Digging below sea level 6 feet down 5 feet from shoring wall question

[Hidestyle]

Hey guys im new to the forum

I got a question if u can help ?

I'm supposed to dig a pad 10 x 6 , 6 feet below grade , which is below sea level and the pad is 5 feet from the shoring wall. With that in mind i was told to cut a 1/4 slop for the side closest to the wall. Problem is knowing that I can get the other three sides good, to have ppl jump in the hole is my concern cause i know the material will just fall back in and create its own slope, just wondering wat u guys would do ?

 

[ttazzman]

have them sign off on liability and permits.........ask for specific instructions in writing ....have them there to sign off on work as its completed....

or just walk away

 

[Hidestyle]

Thanks

have them sign off on liability and permits.........ask for specific instructions in writing ....have them there to sign off on work as its completed....

or just walk away

Thanks , well there plan was to start the slope 3 feet from shot Crete it would be a 1/4 slope i suggested that we dig a larger hole to lower the water table and have a trash pump to keep pumping the water giving me visibility to see wat im doing but the problem is water is coming from all over and the slope pretty much started to fall in making its own slope. I put lock blocks to stabilize the bank from completely caving in. Was wondering if i should have did a straight 6 feet cut and bench the top 2 feet ? Or was thinking just continue using lock blocks to as a wall ? Or a sheet piling wall would work i think ?

Thanks for replying tazz

 

[old-iron-habit]

have them sign off on liability and permits.........ask for specific instructions in writing ....have them there to sign off on work as its completed....

or just walk away

Is it sand? Having someone sign off on liabilitys and permits will do nothing for the dead persons relatives or your conscience when something goes wrong. If you are getting seawater infiltration your conditions are always changing with the tide. When water infiltration suddenly blows a channel and the pump won't keep up, it to easy for the person working in the hole to have a foot stuck in the soft sand and there is a good probably he will not get out before he is buried. The liquified sand can fill that hole in a matter so seconds. For a hole that size it is simple to build a double ring and push some rough 2 inch material down as you dig and do the job safe. This comes from a guy that spent the first ten years of his career on piling and water jobs both onshore and off.

 

[dayexco]

can't you put a trench box in, close the ends and dig inside of that?

 

[CM1995]

Wouldn't sheet piling be the way to go? Drive it down well below low tide level and then excavate? Of course I have no experience in this type of work so I might be way off base.:beatsme

 

[lantraxco]

Sheet piling would be best, but expensive, and the vibration involved in driving and pulling it may be a factor. All things being equal, driving a couple feet or more below water level and a diaphram type dewatering pump would be safest I think.

 

[Turbo21835]

Im with Day. Trench box with appropriate spreaders. On the open ends road plates or sheet piles bucket driver to box it in. Quick dirty and easy

 

[lantraxco]

If it's loose material at all and you're below water level, sinking a box as you go might not be the best. Too easy for water to blow out below the box walls and turn your hole into a quicksand swimming pool. Without being able to actually see the conditions it's really hard to say what would be safe.

 

[Buckethead]

If it's loose material at all and you're below water level, sinking a box as you go might not be the best. Too easy for water to blow out below the box walls and turn your hole into a quicksand swimming pool. Without being able to actually see the conditions it's really hard to say what would be safe.

Yes, I don't know the soil conditions where the OP is working, but if you are close to the ocean in running sand, water can boil up from the bottom, possibly washing sand in with it. I filled in some sink holes close to the beach here after the big storm in 2012, it took a few loads to fill in sinkholes that looked kind of small.

 

[CM1995]

Regardless of method I would assume some sort of dewatering pump would also be needed?

I have turned down jobs on the Gulf Coast (4-5 hour drive away) because sand and water is a totally different animal than what I am used to dealing with.

 

[monster76]

some times the money isn't worth the liability IMO

 

[Acivil]

In my mind, the water is really the only issue, if you have the infiltration rate of the material around the hole, you should be able to set up either a curtain drain, or well points near the corners and do the work in semi dry conditions.