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Homeowner Forum / Construction / December 2005Loose rock wall, code issue questions
How high can you go with an unreinforced natural rock wall (random natural rock about 10 lbs each with moss on them etc.) The home owner has a narrow drive way with a sheer drop off on one side she had the drop off side filled with loose dirt by her gardener, and he built the loose rock wall to hold it as he filled. No concrete in the wall except a handful of mortar in spots. Maybe 10% of what it would take to mortar all the joints solid.) The wall is about 50' long, the rock 'wall' rests on a steep slope, and is angled in about 15 degrees.. the slope it sits on is at least 45 degrees. The wall is about 3' tall on the short end and maybe 8' tall or taller in the highest section. The dirt fill is brought up level with the drive way. Cars occasionally get a wheel onto it. Its a tight drive way. The rock wall may be starting to bulge. Its been in place about two weeks. No permit was pulled by the gardener or the home owner. I am asked to work on the wall. comments? Phil Scott > How high can you go with an unreinforced natural rock wall > (random natural rock about 10 lbs each with moss on them etc.) [quoted text clipped - 20 lines] > > comments? Any retaining wall that tall definitely needs to be permitted. It should be engineered or at the very least built by a stone wall mason with experience. A gardener doesn't cut it. How thick is the wall? What sort of provisions for drainage behind the wall were made? What's the soil like? There are a lot of variables. Mortar is not necessarily a good thing. People rely on mortar to compensate for a lack of stone laying technique - doesn't work. If the mortar crumbles the wall will lose its integrity. I think you have a nightmare on your hands. How to go about fixing it? Take it down and start over. If there were more room than you have on that tight driveway, you could build a more substantial wall in front of the existing. R >> How high can you go with an unreinforced natural rock wall >> (random natural rock about 10 lbs each with moss on them [quoted text clipped - 29 lines] >> >> comments? > Any retaining wall that tall definitely needs to be > permitted. It > should be engineered or at the very least built by a stone > wall mason > with experience. A gardener doesn't cut it. It would probably last for a while at least if no one puts a wheel on it. but thats not going to happen. Collapse mode will be slumping down the hill in a semi safe fashion., it wont be inclined to fall over. > How thick is the wall? The thinkness of the rock, which varies, but average 10" or so. The rock is not well fit at all. What sort of provisions for drainage behind the > wall were made? Good drainage Id say.. just under the top cover is some sort of real thick 'burlap' type material, dark brown about and 1/8" thick, dense, has long fuzzy stringers coming off it, shrubs planted through it, over the top 1" is loose potting soil. I was able to drive a thin aluminum rod down into the fill 3' no problem with just hand pressure. There are a lot of variables. > Mortar is not necessarily a good thing. People rely on > mortar to > compensate for a lack of stone laying technique - doesn't > work. If the > mortar crumbles the wall will lose its integrity. > I think you have a nightmare on your hands. How to go about > fixing it? > Take it down and start over. If there were more room than > you have on > that tight driveway, you could build a more substantial wall > in front > of the existing. Neither her or her gardener realize they have built a disguised tank trap there and that in that location cars putting a wheel on it could take it out and that she cant blame the car drivers for that... the driveway is steep, narrow, turns at the crest with no lights...the wall needs to be up to the job and per code... it isn't... she can see the city if she has any questions. Im going to pass on it and advise her to get it done right ...with permits for liability reasons. Phil Scott > R > "RicodJour" <ricodjour@worldemail.com> wrote in message > [quoted text clipped - 8 lines] > will be slumping down the hill in a semi safe fashion., it > wont be inclined to fall over. I wouldn't bet on that. The footing and tieback into the slope are critical when designing a retaining wall on a slope, as are drainage, climate and soil properties. There are a lot of factors that could cause it to fail. You're looking at a finished product and making assumptions about how it will fail. I took a soils engineering class in college - hated it. The professor was the guy who wrote the book, with a capital T. He'd tell the story about how there was an international soils competition to