Advice

[jfrett75]

I live on a small mountainous island in the Caribbean. Presently, for earth retention canter-lever walls are usually constructed. However, these can become very expensive as the height increases. I recently did some training in the design of alternate retention systems which are generally less less expensive. However, most require equipment which is not available and can be very costly for the turnover on island. Additionally, the terrain make it difficult if not impossible in transporting some of the equipment that may be required. My solution is to design a hybrid and here is my question. Would it be possible to design wall as a tied back structure with wales at a pre-calculated interval to be constructed from the ground up? For instance, a 30' wall is required ad the wales are spaced 3' from the bottom and centered at 6'. The first 6' would be designed with the inclusion of a footing to account for temporary back-fill loads. This sectioned would be constructed back-filled and then tied in and then the next 6' section constructed back-filled and tied and so on until the top. Is the methodology structurally sound? Your responses will be greatly appreciated.

 

[PEinc]

It is hard to answer your question without more information. Based on your posting, I assume this is a fill wall to be built from the bottom up. If so, you still need some type of vertical structural members such as soldier beams or sheet piling. You still need some type of tieback anchors or tie rods with deadmen. To install soldier beams, sheet piling, and tieback anchors, you still need large equipment. It might help us if you could post a cross section sketch of what you are trying to do. Do you have any soil or rock information?

Also, please do not post your question in more than one forum. This is the correct forum for your question.

http://www.PeirceEngineering.com

 

[RFreund]

What about an SRW wall?

EIT

http://www.HowToEngineer.com

 

[PEinc]

An SRW might be OK if temporary sheeting is not needed to support the mountainside.

http://www.PeirceEngineering.com

 

[jfrett75]

The weight of the blocks would be an issue as shipping costs are very high.

 

[jfrett75]

There was a typo, wales was meant to be walers which would be C-channels with anchors evenly spaced. In essence a tieback wall, but constructed from the bottom up. Rock is usually met at shallow depths and the profile is usually a mix of clays and large stones or layers of solid rock and therefore nothing can be driven. The cut usually hold up for long periods of time once there is no rainfall. My intention is to in essence design the wall as a tieback wall but as construction will be from the bottom up. The lowest section would include a footing designed to resist backfill loads until the walers can be installed. And each section will be tied into the lower section and also designed for backfill loads.

 

[GeoPaveTraffic]

I don't see anything that would prevent this type of wall construction, assuming as has been noted that the slope will stand on it's own during construction.

The biggest problem I see is installation of the tiebacks. The soil/rock profile you discus will be very difficult to drill and for tall walls, large equipment will be necessary just to reach the tie-back locations.

Mike Lambert

 

[PEinc]

Tiedback walls are usually built from the top down. If you build one from the bottom up, pay special attention to the intermediate design cases where you have backfilled to the next tie level but before that level's tieback is installed and locked off. You may need heavier than normal soldier beams and higher than expected tieback anchor design loads. You also will need to stand up and temporarily brace the soldier beams until you get some tiebacks installed. This bracing could significanlty affect the access for the tieback drill. GeoPaveTraffic is right on about the difficult installation of the tieback anchors. Installing anchors as high as you will need is difficult and requires a support platform for the drill or requires a crane and suspended platform to hang the drill rig and workers. See attached photo of crane-suspended drill rig installing tiebacks. Finally, you must consider the safety of the work crew in front of the steep slope.

www.PeirceEngineering.com

 

[jfrett75]

Thanks for the input. The drilling aspect is forward straight forward as blasting is usually required when deep cuts are involved. My concern was mainly if a top down system can be modified to a bottom up system. As the wall will be constructed in small lifts (>6ft), and the backfill widths will also be generally small (>3ft) and small compaction equipment will be used, the backfill loads will not be that large, additionally the wall thickness and reinforcement at the toe of each lift will be designed to account for this until the tiebacks are installed.

 

[dcarr82775]

Don't see why it wouldn't work, but you may need to go back and re-stress the lower anchors as the wall gets higher to keep deformations down. I have not given it a lot of thought, but I think under that scenario a equivalent fluid pressure type loading might be more applicable than an apparent pressure (rectangular) type of loading.