Tieback wall detailing 2

[vape]

I am designing a retaining wall which is changing from a cantilevered wall to a tieback wall. I have no problem with designing the reinforced concrete wall to span horizontally between the soldier piles, but I need information about two details:
Are there standard details for the connection between the reinforced concrete wall and the soldier piles? I intend to use headed studs to fasten the wall to the piles, but what considerations should be used to detail the reinf. around this connection. Also, is there a standard for the detailing of construction joints in this type of wall. Are the joints to be placed at the centerline of the piles or held off of the piles?

 

[Lutfi]

My first impression is to suggest that you consult with a colleague who is experienced in retaining walls and soldier piles design. I also would call construction contractors because they have wealth of know how and what works and does not. Retaining structures are tricky business and you need some guidance. Having said that, here are some ideas for your connections:

1. Use H piles and let the concrete panels slide between the pile flanges. This way you will have simple end conditions. This method is used a lot in DOT sound barrier walls.

2. I have seen stones applied in similar manner between soldier piles in West Virginia. This system yields a closer soldier pile spacing.

3. The connection detail depends on all kinds of conditions and construction practices. You need to reduce or eliminate eccentricity, corrosion, while being practical and economical at the same time. It has been my experience that once the tie backs are covered with dirt, most users do not visit them unless they have problems. Keep that in mind when selecting material and finished.

4. Consult Pile Buck web site and may be buy some of their books on retaining structures. They have the most comprehensive library. Their software can be used to design the soldier piles as well. Here is their web site:

http://www.pilebuck.com/

Regards,






Lutfi

http://www.cdeco.com

 

[PEinc]

You can't use precast concrete panels for a wall that will be built in an excavation situation from the top down. Precast panels need to be installed from the bottom up. If the wall is high, it is unsafe to make the open cut to install the precast panels.

Install the soldier beams, Install lagging in safe lifts of about 5 vertical feet to subgrade or to just below the tieback elevation. Install the tiebacks and test them. Continue installing lagging and tiebacks as previously described until you reach subgrade.

After reaching subgrade, install geocomposite chimney drains over the lagging between soldier beams. Pour a concrete work pad or footing at the base of the wall. Weld the headed shear studs to the front flange of the soldier beams. Install the reinforcing steel for the cast in place wall facing. Usually the facing thickness is about 12 inches so that you can easily pour the concrete into the one-sided wall form. The reinforcing steel will overlap the studs. The wall facing will need weep holes at the chimney drains or some other type of pipe collection system to drain the water from the chimney drains and away from the wall.

AASHTO requires vertical contraction joints at 30 feet on center and expansion joints at 90 feet on center. The joint between wall facing panel is usually located mid-way between soldier beams. The facing is designed to span between soldier beams and to cantilever from a soldier beam to the facing joint. Check AASHTO for joint details.

REPEAT!!! Do not design a high, tiedback, soldier beam retaining wall with precast concrete wall panels. Tieback walls are built from the top down and precast panels are not easily installed in lifts from the top down. Many tiedback precast panel soldier beam walls like this were built in Pittsburgh in the 1980's. They all had construction problems and required unsafe, open cut excavations that viotated OSHA regulations.

Get copies of the following:
FHWA-DP-68-1R Permanent Ground Anchors
FHWA/RD-82/047 Tiebacks
FHWA-IF-99-015 Ground Anchors and Anchored Systems
FHWA-SA-96-038 Earth Retaining Systems

Also, as Lutfi said, talk to specialty contractors who build tiedback walls and check out their web sites. They also have publications available. Check out

http://www.schnabel.com

Many of these walls are bid under performance specifications. You might want to do this and let the qualified design-build contractor prepare the final design. You would just have to give them the wall location, limits, soils information, any special surcharge loads, wall elevations, etc.

 

[PEinc]

P.S. I own but do not recommend using Pile Buck's SPW-911 software to design soldier beam walls. It is extremely user-unfriendly for soldier beams. It is better used for interlocking sheet piling. Also, if you have various soil layers, the program can give extremely conservative designs based on the worst soil layer.

 

[DRC1]

I agree with PE Inc. Although his reasons are better, some additional reasons are that it is difficult to drive soldier piles to line, spacing and plumb perfectly. Timber easily accomidates minor missalignment or relocation due to obstructions. Precast does not. Precast may require a driving template at significantly higher costs. Hndling the precast units will require a crane and an operator and be a slow operation. The system described by PEInc. is a better system for installing a concrete wall. I have used the system to build basement wall with success.

 

[vape]

Thanks for the info PEinc. The cast-in-place wall is the method I intend to use. Thanks for the info on the detailing of the reinf. and the joints.