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In the present study, performance of geosynthetic reinforced MSE walls backfilled with locally available marginal lateritic soil at the onset of rainfall infiltration was investigated. Two different types of geosynthetics reinforcements were used. One was a conventional type of geogrids usually used in MSE walls, and the other was composite geogrids. Seepage analysis, stability analysis and strength and deformation analysis were carried out on MSE walls with rainfall simulated for a duration of 3 days. In case of geogrid reinforced soil wall (GR-W), the suction within the backfill was lost completely at the end of 2.176 days of rainfall, whereas suction was maintained even at the end of 3 days of rainfall in walls reinforced with composite geogrids (CGR-W). From the stability analysis, it was observed that the factor of safety of GR-W decreased at the onset of rainfall infiltration with time and reached less than the desirable value of less than 1.5 in 2.125 days of rainfall. The factor of safety of CGR-W was maintained at 1.88 throughout the period of rainfall. The facing deformation in GR-W was found to increase, with a maximum of 3.2 times increase at the end of three days of rainfall. Similarly, there was an increase in maximum tensile load mobilized in the reinforcements in GR-W, whereas in the case of CGR-W, the influence of rainfall was negligible. From the present study, it can be concluded that the presence of composite geogrids improves the overall performance of MSE walls backfilled with marginal lateritic backfills.
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International Journal of Geosynthetics and Ground Engineering (2021) 7:9
Performance ofGeosynthetic Reinforced MSE Walls withMarginal
Backfills attheOnset ofRainfall Infiltration
S.Vibha1· P.V.Divya1
Received: 9 August 2020 / Accepted: 26 December 2020 / Published online: 16 January 2021
© The Author(s), under exclusive licence to Springer Nature Switzerland AG part of Springer Nature 2021
In the present study, performance of geosynthetic reinforced MSE walls backfilled with locally available marginal lateritic
soil at the onset of rainfall infiltration was investigated. Two different types of geosynthetics reinforcements were used. One
was a conventional type of geogrids usually used in MSE walls, and the other was composite geogrids. Seepage analysis,
stability analysis and strength and deformation analysis were carried out on MSE walls with rainfall simulated for a duration
of 3days. In case of geogrid reinforced soil wall (GR-W), the suction within the backfill was lost completely at the end of
2.176days of rainfall, whereas suction was maintained even at the end of 3days of rainfall in walls reinforced with composite
geogrids (CGR-W). From the stability analysis, it was observed that the factor of safety of GR-W decreased at the onset of
rainfall infiltration with time and reached less than the desirable value of less than 1.5 in 2.125days of rainfall. The factor
of safety of CGR-W was maintained at 1.88 throughout the period of rainfall. The facing deformation in GR-W was found
to increase, with a maximum of 3.2 times increase at the end of three days of rainfall. Similarly, there was an increase in
maximum tensile load mobilized in the reinforcements in GR-W, whereas in the case of CGR-W, the influence of rainfall
was negligible. From the present study, it can be concluded that the presence of composite geogrids improves the overall
performance of MSE walls backfilled with marginal lateritic backfills.
Keywords Geosynthetics· Reinforced soils· MSE wall· Marginal lateritic backfill· Rainfall
Mechanically stabilized earth structures (MSE) or reinforced
soil structures have become very popular in enhancing the
stability of soil structures. Often, reinforced soil structures
are used for the construction of approach ways for flyovers
and slope stabilization works. Ideally, freely draining granu-
lar soils such as sand are used as backfill of MSE walls. An
ideal backfill soil ensures proper drainage and load transfer
between the reinforcements and the soil. Reinforced soil
structures require a huge quantity of backfill soil. Backfill
constitutes to about 50–75% of total cost of the wall [1].
FHWA recommends soil with less than 15% fines (pass-
ing through 75µ sieve) and plasticity index less than 6,
as the ideal backfill material for reinforced soil structures
[2]. However, the scarcity of such ideal backfill material
has increased the tendency to use locally available soil in
reinforced soil applications. Any soil which does not meet
the requirements of an ideal backfill material is termed as
marginal backfill soil [3, 4].
