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A GIS/LIS Approach for Study on Suitability of Shallow Foundation at Southern Chennai, India
Derived Soil SPT N Map
The integration of Soil and Iso SPT N map gives a very practical and significant outcome of this research work. The strength and soil properties can be easily estimated at any location within the study area with simple queries . Generally shallow foundation will be laid within 1.5 m from the ground level. In order to decide the suitability of shallow foundation Iso SPT N @ 1.5 m from the ground level is overlaid with Soil map.
The suitability of the shallow foundation is decided by two important governing factors namely allowable bearing capacity also referred as allowable load intensity (ALI ) and super imposed load (load from each floors). Allowable bearing capacity can be computed using Teng’s relation (1). The program for the suitability of the shallow foundation is written in Avenue language. The parameter used for the suitability analysis are SPT N value, width and depth of the foundation, level (terrain) of the ground, ground water table, and soil type. This program will automatically take the values of SPT N from Iso SPT N map with respective depth and the soil type will be fetched from Soil map. For an following input, width of the footing as 2m , depth of the foundation as 1.5 m from ground level (G.L), water table is far off from G.L, G.L is fairly level, Suitability map (Fig 3) is generated. For this input, five zones are demarcated. Zone 5 – highest ALI ( i.e., > 600 KN/sq.m) regime has been observed towards north and middle eastern regions with sporadic northern pockets. This zone is well suited for shallow foundation. The zone 2 to 4 (i.e., 100 – 600 KN/sq.m) are moderately suited for shallow foundation. Proper care has to be taken in zone 2 before designing the foundation. The zone 1 (i.e., <100 KN/sq.m) , unsuitable for any shallow foundation, especially footings.
The present research work aiming the suitability of shallow foundation using GIS/ LIS for the southern part of Chennai, India will be very useful for all Civil engineers, Geotechnical Engineers, Design Engineers, Planners and even the local inhabitant for any future developmental activities in the area concerned. In fact, for any specific location, with suitable queries, the allowable load intensity of soil and the suitable foundation can be obtained, which is found to be close to the actual findings at this location. Another advantage with the present work is its flexibility with respect to adding data as well as adding few non-spatial parameters like depth of water table, surface drainage pattern, soil permeability and infiltration capacity and so forth.
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