predict when an earthern embankment would fail. The top soils people from all over submitted their predictions. The numbers came back +/- 400%! The guy who won? He was a junior highway engineer in Virginia, who noted an embankment similar to the one in the competition. He loaded up the embankment until it failed and submitted his prediction. That sound like a hard science to you? > > How thick is the wall? > > The thinkness of the rock, which varies, but average 10" or > so. The rock is not well fit at all. For that height wall, I'd certainly want a much more substantial wall. She should have gone with interlocking block and a geogrid to tie it back into the slope. > What sort of provisions for drainage behind the > > wall were made? [quoted text clipped - 7 lines] > I was able to drive a thin aluminum rod down into the fill 3' > no problem with just hand pressure. So no compacting of the fill. Strike three! Yer outta there! > Neither her or her gardener realize they have built a > disguised tank trap there and that in that location cars [quoted text clipped - 6 lines] > Im going to pass on it and advise her to get it done right > ...with permits for liability reasons. Okay...the nightmare's on somebody else's hands. ;) R >> "RicodJour" <ricodjour@worldemail.com> wrote in message >> [quoted text clipped - 39 lines] > science to > you? too hard to predict soils under all the variables in the soil and with variable moisture content.. I have not done any civil engineering at all...so I missed all the red flags. Im sure this thing has no tie back at all. And the fill is loose, and the rocks easily dislodged. I will give her a list of the issues in a casual note and send her to city hall if she has any questions. >> > How thick is the wall? >> >> The thinkness of the rock, which varies, but average 10" or >> so. The rock is not well fit at all. > For that height wall, I'd certainly want a much more > substantial wall. > She should have gone with interlocking block and a geogrid > to tie it > back into the slope. I dont think her gardener speaks much english.. neither of them have much of a clue. She has a 10" square 20' tall post for instance supporting her front porch... one hell of a solid timber, it has a 1/2" chip near the base... she thinks its dry rot and wanted to know if it needed to be replaced. I think Im gong to steer clear of this lady. Who knows if I bump a rock in her wall and it jiggles she will want me to rebuild it... that sort of thing is common out here. Tiburon is the worst.. some guys won't even take calls from there. ultra rich, pro chizzlers with attorneys.. most homes in the 5 million dollar plus range in very steep terrain, hard to get a truck up there. I got a call from the areas largest real estate broker a few weeks ago, the receptionist was a bit ...er.. terse. She said they had a lot of business for me. I did one small job and told them to find someone else. Big money (if you can collect) but its mosty a nasty place to do business. A little dust on the floor and some of the people fly into a panic that you have 'ruined their floor' etc. the majority will then refuse to pay the bill, or offer you half etc... the tactics some of these employ are beyond belief. >> What sort of provisions for drainage behind the >> > wall were made? [quoted text clipped - 9 lines] >> 3' >> no problem with just hand pressure. > So no compacting of the fill. Strike three! Yer outta > there! Her plan will be to tell people not to walk on the fill... then if it collapses when they put a tire on it, or walk on it...blame them. I will tell her 'good plan... go to city hall and document it so you can have good grounds to sue for damages'... that will be exciting. >> Neither her or her gardener realize they have built a >> disguised tank trap there and that in that location cars [quoted text clipped - 10 lines] > > Okay...the nightmare's on somebody else's hands. ;) indeed.. thanks for the civil engineering insights. I didnt know about tie back etc and interlocking block... I will mention those and the other issues in my note to the lady. In this area such walls even short ones under 4' are built of heavy timbers with 10 x 10 redwood posts or larger angled into the ground to support the planking.. or are made of steel. the concrete ones you see on occasion are often tilting after a few years. You only see rock walls in gardens for decoration, usually under 2' and not holding much back. They tried decorative stone where they needed a retaining wall structure...... duhh. it went right past me. Phil Scott > R > Tiburon is the worst.. some guys won't even take calls from > there. ultra rich, pro chizzlers with attorneys.. most homes [quoted text clipped - 5 lines] > will then refuse to pay the bill, or offer