Static and Seismic Stability of the Largest Malaysian Sanitary Landfill

In light of the huge landfill failures in South-East Asia in the past 10 years, namely
failures of the Payatas and Leuwigajah landfills in 2000 and 2005 respectively, the
necessity of assessing the stability of Malaysian landfills is signified. This project
aims to investigate the static and seismic stability of the Bukit Tagar Sanitary
Landfill, the largest Malaysian sanitary landfill, serving 8 million people with a
design capacity of 120million m3 to operate for 40 years. This study can be very
insightful in identifying the extent to which geotechnical and hydrological
parameters and earthquakes can affect the stability of landfills in Malaysia. Most
significantly, the objective is to assess how susceptible Malaysian landfills are to
stability failures under both static and seismic conditions. Numerous field
investigations were conducted indicating proper incorporation of stability enhancing
practices in Malaysian sanitary landfills. Static and seismic stability of the landfill
were simulated using the geotechnical software, GeoStudio. Sensitivity analysis was
carried out to study the effects of water level and waste's unit weight and shear
strength parameters (i.e. friction angle and cohesion) on the stability of the Bukit
Tagar landfill. These analyses indicated an adequate stability design of the landfill.
However, inadequate drainage together with heavy precipitations may lead to
stability failures. Generally, landfill stability is sensitive to water levels to a very
large extent, to waste unit weight to a fair extent and to waste shear strength to a
lesser extent. This signifies the vitality of good drainage and best compaction
practices for the waste to increase landfill stability. Frequency analysis indicated that
an earthquake with a return period of 100 years in Malaysia would be of a local
mag1_1itude of7.99. Seismic stability simulations using the equivalent-linear dynamic
analysis showed that Bukit Tagar landfill had an acceptable stability design in
drained and likely undrained conditions against this 7.99 magnitude earthquake. The
necessity of proper drainage for stability of the landfill is highlighted once more by
the critical FS values encountered for the undrained condition in the seismic analysis.

Keywords: Landfill stability, Earthquake, South East Asia, Malaysian landfill, Bukit
Tagar landfill, Municipal Waste