with the finite-element solution, the results were in good agreement. The plastic zone of the soil was determined by the slip-line field. In addition, the slip-line solution gave the active earth pressure of the narrow backfill, the passive earth pressure of the soil in front of the wall, and the foundation bearing capacity. Moreover, several extensive parametric studies were conducted. Thus, the shape of the narrow backfill, the rough soil–wall interface, and the low-strength backfill are all conducive to reducing active earth pressure on a retaining wall.

Limit Analyses of the Active Earth Pressure on Rigid Retaining Walls under Strip Loading on Backfills

Recent studies of retaining walls include experimental studies, numerical analysis and analytical models. Although active earth pressure against retaining structures has received much attention, the evaluation of active earth pressure of backfill when loaded by a strip foundation, has been slightly studied. This paper studies the effect of a strip load on the active pressure force and the distribution of the horizontal stresses on a rigid wall, using a finite element limit analysis. The strip loading is located at different distances from the vertical face of the wall. The OptumG2 code is used to analyze the effect of width of strip surcharge (soil-wall), interface friction angle and soil internal friction angle. New interesting results are demonstrated and presented here: the dependency of the active earth pressure coefficient on both position and width of the strip load, in one hand, and the effect of the internal friction angle of the soil, the soil-wall interface, and the position of the strip loading on the failure mechanism, in the other hand.

Active Earth Pressure of Narrow Backfill against Inverted T-Type Retaining Walls Rotating about the Heel

Inverted T-type retaining walls are commonly used in subgrade or slope support engineering, which inevitably satisfies a narrow backfill. Using the classical earth pressure calculation method in a narrow-backfill case causes an inevitable error. The current narrow-backfill earth pressure theory does not apply to inverted T-type retaining walls. In this study, the failure mechanism in a narrow backfill when the inverted T-type retaining wall rotates about the heel is investigated using adaptive finite element analysis method. Numerical analysis reveals multiple sliding surfaces. A theoretical model for calculating earth pressure using difference and limit equilibrium methods is proposed. The proposed model is suitable for more complex conditions, including narrow backfill, irregular ground, and non-uniform overload, than previous models. Parameter analysis reveals that the cross-sectional area of the plastic zone and active earth pressure have a positive correlation. Further, the interface friction influences the decrease in active earth pressure. Fitting formulas for assessing the cases of long and short heel and the critical size of backfill width are presented to facilitate practitioners to evaluate the backfill.

Stiffness Determination of Backfill-Rock Interface to Numerically Investigate Backfill Stress Distributions in Mine Stopes

Numerical modeling is an effective and efficient method to investigate the stress distributions of backfill in stopes, which should be well understood in underground mining. Interface elements between backfill and rock in simulated stopes had been proved to be essential components, for which the stiffness parameters need to be assessed and assigned. However, few reports have revealed the effects of interface stiffness on backfill stress distributions, and there is not yet a clear solution to determine the interface stiffness to simulate stresses in backfilled stopes, except an empirical method for simply applying a high value suggested in FLAC manual. In this study, a new solution is first proposed to determine the normal stiffness and shear stiffness of interface elements, respectively, in numerical modeling of backfill stresses. The applicability of the solution has been verified by investigating backfill stress distributions in mine stopes of two widely used mining methods with variable stiffness values. The results show that the newly proposed method leads to totally the same backfill stress distributions with models applying the interface stiffness by the method in FLAC manual based on a “rule-of-thumb” but will save at least 20%–30% calculation time to improve modeling efficiency under the same simulation conditions and will carry much clear physical meanings corresponding to the interaction between backfill and rock walls in mine stopes. In addition, the vertical and horizontal stresses show good agreements with the analytical stresses predicted by the Marston equation under the at-rest state, which validates the reliability of the proposed solution for interface stiffness. Moreover, the plotting methods of stress distributions and the coefficient of lateral earth pressure of backfill in simulated stopes with proposed interface stiffness were discussed to further clarify the reasonable methods to investigate the backfill stresses in mine stopes, especially after considering the effects of the convergence from rock walls, which is a very significant and common phenomenon in practical mining engineering.

