Highway embankment design in Bangladesh

At present there is no systematic approach for the design of highway embankments in Bangladesh. To address this issue, this thesis presents a methodology which can be used for the design of embankments in countries with similar conditions to those experienced in Bangladesh. Such conditions include: the large seasonal variation in flood water levels, which can reach up to 5 m in height; the soft soils on and from the embankments are mainly constructed, and; the prevailing socio- economic climate. The large seasonal variation in flood water levels coupled with the underlying soft (clay) soils results in mainly two types of embankment failure. These are broadly associated with excessive amounts and slow rates of embankment foundation settlement and embankment stability. The latter includes slope failure and foundation bearing capacity failure. The chosen methodology to prevent these types of failure took into account the prevailing socio-economic situation. That is the methods selected had to be sustainable, capable of being implemented and economically viable. Design methods were developed to keep the embankment within the allowable settlement limit and make it stable. These methods include performing settlement and stability analyses respectively. To this end, two techniques described in literature, finite difference settlement analysis and Bishop’s method for stability analysis implemented in commercially available software (Settle3D and OASYS SLOPE respectively), were selected from a number of options studied. In addition to the two methods described above, two other methods were identified where the commercial software is not available. These are less accurate and may not be used under certain conditions are easily implemented in a spreadsheet. For settlement analysis Standard method and to perform stability calculations Low’s method were chosen. For the former and Low’s method and developed stability chart were proposed for stability analyses. Under some conditions the developed design processes may identify that some form of remediation is required. Where it is found necessary to increase the rate of settlement of the embankment and foundation beyond that possible naturally prefabricated vertical drain (PVD) and the addition of a surcharge with a horizontal drainage blanket were identified as suitable options. Additional methods to improve stability include the addition of geo-fabrics, stage construction, the use of geo-cells and pressure berms. The top of the embankment, or subgrade, acts as a platform for the pavement and whose properties are the input for pavement design. To assist the pavement design process therefore, a procedure has also been developed in the research to specify appropriate subgrade properties. These included the use of appropriate materials and compacted by suitable amounts so that the fill does not undergo excessive settlement during the life of the pavement. Suitable amounts of compactive effort, layer thickness and construction moisture content were included as part of the specification with appropriate values based on previous research findings.

Name dc:type.qualificationname

m_ph

Level dc:type.qualificationlevel

m_ph

Grantor dc:publisher.institution

University of Birmingham

Year dc:date.issued

2009

Author dc:creator

• Bhattacharyya, Shyamal Kumar

• TG Bridge engineering
• TE Highway engineering. Roads and pavements