Geosynthetic-stabilized flexible pavements: Solution derivation and mechanistic-empirical analysis

https://doi.org/10.1016/j.geotexmem.2020.02.005Get rights and content

Abstract

Geosynthetics have been widely applied in flexible pavements for decades. However, the mechanistic-empirical analytical approach for geosynthetic-stabilized flexible pavements based on the elastic solution derived from the layered elastic theory has not been established. In this study, the solution for a typical three-layer geosynthetic-stabilized flexible pavement was derived according to the layered elastic theory. In the derivation, lateral restraint and tensioned membrane effect of geosynthetics quantified in terms of layer permanent deformations were considered at the interface as a continuity condition. The derived solution was then incorporated into the mechanistic-empirical approach for the calculation of pavement rutting and fatigue cracking. The result indicates that the solution derived in this study is capable of analyzing the geosynthetic-stabilized three-layer flexible pavement. The pavement elastic responses calculated using the solution obtained in this study are in line with those by the previously established solutions in the literature. The rut depths estimated using the proposed solution reasonably match those measured in the previous study. For rut reduction, the geosynthetic placed underneath the base layer is more effective. For the tensile strain relief at the bottom of the asphalt layer, the geosynthetic placed at the bottom of the asphalt shows more benefit.

Introduction

Geosynthetics, e.g., geogrids and geotextiles, have been widely used for weak subgrade and base course stabilization and/or surface cracking mitigation in paved and/or unpaved roads (Sun et al., 2015). Geosynthetics can provide lateral restraint (also referred to as confinement) through friction or interlocking and vertical support through the tensioned membrane effect (Giroud and Han, 2004a, 2004b, 2016). As a result, the stabilized roads with geosynthetics have more resistance to load-related distresses, such as rutting, cracking, etc. and therefore have a longer service life.

The performance of geosynthetic-stabilized roads has been investigated by many researchers using laboratory tests and large scale in-situ tests (Chen et al., 2018; Ferrotti et al., 2012; Gu et al., 2016; Khodaii et al., 2009; Ling and Liu, 2001; Imjai et al., 2019). These studies show that the inclusion of a geosynthetic underneath the base layer widens the vertical stress distribution within the base course layer and therefore reduces the vertical stress applied on the surface of the subgrade. This reduction of vertical stress can reduce the permanent deformation of the subgrade, which accounts for the major portion of the surface deformation, especially for unpaved roads over weak subgrade (Giroud and Han, 2016). An existing study also showed that the inclusion of a geogrid increased the radial stresses within the base course (Sun et al., 2015). Flexible pavements with geosynthetic-stabilized bases typically have less rutting. A few studies investigated the benefits of geogrids in mitigating rutting, fatigue cracking in the asphalt layer, and reflective cracking in asphalt overlays by placing a glass-fiber geogrid underneath a new asphalt layer or asphalt overlay (e.g., Correia and Zornberg, 2015; Khodaii et al., 2009; Lee et al., 2015). For instance, Khodaii et al. (2009) studied the cracking propagation of the glass-fiber geogrid stabilized asphalt overlay on an old asphalt layer with a pre-cut crack. Correia and Zornberg (2015) investigated the performance of asphalt overlays by laboratory accelerated loading. In summary, these laboratory and field tests confirm that the inclusion of geosynthetics is helpful in improving the performance of paved and/or unpaved roads.

So far fewer existing studies have been focused on the theoretical analysis and prediction of geosynthetic-stabilized roads as compared to a large number of experimental studies. Vokas and Stoll (1987) derived the solution for a geogrid-stabilized layered elastic system by considering a geogrid as a thin plate with bending stiffness, which is not compatible with the membrane-like characteristic of the geogrid. Perkins et al. (2004) conducted a study to analyze the effect the geosynthetics through an empirical equation. Giroud and Han (2004a) developed a simplified method for the design of geogrid-stabilized unpaved roads by considering the variation of vertical stress distribution angle along with the number of loading cycles and the increase of subgrade bearing capacity due to the inclusion of the geogrid. Kwon et al. (2005) developed a mechanistic model for geosynthetic-stabilized flexible pavements based on a non-linear finite element analysis. Yang and Han (2013) developed an analytical model for a geogrid or geocell-stabilized soil triaxial sample. Gu et al. (2016) conducted numerical modeling of geogrid-stabilized flexible pavements and validated their results using a large-tank test. Tang et al. (2016) conducted a mechanistic-empirical analysis of geogrid-stabilized roads by using the finite element method to obtain the elastic responses of geogrid-stabilized pavement layers.

