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View Full Version : Building a retaining wall, bobcat big enough?


OilHammer
05-24-2011, 12:49 PM
I have a major home improvement project starting soon, and I'm still trying to pull together some details. As I understand it, I have to put my footings for the wall at least 24" below the grade for frost. At the highest point, I have about 4' of dirt bank before I dig down for the footing. I'm wondering how high the bucket of a bobcat can go and how far forward it can dump. If I come at the bank straight on, can I lift buckets of dirt straight up and dump beyond the dig? Or do I have to dig buckets, then drive somewhere else to dump? Hope that makes sense.... anyway, once the bank is dug back for the footing width, I have to dig down. I'm assuming the bucket is about 4' wide, so I would dig out the full 4' and just build formwork where needed. I have never watched a bobcat do work like this, so I wasn't sure if it was adequate. I hate to go rent one and realize afterwards that it's not going to cut it or take twice as long.

SteveH
05-24-2011, 01:36 PM
I would get an estimate from guys who do this for a living. They are so fast and efficient it'll be a treat to watch. I have hired out dirt work like this, and newbies on Bobcats (or most earth-moving equipment) are 2x as slow, or more.

If the estimate far exceeds the rental cost, then you can still consider doing it yourself. If a guy has equipment in your area, this will offset some of the hauling/transport costs, so look for someone already doing this kind of thing in your neighborhood and ask him for an estimate. Just my .02

LARGEONE
05-24-2011, 10:17 PM
I would have to agree w/ Steve on this one. Last time I started moving equipment around in my yard, I flipped the front loader onto its side and had to upright it with my Land Cruiser!!!

The frost line in Denver is more than 24", I think? Point being...that you may have to dig the footer with a back hoe rather than the bobcat.

SteveH
05-25-2011, 09:20 AM
Echoing this - I thought footers in Colo. (at least around 7000' elevation, but perhaps lower) had to be 40" deep - about like buried water pipes. Your local zoning/code requirements will specify for sure.

A buddy of mine rented a skid steer and flipped it, and the rental company righted it and said that this happens all the time. Many places will drop the skid steer off at your house, as most people don't a suitable tow rig to get one to and from the rental place. I have owned a tractor with a bucket for 10 years and used a backhoe before, and as fun as they are, they're a lot harder to operate with precision than you can guess, if you're a newbie.

Besides, if you call 'Miss Dig' (or whatever PC term they now call the utility locator service) and the 'other guy' wipes out a gas line, then at least you're not at fault. The guy at my house pulled up a big hunk of unused water line from 50 years ago - kinda scary when they first hit the buried steel line and you don't know what it is.

OilHammer
05-25-2011, 10:48 AM
I have run a skid steer before, and also ran a bobcat bucket excavator. I nearly flipped that thing though...my neighbor owned it and let me borrow it to dig up my lawn for sod work. I was running down the street and pushed the "fast" button on the floor to make some time. That thing jumped and nearly ran over backwards on me, then the resulting panic on my end caused it to endo when I let off the gas. Whew...
I've also run a forklift for a few years, but that's really a different animal. Advice taken, but budget really dictactes on this one. I'm getting a few more quotes before I do anything.

The first set of drawings I worked up, I had the footings at 36", but I was talking with a foundation guy in Stapleton and he said 24. 36 is WAY down there...lots more concrete, but at least it makes the wall more stable. The original wall has completely blown out in two spots.

DaveInDenver
05-25-2011, 11:38 AM
Are you within the city limits?

City of Denver follows the 2006 IBC with exceptions adopted in 2008. So follow the 2006 code in section 18 for laterally non-constrained walls. Depth under grade depends on how tall above finished and the code has the ratio formula.

IIRC at least two exceptions apply. One is that the city requires permits and inspections for walls taller than 4 foot from footer bottom to wall top. They have also taken exception in 1805.2.1 to set the frost line for Denver at 36 inches.

I think we still have the IBC at home, but they have the current and previous IBC at the library downtown, too. You can find the exceptions on the denvergov.org website in the Building Department section.

OilHammer
05-25-2011, 01:25 PM
You are correct, the code says 36" plain as day. What threw me was the foundation contractor telling me otherwise this weekend. I assumed someone doing this work for a living would know it off the top of his head, but perhaps he didn't understand my question. He may have been referring to footing width....dunno. And yes, I must have my wall permitted, stamped, and inspected. :( The wall itself will be 7' high at it greatest point (to bottom of footing), then a 6' brick fence on top of it.

DaveInDenver
05-25-2011, 01:56 PM
I assumed someone doing this work for a living would know it off the top of his head, but perhaps he didn't understand my question.
I'd give him the benefit of the doubt, but just because he's doing it for a living doesn't mean he's doing it per code. Denver has a lot of codes and exceptions that other cities and counties don't (for better or worse). If you interpret the wording, if you were doing a short retaining wall, the buried depth ratio might not need to be 3 feet deep. In that case you might not need a footing and the frost line requirement is moot. It's possible he didn't understand the dimension of your wall.

