numerical modelling of the behaviour of
geosynthetic barrier layer in a landfill cap
Mehdi Qoreishi, Muhammad Khalil
AECOM, Edmonton, Alberta, Canada
ABSTRACT
Spyhill landfill is located on the northern periphery of the City of Calgary in Alberta, Canada. It is determined that a
synthetic barrier layer performs better in preventing percolation of water into the waste in lieu of a conventional clay
barrier layer. Linear Low Density Polyethylene (LLDPE) geomembrane is identified to be the most suitable barrier layer
for the current application. The synthetic cap comprises of LLDPE geomembrane underlain by geocomposite gas venting
layer and overlain by a geocomposite drainage layer. The geosynthetic materials are protected with cover soil, geogrid
and surface gravel.
A numerical model is developed using FLAC v.7.0 software to evaluate the settlements, axial strains and tensile forces in
the components of the cap. The soil and the municipal solid waste materials (MSW) are modeled using Mohr-Coulomb
constitutive model. The Synthetic barrier is simulated using structural elements with linear elastic behavior. The soilgeosynthetic interaction is modeled considering interface elements with a linear elastic-perfectly plastic response to take
into account the slippage of geosynthetic layer inside soil elements.
A parametric study is completed to evaluate the response of the geosynthetic elements to the variations in the properties
of the model components. Several simulations are run with heavy and light truck loadings and considering different
configurations of the barrier layer and varying geotechnical properties of MSW. Results of the modeling show that
settlement of the cap under truck loading is significantly dependent on the elastic modulus of MSW. It is also concluded
that stabilizing the cap with surface gravel and geogrid significantly reduces the amount of settlement and the maximum
in-plane strain experienced by the LLDPE barrier layer in the presence of heavy trucks. Heterogeneity of MSW material
is considered in the model by defining a zone with different mechanical properties within the waste material. It is shown
that heterogeneity could increase the tensile forces and strains in the LLDPE barrier layer several times. The model is
run with varying cover material thicknesses and an optimum cap thickness is identified to protect the LLDPE
geomembrane barrier layer from excessive stresses and strains induced by cover soil and truck loadings.
KEYWORDS
Geosynthetic, Soil, Interaction, Numerical Modelling, Waste, Landfill