Compaction-induced Stress Research Articles

Evaluation of the effect of constant and non-constant Poisson’s ratio on reinforcement load of reinforced soil walls

This study analytically and numerically investigates the impact of constant and non-constant Poisson’s ratio on the mobilized maximum load in the reinforcements, Tmax, of reinforced soil walls with vertical facing under working stress conditions. This assessment is carried out considering different controlling factors including reinforcement stiffness, wall height, backfill friction angle, and compaction-induced stress. The analytical procedure and the numerical model are validated against data from an instrumented, large-scale, geosynthetic-reinforced soil wall under working stress conditions. Considering the key factors evaluated in the current study, the results show that the impact of the reinforcement stiffness is dominant over the approach used to consider Poisson’s ratio. A maximum difference of about 20% was obtained between the values of Tmax calculated using constant and variable Poisson’s ratios. This implies that, from a practical standpoint, it may be appropriate to adopt a simpler approach that utilizes a constant Poisson's ratio for the determination of Tmax under operational conditions.

Finite element analysis of compaction load to investigate the stress-deformation behavior of soil geosynthetic composite mass: A case study

When building Soil Geosynthetic Composite (SGC) walls, fill compaction is normally carried out by operating a compactor in a general direction parallel to the wall face. In other words, a moving point or area load is often used to apply a compaction load on a newly installed soil lift. Pham (2009) and Wu and Pham (2010) demonstrated that the compaction-induced stress (CIS) caused by multiple passes of a compactor moving toward or away from a section can be calculated by taking into account the compaction load applied directly above the section under consideration using a simplified stress path proposed by Duncan and Seed (1986). Additionally, by simulating the compaction, the CIS due to fill compaction may be correctly assessed. The CIS resulting from fill compaction can also be accurately assessed by simulating the compaction load, such as by applying a distribution load on top of each backfill layer or a distribution load at the top and bottom of each soil layer, or by applying various widths of strip load to the top of each backfill layer. The objective of this study was to validate the numerical simulation of the compaction load to stress deformation behavior of SGC mass under operating stress conditions. In order to conduct the numerical analysis, data from both a full-scale instrumented SGC mass based on large-scale soil geosynthetic composite (SGC) experiments and a 6 m-high SGC (Pham, 2009) were employed. This study will examine a few SGC behavior parameters, including reinforcement strains, lateral displacements, and reinforcement strains. The objective of the FE modeling is to demonstrate the effect, emphasize the significance of the compaction conditions to the stress-deformation behavior of SGC mass, and validate the findings from the field-scale experiments and proposed model by Pham (2009) and Wu and Pham (2010).

Evaluation of the effect of surcharge on the behavior of geosynthetic-reinforced soil walls

In the current paper, using experimental studies and numerical analyses, the effect of surcharge width on the behavior of geosynthetic-reinforced soil (GRS) walls is evaluated under working stress conditions. Experimental tests were performed at the Geotechnical Laboratory of COPPE/UFRJ, using block and wrapped-face walls. Four well-instrumented GRS walls were examined considering different facing type and surcharge width. The numerical analysis of GRS walls was carried out using the two-dimensional computer program PLAXIS. Parametric studies were carried out with different combinations of surcharge width, wall height, compaction induced stresses (CIS) and face inclination. The results indicate the effect of the surcharge width in combination with other investigated factors on the magnitude and the position of the maximum reinforcement load and the lateral facing displacement of GRS walls.

Stress-dependent method for calculating the modulus improvement factor in geocell-reinforced soil layers

This paper presents an analytical method for determining the modulus improvement factor (MIF) in geocell-reinforced soil layers. Using a modified version of the hyperbolic soil model as a constitutive model, the method is developed based on the soil-reinforcement interaction relating nonlinear elastic soil behavior to the linear elastic response of the reinforcement. The proposed method, in an original way, explicitly takes into account the geometry of the geocell pocket, effects of soil and geocell-reinforcement stiffness, compaction-induced stresses, soil strength and strain compatibility. The method can be used both analytically and using simple and presented non-dimensional charts. Parametric analyses show that the reinforcement, soil relation and the stresses induced during the compaction procedure are the major factors influencing MIF. An evaluation using data from several laboratory, full-scale and field experiments in works is presented showing good predictive capability of proposed method. An application procedure for calculating MIF is presented.

