Browse Forums Landscape & Garden Design 1 Apr 01, 2009 5:20 pm When we purchased our block of land it had an existing retaining wall along 1 of the boundaries (which is next to a driveway to the house up the back of us). Now that we have done the site cut and basically finished building we needed to extend the height of the retaining wall. Our block is only 12m wide so don't have the luxury of doing a seperate stepped in wall so we thought we woud extend the steel by welding extra H channel onto exisiting H channe and insert more sleepers. Originally i contacted our (i work for a builder - doing admin) buidling surveyor & they said just extend it (at that stage it only needed to be 400mm higher) don't worry about permit, how would anyone know that it wasn't already the height it was supposed to be. Anyway, now parts of it have to be 800mm higher than existing wall......is welding going to be strong enough or can you suggest another solution???? Re: Extending the height of timber retaining wall 2Apr 01, 2009 7:38 pm 800mm is a fair extension. Any wall over 1 metre ( varies slightly between councils) must be engineered. Re: Extending the height of timber retaining wall 3Apr 01, 2009 9:15 pm I don't think the welding part of this project is your issue, welding a section on (if done properly) will be more than adequate. It is the depth the existing posts have been concreted into the earth that will be the show stopper. The rule of thumb is that what ever is above the ground should be below the ground. I have heard varying theories on this one being that with a 20:1 lean or batter then 75% of what is above should be below but either way if you are adding 800mm it is safe to say that you will simply not have enough existing meat in the ground to make the wall stable. You will find that most councils will let you go and build a retaining wall under a metre and anything above requires the blessing of an over priced civil engineer however the above rules of thumb still apply to walls under a metre it is not just a case of anything goes. Does the existing wall have a suitable drainage layer behind it??? all the research and recent personal experience says this is crucial especially considering you are thinking of adding more height and asking the wall to do more work. What is the height of your existing wall?? Re: Extending the height of timber retaining wall 4Apr 01, 2009 11:22 pm GottaMow and build a retaining wall under a metre and anything above requires the blessing of an over priced civil engineer Ahem....speaking as an "overpriced" engineer... Your other problem will be that if you whack another 800 mm of fill on top of the existing backfill your bottom sleepers may be overloaded (depending on original design). I doubt the wall is very high therefore one solution may be to weld your extensions on...and then drop another H-section in between the existing ones thereby reducing the span of the sleepers. The logic being that by splitting the span of the sleepers...and effectively halving the load on the old H-sections...so long as the additional fill does little more than increase the load to where it was before, the original H-sections should be OK...not bad for an "overpriced" engineer...all this is dependent on height of existing wall, distance between supports, signs of distress in the existing supports, the amount of fill, and drainage as discussed. Yes you will need an "overpriced" engineer to sign off on the revised design and they may need some "as-constructed" details on the embedment of the existing H-sections. Your case may be helped along if there is some record of the original design and inspection (maybe try council). Incidentally "overpriced" engineers generally have good public indemnity insurance so your can sue them if they stuff up...it's built into the "overpricing"...there's a reason for everything... mmm....donuts Homer Simpson 1956- Links: Site Costs Ready Reckoner | H1 Addiction Medical Advice | Château TDL: The Backyard Re: Extending the height of timber retaining wall 5Apr 02, 2009 7:56 am Ok I may have been a little harsh with the "over priced" comment my appoligies. I think your suggestions are very good especially the one about additional posts in between the existing ones this could be a very effective way to give the exisiting wall more capacity. I am still curious as to how high this wall is?? to use H beams in the first place would surley indicate a substancial wall?? Re: Extending the height of timber retaining wall 6Apr 02, 2009 4:13 pm GottaMow Ok I may have been a little harsh with the "over priced" comment my apoligies. No wuckas...I'm thick skinned... ...besides I serve the public now so I'm cheap... mmm....donuts Homer Simpson 1956- Links: Site Costs Ready Reckoner | H1 Addiction Medical Advice | Château TDL: The Backyard Re: Extending the height of timber retaining wall 7Apr 02, 2009 6:21 pm Thanks for the suggestions....the existing part of the wall where we need to extend the heighest is only about 200-300mm high already. Engineering isn't a problem, i have a friends husband that is an engineer so he has offered to do it.. looks ok to me, round logs retaining walls are better than sleeper walls, more even preservative treatment and stronger since they include the whole tree and not just part… 1 2605 Thank you again Simeon.. I will call my certifier for that. Have a good day 4 5196 If your patio is going to be 35 sqm then that's going to need Council Approval. The fact that they previously approved your 25sqm patio will be irelevant 1 5509 |