Design Of Retaining Wall Pdf

[Laurence Jabali]

Thedesign process for a segmental retaining wall typically has a Wall Design Engineer or Site Civil Engineer responsible for the wall design envelope. Geotechnical engineers should be hired to evaluate the overall stability of the site. For information into the basic concepts behind an Allan Block retaining wall design see page 18 of the AB Spec Book and Best Practices for SRW walls.

Our previous article, Retaining Wall: A Design Approach discusses the principle and concept behind and when and where to consider a retaining wall in our design. We have learned the different checks against the mode of failures in the retaining wall should be considered in the design. To further understand the designed approach, here is a worked example of the design of the retaining wall.

This example is intended to be readily calculated by hand although a lot of structural spreadsheets and software such as Prokon are available. The purpose of this article is for the reader to fully understand the principle behind it.

The next thing to consider is the assumptions that we can make in terms of the geometry of the retaining wall that we are designing. Given the height, H of the retaining wall, we can assume or counter check our initial design considerations should at least according to the following geometric proportions:

Sketches of the retaining wall forces should be considered to properly distinguish the different forces acting on our retaining wall as tackled in the previous article, Retaining Wall: A Design Approach. Based on our example in Figure A.1, we have the forces due to soil pressure, due to water and surcharge load to consider. Figure A.3 below is most likely our analytical model.

Considering the Figure A.3, we can derive the following equation for the active pressures, Pa and passive pressure Pp. Notice that the pressures acting on the wall are equivalent to the area (triangle) of the pressure distribution diagram. Hence,

There are two checks to consider the stability of the retaining wall. One is the check for an overturning moment and the other one is the check for sliding. The weight of the retaining wall including the gravity loads within it plays a vital role in performing the stability check. Refer to Figure A.4 for the mass or weight calculations.

The sliding check should be carried out with reference to the Figure A.4 diagram and considering the summation of vertical forces for resisting force and horizontal forces for sliding force conservatively neglecting the passive pressure, hence:

The foundation bearing capacity usually governs the design of the wall. The soil, particularly under the toe of the foundation, is working very hard to resist the vertical bearing loads, sliding shear, and to provide passive resistance to sliding. The bearing capacity of the soil should be calculated taking into account the effect of simultaneous horizontal loads applied to the foundation from the soil pressure.

For the footing to be safe in soil pressure, the maximum soil pressure under working load shall be less than the allowable soil bearing capacity. The maximum soil bearing pressure under the footing considering 1m strip is:

The presented calculations above are actually too tiring to perform manually especially if you are doing a trial and error design. Thanks to structural design soft wares and spreadsheets, available nowadays, our design life will be easier.

What do you think about this article? Tell us your thoughts! Leave a comment on the section below. Subscribe to our newsletter to be updated with the latest posts or follow us on our social media pages on the below icons.

Thanks for pointing out. We have checked and found out that that is merely a typo error and it has been updated accordingly. We have also double-checked the attached spreadsheet and it is not affecting the results as we conservatively neglect the effect of passive pressure in the calculation.

Also ,would you be able to explain how is the d in critical shear calculated ? number 1.044 is used for similar triangles,however I struggle to find exact theory how you arrived to this number as I get different.

we have to learned the different checks against the mode of failures in the retaining wall should be considered in the design. Here some worked examples of the design of the retaining wall are described.I like the I have also found this resource Rfmasonry.co.nz useful and its related to what you are mentioning.

Hi Ruben, you can actually put your own logo on the space provided. Either editing some option setting on your excel or typing your company name on it. If none of these options are working, do it manually. Once you finish the design, convert the file to pdf and paste your logo from there.

Thanks, Aaron for pointing it out. We have checked and found out that that is merely a typo error and it has been updated accordingly. We have also double-checked the attached spreadsheet and it is not affecting the results in the calculation.

