Browse Forums Paving & Concreting 1 Oct 15, 2012 8:11 pm hi all after much back and forth we are finally deciding to attack our retaining simple question what is the best ratio mix for concreting in the retaining posts? we are building a meter high so obviously need to go a meter down been told 400 wide should be good enough can get hold of a cement mixer and it surely has to be cheaper compared to getting in a small truck load thanks quick pic Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Re: concreting in retaining posts 2Oct 15, 2012 8:20 pm Cement = 1 part. Sand = 2.5 parts. Stone or gravel = 3 parts. Have you checked to see if your council requires you to get a permit? The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: concreting in retaining posts 3Oct 16, 2012 8:01 am no permit to dig a hole ok poor attempt at humor all good thanks anything over 1 meter needs council approval in SA both walls are one meter, this is why we tiered them, otherwise its a two meter wall and council and engineers are required im going to start another thread on the whole process over in the appropriate area thanks for the ratio of mix thats one thing out of about 20 ive got to figure out Re: concreting in retaining posts 4Oct 16, 2012 9:34 am To things to make your life easier. 1.) Hire a dingo or kanga with a 30mm auger. 2.) At .12m3 per hole, you want to call in a mini mix. This is definitely talking from experience. This is a snipit from a tradies insight to building a retaining wall. These are not my words just a cut and paste. I couldn't find the actual thread but if someone can please post. When it comes to protecting the wall from groundwater (given you're dealing with typical hard to dig soils) have a serious think about using doubled over black builders plastic on the back of the wall instead of geotex (and go under the agi pipe, not over it). The filtration nazis and geo tech grade 3 engineers can have their post about filter socks and undies, what I know is what has proven to work for me and a lot of other chipy's. Cut the plastic off just before finished ground level or slip it between the top two sleepers. Combine this with descent drainage pipe and 1/4 minus screenings or scoria backfill and you shouldn't get water seepage and discoloration through your sleepers that leads to premature sleeper failure. For larger walls, areas with high rainfall or surface water problems a surface drain is also a good idea and can be set in mortar mix as shown below. A 45 degree 7-10mm chamfer on the exposed edge of the sleepers has nothing at all to do with engineering design, it simply makes sleeper walls look a lot neater as it hides the typical imperfections of sleepers not butting together neatly. After all they are not engineered LVL or biscuit joined... If you are going to lean your posts into the embankment (1:10) a simple way of ensuring each post is the same angle is clamping a bit wood onto your level as shown below and placing the clamp head on top of each post when installing the post in concrete (sit the clamp head on top of the post, not the timber block). How do you determing 1:10? - it's a trade secret that most building surveyors can't work out. For length of sleepers I tend to stick to 2m when using treated pine and walls above 300mm - it is more sound and increased cost is marginal in you buy 2.4 m lengths. It also allows dud ends to be cut out of the sleepers. If cutting the sleepers have a serious think about priming the ends with some "reseal". For a small wall without drainage problems don't worry to much about burying the lower sleepers as shown below (if you do, make sure you mark the height of your concrete footing on each post to suit the post embedment depth - this generally means a deeper footing to compensate). Most geo-engineers and surveyors don't understand this design or going to such lengths - probably because they never have to warranty their work against defect. Keep in mind you may have to dig some of the soil out and part burry the bottom row of sleepers if the gound is not level along the length of the wall and you want the wall level. If you use galvanised steel posts (which I would use on anything structural near a building) here's a couple of tricks: 1) dig all your footings to roughly the required depth then (take off your blouse &) dig a bit further (I normally bell out the bottom of the holes a little also). I then usually put a bag of rapid set in the bottom of each hole (you could use gravel or the like). If you use rapid set ignore the instructions on the bag for this step and mix it in a bucket with a fork to a fairly sloppy mix so it self levels - get it in the hole ASAP and level it if required. Run a string centre line above the holes to the exact height (and position) you want the wall. Measure the depth of each hole & take 20-30mm off this measurement and you have the length of steel post for each hole - if using timber posts cut them to measured length. I've seen blokes digging and back-filling for hours trying to get holes to an exact depth - it's for mugs. 2) tip 2 was mentioned above but for the sake of grinding steel or a crap finish I thouight it should be restated: if using gal posts get them cut 20-30mm shorter than the length you measured (again it makes the wall look neat) The reason for digging a bit deeper is three-fold. Firstly it lets you take your frock off and act like a bloke who doesn't give a toss if he's got to dig just a little deeper to make a good job of it despite the fact that: a) it will take an extra hour or two; and b) no-one will ever see your work. And the second Firstly, for metal posts it is to install a decent foundation pad and to get yor levels. And Firstly again it is to allow for another bag of rapid set in the hole to set the post in the required position with your level and string line/dumpy/laser line before filling the required depth with a structural concrete mix (follow the instructions on the bag this time). If you missed the point, each of these points is equally important. What I've gone through is the method I was taught that delivers proven results that stand the most improtant test of all - warranty insurance and time. Re: concreting in retaining posts 5Oct 17, 2012 4:50 am theoneandonly? anything over 1 meter needs council approval in SA both walls are one meter, this is why we tiered them, otherwise its a two meter wall and council and engineers are required I hope you are having the tiers at least 2m apart (see this link http://www.anewhouse.com.au/?p=1585 ) The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. Re: concreting in retaining posts 6Oct 17, 2012 5:51 am good call i wondered about this when we first excavated so looked into it i was worried that having them too close would result in more weight going to the bottom and pushing it out causing failure theres a couple of spots that arent quite two meters back from the lower wall but the excavator needs to come back to do a bit more digging for the driveway and remove an old septic system on the block so i'll be getting him to make sure the entire length of the top wall is two meters from the bottom wall. ill continue on about how im going etc etc in a new thread in the appropriate section of the forum Re: concreting in retaining posts 7Oct 22, 2012 9:51 pm ok so 200x100 posts at 1100 in the ground (allow 100mm for a bit of gravel at the bottom) 300 or 400 wide hole in diameter? again im hearing two different things when i ask a few people cheers Re: concreting in retaining posts 8Oct 23, 2012 6:15 pm This is a link to the design guide I quote on my blog: http://www.jimboombatimbers.com.au/Reta ... 0Walls.pdf The Harder You Try - the Luckier You Get ! Web site http://www.anewhouse.com.au Informative, Amusing, and Opinionated Blog - Over 600 posts on all aspects of building a new house. It will be neat but you won't have much freeboard. At least they are not weep holes. Are you in a high intensity rainfall region? The regulatory slope is only required… 3 8245 We've had decent weather for last 7 weeks and now the drvieway has been cut out we had an evening of 50mm of rain including all the water from half the street, ground is… 0 4461 Just get as close as you can without hitting the posts. Once you are close to the edge of the path the chance of cracking is minimised. 7 9146 |