Cohesive Backfill Research Articles

Estimation of the Passive Earth Pressure with Inclined Cohesive Backfills: the Effect of Intermediate Principal Stress is Considered

Estimation of the Passive Earth Pressure with Inclined Cohesive Backfills: the Effect of Intermediate Principal Stress is Considered

Active Earth Pressure on Retaining Walls with Layered Cohesive Backfills and Considering Cracking

Based on the method of level-layer analysis, with the sliding harmonious condition of layered backfills considered , the theoretical answers to the unit earth pressures , the resultant earth pressures and the points of application of the resultant earth pressures on retaining walls with layered cohesive backfills are set up . The comparisons are made with Rankine’s formula.

Estimation of the Active Earth Pressure with Inclined Cohesive Backfills: the Effect of Intermediate Principal Stress is Considered

Estimation of the Active Earth Pressure with Inclined Cohesive Backfills: the Effect of Intermediate Principal Stress is Considered

Estimation of the Passive Earth Pressure with Inclined Cohesive Backfills: The Effect of Intermediate Principal Stress is Considered

Estimating passive earth pressure accurately is very important when designing retaining wall. Based on the unified strength theory and plane strain assumption, an analytical solution has been developed to determine the passive lateral earth pressure distribution on a retaining structure when the backfill is cohesive and inclined considering the effect of the intermediate principal stress. The solution derived encompasses both Bell’s equation (for cohesive or cohesionless backfill with a horizontal ground surface) and Rankine’s solution (for cohesionless backfill with an inclined ground surface).

The influence of roadway backfill on the coal pillar strength by numericalinvestigation

Stability of coal pillars and immediate rock mass is of importance in the bord and pillar extraction method underlying critical surface infrastructure. This paper describes the influence of roadway backfill on the coal pillar stability. Based on over 120 numerical models of various pillar height and backfill percentage, it is indicated that the pillar strength will increase with increasing roadway backfill, while the increase in pillar strength is greater for tall pillars than squat pillars for both cohesive and non-cohesive backfill. Modelling suggests that cohesive backfill is more effective in increasing both peak and post-peak pillar strength than non-cohesive backfill. It is also observed that the post-peak response will change from softening to hardening at a certain percentage of either cohesive or non-cohesive backfill.

Development of a generalised formula for dynamic active earth pressure

The Mononobe–Okabe method is widely used in practice to estimate dynamic active earth pressure. The method, derived from Coulomb's theory, cannot account for the effect of cohesion and hence cannot be used for a cohesive backfill. In addition, the effect of wall adhesion and external load cannot be taken into account. This paper develops a new general formula for dynamic active earth pressure on a yielding wall. The strength of the formula is that it can take into account the effects of cohesion, wall adhesion and external load on dynamic active pressure, while remaining simple in form. The dynamic earth pressures calculated by the proposed formula, the Mononobe–Okabe method, and the graphical solution are compared for validation. The comparisons demonstrate the accuracy of the proposed formula. The formula is used in a parametric study to investigate the influence of cohesion, wall adhesion and external load. This study shows that the additional terms can significantly influence the calculated dynamic active earth pressure.

Reply to Discussion of the Technical Note “Seismic Passive Earth Thrust on Retaining Walls with Cohesive Backfills Using Pseudo-Dynamic Approach” by A.H. Shafiee, A. Eskandarinejad, M. Jahanandish: Geotechnical and Geological Engineering, DOI 10.1007/s10706-010-9327-3

Reply to Discussion of the Technical Note “Seismic Passive Earth Thrust on Retaining Walls with Cohesive Backfills Using Pseudo-Dynamic Approach” by A.H. Shafiee, A. Eskandarinejad, M. Jahanandish: Geotechnical and Geological Engineering, DOI 10.1007/s10706-010-9327-3

Discussion of the Technical Note “Seismic Passive Earth Thrust on Retaining Walls with Cohesive Backfills using Pseudo-Dynamic Approach” by A.H. Shafiee, A. Eskandarinejad, M. Jahanandish: Geotechnical and Geological Engineering, DOI 10.1007/s10706-010-9327-3

Discussion of the Technical Note “Seismic Passive Earth Thrust on Retaining Walls with Cohesive Backfills using Pseudo-Dynamic Approach” by A.H. Shafiee, A. Eskandarinejad, M. Jahanandish: Geotechnical and Geological Engineering, DOI 10.1007/s10706-010-9327-3

Seismic Passive Earth Thrust on Retaining Walls with Cohesive Backfills Using Pseudo-Dynamic Approach

In this paper, the pseudo-dynamic approach is used to estimate seismic passive earth thrust on retaining walls with cohesive-frictional backfills. The time-dependent pseudo-dynamic approach considers the influence of dynamic parameters such as the velocity of primary and shear waves, the period of lateral shaking, and the phase and amplitude variations of horizontal and vertical earthquake accelerations with depth. The failure plane behind the wall is assumed to be planar. The analysis is based on the equilibrium of forces which act within the failure wedge. The obtained results show that the backfill cohesion increases both the seismic passive earth thrust and the failure plane inclination angle with the horizontal plane. It is also observed that both horizontal and vertical seismic accelerations have decreasing effect on seismic passive earth thrust as well as failure plane inclination angle. The results of present pseudo-dynamic analysis propose a lower solution for seismic passive earth thrust compared to earlier pseudo-static solution available in the literature.