Seismic pseudo-static active earth pressure of narrow granular backfill against an inverted T-type retaining wall under translational mode

Rankine and Coulomb earth pressure theories are not applicable when the backfill behind the retaining wall is narrow. This paper analytically investigates the seismic active earth pressure of an inverted T-type retaining wall with narrow granular backfill under translational mode using a pseudo-static method for four typical seismic active failure mechanisms simulated with adaptive finite element software. Considering the failure surface reflections on soil–wall and soil–rock interfaces, four corresponding theoretical solutions using the limit equilibrium method, Rankine theory and the horizontal differential layer method are established to obtain the seismic active earth pressure of the backfill and the inclination angles of the failure surfaces. The derived formulae can be degenerated into either the static or the semi-infinite backfill situations. The proposed theoretical solutions are verified by comparisons with the finite element results and several existing theoretical solutions.

Analytical solutions for the earth pressure of narrow cohesive backfill with retaining walls rotating about the top

Currently, knowledge of the failure mechanisms of narrow backfills with retaining walls rotating about the top (RT mode) is still lacking which leads to inaccurate estimations of the earth pressure. Numerical simulations using finite element limit analysis find that under the effects of backfill geometries, interface strengths, and soil properties, the upper soil layer supported by soil arching retains its integrity and the lower soil layer is sheared by multiple curved sliding surfaces in the limit state. Based on the failure mechanisms of narrow backfills, a calculation model is established which considers the soil arching effect, curved sliding surface, and cohesive soils. Analytical solutions for the earth pressure of narrow cohesive backfills with retaining walls rotating about the top are derived by using the limit equilibrium horizontal slice method. Compared with previous studies, the present method predicts the earth pressure distribution with higher accuracy. Several extensive parametric studies have also been conducted. Thus, decreasing the aspect ratio of backfills, increasing the inclined angle of natural slopes, interface strengths, and soil cohesion are beneficial for maintaining backfill integrity and reducing earth pressure against retaining walls.

Active earth pressure of narrow cohesive backfill on rigid retaining wall of rotation about the bottom

Retaining wall construction often encounters narrow cohesive backfill and the traditional theories are no longer suitable. Hence, analytical solutions for active earth pressure of narrow cohesive backfill on a rigid retaining wall rotating about the bottom are proposed in this paper. The principle stress rotation caused by interface friction is also included. Through a typical FEM analysis and analytical derivation, the multi-segmented failure surface composed of a logarithmic spiral curve in the lower part and a tangent line in the upper part is quantitatively determined. According to the aspect ratio of the narrow backfill, three basic failure models of the narrow cohesive backfill are found together with three types of differential elements. A program is coded to automatically identify these three failure models to quickly obtain the distribution, the resultant and the application point of the active earth pressure. The proposed analytical solutions are then verified through a two-step procedure of elaborate comparisons with the FEM results and good agreements are observed. Subsequently, a parametric investigation indicates the active earth pressure is positively correlated to the aspect ratio and slope inclination angle, while is negatively correlated to the soil cohesion and interface friction.

A spreadsheet-based technique to calculate the passive soil pressure based on the log-spiral method

This paper presents an efficient technique to calculate the passive earth pressure of a cohesionless sloping backfill on a rigid retaining wall which is an extension of the Terzaghi’s log-spiral approach. Moment equilibrium conditions are used to compute the minimum value of the passive pressure required to mobilize the passive failure. Terzaghi assumed that the pole of the log-spiral failure surface lies inside the soil mass, whereas the proposed technique and solutions show that the pole can lie inside or outside the soil mass. Thus, the developed technique has extended the log-spiral method reported by Terzaghi by providing a generalised solution. The distinctive feature of the proposed technique is the explicit and rigorous solutions developed which allow to evaluate the passive earth pressure with different friction angles for the soil and wall-soil interface, backfill slopes and wall inclination angles. These solutions are relatively simple to incorporate into a spreadsheet to derive the passive force and pressure. A series of experiments were carried out using a physical model and the Particle Image Velocimetry (PIV) technique to analyse the failure surface. The developed solutions were then validated with data obtained from model tests as well as experimental data found in the literature.

