Wednesday, April 30, 2014

Freezing soil movements

As soil freezes, the moisture changes from water to ice, it expands by 9.08 percent. Water density goes from essentially 1.0 to 0.9167 gm/cc on the old metric system notation, gm/ml now. When a saturated soil freezes, the free water expands. The attached plastic water depends on the temperature drop whether it freezes or not. If we have a silty sand at 30 percent moisture saturated. Gs=2.65, 1 cubic metre is composed of 1476 kg solids, 443 kg of water. If the free water was 25% (25/30) of the total water 369 liters, that new volume after freezing is 402.7 liters, or expansion of 33.7 liters. Since the only way soil can expand is upwards, that is 0.0337 of the depth of freezing from phase change only.

As freezing is occurring, water is drawn to the freezing front by thermodynamic forces. This can produce ice lensing, in addition to phase change. The amount of heave can be considerable, 150 to 300 mm in a season is not uncommon, I have often seen 100 in addition to phase change. For these to happen, all you need is a frost susceptible soil, a lower source of water, and a freezing front. These often show up around water line leaks and frequently cause water line failures as these start to mellow in spring, driving the frost front down further.

When a trench is insulated and drained, through a wet sandy silt deposit, you are designing in a seasonal settlement over the trench, in addition to any line settlement.

How many people with ADHD does it take to change a lite bulb?
           Look, ... there goes a rabbit. 

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