Ripon Hore, PhD :
Wrap faced reinforced soil retaining wall on soft clay is popular all over the world because wrap faced layer consumes less space in both sides of the wall, which is economical and less susceptible to dynamic loading. Wrap Faced embankment is basically a sand embankment wrapped around by geotextile layers as a steep embankment. This wrap-faced embankment is filled with different characteristics of sand (example: Sylhet and local sand which are available in Bangladesh). A research on “wrap faced embankment on soft soil” conducted by Bangladesh University of Engineering and Technology (BUET) found that the wrap faced embankment which is great resistance to earthquake and wave action saving huge land acquisitional cost of Bangladesh Government. This research output has already been published on five renowned international Journals. The Journals are Arabian Journal of Geosciences, Geotechnical and Geological Engineering, International Journal of Geosynthetics and Ground Engineering, Transportation Infrastructure Geotechnology and GEOSFERA Indonesia.
In this research, the wrap faced embankment is model by reduce scale in BUET Geotechnical Lab. The shaking table test machine was used to induce earthquake and wave action. The artificial recorded kobe 1995 and lomaprieta 1989 earthquakes were used to conduct this research. The fifteen sensors have been placed in the wrap faced embankment and clay soil layer. The different soil characteristics like accelerations, displacement, pore water pressure and strain has been analyzed in this research. This embankment showed better response to the earthquakes and wave action means stable to seismic and wave action. The results of the research have also been verified by numerical analysis by PLAXIS 3D software. The variation of results is less than 15%. It was very challenging to find out the characteristics of such type of embankments on soft clay soil in Bangladesh during the earthquake and wave action. Without knowing the characteristics of the wrap faced embankment during an earthquake, it is impossible to build this type earthquake/wave resisting embankment. The dynamic behavior of wrap faced embankment on soft soil in Bangladesh has been invented by this research. Now, it is possible to design and construct earthquake resistant wrap faced embankments on the soft soil.
A 6.1 magnitude earthquake shook Dhaka, Chattogram and some other parts of the country on 26 November 2021. Earlier another earthquake of 5.6 magnitude jolted Myanmar on 8 October this year, with tremors being felt in parts of Bangladesh. Four successive mild earthquakes had shaken Sylhet on 29 May 2021. Experts say it could be a warning sign of a major earthquake. Multiple small earthquakes at once in the region are forecast for the next major earthquake. Moreover, Bangladesh is an earthquake prone area. It has experienced severe earthquakes such as Great Indian earthquake (8.7) of 1897 and Bengal earthquake (7.0) of 1885 which damaged not only building infrastructure but also road embankments. This is high time to induce the Seismic design on the infrastructures in Bangladesh. But it is very challenging to predict the dynamic soil condition in Bangladesh. Solution is wrap faced embankment. This type of embankment is a great resistance against severe earthquakes. Finally, we know that Bangladesh is acceptably vulnerable to climate change. Due to climate change, the water level of the river is increasing during the rainy season day by day. So, at this time the river bank protection is challenging. It is inevitable that embankment slope stability failure has been occurred without induced proper measure against wave action. The wrap faced embankment which induces vertical reinforcement raises a new hope to resist the wave action. Finally, the huge land acquisition cost of the government in Bangladesh has been reduced using the wrap faced embankment. Traditional embankment requires huge land space to construct the embankment (example: if 2:1 or 1:1 slope is provided, they need to acquire large agricultural land on both sides of the embankment). Wrap-faced walls allow us to use less space horizontally, saving crores of Taka for the construction of traditional embankments in Bangladesh. The embankments method, proved in the research to be applicable to the soft soil of Bangladesh, can be made 70 less costing than the traditional embankments as it allows making embankments using 60-70 per cent less land space. Secondly, it saves huge agricultural land. Agricultural production has been accelerated in this land. The different government implementing agencies in Bangladesh like Roads and Highway Department (RHD), Local Government Engineering Department (LGED), Water Development Board (WDB) and Bangladesh Railway (BR), may construct the large amount of the wrap faced embankment in Bangladesh. In fine, it is mentioned that the invented wrap-faced embankment raises a new hope for Bangladeshi people and this opens a new milestone for the transportation sector of Bangladesh.
(Ripon Hore is Senior Assistant Engineer, Local Government Engineering Department).