Beater
05-25-2011, 02:59 PM
also in the city of denver - don't forget your variance for fencing over 72"
DAMHIK

OilHammer
05-25-2011, 04:11 PM
The fence isn't over 6'...it just sort of "blends" with the wall, though there will be a material color change.

Beater
05-25-2011, 04:22 PM
read the code. it's from street height! never really enforced, but yeah, I got nailed. (no pun intended)

Inukshuk
05-25-2011, 08:05 PM
The rules are easy, the city inspectors great, permits no big deal and little expense (unless you need to close the sidewalk because then you have to do the entire block, you pay per foot and per day and you have to rent signage). I have an engineer for you and suggest you consider some laborers and shovels. Otherwise, a small trackhoe rather than bobcat since the bobcat won't get you 36" deep (and the bucket will not allow you to "dump beyond the dig" and you will have to haul it away anyway, no?). For the extra foot of depth you will have a much more stable wall. If you can wait a bit and spend time planning, I'm sure I can help you save $$ (remember that I have built houses in Denver), but I am about to go away for two weeks and can't do much of anything till after.

RockRunner
05-25-2011, 09:25 PM
36" is correct and do keep the height in mind of the fence. Do you live in Denver or another county? Best thing to do is to go to the permit office and show them your drawings, they can save you money and time. If you can wait ask Daniel for his "helper " folks, it will save your back and marriage.

It sounds like you got your stuff figured out pretty well ow just the permit.

Inukshuk
05-25-2011, 10:33 PM
FWIW, if you (or anyone) need engineering or architecture help both Kirsten and I are licensed professional engineers (she's a civil/structural, I'm electrical) in Colorado. Her most recent few years of experience during and after architecture school is primarily residential in Denver but before going back for her masters she did engineering on commercial buildings, transportation, etc. She worked on lots of the retaining walls along I-25 in Denver and the Springs, for example...

Good point!

OilHammer
05-26-2011, 08:15 AM
Yeah, probably need her to at least look at the drawings. I can stamp at the office, but don't have much experience with retaining walls, and none with Denver.
6' from the street doesn't make any sense unless that's new with this year's code. My whole street has retaining walls with fences on top... I would call that a loophole. The "fence" is the portion that has air on both sides. It's not my fault my lot is higher than the street, and a 2' fence wouldn't be a fence at all. My guess is that any permitter or inspector leaves that up to interpretation, and that should be pretty clear.

Yeah, I do have to close the sidewalk when excavating...no way around that. I can get away with not closing it when building forms, but would have to close it again when doing the pour.

farnhamstj
05-30-2011, 10:48 PM
I have driven a bob cat a good deal. To answer your questions. You can lift the bucket to about 7' it is tippy when you to. You can not scoop and dump without moving the machine to another location. Trying to dig down with a bobcat doesn't work well. The force of the bucket edge driving downward just isn't that great. I think a mini-ex is maybe better suited for what you're trying to do.

Caribou Sandstorm
05-31-2011, 09:50 AM
You are correct, the code says 36" plain as day. What threw me was the foundation contractor telling me otherwise this weekend. I assumed someone doing this work for a living would know it off the top of his head, but perhaps he didn't understand my question. He may have been referring to footing width....dunno. And yes, I must have my wall permitted, stamped, and inspected. :( The wall itself will be 7' high at it greatest point (to bottom of footing), then a 6' brick fence on top of it.

24" is pretty standard for simple fencing depth. Like my black iron fence footers out front. For deck footers and retaining walls, I was also always told 36".

Once I used a post whole digger by my self and the thing got a way from me, spinning freely, that was a bit sketchy...Kind like a jump rope, you just gotta dive in and grab on..haha..back hoe would be way more fun!!

There is a place on South Broadway that rents that stuff...

OilHammer
05-31-2011, 02:43 PM
You know, maybe I have been thinking about this project all wrong. I'm going to wind up with 3' of "dead" space between my wall and the sidewalk because of where the property line is. I've noticed others building retaining walls all the way up to the sidewalk (in the ROW) b/c they use a engineered block that doesn't use mortar.
This has me wondering if I couldn't just build a similar wall and then dig the footing for the brick fence back at the property line. This would make the wall seem less tall, and give me some valuable planting space to break up the walls as well. Anybody know the rules on those "block" walls?

OilHammer
06-06-2011, 11:15 AM
Just got the thumbs up from the city to go ahead with the wall and 6' fence. I read the code just like everyone else to say that fences could only be 6' tall, but the "fence" is different from wall as they see it. Whew....thought I was going to have to go incognito on that one, and I have one nosy neighbor that would love to blow a whistle on me for anything he could. Old bag just needs to move on to his retirement home. (I've even played nice with him despite his rants about me moving the dumpster.

RockRunner
06-06-2011, 01:03 PM
glad to hear you got it all figured out. I have some guys that may be able to help you. PM me or call me 3o3- 8 2 9 = o7o3