Passive earth pressure of narrow cohesionless backfill against inclined rigid retaining walls under translation mode

In engineering applications, narrow backfills are often squeezed by retaining walls. Insufficient information is available with respect to the passive earth pressure, whereas the active earth pressure of narrow backfills against retaining walls has been considerably investigated. In this study, the passive failure mechanism of a narrow cohesionless backfill under translation mode has been investigated via a finite element lower-bound limit analysis, considering the effect of backfill geometries and external friction on the failure mechanism. Multiple-slip surfaces could be observed in a narrow backfill in the passive limit state. Further, we summarized the number of slip surfaces under various conditions and proposed a fitting function for the inclined angles of the slip surfaces. In addition, a multiple-slip surface calculation mode was developed. Subsequently, a method was derived for calculating the passive earth pressure of a narrow cohesionless backfill using the differential slice element method, the wedge limit equilibrium, and the finite difference method. Parametric studies explored the effects of the backfill geometries and internal and external frictions on the passive earth pressure. The results demonstrated an increase in the passive earth pressure and the number of slip surfaces when the backfill space decreased, in which the passive earth pressure was nonlinearly distributed.

Experimental study of the “short-term” pressures of uncemented paste backfill with different solid contents for barricade design

The successful application of paste backfill in underground mines depends on the stability of a confinement structure, called barricades, constructed at the base of stopes to hold the backfill slurry in the stopes. The stability analysis of barricades needs the knowledge of the pressures during or shortly after the placement of the paste backfill exerted on the barricades. The recommendation of slight construction of barricades for paste backfill given in the few handbooks on paste backfill implicitly indicates that the paste backfill pressure is very small. This does not correspond to the field pressure measurements reported in the literature, which indicated that the pressures of paste backfill during and shortly after the placement can be as high as the iso-geostatic overburden pressure. To understand this dilemma, the difference between the paste backfill defined in the handbooks and that used in underground mines is for the first time highlighted. The former requires a high enough solid content and the backfill should be unsaturated. In practice, enough water has to be added in the backfill to facilitate its transportation by pipes. The solid content cannot be as high as that required in the handbooks. The dilemma between the recommendation of handbooks and field pressure measurement is for the first time solved. However, this analysis tends to indicate that the pressure of paste backfill depends on the solid content. To verify this hypothesis, a series of laboratory tests were conducted to measure the vertical total stresses of paste backfill having different solid contents at the end of filling operation. The results show that the vertical total stresses decrease as the solid content increases. The solid content should be taken into account in the pressure estimation of paste backfill for the design of barricades.

Pressure evaluation of bridge abutment backfill made of waste tyre bales and shreds: Experimental and numerical study

Abstract The disposal of waste tyres in a landfill has been outlawed in Europe since 2000, with some exceptions being made for construction works. Since then, tyre-derived products have been widely used in road applications. One of these applications is in tyre bales, comprising 100–140 car vehicle tyres compressed into a lightweight block and secured by galvanised steel tie wires running around the length and depth of the bale. In the scope of the project reported here, the authors conducted comprehensive laboratory and field tests on applying tyre bales and shreds as a backfill to integral bridges. In this paper, a full-scale experiment is described in which the pressure of a tyre-baled backfill supplemented with medium sand filling and a tyre shreds buffer layer has been evaluated. The experiment was prepared and conducted by means of a special full-scale trial built to simulate real bridge abutment conditions. Test results clearly revealed the efficiency of the backfill composed of tyre bales, tyre shreds and medium sand filling in terms of pressure reduction on a bridge abutment in comparison with pressure distribution of homogeneous soil pressure. A finite element 2D analysis was also conducted to model the behaviour of a waste tyre/sand backfill. Since there was pretty good agreement between numerical and experimental results, the validated FE analysis might be reliably adopted in further design for a sustainable bridge solution. The first Polish application of the abutment backfill from waste tyres has been briefly described as well.

