Analytical model for predicting time-dependent lateral deformation of geosynthetics-reinforced soil walls with modular block facing

To date,few models are available in the literature to consider the creep behavior of geosynthetics when predicting the lateral deformation(d)of geosynthetics-reinforced soil(GRS)retaining walls.In this study,a general hyperbolic creep model was first introduced to describe the long-term deformation of geosynthetics,which is a function of elapsed time and two empirical parameters a and b.The conventional creep tests with three different tensile loads(Pr)were conducted on two uniaxial geogrids to determine their creep behavior,as well as the a-Pr and b-Pr relationships.The test results show that increasing Pr accelerates the development of creep deformation for both geogrids.Meanwhile,a and b respectively show exponential and negatively linear relationships with Pr,which were confirmed by abundant experimental data available in other studies.Based on the above creep model and relationships,an accurate and reliable analytical model was then proposed for predicting the time-dependent d of GRS walls with modular block facing,which was further validated using a relevant numerical investigation from the previous literature.Performance evaluation and comparison of the proposed model with six available prediction models were performed.Then a parametric study was carried out to evaluate the effects of wall height,vertical spacing of geogrids,unit weight and internal friction angle of backfills,and factor of safety against pullout on d at the end of construction and 5 years afterwards.The findings show that the creep effect not only promotes d but also raises the elevation of the maximum d along the wall height.Finally,the limitations and application prospects of the proposed model were discussed and analyzed.

ANALYSIS OF GEOSYNTHETICS REINFORCED EMBANKMENT ON SOFT SOIL BY FEM

The reinforcement effects of geosynthetics in thick soft subsoil case and thin soft subsoil case are studied in this paper,and a Duncan Chang nonlinear numerical model based on the finite element method (FEM) is developed.Moreover,an important conclusion that the thickness of soft subsoil affects greatly the geotechnical behavior of geosynthetic reinforced embankments is drawn.A series of embankment built on soft subsoil is calculated using the FEM program.The results of the computer program,such as the lateral displacements,settlements,and stress level and shear stresses in the subsoil,are presented in great detail and the comparison of those results disposes clearly the huge discrepancy of reinforce benefit between the thick subsoil embankment and thin subsoil embankment.Reinforcement mechanism of geosynthetics is also discussed in this paper and several conclusions are reached.This paper also gives recommendations for design.

Kinematic analysis of geosynthetics-reinforced steep slopes with curved sloping surfaces and under earthquake regions

A procedure of kinematic analysis is presented in this study to assess the reinforcement force of geosynthetics required under seismic loadings, particularly for steep slopes which are hardly able to maintain its stability. Note that curved sloping surfaces widely exist in natural slopes, but existing literatures were mainly focusing on a planar surface in theoretical derivation, due to complicated calculations. Moreover, the non-uniform soil properties cannot be accounted for in conventional upper bound analysis. Pseudo-dynamic approach is used to represent horizontal and vertical accelerations which vary with time and space. In an effort to resolve the above problems, the discretization technique is developed to generate a discretized failure mechanism, decomposing the whole failure block into various components. An elementary analysis permits calculations of rates of work done by external and internal forces. Finally, the upper bound solution of the required reinforcement force is formulated based on the work rate-based balance equation. A parametric study is carried out to give insights on the implication of influential factors on the performance of geosynthetic-reinforced steep slopes.

Novel experimental techniques to assess the time-dependent deformations of geosynthetics under soil confinement

A new experimental approach to assess the impact of soil confinement on the long-term behavior of geosynthetics is presented in this paper.The experimental technique described herein includes a novel laboratory apparatus and the use of different types of tests that allow generation of experimental data suitable for evaluation of the time-dependent behavior of geosynthetics under soil confinement.The soil-geosynthetic interaction equipment involves a rigid box capable of accommodating a cubic soil mass under plane strain conditions.A geosynthetic specimen placed horizontally at the mid-height of the soil mass is subjected to sustained vertical pressures that,in turn,induce reinforcement axial loads applied from the soil to the geosynthetic.Unlike previously reported studies on geosynthetic behavior under soil confinement,the equipment was found to be particularly versatile.With minor setup modifications,not only interaction tests but also in-isolation geosynthetic stress relaxation tests and soil-only tests under a constant strain rate can be conducted using the same device.Also,the time histories of the reinforcement loads and corresponding strains are generated throughout the test.Results from typical tests conducted using sand and a polypropylene woven geotextile are presented to illustrate the proposed experimental approach.The testing procedure was found to provide adequate measurements during tests,including good repeatability of test results.The soilegeosynthetic interaction tests were found to lead to increasing geotextile strains with time and decreasing reinforcement tension with time.The test results highlighted the importance of measuring not only the time history of displacements but also that of reinforcement loads during testing.The approach of using different types of tests to analyze the soilegeosynthetic interaction behavior is an innovation that provides relevant insight into the impact of soil confinement on the time-dependent deformations of geosynthetics.

