Nomenclature
Chapter 8 Conclusions
The conclusions presented below were drawn based on the measured water retention characteristic curve (WRCC) of fly ash, bentonite and fly ash-bentonite mixes, sensitivity of WRCC model parameters on unsaturated seepage modeling and lead (Pb2+) interaction on fly ash, bentonite and fly ash-bentonite mixes.
The present study identifies the measurable range of suction as 0-1000 kPa for fly ash.
This range of measured suction encompasses near saturation, desaturation and residual saturation portions of water retention characteristic curve.
The WRCC fitting parameters obtained using different methodologies are not unique for fly ashes considered in this study and hence cannot be generalized.
A new framework for WRCC parameterization of high volume change soils like bentonite was suggested to overcome ambiguities in obtaining WRCC parameters.
This was done based on experimentally measured volumetric shrinkage characteristics of bentonites.
The extent of influence of fly ash type and content on the WRCC of fly ash-bentonite mixes was brought forth.
Statistical assessment of the variability of WRCCs of bentonite and fly ash-bentonite mixes showed that the variability of WRCC for materials from different sources was within 20%.
The WRCC results of all the materials merged towards the residual portion. This observation has its significance because most of the landfill liners are compacted at optimum moisture content (OMC). For a high volume change soils like bentonite, OMC will be close to residual state. This means that bentonites from different sources can be used with a minimal quality check for the construction of liners.
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The variation in pore water pressure (PWP) with time obtained from unsaturated seepage modeling for different fly ashes was mainly due to the variation in the WRCC parameters since the ksst value of all the fly ashes were comparable.
The seepage modeling results of bentonites indicated significant variation in PWP and volumetric water content (VWC) with time for WRCC parameters obtained using two approaches (i.e. with and without the use of shrinkage test results).
The seepage modeling result obtained for fly ash-bentonite mixes showed considerable influence of fly ash types and fly ash content.
Fly ash acts as good sorbent for Pb2+ which is an added advantage of using fly ash instead of sand for constructing landfill liners.
The Pb2+ sorption result of 50:50 fly ash-bentonite mix showed that results were close to bentonite sorption results, which was mainly attributed to high specific surface area of the latter.
Major contributions from this study
1. Establishing the range of measurable suction for Indian fly ashes and determination of WRCC parameters.
2. Proposing a systematic methodology based on shrinkage characteristic curve for determining WRCC of high plastic bentonites.
3. Measurement of WRCC of fly ash-bentonite mixes and studying the sensitivity of fly ash types and fly ash content on the WRCC of fly ash-bentonite mix.
4. Investigating the sensitivity of variation in WRCC parameters on unsaturated seepage modeling for different cases considerd in this study.
5. Understanding the potential of different fly ashes, bentonite and fly ash-bentonite mixes for the retention of heavy metal such as lead and comparing their removal efficiency.
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Chapter 8 Conclusions
The conclusions presented below were drawn based on the measured water retention characteristic curve (WRCC) of fly ash, bentonite and fly ash-bentonite mixes, sensitivity of WRCC model parameters on unsaturated seepage modeling and lead (Pb2+) interaction on fly ash, bentonite and fly ash-bentonite mixes.
The present study identifies the measurable range of suction as 0-1000 kPa for fly ash.
This range of measured suction encompasses near saturation, desaturation and residual saturation portions of water retention characteristic curve.
The WRCC fitting parameters obtained using different methodologies are not unique for fly ashes considered in this study and hence cannot be generalized.
A new framework for WRCC parameterization of high volume change soils like bentonite was suggested to overcome ambiguities in obtaining WRCC parameters.
This was done based on experimentally measured volumetric shrinkage characteristics of bentonites.
The extent of influence of fly ash type and content on the WRCC of fly ash-bentonite mixes was brought forth.
Statistical assessment of the variability of WRCCs of bentonite and fly ash-bentonite mixes showed that the variability of WRCC for materials from different sources was within 20%.
The WRCC results of all the materials merged towards the residual portion. This observation has its significance because most of the landfill liners are compacted at optimum moisture content (OMC). For a high volume change soils like bentonite, OMC will be close to residual state. This means that bentonites from different sources can be used with a minimal quality check for the construction of liners.
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The variation in pore water pressure (PWP) with time obtained from unsaturated seepage modeling for different fly ashes was mainly due to the variation in the WRCC parameters since the ksst value of all the fly ashes were comparable.
The seepage modeling results of bentonites indicated significant variation in PWP and volumetric water content (VWC) with time for WRCC parameters obtained using two approaches (i.e. with and without the use of shrinkage test results).
The seepage modeling result obtained for fly ash-bentonite mixes showed considerable influence of fly ash types and fly ash content.
Fly ash acts as good sorbent for Pb2+ which is an added advantage of using fly ash instead of sand for constructing landfill liners.
The Pb2+ sorption result of 50:50 fly ash-bentonite mix showed that results were close to bentonite sorption results, which was mainly attributed to high specific surface area of the latter.
Major contributions from this study
1. Establishing the range of measurable suction for Indian fly ashes and determination of WRCC parameters.
2. Proposing a systematic methodology based on shrinkage characteristic curve for determining WRCC of high plastic bentonites.
3. Measurement of WRCC of fly ash-bentonite mixes and studying the sensitivity of fly ash types and fly ash content on the WRCC of fly ash-bentonite mix.
4. Investigating the sensitivity of variation in WRCC parameters on unsaturated seepage modeling for different cases considerd in this study.
5. Understanding the potential of different fly ashes, bentonite and fly ash-bentonite mixes for the retention of heavy metal such as lead and comparing their removal efficiency.
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