October, 2006

October, 2006   ||  Volume 10 No.4

Comparison of Pseudo-Static and Pseudo-Dynamic Methods for Seismic Earth Pressure on Retaining Wall

Deepankar Choudhury, Sanjay S. Nimbalkar and J.N.Mandal

Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai – 400 076.
E.mail: dc@civil.iitb.ac.in, sanjay_nimbalkar@iitb.ac.in, cejnm@civil.iitb.ac.in

Design of retaining wall needs the complete knowledge of earth pressures for both active and passive conditions. Under earthquake condition, the design requires special attention to reduce the devastating effect of this natural hazard. But under seismic condition, the available literatures mostly give the pseudo-static analytical value of the earth pressures as an approximate solution to the real dynamic nature of the complex problem. In the present work, a recently developed pseudo-dynamic method, which incorporates time dependent effect of applied earthquake load and effect of shear and primary waves, is applied to study effect of variation of parameters like soil friction angle, wall friction angle, time period of earthquake ground motion, seismic shear and primary wave velocities of backfill soil and seismic peak horizontal and vertical ground accelerations on the seismic earth pressures. Again a complete analysis between these two design methodologies shows that the time dependent non-linear behaviour of the pressure distribution obtained in the pseudo-dynamic method results more realistic design values of earth pressures under earthquake condition.


Heat Transport through Indonesian throughflow
Vivek Kumar Pandey and Avinash Chandra Pandey
K. Banerjee Centre of Atmospheric and Ocean Studies, Institute of Interdisciplinary Studies,
Nehru Science Centre, Allahabad University, Allahabad - 211002
E.mail: vivekkpandey@rediffmail.com

Approximately 10.5 Sv (1 Sv=106m3/s) of water flows from Pacific Ocean into the Indian Ocean through the Indonesian archipelago region, which is composed of three major passages, Lombok (115° 50 E, 8° 30¢ S), Savu (122°E, 9° 30¢ S) and Timor (128°E, 11°S).The Indonesian seas provide a pathway for substantial transfer of Pacific Ocean waters to the Indian Ocean (Rochford, 1961; Wyrtki, 1961; Gordon, 1986; Wyrtki, 1987). The Indonesian Throughflow (ITF) heat transport is estimated on the basis of volume transport and surface temperature obtained from model output of one-year run of Princeton Ocean Model (POM) of 0.25X0.25 degree resolution. On the basis of model study the obtained heat transport is of the order of 1.087 PW (1 PW=1015W), which shows dominant warm water transport.

Features of atmospheric Carbon Monoxide at two different coastal environments

G.Mohan Kumar, V.S.Jeena and S.Sampath
Atmospheric Sciences Division, Centre for Earth Science Studies
PB 7250, Thiruvananthapuram - 695 031

Trace gases in the atmosphere influence the radiation budget of our planet and their abundance often determines the air quality of a region. Though carbon monoxide (CO) is not a potent green house trace gas, it affects human health. Using a non-dispersive IR analyzer, CO in ambient air is being measured at a tropical clean coastal site, Thiruvananthapuram (8.5oN, 77.6oE) from 2003. The location of the instrument is in a pristine coastal environment with ample vegetation. A similar CO analyzer is functional in a coastal industrial city, Kochi (10.08oN, 76.3oE) from 1997. The diurnal and seasonal CO patterns at these two coastal stations are compared with reference to their environments. Besides, the differences in weekday and weekend CO abundance were examined for both the sites. Since Kochi has data for the last eight years, the long-term trends and temporal variations in CO are also examined.