Numerical analysis of reinforced soil-retaining wall structures with cohesive and granular backfills

The failure mechanisms of reinforced soil segmental walls with extensible reinforcements were studied by performing a numerical analysis using the finite element method. The numerical approach was first verified against the results of three instrumented full-scale structures reported in the literature. Finite element models with different combinations of reinforcement spacing, reinforcement length and backfill soil were analysed. The ϕ–c reduction method, which is a special shear strength parameter reduction technique, was applied to simulate the failure conditions. The results of ϕ–c reduction analysis were used to evaluate assumptions used in current design procedures for geosynthetic-reinforced soil walls. In particular, shear strains were used to identify failure surfaces. Interpretation of the results indicated that, for both granular and cohesive backfills, the potential failure surface gradually shifts to a direct sliding mode as the system approaches failure. As a result, under working loads the potential failure surface used in current design analysis is correct, but the failure plane of a geosynthetic-reinforced soil-retaining wall at failure approaches a direct sliding type or a bilinear plane, which starts from the toe of the wall with a very shallow slope.

Limitations of the theorem of corresponding states in active pressure problems

This paper analyzes the application of the theorem of corresponding states or the correspondence rule, as found in a number of advanced soil mechanics textbooks, and shows that it results in approximate solutions to limit-state problems. The limitations of the rule are made apparent by applying it to the determination of active pressures exerted on vertical retaining walls by cohesive–frictional backfills with inclined ground surfaces. A correct derivation of the correspondence rule is obtained for this case. An example is given that illustrates the inadequacy of this rule when boundary conditions are not properly accounted for in the analysis.Key words: theorem of corresponding states, active pressure, vertical retaining wall, inclined ground surface, cohesive–frictional backfill.

Comparison of Field and Laboratory Pullout Tests on Geosynthetics in Marginal Soils

The increasing use of geosynthetics to reinforce soils in many geotechnical engineering applications requires better evaluation of the soil–geosynthetic interface properties for use in the design and analysis of the different reinforced soil structures. The soil–geosynthetic interaction can be determined from direct shear tests or pullout tests. Until now, most research was focused on investigating the interface properties between geosynthetics and granular materials. Interest has increased in the use of marginal soils as backfill materials in mechanically stabilized earth (MSE) walls and embankments because of the cost-effectiveness of using the available cohesive soils. This strategy requires the evaluation of interaction parameters between geosynthetics and marginal soils. For this purpose, a series of laboratory and field pullout tests was carried out with different types of geosynthetic reinforcements in marginal silty clay soil of medium plasticity. Four types of geogrids and three types of geotextiles were used in this study. Laboratory and field pullout tests were compared. The coefficient of interaction ( Ci) between geosynthetics and cohesive backfill, the variation of pullout design parameters ( F*, α) with overburden depth, and the shear stress distribution along the reinforcement specimen also were evaluated.

Rotation of Cantilever Sheet Pile Walls

Cantilever sheet pile walls are used routinely to retain medium heights of earth in geotechnical practice. Earth pressures developed on either side of the sheet pile wall ensure its moment and force equilibrium. Cantilever sheet pile walls suffer rotation about a pivot point close to the base and generate passive and active earth pressures. Earlier methods to determine the pivot point either use iterative procedures or rely on centrifuge data or finite element analyses. In this paper a new method based on minimization of the moment ratio is proposed to determine the location of the pivot point. This method is applicable to both cohesionless and cohesive backfills. Consideration of moment equilibrium is sufficient to determine the pivot point and force equilibrium is automatically satisfied. The location of the pivot point obtained by this approach compared satisfactorily with the centrifuge and laboratory test data. The shear strength demand computed for these tests could predict when sheet pile walls became unstable. Finally the shear strength demand was linked to the shear strains and hence to the wall deflections that compare satisfactorily with experimental wall deflections.