Experimental, numerical, and analytical investigation of the effect of compaction-induced stress on the behavior of reinforced soil walls

Experimental, numerical, and analytical investigation of the effect of compaction-induced stress on the behavior of reinforced soil walls

Impacts of Compaction Load and Procedure on Stress-Deformation Behaviors of a Soil Geosynthetic Composite (SGC) Mass—A Case Study

Fill compaction in the construction of Geosynthetic Reinforced Soil (GRS) mass is typically performed by operating a vibratory or roller compactor, which in turns imposed a compaction load in direction perpendicular to the wall face. The compaction process resulted in the development of the so-called compaction-induced stress (CIS), which may subsequently increase the stiffness and strength of the fill material. Compaction process is normally simulated using one of the following compaction procedures—(i) a uniformly distributed load acting on the top surface of each soil lift, (ii) a uniformly distributed load acting on the top and bottom surface of each soil lift, and (iii) a moving strip load with different width. Uncertainties such as compaction procedures, compaction and surcharge loads led to the disparity in studying the mechanism of GRS mass. This paper aimed to study the impact of compaction load, compaction procedure, surcharge load and CIS on the stress-deformation behavior of GRS mass via the simulation of a 2 m high Soil Geosynthetic Composite (SGC) mass and a 6 m high GRS mass. The results were examined in terms of reinforcement strains, wall lateral displacements, and net CIS. Results from the analysis show the important impacts of compaction conditions on the stress-deformation behavior of SGC mass and the CIS.

Numerical- simulation of compaction-induced stress for the analysis of RS walls under surcharge loading

This study numerically investigates the behaviour of a geosynthetic-reinforced soil (GRS) wall under surcharge loading. Data from a full-scale GRS physical model wall was used to verify the numerical analysis. The modelling was carried out using the two-dimensional finite difference computer program FLAC to verify the post-construction performance of a full-scale GRS segmental wall under surcharge loading. The real value of compaction induced stress (CIS) specified for the vibrating plate compactor used in the physical model wall was employed in the analyses. Two procedures for modelling the CIS found in the literature were used in the analyses: uniform vertical stress applied to the surface of each layer (type I) and uniform vertical stress applied at the top and bottom of each layer (type II). The results clearly showed that the numerical analyses using compaction procedure type II accurately represent the measured values obtained from the full-scale wall under surcharge loading as well as during construction. The numerical analyses considering type I compaction modelling overestimated the measurements during both construction and surcharge application.

COMPACTION–INDUCED STRESS IN GEOSYNTHETIC REINFORCED SOIL WALLS

Compaction equipment worked behind the retaining walls causes additional lateral earth pressures acting on the wall. The effect of compaction-induced stress (CIS) usually neglected when designing the retaining walls. Geosynthetic-Reinforced Soil walls (GRS walls) have increasing popularity in Egypt in the last years. The earth pressure at the facing of a Geosynthetic Reinforced Soil wall (GRS wall) is different from that in the natural soil. The internal lateral pressure in the GRS soil is governed by compaction-induced stresses (CIS) and additional confining effects that the reinforcement provides to the soil. The compaction-induced stress for GRS wall is difficult to be predicted during the design stage because it depends on the characteristics of compaction equipment and other factors. The objectives of the research are:1) Studying the effect of compact the backfill of GRS wall by vibratory plates on the internal stability, the external stability, and the foundation soil for GRS wall. 2) Evaluating the performance of the various types of vibratory plates which used to compact the backfill for GRS wall. So, a finite element analysis using GEO5 program was used to achieve these objectives. Finally, the recommendations for the design and construction of GRS walls were highlighted.

“Numerical simulation of compaction-induced stress for the analysis of GRS walls under working conditions” by S. H. Mirmoradi and M. Ehrlich, Geotextiles and Geomembranes, 46 (2018), pp. 354-365

“Numerical simulation of compaction-induced stress for the analysis of GRS walls under working conditions” by S. H. Mirmoradi and M. Ehrlich, Geotextiles and Geomembranes, 46 (2018), pp. 354-365

“Numerical simulation of compaction-induced stress for the analysis of RS walls under working conditions” by S. H. Mirmoradi and M. Ehrlich, Geotextiles and Geomembranes, 46 (2018), pp. 354-365

“Numerical simulation of compaction-induced stress for the analysis of RS walls under working conditions” by S. H. Mirmoradi and M. Ehrlich, Geotextiles and Geomembranes, 46 (2018), pp. 354-365

Compaction-induced stress in geosynthetic-reinforced granular base course – A discrete element model

