Browse Forums Landscape & Garden Design 1 Dec 30, 2008 8:29 pm Hi Guys,
Would love to hear peoples opinions on battering a timber cantilever retaining wall. I have to build two retaining walls in my back yard. 1. 15m long by 0.8m high. and 2. 10m long by 1m tapering to 0m high. Both will be built from Treated Pine and there is level ground above them (they will create terracing in my backyard) with no additional surcharge such as cars etc. The walls will be down hill from the house and all roof rain water will be captured and fed through sealed pvc pipe away from behind the walls. Ideally I would like to build the walls vertically, with proper drainage of course (aggregate wrapped in geotec fabric) and slotted pipe in the bottom behind the wall for further drainage. The timber will be treated pine sleepers 150mm x 75mm posts with 200mm x 50mm wailings. I will be orientating the posts so the long side is at right angles to the wailings....hope I explained that right.....basically the stongest orientation of the post will be holding the wailings back not the other way round as many documents I have read suggest. Now I have been told the rule of thumb is as follows:- * Vertical wall - Length above the ground should be buried in the ground. * 1 in 10 battered wall - 3/4 of the length above the ground should be buried in the ground. I as said, for appearance, I would much prefer to build vertically however all literature I have read indicates batter......but I am sceptical.....is it just timber distributors covering their backsides by over engineering their product in DIY brochures??? Would really appreciate your thoughts. Oh I intend to paint the treated pine to extend the service life and improve the appearance....I contemplated blocks but they are too expensive for my budget and as the walls face away from my house I won't really see them when the job is finished. Re: Retaining Wall Batter 2Dec 30, 2008 8:43 pm Vertical looks best, but will always shift slightly overtime... Nothing looks worse than a reverse batter wall!!
1/10 might be a bit steep... 1/20 could be a better option, but still bury the posts 1:1.. Electrical Engineer... Don't hold that against me... And keen owner builder... Mainly the building part!! Re: Retaining Wall Batter 3Dec 31, 2008 8:15 am chuth77 Vertical looks best, but will always shift slightly overtime... Nothing looks worse than a reverse batter wall!! 1/10 might be a bit steep... 1/20 could be a better option, but still bury the posts 1:1.. Thanks for the reply chuth77.......deep down I know there will be some movemoment over time but I just don't want to accept it and put batter on the posts it is so much easier to build vertically and, as we both seem to agree, the vertical apperance is far better. My next door neighbour has extensive retaining on his property (1m high, with vertical posts) and he has only set them 600mm deep and on top of that he has put black plastic behind them and then backfilled with a layer of rubble for drainage with no geotec cloth and no slotted pipe. The black plastic combined with the rubble becoming clogged with dirt fines has in effect created a mini dam during a torrential down pour........having said this it has been up for 10 years now and when I checked it with a level the other day (the wall is on our boundary in soft slushy soil) there was only minor reverse batter (maybe 1 in 50 maximum) certainly not noticable to the naked eye, I needed a level to detect it. I wonder if any of the other forum members have similar 1m vertical retaining walls that have been in place for a long period that could comment first hand on the walls performance.....I would certainly appreciate it. Re: Retaining Wall Batter 4Jan 02, 2009 5:25 pm the building standards to 1 mtr only are upright depth at min. should be 3/4 of the above ground wall height. and these walls generally fail in reactive soils. over time they generally move more than full wall height depth
for 1 mtr or below i install uprights at same height as expossed panel above 1 mtr i have my walls engineered to be expossed wall height plus 100mm per 200mm of wall ie : if the wall is 1.2 mtrs tall then the post etc is 1.3 mtrs down. depth and diameter of hole depends on what you are holding back scoria beam depth and width can vary, dont use black plastic behind wall, plastic can and does cause negative hydrostatic pressure and can make walls fail, but i have had several engineers recommend plastic against my recommendations as for fall back this also depends on what you are holding back, soils types etc as a general rule use 10/1 fall back when you back fill uprights will slightly flex forward reducing to around 9.5-9.8 / 1 fall back you wont really see 10/1 fall back on a wall Da Vinci Outdoor Living Architectural landscaping http://www.davincioutdoor.com Re: Retaining Wall Batter 5Jan 04, 2009 7:29 am Hi Davinci,
