Retaining Wall Key Design

[Nadal Braymiller]

Ourprevious 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.

The design 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.

Since retaining walls are often used in sloped areas to transform that part of the yard into usable space, consider adding steps to your retaining wall for easy access to the different levels of your yard.

Another way to make a retaining wall more functional is to include a doorway in the design. Either carve out an opening or add a rustic door to allow easy access between spaces. Frame the entrance with greenery for an added touch of whimsy in your garden.

For a rugged look, consider a retaining wall made from large boulders. In some cases, they can be less expensive compared to other options and complement a more rustic backyard. One of the biggest advantages of boulder walls is that they offer natural drainage.

Consider a retaining wall that incorporates oversized stone steps into the design. Flagstone, bluestone, and fieldstone are all popular choices among homeowners. Premium materials, such as slate or granite, add panache.

Consider a brick retaining wall to add classic charm to your front or backyard landscaping. Choose between traditional red brick (well suited for colonial-style homes) or a natural stone retaining wall that may look good with a craftsman exterior.

Tiered retaining walls are fantastic ways to dress up a hill or slope in your yard and make the space more usable. Walls like these also create greater possibilities for your garden design, opening up plenty of usable space for plantings.

A short stacked-stone retaining wall is the perfect complement for a prairie or native plant garden. Native plants have a distinctly wild look, so pairing them with natural stone creates more realistic imagery and a low-maintenance design.

Steel retaining walls offer a distinct look to a project, and the rust color from the materials can add an extra pop to a garden. In some ways, this landscaping idea embodies a farm or agricultural setting where steel barns and tractors are common. For this reason, steel retaining walls may look good if you like farmhouse-style decor.

Many retaining walls provide the perfect space to create a vertical garden. Stacked stone walls or block retaining walls make good choices for vertical gardens as they have plenty of nooks to tuck plants into. If you plan to create a vertical garden retaining wall, consider how much sun you expect the wall to get and be sure to integrate an irrigation system.

Consider crafting a retaining wall out of concrete planters. Use ridges to trick the eye into thinking that the series of planters is one elongated piece. The mix of natural and artificial elements is sure to make the scene pop.

A retaining wall that encircles different areas of your yard can help unify the space into a coherent whole. In this yard, the open-ended retaining wall distinguishes the shrubs, while spilling into the gravel of the patio for an easy transition.

Traditionally, rock gardens include a hearty collection of rocks (obviously) and alpine plants, which are plants that grow in a mountain climate above tree lines. If you opt for a rock retaining wall, consider including these types of plants in the design to emulate a mountainous garden. Popular alpine plants include Primula, Dianthus, and thyme.

Use lush greenery, or even plant a lettuce garden, to create a cottage-like feel, as well as Wicker-style retaining walls that add to the charm. Stacked worn rocks work equally well when paired with moss and native flowers that give nod to a fairy-tale backyard.

Elevation changes, big or small, can make a big difference in your landscape design. Adding a wee retaining wall to a yard that may not technically need one makes a statement and creates visual interest.

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