Estimating Consolidation Settlement within Fill
Estimating Consolidation Settlement within Fill
(OP)
It is my understanding that 1D consolidation testing is generally best for sedimentary type soils; however, I'm not sure about engineered fills. Would consolidation testing of remolded samples (proposed fill) provide useful information? If so, what does one use for a preconsolidation pressure when estimating settlement WITHIN the fill?





RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
Nwabuokei, S.O., and Lovel, C.W., "Compressibility and Settlement of Compacted Fills"; 1986
RE: Estimating Consolidation Settlement within Fill
Secondly, and related, if the soil is fill and it is compacted, the compaction takes out most of the consolidation issues and leaves mostly elastic conditions for settlement.
If you have very thick fill (say 8 to 10 feet) that is simply dumped in with no compaction, some settlement can occur. You can consider this and compute it from the void ratio change between the loose state and the compacted state.
RE: Estimating Consolidation Settlement within Fill
To Some - Structural Fill is always an imported Granular, usually non- or very low plastic material. The compaction spec and control should be commensurate with the thickness of fill and final use (i.e. what kind & type of structural loads are to be applied).
To others, myself included - Structural Fill is a pre-approved (by the Geotech & in full knowledge of the design/Structural Engineer) soil or material, may be native, placed under controlled conditions (compaction specs, appropriate testing & observation), all commensurate with the anticipated use.
There are also many areas between these extremes.
RE: Estimating Consolidation Settlement within Fill
When we haven't respected this settlement we've been sorry, with cracked walls, misaligned stairs and other unfortunate events.
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
Mike Lambert
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
Again, the reference I posted seems to have a rational approach to estimation of fill settlement (settlement within a lean clay, lacustrine, fill); however, I haven't mulled through it completely. Ref: Nwabuokei, S.O., and Lovel, C.W., "Compressibility and Settlement of Compacted Fills"; 1986
My gut feel is that the settlements would be on the order of 1 to 2 percent of the fill thickness as most have suggested.
RE: Estimating Consolidation Settlement within Fill
I'd use settlement plates and periodic survey to gauge the post-placement compression as much of what you think may happen will occur during placement.
f-d
¡papá gordo ain’t no madre flaca!
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
I this example it could be either. If the mode of settlement is directly related to the relief of excess pore pressure over time, then it's consolidation. However, if the fill is not saturated and the settlement response is related to modulus (or C-sub Alpha), I'd call it compression. Bear in mind that secondary compression (i.e., the change of void ratio in the absence of changing effective stress) is called "compression" for a reason. Consolidation is not taking place!
It is pseudo-elastic. So, you are correct, it's not precisely elastic. I think geotechnical engineers use the term compression and think in terms of "elastic" behavoir, 'cause it's a way to approach the problem. In granular soils (i.e., where permeability is to great to really affect the analysis, we'd consider some "elastic response" to loading (modulus based) and then add (roughly) 20 percent for the anticipated long-term "creep" effects. You see in most instances, the compression that you'd calculate would occur during construction (i.e., as the fill is being placed). So, now the question is what would you expect post-construction (i.e., after delivery to the owner)?
f-d
¡papá gordo ain’t no madre flaca!
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
Very interesting question when it comes to how the fill is placed and finally is found to settle. Say the job lasts three months, in the case of a dam built on hard rock. Let's say it takes about a week to get 50% "compression effect", a month to get 90% for a typical layer of the fill material for a given layer thickness and loading pressure. Each layer however gets a different loading situation and with time and any "drainage" may be different. So when the job finally is done, which layer is then contributing how much to the total settlement of the final surface, as related to time? A good job for a computer programmer to predict the final settlement rate and amount at the top surface. Then, when all is done, work backwards and compare to lab consolidation test data to see how you did in predicting when job schedules are subject to variations with time..
I think the guess of 1 or 2 percent might be easier.
RE: Estimating Consolidation Settlement within Fill
RE: Estimating Consolidation Settlement within Fill
When building on fill one would usualy dig out the virgin ground and replace it with controled fill material that will be compacted.
Before the placement of the fill we usualy have geotehnical team mesuring the "constrained modulus of compressibility" kN/m2 of the virgin soil wich will give you some idea of the compressibility of the ground on wich you are planning to fill.
"constarined modulus of compressibility" is obtained from field results while loading an 15cm diametar circular plate into the ground. I think it messures increas of vertical stress wich is then divided by vertical strain.
Depending on the result eg. if below 15000kN/m2 we place geosythetics before the first fill layer.
If the readings are above 20000kN/m2 we just fill the ground and start compacting.
When finished with compaction, modulus is messured one more time for the new soil.
Results should range from 20000kN/m2 to 40000kN/m2 for well compacted fill.
If mv=30000kN/m2, and let say that you new net loading due to the foundation is 150 kN/m2, strain=150/30000 you would expect settlement in range of s=strain x h (thickness of the fill).
Anyway, you should always pay attention to the geometry of your container (ground hole geometry).
Try avoiding that the container edges are touched by the fictive 45` load disspresion line from the foundations since edges will always be problematic for good compaction.