2018 Fiscal Year Research-status Report
Aging Effect on the S-p relationship due to repeated drying/wetting cycles on the Subsoil
| Project/Area Number |
18K04344
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| Research Institution | Kyoto University |
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Principal Investigator |
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| Co-Investigator(Kenkyū-buntansha) |
勝見 武 京都大学, 地球環境学堂, 教授 (60233764)
高井 敦史 京都大学, 地球環境学堂, 准教授 (30598347)
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| Project Period (FY) |
2018-04-01 – 2020-03-31
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| Keywords | Aging effect / S-p relationship / SWCC / Contaminant / Subsoil |
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| Outline of Annual Research Achievements |
During FY2018, we have tested the changes in the S-p (SWCC) curve of water and an LNAPL (low viscosity paraffin liquid) in both, low compacted and highly compacted Toyoura sand samples, when subject to repeated water table fluctuations. We focused on the changes in residual and irreducible saturations (Srf and Sra) and found that:
1. The entry pressure of air-water system is higher than that of air-NAPL system, and the largest variation on residual saturation Srf occurred at the beginning of the first drainage.
2. The values of irreducible saturation Sra seem to be related to initial void ratio and type of fluid.
3. After multiple drainage and imbibition cycles, the residual saturation Srf reduced and reached a stable condition in all samples. The best fit is an exponential decay curve, described by: Srf(N) = (1 - Srf*) exp(-b N) + Srf*, where Srf* is the final value of residual saturation for the sample, N is the number of cycles, and b is a scaling parameter related to the easiness in reaching stability.
4. The value of residual saturation Srf of both low-density cases changed more than that of high-density cases, and the final value of residual saturation Srf* of air-NAPL system was higher than that of air-water in both states.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
As the number of cycles required to reach stability seems lower than initially expected, we could perform both, water and LNAPL tests (originally planned to be performed in one year, each) during the first year. We have also tested two different density conditions that were not originally planned, that is giving us additional information to proceed with the next steps.
Our plan, however, included the study of additional LNAPLs that we still haven't performed (originally planned for the second year, so we're still on schedule for this), and we have found some volumetric changes in soil samples that we need to carefully asses (not considered in our original plan).
All in all, I believe we are advancing rather smoothly with this project.
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| Strategy for Future Research Activity |
Our original schedule for the second year focused on the study of the changes in the S-p (SWCC) relationship for different LNAPLs. As we have already performed the planned tests for one LNAPL (low viscosity paraffin liquid), and as we have found one additional variable to study (volumetric change), we will focus our second year in the careful study of soil volumetric changes, for both water and LNAPL, using an oedometer. We are planning on performing these tests with fluctuationg water table conditions (as in our first-year tests), and will perform ten of them (as that was the upper limit we have already found for this).
We expect that the obtained information will better help us improve our theoretical models during year-three.
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| Causes of Carryover |
For our first year work we purchased the planned computers and tempe cells, that helped us smoothly proceed with our S-p (SWCC) curve tests under dense/loose conditions, for both water and a chosen LNAPL. We also used some other equipment (pumps, sensors, valves, etc.) that we have already in our laboratory.
We had planned to use a data logger with some tensiometers we currently have to more precisely measure pore pressure, but the equipments were not working as expected. Therefore, we plan on purchasing additional tensiometers and some oedometer parts to continue with our work.
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