The role of rainfall in triggering the failures in geotech-
nical structures is widely recognized. The pores in soil are
partially filled with water and remains unsaturated in the
region above the ground water table [5]. Rainwater infil-
tration and associated fluctuations in the pore water pres-
sure and shear strength are influenced by the unsaturated
soil properties. The stability of residual soil slopes during
rainwater infiltration is greatly influenced by the mechani-
cal and hydraulic behavior of unsaturated soils [69]. In the
case of unsaturated soils, both volumetric water content and
the co-efficient of permeability are significantly affected by
the combined changes in matric suction and void ratio [10].
Unlike saturated soils, the stress state in unsaturated soils are
expressed in terms of two independent stress state variables,
net normal stress (σua) and matric suction (ua−uw) [11].
The shear strength of unsaturated soil is given by extended
Mohr–Coulomb criteria [12] as shown in Eq.1:
* P. V. Divya;
1 Department ofCivil Engineering, Indian Institute
ofTechnology Palakkad, Palakkad, Kerala, India
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... This geosynthetic material is a geocomposite of a geogrid combined to a nonwoven geotextile. Many authors demonstrated the efficiency of this type of reinforcement to dissipate pore water pressure developed inside the reinforced zone (Portelinha et al., 2013, Bui Van et al. 2017, Portelinha and Zornberg, 2017, Yang et al., 2018, Razeghi et al., 2019, Bhattacherjee and Viswanadham 2019, Albino et al., 2020, Vibha and Divya, 2021, Yoo et al. 2022. Meanwhile, some of these authors the adverse capillary break effect on unsaturated soil-geosynthetic interfaces, halting the wetting front, and leading to positive PWP accumulated at the interface between the soil and the underlying geotextile. ...
Full-text available
Geosynthetic-reinforced soil (GRS) walls using marginal soils can operate under unsaturated conditions depending on climate conditions and drainage inside the reinforced zone. Geocomposite reinforcements have been suggested to act as internal drainage layers, but their hydraulic behavior can also be strongly affected by climate conditions. Numerical analyses were conducted to observe the impact of four distinct tropical climate conditions (arid, semi-arid, humid subtropical and humid tropical) on suction profiles and stability of reinforced soil walls constructed using geogrid and geocomposite reinforcements. The climate simulation involved the incorporation of a soil-atmosphere interaction on water balance and on the unsaturated transient infiltration. Results indicate the GRS walls can operate under relatively high suction levels under arid climates in which cumulative evaporation overcomes infiltration. Any climate that has rainy seasons with consecutive rainfalls with intensities close to the infiltration capacity of soil and/or monthly cumulative precipitation higher than 200 mm/day led to critical conditions in terms of soil water saturation and stability. Under unsaturated conditions of soil, the drainage effectiveness of geocomposites is significantly reduced and adverse capillary break effects become critical.
... The geosynthetic has been considered as a premium geotechnical engineering material to build reinforcements [22,23]. The geotextile tube made of geotextile sheets can also be used for soil strengthening [24][25][26]. Tubes can be filled with tailings slurry through the hydraulic transport process [27]. After the slurry is consolidated, the geotextile tubes are accumulated to form a dam or other types of geotechnical structures. ...
Full-text available
Geotextile tubes are one of the emerging and promising technologies to build fine-grain tailings dams. In this study, shaking table model tests are conducted to evaluate the seismic performance as characterized by horizontal acceleration and displacement of the tailings dam subject to horizontal peak ground accelerations (HPGAs). The test results indicate that the tailings dam is sustainable, whereas the whole dam tends to slide forward. Test results reveal a W-pattern variation of acceleration amplification coefficient (A m) at the same elevation despite different HPGA, whereas A m on the geotextile tubes exhibits minimal changes with increasing HPGA. A m inside the dam is highly variable in terms of the elevation and the specific position. The maximum vertical displacement occurs at the top of the geotextile tubes as the side of the geotextile tubes tilting upward. The highest horizontal displacement is observed in the middle section of the geotextile tubes, resulting in an overall convex deformation pattern. Two reinforcement schemes are proposed accordingly including strengthening the drainage and installing the anti-slide piles. The dynamic behaviors of the tailings dam subject to earthquakes from this study can serve as guidance for seismic design and technology promotion.
