Hydraulic Conductivity, Microstructure, and Compositional Changes of Sand–Bentonite Backfill in Cutoff Walls Exposed to Organic Acids
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 149, Issue 8
Abstract
Leachate, consisting of organic acids such as acetic acid (AA) and oxalic acid (OA), commonly is released into groundwater from municipal solid waste dumps and uncontrolled landfills. Slurry trench cutoff walls commonly are used to contain such contaminated groundwater, thereby protect the surrounding public and the environment. However, no studies have assessed comprehensively the effects of organic acid–laden groundwater exposure on the hydraulic conductivity and microscopic characteristics of sand–bentonite (SB) backfill in the cutoff walls. Several series of free swell, liquid limit, and flexible-wall hydraulic conductivity tests were conducted to quantify the effects of AA and OA exposure on the free swell index of bentonite and hydraulic conductivity and liquid limit of SB backfill. Results showed that the free swell index of bentonite and the liquid limit of SB backfill decreased with increasing concentrations of AA and OA. Exposure to AA yielded a lower free swell index of bentonite and liquid limit of SB backfill than those of OA with the same concentration. Increasing concentrations of AA and OA resulted in an increase in the hydraulic conductivity of SB backfills. Exposure to AA yielded higher hydraulic conductivity of SB backfill than OA with the same concentration. Mechanisms for increased hydraulic conductivity under organic acid exposure were ascertained based on the microstructure and compositional changes quantified by field-emission scanning electron microscopy (FESEM), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), X-ray fluorescence (XRF), cation exchange capacity (CEC), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR) analyses.
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Data Availability Statement
All data generated during the study appear within the published paper.
Acknowledgments
Financial support for this project was provided by the National Natural Science Foundation of China (Grant Nos. 42177133 and 41877248), the National Key Research and Development Program of China (Grant Nos. 2018YFC1802300 and 2018YFC1803100), the Primary Research and Development Plan of Jiangsu Province (Grant No. BE2022830), and the Postgraduate Research and Practice Innovation Program of Jiangsu Province (Grant No. KYCX21_0122). The first author also acknowledges the China Scholarship Council (CSC) for supporting his study at Nanyang Technological University, Singapore.
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 149 • Issue 8 • August 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Sep 9, 2022
Accepted: Mar 27, 2023
Published online: May 27, 2023
Published in print: Aug 1, 2023
Discussion open until: Oct 27, 2023
ASCE Technical Topics:
- Acids
- Backfills
- Bentonite
- Chemical compounds
- Chemicals
- Chemistry
- Clays
- Construction engineering
- Construction methods
- Diaphragm walls
- Environmental engineering
- Excavation
- Geomechanics
- Geotechnical engineering
- Groundwater
- Hydraulic conductivity
- Material mechanics
- Material properties
- Materials characterization
- Materials engineering
- Microstructure
- Soil mechanics
- Soil properties
- Soils (by type)
- Structural engineering
- Structural members
- Structural systems
- Swelling (material)
- Walls
- Water (by type)
- Water and water resources
- Water management
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