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Hydrochar Amendment of Microstructur...

Dong, Huan,

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Hydrochar Amendment of Microstructure and Hydromechanical Behaviour of Compacted Soil /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Hydrochar Amendment of Microstructure and Hydromechanical Behaviour of Compacted Soil // Huan Dong.
Author:	Dong, Huan,
Description:	1 electronic resource (266 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 86-05, Section: B.
Contained By:	Dissertations Abstracts International86-05B.
Subject:	Geoengineering. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31718187
ISBN:	9798346545262

Hydrochar Amendment of Microstructure and Hydromechanical Behaviour of Compacted Soil /
Dong, Huan,

Hydrochar Amendment of Microstructure and Hydromechanical Behaviour of Compacted Soil /Huan Dong. - 1 electronic resource (266 pages)

Source: Dissertations Abstracts International, Volume: 86-05, Section: B.

The increasing amount of yard waste generated by daily landscape activities and associated release in greenhouse gases following waste degradation has introduced various environmental issues, including climate change. Extreme drought and precipitation exacerbate negative impact on the slope stability and the health of plants covering the slopes. Soil microstructural evolution due to amplifying dry-wet cycles directly affects the soil's hydromechanical behaviour. Biochar has been a solution to sequestrate carbon from yard wastes for carbon neutrality and has been used to improve the soil quality. Hydrochar, which is produced by hydrothermal carbonisation (HTC) process, is a more energy-saving alternative to biochar. The microstructure of hydrochar and how it affects the soil pore size distribution (PSD) have rarely been studied. Study on the influence of hydrochar addition on soil's hysteretic hydraulic and mechanical properties is lacking.This thesis presents comprehensive experimental campaigns to conduct cross-scale study of the effects of hydrochar amendment on the changes in the microstructure and hydromechanical behaviour of compacted soils. Through detailed microstructural analysis, it is discovered that under the same as-compacted dry density, the addition of a low mass proportion (݂fH of 2.5%) of hydrochar increased the volume of macro-pores provided by the hydrochar particles, yet reduced that of the micro-pores due to the pore-filling mechanisms by the smaller hydrochar particles. However, with ݂fHwas increased further to 5% and 10%, the macro-pores were compressed by the higher compaction energy required to achieve the same as-compacted dry density, accompanied by the increase in the micro-pores.Effects of hydrochar on the soil hydraulic properties were investigated. Results of saturated hydraulic conductivity (ks) tests revealed a threshold (2.5% to 5%, depending on the HTC temperature used to produce the hydrochar) at which the ks exhibited the greatest improvement corresponding to the largest macro-pore void ratio. Results from evaporation tests showed that the hydrochar addition at ݂fH of 5% and 10% improved the soil water retention curve (WRC) due to the reduction in the macro-pore void ratio. The hydraulic conductivity function was also increased by the hydrochar addition, which might be related to the increase in throat frequency and the contribution of micro- and nano-scaled pores on hydrochar surface. It is further discovered from wide-suction range hysteretic WRC tests that the hydrochar addition increased the suction where the first peak of degree of hysteresis (Dh) appeared, yet reduced the suction where the second peak of Dhwas detected. A linear correlation existed between the air-entry values and the peaks of the degree of hysteresis. Decomposition of 84.7% hydrochar by mass after 120 days accompanied by the emergence of microorganism introduced negligible effects on the PSDs and WRCs.Effects of hydrochar on the mechanical behaviour of compacted soil were studied through double-cell triaxial tests. During constant-suction drained shearing, the addition of hydrochar had limited effect on the slope of the the critical state line (CSL) in the shearing plane and the critical state friction angle, attributable to the similar particle morphology of hydrochar and soil particles. However, the intercept (apparent cohesion) of the CSL and hence the shear strength increased substantially with the increase in suction, and the amount of increase for the case of H240-amended soil was larger than that of unamended soil possibly due to the alteration of the pore morphology following the addition of hydrochar.

English

ISBN: 9798346545262Subjects--Topical Terms:

3538885
Geoengineering.

Hydrochar Amendment of Microstructure and Hydromechanical Behaviour of Compacted Soil /
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245 1 0 $a Hydrochar Amendment of Microstructure and Hydromechanical Behaviour of Compacted Soil / $c Huan Dong.
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520 $a The increasing amount of yard waste generated by daily landscape activities and associated release in greenhouse gases following waste degradation has introduced various environmental issues, including climate change. Extreme drought and precipitation exacerbate negative impact on the slope stability and the health of plants covering the slopes. Soil microstructural evolution due to amplifying dry-wet cycles directly affects the soil's hydromechanical behaviour. Biochar has been a solution to sequestrate carbon from yard wastes for carbon neutrality and has been used to improve the soil quality. Hydrochar, which is produced by hydrothermal carbonisation (HTC) process, is a more energy-saving alternative to biochar. The microstructure of hydrochar and how it affects the soil pore size distribution (PSD) have rarely been studied. Study on the influence of hydrochar addition on soil's hysteretic hydraulic and mechanical properties is lacking.This thesis presents comprehensive experimental campaigns to conduct cross-scale study of the effects of hydrochar amendment on the changes in the microstructure and hydromechanical behaviour of compacted soils. Through detailed microstructural analysis, it is discovered that under the same as-compacted dry density, the addition of a low mass proportion (݂fH of 2.5%) of hydrochar increased the volume of macro-pores provided by the hydrochar particles, yet reduced that of the micro-pores due to the pore-filling mechanisms by the smaller hydrochar particles. However, with ݂fHwas increased further to 5% and 10%, the macro-pores were compressed by the higher compaction energy required to achieve the same as-compacted dry density, accompanied by the increase in the micro-pores.Effects of hydrochar on the soil hydraulic properties were investigated. Results of saturated hydraulic conductivity (ks) tests revealed a threshold (2.5% to 5%, depending on the HTC temperature used to produce the hydrochar) at which the ks exhibited the greatest improvement corresponding to the largest macro-pore void ratio. Results from evaporation tests showed that the hydrochar addition at ݂fH of 5% and 10% improved the soil water retention curve (WRC) due to the reduction in the macro-pore void ratio. The hydraulic conductivity function was also increased by the hydrochar addition, which might be related to the increase in throat frequency and the contribution of micro- and nano-scaled pores on hydrochar surface. It is further discovered from wide-suction range hysteretic WRC tests that the hydrochar addition increased the suction where the first peak of degree of hysteresis (Dh) appeared, yet reduced the suction where the second peak of Dhwas detected. A linear correlation existed between the air-entry values and the peaks of the degree of hysteresis. Decomposition of 84.7% hydrochar by mass after 120 days accompanied by the emergence of microorganism introduced negligible effects on the PSDs and WRCs.Effects of hydrochar on the mechanical behaviour of compacted soil were studied through double-cell triaxial tests. During constant-suction drained shearing, the addition of hydrochar had limited effect on the slope of the the critical state line (CSL) in the shearing plane and the critical state friction angle, attributable to the similar particle morphology of hydrochar and soil particles. However, the intercept (apparent cohesion) of the CSL and hence the shear strength increased substantially with the increase in suction, and the amount of increase for the case of H240-amended soil was larger than that of unamended soil possibly due to the alteration of the pore morphology following the addition of hydrochar.
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