... In addition, the use of internal drainage materials (e.g. nonwoven geotextiles, geocomposites, sand cushions, chimney sand drains) are reported to be useful to keep high levels of soil suction and increase factors of safety of geosynthetic reinforced slopes (Balakrishnan and Viswanadham, 2019;Razeghi et al., 2019;Vibha and Divya, 2021). Hence, there arises the necessity to investigate the mechanical response of GMSE walls as rainwater infiltration progress into the reinforced zone, quantifying loads and strains related to suction induced by various rainfall intensities and patterns. ...
A laboratory testing that simulates the mechanisms of a geosynthetic-reinforced layer was used to assess the impact of rainwater infiltration on reinforcement loads and strains in mechanically stabilized earth (MSE) walls. The testing device allows measuring loads transferred from a backfill soil subjected simultaneously to surcharge loading and controlled irrigation. Load-strain responses of geosynthetic-reinforced layers constructed with three different geosynthetics under a moderate rainfall are related to suction captured along the depth of reinforced layers. Results show infiltration leading to increases on strains and tensile loads mobilized by reinforcements. Rates of increases of both parameters were found to be dependent of global suction, geosynthetic stiffness and hydraulic properties. In addition, increases in water content at soil-geotextile interfaces due to capillary breaks also had a significant effect on mobilized loads. The loss of interaction due to the interface wetting was observed to affect the stress transference from soil to geosynthetic reinforcement. An approach suggested for calculation of lateral earth pressures in unsaturated GMSE walls under working stress conditions and subjected to rainfall infiltration demonstrated a reasonable agreement with experimental data.
The scarcity and fast depletion of granular materials necessitated to find alternative backfill materials in MSE walls. In the present study, application of construction and demolition waste (CDW) as a backfill for MSE walls was investigated. The physical, chemical, hydraulic and mechanical properties of CDW were found to meet the requirements of ideal backfills mandated by various design standards of MSE walls. At the end of construction, maximum facing deformation was at lower one-third height of the wall for MSE wall resting on a firm foundation. Influence of yielding foundation on the performance of MSE wall was also studied by varying the distortion levels to 0.2, 0.4 and 0.6. At the onset of differential settlements, the location of maximum facing deformation changed to the bottom of the wall. The maximum facing deformation and axial strain increased by 15 times and 2.5% respectively, when the wall underwent a distortion of 0.6.
With the advent of ever-growing urbanization and industrialization, there exists a requirement for heavy infrastructures that can retain heavy earth masses and are sustainable in its functioning. The conventional earth mass retention methods using rigid retaining walls are not preferred for most of the projects, as they are expensive and are time-consuming for the construction when compared to the recently developed methods of earth mass retention by Mechanically Stabilized Earth (MSE) structures. MSE walls having large height when constructed in a single tier, often require a huge volume of excavation and an effective land area which is impossible to attain every time. Therefore, the most suitable alternative is to construct it in a tiered fashion. The tiered MSE walls can tolerate large differential settlements without distress, give a sound performance, are aesthetically appealing, are cost-effective, convenient, and provide simplicity in construction. However, the configuration of such walls may present several engineering challenges that have not been covered by the conventional design methods and calculations. This study aims to assess the performance and response of a multi-tiered 12 m high (H) MSE wall and compare it with a single-tiered MSE wall through numerical solutions based on finite element modeling. From the outcomes of this study, it is found that the normalized maximum lateral displacement of the facing of the wall (Δ/Η) is 5.4% and 1.71% in the single-tiered and three-tiered wall system respectively. Also, the factor of safety in three-tiered and single-tiered wall systems observe a growth of 9.4% and 8.4% respectively when the reinforcement length is increased, which establishes the improved performance of the tiered MSE walls and justifies its usage in place of single-tiered MSE walls.