Inclined Slice Method to Earth Pressure of Narrow Cohesionless Backfill against Rigid Walls under Various Displacement Modes

The displacement modes of retaining walls in engineering are complicated, and the backfill behind retaining walls is often narrow. Failure mechanisms of soils under various displacement modes of retaining walls have not been clarified yet in previous studies. According to results of the finite element limit analysis, multiple sliding surfaces were observed developing reflectively between interfaces on both sides in the active limit state. In rotational displacement modes, some layers of soil near the rotated point maintained in the non-limit state which was not considered in the previous studies. Based on numerical analysis results, failure wedges were divided into differential soil slice elements by an inclined slice method. An analytical model was established to estimate the earth pressure of the narrow backfill under various displacement modes using the limit equilibrium method. The calculated results are consistent with the data gathered from previous tests. Compared with previous studies, the proposed method can reflect failure mechanisms of the narrow backfill and be adapted to various displacement modes of the retaining wall. The accuracy of the calculation results is high in the non-limit state soil layer. In addition, the boundary criterion between the narrow and semi-limit backfills was determined. Based on extensive parametric studies, it can be concluded that increasing the soil-wall interface friction and decreasing the backfill area would be conducive to decreasing the earth pressure and the depth of resultant application point.

Experiment on Interaction of Abutment, Steel H-Pile and Soil in Integral Abutment Jointless Bridges (IAJBs) under Low-Cycle Pseudo-Static Displacement Loads

Soil-abutment or soil-pile interactions under cyclic static loads have been widely studied in integral abutment jointless bridges (IAJBs). However, the IAJB has the combinational interaction of soil-abutment and soil-pile, and the soil-abutment-pile interaction is lack of comprehensively study. Therefore, a reciprocating low-cycle pseudo-static test was carried out under an cyclic horizontal displacement load (DL) to gain insight into the mechanical behavior of the soil-abutment-pile system. Test results indicate that the earth pressure of backfill behind abutment has the ratcheting effect, which induced a large earth pressure. The soil-abutment-pile system has a favorable energy dissipation capacity and seismic behavior with relatively large equivalent viscous damping. The accumulative horizontal deformation in pile will be occurred by the effect of abutment and unbalance soil pressure of backfill. The test shows that the maximum horizontal deformation of pile occurs in the pile depth of 1.0b~3.0b of pile body rather than at the pile head due to the accumulative deformation of pile, which is significantly different from those of previous test results of soil-pile interaction. The time-history curve for abutment is relatively symmetrical and its accumulative deformation is small. However, the time-history curve of pile is asymmetrical and its accumulative deformation is dramatically large. The traditional theory of deformation applies only to the calculation of noncumulative deformation of pile, and the influence of accumulative deformation should be considered in practical engineering. A significant difference of inclinations in the positive and negative directions increases when the displacement load is relatively large. The rotation of abutment when bridge expands is larger than that when bridge contracts due to earth pressure of backfill.

Experimental Study on the Active Earth Pressure of Narrow Cohesionless Backfills against Rigid Retaining Wall under the Translation Mode

In engineering, the new retaining walls are often constructed near the existing structure owing to the space limitation. The backfill behind the retaining wall is narrow, which causes an overestimation in the active earth pressure by using Coulomb’s earth pressure theory. In previous studies, experimental observations for the failure modes of narrow backfills are still rare. To confirm the failure mode of the narrow backfill, the experimental method and the geotechnical particle image velocimetry method are employed to observe the active failure process of the cohesionless narrow backfill with various widths under the translation mode. The experimental results revealed that the decrease in the length of the backfill width led to the increase in the inclined angle of the sliding surface. When the backfill width was sufficiently small, the sliding surface developed from the wall toe to another wall face, and then another sliding surface occurred as a reflection. In addition, the active earth pressure of the narrow backfill is significantly smaller than that calculated using Coulomb’s method. The active failure calculation models are established based on the experimental results. The active earth pressure of the narrow cohesionless backfill under the translation mode is derived by using the limit equilibrium methods. The proposed method was validated by comparing with the previous method and the experimental data.

Active Earth Pressure of Narrow Granular Backfill against Rigid Retaining Wall Near Rock Face under Translation Mode

AbstractWhen a retaining wall is built near a building or a mountain, the backfill width is often limited. It limits the use of the classical theoretical formula based on the assumption of an infin...