Use of geosynthetics for performance enhancement of earth structures in cold regions

Earth structures, such as roadways, embankments and slopes, and earth retaining walls, have been commonly used in cold regions for transportation and other applications. In addition to typical design considerations for earth structures at normal temperature, a design must also consider the unique problems associated with low temperature, such as frost heave, lateral expansion, thaw settlement and weakening, and degradation of material properties. Geosynthetics have been used in cold regions to stabilize earth structures during construction and mitigate potential problems during their service at low tem- perature. This paper provides a state of practice review of the use of geosynthetics for performance enhancement of earth structures in cold regions. This paper starts with basic information on available geosynthetic products and their functions, evaluates properties and behavior of geosynthetics and soil-geosynthetic systems at low temperature, and discusses past studies and their key results on the use of geosynthetics to enhance the performance of roadways, embankments, and earth retaining walls in cold regions. This review reveals that geosynthetics at low temperature have higher tensile strength and stiffness, lower creep rate, and lower elongation at failure. The effect of temperature becomes significant when nonwoven geotextiles are subjected to moistening and soil intrusion at subfreezing temperature. Freeze-thaw cycles may degrade hydraulic and mechanical properties of geosynthetic-soil systems. The inclusion of geosynthetics in soil provides drainage and/or barrier to water flow, retains mechanical properties, and reduces frost heave during and after freeze-thaw cycles. Effectiveness of geosynthetics has been confirmed in the field in bridging over voids, stabilizing roadways over temper- ature-susceptible soils during thaw, and proving drainage and barrier to temperature-susceptible soils before freeze. To avoid frost heave and lateral expansion of backfill in earth retaining walls, granular fill without fines should be used. When backfill with fines is used for earth retaining walls, additional lateral earth pressure induced by soil freeze and thaw set- tlement should be considered in the design.

Elastic-viscoplastic behaviors of polymer-blend geocell sheets:Numerical and experimental investigations

Polymer-blend geocell sheets(PBGS)have been developed as substitute materials for manufacturing geocells.Various attempts have been made to test and predict the behaviors of commonly used geogrids,geotextiles,geomembranes,and geocells.However,the elastic-viscoplastic behaviors of novel-developed geocell sheets are still poorly understood.Therefore,this paper investigates the elastic-viscoplastic behaviors of PBGS to gain a comprehensive understanding of their mechanical properties.Furthermore,the tensile load-strain history under various loading conditions is simulated by numerical calculation for widespread utilization.To achieve this goal,monotonic loading tests,short-term creep and stress relaxation tests,and multi-load-path tests(also known as arbitrary loading history tests)are performed using a universal testing machine.The results are simulated using the nonlinear three-component(NLTC)model,which consists of three nonlinear components,i.e.a hypo-elastic component,a nonlinear inviscid component,and a nonlinear viscid component.The experimental and numerical results demonstrate that PBGS exhibit significant elastic-viscoplastic behavior that can be accurately predicted by the NLTC model.Moreover,the tensile strain rates significantly influence the tensile load,with higher strain rates resulting in increased tensile loads and more linear load-strain curves.Also,parametric analysis of the rheological characteristics reveals that the initial tensile strain rates have negligible impact on the results.The rate-sensitivity coefficient of PBGS is approximately 0.163,which falls within the typical range observed in most geosynthetics.

