Bearing Reinforcement Earth Wall Research Articles

Pullout resistance mechanism of bearing reinforcement embedded in coarse-grained soils: Laboratory and field investigations

Abstract The bearing reinforcement system has been invented as a cost-effective earth reinforcement and comprises a longitudinal member and a set of transverse members. This research was undertaken to determine the pullout resistance mechanism of bearing reinforcement embedded in coarse-grained soils. The effect of water content and gradation on the pullout mechanism of the bearing reinforcement was also investigated. The pullout resistance is the sum of pullout friction contributions from the longitudinal member, Pf,max and bearing resistance contributions from the transverse members, Pbn. The interface angle between the longitudinal member and backfill ( δ ) is dependent upon the water content and gradation. The δ / ϕ is a constant and can be taken as 1.51, where ϕ is the friction angle. Generalized Pbn predictive equations in terms of transverse member interference factor (F), inherent failure angle ( β ) and interlocking were verified based on laboratory pullout testing data. The field investigation on the bearing reinforcement earth (BRE) wall indicated that the measured Pbn of bearing reinforcement is higher than the predicted one as field reinforcements are subjected to transverse displacement and oblique pullout due to the deformation of backfill. From the critical analysis of laboratory and field investigations, proposed methods for predicting the pullout resistance of bearing reinforcement and for estimating final lateral movement of the BRE wall on the hard stratum are presented, which are useful for BRE wall design.

Performance of the bearing reinforcement earth wall as a retaining structure in the Mae Moh mine, Thailand

In this research, a Bearing Reinforcement Earth (BRE) wall with a residual clay stone backfill was successfully implemented as an alternative truck ramp support for an on-site crusher plant in the Mae Moh mine, Thailand. The performance of the BRE wall during and after the end of construction as well as during the service state was evaluated in terms of, settlement, bearing stress, lateral movement, lateral earth pressure and tension force in the reinforcements. Bearing reinforcement is a cost-effective inextensible earth reinforcement, which is composed of a longitudinal member and transverse members. The maximum settlement at the end of construction (20 days) was about 5 mm. The installation of the truck ramp (10 days after the end of construction) resulted in an immediate settlement of about 2 mm. The final settlement due to the backfill, truck ramp and truck load after 270 days was found to be uniform due to the contribution of bearing reinforcement and was approximately 25 mm. The bearing stress which was uniformly distributed was found to increase rapidly with construction time, which was in agreement with the relatively uniform settlements. The lateral wall movement at the front and lateral sides at the end of construction was very small with the maximum movement (at the top of the wall) found to be less than 10 mm. As such, the ratio of lateral movement to height (δ/H) was found to be approximately 0.12%, which was lower than the allowable value of 0.4%. With this low δ/H and the insignificant change in the measured settlement and lateral movement during service, the BRE wall was considered to have a very high stability. The coefficients of lateral earth pressure, K and depth relationship were proposed based on the analysis of measured maximum tensile force in the reinforcements. The maximum tension plane of the BRE wall could be represented by the coherent gravity hypothesis. Using the proposed K and maximum tension plane, the internal stability of the BRE wall was furthermore examined. A proposed method of designing the BRE wall with claystone backfill was also proposed.

Pullout resistance mechanism of bearing reinforcement embedded in residual clayey soils

A bearing reinforcement earth (BRE) wall was proposed as an alternative, temporary structure replacing a natural slope to enhance performance and slope stability. The pullout resistance mechanism of the bearing reinforcement embedded in the compacted residual soils (red clay and claystone), which is required for BRE wall design, is investigated in this paper. The pullout resistance predictive method is recommended for both soils. The pullout resistance of the bearing reinforcement comprises both friction and bearing components. The peak interface factor (αp) between the soil and the longitudinal member is found to be 0.66 and 0.40 for red clay and claystone, respectively, while the residual interface factor (αr) is 0.47 and 0.22 for red clay and claystone, respectively. Though the red clay has a higher αp and αr than the claystone, the friction pullout resistance is lower than that of the claystone due to a lower shear strength. The pullout bearing resistance of transverse members (Pbn) can be calculated ...

Numerical parametric study on behavior of bearing reinforcement earth walls with different backfill material properties

