below water table and excavation ideas & solutions?

[863bobcat]

I am looking for some possible solutions for this project that we have at the beach. Electrical vault for Hotel. Shoring in place, hole is approx 9.4' deep and it needs to be 10.3'deep. Problem we are having is the water does not pump out water fast enough to reach my backhoe down in hole before water and sand keep me a 9.4'.We are not gaining depth no matter what we try. First the shoring was not wide enough so we had to widen it, not easy when it's already down in the sand, Weld some metal pipes together to keep the shoring from caving in, then SCE blue prints were wrong AGAIN; the shoring is not long enough, so the hydrolic pumps in the shoring had to come out, agian not easy when it's already buried. Would of just pulled the shoring out, but two very tall palm trees stopped that. This has been a nightmare job, now can't get it deep enough. TOO MUCH WATER . HOLE MUST BE DRY IN ORDER TO DUMP 3/4" GRAVEL before electrical vault can be placed...Thanks for any feedback...by the I'm the girlfriend looking to come up with the best idea yet.
My boyfriend would think I was the biggest dork for doing this..............so shhhhhhhhhhhhhhh thanks .sorry if I went on and on and I hope it makes scense...

 

[Ussuri]

How are you currently pumping your excavation out? Are your using a single pump to pump out the excavation directly, or have you installed a de-watering arrangement on the outside of the excavation.

Also when you mean shoring, do you mean intermittent shoring to support the excavation, or do you have a continous sheetpiled support? How big is your excavation on plan?

 

[StephenA]

If the water pressure is enough the water will come in under the shoring and you will never dry it out enough. The shoring needs to be deep enough to "cut off" the water supply by increasing length of the path of the water.

 

[Ussuri]

In the past I have used mutiple de-watering rings around an excavation. The first set of dewatering points at say 1m below then another set at say 2m below (or whatever the installer recommends)

This has a similar effect on length of flowpath for the water and is useful if you didnt put the shoring in deep enough in the first place and no longer have the plant on site to push them in further.

 

[oldestguy]

This is an old thread, but this may be of use. If not, how did it work out?

Site now is very likely "much worse" than if it had been done per the help indicated above.

Even if you can "dewater" it by these methods, it is very likely that what ever is placed there will settle.

Why does one have to go below water with the structure anyhow? Clean gravel can go into water, no problem as long as it is free of silt and clay. Do some compaction of it also.

If you need only a layer of gravel there, place what you can and get on with it. You might even place a "mud" layer of concrete to then place "good" concrete on for the structure.

Then, install some tubes into the sand below, possibly through the concrete base foundaion.

Then, at some time before all is done, plan to pressure grout that loosened subsoil via these tubes. You may have to pressure grout sufficiently to even raise the structure a little.

Do not look to a "mud jacker". You need a firm well experienced in fixing up sites like this.

Without some improvement of the subsoils, plan to accept some settlement later.