Shoring for a sewer tie in

[oceanobob]

Always wondered how I get from the classroom or the catalog to work on an existing pipe while using trench shoring. Now I get to know: have to go 7' down at the street shoulder to install a sewer lateral. The existing pipe (as observed in the manhole at the next intersection) is 8" clay. Locator says it is 6 to 8 feet down; manhole tape measuring and logical eyeballing indicates just shy of 7'. Soil is a sandy loam but low on the clay; yes, a hand dug hole will stand 5' deep.
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Local shoring rental is either a shield or a box that can be lowered into the trench, or, pieces of thick plywood and hydraulic shoring jacks.
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Excavation plan is to position the machine off and square to street and trench a nice square hole with the end near the tractor being a slope to facilitate the new 4" plastic pipe for the sewer lateral. At some point it will be necessary to enter the trench and explore the next depth with a shovel in order to locate the pipe; if not located, dig that next thin depth using the tractor, repeating this process until the pipe is located, hand dig around the pipe using the tractor to remove the spoils. That plan doesn't mention the shoring and the next section asks about that.

Here is my question: if the trench gets to 4' and then the shoring is installed, how does the additional digging proceed? Seems the space is kind of small for the bucket to enter and remove the soil. All the pictures shown in the trench safety classes and the catalog show a standing wall trench cut where there is no pipe, the shoring is then installed, then the pipe is magically installed and folks inside the trench with nice clean hardhats and clothes and new shovels happily working (if work means taking pictures of themselves).

If I get a shield or box we can lower it in the trench and then enter and look for the pipe, then remove it, dig a little etc. But that means the trench walls will have to stand and that may be asking a lot for this type of soil, especially when we get near the final depth. A slough off may occur under the asphalt of the road and a repair as well as a traffic plan will have to be enacted. Obviously a slough off not a good occurrence: to be avoided.

If I excavate to 4' then install the two sets of jacks per each sheet of plywood, digging with the tractor will be tedious if not impossible as the backhoe bucket is around 5' horizontal measured from teeth to ram and the spacing of the jacks will not accommodate this. I can also get some shoring items that are longer and these have horizontal whalers to allow the jacks to be spaced further apart.

The other point is once the shoring is installed with the jacks at the four feet or so depth, and if there is some trick to deepening the excavation, does one excavated quite a ways below the shoring in order to install the lower row? Seems unlikely - I am thinking the trench is dug and the lower row is installed then the upper. Which is ok as long as noone enters the trench.....but that is the rub: if we cant enter we cant find the pipe, if we shore then subsequent excavation is a challenge with the shoring in place. Rental inferred we could trench to 5', install shoring and then trench below the shoring for the additional 1 to 2 feet to access the existing pipe. If this is done, how to get that last bit of dirt out - one pail at a time? LOL.

Basically: how to dig a hole and enter to find an existing pipe with the goal of not damaging the pipe and not having a trench collapse. Thanks in advance.

 

[Ronsii]

Going as deep as you say and the soil as it is I would go with a box, the box has the advantage of sliding down as you dig and yes it can be tight digging inside of shoring... this is where thumbs really get in the way

 

[jprefect]

I use trench boxes regularly, depending on what we are doing depends on how wide of spreaders we use. If we are installing new pipe we will use as narrow of spreaders as possible but still get the bucket in the box. If we are doing a tap ( like you are talking about) or repair we put 8-12 ft spreaders on and place the box so we can get the bucket beside the pipe. But their will always be a shovel near by.

 

[oceanobob]

The box has merit indeed. Is it possible to trench with reasonable accuracy to say about three feet, then lower the box into the area...not that I am in a hurry but the method of pushing down the sole box and using the bucket to remove spoils seems difficult in particular due to the spoil pile at the narrow end(s). The end that is farthest from the bucket suggests trouble. Is it necessary to use hand tools to loosen the soil under that edge?

 

[CM1995]

A manhole or short box with adjustable spreaders may fit the bill. Some examples - http://shoring.com/8-10-12-steel-trench-boxes

What machine will you be using to dig with? Lifting capacity will play a roll on what type of box.

How wide can you dig the hole at the tap connection?