The land scarcity has built up the pressure on the engineers to bring a cost-effective and time-saving solution to utilize the ground with poor strength as a foundation bed for various structures. With the recent progress in the area of ground reinforcing techniques using geosynthetics, the extensive usage of geotextile materials as a reinforcing element in the soil to strengthen the load-bearing capacity of the soil mass and reducing the anticipated settlement of the footing pushes the researchers to evolve new methods to maximize the advantages received from the reinforced earth beds. In the above context, the provision of reinforcing layers with wraparound ends has brought additional improvement in the load settlement behavior of a strip footing resting over such reinforced soil mass but this recently developed technique lacks the appropriate guidelines/recommendations for the geometrical configuration parameters of the reinforcing layer to maximize the benefit from the reinforcing layer. Given the above, a comprehensive numerical study has been conducted to propose some recommendations on the geometrical configurations of the reinforcing layers. Furthermore, this study also investigates the influence of the geogrid–soil interface on the load-settlement response of the reinforced bed under vertical footing load. From the findings of the study, it is concluded that the width of the geogrid layers, governs the overall load-bearing capacity of the reinforced soil mass system, besides it, also suggests an optimum width of the geogrid layers, which equals 1.5 times the width of the footing should be used to maximize the effective utilization of the wraparound technique. Furthermore, it was also noted that appropriate assessment of the interface between soil and geogrid may bring an optimized design of the reinforced soil mass as a foundation bed for the footings.
Full-text available
Climate change is expected to alter statistics of extreme events in the future. Adapting geotechnical infrastructure to a changing climate necessitates quantitative assessment of the potential climate change impacts on the performance of infrastructure. This study numerically investigates the hydromechanical response of a mechanically stabilized earth (MSE) wall constructed with marginal backfill to extreme rainfall events under a changing climate. The need for investigating the effects of extreme precipitation on marginal backfill is more pronounced because larger matric suction can be developed in such backfills. To address this need, this paper compares the performance of an MSE wall using two sets of rainfall intensity-duration-frequency (IDF) curves, denoted as baseline and projected, for the Seattle area. The baseline IDF curves are provided by the National Oceanic and Atmospheric Administration (NOAA) and currently used for design purposes, and the projected IDF curves are obtained using 20 climate model simulations of the future. The results show that use of the baseline IDFs can lead to underestimation of the wall deformation and loads carried by reinforcements. The results highlight the importance of site-specific assessments to quantify the potential impacts of climate change on the performance of current and future MSE walls. Such consideration gains even more importance considering the increasing interest in using marginal backfills in earth retaining structures due to economic and environmental considerations.
Full-text available
Unsaturated soil slopes introduce complex hydro-mechanical coupled processes which greatly alter matric suction distribution of an unsaturated soil during rainfall. In order to investigate matric suction and volume change of unsaturated soils, a two-dimensional hydro-mechanical coupled infiltration model (YS-Slope) is developed by incorporating the hydraulic and mechanical characteristics of unsaturated soils, such as the soil-water characteristic curve, permeability function, shear strength, and porosity. Special attention is given to the porosity-dependent permeability function of unsaturated soils. In addition, in order to highlight effectiveness of YS-Slope and coupling effects of hydro-mechanical processes on the infiltration behavior of unsaturated soils, a series of infiltration analyses for a soil column under various soil properties is conducted and their results are compared with those of commercial software, GEO-SLOPE (2012). The results of the numerical analyses show good agreement with data from the analytical solution and laboratory tests, which indicates that the proposed model is appropriate for use in the simulatfion o the infiltration of rainwater into deformable soils. The transient seepage and rainwater flow in deformable soils are influenced by the volume change of the soil. The change in matric suction on a slope due to rainfall infiltration influences change in effective stress while the effective stress alters seepage processes according to hydraulic properties. The results indicate that hydro-mechanical coupled behavior of soils has a positive effect on the stability of unsaturated soil slops during rainfall.
Conference Paper
Major part of Kerala is covered with lateritic soil. Lateritic soils, in general, can withstand high stress under unsaturated conditions. However, during rainfall infiltration, there is a tendency that the lateritic soil may undergo large and sudden deformation. In the recent past, Kerala experienced heavy rainfall induced distress. Associated with the rainfall event, a series of landslides and formation of cavities and subsidence of ground were observed in many parts of Kerala. Mechanically stabilised earth (MSE) structures such as reinforced soil walls and slopes can be used in landslide mitigation; especially in slide repair using the slide mass as the backfill. In the present study, soil was collected from a nearby site where landslide has occurred due to heavy rainfall. Experimental studies were conducted to study the collapse potential of the soil. An attempt was also made herein to investigate the deformation behaviour of geosynthetic reinforced soil slope resting on foundation soil subjected to rainfall induced subsidence.
