Paper Title
Geotechnical Interpretation of Soil For The Proposed Underground Utility Tunnel From Kuril to Malibagh in Dhaka City
Abstract
For the proposition of establishment of upcoming 7.7 km common utility tunnel under Progoti Sarani in Dhaka
between Kuril flyover and Malibagh Chowdhurypara, Dhaka North City Corporation (DNCC) has stepped forward to
complete a feasibility study report accumulating all soil test data around Dhaka city found from different secondary
organizations. Besides that, four boreholes to a depth of about 30m each were drilled at different locations and consequent
laboratory tests are also done as per the requirement. In that perspective, a new aspect of geological and geotechnical site of
Dhaka city soil profile is prepared based on those primary and secondary data focusing a single part of city from Kuril to
Malibagh. The prepared soil profile is compared with the geomorphological map of Dhaka city published by Geological
Survey of Bangladesh (GSB) and found that most of the soil in Dhaka city is of Madhupur terrace (clayey silt and silty clay)
of Pleistocene era. The range of liquid limit of maximum data in the project is between 40 and 60, plasticity index is greater
than 4 and limit values between 'A' line [0.73(LL-20)] and 'U' line [0.9(LL-8)] of plasticity chart, so the soil criteria will be CL
(Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays) and CH (Inorganic clays of high
plasticity, fat clays). The soil is found Over Consolidated Clay (OCC) because in most of the cases natural water content (W)
is close to Plastic limit (PL). Most of the clay minerals are found Illite and Kaolinite which is classified between Inactive and
Normal clays (Activity ratio, A = 0.38 to 0.90) which means that there may be no significant swelling and shrinkage
characteristics in the project area along with changing of water contents as well as the possibility of structural damage is also
negligible. But a matter of concern is that in some points soils are collapsible according to plasticity index. Results of chemical
analysis indicate that the sub-soils are not aggressive to concrete and not corrosive to reinforcement steel.
Index Terms— Dhaka City, Geotechnical Interpretation, Subsurface Soil Profile, Soil Properties.