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what are criteria for using soldier piles [eg ground water table, soil 4
- Thread starter raven77
- Start date
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3
- #3
Generally, soldier piles (with timber lagging) are appropriate when:
1. Uncontrolled ground water is not present above excavation subgrade.
2. The ground to be retained is not very soft and bottom heave is not a problem.
3. Ground conditions are not so difficult that soldier beams can not be economically installed by driving or drilling.
4. The total lateral pressures are low enough to allow use of soldier beams at an economical spacing (approximately 6 to 10 feet on center). With higher pressures, steel sheet piling, slurry walls, or secant piles may be more appropriate (and more expensive).
5. Overhead obstructions do not prevent soldier beam installation.
1. Uncontrolled ground water is not present above excavation subgrade.
2. The ground to be retained is not very soft and bottom heave is not a problem.
3. Ground conditions are not so difficult that soldier beams can not be economically installed by driving or drilling.
4. The total lateral pressures are low enough to allow use of soldier beams at an economical spacing (approximately 6 to 10 feet on center). With higher pressures, steel sheet piling, slurry walls, or secant piles may be more appropriate (and more expensive).
5. Overhead obstructions do not prevent soldier beam installation.
- Thread starter
- #4
Soldier piles are used more often than steel sheeting unless the contractor already owns the sheets and can pull and reuse them.
Soldiers are used when the excavation support system does not need to retain water and resist hydrostatic pressures.
Soldiers are used when the soils are reasonably competent. Soldiers are not good in very loose running sands or very soft fine grained soils.
If displacements are a concern, soldier piles may not be as rigid as some steel sheet piling.
If noise and vibrations are concerns, drilled-in soldier beams may be better than driven steel sheet piling.
Soldier piles will not provide resistance to bottom heave, piping, or boiling at the base of the excavation.
Generally, soldier beams and lagging are not used to support adjacent structures. Steel sheeting also should not be used to support buildings unless it is the only alternative and everyone recognizes the increaded risks of using one of these relatively flexible wall systems. Along structures, it is better (and more expensive) to use underpinning, slurry walls, secant pile walls, or some other similar, stiffer system.
If it appears that lagging will be difficult to install and that ground could be lost while installing the lagging, then soldier beams may not be the best support wall.
Soldier beams with lagging are usually the cheaper support wall. Usually, the soldier beams and lagging get abandoned in place when the excavation is backfilled. Rarely are soldier beams removed. Sheet piling is almost always removed after the excavation is backfilled.
Specialty design/build contractors who specialize in excavation support almost always chose soldier beams and lagging as their 1st choice. General contractors, frequently choose sheet piling as their 1st choice because they often own and reuse sheets and do not want to buy soldier beams and lagging.
Railroads usually require the use of steel sheet piling and allow soldier beams and lagging only if the sheet piling can not be driven as required due to ground conditions such as obstructions and high bedrock.
Does this answer your questions?
Soldiers are used when the excavation support system does not need to retain water and resist hydrostatic pressures.
Soldiers are used when the soils are reasonably competent. Soldiers are not good in very loose running sands or very soft fine grained soils.
If displacements are a concern, soldier piles may not be as rigid as some steel sheet piling.
If noise and vibrations are concerns, drilled-in soldier beams may be better than driven steel sheet piling.
Soldier piles will not provide resistance to bottom heave, piping, or boiling at the base of the excavation.
Generally, soldier beams and lagging are not used to support adjacent structures. Steel sheeting also should not be used to support buildings unless it is the only alternative and everyone recognizes the increaded risks of using one of these relatively flexible wall systems. Along structures, it is better (and more expensive) to use underpinning, slurry walls, secant pile walls, or some other similar, stiffer system.
If it appears that lagging will be difficult to install and that ground could be lost while installing the lagging, then soldier beams may not be the best support wall.
Soldier beams with lagging are usually the cheaper support wall. Usually, the soldier beams and lagging get abandoned in place when the excavation is backfilled. Rarely are soldier beams removed. Sheet piling is almost always removed after the excavation is backfilled.
