We are dealing with a 230mm concrete pavement to be placed on top of an expansive clay, expansions are about 4% to 5%. We will place a 100mm cement treated granular base beneath the slab and we want to place a lime treated sub-base for swelling control. We would appreciate your advice on determining the thickness of this sub-base to control the swelling.
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expansive clays
- Thread starter roso
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The thickness of the subbase will be a function of the seasonal moisture changes and possibly the depth to groundwater level and the water level fluctuations. It will also be a function of the in-place soil moisture profile. Typically, however, the lime treated subbase is installed to depth range of 12" to 18" depending on the local conditions.
dear roso
behavior of expansive clays are essentially related to their in-situ water content and compaction state (Dry density) and as UdayRB said to seasonal change of water content. if you are dealing with high plastic dry modarately high density compacted clay with change of ground water lavel or persipitations your case is considarable to study more in lab. 4 to 5% swell is high but at which conditions?, a constant volume swell pressure test on an undisturbed sample will help you to know your uplift swell pressure. and that can help you to design the slab and sub-base.
keep in touch
behavior of expansive clays are essentially related to their in-situ water content and compaction state (Dry density) and as UdayRB said to seasonal change of water content. if you are dealing with high plastic dry modarately high density compacted clay with change of ground water lavel or persipitations your case is considarable to study more in lab. 4 to 5% swell is high but at which conditions?, a constant volume swell pressure test on an undisturbed sample will help you to know your uplift swell pressure. and that can help you to design the slab and sub-base.
keep in touch
roso,
I would say that a simple expansion test is probably not enough to characterize your soil in regard with your topic. I suppose you ask the sub-base to level the global value of expansion and to limit differential displacements. The first point is obtained because you increase the value of the stress under the sub-base. And the higher the stress on the expansive soil, the lower the expansion caused by water content increase. So, I would recommend to determine the stress value under which expansion is prevented. You can find it very easily in an oedometer device by applicating different stress value to identical samples of the soil (same water content, same dry density) and determine for each stress the deformation caused by an inundation of samples.
I don't say the stress you'll find will exactly determine the thickness of the sub-base, but you will be able to decide with objective data.
Best regards.
I would say that a simple expansion test is probably not enough to characterize your soil in regard with your topic. I suppose you ask the sub-base to level the global value of expansion and to limit differential displacements. The first point is obtained because you increase the value of the stress under the sub-base. And the higher the stress on the expansive soil, the lower the expansion caused by water content increase. So, I would recommend to determine the stress value under which expansion is prevented. You can find it very easily in an oedometer device by applicating different stress value to identical samples of the soil (same water content, same dry density) and determine for each stress the deformation caused by an inundation of samples.
I don't say the stress you'll find will exactly determine the thickness of the sub-base, but you will be able to decide with objective data.
Best regards.
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