Studies on silt deposition in Gambhiram Reservoir – A Remote Sensing Approach
P.Jagadeeswara Rao, P.Harikrishna1 and B.Surya Prakasa Rao
Department of Geo-Engineering, Andhra University, Visakhapatnam-530 003.
1Rolta India Ltd., MIDC, Andheri (East) Mumbai-400 093
Email: pjr_geoin@rediffmail.com, bosukonda@rediffmail.com and p_hari123@yahoo.com

The non-perennial Pedda Gedda, a minor watershed located in the hilly terrain of Eastern Ghats Mobile Belt (EGMB) region of Visakhapatnam District of Andhra Pradesh, has a drainage area of 184.9 sq.km with a reservoir called Ghambhiram in the middle of the basin. It is characterized by khondalite suite of rocks. Thematic information has been generated on the drainage pattern of the river, geological setting, geomorphological evolution of fluviatile landforms, lineament/structural trend and landuse/landcover. In this study, the Silt Yield Index (SYI) technique has been used to assess the effects of silt on the storage capacity of the reservoir. The study has been conducted at watershed level to understand the fluviatile activity of the river system. The study area is divided into 7 micro watersheds on the basis of drainage conditions. The micro watersheds 5 and 6 adjacent to the reservoir have rolling topography with moderate slopes contributing more silt to the reservoir. The micro watersheds 1 and 7 have no role in silt deposition to the reservoir. Sheet, gully and stream erosions are responsible for the reduction of the storage capacity of the reservoir to around 40% of its designed capacity. Mitigation measures like check-dam, afforestation and concrete have been suggested to arrest silt deposition.

Effect of forest canopy on the tropospheric ozone concentration of Indian States
Nandita D.Ganguly and K.N.Iyer
Department of Physics, St.Xavier’s College, Ahmedabad-380009.
Department of Physics, Saurashtra University, Rajkot-360005.
E.mail :nanditad@icenet.net

The tropospheric ozone concentration for few Indian States have been studied using the data obtained from the Tropospheric Ozone Residual (TOR) method to determine the impact of forest canopy on atmospheric ozone and the importance of plant emissions to our climate. The impact of forest canopy on tropospheric ozone concentration depends on factors like the amount of isoprene and monoterpene emitted by the plants, the type and area of forests, humidity and background NOx levels. The NO2, isoprene and humidity levels in the forests of northeastern India are found to be higher compared to those observed over the remaining parts of India. This may be one of the reasons why the ozone concentration observed in the forests of northeast India is also higher compared to that observed over the remaining parts of India.



Modeling of Indian Ionosphere using MMSE Estimator for GAGAN Applications
D.Venkata Ratnam and A.D.Sarma
Research and Training Unit for Navigational Electronics,
Osmania University, Hyderabad – 500 007
E-mail: ad_sarma@yahoo.com

With the advent of Global Positioning System (GPS), there has been significant change in aircraft navigation. For improving positional accuracy of GPS and for wide coverage, a Satellite Based Augmentation System (SBAS) is being developed in India popularly known as GAGAN. As the Indian ionosphere is characterized by large gradients, intense irregularities and an equatorial anomaly condition, a suitable ionospheric model is necessary for GAGAN. In this paper, an algorithm based on Minimum Mean Square Error (MMSE) technique is presented for computing the vertical delay at each Ionospheric Grid Point (IGP) and the Grid Ionospheric Vertical Error (GIVE). Several days of GPS data corresponding to multiple stations provided by Space Applications Centre (SAC), Ahmedabad is processed and applied to these models. It is found from the results that the estimated error bound on IGP delay (i.e., GIVE) is less than 2.0 m indicating that this model is one of the contenders for GAGAN applications.



Geological interpretation from Bouguer gravity data over the Singhbhum-Orissa Craton and its surroundings: A GIS approach

S.K.Pal, Amit K.Bhattacharya and T.J.Majumdar*
Department of Geology & Geophysics, Indian Institute of Technology,

Kharagpur – 721 302
Earth Sciences and Hydrology Division, Marine and Earth Sciences Group, Remote Sensing Applications and Image Processing Area, Space Applications Centre (ISRO), Ahmedabad – 380 015
*Corresponding Author E.Mail : tjmajumdar@sac.isro.gov.in

The Digitized Gravity Model (DGM) of the Bouguer anomaly map of Singhbhum – Orissa Craton and its surroundings obtained using GIS techniques brought out several gravity highs and lows which bear a strong correlation with the surface geology. The aspect map of the Bouguer anomaly is calculated, which helps in demarcating transitions in gravity values and thereby indicates subsurface geology. Thus the gravity transitions observed in aspect map also delineate aspect lineaments and infer a new horizon to understand the tectonic activity over the Singhbhum Shear Zone