Spatial Variability of Subsoil Properties of Guwahati City Using GIS Based Maps

Guwahati, the major city in the North Eastern region of India is growing rapidly in every aspect with
major infrastructures like sports complex, educational institutions, hospitals, flyovers, multiplex halls,
etc. Knowledge of the subsurface soil condition is necessary to ensure the structural safety and
serviceability of the above mentioned structures before any construction. Therefore Liquefaction
potential map and shear wave velocity map using Geographical Information System (GIS) platform
and contour maps of Standard penetration test N value, ground water table will be of great help to the
foundation designers at the initial stage for site selection and preliminary foundation design under
static and seismic condition. Contour maps of Standard penetration test N value at different depth and
average contour map of N value of Guwahati city have been prepared. Standard penetration Test N
values and depth of water table were taken from a data base of 200 boreholes upto 30 meter depth to
prepare N value contour map of Guwahati city. A regression equation between shear wave velocity Vs
and Standard penetration test N value based on twenty seven previous similar correlations was also
developed. This regression equation was used to determine shear wave velocity of Guwahati city. The
average shear wave velocities for 30m depth for all locations had been determined and used to
generate map on (GIS) platform. Seismic soil liquefaction in Guwahati city in terms of factor of safety
against liquefaction and probability of liquefaction along the soil profiles have been evaluated and
presented as maps showing zones of levels of risk of liquefaction. Other subsurface geotechnical
information of Guwahati city like soil classification, depth to water level from ground surface are also
presented in the form of GIS based maps in order to form a data base.