About emerging soil due piles driven (in Mexico City)

[JCAZ15]

Hi, this is my first post, but I have been reading a lot of threads for years, since I was studying my bachelor. (1.5 years ago). Sorry for my English. I am in Mexico City.

I work in the geotechnical area here in Mexico city , and some days ago I went to field to observe the piles´driving. Imagine that there is a drainage pipe, well it is not a pipe, but don´t know the English word for colector, it does the same work that a pipe, but has a rectangular cross section (made of concrete), and the nearest pile is about 1 mt from both side, (the bridge has two bodies).

After some days of starting the driving, some cracks start to appear and at the middle of the "colector" (at ground level), it started to heave???? (to emerge the soil), and I asked my self, is there any numerical method or empirircal rule to describe this behavior??????

Thank you a lot, to all the people who write in this forum, I have learnt a lot from you, bigH, dgillete, PEinc,SlideRuleEra , fattdad, dont remember more nicks, but I want to thanks a lot to you.

Finally, someone has solve by hand or has a hand example or can tell me where can I find? of how to calculate the stress with mindlin solution, or some other solution based on it, cuz I have tried but always fail.

Thanks

 

[BigH]

Welcome to your first post! I am aware that Mexico City is characterized by the deep clayey lake deposits that have and are undergoing serious consolidation settlement. Can you please provide some details of the problem:
1. Type of pile driven (displacement (e.g., end-capped steel pipe pile, timber pile, concrete pile) or non-displacement (e.g., H-pile). Did you pre-bore to a depth below the founding level of the concrete "collector" pipe?
2. Depth of driving - typical blow counts with depth - and what type of hammer.
3. Founding depth of the square concrete "collector" conduit. Age of collector pipe? - was its condition noted before pile driving?
4. Depth to water table. - is the pipe in the upper part of the clay that perhaps is desiccated (dried out - not saturated).
5. Swelling characteristics of the clay - Atterberg limits, natural water content, free swell or swelling pressure/surcharge pressure.
I assume that the collector pipe carries water. While the time frame for the cracking is quite short, one wonders if the driving - or natural cracking of the pipe that may have been opened up due to the driving would have caused water leakage - and if the clay is has the right conditions for swelling . . .

 

[fattdad]

I'm imagining a box culvert that is made from concrete and buried beneath the ground. Storm water flows in this culvert, perhaps.

I'm also imagining piles being driven on either side of this box culvert.

Is it possible that the displacement of the pile into the soft material is causing heave to occur?

f-d

¡papá gordo ain’t no madre flaca!

 

[JCAZ15]

Hi, again.

This is the description of the problem.

The box culvert, its buried like 5 m beneath the ground, in both sides of it there will be driving piles to 26 m below the ground level, the piles work by means of friction.

The piles are precast with a 0.40 x 0.40m cross section, and will be a pre-bore until 15 m, because there are some “hard” lenses. Don’t have the number of blow counts.

I will attach a borehole using the CPT and SPT tests, also I attach a representative cross section of the foundation solution and the box culvert (the culvert is fully functional).

In the borehole attached, there are some of the mechanical and index propierties of the soil, in Mexico City we divide the city in three zones. Lake, Transition and Hills.

This project its located in the lake zone, wich is the most problematic zone, due settlements and the regional subsidence, the normal w% are above 100% and some times above 400%.

And what I am looking for is to know:
1.- Is it possible that driven of the piles are causing the heave, (don´t have photos , but I´ll trie to get some)

2.- Is there any numerical method to estimate this????.

Thank you for your time and knowledge.

 

[aeoliantexan]

Driving piles in saturated clay can indeed cause ground heave. the clay can't consolidate much and it has to go somewhere. It can also crowd the previously-driven piles sideways.

If the group of piles is very large, the heave should be roughly equal to the volume of the piles divided by the area of the group. I don't know how to calculate heave for smaller groups, but there is probably something inthe literature.

The pre-drilling will reduce the heave.

 

[BigH]

The first thought that one has is that driving displacement piles are causing the concrete box culvert to heave. I asked the question on the types of piles and if preboring because of this. JCAZ15 indicates that they are preboring to 15 m - which is 10 m below the invert of the box culvert. This would, in my view, mitigate heave due to the driving of the displacement concrete piles - unless of course, the driving gets "hard" at the bottom and adjacent piles are heaving (I had this happen in Michigan when adjacent piles which were mostly in fill but founded in till heaved as the new pile penetrated into the till). JCAZ15 - have you monitored if any adjacent piles heaved during driving?