Model tests on interaction between soil and geosynthetics subjected to localized subsidence in landfills

In a landfill, excessive tensile strains or failure of the liner system due to localized subsidence underneath the geosynthetic liner, is a concern in design and operation of the landfill. The localized subsidence can be commonly withstood by reinforcements such as geogrids. A total of nine model tests were carried out to study the influence of soil arching in overburden sandy soil on the geosynthetics and the interaction between the soil and the geosynthetics. The localized subsidence was modeled by a strip trapdoor under the geosynthetic reinforcements. The reinforcement includes several layers of polyvinylchlorid （PVC） membrane or both PVC membrane and a compacted clay layer. Test results show that the vertical soil pressure acting on the geosynthetics within the subsidence zone is strongly related to the deflection of the geosynthefics. The soil pressure acting on the deflected geosynthetics will decrease to a minimum value with respect to its deflection if the final deflection is large enough, and this minimum value is almost independent of the overburden height. Otherwise, the deflection of geosynthetics cannot result in a full degree of soil arching, and the soil pressure within the subsidence zone increases with the increase of overburden height. Deflections and strains of the geosynthetics obviously decrease with the increase of their tensile stiffness. The presence of a compacted clay layer buffer can therefore reduce both deflections and strains of the geosynthetics. Finally, a composite liner structure is recommended for landfills to withstand the localized subsidences.

Use of Geosynthetic Access Mats in Construction

A stable surface to move manpower and equipment is a key for the construction operations. To create a stable road surface, the road construction techniques are time-consuming and expensive for a traditional construction which requires compaction of soil, aggregate base, sub-base and asphaltic layers. A Geosynthetic Access Mat (GAM) system can serve as an alternative to other traditional construction techniques to accommodate temporary construction. Due to its rigidity, the mat system can provide substantial vertical resistance to the applied load under a large deflection subject to soil conditions. This paper provides details of GAM specifications, soil conditions, applications, installation procedure, comparison with other soil stabilization methods and Aramco experience for deployments of these mats.

Geosynthetics used to stabilize vegetated surfaces for environmental sustainability in civil engineering

Geosynthetics, factory-manufactured polymer materials, have been successfully used to solve many geotechnical problems in civil engineering. Two common applications are earth stabilization and erosion control. Geosynthetics used for earth stabilization include but are not limited to stabilized slopes, walls, embankments, and roads. Geosynthetics used for erosion control are mostly related to slopes, river channels and banks, and pond spillways. To enhance environmental sustainability, vegetation has been increasingly planted on the facing or surfaces of these earth structures. Under such a condition, geosynthetics mainly function as surficial soil stabilization while vegetation provides green appearance and erosion protection of earth surfaces. Recently, geosynthetic or geosynthetic-like material has been used to form green walls outside or inside buildings to enhance sustainability. Geosynthetics and vegetation are often integrated to provide combined benefits. The interaction between geosynthetics and vegetation is important for the sustainability of the earth and building wall surfaces. This paper provides a review of the current practice and research in the geosynthetic stabilization of vegetated earth and building surfaces for environmental sustainability in civil engineering with the emphases on geosynthetic used for erosion protection, geosynthetic-stabilized slopes, geosynthetic-stabilized unpaved shoulders and parking lots, and geosynthetic-stabilized vegetated building surfaces.

The Efect of Rich Synthetic Copper-rich Solution on Antiseepage Dense Pre-hydration Geosynthetic Clay Liner

Dense pre-hydrated geosynthetic clay liners(DPH GCLs)were manufactured as innovative materials accompanied by the advantage of lower hydraulic conductivity(k).The k of DPH GCLs permeated with de-ionized water(DIW)was 9.8×10^(−12) m/s.The effect of Cu^(2+)synthetic solution on DPH GCLs was discussed.Furthermore,the effect mechanism was studied on the basis of test technologies.A significant adverse impact on hydraulic performance of DPH GCLs is found when the concentration of Cu^(2+)is greater than 1 g/L.SEM,XRD,XRF,FTIR,and XPS analyses show that the effect of Cu^(2+)on DPH GCLs includes two steps.Firstly,Cu^(2+)interacts with hydrophobic organic matter(HOM),and the adhesion of bentonite is destroyed,and some holes appear.The Cu^(2+)contacts with bentonite directly,and Cu^(2+)interacts with bentonite through ion exchange.Passivated phenomenon occurs on the surface of the bentonite,and swelling ability of bentonite is reduced,which causes permeable DPH GCLs.