Reinforcement stiffness is a key parameter that influences the magnitude of tensile loads in geosynthetic mechanically stabilized earth (MSE) walls under operational conditions. An estimate of reinforcement creep stiffness at 2% strain and 1000 hours is required to carry out internal stability design using the Simplified Stiffness Method. This paper provides equations that can be used to estimate the reinforcement creep stiffness based on the tensile strength for different reinforcement product types. The paper also explores how the tensile strength values of a product can vary depending on the population of tests used to compute strength values. The differences in choice of nominal tensile strength based on lot-specific and minimum average roll value (MARV) are discussed. The paper demonstrates that the Simplified Stiffness Method soil failure limit state will usually control the selection of the reinforcement and not the tensile strength limit state. While the primary motivation for this study is to find creep stiffness values for the Simplified Stiffness Method, the stiffness-strength equations are useful in other applications such as numerical modelling of geosynthetic reinforced structures where a reinforcement stiffness value corresponding to post-construction low tensile strain conditions is required.
This paper investigates the effect of geocomposite layers (as an internal drainage system) and a chimney sand drain (as an external drainage system) on the performance of reinforced soil walls with panel facing and marginal backfill. Four models subjected to seepage simulating a rising groundwater surface were tested at 40 gravities using a 4.5 m radius large beam centrifuge. In this study, geocomposite layers played a dual function of drainage and reinforcement. The behaviour of wall models was monitored using displacement and pore water pressure transducers during centrifuge tests. An image analysis technique was also used to measure displacement and strain fields. A geogrid reinforced soil wall with no drainage system experienced catastrophic failure at the onset of seepage. Provision of geocomposite layers at the bottom portion of the wall improved the wall behavior. Further, including geocomposite layers up to the mid-height of the wall resulted in superior performance compared to geogrid-reinforced soil walls. The model with the chimney sand drain experienced piping failure at the toe of the wall. The performance of reinforced soil walls with geocomposite layers was found to be superior to the geogrid reinforced soil walls with the chimney drain.
In 2013, the authors wrote a paper which was published in the Journal of Geotextiles and Geomembranes on the failure of 171-mechanically stabilized earth (MSE) walls reinforced with geotextiles or geogrids, Koerner and Koerner (2013). The paper generated many reprint requests via both the publisher and the authors, and it won the best paper of the year award. Furthermore, it generated considerable awareness of the situation and generated additional case histories while providing details of such failures. Presently, we have 320 failures which are reported in this paper. The database includes 99 cases of excessive deformation and 221 cases of collapse of at least part of the respective walls. The main statistical findings (including the original 171 failures) are as follows: 1.313 (98%) were private (as opposed to public) financed walls. 2.253 (79%) were located in North America; the vast majority being in the U.S. 3.240 (75%) were masonry block faced. 4.226 (71%) were 4–12 m high. 5.301 (94%) were geogrid reinforced; the other 6% were geotextile reinforced. 6.246 (77%) failed in less than four years after their construction (12 of which actually failed during construction). 7.232 (73%) used silt and/or clay backfill soils in the reinforced zone. 8.245 (76%) had poor-to-moderate compaction. 9.317 (99%) were caused by improper design or construction (incidentally, none were caused by geosynthetic manufacturing material failures). 10.201 (63%) were caused by internal or external water (the remaining 37% were caused by soil related issues). While the number of reported walls in this paper is almost double the number reported in 2013, the change in percentages of the above items is relatively small with the notable exceptions of walls failing in longer time intervals (by 9%) and even greater use of fine grained backfill soils (by 12%). As with the original paper, updated opinions and recommendations in several of the above listed areas are presented. Also, several new types of failures are reported, such as guard fence instability and soil erosion at the toe of the wall. However, the overall critical issues continue to occur and no lessening of failures is apparent with this new set of data. The critical issues are the following; •fine grained silt and clay soils continue to be used for the reinforced zone backfill. •poor placement and compaction of these same fine grained backfill soils is regularly reported. •drainage systems and utilities continue to be located within the reinforced soil zone. •there is little attempt at water control either behind, beneath or above the reinforced soil zone, and. •design details appear to be inadequate or not followed by the installation contractor. While the issues reported in 2013 did indeed prompt the initiation of an inspector's certification program (Geosynthetic Certification Institute - Inspector Certification Program) it has not been very successful and has attracted only 24-participants to date. Hopefully this updated paper will energize the parties involved and the MSE reinforced wall community at large to take appropriate action in correcting the situation described herein.