Active earth pressure in cohesive soils with an inclined ground surface: Discussion

The author presents a solution for the active pressure acting on a vertical wall that retains a cohesive–frictional backfill with sloping ground surface (i.e., the general active Rankine problem in cohesive backfill). The first analytical solution to this problem was obtained by Resal (1910), and Frontard (1922) derived the equations of the sliding surfaces in the active and passive cases. These solutions are part of the graduate curriculum in geotechnical engineering at Ecole Polytechnique de Montreal. In addition, Kezdi (1974) presented a graphical procedure for the active case. The expressions for critical depth and limiting depth may be found in several good textbooks in soil mechanics, including that by Das (1994). A solution to the same problem appeared quite recently in the geotechnical literature (Mazindrani and Ganjali 1977), and Silvestri (1999) wrote a discussion to this paper. Equation [16] of Mazindrani and Ganjali (1997), despite missing a parenthesis, is the same equation as that obtained by the author (i.e., eq. [11]). As for the expression giving the inclination angle α of the failure plane as a function of depth, it can be simply derived by considering the angle ABG in Fig. 2. Let this angle be denoted by w. Silvestri (1999) gives the following expression for w:

Upper bound estimate of scaled reinforced soil retaining walls

A kinematic approach based on the framework of limit analysis is applied for stability analysis of model reinforced vertical and sloping walls with cohesive backfill that were brought to failure under self-weight in a geotechnical centrifuge. A rotational failure mechanism is used to compute critical heights of the unreinforced and reinforced models; and the Constrained Simplex method is employed in the optimization scheme. The prototype equivalent heights predicted by the analyses are within the distress range; i.e., development of tension crack and collapse of the retaining walls occurred during centrifuge tests.

Active earth pressure in cohesive soils with an inclined ground surface

An analytical solution is developed to determine the active lateral earth pressure distribution on a retaining structure when it consists of a cohesive backfill (internal friction angle ϕ > 0, cohesion c > 0) with an inclined ground surface. The solution derived encompasses both Bell's equation (for cohesive or cohesionless backfill with a horizontal ground surface) and Rankine's solution (for cohesionless backfill with an inclined ground surface). The orientation of the failure surface is also determined. Results indicate that, unlike the soil-wall scenarios of Bell and Rankine where the failure planes are parallel with a fixed orientation independent of the overburden pressure, for sloping cohesive backfill (ϕ > 0, c > 0) the slope of the failure surface is a function of the overburden pressure and becomes shallower with depth, thus forming a curvilinear failure surface. The solution developed can also be used to check the sustainability of a slope. The analytical solution can be programmed conveniently in a computer.Key words: retaining structure, active earth pressure, cohesive backfill.

Tire-reinforced earthfill. Part 1: Construction of a test fill, performance, and retaining wall design

The satisfactory disposal of scrap tires is a major environmental problem worldwide. This waste occupies valuable space in landfill sites, and tire stockpiles pose serious health and fire hazards. The use of scrap tires as reinforcement for construction of retaining walls and slopes is a viable method towards reduction of this waste. This paper describes the construction of a 57 m high × 17 m wide instrumented test fill, comprising both retaining wall and reinforced slope sections. Approximately 10 000 whole tires and tires with one sidewall removed, tied together with polypropylene rope, were used in both cohesionless and cohesive backfills. The testing program also included plate loading tests, field pull-out tests on tire mats, water-quality assessment in the field and laboratory, and other complementary laboratory testing. This first paper, in a series of three, demonstrates the practical feasibility of constructing reinforced earth fills using scrap tires. Results of large plate load tests and the field behaviour with particular reference to the design of the retaining wall sections are presented. The paper emphasizes the role of negative wall friction in increasing the active thrust when the retaining wall becomes more compressible than the backfill. Recommendations for the design of retaining walls using scrap tires are presented.Key words: scrap tires, earth reinforcement, retaining walls, reinforced slopes, plate load test, construction, performance.

Tire-reinforced earthfill. Part 2: Pull-out behaviour and reinforced slope design

The disposal of scrap tires has become a major environmental concern. The reuse of scrap tires in the reinforcement of earth structures can provide an attractive solution in reducing the number of used tires disposed in overcrowded landfills. This paper, the second in a series of three papers, discusses the behaviour of slopes reinforced with scrap tires and proposes design recommendations. A mat-reinforced slope can either fail by pull-out of the reinforcement or due to rupture of the attachment tying the tires. A large number of pull-out tests were performed on whole tires and tires with one sidewall removed embedded in sand and cohesive backfill. The pull-out resistance of tire mat reinforcement was primarily governed by the effective shear strength of the soil, and therefore it can provide an efficient means of reinforcement. However, large displacements were required to fully mobilize the ultimate pull-out capacity which must be considered in design.Key words: pull-out tests, scrap tires, reinforced slope, performance, design guidelines.

Discussion of “Lateral Earth Pressure Problem of Cohesive Backfill with Inclined Surface” by Z. H. Mazindrani and M. H. Ganjali

Discussion of “Lateral Earth Pressure Problem of Cohesive Backfill with Inclined Surface” by Z. H. Mazindrani and M. H. Ganjali

Discussions: Lateral Earth Pressure Problem of Cohesive Backfill with Inclined Surface

Discussions: Lateral Earth Pressure Problem of Cohesive Backfill with Inclined Surface