Thank you very much for your informative response I really appreciate it. I must come clean though I have actually been holding back some information. I have already taken a leap of faith and replace an old retaining wall on my western boundary that was standing in the way of my master plan of reshaping my backyard. I have made the posts vertical and have been sweating over the decision to do so ever since. I organised a bobcat and excavator to come onto my block to cut some levels and at the 11th hour I decided to go the whole hog and do the western boundary wall in the process....it made sense at the time as the guy was on site so I might as well go for it. He had an auger attachment on his excavator so I wanted to make maximum use of that and originally I did have batter planned for the posts but in the heat of battle (it was also the end of a very long hot day) the post holes did not end up in the exact place I needed them.....close but maybe 50mm ot 150mm out in some places. Well I thought I would scrape the walls and elongate the holes to where I wanted them and everything would be fine however when I started chipping at the holes it turns out they where in ground that was so hard the pinch bar would just bounce of it (the 3 1/2 excavator actually had trouble driving the auger in)......I spent litterally hours going flat out just to elongate one hole. This is when I made the decision to go vertically I figured if the ground was that hard the post would need to completely snap in half for the wall to fail. The posts are 200mm x 75mm Iron wood H4 sleeper with 200mm x 50mm wailings behind. Posts are spaced at 1200mm. I have gone with a "whats above the ground is in the ground theory however you will notice the bottom section of the wall is 1600mm high so I only have 1400mm in the ground since they where 3m posts. You will also notice that the last post (closest to the existing brick wall) is not spaced at 1200 this is because there was my neighbours sewer main right where I wanted to put the post so I made a last minute adjustment. Love to hear you opinion on how this wall will fair Davinci....please go easy on me though...what is done is done......I just hope I have done the right thing. Original Wall_1 http://i375.photobucket.com/albums/oo192/GottaMow/IMG_5027.jpg Original Wall_2 http://i375.photobucket.com/albums/oo192/GottaMow/IMG_5028.jpg Posts in position. We did open a can of worms the excavator operator and I when we started to dismantle the old wall as the neighbour had raised the level of his property and there was heaps of old rubble that kept caving in and caving in...my heart sank when we started as I thought I was going to end up with my neighbours entire yard in mine. Note the position of the neighbours sewer vent (sitting behind the second post in from the brick wall) the dirt height here is about 1m so really the wall only has to hold back the full 1500mm to 1600mm across three posts. http://i375.photobucket.com/albums/oo192/GottaMow/IMG_5179.jpg Semi finished wall....I am going to cap it with more 200mm x 50mm sleepers and paint it to improve apperance and longevity. The levels do step up and short part of the wall will end up at 900mm. My new walls (with batter) will create the level. http://i375.photobucket.com/albums/oo192/GottaMow/IMG_5229.jpg There is 200mm of 20mm recycled concrete gravel behind the wall wrapped in geotec cloth with a 65mm ag pipe in the bottom. http://i375.photobucket.com/albums/oo192/GottaMow/IMG_5196.jpg I also intend to place a colourbond fence on top so I put in some tubes I made out of the old fence corrugated sheets for when I want to concrete in the posts. http://i375.photobucket.com/albums/oo192/GottaMow/IMG_5233.jpg Thanks for taking the time to read my post...appreciate all comments postive or negative I can learn from both. Cheers. Re: Retaining Wall Batter 6Jan 04, 2009 7:37 am All looks like a pretty good job! And very sturdy... I assume the posts are concreted into position? Electrical Engineer... Don't hold that against me... And keen owner builder... Mainly the building part!! Re: Retaining Wall Batter 7Jan 04, 2009 4:49 pm chuth77 All looks like a pretty good job! And very sturdy... I assume the posts are concreted into position? Thanks for the compliment chuth77 I am pretty pleased with how it is coming together Yes the post are concreted in (1 Cement, 2 Sand, 3 Aggregate) Re: Retaining Wall Batter 8Jan 04, 2009 6:02 pm the depth should have been same as exposed and at that height out of h beam but the way you have orientated the uprights will help reduce flex
geotech is good scoria or 7mm beam should be min 200mm but as you said whats done is done but as long as your soil isnt highly reactive then you should be ok 1.2 mtr spacings will also help with flex reduction Da Vinci Outdoor Living Architectural landscaping http://www.davincioutdoor.com Re: Retaining Wall Batter 9Jan 05, 2009 8:40 am Thanks for the reply Davinci.
davinci scoria or 7mm beam should be min 200mm but as you said whats done is done but as long as your soil isnt highly reactive then you should be ok I used 200mm of 20mm recycled concrete behind the wall....I didn't even think of using scoria (never heard of it before) behind the wall. Do you think the recycled concrete will be ok? I have read the term "highly reactive soil" many times now....how do I determine if I have highly reactive soils or not??? I have ascertained that it is related to the amount the soil swells when wet and shrinks when dry but how do you identify such soil?? I know most of what I am holding back is old building rubble and a very sandy soil however at the very bottom of the wall on the 1600mm high section there is a band of the original soil about 400mm in height that is a firmer tan road base type of soil with some richer dark garden top soil ontop then rubble and sandy soil makes up the rest to finished ground level. Would the road base be considered reactive?? I have included a photo showing the soil bands. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Thank you again Simeon.. I will call my certifier for that. Have a good day 4 5188 Thanks for the insights, that makes perfect sense, and yeah, I will be leaning on the experience of the excavator operator entirely. 6 16147 Hi All, I engaged a tradie to install concrete retaining wall 600-800mm high over 32 meters in Victoria. Sleepers are 200*75*2000 mm installed over 17 steel posts. I… 0 6917 |