Specialty design/build contractors who specialize in excavation support almost always chose soldier beams and lagging as their 1st choice. General contractors, frequently choose sheet piling as their 1st choice because they often own and reuse sheets and do not want to buy soldier beams and lagging.
Railroads usually require the use of steel sheet piling and allow soldier beams and lagging only if the sheet piling can not be driven as required due to ground conditions such as obstructions and high bedrock.
Does this answer your questions?
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1
- #6
PE Inc does a good job of covering soldier piles. I would disagree that soldier piles are usually left in place. In my experience, if they can be pulled relatively easily, they will be. The lagging is almost always left in place. Soldier piles can be driven but are most often vibrated into place. HP sections 12x53 and up are usualy used for the walls. Soldier piles and sheeting are similar in total cost. Soldier piles have less material costs, but higher labor costs. Sheeting has lower labor costs but higher material costs.I disagree that specialty contractors will usually chose soldier piles, it depends greatly on the nature of the work. One area where soldier piles are preferred is in areas with obstructions. If the pile is obstructed, it can be extracted and moved over. On disadvantage of soldier piles is that the excavation is paced by the lagging instalation. On a multiple sub site if one contractor is installing the soldier piles and onne is doing the mass excavation, they need to coordinate closely.
Usually the lagging is installed behind the beams for the first three feet, then behind the front flange. This allows the pile to be burned off below grade as the job is backfilled. We occasionally reclaimed the tieback wales, but not the piles.
jheidt2543
Civil/Environmental
DRC1,
I'm confused, if, "In my experience, if they can be pulled relatively easily, they will be. The lagging is almost always left in place.", what holds the lagging in place?
I'm confused, if, "In my experience, if they can be pulled relatively easily, they will be. The lagging is almost always left in place.", what holds the lagging in place?
jheidt2543,
Lagging can either be clipped to the piles using a large plate washer and a varity of attachments such as J bolts, studs welded to the piles or specail clips. Most often however, it is tucked behind the flanges. As the excvation is backfilled the clips are generally removed if they were used. Thus in the case of the tucked lagging or the clipped lagging, there is no physical connection of the lagging to the soldier piles once the excavation is backfilled. Thus once the backfill is complete the piles are vibrated out of the ground and the lagging remains in the backfill.
Lagging can either be clipped to the piles using a large plate washer and a varity of attachments such as J bolts, studs welded to the piles or specail clips. Most often however, it is tucked behind the flanges. As the excvation is backfilled the clips are generally removed if they were used. Thus in the case of the tucked lagging or the clipped lagging, there is no physical connection of the lagging to the soldier piles once the excavation is backfilled. Thus once the backfill is complete the piles are vibrated out of the ground and the lagging remains in the backfill.
jheidt2543,
I've designed and built hundreds of soldier beam and lagging walls and have never removed the soldier beams. The few times I have seen soldier beams removed were when they had been installed by the general contractor on a highway project where the contractor was still on the job when the soldier beams were no longer needed and there was still equipment available on site to pull the soldiers.
On many projects, the sheeting is installed by a subcontractor who is long gone from the site when the structure is backfilled. It is not worth the salvage value of the steel for the sheeting subcontractor to return to the site with equipment to pull the beams. Therefore, the soldier beams are usually cut off and removed to about 3 feet below finished grade when the backfill reaches that level.
When soldier beams are drilled-in-place, after the beams are set into the drill holes, the drill holes are usually backfilled with at least a lean concrete or flowable fill. When this is done, the soldier beams cannot be removed. Steel sheet piling is almost always removed for reuse.
As for removal of lagging, DRC1 explained it well in the previous posting. However, again, it is unusual for the lagging to be removed. I've seen it on a few projects where the owner or owner's engineer is overly concerned about termites or voids forming due to decomposition of the lagging over time. I've dug up a lot of old sheeting systems that have been buried for years. The lagging is still there. It may have lost most, if not all, of its structural value but there are no voids and I've never noticed any termites. Rarely is treated lagging needed although it is frequently required.
