Behaviour of landfill systems under monotonic and earthquake loading

Indrasenan Thusyanthan, Cambridge University
Geotechnical Engineering Group


An investigation into the behaviour of landfill systems under monotonic and earthquake loading is presented in this thesis. The research investigated four main areas; (1) seismic behaviour of municipal solid waste (MSW) landfills; (2) tensile behaviour of geomembrane on landfill slopes; (3) the integrity of landfills founded on liquefiable foundations and (4) cracking in clay.

A model waste whose physical and dynamic properties match those of a typical MSW was designed. Shear modulus reduction and damping curves of the model waste were obtained from dynamic centrifuge test data and shown to match with that reported for MSW. Seismic behaviour of MSW was then studied by performing dynamic tests on landfill models with the model waste. The test results provided useful amplification charts for MSW landfills.

Tension induced in geomembranes on landfill slopes under static and earthquake loading was investigated by using a model geomembrane in a centrifuge model with clay liner on side slope laid at an angle of 45°. Results showed that an earthquake loading induces additional permanent tension in the geomembrane. For earthquake loading of intensity 0.2g to 0.3g at the foundation level, the geomembrane tension can have a permanent increase of up to 30% of pre-earthquake value. This increase in geomembrane tension was related to the decrease in the earth pressure coefficient of waste caused by the earthquake loading.

Liquefiable foundation soils particularly next to the side slope of a landfill can lead to damage of the clay liner. Results from dynamic tests on MSW landfill models on liquefiable foundation soil gave important insights into the failure mechanism of clay liner system under earthquake loading following the liquefaction of soil beneath the side slope of the landfill.

The criteria for crack initiation in clay were investigated by performing 4-point bending tests on consolidated clay beams. The results provided strain and strength criteria for crack initiation in clay. The stress states of the extreme fibre in tension of all the beams at initiation of a crack showed that cracks initiated when the effective stress state reaches either the tension cut-off line for low mean effective stresses or the ‘apparent failure line’ for higher mean effective stresses corresponding to Hvorslev’s normalisation of the Mohr-Coulomb failure envelope.

This research has shown the effectiveness of dynamic centrifuge testing of MSW landfills and provided valuable information that may be used in designing of new landfills or risk assessment of old landfills. Keywords :- MSW landfills ,earthquake, geomembrane tension, cracking, centrifuge testing