Bagman2524
Structural
Does anyone have any experience with a design method using piles as a means of soil stabilization? Is it recognized in any codes?
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Pilings used as soil stabilization 2
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palmahouse
Geotechnical
I doubt there is anything is codes on this - but not exactly sure. these systems should be designed by a geotechnical engineer because the design loads come from slope stability evaluation.
One thing is for certain: The design loads and structural demands can be huge, and other methods should be considered. Drainage galleries can be effective if ground pore pressures are an issue.
Assuming we are back to piles, here is one method I have used successfully (which means I may have been too conservative?):
Slope stability analysis to calculate the unbalanced force required per pile to achieve an adeqaute factor of safety against slope failure. Use L-Pile to determine the unfactored shear and moments on the piles for some accepted deflection. Consider factoring the shear and moments and design the piles using the building code requirements for deep foundations.
Better yet, but perhaps too sophisticated: do a coupled analysis with the piles and ground in a model - like a finite element model. This should be done only by a geotechnical engineer with numerical modeling experience, or time and budget to get experienced.
One thing is for certain: The design loads and structural demands can be huge, and other methods should be considered. Drainage galleries can be effective if ground pore pressures are an issue.
Assuming we are back to piles, here is one method I have used successfully (which means I may have been too conservative?):
Slope stability analysis to calculate the unbalanced force required per pile to achieve an adeqaute factor of safety against slope failure. Use L-Pile to determine the unfactored shear and moments on the piles for some accepted deflection. Consider factoring the shear and moments and design the piles using the building code requirements for deep foundations.
Better yet, but perhaps too sophisticated: do a coupled analysis with the piles and ground in a model - like a finite element model. This should be done only by a geotechnical engineer with numerical modeling experience, or time and budget to get experienced.
GeoPaveTraffic
Geotechnical
I have designed and installed two slide repairs using drilled shafts to reinforce the slope. Piles have never proved effective due to their low section modulus.
Drilled shafts are not a very economical means of remediaing a slide, drainage, grade changes, rock buttress are all generally cheaper and quicker to install. However, in both cases, for very different reasons, none of these would work.
One of the systems was 48-inch diameter shafts installed at 8-foot centers. The other one was 36-inch diameter shafts installed at 7-foot centers.
Drilled shafts are not a very economical means of remediaing a slide, drainage, grade changes, rock buttress are all generally cheaper and quicker to install. However, in both cases, for very different reasons, none of these would work.
One of the systems was 48-inch diameter shafts installed at 8-foot centers. The other one was 36-inch diameter shafts installed at 7-foot centers.
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Bagman2524
Structural
This particular case uses piles as "soil stabilization" for a slab on grade design.
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There have been a number of case studies using lime piles as a means of ground improvement. It is used a lot in northern Europe, and in particular in Norway for treating peat soils believe it or not!!. There were a couple of section of the CTRL (Channel Tunnel Rail Link) bewteen Dover and London where lime piles were used to cross peat/bogs for the construction of the rail embankment on top. I have got saved somewhere a couple of case studies of this, [plus the name of the Norwegian Company who did the work], but I changed jobs recently so will have to track the info down.
As for use in structures, we did look at using them or something similar on a project where we were looking to improve the performance of PFA Lagoons, with the idea that the lime could act as a catalyst and aid the stabilisation of the PFA. However no Contractor was willing to put their name to it so it never got past the Blue Sky thinking phase and on to the drawing board, never mind off of it!
Other than that, back in the early 90's we did use augered columns of lime as a means of pre-treating soil with the binder, before excavation and stockpiling. This was done in this manner as the bulk soils were required to be stored for around 18 months before use, and there was a risk of sulfate attack. The lime was added in this manner, soils excavated (which mixed the lime throughout the soil) and stockpiled with the sulfate and lime left to react. 18 months later checks carried out to see if there was any future potential expansion, and when the soils were cleared, they were re-engineered back in as 'modified' soils (not stabilised).
There has not been much use of this type of technique, probably because not only is it relatively unproven, but simiar ground improvement methods, such as vibro-stone or vibro-concrete are not much more expensive, have less risk (sulfate attack) and have been used for a long time (civil engineering can be conservative)
One thing to note if you are considering this, is to get a complete vertical profile of the sulfates in the ground, and in particular between the weathered and unweathered zones.
As for use in structures, we did look at using them or something similar on a project where we were looking to improve the performance of PFA Lagoons, with the idea that the lime could act as a catalyst and aid the stabilisation of the PFA. However no Contractor was willing to put their name to it so it never got past the Blue Sky thinking phase and on to the drawing board, never mind off of it!
Other than that, back in the early 90's we did use augered columns of lime as a means of pre-treating soil with the binder, before excavation and stockpiling. This was done in this manner as the bulk soils were required to be stored for around 18 months before use, and there was a risk of sulfate attack. The lime was added in this manner, soils excavated (which mixed the lime throughout the soil) and stockpiled with the sulfate and lime left to react. 18 months later checks carried out to see if there was any future potential expansion, and when the soils were cleared, they were re-engineered back in as 'modified' soils (not stabilised).
There has not been much use of this type of technique, probably because not only is it relatively unproven, but simiar ground improvement methods, such as vibro-stone or vibro-concrete are not much more expensive, have less risk (sulfate attack) and have been used for a long time (civil engineering can be conservative)
One thing to note if you are considering this, is to get a complete vertical profile of the sulfates in the ground, and in particular between the weathered and unweathered zones.
palmahouse
Geotechnical
Describing the soil conditions and ground surface slope conditions would help with understanding your question. But, if you are trying to reinforce soft ground so it improves bearing capacity, then there is nothing in the codes that can be used for design.
Not only in Norway. In Calatayud (Zaragoza) Spain all the low village takes its foundation on silty clayey soil, and it was traditional practice for those wanting better foundations enhance the soil behaviour by the use of estacas de sabina (wood somewhat conical stakes of good durability underground). I myself codirected the works of a building designed by my partner, a natural of the place, without foundations giving any problem; were however placed under a mat foundation.
If modest, they can be counted as piles for what they are worth.
We are talking of very old traditions of foundations, coming from palafitos maybe even through amphora: always trying to regularize strength.
If modest, they can be counted as piles for what they are worth.
We are talking of very old traditions of foundations, coming from palafitos maybe even through amphora: always trying to regularize strength.
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