Enhancing mechanical behavior of micaceous soil with jute fibers and lime additives

Micaceous soils are common in many tropical countries and regions,and in some locations with moderate climate.The soils are spongy and unstable when loaded and are not considered suitable as construction material in earth structures.To resolve the issue,this work examined performance of micaceous soil reinforced with a combination of jute fibers,hydrated lime or slag-lime.A total of 28 sample sets were prepared at various dosages.Unconfined compression tests were conducted on the samples cured for 7 d and 28 d,respectively.The test results suggested that the unconfined compressive strength(UCS)and material stiffness were increased with the inclusion of up to 1%fiber and decreased if additional fibers were used.The ductility was improved consistently with up to 1.5%fiber content.The inclusions of fibers combined with hydrated lime or slag-lime further enhanced strength and stiffness of micaceous soil,and the improvement depended on the dosages used.For the dosages examined,jute fibers outweighed lime and slag in gaining ductility,and the optimal fiber content was 1%where strength and ductility were considered.

Controlling strain in geosynthetic liner systems used in vertically expanded landfills

According to relevant new regulations in China,a composite liner system involving geosynthetic materials must be installed at the bottom of an expanded landfill.The deformation and integrity of the composite liner under a variety of factors are important issue to be considered in the design of a landfill expansion.In this paper,we investigate the strain distribution in geosynthetic materials within the composite liner system of expanded landfills,including strains in geosynthetic materials resulting from overall settlement and lateral movement of landfills,localized subsidence in landfills,and differential settlement around gas venting wells.The allowable strains of geosynthetic materials are discussed based on the results of tensile tests,and the corresponding design criteria for composite liner systems are proposed.Meanwhile,practical measures allowing strain control in geosynthetic materials used in landfill engineering are proposed.

Pseudo-static/dynamic solutions of required reinforcement force for steep slopes using discretization-based kinematic analysis

This paper presents a procedure for assessing the reinforcement force of geosynthetics required for maintaining dynamic stability of a steep soil slope. Such a procedure is achieved with the use of the discretization technique and kinematic analysis of plasticity theory, i.e. discretization-based kinematic analysis. The discretization technique allows discretization of the analyzed slope into various components and generation of a kinematically admissible failure mechanism based on an associated flow rule.Accordingly, variations in soil properties including soil cohesion, internal friction angle and unit weight are accounted for with ease, while the conventional kinematic analysis fails to consider the changes in soil properties. The spatialetemporal effects of dynamic accelerations represented by primary and shear seismic waves are considered using the pseudo-dynamic approach. In the presence of geosynthetic reinforcement, tensile failure is discussed providing that the geosynthetics are installed with sufficient length. Equating the total rates of work done by external forces to the internal rates of work yields the upper bound solution of required reinforcement force, below which slopes fail. The reinforcement force is sought by optimizing the objective function with regard to independent variables, and presented in a normalized form. Pseudo-static analysis is a special case and hence readily transformed from pseudodynamic analysis. Comparisons of the pseudo-static/dynamic solutions calculated in this study are highlighted. Although the pseudo-static approach yields a conservative solution, its ability to give a reasonable result is substantiated for steep slopes. In order to provide a more meaningful solution to a stability analysis, the pseudo-dynamic approach is recommended due to considerations of spatial etemporal effect of earthquake input.

Experimental study on repeatedly loaded foundation soil strengthened by wraparound geosynthetic reinforcement technique

In the recent past,the potential benefits of wraparound geosynthetic reinforcement technique for constructing the reinforced soil foundations have been reported.This paper presents the experimental study on the behaviour of model strip footing resting on sandy soil bed reinforced with geosynthetic in wraparound and planar forms under monotonic and repeated loadings.The geosynthetic layers were laid according to the reinforcement ratio to minimise the scale effect.It is found that for the same amount of reinforcement material,the wraparound reinforced model resulted in less settlement in comparison to planar reinforced models.The efficiency of wraparound reinforced model increased with the increase in load amplitude and the rate of total cumulative settlement substantially decreased with the increase in number of load cycles.The wraparound reinforced model has shown about 45% lower average total settlement in comparison to unreinforced model,while the double-layer reinforced model has about 41% lower average total settlement at the cost of approximately twice the material and 1.5 times the occupied land width ratio.Moreover,wraparound models have shown much greater stability in comparison to their counterpart models when subjected to incremental repeated loading.

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 longrange 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 geogridreinforced 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.

