specific questions about soldier piles

[raven77]

When are soldier piles appropriate?
Specifically
1.soil conditions
2.ground water table
3.displacement considerations
4.boundary constraints
etc

 

[Focht3]

Get a copy of the FHWA drilled shaft manual by Reese and O'Neill. Volume I has a good discussion of the advantages of drilled shafts -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[geoeng05]

Dear Focht3,

I read a discussion about whether the soldier pile should be left in place or extracted from the site. In the discussion you wrote:

"In my experience, the issue of removing or abandoning the soldier piles depends an awful lot on local practice. If the soldier piles are placed in pre-drilled holes that were backfilled with lean concrete, then the contractor would have HELL getting them out. However, if they were installed using a vibratory hammer or were placed in gravel-filled holes the extraction process may not be a big deal. ..."

I am designing a soldier pile and lagging wall. I am asked the question: which is better - leave the soldier pile in place or extract them out. With this question I searched the web and found your above discussion. Your comments are very important to me because you mentioned about "gravel-filled holes" which I have no experience.

This soldier pile wall is a temporary wall for a cut-and-cover tunnel. The maximum wall height is around 35 ft. During excavation, three struts will be used for lateral support. Since the boulders are expected in site, the driven pile is not recommended. Our original design is to drill a 3 ft diameter hole and fill with concrete up to the dredge line elevation (to make a 3' dia concrete shaft), and fill sand or granular to the hole above dredge line to function as casing. After the box is constructed, the top 5 ft of the soldier pile will be cut, and the rest of the steel beam is left in place.

Then the question came to me: can we use well graded gravel, instead of concrete, to fill the bottom of the hole so that after the box is constructed the soldier beam can be easily extracted and reused?

I summary my questions as following:

1. Could you be more specific on the "gravel-filled holes" design method? Are there any practical examples I can follow? How well should the gravel be compacted to prevent the soldier beam from kicking in? (if the hole is filled with sand to a 37 ft high, the pressure on top of the gravel-fill shaft will be 37ft x 0.12 kcf = 4.4 ksf = 2 tons/SF. Is the gravel well compacted by that?)

2. The height of the wall is 37 ft, what is the depth of embedment? ( I used 10 ft embedment for concrete shaft before, with the center-to-center spacing of piles of 10 ft. But that is designed to take the vertical load component of the tiebacks, now since we use struts, the only vertical load will be the weight of the beam. Theoretically, the depth of embedment is not needed much since we have multi struts, is that correct? )

3. I agree with you on that "I don't think that either the 'abandon' or 'salvage' is inherently "right"; to me, it comes down to contract requirements, local practice and economics". My question is, how do I compare the cost of the two methods? (The contractor will install the soldier piles first, it has to wait until the box is installed can the piles be pulled out, maybe it’s not worth it managing all the equipment back to do the pulling-out?) How do I do the cost estimate to choose the better way out of the two?

Please advise. Thank you very much in advance.

I'm sorry if I post this email in a wrong place - I've not been familiar how to use this forum.

 

[PEinc]

geoeng05,

Keep searching for other threads where we have discussed filling the drill hole with lean concrete, low strength flowable fill, or some granular material like sand or gravel. As I said before, I do not recommend filling with the granular material. Doing so can cause difficulties when installing lagging when the loose granular material falls out when you excavate for the next lower lever of lagging. You do not want any voids around the soldier beams. This can cause settlements at the surface and can cause bowing of the lagging when you prestress or jack struts or load tiebacks. AASHTO and FHWA call for the soldier beam holes to be filled with cementitious material, not granular soils or gravel.

Except for walls with steeply installed tieback anchors, studies have shown that little of a tieback anchor's vertical component is actually transferred to the soldier beam toe. The required toe embeddment is usually more dependent on the required horizontal passive resistance which is a function of the height of the lowest tieback or strut above the subgrade.

With respect to removing soldier beams, Focht3 is correct. Also, sometimes the contractor who installed the soldier beams is long gone when the time comes that they can be removed. Often the cost to remobilize and remove the soldiers is more than the worth of the beams. In, 30 years of work on soldier beam walls, I never removed them once. I saw it done once by Perini because their beams were gigantic and they thought they could remove them cheaply. They were wrong.

 

[Focht3]

I agree with most of what [blue]PEinc[/blue] has posted. But over the years I have learned to be more tolerant of other construction methods when site conditions don't require "best performance", only "ordinary performance." I know almost nothing about [blue]geoeng05[/blue]'s alignment; but it is quite possible that significant settlement within 5 to 25 feet of the tunnel alignment won't affect any buildings or other significant improvements. If this is the case, then a soldier pile and lagging wall can provide acceptable performance.

Having said that, I am presently working on a hotel site in downtown San Antonio. The site is L-shaped, and wraps around 2 sides of a city-owned performing arts theater that was built for HemisFair '68. And it has some structural "issues." Some members of the project team (I don't know which) kept pushing for soldier pile and lagging, even though the excavation will only be a few feet from the theater in places. The excavation will be 55 feet deep, with a water-bearing gravel extending to depth of 20 to 25 feet. Oh, and did I mention that the site is on San Antonio's Riverwalk?

Needless to say, a soldier pile and lagging wall at this site scares the hell out of me. But I'd use one if the site were well away from any significant structures and a waterbearing gravel wasn't present at the site.

How to design a "gravel" soldier pile at [blue]geoeng05[/blue]'s site? S/he didn't provide site details or information about geology and groundwater. At this point, I can't offer much -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[DRC1]

When intsllig soldier piles in drilled shafts, we typicaly prefer to use lean concrete to the mud line and then backfil with a fine- med. sand which is jetted for compacton. Wehave had experiencece with filling the whole shaft with the lean concrete. This is a slower process. We would weld threaded studs to face of the pile after chiping the concrete off the face of the pile. The lagging would attach to the piles via the studs. However, it adds cosiderable cost and time to the pull the sheeting.We generally pull the soldier piles unless he contact requies left in place. Typically the beams are pulled after the toportion of the laggin ( about 5' +/-) and the the balance of the lagging is abandoned in place.

 

[PEinc]

I have designed and built many, many soldier beam walls with lagging. If the soldier beams are driven in stiff clay or are drilled and set into lean concrete or flowable fill holes, I use lagging attached to the front flange like DRC1 described. If the beams are driven into more granular soils, the lagging is usually tucked behind the flanges. Welded stud lagging costs a little bit more material wise, but the labor required is usually about the same for both methods.

However, I learned long ago that if I insist that a foreman install the lagging one way when he wants to install it another way, he will make sure that my way is more expensive than his way. It's usually not worth arguing about. He'll be more motivated if you let him lag it his way.