This paper presents a comprehensive failure investigation of a geosynthetic-reinforced soil (GRS) slope subjected to rainfall. The investigated slope is a 26-m high, four-tier, geogrid-reinforced structure backfilled with low plasticity silty clay that contains more than 60% of fines. The GRS slope first exhibited excessive deformation after typhoons and heavy rainfall from 2010 to 2012. The slope collapsed in 2013 due to two sequential typhoon events with a total accumulated rainfall of more than 600 mm. The slope failed in a compound failure mode in which the failure surface partially cut through the reinforced zone and partially passed along the interface between the weathered sandstone and intact shale. By using the recorded rainfall, site geology, and measured soil and reinforcement parameters, a series of coupled hydro-mechanical finite element analyses were performed on the basis of the unsaturated soil mechanics to examine the failure mechanism and factors triggering the slope failure. The numerical results indicated that the slope failure occurred due to the development of positive porewater pressure within the reinforced zone and retained weather sandstone layer. Observations and lessons learned from this case history are discussed and remedial measures to improve the overall slope stability are proposed and evaluated.
Slope instability due to rainwater infiltration poses a serious problem, and causes thousands of deaths and severe damage to infrastructures each year. In the present study, the effect of inclusion of hybrid-geosynthetic layers within a slope subjected to rainfall was investigated numerically. The analysis was done with and without hybrid-geosynthetic layers embedded in a silty sand slope having 2V:1H inclination with rainfall intensities ranging from 2 mm/h to 80 mm/h. The rainfall was simulated numerically for 24 h, and seepage, deformation and stability analyses were performed at the onset of rainfall, during rainfall, and up to 24 h after rainfall. Further, the need for both drainage and reinforcement function in the reinforced slope was highlighted by analysing the effect of geotextile and geogrid layer inclusions separately on the slope subjected to rainfall. The results indicate that, the inclusion of hybrid-geosynthetic layers was effective, as it lowered the phreatic surface by causing a reduction in excess pore water pressure. Further, the static global stability of a hybrid-geosyntheticreinforced slope was found to increase considerably under all intensities of rainfall, while the deformation values were significantly lower for the reinforced slope as compared with that of the unreinforced slope.
Mechanically stabilized earth (MSE) walls reinforced by geogrids and geotextiles have seen a tremendous growth over the past thirty years. However, along with this growth has come numerous failures consisting of excessive deformation and, in some cases, actual collapse. Of the 82-cases in the authors data base, improper drainage control was the cause in 68% of them. As a result, this paper is focused on both internal drainage issues within the reinforced soil mass within the reinforced soil mass (46%) and external drainage issues around the soil mass (22%). After a brief introduction of the technology some elements of traditional design will be presented. The issue of proper versus improper methods of drainage control will then form the core of the paper. A summary and recommendations section aimed at preventing drainage problems in the future will conclude the paper.
IntroductionVolume-Mass Constitutive RelationsEquations for SWCCRegression Analysis on SWCC EquationsHysteresis, Initialization, and Interpretation of SWCCPham and Fredlund (2011) Equation for Entire SWCCGitirana and Fredlund (2004) SWCCMeasurement of SWCC Using Pressure Plate DevicesSingle-Specimen Pressure Plate Devices for Geotechnical EngineeringVacuum Desiccators for High SuctionsUse of Chilled-Mirror or Dew-Point Method Estimation of SWCCTwo-Point Method of Estimating SWCCCorrelation of Fitting Parameters to Soil PropertiesApplication of SWCCGuidelines and Recommendations for Engineering Practice