A discrete element method (DEM) model was used to simulate the development of compaction-induced stress in a granular base course, with and without geogrid reinforcement. The granular base course was modeled as a mixture of uniformly sized triangular particles. The geogrid was modeled as a series of equally spaced balls that interact with each other through long-range interaction contacts. The long-range interaction contact was also used to simulate a deformable subgrade. The compactor was modeled as a solid cylinder rolling at a constant speed. The DEM model shows that the geogrid-reinforced granular base course gains additional compaction-induced stress due to the residual tensile stress developed in the geogrid. The residual tensile stress in the geogrid increases with the number of compaction passes. Parametric analyses were also conducted to assess the effects of geogrid stiffness and subgrade modulus on the compaction-induced stress.

Numerical simulation of compaction-induced stress for the analysis of RS walls under working conditions

This paper aimed to verify numerical modelling of compaction-induced stress (CIS) for the analysis of geosynthetic-reinforced soil (GRS) walls under working stress conditions. Data from a full-scale well-instrumented GRS wall was used for a numerical analysis. The results from the wall used in this study have already been used for validation in several other numerical modelling studies. Nevertheless, in none of these studies was the real value of CIS specified for the vibrating plate compactor used in the wall employed. In the present study, the real value of CIS is employed. The CIS is modelled using a new procedure presented in this paper in addition to two other procedures found in the literature. The results indicate that when the real value of CIS was simulated using a strip load applied to the top of each backfill layer, the numerical model accurately represented the measurements. The accuracy of the results, however, depends on the width of the strip load used to model the CIS. Nevertheless, as this type of compaction modelling procedure is time consuming, modelling of CIS by applying a distribution load at the top and bottom of each soil layer is suggested as an alternative procedure.

Inversion of multicomponent seismic time shifts for reservoir pressure and length: a feasibility study

Pressure drops associated with reservoir production generate excess stress and strain that cause travel-time shifts of reflected waves. Here,we invert time shifts of P-, S-, and PS-waves measured between baseline and monitor surveys for pressure reduction and reservoir length. The inversion results can be used to estimate compaction-induced stress and strain changes around the reservoir. We implement a hybrid inversion algorithm that incorporates elements of gradient, global/genetic, and nearest neighbour methods and permits exploration of the parameter space while simultaneously following local misfit gradients. Our synthetic examples indicate that optimal estimates of reservoir pressure from P-wave data can be obtained using the reflections from the reservoir top. For S-waves, time shifts from the top of the reservoir can be accurately inverted for pressure if the noise level is low. However, if noise contamination is significant, it is preferable to use S-wave data (or combined shifts of all three modes) from reflectors beneath the reservoir. Joint wave type inversions demonstrate improvements over any single pure mode. Reservoir length can be estimated using the time shifts of any mode from the reservoir top or deeper reflectors. We also evaluate the differences between the actual strain field and those corresponding to the best-case inversion results obtained using P- and S-wave data. Another series of tests addresses the inversion of the time shifts for the pressure drops in two-compartment reservoirs, as well as for the associated strain field. Numerical testing shows that a potentially serious source of error in the inversion is a distortion in the strain-sensitivity coefficients, which govern the magnitude of stiffness changes. This feasibility study suggests which wave types and reflector locations may provide the most accurate estimates of reservoir parameters from compaction-induced time shifts.

Modeling of the compaction-induced stress on reinforced soil walls

A new simple analytical procedure (AASHTO modified) that includes the effect of the induced stress due to backfill compaction for use with conventional design methods of geosynthetic reinforced soil (GRS) walls is proposed. The proposed analytical procedure may be used with any conventional design methods that do not take into consideration the effect of the compaction-induced stress in their calculations. This approach is based on an equation suggested by Wu and Pham (2010) to calculate the increase in lateral stress in a reinforced soil mass due to compaction. Additionally, two numerical procedures for modeling of compaction are described. Analyses using these procedures were performed to evaluate the capability of the proposed analytical procedure. The results were compared with values predicted using the Ehrlich and Mitchell (1994) method, the modified version of the K-stiffness method (Bathurst et al., 2008) and the AASHTO simplified method. The results show that the AASHTO modified method and the numerical analyses, in which the compaction-induced stress was modeled using two distributed loads at the top and bottom of each soil layer, resulted in values of the maximum reinforcement tension, Tmax, that agree with those from the full-scale test and those calculated by Ehrlich and Mitchell (1994). On the other hand, the K-stiffness method under-predicts the measured Tmax values. Moreover, numerical modeling of compaction using a distribution load only at the top of each soil layer overestimated the measurements.