you half etc... > the tactics some of these employ are beyond belief. I believe tiburon means shark in Japanese - maybe the residents took that to heart! This is an interesting site for fast information on the places you're interested in: http://www.city-data.com/city/Tiburon-California.html Have a Merry, Phil R > comments? > > Phil Scott i've read all the replies and your posts I think I would exclude the existing death trap there and just work her up an estimate, and of course explaining to her the benefits of doing it right. so far, you haven't said how you would have built it something to think about it sounds like you kneed a bobcat for a couple of days and widen the drive. hell, build her a good one, a straight one, with a footer under it. blow her socks off with a $9,200.00 estimate Merry Christmas another idea, instead of retaining the whole thing in one wall maybe have 3 successive walls, this way each one is not as big and it could look nice... >> comments? >> [quoted text clipped - 12 lines] > > something to think about Thats not my business... I dont do that kind of work and now I know why. > it sounds like you kneed a bobcat for a couple of days and > widen the [quoted text clipped - 3 lines] > > blow her socks off with a $9,200.00 estimate. Thats what she needs alright, what she has though is not too bad.. just not quite OK either. This whole area is like that. > Merry Christmas > [quoted text clipped - 3 lines] > big > and it could look nice... She is not going to want to spend the money..and she just loves her new mossy rock thingie... I just sent her a nice chatty email that points up the magnitude of the disaster and how she wont be able to blame anyone that puts a wheel on it ... if it collapses. I hate to see the illegal alien guy who built it get burned this way.. but thats going to happen. I hope she paid him already... maybe he was working under her direction.. in that case it would be her problem. The cost would have been a small fraction of what a legitimate retaining wall would have cost... so if she has to pay to do it right, there is not that much actual cash lost. Phil Scott > I hate to see the illegal alien guy who built it get burned > this way.. but thats going to happen. nah, it never happens like that. and it will probably never fall the appearance of things can be extremely deceptive, extremely. You could look at the leaning tower of pizza and say...dang, that thing is going to fall and who woulda thought, but there it stands. and...Ms Robinson will probably pay hulio to fix the tight spot where wheels can hit it. > > I hate to see the illegal alien guy who built it get burned > > this way.. but thats going to happen. [quoted text clipped - 4 lines] > > the appearance of things can be extremely deceptive, extremely. So you're telling the guy who eyeballed it that he doesn't know what he's looking at - this from the chair in your house. Good logic. > You could look at the leaning tower of pizza and say...dang, that thing > is going to fall > and who woulda thought, but there it stands. And without corrections during construction and major open heart surgery on the foundation, it probably would. The gardener's wall ain't the Leaning Tower. > and...Ms Robinson will probably pay hulio to fix the tight spot where > wheels can hit it. And what's he going to do? Undercut the already precarious slope the wall sits on? You gotta be kidding. R Accident waiting to happen, and you'll be pulled in as a culprit if you do any work on it.  SignatureJonny > > How high can you go with an unreinforced natural rock wall [quoted text clipped - 23 lines] > > Phil Scott > Accident waiting to happen, and you'll be pulled in as a > culprit if you do > any work on it. The understatement of all time... especially here in Marin County Calif. the entire thing is a complete disaster in every aspect... its too tall, rocks too small, no foundation (it will sink into the mud), and with soft dirt fill behind the wall. I sent her the links to some web sites with pictures and diagrams on how to do rock walls. Soon I will find out if she tries to claim that I bumped one of her rocks and have caused the entire fiasco... that will be tough for her though since it was built without engineering or permits and is clearly out code in all aspects.. its pretty though. Phil Scott >> How high can you go with an unreinforced natural rock wall >> (random natural rock about 10 lbs each with moss on them [quoted text clipped - 31 lines] >> >> Phil Scott > the entire thing is a complete disaster in every aspect... its > too tall, rocks too small, no foundation (it will sink into > the mud), and with soft dirt fill behind the wall. I sent her > the links to some web sites with pictures and diagrams on how > to do rock walls. well, for as much care as you have given a project that you don't plan to do Im sure you will do well on the ones you do plan to do. Researching a project before doing it, is always a good idea.