LoveThiccPavements
Civil/Environmental
- May 4, 2025
- 1
I have limited experience on the placement and testing side pavement construction, but was recently involved with a deep pavement (heavy industrial) on a weak (10 day soaked 1-3% CBR) subgrade.
Due to construction occuring in winter/autumn, rainfall was sporadic. Enough to require a substantial perimeter drain and holding off until the sub layers were sufficiently dry to proceed - when MDD was reached within tolerance prior.
My question(s) revolve around the theory side of achieving a moisture target to proceed with further pavement lifts, not so much years of experience by a contractor suggesting it's 'fine' to continue on.
My general understanding is that for course grained materials, after OMC and MDD are reached, you nominally want to be dry of OMC before proceeding with the next pavement lift. I've found a few research papers and other standards using degree of saturation rather than OMC as a hold point but it more or less seems to be an arbitrary value.
I assumed this dryback was for two reasons, the underlying being that the plastic limit of coarse grained materials was comparatively close or higher than OMC and therefore sufficiently "rigid" to continue with the pavement if dried out to some % lower than OMC, additionally moisture from proceeding lifts or wet subgrade may pump/push moisture to the layer. After a lot of googling I can't seem to find anything to confirm this beyond anecdotal discussion.
Is this sort of correct? Am I missing anything else?
For fine grained materials (particularly subgrade) with a relatively high degree of reactivity, there seems to be even less rationale. I understand at that point it would be worth considering stabilisation, shot rock etc. but assuming a poor subgrade was compacted, what is normally the moisture content threshold or trigger point?
Research suggests there's almost no point drying back substantially when MDD is reached due the soil reaching an equilibrium moisture content (EMC) in the medium term anyway. The difference between compacting and drying out so that it's somewhat driveable/traversable (again presumably before plastic limit) compared to the EMC, likely means future heave/settlement issues as it reaches EMC.
Does anyone work with a basis or theory for progressing/approving a pavement layer? E.g. based on moisture content of the subgrade or similar to course grained materials.
Broadly, it seems the only option would be to consider some form of remediation or working pad but I assume there would be many pavements around, some working fine, where this wasn't the case. Particularly for not-so-reactive subgrades.
Due to construction occuring in winter/autumn, rainfall was sporadic. Enough to require a substantial perimeter drain and holding off until the sub layers were sufficiently dry to proceed - when MDD was reached within tolerance prior.
My question(s) revolve around the theory side of achieving a moisture target to proceed with further pavement lifts, not so much years of experience by a contractor suggesting it's 'fine' to continue on.
My general understanding is that for course grained materials, after OMC and MDD are reached, you nominally want to be dry of OMC before proceeding with the next pavement lift. I've found a few research papers and other standards using degree of saturation rather than OMC as a hold point but it more or less seems to be an arbitrary value.
I assumed this dryback was for two reasons, the underlying being that the plastic limit of coarse grained materials was comparatively close or higher than OMC and therefore sufficiently "rigid" to continue with the pavement if dried out to some % lower than OMC, additionally moisture from proceeding lifts or wet subgrade may pump/push moisture to the layer. After a lot of googling I can't seem to find anything to confirm this beyond anecdotal discussion.
Is this sort of correct? Am I missing anything else?
For fine grained materials (particularly subgrade) with a relatively high degree of reactivity, there seems to be even less rationale. I understand at that point it would be worth considering stabilisation, shot rock etc. but assuming a poor subgrade was compacted, what is normally the moisture content threshold or trigger point?
Research suggests there's almost no point drying back substantially when MDD is reached due the soil reaching an equilibrium moisture content (EMC) in the medium term anyway. The difference between compacting and drying out so that it's somewhat driveable/traversable (again presumably before plastic limit) compared to the EMC, likely means future heave/settlement issues as it reaches EMC.
Does anyone work with a basis or theory for progressing/approving a pavement layer? E.g. based on moisture content of the subgrade or similar to course grained materials.
Broadly, it seems the only option would be to consider some form of remediation or working pad but I assume there would be many pavements around, some working fine, where this wasn't the case. Particularly for not-so-reactive subgrades.
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