Numerical modeling of the nonlinear mechanical behavior of multilayer geosynthetic system for piggyback landfill expansions

Abstract

Citation: TANO, F. ...et al., Numerical modelling of the nonlinear mechanical behavior of multilayer geosynthetic system for piggyback landfill expansions.Geotextiles and Geomembranes, 44 (6), pp. 782-798.Additional Information:• This paper was accepted for publication in the journal Geotextiles of the GSYs and of the interfaces between GSYs must be considered. Designers, however, often 31 use simplistic assumptions without further analyzing the implications of these assumptions on the 32 results. Such simplifications mainly concern the nonlinear axial stiffness of GSYs, the strain 33 softening at interfaces between GSYs, and the difference between the compressive and tensile 34 behavior of GSYs. By, considering these key aspects, the present study aims to understand the 35 extent to which the results of numerical calculations can be influenced both by the differing 36 compressive and tensile behavior of GSYs and by the assumption of strain softening at interfaces 37 between GSYs. For this purpose, several numerical models are implemented by using the finite-38 difference code FLAC 2D on a typical PBLE that involves four GSYs and six interfaces. The 39 present work also applies comprehensive, state-of-the-art numerical modelling to study the 40 interactions between multiple layers of GSYs. This study also investigates the nonlinear axial 41 stiffness of GSYs through a series of uniaxial tensile tests. The numerical results show that, if the 42 GSY axial compressive and tensile characteristics are the same, then tensile force is minimized, 43 which induces significant compressive force in the GSYs. The results also indicate that 44 3 neglecting strain softening at the interface between GSYs affects interface shear stresses, 45 displacements of GSYs at the interface, and the GSY force distribution, potentially rendering the 46 model unrealistic. Including strain softening, however, allows the assessment (location) of 47 unstable areas along the interface where large displacements occur. 48 49

A numerical modelling technique for geosynthetics validated on a cavity model test

“…Concerning , as recommended by Itasca (2005) and Fowmes et al (2008), an arbitrarily large value was considered to avoid node interpenetration during computation. A value of 100 MPa was considered following previous studies (Tano et al, 2016a, Tano et al, 2016b. Moreover, zero cohesion was assigned to all interfaces because the geosynthetic interfaces are assumed to have zero shear resistance when there is no confining pressure.…”

“…As mentioned in section 2, Tano et al (2016a) proposed a numerical model technique to simulate the behaviour of a multilayered geosynthetic lining system in the context of piggy-back landfill expansions. This technique was based on five criteria (CR1 to CR5).…”

“…This technique was based on five criteria (CR1 to CR5). In the present study, the authors use this same numerical modelling technique (Tano et al, 2016a) to model the three experimental tests (UTT, DST, and LSTA). However, CR2 is not considered herein because none of the three experimental tests included waste.…”

“…None of the previous studies consider the nonlinear axial stiffness of the geosynthetics in modelling the interactions between these geosynthetics in the lining system. However, the stressstrain response of geosynthetics is typically nonlinear (Giroud, 1994, Wesseloo et al, 2004, Tano et al, 2016a, which means that the axial stiffness (e.g., the modulus) of the geosynthetic evolves as a function of strain. Thus, neglecting the true characteristics of the geosynthetics could lead to inaccuracies and discrepancies, as exemplified in the studies just mentioned.…”

“…For a more rigorous numerical analysis, Tano et al (2016a) proposed a numerical modelling technique based on the following five criteria: all geosynthetic interfaces in the lining system are modelled [criterion 1 (CR1)], the staged construction or evolution of the waste properties depends on depth or stress (CR2), the strain softening occurs at interfaces between geosynthetics (CR3), geosynthetic compressive characteristics differ from the tensile characteristics (CR4), and the geosynthetic has nonlinear axial stiffness (CR5). However, Tano et al (2016a) did not compare their numerical results with experimental results.…”