Abstract
Geomorphological, geological and engineering geological information is used as the base data to characterize the subsurface condition and for sustainable urban planning and development of the rapidly expanding Mymensingh city. Extensive field work has been completed to get the realistic scenario, data and samples have been collected from surface and subsurface with auguring and geotechnical boring. The laboratory tests have been performed following standard laboratory procedures. Geomorphologically the area is broadly classified into Older Floodplain or Mymensingh Terrace and Younger Floodplain. These two flood plains are separated by Old Brahmaputra River. Geologically the area is mainly covered by the recent alluvial flood plain deposits which are underlain by the Pleistocene Madhupur clay deposits. The Younger Flood Plain deposit consists of mainly unconsolidated fine to medium sands with some silt and clay whereas the Older Flood Plain deposits are mainly consisting of silty clay and fine to medium sand. Moderately compacted sediments of older flood plain deposit are suitable for urban development. Based on geotechnical characteristics and the N values (blow counts of Spontaneous Penetration Test, SPT) of the subsurface sediments, the study area is classified into four Engineering Geological Units. Unit I indicates loose soil and is suitable for shallow foundation. Unit II is indicating compact soil packing; N value of these two units increase with depth and would be good for heavy foundation. Unit III is suitable for shallow structures. Unit IV, which is composed of mostly clay, silty clay and sand with highly compressive organic clay, is recommended to avoid any heavy construction and could be used as open place, water retaining zone etc. Beside the geological and engineering geological study details hydrology and hydrogeological and a systematic study on seismic hazards are strongly recommended before planning of urban area.
Highlights
The need and importance of geological and engineering geological information and their role in urban planning have been highlighted with many examples from around the world (e.g. Berhane, 2012 [1]; Anderson, 2006 [2]; Bathrellos et al, 2008 [3], 2011 [4]; De Abreu and Filho, 2011 [5]; Legget, 1973 [6]; Pueyo-Anchuela et al, 2011 [7]; El May et al, 2010 [8]; Culshaw and Price, 2011 [9])
The area is mainly covered by the recent alluvial flood plain deposits which are underlain by the Pleistocene Madhupur clay deposits
Mymensingh Terrace is situated in the southern part of the Brahmaputra River and Younger flood plain is situated in the northern part of the Brahmaputra River (Figure 2)
Summary
The need and importance of geological and engineering geological information and their role in urban planning have been highlighted with many examples from around the world (e.g. Berhane, 2012 [1]; Anderson, 2006 [2]; Bathrellos et al, 2008 [3], 2011 [4]; De Abreu and Filho, 2011 [5]; Legget, 1973 [6]; Pueyo-Anchuela et al, 2011 [7]; El May et al, 2010 [8]; Culshaw and Price, 2011 [9]). In Bangladesh the practices of using geological and engineering geological study before urban planning were ignored in past decades. Mymensingh is one of the fastest growing city of Bangladesh which is close to the capital Dhaka and is developing rapidly both industrially as well as agriculturally. The aim of the study is to provide geomorphological, geological and engineering geological data prior to develop Mymensingh city plan. For proper urban planning of the city these sub-surface parameters of the area could help for the future detail planning of the Mymensingh as mega city. This would reduce the population pressure on the Dhaka City
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