Anchored Sheet Pile Wall 6

[3of12]

I recently designed an anchored sheet pile wall for a construction contractor. The trench is 20'deep and 12' wide. My design called for the anchor rods to be 1 and 1/2 inch diam.steel rods at 10' spacing. Each rod was subject to approx. 50,000 lbs tension based on my calculations. The contractor recently requested that he be able to use galvanized cable
(5/8" diameter) since he has lots of it from a previous job. I personally don't like the idea due to fastening issues but wanted to hear from others in the group. I greatly appreciate the opinions on this website.

Thanks to all

 

[SlideRuleEra]

The allowable load on typical 5/8" diameter wire rope (not just the connections) is far less the 50 kips. Galvanized wire rope allowable loading is even lower (about 10% less). Wire rope stretches about 1% under heavy load. Even though galvanized, corrosion will have the tendency to attack all strands simultaneously.
To me, this does not sound like a wise thing to do in this situation.

There are many kinds of wire rope, here is a link for some good background information

http://www2.engr.tu.ac.th/~cdulyach/me414/wirerope.pdf

http://www.SlideRuleEra.net

 

[PEinc]

How will the contractor install these anchor rods? The trench width is only 12 feet. Therefore, if drilling quipment is needed, the anchors will need to be located near the top of the sheeting so that they can be installed after some minimal trench excavation.

I do a lot of work with post-tensioning strands for ground anchors. I don't know of any good way for the contractor to use his galvanized cables.

At only 20 feet deep and 12 feet wide, why doesn't the contractor just cross brace the sheeting?

 

[3of12]

To PEinc: Thank you for your input. This trench will be used to lower a horizontal boring machine into for a 20" pipeline laying project. They don't want to use bracing or struts since they would tend to get in their way. The anchors are located 3' down from grade.

 

[GeoPaveTraffic]

3of12,

How long is the excavation? If it is relatively short, you could install a waler with corner braces. This leaves the center of the excavation open for the machine but eliminates the anchors.

 

[PEinc]

A small quantity of anchors should be avoided unless the contractor can install his own cheaply. GeoPaveTraffic is right. Look at wales and corner braces if the boring machine is small enough.

 

[3of12]

Thank you again PEinc and Geopave: I understand your suggestions. Unfortunatley the trench is at least 50' long.

 

[GeoPaveTraffic]

Then you are likely back to either a cantilevered wall or tying it back as you originally indicated. Cantilevering 20 feet is possible, depending on soil conditions and acceptable movements, but is likely going to be difficult.

As for the tiebacks, you could either use a few relatively high strength/load anchors as you originally indicated or you could use a large number of low strength/load anchors. If you or the contractor want the low load option, you may want to use deadmen instead of drilled in anchors. Install the deaden well out of the active zone and run as many of the cables as needed between the wall and deadmen. As I recall in the one I have done like this the deadmen were constructed as a trench 5 or so feet below grade. The cables are attached at the resultant location of the deadman and to a waler on the inside of the wall. The connections have to be carefully designed and thought out, but it can be done.

 

[PEinc]

Again, how big is the boring machine? L, W, Ht????

 

[LCruiser]

50' long? Roll it in, then finish the back of the excavation.

 

[3of12]

Answer to inquiries by Geopave, PEinc and Lcruiser: Thank you very much for your input, I appreciate it greatly being able to benefit by your insight. Now, the boring machine is the size of a pickup truck. I am using 2 or 3 sections of sheet pile as the anchor and doubled channel(back to back) as the wale which is placed on both the anchor sheet piles and the trench sheet piles.
The anchor rod is 3' below grade. The anchor rods are spaced at 10'and I have told the contractor I will not accept cable as a tie back alternative to the rod (which he did not like, of course) since he told me finding large diameter rod was a pain in the ___)

 

[DRC1]

I have used cable to a deadman to support sheeting and it does work. You will get a little more movement of the top as the system has more slack than the rods. The 1 12 in. rods are epensive, esp. if you want upset ends. You can loop several lengths of cable at a location and connect with cable clamps. Form a loop in the end of the cable and pull a little tension in it with a come along. Be sure to use the right size shackles to maintain decent radius at the bends. I dont have my cable book with me but I am pretty sure you wont get 50 kips out of a connection, so you will probably have more anchor locations.

Good Luck!

 

[eric1037]

If this is a temporary system, it seems like cable would be acceptable. If it is only designed to retain soil and there are not sensitive structures above, you can probably tolerate some movement.

 

[SlideRuleEra]

3of12 - Contractor complaining about finding the rods? You can solve that problem for him - here is one link (see page 7)

http://www.clevelandcityforge.com/products/images/ccf_catalog.pdf

I expect that paying for them is his real problem, as DRC1 stated.

http://www.SlideRuleEra.net

 

[PEinc]

I don't think many people still use tie rods with upset ends. You can get Grade 60, 75, and 150 KSI threadbars, in a number of diameters, with nuts and bearing plates quickly, from stock, at Williams Form Engineering or DSI-Lang Geotec. Lengths come up to 50 or 60 feet per rod. They also have Grade 270 post-tensioning strands with appropriate hardware if you want to use "cable."