In recent years, the Mechanistic-Empirical Pavement Design Guide (MEPDG) has been developed and increasingly adopted in pavement design (NCHRP, 2004a). In this design guide, the elastic responses (including stress and strain) are obtained through the layered elastic theory and the pavement distresses are then estimated through transfer functions (i.e., empirical equations). An NCHRP research proposed an MEPDG design method for geosynthetic-stabilized flexible pavements, in which the elastic responses caused by the inclusion of geosynthetics were estimated based on the finite element method and the artificial neural network model (NCHRP, 2017). Sun and Han (2019a) developed the solution for geogrid-stabilized bases over subgrade according to the layered elastic theory. In their study, lateral restraint and tensioned membrane effect of the geogrid were quantified based on the permanent deformations of soil layers, which were estimated based on the soil damage model in the current MEPDG. However, their solution was derived based on a two-layer model, which is suitable for unpaved roads but not for paved roads. So far, the mechanistic-empirical design method for geosynthetic-stabilized flexible pavements based on the layered elastic theory is still not well developed. Since the MEPDG design method has been increasingly adopted by more agents, it is necessary to establish a mechanistic-empirical analytical method for geosynthetic stabilized flexible pavements.

One of the objectives of this study was to derive the solution for geosynthetic-stabilized flexible pavements with a typical three-layer system, as shown in Fig. 1, based on the layered elastic theory. Subsequently, this study performed a mechanistic-empirical analysis to quantify the accumulated pavement rut and damage. The measured rut depth in the previous study was used to validate the mechanistic-empirical approach proposed in this study. This paper will also discuss the effects (including lateral restraint and tensioned membrane effect) of the double-layer geosynthetics. It should be pointed out that in real applications, the number of geosynthetic layers can be zero, one, two, or more.

Section snippets

Effect of geosynthetic

In the geosynthetic-stabilized flexible pavement, the geosynthetic is mobilized by the permanent deformations of the pavement layers below and above the geosynthetic through interlocking or interaction at their interfaces. With the vertical and horizontal permanent deformations (w and u) at their interfaces, the effects of the geosynthetic (i.e., lateral restraint, sr, and tensioned membrane, q) can be estimated based on the following equilibrium (Sun and Han, 2019a):sr=ηEghg1μg2(2ur2+1r

Solution derivation

In the derivation, the lateral restraint and the tensioned membrane effect provided by geosynthetics were applied at the interface of the three-layer elastic system (Fig. 1) as the boundary and continuity conditions of the system. Subscripts a, b, and s denote the elastic modulus and Poisson's ratio of the asphalt layer (Ea and μa), the base course (Eb and μb), and the subgrade (Es and μs), respectively.

Comparison with the established solutions

The geosynthetic-stabilized three-layer elastic system in this study (Fig. 1) can be degenerated into a two-layer system or even a semi-infinite elastic system by adjusting the layer elastic moduli into an identical value. Therefore, the solution can be verified based on the established solutions in the literature, such as Boussinesq's solution, Burmister's solution (Burmister, 1945a, 1945b), and the solution of the geosynthetic-stabilized two-layer system developed by Sun and Han (2019a). In

Discussion

Fig. 6 shows that the inclusion of the geosynthetics underneath of the base course did cause a considerable reduction of the total rut, but its benefit on the rut reduction in the asphalt layer is negligible. In fact, geosynthetics would have different effects when included at different interfaces (asphalt-base or base-subgrade). Assuming that both the asphalt-base and base-subgrade interfaces of Section 4 in Chen et al. (2018) are included with two identical geosynthetics (Geogrid 1 and

Application and limitation

The solution and the mechanistic-empirical analysis approach developed in this study can be adopted to predict rut depths and fatigue cracks of geosynthetic-stabilized flexible pavements with a three-layer pavement system. It is easy and feasible to derive the solutions for the geosynthetic-stabilized flexible pavements with more than three layers by following the method of this study. In actual applications, the local calibration factors and the interaction reduction factor need to be further