This paper presents a numerical parametric study on behavior of bearing reinforcement earth (BRE) walls with different backfill properties using the finite-element method software PLAXIS 2D. The primary objective of this study was to improve the understanding of bearing stress, settlement, lateral earth pressure, and horizontal wall movement of BRE walls with different backfill materials. The second objective of this study was to evaluate the effects of various soil–structure interactions, foundations, and stiffness of reinforcements on horizontal wall deformations. The backfill materials consisted of four types of soil, which were mixtures of silty clay and sand at different fine contents of 2, 20, 40, and 80% by dry weight. The model parameters for the numerical simulation were obtained from the conventional laboratory tests and back-calculated from the laboratory pullout tests of the bearing reinforcement. The geotextile elements were used to model the bearing reinforcements by converting the contribution of friction and bearing resistances to the equivalent friction resistance, which was represented by the soil–bearing reinforcement interaction ratio, Rinter. The values of Rinter decreased following a polynomial function as an increase of fine content in the ranges of 0.65–0.38 and 0.75–0.40 for the numbers of transverse members, n = 2 and 3, respectively. The simulated bearing stress in the reinforced zone decreased from the front to the back of the wall because the BRE wall behaved as a rigid body built on the relatively firm foundation retaining the unreinforced backfill. The foundation settlement decreased from the facing of the wall to the unreinforced zone for all backfill properties due to the slight rotation of the wall. The relationship between the maximum horizontal wall movement and the fine content can be expressed by a polynomial function. The maximum horizontal wall movement significantly increased as the fine content increased. The excessive movement was realized when the fine content was greater than 45%. The increase of the fine content moved the location of the maximum wall movement higher up from the mid to the top of the wall. A numerical parametric study was conducted to investigate the soil–structure interaction, foundation, and stiffness of reinforcement. These parameters affected the horizontal wall deformation, which is especially important for serviceability of BRE walls. The knowledge gained from this study provides a preliminary guideline in predicting the behavior of BRE walls and may be used to investigate other BRE walls with different wall heights and features of bearing reinforcements.

Numerical and sensitivity analysis of Bearing Reinforcement Earth (BRE) wall

Numerical and sensitivity analysis of the Bearing Reinforcement Earth (BRE) wall were carried out using PLAXIS 2D. The numerical and sensitivity analysis was performed by varying the foundation conditions (thickness, T and modulus of elasticity, E of the weathered crust) and the BRE wall properties (number of transverse members, n, reinforcement length, L, wall height, H, reinforcement vertical spacing, Sv and axial stiffness of reinforcement, EA). The studied L/H ratio is between 0.7 and 1.0 and the geotextiles elements were used to model the reinforcement. The settlement of the BRE wall is governed by E, T, and H, irrespective of the BRE wall properties. The bearing stress distribution is essentially the same even with different E, T, n, Sv, EA. The magnitude of bearing stress is mainly controlled by H. The lateral movement pattern is primarily dependent upon Sv for a particular H. The inward movement exists for small Sv value while the outward movement exists for large Sv value. The magnitude of lateral movement is controlled by E, T, L and n. For a particular foundation condition (E and T), an increase in n is more advantageous than an increase in L because the lateral movement is insignificantly reduced when L/H > 0.8. The maximum tension and AASHTO recommended failure plane were found not to coincide in the serviceability state. In the serviceability state, the tie points must be stronger than the reinforcements for the wall height > H/2 while the reinforcement must be stronger than the tie point for the wall height < H/2. The simplified K versus H relationship is a practical tool to examine the factor of safety based on the conventional method.

Pullout resistance of bearing reinforcement embedded in marginal lateritic soil at molding water contents

The effect of molding water contents (on dry and wet sides of optimum water content) on the pullout resistance mechanism of the bearing reinforcement embedded in a marginal lateritic soil is investigated in this paper. The total pullout resistance is contributed from the pullout friction and bearing resistances. The pullout friction resistance is approximated from the soil shear strength and interaction factor, α. The peak and residual interaction factors (αp and αr) are independent of molding water contents tested and are approximately 0.63 and 0.46, respectively. The bearing pullout resistance of a single isolated transverse member is dependent upon both shear strength and failure mode and can be approximated from the modified punching shear solution with various angles of transformation, β. The β values of the compacted soil at 0.67≤w/wOWC≤1.0 are essentially constant and equal to π/2 (where wOWC is the optimum water content). For 1.0<w/wOWC≤1.33, the β value decreases polynomial with an increase in w/wOWC. The failure mechanism of the bearing reinforcement is classified into three zones (block, interference and individual), depending upon spacing and dimension of transverse member, S/B ratio. The transverse member interference zone is independent of water content when 0.67≤w/wOWC≤1.0 and decreases as w/wOWC increases when 1.0<w/wOWC≤1.33. Based on a critical analysis of the test results, the pullout resistance equations in term of normal stress, shear strength parameters, S/B and molding water content are proposed. The proposed equations are useful for the internal stability analysis of bearing reinforcement earth walls during construction and at the end of construction.

Effect of fine content on the pullout resistance mechanism of bearing reinforcement embedded in cohesive–frictional soils

Bearing reinforcement, which is composed of a longitudinal member (steel deformed bar) and transverse (bearing) members (a set of equal angle steel), has been established as an effective earth reinforcement material. The equation for estimating the pullout resistance of this reinforcement in coarse-grained soils has been previously developed. The usage of locally available soils as a backfill is particularly cost effective for construction sites where there is a lack of available quality materials. The pullout resistance mechanism of the bearing reinforcement embedded in cohesive–frictional soils with various fine contents is presented in this paper. The total pullout resistance is the sum of the pullout friction and bearing resistances. The pullout friction resistance is approximated from soil shear strength and interaction factor α, which is linearly related to fine content. The bearing pullout resistance of a single isolated transverse member can be approximated from the modified punching shear mechanism where the failure plane angle, β is primarily dependent upon fine content. The relationship between β and fine content is expressed by a polynomial function. The β value of π/2 is suggested for fine contents less than 45%. The transverse member interference is classified into three zones, depending upon spacing and dimension of transverse member, S/B ratio. The larger softened region caused by transverse member interference develops with smaller fine content. Based on a critical analysis of the test results, the pullout resistance equations for bearing reinforcement with different normal stresses, dimensions and spacing of transverse members embedded in different cohesive–frictional soils compacted at optimum point (optimum water content and maximum dry unit weight) are developed in term of total strength parameters. The application of the proposed equations are finally illustrated and verified. The developed equations is useful for the internal stability analysis of bearing reinforcement earth walls during construction and at the end of construction.

