Concrete soldier piles instead of wood laggings

[zaqqaz]

Hi,

I want to use concrete soldier piles instead of wood laggings. The plan is to use reinforced concrete piles every 8 to 10 feet, and cast plain concrete piles in between them. Thus, there will be no need to wood laggings.

The structural engineer do not agree with the plan based on his calculations. Though, it seems that nowadays this type of soldier piles in between of master piles are getting more common. The plan is to use them as a general plan in different conditions so the depth of excavation and soil type could vary.

I am looking for references (if available) and your comments and experiences with this respect.

Thanks

 

[VAD]

At first thought I tend to agree with the structural. Is your thinking that the reinforec piles would be called upon to take the majority of load through an arching action

 

[zaqqaz]

Yes I want to see how the arching effect works in this case. As far as I know in the design of laggings arching effect is considered. From a practical point of view it seems wierd to me that a concrete pile will not serve properly where a lagging can sustain a load.

 

[VAD]

Ther is apaper that discusses this effect in relation to piles used to stabilize landslides. I cannot remember the reference offhand. For arching to take plece there must be some movement of the piles. Your structural may have determined that this movement would result in bending of the unreinforecd piles and has determined that this is too risky. Lagging on the other hand is probably able to have a greater flexibility than the concrete pile.

I would suggest that you and the structural go over his calculations and see if you agree with his findings as the first step. You may find that he has used too large a load on the unreinforced sections. Some deflection evaluation may be required as well.

 

[DRC1]

I,m not sure I follow. My understanding of your proposal is that you would use reinforced conc. ples 8-10 ft as master piles and plain concrtete piles in between. Are the master ples prestressed or cast in place? The plain concrete ones I assume are poured in place in drilled shafts. The two problems I have ould be waiting to exavate utill all the concrete comes up to strength and unless several levels of wales are installed, I do not see how the soil loads on the plain concrete piles transfer to the master piles.Perhaps I am missing something.

 

[zaqqaz]

DRC1 thanks for your response,

To give you a better understanding of the geometry of problem assume that we have 9 piles from west to east along a straight line. Piles no. 1, 5 and 9 are king piles (or master piles which are reinforced). The diameter of the piles is 1.0 m and center to center distance between the piles is 0.8 m. Therefore, each pile overlaps with the adjacent piles.

From a construction point of view piles no. 1, 3, 5, 7, and 9 are drilled first and will be filled with concrete. The day after, when the concrete is still fresh, piles no. 2, 4, 6, and 8 are drilled in between. In the latter procedure part of the fresh concrete of the adjacent piles (which were poured the day before) will be drilled as well. When the new concrete for piles no. 2, 4, 6, and 8 are poured a bond will be formed between the adjacent piles (new and old concrete). Therefore the adjacent piles are attached to each other and are assumed thatwill transfer loads to the king piles.

My main problem is with the bonding between the concrete in the adjacent piles. Further, I want to have an estimation of the loading on the plain concrete piles.

Hope that the above helps.

Tahnks

 

[Panars]

To help you find references, I have heard this type of wall referred to as a secant pile wall or secant drilled shaft wall.

 

[PEinc]

So, why don't you want to use wood lagging? It has to be cheaper than drilled and concreted "lagging."

 

[DRC1]

I would have to agree with PEinc. Althogh this is similar to secant piles, those are rinforced. Secant piles ovelap each other only for water and soil tightness. You will still have bending vertically in the plain piles and significant shear forces between the piles. A 3 foot diameter shaft for a soldier pile is huge, and expensive. How deep is the excavation and are there special site conditions necessitating an unusual retenion system?

 

[PEinc]

I agree with DRC1. I'd be interested in knowing why zaqqaz is even considering reinforced concrete soldier beams. These too are very expensive. Is he trying to design a very high cantilevered retaining wall? Why not drilled-in or driven, steel, soldier beams? Is he trying to use these concrete soldier beams instead of underpinning an adjacent building? We can talk about this all day but it would be nice to have a few facts.

 

[zaqqaz]

Hi,

Thanks for all the usefull responses. One of my clients requested for replacing conventional soldier pile and lagging system with secant piles for various projects. As I did not have any experience with this system, my first step was to understand the pros and cons of it. My client claims that this system is growing fast and there is a trend to use it, though I am not sure about it.

Anyways looking for sharing your experiences and opinions on this subject.

Best

 

[CelticJam]

A trend I have noticed in home construction for shoring excavations between 10 to 12 feet deep is to drill caisson holes (10" to 12" diameter) 2 to 3 feet apart, reinforce the holes with 4 -#5 bars, fill the holes with concrete then begin excavation after a seven day cure. Typically the caisson holes are drilled twice the depth of the excavation. Lagging, shot-crete, etc. is not used between the drilled shafts.

 

[EdGeotech]

I have used secant pile systems in the past on projects where neat face instability was anticipated. However, as DRC1 indicated, it is a much more expensive system than conventional soldier pile and lagging and, since excavation generally can not commence until all piles are constructed, its generally not as efficient. Therefore, I wouldn't use the system on every project.

 

[kgeot]

Tangent pile walls are very similar to secant walls, but a spaced from 1' to about 3' apart and can be used without lagging in competent soils, and with or without tiebacks.They can usually be constructed with ACIP piles or DMM prior to excavation.

 

[rchanke]

An advantage of the secant pile/column system is controlling groundwater infiltration into the excavation. This is used quite often for deep shaft construction for tunneling operations or any excavation within permeable strata below the groundwater table. Variations of this system can use either cement soil mixing or jet grouting as the lagging. Similarly, the jet grouting could be used to construct a bottom plug within the excavation in place of a concrete tremie slab.

It all comes down to constructability, cost and schedule.

 

[DRC1]

For holes of moderate depth, say less than 40 feet, stel shet piling is a an effective, cost effeicent, controls seepage and is a relatively quick means of excavation support. Generally there is a significant number of contractors in a given area to make pricing competitve. This is not to say it works on all sites, but it does work on many sites

 

[PEinc]

zaqqaz mentioned the need for 9 piles. Therefore, it is probably a very short wall along one side of an excavation. Therefore, groundwater is most likely not a problem that can be controlled by a "one sided" cofferdam. If he needs to dewater, then he does not need a single run of impermeable sheeting wall. Unless he needs a very stiff sheeting wall, he may be throwing away his client's money by using concrete soldier piles with concrete lagging.