 

[oceanobob]

As to the handling of the box, my telehandler is around the vicinity to get some pm's and maintenance, thus handling the box off the truck, lowering place etc - that machine is a true 'good hand'. As to the digging, prolly a TLB (eg backhoe) w extendahoe....but the issue of those outriggers and the length of the machine especially once a few jobs have been accomplished with a minimal tail mini and the offset boom of these machines .... maybe rent a mini to almost midi. I remember when the shoring boxes first arrived and if ya mentioned you didnt have an excavator only a TLB backhoe, they sorta scoffed at ya. As I recently did some surfing and OEM promo you tube watching, I notice some companies promote using the box with a backhoe and there are even some that have em light enough to work with a bigger mini.

Once the beautiful trench is cut and squared up and the box set into it, what basically happens when one ladles out the soil below the bottom, then somehow the box slides down and what then, pushes some material sideways into the box?
Is it important to move the hoe in order to achieve the back angle on the bucket at full open such as when one wants the far side to be as plumb as possible? Because the near side, the teeth can poke under and more easily allow the box to slide down.

On the old hoes the outrigger controls were in the center and one could quickly place a hand and fin-angle a tilt? Would this maneuver be expected to clean as much as practical under the (parallel to the dig) sides of the box?

I am figuring 3' wide [ends] by 7 or 8' ling [sides].

Thinking on running the box down until it is about 6 or so inches above the pipe then 'undermine' with a shovel to access the pipe to place the saddle for the lateral.

If these tricks are the norm, then I will get the backhoe.

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I have a line card from the shoring supply: for example, a steel manhole box 6 x 8 x 8 is way too big but it weighs 5325#. And all four sides are full depth. There is another item called Build-a-Box, it is aluminum and it can set up with two or three sides ... I like the three sided version as that allows a ramp/slope for the lateral to pass...sizes are 3', 4', 5', 6', 8' ..... but this idea never shows the item being quasi forced into the ground using the excavating tips & questions I mentioned above. If one looks at the pics/video, there is a small clearance on all sides .... oh yes they show an existing pipe so I surmise they lower the box in, hop in the box and look for pipe, having found no pipe yet, they pull the box out and dig a foot more, then they lower it back in, dig around and look for pipe, iterative process until the pipe is found. I tend to call these things "shields" where one is basically actually working in a standing trench but in the event it falls/collapses, then you are safe. Like a seatbelt in a way.

 

[oceanobob]

Visited a shoring supplier and they suggested a three sided aluminum box, 900# it would weigh. The depth would be 6 feet and the inside work area is 3' by 6' clear. The plan is to locate the line using sonde and then carefully excavate a rectangular neat hole to a certain depth, not hitting the pipe of course, and then insert the box, where the workers could enter the box and hand excavate to find the line. It would be nicer if the box was 5' deep as the top needs to be a hair below flush in order to trench plate for the evening when work is done.
Another alternative is a pair of twin ram hydraulic shores and some sheathing to prevent ravelling. This method is incomplete as it doesn't address the endwall of the trench because the 'Trench End shore' isnt available for rental in our area.
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Soil classification is C-60. Not B.
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Both systems provide a hoe bucket access of six feet (seems minimal but can be performed) in order to remove the spoils while the hand digging is acting to locate the pipe.
Both systems at this depth allow 2' below the bottom of the shoring; that is why a 5' shore depth (in lieu of the 6' box depth) is desired for a 6 to 7 foot depth of the sewer line.

Any ideas on how to handle the so termed 'trench end' if I use a pair of twin hydraulic jacks to hold the sides?

 

[brianbulldozer]

Have you considered hiring a vactor truck? Excavate to whatever depth you are comfortable with using your hoe, and then hydro excavate the remainder letting them find and expose the pipe. Set your shoring box when done or when it becomes necessary to support the walls. The rental yards around here all have leg kits available with their aluminum boxes. You might consider that to keep the box off the pipe. The vactor truck will cost you some money but you might sleep a whole lot better the night before you do the job. Get a few of these jobs under your belt and you will be a lot more comfortable working with shoring.

 

[John Shipp]

At the open trench end, could you use strong plywood and timber battens that span as wide as the outside edges of box, & fix in place with wire or timber. If the jacks are close to end they may offer support to the timbers.

 

[DanFawkes]

The box is best for potholing, like you are doing. Hydraulic jacks and plywood work for trenching, where you don't have to do any work inside the trench until it is dug. The fine, hand work, can be done safely

 

[John Shipp]

I took it that he wanted to close off part of the end of a three sided box.

 

[oceanobob]

Yes, thanks ... my question about the end of the trench was aimed at deciding if I should use the three sided box,
or
could I use the shoring jacks and the plywood with some contrivance for the trench end.

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In C60 soil, both versions allow 2' of excavation below the bottom of the "shoring".