(you know, if you're first time, or so doing something like that)... Don't think people wont drop 10 G on something like that either. it's all a matter of neccessity and importance to them. 50' is not too long...maybe 8,600 could get r done > > the entire thing is a complete disaster in every aspect... its > > too tall, rocks too small, no foundation (it will sink into [quoted text clipped - 8 lines] > before doing it, is always a good idea.(you know, if you're first time, > or so doing something like that)... Obviously you don't know Phil's background. You're preaching to the choir. > Don't think people wont drop 10 G on something like that either. > > it's all a matter of neccessity and importance to them. > > 50' is not too long...maybe 8,600 could get r done It's a loaded community, and a substantial wall. I'd think the price to do it right would be at least two or three times that. R >> > the entire thing is a complete disaster in every >> > aspect... its [quoted text clipped - 30 lines] > the price > to do it right would be at least two or three times that. In this area, with the conditions...to do it right. Id guess at least 20-30k to the standards on Bob Villa's web site.. those guys are serious about all of it, foundations, drainage and tie backs. Out here the plan often seems to be to chizzle the price to below cost, then refuse to pay, then call the contractor lying scum to his face for half an hour or so.... to see if you can taunt him into saying something regrettable..... then call your attorney with the tape recording...then sue anyone that even bumps the thing. An administrative solution so to speak. If the contractor stays cool and provides no ammo for the attorney then you get an offer of half pay with a threat to file against your bond..... or in the case of illegal aliens a threat to call imigration or the mafia. In my previous 40 years in business Id say I had less than 1/2 of 1% refused to pay or made threats. Out here in the not so rich areas its like that too. Pretty decent people. In the rich areas Id guess the percentage approachs 20 to 30% generally...and in some demographics (very very graceful people up front, gushingly graceful, thankful, appreciative, for days even, then near the end of the job... nit picky, then at the end a refusal to pay or you get the low ball offer)... in that demographic the refusal to pay is maybe 70% or higher. Nice houses though..... but in some older areas with serious dry rot problems. The homes are being sold that way too, with no mandated repairs as far as I can tell. The cheapest house sold recently in Mill Valley went for $570,000 a 500 sq ft hunting cabin (with no view) built in the 40's...featured on the tube, they mentioned dry rot I think also. Phil Scott > R >> the entire thing is a complete disaster in every aspect... >> its [quoted text clipped - 21 lines] > > 50' is not too long...maybe 8,600 could get r done "This old house web site says 20 to 25 dollars a sq ft of face area for rock wall.. this is maybe 300 sq ft or so... thats 6,000 dollars? Sounds low to me. maybe thats what she would of paid Julio though or even a little less since it has no foundation etc rock fill behind it etc.. she propbably paid him 3,000 dollars or so. No huge loss if she has to do it over. Phil Scott > "This old house web site says 20 to 25 dollars a sq ft of face > area for rock wall.. this is maybe 300 sq ft or so... thats [quoted text clipped - 3 lines] > him 3,000 dollars or so. No huge loss if she has to do it > over. If she paid someone $3K, she got what she paid for. She might not see it that way, but serves her right for trying to cheap out. Some people only learn the hard way. The $20-25/SF price is probably for a straightforward rock wall running on level ground. A retaining wall would require more strength and more dollars. Building a foundation that will support the stone wall and won't slip down the slope would cost more. Drainage, tiebacks, engineering, permit, etc. would add to the price. The swanky location would cost more. The 8' height would add more. R > "This old house web site says 20 to 25 dollars a sq ft of face > area for rock wall.. this is maybe 300 sq ft or so... thats [quoted text clipped - 3 lines] > him 3,000 dollars or so. No huge loss if she has to do it > over. If she paid someone $3K, she got what she paid for. She might not see it that way, but serves her right for trying to cheap out. Some people only learn the hard way. The $20-25/SF price is probably for a straightforward rock wall running on level ground. A