Abstract
In order to quantify the migration rule of water in composite lining canal foundation soil during the freeze-thaw process, the outdoor prototype test is performed to prove the change rules of water in different positions and depths of the rigidflexible mixed composite lining canal foundation during the whole freeze-thaw cycle. The prototype observation test shows that during the freezing period, the water content within the 0~80cm depth of the canal foundation soil increases with the depth, and that within the depth of 80~160cm decreases gradually with the depth. In the freezing period, water accumulates in the depth of 60 ~ 80cm, with a maximum water transfer amount of +13.2%, which occurs at the canal bottom. In the thawing period, the maximum water content also occurs at the canal bottom, with a maximum water transfer amount of -11.0%. Through the laboratory test of soil samples, the water migration development and change rules of the canal foundation soil, under different moisture contents and temperature gradients are studied in unilateral pattern. In the case of the same top plate control temperature, soil samples with similar initial water contents have similar water transfer amounts. The samples with higher initial water content have higher water transfer amount, with higher water accumulation, normally accumulating in the depth of 16~18cm. The results indicate that high water contents make it easy to gather water in soil samples during the freezing period.
Highlights
In order to quantify the migration rule of water in composite lining canal foundation soil during the freeze-thaw process, the outdoor prototype test is performed to prove the change rules of water in different positions and depths of the rigidflexible mixed composite lining canal foundation during the whole freeze-thaw cycle
For the freeze-thaw test, three groups of samples taken from the composite lining canal foundation were tested, and 9 samples were taken from the shady slope, sunny slope and canal bottom, 3 for each position, respectively
Considering the effects of different temperature patterns and different water contents on the water migration during the freeze-thaw process, totally 9 groups of soil samples taken from composite lining canal foundation were tested in the laboratory, with 9 samples taken from the shady slope, sunny slope and canal bottom, 3 for each position, for the freezethaw tests
Summary
The prototype observation test region is located in a large irrigation district in Fukang, Xinjiang autonomous region in northwest of China. The region has a maximum average frozen soil depth of 1.45m, and a measured annual maximum frozen depth of 1.72m, belonging to seasonal frozen soil region. According to the soil test data, the mass of canal foundation soil with the particle size smaller than 0.075mm is over 10% of the total mass, which belongs to the frost heave soil. The yearly average temperature of the test area is 6.5! According to the soil test results, the canal foundation soil has a water content of 16%~23%, density of 1.51~ 1.65g/ cm, porosity of 0.69~0.80 (belonging to low liquid limit silt), plasticity index of 5.8~6.4, liquid index of 0.53~0.82, permeability coefficient of 2.25×10–4~8.49×10–4cm/s, compression coefficient of 0.25~0.31MPa–1, compression modulus of 6.0~7.3MPa (belonging to medium compressibility), cohesion of 6.2~11.6kPa, and internal friction angle of 16.5°~22.3°.
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