Conclusions

In this study, the solution for geosynthetic-stabilized three-layer flexible pavements was derived according to the layered elastic theory. Based on the solution, a mechanistic-empirical analytical method was proposed. The method proposed in this study was then verified using the established solutions in the literature and measured rut depths from a previous study. The following conclusions can be drawn:

  • (1)

    The solution derived in this study is capable of analyzing the geosynthetic-stabilized

Acknowledgements

This study was sponsored by the National Natural Science Foundation of China (No. 51809172), the Natural Science Foundation of Guangdong Province (No. 2019A1515011660), the New Faculty Start-up Fund of Shenzhen University (Grand No. 2019091) for the first author, the Fundamental Research Program of Qinghai Province (Grant No. 2020-ZJ-738 and 2017-ZJ-792), and the Technological Innovation Service Platform of Qinghai Province (Grant No. 2018-ZJ-T01).

References (28)

  • J. Giroud et al.

    Mechanisms governing the performance of unpaved roads incorporating geosynthetics

    Geosynthetics

    (2016)
  • J.P. Giroud et al.

    Design method for geogrid-reinforced unpaved roads. I. Development of design method

    J. Geotech. Geoenviron. Eng.

    (2004)
  • J.P. Giroud et al.

    Design method for geogrid-reinforced unpaved roads. II. Calibration and applications

    J. Geotech. Geoenviron. Eng.

    (2004)
  • D. Guo et al.

    Mechanics of Layered Elastic System

    (2001)
  • Cited by (15)

    • Analytical method for quantifying performance of wicking geosynthetic stabilized roadway

      2023, Geotextiles and Geomembranes
      Citation Excerpt :

      Tang et al. (2016) calculates the elastic response of a geosynthetic stabilized roadway section through a finite element method. Sun et al. (2020) derived the elastic solution for a typical three-layer geosynthetic stabilized flexible pavement based on the layered elastic theory. Kwon et al. (2005) developed a mechanical model for the geosynthetic-stabilized flexible pavement based on a nonlinear finite element analysis.

    • Evaluating long-term benefits of geosynthetics in flexible pavements built over weak subgrades by finite element and Mechanistic-Empirical analyses

      2022, Geotextiles and Geomembranes
      Citation Excerpt :

      The idea of utilizing geosynthetics as reinforcement in pavement construction was introduced in 1970. After that, many studies have been conducted to measure the benefits of using geosynthetics as reinforcement in pavement applications (e.g., Al-Qadi et al., 1994; Perkins 1999; Perkins 2002; Chen and Farsakh 2012; Gu et al., 2016a; Tang et al., 2016; Luo et al., 2017; Roodi and Zornberg 2020; Sun et al., 2020). Among the different types of geosynthetics, geotextiles and geogrids are frequently used in experimental research in the literature.

    • Experimental evaluation of wicking geotextile-stabilized aggregate bases over subgrade under rainfall simulation and cyclic loading

      2021, Geotextiles and Geomembranes
      Citation Excerpt :

      In addition, under channelized traffic the tensioned membrane effect can further reduce the vertical stresses over the subgrade at large deformations (e.g., >100 mm). The function of a geosynthetic layer by providing lateral restraint is often referred to as mechanical stabilization in roadway applications (Giroud and Han, 2016; Sun et al., 2019, 2020). On the other hand, nonwoven geotextiles have been successfully used for separation and filtration purposes in roads but also used for drainage purposes.

    • Effect of polypropylene fiber and nano-zeolite on stabilized soft soil under wet-dry cycles

      2021, Geotextiles and Geomembranes
      Citation Excerpt :

      The addition of fibers is considered to be an appropriate solution for the created tensile stress, providing greater durability of the stabilized soils. The use of fibers significantly improves the geotechnical parameters by increasing tensile and shear strength, increasing ductility, and reducing mass loss and cracks (Hojjati and Sarkar, 2020; Sun et al., 2020b; Consoli et al., 2017; Behnood, 2018; Kafodya and Okonta, 2018). The use of polypropylene fibers for soil reinforcement has been confirmed by many researchers (Roshan et al., 2020; Boz and Sezer, 2018; Festugato et al., 2018; Wei et al., 2018; Kumar and Gupta, 2016; Anggraini et al., 2015; Chen et al., 2015; Correia et al., 2015; Hejazi et al., 2012; Tang et al., 2012) due to its efficiency, low-cost, availability, and resistance to environmental conditions.

    View all citing articles on Scopus
    View full text