Estimating Consolidation Settlement within Fill

[nbr1]

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?

 

[nbr1]

Aside from a philosophical debate about mechanism; how does one go about calculating the 'within fill settlement' of a large clay fill (moisture conditioned to optimum and specified compaction....call it what you will; engineered fill or otherwise) in normal practice due to self weight or expected moisture changes.

 

[oldestguy]

nbr:

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.

 

[moe333]

Predicitng the settlement accurately is extremely difficult. Estimating 1% (or 2%) of fill height would likely be the most practical. For detailed analyses, try googling "deep fill hydrocompression by Noorany, Bandon, Duncan"

 

[mar2805]

Ill throw in my 2 cents but please bear in mind that my terminology might be wrong since english is not my native laguage.
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.