Soil springs

[DougHole]

When geotechnical and structural engineers talk about "Soil springs", what do they mean in the context of lateral pile analyses? is this just a p-y curve? or is it just subgrade modulus (k) or is something else. How do I come up with "soil springs"? Can I do this in LPILE and if so, how?

 

[Mccoy]

Dougfunny, are you sure the section is the correct one (slope stability)?.
Usually, by soil springs in your case I would construe a linear law relating lateral loading against strain, represented conceptually by a spring.
Sometimes the models are merely elastic (linear) springs, sometimes they can be elastic-plastic, with a rupture treshold calculated by active and passive resistance of pile shaft. P-Y curves might be defined non linear soil springs, where the spring softens when the loading increases, up to a treshold level (plastic yielding). As far as I know Lpile carries the classic Matlock & Reese p-y curves models, if not somthing more recent, so you can actually model lateral springs. I'm not an Lpile user so I cannot say you how, it should be straightforward though since you just choose the p-y analysis option and input the appropriate soil types, which are few and basic ones.

 

[DougHole]

Hi McCoy. thanks you are right. I just realized its in the slope stability forum! thanks for the reply.

 

[DougHole]

So it sounds like lateral "springs" come in various forms and a p-y curves is one type of "Spring" i.e. a non-linear one. How do you come up with linear lateral springs for a pile? is that just the same as a subgrade modulus reaction (k value)? Also, how does one come up with vertical springs for a pile. By the way, I will leave this post under "Slope Stability" for now. Sorry about posting it in the wrong place

 

[Mccoy]

How do you come up with linear lateral springs for a pile? is that just the same as a subgrade modulus reaction (k value)?

Exactly, that would be similar to the Winkler model adopted for shallow foundations. For very small strains, the K value would be the same as the initial part of the p-y curve but a modulus secant to the p-y curve is strongly advised in operational conditions.

There are 2 kinds of vertical springs, the ones along the shaft and the one at the bottom of the pile, although in many models the whole pile is modeled as a single huge vertical spring + one huge horizontal spring. In more evolved programs the pile is modelled by finite elements, every lenght having its springs (I'm working on a model where each pile element has 3 kinds of springs, vertical, lateral horizontal springs and torsional springs. The base element carries four springs, since there is a vertical one at the base added.

 

[DougHole]

Thanks so much McCoy for helping me understand "springs". Much appreciated