Pullout resistance of bearing reinforcement embedded in coarse-grained soils

The bearing reinforcement was developed as a cost-effective earth reinforcement. It is composed of a longitudinal member and transverse members. The longitudinal member is made of a steel deformed bar and the transverse members are a set of equal angles. The present article studies the influence of soil properties (friction angle, grain size and gradation) and dimension and spacing of the transverse members on the pullout mechanism of the bearing reinforcement. The total pullout resistance is the sum of the pullout friction and the pullout bearing resistance. The tan δ/tan ϕ ratio, where δ is the friction angle between soils and the longitudinal member and ϕ is the internal friction angle of soil, is greater than unity because of the roughness and rigidity of the steel deformed bar. The bearing failure mechanism of a single transverse member is dependent upon the B/D50 value, where B is the leg length of the transverse member and D50 is the average grain size of the soil. The transverse member interference is dependent upon the ratio of spacing between transverse members and the leg length of transverse members, S/B. Based on a critical analysis of the test results, the pullout resistance equations of the bearing reinforcement with different dimensions and spacing between transverse members embedded in different coarse-grained soils are introduced and verified. These equations were developed based on a limit equilibrium analysis, which is a simple rational method for analyzing the internal stability of bearing reinforcement earth walls.

Numerical analysis of bearing reinforcement earth (BRE) wall

This paper presents a numerical simulation of the bearing reinforcement earth wall by PLAXIS 2D. The bearing reinforcement was regarded as a cost-effective earth reinforcement. The model parameters for the simulation were obtained from the conventional laboratory tests and back analyses from the laboratory pullout tests of the bearing reinforcement. The simplified method for modeling the bearing reinforcement, which converts the contribution of friction and bearing resistance to the equivalent friction resistance, is introduced. This method is considered to be acceptable and practical in working state with sufficient factor of safety and small pullout displacement. The bearing reinforcement is modeled as the geotextile and the equivalent friction resistance is represented by the soil/reinforcement interface parameter, R, which was obtained from a back analysis of the laboratory pullout test results. The R values are 0.65 and 0.75 for the bearing reinforcement with 2 and 3 transverse members, respectively. The change in bearing stresses, settlements, lateral earth pressures and tensions in the reinforcements during and after construction is simulated. Overall, the simulated test results are in good agreement with the measured ones. The simulated results show that the BRE wall behaves as a rigid body, retaining the unreinforced backfill. The simulated bearing stress presents a trapezoid distribution shape as generally assumed by the conventional method of examination of the external stability of MSE walls. The simulated settlement is almost uniform due to a high stiffness of the rigid foundation and the bearing reinforcements. The maximum lateral movement occurs at about the mid-height of the wall, resulting in the bi-linear maximum tension plane. The knowledge gained from this study can be applied to other BRE walls with different wall heights, foundations and features of bearing reinforcements.

Performance of an earth wall stabilized with bearing reinforcements

This article presents the performance of a fully instrumented test wall reinforced with bearing reinforcement. Bearing reinforcement is an inextensible earth reinforcement. It is composed of a longitudinal member and transverse members. The longitudinal member is a deformed steel bar and the transverse members are a set of equal steel angles. The test wall was 6 m high, 9 m long at the top, 6 m wide at the top, and 12 m long, 21 m wide at the base and was constructed on a hard stratum. The facing panels were made of segmental concrete block which measured 1.50 × 1.50 × 0.14 m in dimension. From the full-scale test results, the bearing stress distribution is a trapezoid shape as generally assumed for the examination of the external stability of MSE walls. The tilt of the bearing reinforcement earth (BRE) wall indicates that the BRE wall behaves as a rigid body. The coefficients of earth pressure decrease with depth and approach the active state at deeper reinforcement level. From the variation in the stiffness factor as a function of depth and lateral earth pressure, the bearing reinforcement has a stiffness factor of K/ K a = 1.7, which is much lower than that of steel grids and metal strips. The lower tension (coefficient of lateral earth pressure) reduces the cross-sectional area of the longitudinal members and hence cost effectiveness. The maximum tension line (possible failure plane) of the BRE wall is bilinear, similarly to the coherent gravity structure hypothesis, which is commonly used for the analysis of inextensible reinforcements. Finally, the suggested method of designing the BRE wall is presented. It has been successfully used to design several BRE walls founded on the hard stratum in different areas in Thailand.