I've designed and built hundreds of soldier beam and lagging walls and have never removed the soldier beams. The few times I have seen soldier beams removed were when they had been installed by the general contractor on a highway project where the contractor was still on the job when the soldier beams were no longer needed and there was still equipment available on site to pull the soldiers.
On many projects, the sheeting is installed by a subcontractor who is long gone from the site when the structure is backfilled. It is not worth the salvage value of the steel for the sheeting subcontractor to return to the site with equipment to pull the beams. Therefore, the soldier beams are usually cut off and removed to about 3 feet below finished grade when the backfill reaches that level.
When soldier beams are drilled-in-place, after the beams are set into the drill holes, the drill holes are usually backfilled with at least a lean concrete or flowable fill. When this is done, the soldier beams cannot be removed. Steel sheet piling is almost always removed for reuse.
As for removal of lagging, DRC1 explained it well in the previous posting. However, again, it is unusual for the lagging to be removed. I've seen it on a few projects where the owner or owner's engineer is overly concerned about termites or voids forming due to decomposition of the lagging over time. I've dug up a lot of old sheeting systems that have been buried for years. The lagging is still there. It may have lost most, if not all, of its structural value but there are no voids and I've never noticed any termites. Rarely is treated lagging needed although it is frequently required.
Some points on PEinc comments.
Typically soil conditions drive preference in using soldier beam & lagging or sheet piling. Across the US there are areas that are exclusively sheet piling and similarly areas where practice is geared to beam & lagging.
Modern hydraulic press in hammer systems that are available from a number of companies allow sheet piling to be installed without noise or vibration. If noise /vibration is an issue then the press in hammers give sheet piling an edge.
Sheet piling is being used as both axial and earth retention menber in bridge abutments, basements and parking garages in the US and Europe. Additionally sheet piling has been designed to be used in integral bridge abutments where the sheet pile will not only carry horizontal earth pressures, axial loads from the bridge but is also used as part of the bridge structure where its flexibility accommodates the contraction and expansion forces of the bridge deck. There is no difficulty in designing sheet piling to carry axial loading at all. The design methodology is well developed.
Typically soil conditions drive preference in using soldier beam & lagging or sheet piling. Across the US there are areas that are exclusively sheet piling and similarly areas where practice is geared to beam & lagging.
Modern hydraulic press in hammer systems that are available from a number of companies allow sheet piling to be installed without noise or vibration. If noise /vibration is an issue then the press in hammers give sheet piling an edge.
Sheet piling is being used as both axial and earth retention menber in bridge abutments, basements and parking garages in the US and Europe. Additionally sheet piling has been designed to be used in integral bridge abutments where the sheet pile will not only carry horizontal earth pressures, axial loads from the bridge but is also used as part of the bridge structure where its flexibility accommodates the contraction and expansion forces of the bridge deck. There is no difficulty in designing sheet piling to carry axial loading at all. The design methodology is well developed.
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.
If the H-piles are abandoned in place, someone has to pay for them. Most of the contractors that I have dealt with are reluctant to leave anything of salvageable value behind unless it is required by the contract documents or it is not economical to retrieve.
Put another way: 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 -
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Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.
If the H-piles are abandoned in place, someone has to pay for them. Most of the contractors that I have dealt with are reluctant to leave anything of salvageable value behind unless it is required by the contract documents or it is not economical to retrieve.
Put another way: 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 -
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.
g7mann [geotechnical]
Typical practice in my area virtually requires that the soldier piles and lagging be left in-place. Since the soldier piles are almost always set in concrete they truly cannot be pulled. Also, in the great majority of situations, the soldier pile and lagging walls are used as a back form for the below ground construction, although their structural competency is neglected in the design of the permanent structure. In this respect they are considered "unsalvagable."
Typical practice in my area virtually requires that the soldier piles and lagging be left in-place. Since the soldier piles are almost always set in concrete they truly cannot be pulled. Also, in the great majority of situations, the soldier pile and lagging walls are used as a back form for the below ground construction, although their structural competency is neglected in the design of the permanent structure. In this respect they are considered "unsalvagable."
