The aim of the study
is to avoid or mitigate seismic site effect, such as: landslides, amplification
and faulting systems. Seismic refraction technique was used to investigate the
city of Rawabi Site. More than 30 seismic
profiles have been shot to figure out the subsurface geology and to delineate
if there are cavities beneath the selected landfill site. The underground
seismic models beneath the profiles show different velocities to two or three
layers; the first layer represents the soil cover (weathered surface material)
with maximum thickness of about 5
m overlaying a layer of sediment material (marly and
clay- marly materials) or directly on consolidated carbonate materials of
limestone, chalky limestone, and dolomite limestone. The underground seismic
models and the time-distance results don't show clear cavities at shallow
depths except slight morphological variations at bottom of marly layer which
may indicate small voids. The shear wave velocity values (Vs) vary between 500 m/sec and 1500 m/sec for marly materials
and hard limestone respectively. Based on thicknesses of layers and the values
of Vs for each layer, the type of soil profile at the foundation levels varies
between SB and SC.
The effects of local geology on ground-motion
amplification and building damage were studied in Rawabi City
(first stage – phase 1). Nakamura’s method of microtremor analysis was applied
in this investigation. The measurements showed large differences in
amplification between few selected sites. Calculating the natural period of the
proposed common buildings (Tb) in the studied, the values obtained
were closed to the site dominant natural period (Ts) in few locations. On the
other hand, reducing the marly stratum level in city center area by 10 – 20 meters
as proposed in the master plan, will have a positive effect on reducing the
seismic amplification factor measured at city center area. In the other areas (Sector
1 to 6), the amplification factor is relatively small.
To avoid landslides phenomenas, several slope
stability analysis sections have been done in the proposed site of Rawabi City.
The study models all expected cases such as excavation, building loads,
backfill materials behind retaining walls and embankments and expected
seismic loads. Analysis was carried out for given sections through Sector 1 and
for virtual sections according to topography and local geology through the rest
of the sites. Results show that the stability of slopes within the site is
safe. However, it is recommended to construct the buildings on the hard
limestone bedrock layer and using backfill materials according to standards.