Pullout behavior of polymeric strip in compacted dry granular soil under cyclic tensile load conditions

Assessment of the reinforcement behavior of soil under cyclic and monotonic loads is of great impor- tance in the safe design of mechanically stabilized earth walls, In this article, the method of conducting a multistage pullout （MSP） test on the polymeric strip （PS） is presented, The post-cyclic behavior of the reinforcement can be evaluated using a large-scale pullout apparatus adopting MSP test and one-stage pullout （OSP） test procedures, This research investigates the effects of various factors including load amplitude, load frequency, number of load cycles and vertical effective stress on the peak apparent coefficient of friction mobilized at the soil-PS interface and the pullout resistance of the PS buried in dry sandy soil. The results illustrate that changing the cyclic tensile load frequency from 0,1 Hz to 0,5 Hz does not affect the pullout resistance. Moreover, the influence of increasing the number of load cycles from 30 to 250 on the peak pullout resistance is negligible. Finally, the effect of increasing the cyclic tensile load amplitude from 20% to 40% on the monotonic pullout resistance can be ignored. The peak apparent coefficient of friction mobilized at the soil-PS interface under monotonic and cyclic load conditions decreases with the increase in vertical effective stress.

Drainage performance and capillary rise restraint effect of wicking geotextile

Wicking geotextile(WG)is considered as a possible countermeasure to reduce water content in unsaturated soil.In this research,rainfall tests were carried out to verify the drainage performance of WG.And capillary rise tests were conducted to study the effect of WG on the prevention of capillary rise.Test results indicated that WG with good drainage performance could drain gravitational and capillary water out of kaolinite soil.For kaolinite soil column with water content of 12%and compaction degree of 90%,the whole process of capillary rise in soil column with a layer of WG was a typical two-stage mode,and the maximum capillary height was about 380 mm,which provided that the WG could work as a barrier to prevent capillary rise effectively.In addition,the total vertical influential regions of WG in kaolinite soil above and below the WG layer were 400 and 100 mm,respectively.

Impact of repeated loading on mechanical response of a reinforced sand

Pavements constructed over loosely compacted subgrades may not possess adequate California bearing ratio (CBR) to meet the requirements of pavement design codes,which may lead to a thicker pavement design for addressing the required strength.Geosynthetics have been proven to be effective for mitigating the adverse mechanical behaviors of weak soils as integrated constituents of base and sub-base layers in road construction.This study investigated the behaviors of unreinforced and reinforced sand with nonwoven geotextile using repeated CBR loading test (followed by unloading and reloading).The depth and number of geotextile reinforcement layers,as well as the compaction ratio of the soil above and below the reinforcement layer(s) and the compaction ratio of the sand bed,were set as variables in this context.Geotextile layers were placed at upper thickness ratios of 0.3,0.6 and 0.9 and the lower thickness ratio of 0.3.The compaction ratios of the upper layer and the sand bed varied between 85% and 97% to simulate a dense layer on a medium dense sand bed for all unreinforced and reinforced testing scenarios.Repeated CBR loading tests were conducted to the target loads of 100 kgf,150 kgf,200 kgf and 400 kgf,respectively (1 kgf=9.8 N).The results indicated that placing one layer of reinforcement with an upper thickness ratio of 0.3 and compacting the soil above the reinforcement to compaction ratio of 97% significantly reduced the penetration of the CBR piston for all target repeated load levels.However,using two layers of reinforcement sandwiched between two dense soil layers with a compaction ratio of 97% with upper and lower thickness ratios of 0.3 resulted in the lowest penetration.

Application of Geotechnical Synthetic Materials in Sponge City Construction

Along with the overall progress and development of market economy,Sponge City has received extensive attention,in order to establish a more compatible with the market development trend and environmental protection requirements of the control mechanism,it is necessary to scientifically plan synthetic materials,to a certain extent,to maintain the basic level of sponge city supervision work.In this paper,the research background of Geosynthetics applied in Sponge City construction is briefly analyzed,and the basic principles and specific application paths are discussed,which are for reference only.

Simulation of Accelerated Ageing of UV-Radiation for Photodegradable Geotextiles/Geomembranes

Geosynthetics used as geotextiles/geomembranes lose their mechanical properties when exposed to outdoor solar radiation. The UV-component present in the solar radiation is main cause for such degradation of mechanical properties. The life of geosynthetics has to be predicted before the intended purpose by exposing the material under artificial UV-radiation in the laboratory. Simulation of UV-radiation has been set up for accelerated ageing condition of Mumbai climate.