Soldier piles with lagging using helical piles
Soldier piles with lagging using helical piles
(OP)
Hi everyone,
I am a geotechnical EIT and I have been asked to design a temporary shoring for an excavation depth of 10 feet below the existing ground surface. The owner and contractor have insisted on using helical piles as soldier piles with wood lagging. The geotechnical report says that there is very dense mixture of till, silt and clay down to 4 feet below the existing grade and compact sand below that. It also says that minor seepage was encountered in the sand layer. I do not have a lot of experience designing shoring systems so any help would be appreciated. I started using the California trenching and shoring manual and I believe it offers some good advice. I was however not able to compute the embedment depth required below the dredge line. Also the helical piles that are to be used have a circular section (5.6" dia).
I am a geotechnical EIT and I have been asked to design a temporary shoring for an excavation depth of 10 feet below the existing ground surface. The owner and contractor have insisted on using helical piles as soldier piles with wood lagging. The geotechnical report says that there is very dense mixture of till, silt and clay down to 4 feet below the existing grade and compact sand below that. It also says that minor seepage was encountered in the sand layer. I do not have a lot of experience designing shoring systems so any help would be appreciated. I started using the California trenching and shoring manual and I believe it offers some good advice. I was however not able to compute the embedment depth required below the dredge line. Also the helical piles that are to be used have a circular section (5.6" dia).





RE: Soldier piles with lagging using helical piles
Helical anchors can be difficult, if not impossible, to install in very dense or stiff soils. Boulders, cobbles, and other obstructions can be enough to rule out using helical anchors.
If the dense till extends only down 4' from original grade, the helical anchors should be in the compact sand. Talk to an anchor installer to get an opinion if the soil profile is OK for helical anchors.
Some of the helical anchor manufacturers can provide you with software to design helical anchors and piers. Or, you can write your own program.
CALTRANS, FHWA, AASHTO, and other organizations have manuals that will show how to design the sheeting wall, including embedment.
For a 10' high, tiedback wall, sum the moments about the anchor location. Solve for the embedment depth that gives moment equilibrium. Increase the calculated embedment depth by at least 20%.
When calculating the passive soil pressure, don't forget to consider buoyant soil weight if there is ground water below subgrade. The seeping water above subgrade should drain through the lagging. If it doesn't, you should not use soldier beams with lagging and you may need to add hydrostatic pressure.
www.PeirceEngineering.com
RE: Soldier piles with lagging using helical piles
RE: Soldier piles with lagging using helical piles
RE: Soldier piles with lagging using helical piles
Is the cantilevered wall to be temporary or permanent? You could drill in pipe piles as your vertical soldier beams. Then, you could attach lagging to the front of the pipe piles. Or, you could just drill in WF or HP soldier beams.
www.PeirceEngineering.com
RE: Soldier piles with lagging using helical piles
RE: Soldier piles with lagging using helical piles
RE: Soldier piles with lagging using helical piles
EIT
www.HowToEngineer.com
RE: Soldier piles with lagging using helical piles
www.PeirceEngineering.com
RE: Soldier piles with lagging using helical piles
www.PeirceEngineering.com
RE: Soldier piles with lagging using helical piles
RE: Soldier piles with lagging using helical piles
If Chance thinks the design can be done (and work!), then good luck with your boss. You will need it.
www.PeirceEngineering.com
RE: Soldier piles with lagging using helical piles
I'd like to tell you that in my case everything worked great. However it didn't. I think it would have been just fine. However the contractor did not drill the helical piers to the specified embeddment. He stopped about 18" below the dredge line. Sure enough we got a major rainstorm (on the order of 25 year reoccurrence if I remember correctly). The bottom bulged/pushed out. Luckily there was no damage. The contractor they had install the system seemed to be a fly by night kinda guy and we actually didn't know about the incident until the shoring was removed and the project was completed.
EIT
www.HowToEngineer.com