retaining wall would require more strength and more dollars. Building a foundation that will support the stone wall and won't slip down the slope would cost more. Drainage, wall tieback, engineering, permit, 8' height, swanky location, etc. would add to the price. R Phil- Rico has given you good suggestions, but I'll bet based on your gut feel for this situation (the customer & the project) you were already leaning towards......... "run, don't walk away from this one" from the San Anselmo BD When a Permit is Not Required (Uniform Administrative Code Section 301; CBC 106.2; CMC 112.2; CPC 103.1.2) Though all the work must comply with the requirements in the codes, it is not necessary to obtain a building permit for construction, either new or replacement, of the following: SNIP Retaining walls supporting only level dirt and not over 4 feet in height measured from the bottom of the footing to the top of the wall. SNIP what footing? :) She's has built a "kinda crib wall" w/o the benefit of interlocking blocks, tie backs or What's down slope of the wall? paraphrasing the words of a famous American "you touch it, you own it!" cheers Bob Phil- Rico has given you good suggestions, but I'll bet based on your gut feel for this situation (the customer & the project) you were already leaning towards......... "run, don't walk away from this one" from the San Anselmo BD When a Permit is Not Required (Uniform Administrative Code Section 301; CBC 106.2; CMC 112.2; CPC 103.1.2) Though all the work must comply with the requirements in the codes, it is not necessary to obtain a building permit for construction, either new or replacement, of the following: SNIP ? Retaining walls supporting only level dirt and not over 4 feet in height measured from the bottom of the footing to the top of the wall. SNIP what footing? :) OK ok..thats their loop hole... it has no footing. so cant be measured :) She's has built a "kinda crib wall" w/o the benefit of interlocking blocks, tie backs or What's down slope of the wall? House is 15' away. paraphrasing the words of a famous American "you touch it, you own it!" She thinks I might have stepped on the top of the wall and dislodged a rock...and that might have shifted the axis of marin county relative to the moon, and that the resulting gravitational torque might be causing her wall to dislocate.....requiring Hullio to come out with his team and make it all right again. so now she has an email with links on how to build walls and advice to tell it the city building dept. Phil Scott cheers Bob > She thinks I might have stepped on the top of the wall and > dislodged a rock... well did you? i mean why bring it up heh heh heh you probably did >> She thinks I might have stepped on the top of the wall and >> dislodged a rock... [quoted text clipped - 4 lines] > > you probably did Maybe. I poked a couple of reflectors on long 1/4" aluminum stems into the fill dirt, I could easily have bumped one of the top wall rocks. Do you think that would take out a 50' wall? Phil Scott > "chickenwing" <bigbadbarry@adelphia.net> wrote in message > > [quoted text clipped - 9 lines] > the top wall rocks. Do you think that would take out a 50' > wall? Maybe. I read that a butterfly flapping its wings in Japan can cause Hurricanes in Florida. Maybe you're a butterfly, Phil. ;) R > Maybe. I read that a butterfly flapping its wings in Japan can cause > Hurricanes in Florida. Maybe you're a butterfly, Phil. ;) > > R there's a known fact with builders and cats how a cat can shake the whole house?...it's sort of a saying they seem to find the inner rythm of a floor and MAKE THE WHOLE HOUSE FALL! (it's a real problem) bullshit! bullshit! Barry Merry Christmas Phil goes > Maybe. I poked a couple of reflectors on long 1/4" aluminum > stems into the fill dirt, I could easily have bumped one of > the top wall rocks. Do you think that would take out a 50' > wall? how about.... put a stone/block knee wall at the bottom of the rocks (Next to drive) then widen the driveway on the other side behind you > Phil goes >> Maybe. I poked a couple of reflectors on long 1/4" [quoted text clipped - 11 lines] > > then widen the driveway on the other side behind you You missed the other issues... the wall is too tall to meet code, there is no footing trench. Its soft dirt fill ... all of that is *illegal, unsafe, and unstable...it amounts to a trap. The driveway by the way is at the top of the wall. the wall was put there because cars had been going off the edge occasionally. so now whats there is soft dirt backed by loose rock wall, at least 2' too too tall to meet code and with no tie backs... so that if a car goes off the cement drive onto the fill dirt, the wall will give way and the car will end up rolling through the ladies living