Estimating lateral squeeze 4

[geonet]

I am attempting to evaluate lateral squeeze outside toe slope without utilizing FEM model, which I do not have access to. I have reviewed a number of papers regarding the topic but most seem to provide ways to estimate maximum lateral movement at or near toe of slope where most movement is anticipated. I am most interested in the distance away from the toe of the slope I can anticipate movement. Does anyone have a good reference that may offer some guidence on this. My embankment hight is on the order of 7.5m and the soil beneath the embankment has a undrained shear stength of around 34kpa (700psf or so). A friendly point to a good reference(s) would be appreciated.

 

[BigH]

As a quickie reply, I would check out Zeevaert's Foundation Engineering for Difficult Subsoil Conditions. He practices/practiced in Mexico City - one of the "worst" foundation areas in the world, likely. I've just got a copy of his book to glance through and he has several items on expansion due to excavation and in soft clay.

Hope this helps.

 

[geonet]

Thanks Big H for the information. I will look up the reference suggested. However let me clarify the question at hand. I am attempting to determine the distance away from a proposed embankment where the said embankment will induce "significant" lateral deflections. Of concern are piling for a nearby bridge pier, which according to the bridge engineer are near there lateral capacity without further load from ground movement. I'm also interested in estimating lateral deflections at or near the toe, however I do have a number of papers regarding this, though the proposed empirical relationships appear to vary considerably. Most seem to estimate max lateral movement at the toe at around 0.25*max vertical settlement, however a paper by Tavernas appears to indicate max lateral ground movement at the toe of an embankment to approximately equal to that of the max vertical settlement. Do you have any thoughts on which is more likely to be correct?

 

[jdmm]

This is a tough problem even if you have access to finite element programs. Elastic solutions don't work well beyond the toe of the fill due to assumptions about tensile stresses but it might be instructive to look at estimated displacements within a zone of 2(V) to 1(H) below the toe since the elastic stresses here will be better behaved.

Since this is a difficult problem to predict with any certainty you might consider eliminating or reducing the potential by utilizing geogrid beneath the embankment to limit stress transfer through the bottom of the fill. Perloff (see Fang and Wintercorn) showed that the vertical stresses beneath an embankment can actually be less than geostatic as a result of shear stresses that develop in the embankment during construction.

 

[VAD]

Hello Geonet:

Generally, if your embankment is not constructed on peat/muskeg and your height of fill doen not induce slope stability failure, you will not experience significant lateral squeeze. You may wish to simply establish your critical failure circle based on your embankment height and use this to determine if your bridge piles are within this zone. Even if they are within then, if you are not down to FOS close to 1, your piles should/would not be subjected to any significant lateral forces. Generally, the incidence of lateral squeeze in minimal at FOS of 1.25 or greater. The worst situation for your piles is when the approach fill is unstable due to slope instability.

It seems that you are concerned about pier piles rather than abutment piles and the discussion above also pertains to this type of pile which may be associated with a three span structure.

It appears that you have a FOS of 1.25 to 1.4 min using the classical bearing capacity failure approach for undrained condition. These values could even be larger, if other aspects are taken into consideration.

From my past experience, I see no problems with your piers or abutments outside or within the approach fill.

The work of Tavenas and most literature information concentrate on abutments within the fill and hence are directly subjected to the effects even minor laterally induced movements.

Now for some references. I note that you have done some literature review. Have you looked at a publication by the Maine Department of Transportation entitled "Evaluation of Lateral Squeeze", Final Report, Technical Report 91-3, October 1994, by Thomas C. Sandford of Dept of Civil Engineering University of Maine. This would be worthwhile reading if you have not done so as yet, as it provides many pertinent references.

Please note that the above is based on my personal experience which may or may not be applicable to your situation. Very often my approach is based on detailed site observations and evaluation, and of what is to be built and how it is to be undertaken along with calculations on the back of a "cigarette pack"/scratch pad. Sometimes one can avoid problems by recommending construction sequencing etc.

In one instance on how construction approach makes a difference is one in which I was involved in the geotechnical investigation, evaluation and assessment of a 20 m high fill constructed on soft ground for an overpass over CNR mainline tracks which were very close to the toe of fill. The use of a sand wedge at the toe installed before placement of approach fill helped to prevent the possible lateral movement of the tracks which was a concern. This site was monitoted at the time of construction with slope indicators etc and is still functioning satisfactorily now some 17 years later.

Good Luck and

 

[geonet]

Thanks jdmm and Vad. Vad I will look up the paper recommended. In case your interested I was able to find a decent paper of a case study by Ladd involving 14m high test embankment on Boston Clays 35-60Kpa.

 

[BigH]

Geonet - reference????

I received a ASCE Geo Journal today and by glancing at its table of contents, it appears that there might be a paper in there of interest to you on squeeze. Might want to check it out.

 

[ishvaaag]

I have a question for VAD.

One may find examples where the use of circular surfaces of failure give a satisfactory safety factor, say, 1.5, whereas examining the same with spiral curves gives SF under 1. Both of course are engineering approximations not meeting the ultimate requirements of a scientific approach, but when reading texts about these things some assert the spiral surface of failure more perfectly represents the situation when the top resistance is attained. How does this fits with the experience of low safety factors with circular surfaces behaving well? Is this a device of conservative properties assigned to the soil?