To PEinc:
Can I use soldier pile and lagging to support a 4 m deep trench excavation? The soil is generally firm to stiff silty clay and compact silty sand fill with water table at 2-3 m. This is the first time I am dealing with a sanitary sewer excavation. If yes, what kind of material and what size is normally used for trenching?
Thank you very very much!
Can I use soldier pile and lagging to support a 4 m deep trench excavation? The soil is generally firm to stiff silty clay and compact silty sand fill with water table at 2-3 m. This is the first time I am dealing with a sanitary sewer excavation. If yes, what kind of material and what size is normally used for trenching?
Thank you very very much!
You probaly can, although you are at about the limit you cantilever economically. You will need to draw the water table down below the excavation level with sump pumping. This may be challenging in the silty clay. If you have not designed a soldier pile retention system before, I would have someone with experience look at it. Getting into water and silty sands and clay 14 feet down is complicated. My first inclination is if you dont have to protect any foundations or traffic, would be to work out of boxes. A lot of sewer work is down that way, especially in the streets. The boxes allow you to dig in advance of the work so you can locate other utilities. If you have other utilities, hitting them when driving soldier piles is a significant concern.
DRC1 gave a very good answer. Water is an important concern. Lagging does not hold back water and soldier beams and lagging usually are not an acceptable way to support closely adjacent structures.
The trench box with sump pumping may work well IF you are not supporting structures or critical utilities AND if the water can be controlled without the soils running. Trench boxes protect people in the trench. They do not properly protect or support adjacent structures or utilities and they do not control ground water. Remember, digging in front of the box (so that the box can be moved ahead)is an open, unsupported cut which under poor soil or water conditions could cause a collapse before the box can be moved ahead.
Depending on the design method, soil conditions, and adjacent surcharges and after dewatering to or below subgrade, I would expect a 13' cantilever to require 50 ksi soldier beams in the range of HP12x74 to HP14x89, with a length of 30 to 40 feet, with a spacing of 7 or 8 feet. Lagging would be rough cut, 3 inch nominal thickness, untreated, mixed hardwood or better. This is just my rough guestimate. There are too many unknown variables at this time to give you a more accurate guess. Bracing the soldier beams would greatly reduce the size and lentgh of the soldier beams. You could directly brace one soldier beam to an opposite soldier beam or you could install a continuous wale along each opposite wall and then cross brace at every other pair of soldier beams. The brace spacing should be such that you can set a length of pipe into the trench and that you can easily dig the trench to subgrade.
The trench box with sump pumping may work well IF you are not supporting structures or critical utilities AND if the water can be controlled without the soils running. Trench boxes protect people in the trench. They do not properly protect or support adjacent structures or utilities and they do not control ground water. Remember, digging in front of the box (so that the box can be moved ahead)is an open, unsupported cut which under poor soil or water conditions could cause a collapse before the box can be moved ahead.
Depending on the design method, soil conditions, and adjacent surcharges and after dewatering to or below subgrade, I would expect a 13' cantilever to require 50 ksi soldier beams in the range of HP12x74 to HP14x89, with a length of 30 to 40 feet, with a spacing of 7 or 8 feet. Lagging would be rough cut, 3 inch nominal thickness, untreated, mixed hardwood or better. This is just my rough guestimate. There are too many unknown variables at this time to give you a more accurate guess. Bracing the soldier beams would greatly reduce the size and lentgh of the soldier beams. You could directly brace one soldier beam to an opposite soldier beam or you could install a continuous wale along each opposite wall and then cross brace at every other pair of soldier beams. The brace spacing should be such that you can set a length of pipe into the trench and that you can easily dig the trench to subgrade.
Thanks DRC1 and PEinc!
Your replies are great helps to me.
The trenching is through a downtown street with very close adjacent buildings. Therefore I am so concerned about the affect of dewatering.
I used to deal with excavation for high-rise building construction and this is the first time for trenching and in different country, not so confident.
Your replies are great helps to me.
The trenching is through a downtown street with very close adjacent buildings. Therefore I am so concerned about the affect of dewatering.
I used to deal with excavation for high-rise building construction and this is the first time for trenching and in different country, not so confident.
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