Desiccation of clay under elevated temperature tank
Desiccation of clay under elevated temperature tank
(OP)
Hi all,
We design foundations of the oil tanks (diameters vary from 30-55m, height 12-13m) with concrete ring walls (the ring wall is required for uplift resisstance). Inside the ring wall the bottom of the tank is rested on the 80mm minus run gravel compacted to 100% SPMDD, with thickness of 1m. under the gravel layer is the engneered fill of about 1.5m thick, then the stiff to very stiff native clay. And we intended to install the high temperature geotextile for secondary liner under the tank.
The problem now is the temperature of the oil inside the tank is up to 90 degree celsius. Geotechnical engineer for the project said that the 2.5m of gravel and engineered fill above the clay is enough for the dissipated of the temperature when it transered to clay. but still warry about the desiccation settlelemnt of clay down bellow.
Any document or reference to check that problem. or any experience with that kind of design?
We design foundations of the oil tanks (diameters vary from 30-55m, height 12-13m) with concrete ring walls (the ring wall is required for uplift resisstance). Inside the ring wall the bottom of the tank is rested on the 80mm minus run gravel compacted to 100% SPMDD, with thickness of 1m. under the gravel layer is the engneered fill of about 1.5m thick, then the stiff to very stiff native clay. And we intended to install the high temperature geotextile for secondary liner under the tank.
The problem now is the temperature of the oil inside the tank is up to 90 degree celsius. Geotechnical engineer for the project said that the 2.5m of gravel and engineered fill above the clay is enough for the dissipated of the temperature when it transered to clay. but still warry about the desiccation settlelemnt of clay down bellow.
Any document or reference to check that problem. or any experience with that kind of design?





RE: Desiccation of clay under elevated temperature tank
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RE: Desiccation of clay under elevated temperature tank
Joe Tank
RE: Desiccation of clay under elevated temperature tank
I'd accept the condition of heated soil under the tank. I'd then look at the various moisture transfer mechanisms to develop a procedure for negating the moisture loss situation.
This reminds me of how I have successfully prevented drying of soil (and shrinkage) due to fast growing trees near buildings by a simple means of wetting the soil and leaving the trees there.. That may not work here, however.
For instance if vapor transfer from warm to cold is present, can you reverse the temperature gradient some place as a barrier?
You know if you dry clay soil far enuff, it won't shrink any more. Would pre-drying be in the picture?
RE: Desiccation of clay under elevated temperature tank
I would run a few Atterberg shrinkage limit tests.
Potential shrinkage volume could be estimated from the difference
between the natural (in-situ) moisture content and the shrinkage limit.
I think an estimate of total settlement under these conditions is complicated by three factors:
1) The zone of influence for consolidation foundation settlement is likely larger than the zone of expected temperature increase.
2) Potential dessication settlement may be more or less than consolidation settlement in the same location.
3) The rate of dessication may be greater or less than the rate of consolidation.
I think a conservative approach would be to simply add the expected dessication related settlement to the expected consolidation settlement.
Otherwise, crank up those diff-eqs.
RE: Desiccation of clay under elevated temperature tank
RE: Desiccation of clay under elevated temperature tank
The geotextile would be install about 1.5m (5') below the tank bottom, and on top is the structural gravel fill minus 40mm. The concern only if below the 5 feet depep of fill, should the temperature drop from 90 degree to below 60. I did some literature review but have yet found any info about earth fill properties to pratically estimate. any info about the references would be really appreciate.
RE: Desiccation of clay under elevated temperature tank
Heat flow is similar to water flow in soil. Imagine a flow net with flow paths beginning at the tank floor and ending at the ground surface outside the tank. If the heat source were a long strip, the problem becomes 2-dimensional and easier to imagine. The flow paths are then semicircular, starting straight down (at right angles to the boundary) and ending straight up. The longest path is from the center, and its length is 3.14 times the width of the strip. Very crudely, then, for a tank, the longest path is 3.14 R in length, or 47 M for a 30M diameter tank. If the average annual air temperature outside is 15 degrees C, the average gradient is (90 - 15)/47 or 1.6 degrees C per meter. The temperature at the bottom of the gravel fill will be roughly 87 degrees C. Correcting this to radial flow will change the answer considerably, but surely the temperature will not be below 80 degrees at the geotextile.