room windows. In summary, the wall offers no support for the dirt load, especially as it turns to mud in the rain, hydraulic forces against the loose rock wall will be in the 500 to 1,000 lb per sq ft range, thats against each of the *loose rocks... the closer to the bottom of the wall you get the higher the pressure on the wall. add to that say half the wt of large car or truck and the wall gives way... loose rock is not structurally sound for a tenth that sort of load...it is good for a 12" high wall in a garden though. this wall is 8' at least for over 20'.. maybe 10 or 11' in spots... max for a rock wall, grouted, is 6.5'... this wall is NOT even grouted. Base of such a wall needs to be wide enough to support the load...base rock unless he doubled up which I doubt is about 10" wide..sitting on a dirt base prone to water saturation... a 10' tall section of rock say its 12" square for easy calculation purposes, is 12 cubic ft ... guessing at the density of the rock, to be 100 lbs per sq ft the load per sq foot on the mud is 1,200 lbs. thats 100 lbs per inch on the mud base. The mud is not going to hold that load.... the wall will start sinking unevenly in spots, that will distort the loose wall structure. The same rain that turned the narrow base to mud will also turn the soft fill dirt to mud, figuring that at 4x the wall load since its about 4' wide you get 1,200x4 for the hydraulic mud load against the base rock trying to push it out (since there is no base trench to hold the rock in even if it were fully grouted). Ok.. so thats 1200 x 4 or 4,800 lbs side load **per linear foot against the rock at the base of the wall....IF it all turns to mud. which it will probably not... so the actual side load against the base rock will probably be in the 4,000 lb per ft range. Now the question is will that move the base rock out instantly? No. It hasnt so far and its been a whole week already since the wall was installed. That pressure will be a constant wedging action against the wall over time... if it lasts a year it will be a miracle..if a car puts some weight on the dirt it will last maybe 20 seconds. Not bad... thats enough time for the occupant to jump clear if they are fast. ...adding to that mess with a knee wall just makes it more illegal, and more dangerous...but yes it would extend the life of the wall a bit, but would not reduce the net hazard. Phil Scott > ...adding to that mess with a knee wall just makes it more > illegal, and more dangerous...but yes it would extend the life > of the wall a bit, but would not reduce the net hazard. > > Phil Scott sounds like the rocks are the hazard not the ground alone.... sooo she looses some dirt..but..that can be maintained until such a time that she is willing to pay 30G to have it done right mhmmm > sounds like the rocks are the hazard > not the ground alone.... i mean to say... the rocks have created their own set of problems throw the rocks down the hill? In a previous post Phil Scott wrote... > No permit was pulled by the gardener or the home owner. I am > asked to work on the wall. > > comments? Phil: I think you already answered your own question. Run, don't walk, away from this potential nightmare. The work should have been done with an engineered design, probably using modular blocks and geogrid fabric -- think MESA block or similar type product. Another option might be some sort of soldier pile wall. I wouldn't touch the design of this wall without some geotechnical engineering to determine the design parameters. This is because of the steep slope below the wall. You want to make sure the supporting soil is stable. The wall as built is going to collapse. It's only a matter of time and the right amount of rain and the right load (or no load for that matter). Or the right earthquake. As I'm sure you know, retaining structures are subject to seismic loads. If the local building department has any guts (and smarts) they will "red tag" this wall ASAP to force the owner to get a proper design. This thing is a definite risk to life safety. SignatureBob Morrison, PE, SE R L Morrison Engineering Co Structural & Civil Engineering Poulsbo WA I thought I remembered one of the earlier posts saying the hill was about 45*. I am not saying that it is safe, serviceable, or anything else. I am wondering if the "wall" functions as a retainer at all or as a hardscape. I would think it has much more to do with the angle of repose for the base hillside material. Hydrostatic pressure should have little or no force on the loose wall. If the hillside exceeds the angle of repose, the entire hillside may well slide downhill, but I think this would be a different issue. IMO Phil did not indicate that the rocks and fill dirt were installed as a retaining wall. Unless