Replies

1. 
   Wet_Head | May 01, 2003 08:31pm | #1

   Look for a trench box with a side opening.  Saw one one time a long time ago.  It was made for this kind of application.

1. 
   joetool | May 01, 2003 09:10pm | #2

   I looked for a trenchbox but no one within 100 miles has one .

1. 
   Catskinner | May 01, 2003 09:34pm | #3

   How about making a locally-fabricated trench box?

   You could probably get an engineer to help for a few bucks, a good welder could do this in an afternoon easily.

   Any how you cut it, anything is better than getting buried.

   DRC

2. 
   AndyEngel | May 01, 2003 09:35pm | #4

   Sounds like you might have to close the sidewalk, tear it out and replace. That would be pricey. Have you talked to a civil engineer about other solutions?Andy Engel, The Former Accidental Moderator

1. 
   joetool | May 01, 2003 09:48pm | #5

   I've thought about tearing up the sidewalk, but man what a pain. After looking up trench boxes, I realize it probably wouldn't work. We have to apply a rolled sheet product with an asphault adhesive on the back. It has to go on all at once, plus the wall hass a 3 ' 90degree jog in it. I thought of using sheets of 3/4" ply with walers and struts that angle down to the footing but I'd like to get some specs on building that system ( wood type, size, # of walers, etc...), or find some other system. tearing out the sidewalk is a last resort. I volunteer with a technical rescue team, so I want this to be as safe as possible; our team would respond if there was an accident, talk about embarrising!

1. 
   AndyEngel | May 05, 2003 07:14pm | #6

   My thinking was that if you took out the sidewalk, you could probably avoid the trench box by stepping the excavation.Andy Engel, The Former Accidental Moderator

2. 
   Catskinner | May 05, 2003 09:59pm | #7

   I think Andy's right.

   The only other solutions I can think of are 1) driving corrugated steel sheets and pulling them when you're done, which will necessitate a crane and a hammer (used to do this way too often) and 2) building a 1-sided concrete form. I think to make this form strong enough you're probably better off replacing the sidewalk is practical.

   I recently had an engineer review 1-sided forms for a similar situation, and the loads on them are amazing. Uplift can be really tough to defeat if you're dealing with any appreciable equivalent hydraulic pressures.

   Type A soil is OK at a 3/4 to 1 slope (53 degrees), so you really aren't talking about removing that much soil, are you?

   As long as there's some place to put it, that is.

   If there's no place to put it, I would say your original idea of the form is the way to go, but I would consult an engineer. I was pretty surprised when I did.

   DRC

3. 
   Davo304 | May 08, 2003 03:39am | #8

   "I thought of using 3/4 ply with whalers".....

   Joetool, please put that thought out of your head...3/4 ply is not adequate...PERIOD!

   I cribbed many a trench. A few times our bosses had us use plywood, and luckily there were no mishaps, but in those instances the trench was never deeper than 5 feet.

   Normally, this was how we cribbed a trench. But , I don't know your whole situation, and I am by no means advocating you to use this technique...I'm just reiterating a method we used to use:

    First off, we would install 2x12 plank vertically into the trench pit. These plank would rest against, or almost against the trench walls. The planks would be spaced approx 1 to 2 inches apart. Inside the trench, we would nail on 4X4 whalers across the front faces of these planks.  We normally just toe-nailed the 4X4s in place using 16 penny spikes. Every plank received a toe-nail. Our bottom whaler would be approx 2 feet off the trench bottom. Our top whaler would be even with the top of the trench line. We would install intermediate whalers in the middle area however high we thought it was needed. ( for an 8 ft deep trench, install one middle whaler at the midpoint between the top and bottom whalers.

   After inserting the planks and installing whalers, we repeated the same procedure on the opposite side of the trench face wall. Make sure that the whalers are nailed off at the same height on the other side. Once this was done, we would then cut 4X4 braces. The braces would fit tight between 4X4 whaler at each end. To attach these braces, measure distance between both whaled wall sections and cut this brace to fit in-between.

   After cutting the 4X4 brace, nail on a piece of 3/4 plywood . This ply piece should be approx 3-1/2 inches wide and 12 inches long. Nail the ply "scab" onto the top side of the brace at each end. The scab should extend approx 3-1/4 to 3-1/2 inches past the end of the brace before being nailed on. Once these scabs are nailed on, they weill act as "hangers" whereby the scabs will hang off the whalers at each end, helping to keep the braces in position so they can be nailed off. Nail through the top of the scab into the whaler using 12 penny nails. Toe-nail the brace into the whaler using 16 penny spikes. Use 2x4 wedges between the braces and whlers if needed to make the joint more tight.

