EFFECT OF GEOTECHNICAL AND HIDROGEOLOGICAL PARAMETER HETEROGENEITY ON THE SLOPE STABILITY MODELLING OF SOLID WASTE LANDFILLS RODRIGO ILARRI, JAVIER , GÓMEZ HERNÁNDEZ, J. JAIME Universidad Politécnica de Valencia, Departamento de Ingeniería Hidráulica y Medio Ambiente, Valencia (Spain) –
[email protected]
Abstract Model parameters Landfills are currently the world most-used available technique for solid waste final management. Following the most recent environmental regulations on solid waste management, it is necessary to perform a stability analysis of the waste-slopes in order to obtain the environmental authorization prior to the opening of the facility. These analyses have usually been performed considering a homogeneous distribution of geotechnical and hydrogeological parameters, such as cohesion, wet content or permeability. This poster shows the first results obtained when considering both homogeneous and hetereogeneous parameter distribution on the slope-stability of a municipal landfill using a commonly used 2D slope stability model. Several classical methodologies (Bishop method, Janbu method or Morgestern-Price method) have been applied to obtain the slope stability security factors under different scenarios. The modelling has been applied to several solid waste landfills of Valencia Region in Spain.Results shown here are those obtained on the waste landfill of Aspe (Alicante.
Objectives & Methodology
Definition of scenarios
Soil parameters: Cohesion C=40 KPa Internal friction angle Ø=24º Density γ=22 KN/m3 Solid waste parameters: Cohesion C=10 KPa Internal friction angle Ø=21º Density γ=10 KN/m3 Seismic action Horizontal acc. Coefficient: 0,12 Vertical acc. Coefficient: 0,12
47 slopes have been analyzed considering different combinations of parameters: • Considering uploads or not • Considering saturation of the waste mass or not • Considering seismic action or not Example: PT1_ norte _w_e means Transversal Profile #1 North direction analysis w: waste mass saturation e: seismic action
• Verify the stability of the waste slopes of the landfill • Determine the adequate slope to maximize the volume of the landfill performing a sensibility analysis of the geotechnical parameters. • Verify the influence of the different available techniques over the results of a 2D slope stability model • Analyze the importance of the correct design of the leachate control network.
Site location
Fig. 3.- Security Factors obtained for different scenarios on profiles PL1 and PT1
Fig. 1.- Location of the Aspe solid waste landfill. Alicante (Spain)
Available methodologies Simplified Bishop method c: cohesion β: slices base length N: weight component orthogonal to the base = W cos α Ø: internal friction angle W: slice’s weight α: slope angle of the slice’s base
Fig. 4.- Stability analysis of scenarios PL1_east_w_e (left) and PT1_south_w_e (right)
Simplified Janbu method • Iterative method similar to Bishop method • Only the horizontal forces equilibrium is satisfied • The momentum equilibrium is not satisfied • The method considers the normal stresses between slices but ignores the tangential stresses.
Morgestern-Price method Fig. 2.- Location of the profiles PL1 and PT1
GEOSLOPE/W Model Setup •Geometry definition and dimensions •Geotechnical parameters • Cohesion • Internal friction angle • Density •Uploads •Seismic actions •Saturation degree
• Normal and tangential stresses are considered on the equilibrium between slices. • Forces and momentum equilibrium is satisfied. • It allows the use of a variety of different functions to relate the normal and tangential stresses between slices.
It can not be guaranteed that the use of a more complex model lead to lower or higher Security Factors but only to more realistic ones.
Fig. 5.- General view of the landfill before filling with waste
Fig. 6.- Operations on Profile PL1
Conclusions and future research • The stability of the landfill slopes has been analyzed using a 2D numerical model • Several scenarios were defined, considering different geotechnical parameter values • The most critical scenario is that in which the seismic action ad the saturation of the solid waste mass is considered • Waste heterogeneous distribution and parameter heterogeneity should be considered
References GEOSLOPE/W. GEO-SLOPE International. 1400, 633 - 6th Avenue S.W. Calgary, Alberta, Canada T2P 2Y5. E-mail:
[email protected] Web: http://www.geo-slope.com