large quantities of driveway fill was imported and added or a major cut was made in the existing hillside, has mother nature been changed? I would want more information about the pitch of the hill. If the whole deal smells bad to a contractor, he should follow his gut reaction. Enough projects get squirrelly without taking on something that does not feel good at the outset. (top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) dgriff237@7cox.net > In a previous post Phil Scott wrote... >> No permit was pulled by the gardener or the home owner. I am [quoted text clipped - 34 lines] > This thing > is a definite risk to life safety. > I thought I remembered one of the earlier posts saying the hill > was about 45*. I am not saying that it is safe, serviceable, or [quoted text clipped - 11 lines] > hillside, has mother nature been changed? I would want more > information about the pitch of the hill. Phil said, "The driveway by the way is at the top of the wall. the wall was put there because cars had been going off the edge occasionally." and "The wall is about 50' long, the rock 'wall' rests on a steep slope, and is angled in about 15 degrees.. the slope it sits on is at least 45 degrees." The wall is sitting on a slope, is built with a slope and the load is on top. This in California... What was that song from MASH? Suicide is painless. I wouldn't want to visit a house that had such a situation, much less live in it. > If the whole deal smells bad to a contractor, he should follow his > gut reaction. Enough projects get squirrelly without taking on > something that does not feel good at the outset. Right. R >I thought I remembered one of the earlier posts saying the >hill was about 45*. I am not saying that it is safe, >serviceable, or anything else. The wall is almost vertical.. at the time I wasn't measuring so I dont know the exact height at the highest, but it is probably well over 8' or 10' in the middle section, 20' or so in length at that height..it could be higher probably not over 15'... thats a disaster waiting to happen. > I am wondering if the "wall" functions as a retainer at all > or as a hardscape. I would think it has much more to do > with the angle of repose for the base hillside material. > Hydrostatic pressure should have little or no force on the > loose wall. Yes water will leak out of the wall so is not a factor as pure water...mud though... that wont leak... and mud is half water, dense, heavy and produces 'hydrostatic' loads. If the hillside > exceeds the angle of repose, the entire hillside may well > slide downhill, The loose dirt fill behind the wall is about 4' wide at the top, and zero ft wide at the bottom, the wall angle is maybe 5 degrees max. Behind the fill is the original solid ground with a concrete driveway poured on top..thats been in place for decades. but I think this would be a different issue. IMO Phil > did not indicate that the rocks and fill dirt were installed > as a retaining wall. Yes its installed as a retaining wall... the gardener just did the gardening thing but took it up 10' or whatever. Unless large quantities of driveway fill was > imported and added or a major cut was made in the existing > hillside, has mother nature been changed? I would want more > information about the pitch of the hill. The attempt was to fill a vertical drop from the driveway with some dirt so that when cars went wide they didnt chance going over the cliff into the front yard of the owners house just below. The drive is concrete, curved at the crest and 10' wide. > If the whole deal smells bad to a contractor, he should > follow his gut reaction. I am not a civil dood, I wasnt paying attention to the wall at all..it looked natural enough just sitting there until the lady mentioned it had just been installed and got all whinny about a loose rock on top... thats when I posted and began searching the issue on the web.... its been an education. > Enough projects get squirrelly without taking on something > that does not feel good at the outset. Indeed, ignoring the gut instinct is always a mistake. Phil Scott > (top posted for your convenience) > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [quoted text clipped - 42 lines] >> design. This thing >> is a definite risk to life safety. > Indeed, ignoring the gut instinct is always a mistake. Yes, and it can be less than a Charmin one. ;) R In a previous post DanG wrote... > I thought I remembered one of the earlier posts saying the hill > was about 45*. I am not saying that it is safe, serviceable, or [quoted text clipped - 10 lines] > imported and added or a major cut was made in the existing > hillside, has mother nature been changed? A 45° ground slope is very steep and generally indicates a the presence of small