Vol. 8(5) May 2015
Stability of seawalls by considering non-breaking
wave forces during earthquakes
Rajesh B.G. and Choudhury Deepankar
Pseudo-static stability analysis has been carried out
for seawall, supporting submerged cohesion less backfill under the combined actions
of earthquake and non-breaking wave forces. Closed-form design solutions in terms
of factor of safety against sliding and overturning modes of failures have been
obtained by using the limit equilibrium method for active condition of earth pressure.
From the sensitivity study, it is found that when the horizontal seismic acceleration
coefficient is increased from 0 to 0.2, there is about 67% decrease in the factor
of safety of the seawall in sliding mode. It is also observed that seismic horizontal
acceleration, soil and wall friction angles and base friction angle significantly
dominate the seismic stability of seawalls. Comparison of present results with a
few specific available results in literature has indicated a very good agreement.
The proposed design charts will be extremely useful for the seismic design of seawall
against sliding and overturning modes of failure under the combined action of earthquake
and non-breaking wave.
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Soil liquefaction and bearing capacity at a building
site in Lucknow, India under earthquake conditions
Chatterjee Kaustav and Choudhury Deepankar
Problem of soil liquefaction below building foundation
during earthquake shaking due to high pore water pressure in loosely packed sand
deposits located below the ground water table, leading to significant loss in shear
strength and causing it to flow like a viscous fluid, is a severe concern for civil
engineers. In the present study, liquefaction susceptibility under earthquake conditions
has been computed for 12 boreholes till a depth of 9m at a soil site in Lucknow,
India. The mentioned site comes under seismic zone III as per Indian seismic design
code IS 1893–Part 124and hence a design acceleration of 0.16g was considered for
building design. The seismic acceleration coefficient was also computed as per Eurocode
EN1998–Part 519 and comparison in liquefaction susceptibility was carried out for
the soil site. This was followed by computation of seismic bearing capacity and
factor of safety at a depth of 1.5m below ground surface for the proposed building
foundation. Based on the results it was observed that some selected boreholes showed
susceptibility to liquefaction at certain depths under earthquake shaking. Moreover
some of the selected boreholes are found to be prone to bearing capacity failure
at 1.5m depth as per Eurocode EN1998–Part 519 for certain foundations. Hence the
proposed results show the need for such analysis with future recommendations of
remedial measures for safe design of building foundations at the site under earthquake
conditions.
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Ionospheric Precursor before a 547 km deep Indonesia
Nebe Earthquake on 27 February 2015, Mw=7.0 using Two-Dimensional Principal Component
Analysis (2DPCA)
Lin Jyh-Woei
In this study, the ionospheric Total Electron Content
(TEC) data of 5 days before Indonesia Nebe earthquake occurred at 13:45:05 (UT)
on 27 February 2015 ( =7.0) with the depth of 547km and the epicentre of 7.277°S,
122.534°E were examined to detect TEC precursor by using Two-Dimensional Principal
Component Analysis (2DPCA) because such TEC precursor could not be found by observation
analysis. Results have shown that a TEC precursor was highly localized and increased
in intensity during the time period from 05:55 to 06:00 (UT) on 26 February 2015.
The duration time of TEC anomaly was at least 5 minutes. Possible reason of the
TEC precursor over the epicenter before this earthquake should be radon gas release.
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Last Mile Warning: A review of Tsunami Warning Measures
in Thailand
Fakhruddin S. H. M.
The most vital operational responsibility of a tsunami-warning
center is to offer real-time monitoring of earthquake and tsunami events. It has
to provide timely alerts based on rapid decision-making and to disseminate warning
information at the least possible time through multiple avenues up to the last mile.
To provide rapid alert notification system, Thailand has installed 328 warning towers9
in the coastal and flood prone areas. This paper examines the status of tsunami
warning system after 10 years of devastating tsunami 2004 and community perception
and usefulness of tsunami warning towers. We surveyed two hundred households in
three provinces (Phuket, Pangnga and Ranong) in order to get a representation of
the level of knowledge concerning tsunami warning system and status of the tsunami
warning towers. The results show a common trend in all the provinces. There is lack
of knowledge on tsunami warning system, evacuation drills; many community know little
about the warning towers; false alarm reduces the trust of community, the Burmese
population is often not considered; the beach guard towers are generally not considered
useful and overall there is a lack of knowledge and education regarding disaster
preparedness and tsunami information.
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Comparison of Frequency Ratio Model and Analytic Hierarchy
Process methods upon landslide susceptibility mapping using Geospatial techniques
Kartic Kumar M. and Annadurai R.
This paper present the comparison result of landslide
susceptibility mapping on Kothagiri Taluk, Tamil Nadu using Frequency ratio model
(FRM) and Analytic Hierarchy Process (AHP) methods with the aid of GIS tool. Landslide
locations are identified and an inventory map is constructed by field surveys and
satellite images. A IRS P6 LISS IV MX satellite acquired in February 2012 is used
for preparing landuse. The susceptibility index map developed by considering the
causative factors such as slope, aspect, curvature, geology, land use, distance
from drainage, the Stream Power Index (SPI), soil texture, normalized differentiate
vegetation index (NDVI), precipitation, soil erosion, distance from lineament and
the proximity to the road. Two landslide susceptibility maps are constructed on
the basis of landslide inventories and thematic layers using FRM and AHP model.
The two model results are compared by existing landslide locations. Total of 84
landslides are mapped in GIS out of which 70% locations are chosen for the modeling
purpose and the remaining 30% cases are used for validation. To achieve the best
accuracy, landslide susceptibility maps are cross- validated using respective Receiver
Operating Characteristic (ROC) curves. The verification results revealed that the
frequency ratio model (AUC = 87.50%) is slightly better in prediction than AHP (AUC
= 83.30 %). The investigation results explain reasonable acceptance between the
landslide susceptibility map and the existing landslide location. On the basis of
the higher percentages of landslide bodies predicted in very highly hazardous and
highly hazardous zones, the results obtained by use of the frequency ratio model
are slightly more accurate than the AHP model used for landslide susceptibility
analysis.
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