   The braces should not be nailed onto the whalers at the very ends, the braces should be moved in approx 6 inches or so before being installed. Nail 2X4 blocks onto the whaler on both sides of the 4X4 brace postion to help keep lock the brace into position.

   Do this procedure (4X4 braces nailed between whalers) at all whaler heights. You can add additional braces in the middle area for extra strength where you feel it is needed.

   In conclusion...when finished, you have a planked wall opposing another planked wall, with 4X4 bracing seperating them...any "push" by the dirt trench will push this planked wall in toward itself. The 4X4 braces keep the plank in place and pressure from one side is negated from opposite pressure from the other wall side.

   I hope this explanation makes sense. If I had a cad program, I would draw you a diagram which is much easier. 

   In any case, 2X12 plank should be considered the "bare bones" minimun  for shoring material...infact, I don't think OSHA even approves this anymore...though this is still the standard used in our mill location for trench "cribbing."  BUT, no way is plywood suitable.

   LOL.

   Davo

   Edited 5/7/2003 8:41:34 PM ET by Davo

4. 
   RalphWicklund | May 08, 2003 04:43am | #9

   Unless you plan to hand dig this trench, just about anything you do is going to damage or destroy the sidewalk. So go ahead and get it over with and do the step sided trench thing. It will be the most economical way to go.

   If you still want something else......... You could try soldier piles instead of sheet piling. You would still have to have a driver to get the I shaped steel piles into the ground, about 6 - 10' o.c. Then you place horizontal timbers, 3-4" thick, in the flanges to hold back the trench walls. Still gonna mash up that sidewalk pretty good and cost more than a step sided trench - back to square one.

   Don't try to cart away the sidewalk rubble you can put that in the bottom of the trench when you backfill. It's easier to find a home for the ordinary dirt you'll have left over, even after compaction. A couple/three yards of concrete and some 1x forms and they have a nice new clean sidewalk (with your initials in it)<G>

5. 
   Ward | May 08, 2003 05:24am | #11

   >>>Don't try to cart away the sidewalk rubble you can put that in the bottom of the trench when you backfill

   Your kidding, right?

   Damage the high dollar wall membrane he just installed?

6. 
   RalphWicklund | May 08, 2003 05:46am | #12

   The guy is going to excavate close to 60 cubic yards of material from a 5 foot wide, 8 foot deep, 33 foot long trench, possibly with a stepped far side so he can put on that high dollar membrane. Unless he is a complete idiot he can find room, 5 feet away from that membrane, for roughly 1.5 cubic yards of rubble.

7. 
   Davo304 | May 08, 2003 05:10am | #10

   Here's a picture of the cribbing method I was describing.

   
8. 
   timkline | May 08, 2003 06:41am | #13

   Davo,

   Nice drawing. That would definitely hold things up. How should he install the waterproofing membrane once he builds a shoring wall against the house foundation ?

   carpenter in transition

9. 
   Davo304 | May 09, 2003 09:00pm | #14

   Tim,

   The shoring (cribbing ) method that I talked about and showed a drawing of was for cribbing a "typical" trench. I simply showed this method so that Joetool could use it and then "brainstorm" from it.

   One possible solution would be to not crib the entire length of the trench at once, but instead crib just a section (perhaps 8 ft) at a time. It may be possible (but maybe not , I don't know all the circumstances here) to build the cribbing and set in place against the dirt side of the tench wall only; then instead of cribbing another wood wall which would be set against the building's structure, you could possibly just extend a 2X12 plank vertically at each end where the 4X4 bracing can be connected to the whalers and be attached back to the 2X12 resting against the buildng's wall.  Inside this 8ft span, install the membrane, then move the 8ft long cribbing down the line, reattach the braces to the 2X12s resting in a new location, and then continue to install the membrane.

   Whether or not this is feasible in Joetool's situation...I really don't know. BUT, Joetool openly discussed his idea of cribbing the trench ( so he must have some sort of a "game plane" as to how cribbing might work) BUT, Joetool mentioned using 3/4  plywood as his wood of choice for cribbing. I wanted Joe and anyone else out there reading his post to know that 3/4 plywood is NEVER acceptable as a use for wood shoring...Period. Infact, OSHA doesn't approve 2X material either...wood used as cribbing material for trenches up to 8 ft deep is supposed to be a FULL 2 inches thick.

   Of course, the best method when working in a trench, which was already earlier suggested, is to "step" the trench back so the threat of a trench collapse is eliminated.

   Davo