grain size in the soil or a high clay content. Most granular soils won't be stable at more than about 30° or so. That's why grading plans typically call for slopes to be 2H:1V (26.6°) for slope stability. Having said that, the pile of rock does act as a retaining wall as soon as fill is placed against it. In this case the wall is not stable, especially not during a seismic event, and most probably not in the event of heavy rains. The wall should be torn down before somebody gets hurt or worse. SignatureBob Morrison, PE, SE R L Morrison Engineering Co Structural & Civil Engineering Poulsbo WA > In a previous post DanG wrote... >> I thought I remembered one of the earlier posts saying the [quoted text clipped - 41 lines] > The wall should be torn down before somebody gets hurt or > worse. Great info as usual Bob...I hadn't considered the seismic situation, its good to know the slope issues as well. The lady hasn't responded at all to my emails with links to Bob Villa's superb web site on the issues...he has great diagrams. ..she was going to have her gardener call me about the rock I bumped but...dang...no call yet. I had advised her extensively to call a civil engineer on the situation.. of course as soon as he or she goes out there and fails to report it to the city the civil engineer becomes liable for life along with his heirs. I wonder if they will tell her that when she calls? I told her that if someone goes over the edge and she tries to put a claim in with her insurance that they would probably refuse to pay since she has built what appears to be solid ground but is actually more like a tank trap. I won't mention the possibility of a car turning into a ball of fire as it tumbles though the living room just yet... one would not want to upset the lady, especially since she was so concerned that I bumped one of her rocks ...and now Lope has to come out and put it back like its supposed to be. Phil Scott > In a previous post DanG wrote... > > I thought I remembered one of the earlier posts saying the hill . That's why grading plans > typically call for slopes to be 2H:1V (26.6°) for slope stability. > > Having said that, the pile of rock does act as a retaining wall as soon as > fill is placed against it. In this case the wall is not stable, > especially not during a seismic event, and most probably not in the event > of heavy rains. This thread reminds me of Ben Lomond, Ca. when they had their slide (Love Creek) in '82. Killed more then a few people and the slope was less then what's described here. Whole damn side hill went down after 20+ years of "stability". http://www.santacruzsentinel.com/archive/2005/January/13/local/stories/02local.htm I take special note of Bobs reference to; A 45° ground slope is very steep and generally indicates a the presence of small grain size in the soil or a high clay content. Most granular soils won't be stable at more than about 30° or so. I've seen to many drives in the Santa Cruz mountains 'just disappear' one day after some rains & small quakes. Run! Dan > The wall should be torn down before somebody gets hurt or worse. >> In a previous post DanG wrote... >> > I thought I remembered one of the earlier posts saying [quoted text clipped - 19 lines] > 20+ years of > "stability". Ha! Amazing. I met a babe in Honollulu who came back to LA with me in 1982..., she hated LA so I gave her my credit card and told her to find a place she liked... she ended up in Ben Lomond and rented the Smothers Brothers old house next to Love Creek... but up on the hill on the other side of the road about 20' fortunately. She called me in LA a few nights later...all upset saying that houses and refrigerators cars and dead cows were washing past the front door... I had no idea how bad it was. She never forgave me for that and began stocking the upper shelf kitchen cabinets with 90 proof white lightening from North Dakota in case it ever happened again. Phil Scott > http://www.santacruzsentinel.com/archive/2005/January/13/local/stories/02local.htm > [quoted text clipped - 15 lines] >> The wall should be torn down before somebody gets hurt or >> worse. Phil, That is funny! Unfortunately, most of the Santa Cruz mtns. are just like Ben Lomond with a lot of buried clay. Hence, enough water goes a looooonnngggg way. I've had to dig out more then a place or two cause the hillside came/went down............Course if you build on 10+ degree slopes......... Dan > Ha! Amazing. I met a babe in Honollulu who came back to LA > with me in 1982..., she hated LA so I gave her my credit card [quoted text clipped - 6 lines] > houses and refrigerators cars and dead cows were washing past > the front door... I had no idea how bad it was. > Phil Scott |
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