elastic settlement

[killswitchengage]

Hi
Is it truly unnecessary to compute elastic settlement in soils and rocks ? the argument my colleague gave me was that elastic settlement happens instantaneously while the concrete is poured and only consolidation settlement should be of concern
On the other hand what about rigid fresh rock mass with little to no discontinuities ? should one compute its elastic settlement either ?
thanks

 

[fattdad]

For large embankments, elastic compression can develop beyond the limits of the property line (right of way).

For unsaturated soils, the time frame for elastic compression can be, "Immediate." That said, there is also the "Creep" term, or the, "Time Rate Factor," C-sub-t. Depending on the elastic modulus you may want to consider this for both areal fills and loading from foundation elements?

How much creep can develop in the one month after all the elastic compression has occurred? I'd go with zero. How much creep can develop in the one year after elastic compression has occurred? I'd use 20 percent. For 30 years, I'd use 50 percent.

I refer you to CGPR (Virginia Tech, Center for Geotechnical Practice and Research) publication #2 for more information.

f-d

ípapß gordo ainÆt no madre flaca!

 

[Okiryu]

I think that elastic settlements need to be estimated. For example, what can happen if you have a building with underground utilities connected to it, it does not matter if elastic settlements occur fast. If elastic settlements are large, you will be damaging these utilities and their connections to the building...

f-d, the Virginia Tech website looks interesting...

 

[killswitchengage]

Lets forget about creep for a moment , most of the clays i worked with are usually of low plasticity . So i get from your reply that elastic compression can be a major issue if large embankment are used or perhaps raft foundations ?
I've checked this CGPR , but as you may know i am out of the USA and can't afford to buy anything . Anyway what's your comment on rock elastic settlement ?
thanks

 

[fattdad]

elastic compression for rock will be informed by the modulus of the rock mass. The modulus will be lower than for soil. To the extent that you calculate some measure of elastic compression you'd calculate the immediate response to loading. I'd still consider the long term performance (i.e., over decades) and apply the C-sub-t term for post construction compression.

That's my comment, for what its worth.

f-d

p.s., I used the term, "Creep" to characterize the compression that can develop after the immediate compression. I'm not referring to horizontal consolidation response or the toothpaste-tube-type displacement. Sorry, if I got the OP off track. The term C-sub-t relates to both coarse- and fine-grained soils.

ípapß gordo ainÆt no madre flaca!

 

[killswitchengage]

"The modulus will be lower than for soil" are you referring to young's modulus ? if so i believe you are wrong since for rocks its much much greater than for soils . Still my main issue was not answered properly , only Okiryu gave me a nice thing to think about . I repeat myself can we ignore elastic settlement for ordinary constructions like small houses ?

 

[Okiryu]

I still think that you cannot ignore elastic settlements. Other example can be: possible differential settlement issues between slab-on-grades (large area-low loading) and the surrounding foundations (small area-medium/high loading)...

 

[fattdad]

Yes, I meant the settlement will be lower and I was typing faster than thinking.

No for residential construction, I doubt I much worry about elastic compression of rock.

Sorry I wasn't more helpful. . .

f-d

ípapß gordo ainÆt no madre flaca!

 

[killswitchengage]

anyway thank you both have a great day

 

[Okiryu]

killswitchengage, I just also remembered that you can neglect elastic settlements when you have saturated clay soils under one-dimensional loading (i.e. uniform fill surcharge applied over a very large area). In this case, since the loading is considered as one-dimensional loading, there will not be horizontal strains into the soil and therefore elastic settlement is zero (elastic settlements do not produce a volume change in soil -contrarily to consolidation settlement-, so the amount of elastic settlement of the structure must be compensated by an equivalent amount of lateral deformation). With no horizontal strains, the lateral deformation is zero and consequently elastic settlements (in saturated clay soils) is zero.

 

[killswitchengage]

thank okiryu i already established that with the EuroCode