Can you post the dwg file as a pdf? I can't open a dwg file on my computer here.

If this is not it and it seems unlikely to me, then perhaps the upper part of the clay (or clayey fill) is desiccated. Mexico City clay is sensitive and I presume active (high Activity Index) given the very high liquid limits and Plasticity indices (see Peck Hanson and Thornburn - or Zeevaert). If the water content was low due to the desiccation and the concrete culvert was seeping water through minor cracking, joints, etc., then the clay could swell causing the heave.

JCAZ15 - is there any other experience in the area of similar heaving of large diameter pipe culverts or box culverts (without pile driving nearby)????

 

[escrowe]

The prebores may not have been of sufficient diameter,
and/or may have swelled shut prior to pile driving.
What was the time lag and prebore diameter?

If the prebores were completed even just an hour or two before driving,
then swelling and displacement seems likely.

Predicting the extent of heave is problematic.
Certainly it would depend on the size of the member
and the consistency of the surrounding soil.
Here is a link to Nelson's book, which has
a chapter on predicting heave in expansive soils:

http://books.google.com/books?hl=en...XRq0&sig=-pdlmwkLnlblXtlAS04OfcwLRsw#PPA58,M1

The chapter introduction provides a number of caveats.

In hindsight auger-cast piles or drilled shafts
might have been a better choice for this location (oh well!).

 

[BigH]

JCAZ15 - what were the diameter of the prebores? Did you notice any "squeezing" of them. Still, even if they squeezed a bit presuming that you made the bores larger than the pile diameter (or the same) and discounted adhesion along them which I presume you do since it is in the consolidating Mexico City clay, I find it hard to believe, after you have removed 90% of the pile volume that there is enough volume yet to displace to cause such heaving. Thanks for the reference, escrowe.

 

[fattdad]

So, if the predrills are appropriatly sized, then the likelihood of heave would seem to go away, eh? Now I'm wondering whether driving forces could be causing some settlement of the soil mass to either side of the culvert with the culvert and overlying soil backfill less prone to the similar settlement. I would consider this as a likely scenario only if you are below the water table and the soil includes layers of loose sand or non-elastic silt. This would not be a likely behavoir for soft clay. . .

Just throwing out ideas from over here in Richmond, Virginia USA!

f-d

¡papá gordo ain’t no madre flaca!

 

[JCAZ15]

Hi. sorry for the delay I was doing some field work... BigH here are the pdf´s files.Escrowe, thank you for the link.

The usual prebore, recomended by some investigations done here in the mexican clay, is a circular inscribed of the 0.40 x 0.40 pile cross section. or the 80% of the cross seccion area of the pile.

This is the first time I a(we) have seen this behaviour of a box culvert. the phreatic level GWT is 3.20 m , below.

Yesterday, A field engineer told me that a house near the site, started to presen some crack, but he say that that cracks seems to be old, so we suppose they are not caused by the pile´s driving.

Thank you all.

 

[escrowe]

GWT is 3.2m below ground surface?
Given the proximity of the piles to the culvert,
I would be surprised if the culvert did not move.

It's not unususal for existing cracks to open during pile driving.
You should consider a precondition survey for the adjacent structures.
But once driving starts, it's probably too late to determine the cause of cracking.

 

[aeoliantexan]

OK, this is crude. I assume the pile groups are square and look the same from the side as from the end. If so, each pair of groups includes 32 piles. The pile volume from 15 to 26 meters is 55 cubic meters. If we assume it all goes to heave within a zone bounded by planes extending upwards from the pile tips at 1h:2v, the affected area at the level of the culvert is roughly 1100 square meters. 56/1100 gives an average heave of 0.05 meters or about 2 inches. The culvert is in the middle of the pattern so it probably experiences more than the average, say between 2 and 4 inches. That should be noticeable.

I'm not sure from the drawing if both lanes of the elevated road are being built, or just the left one. If only one, the heave would be about half the above, probably less.

Alternatively, I have heard, but not seen, that sometimes piles driven into sensitive clays can cause settlement, due to the remolding of surrounding soil.

Assuming there will be addtional similar pile groups driven, I suggest shooting elevations on the box culvert and monitoring for heave or settlement as the work progresses.