MODELING OF THE COMPACTION-INDUCED STRESSES IN NUMERICAL ANALYSES OF GRS WALLS

This article presents a numerical approach for modeling of the compaction-induced stresses on the analyses of geosynthetic reinforced soil (GRS) walls. The modeling of the backfill compaction stresses was described and analyses were performed using this suggested procedure. Two distribution loads at the top and bottom of each soil layer were used to simulate the vertical induced stress due to backfill soil compaction. The suggested procedure was validated with the results of a wrapped-faced full-scale reinforced soil wall performed at the Geotechnical Laboratory of COPPE/UFRJ. The results of the simulation using this procedure were compared with another procedure reported in the literature. Parametric studies were carried out to verify the effect of compaction induced stress and surcharge loads on the behavior of GRS walls. Results show that the compaction procedure suggested in the present paper was able to properly represent the measured values of the summation of the maximum tension in the reinforcement and lateral movements. It was verified that the compaction procedure used in the literature overestimated the measured values, and this discrepancy increases with depth and also with compaction effort.

Modeling and analysis of compaction-induced traveltime shifts for multicomponent seismic data

Modeling of time shifts associated with time-lapse (4D) seismic surveys is helpful in evaluating reservoir depressurization and inverting for subsurface stress. Using coupled geomechanical and full-waveform seismic modeling, we study the influence of compaction-induced stress and strain around a simplified reservoir on compressional (P), shear (S), and mode-converted (PS) waves. We estimate compaction-induced time shifts and analyze their dependence on reflector depth and pressure drop inside the reservoir. Time shifts between synthetic baseline and monitor surveys are obtained by processing techniques that are potentially applicable to field data. Although P-wave time-shift lags for reflectors in the overburden are indicative of induced anisotropy, they are two to three times smaller than S-wave time-shift leads for reflectors beneath the reservoir. We also investigate the contributions of the deviatoric and volumetric stains to the time shifts for all three modes. Time shifts for S- and PS-waves are strongly influenced by elevated volumetric and deviatoric strains inside the reservoir. Almost constant S-wave time shifts for a range of offsets and source locations indicate that the contribution of stress-induced velocity anisotropy to shear-wave signatures is weak because the symmetry is close to elliptical. Our modeling also shows that mild tilt of a rectangular reservoir, or its replacement with an elliptically shaped reservoir of the same aspect ratio, has little influence on time shifts. Potentially, the developed methodology can be applied to estimate compaction-induced stress fields using simple compartmentalized reservoir models.

An analytical model for evaluation of compaction-induced stresses in a reinforced soil mass

When an earth fill is subject to loading and subsequent unloading, it will bring about an increase in the lateral stress, provided that there is sufficient constraint to lateral deformation of the soil mass. The increase in lateral stress is commonly known as the "residual" or "lock-in" lateral stress. The residual stress resulted from compaction operation, which involves a series of loading and unloading onto a soil mass, is referred to as "compaction-induced stress" (CIS). The CIS will increase the stiffness and strength of the soil mass, and is an important factor to be considered in the behavior of compacted soil. A number of studies have been conducted on the CIS in an unreinforced soil mass. With a reinforced soil, the CIS is likely to be much more pronounced because there is a higher degree of constraint to lateral deformation in a reinforced soil mass due to soil-reinforcement friction. An analytical model, referred to as the CIS model, is developed for evaluation of compaction-induced stress in a reinforced soil mass. Correlations for determination of model parameters are given so that the parameters can be estimated through reinforcement spacing and stiffness, and common soil parameters, such as the angle of internal friction (Φ), and overconsolidation ratio (OCR). In addition, the stress paths of typical fill compaction operation are discussed, including compaction with a plant moving toward and away from a section under consideration, and compaction with multiple passes. The CIS model presented in this paper is found to give CIS values very close to those obtained from sophisticated finite element analysis of a 6-m high GRS mass under different values of compaction pressure. The CIS in the reinforced soil mass is significant under compaction pressures typically used in actual fill compaction.

FE analyses: compaction-induced stresses and deformations : J Geotech Engng Div ASCEV112, N1, Jan 1986, P23–43

FE analyses: compaction-induced stresses and deformations : J Geotech Engng Div ASCEV112, N1, Jan 1986, P23–43