There is also a comment earlier about a typo of MoT = 57.91, the figure was right at 60.02, the weight of section 1 was not added to the equation. Though all of these moments are taken from the top of the toe and not the furthest point, thus moments are not accurate.

sir, Thank you for your valuable information. this is very much useful and one more plea that can we have any examples for considering wings & returns with head wall can be treated as a retaining wall any such kind of examples please post to mail if any thanks in advance

The shear strength is based on an average shear stress on the full effective cross section (bw x d). In a member without shear reinforcement, shear is assumed to be carried by the

concrete web. In a member with shear reinforcement, a portion of the shear strength is assumed to be provided by the concrete and the remainder by the shear reinforcement.

Thank for this detailed design to follow; It has been very helpful. One thing I noticed is that the calculation for the wall stem does not match the value you then indicated for the moment when checking for wall stem flexure. You have listed that Mu=19.40KNm again for tension, but the calculation comes out to the 29.33KNm you used. I believe it was just a typo but it made it a bit confusing to follow then. Thanks again, and God bless.

I have a site model built with survey data between approx 45.6M (45600mm) and 51.6M (51660mm). All design layer levels are all at Z:0. I am now in the processor of adding terraces in 3D space and associated retaining walls.

From the 3 walls, I have created a retaining wall site modifier. On the inner (terrace) side, the retaining wall is offset:0 below wall top. On the outer (grass) side, the site modifier follows the terrain.

On creation of the site modifier, I can see that the site modifier has gone wrong, or is not as I would have expected. The pad offset and side that follows wall top would appear to be correct (pad offset at 46725 [bottom of wall] and right modifier edge elevation at 48225 [top of wall]), but the side that followed the terrain has a modifier edge at 0.

Updating the side model to reflect the retaining wall modifier predictably goes horribly wrong, with the outside edge being incorrectly forced at 0 elevation rather than somewhere between 46725 and 48225 depending on the terrain.

I cannot seem to fix this. Setting the elevation of the outside modifier edge to within the expected bounds simply shows a flat line - so it has not followed the site model but simply offset by 46725. So I cannot fix the issue.

This only appears to affect the creation of the retaining wall side modifier when the follow terrain option is used. If I set if as an offset from the wall, it works as I would expect, but not how I need.

Thinking that this might be an issue with having the level data at 50000 or so and design later Z at 0, I tried this on a simple test model. The result was correct and as I would have expected. So it is something to do with this file/model.

I hope that its user error that I can fix, but I cannot find anything obviously different between this and the text model other than complexity. I cannot even find a work around and am basically stuck. If I convert the pool terrace to a pad, which I will eventually do, the modification to the site model is not as desired, so it needs the retaining wall modifier to follow the site model data to achieve the correct result.

Thanks for the suggestion but unfortunately it did not work. It was really odd but I could not send to the surface. Maybe a clue to the underlying issue, but if I have created only one site model, would you expect send to surface to give me the option of sending to 'site model' and 'site model-1'? I tried sending to both but either way, no joy.

I found that the result seemed to be dependant on either class or layer visibility - I think layer visibility. I had the site model on its own layer and when I was in 2D I had turned this layer off. I also had two saved views, which changed the working layers and class/layer visibilities. As a belt and braces approach, after I had set these all to all visible and show/snap/modify others I found that the edge modifier that followed the terrain came to within expected values. However, the whole site modifier got shifted about 12m off from its correct position and could only be fixed by restarting VW. Also, whilst the terrain modifier did follow some terrain, it was not the correct terrain as part of the model exceeded the height of the retaining wall. So I could not even move the site modifier back to its correct position. Something is definitely not right - this shifting should not be happening at the very least, but without being able to recreate the issue with a smaller model and a few steps, its not going to be worth submitting a bug, especially with me being on VW11.

What I did end up doing in the end was taking your suggestion of creating a 3D polyline, sending it to surface and turning it into a site modifier. Visually the results look correct although I suspect that cut and fill calculations are way off.

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