Power Hammers and Wet Soils?

[Crunch]

Does anyone have experience running a power hammer on a slab lying on a wet sand/loam soil?

I'm considering a shop with the following characteristics:
10 feet above sea level
water table is ~ 1 foot below grade
soil is a sandy loam (sand, clay and organics on E side of the Chesapeake). It's a real nice loam up on top but gets much denser with clay mixed with sand about 18" below the surface.

The soil transmits vibration pretty well. If a real heavy truck goes by, it can shake the house more than 100' from the road.

Anyone have any insight on whether a power hammer would annoy neighbors maybe 500 feet away in a situation like this, and if so, how to remedy it?

I've heard of suspending the hammer in a bed of sand, but as I understand it, the sand bed would need to be dry.

If anyone has any insights, I'd sure appreciate them.

Thanks in advance.

[brian robertson]

First off, make something nice for each of your neighbors every so often; secondly don't run the hammer after 9pm or before 8am or on Sunday.

I live on a 70ft deep clay layer (think of a bowl of jello), my former 50lb & 100lb Little Giants would rattle the dishes in the neighbors' china cabinets and the bases for those hammers were 2 & 4 yds concrete respectively. The 155 big blu hammer mounted on the 4yd base will also make the neighbors' dvd players skip. My engineer friend said the solution would be to drive pilings down to bedrock and set foundation on top of those.

My solution: smooze your neighbors as best you can; it's alot cheaper. The litle old lady says, my forging makes her china sound like soft wind chimes and she likes it. The folks with the skipping dvd player said they shouldn't be waqtching so much tv anyway. So, it's all good...

[Marksnagel]

Hey Crunch,

It sounds like you are on the eastern shore. I'm not too far from you in ne NC. Very sandy and clay here too. I work on the outer banks of NC with the DOT and I agree with the engineer that driving piles down will transfer the disturbance to the bedrock. However, in our area the bedrock can be out of sight down there. I have seen piles driven down expecting the point of refusal to be @ 80ft down and never hitting bottom.
Best to make peace with your neighbors.

Mark <><

[ptree]

Much as Brian Robertson suggests the only way to set a power hammer on wet bouncy soils so as to not transmit too much vibration is to piling down to solid.
At the valve and fitting shop I worked at we had steam drop hammers up to 25,000#. And we were in an oxbow bend of the Ohio river, sitting on 90+' of river sand/sediment. So wet from the river that a steady flow moved under most of Louisville. The big hammers set on an anvil, on a subplat, on a 12' thick timber cushion on top of a pyramid concrete foundation down to bedrock. Now the bedrock was a slab that was about 20 city blocks by 35 city blocks, and that floated on more sand. When the 25,000# Erie hit, everything on the slab bounced. We were near on corner of the slab, and 30 block away the folks waiting for the bus would get bounced when that big boy hit. There was a city ordinance limiting use hours so we would not wake folks up!

In the 7 story machine shop 50' away, the tool and die shop was on the 7th, and when that big boy hit coffee would go straight up about 2" from a coffee cup on top of the headstock of a 50,000# lathe! The tool and die makers would get a warning call when the bigger hammer were scheduled to run. They knew the timing of the sequence and would pull out of the cut when the hammers would hit, and then go back to making chips till they knew another sequence was due:)

[macbruce]

If your nearest neighbor is 500 ft away I seriously doubt you will have any problems with them, assuming you have a hammer less than 500lb....Mine are 300ft away and I run a 250 on top of bentonite and never a word....

[Crunch]

Thanks for the replies, everyone. Unfortunately, driving piles down to bedrock is out of the question. Some kind of object hit this area 35 million years ago and made a huge crater. Everything is mixed up and jumbled pretty deep, and Lord only knows how far down you need to go to hit bedrock.

I guess making nice with the neighbors is the way to go...

[gearhartironwerks]

Crunch,

My 6 " shop slab is about the same as yours above sea level in sand. For the 400lb DeMoor weighing 18k, I cut out a 4 x 8' chunk of concrete from the shop floor, then dug out under the floor to mushroom the the new base. I also added a lot of rebar and whatever else I had in the shop to stiffen the pour. I used about 4 yards of concrete.
The result after 5 yrs is that the pour is very slowly beginning to sink with the angle tilted very slightly toward the weighted flywheel side. An outside observer would probably not notice.
If I was to redo the pour, I would add more concrete overall, expand the mushroom and weigh the amount of concrete to a greater amount on the flywheel side.
The current mushroom extends about 3' beyond the cutout. I would extend that and double the concrete. I think the mushroom makes a big difference.
Also, I use the hammer a fair amount. The neighboring businesses know when it's running. No whiners yet.
John

[Sask Mark]

You don't necessarily have to get to bedrock with piles. Straight shaft cast in place piles rely on skin friction with surrounding soils (they do not rely on end bearing capacity). If the water table doesn't recharge very quickly this might be an option. These piles are fairly inexppensive as smaller ones can be turned with a skidsteer (no big piling rig necessary). If the water table recharges quickly and the hole fills up with water the concrete can be placed down the hole with a tremie pipe or concrete pump so the concrete gets placed at the bottom of the hole and displaces the water.

Another piling alternative is CFA piles. In this type of pile, concrete is injected directly down the drill stem to displace the water. This type of piling requries a specialized rig and uses more concrete (i.e. more expensive). They were originally designed for piling in water conditions.

Yet another option might be micro screw piles. There are some small micro screw pile rigs that can get into smaller areas.

A structural engineer familiar with the soils in your area can probably provide some input for what would work best.

[macbruce]

Crunch, How big is your hammer?

[Crunch]

Thanks again, everyone. Lots of good information to think about.

Macbruce, no hammer yet, but I'd like to get something in the 50# to 100# range.