L-shaped Retaining Wall Design Example

[Melany Odeh]

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.

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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.

A seat wall can add something very different to the every day patio design. It provides something vertical in what is otherwise a flat hardscape. In addition, different (but coordinating) wall materials can add even more interest.

Aside from their looks, they are functional also as theyprovide extra seating. More places to sit is not only a nice thing tohave, but since these hardscape features are typically located along thepatio perimeter, they do not take up much space. At times these smalllandscape structures can also be located where they divide aspace...such as a large patio into two separate areas.

Thepiers may have lights on top of them, urns with plants, or be leftsimple. Also, the walls can be planters. Leave a wide enoughborder/edging for sitting. This does necessitate the wall being muchwider. As an example, place 12" wide bluestone along the top perimeterof the planter, allowing a minimum of 12" planter space in width. The structure would then be 36" wide.

This was large garden overhaul with the aim to transform a sloping garden into two level tiers. The right-hand side offers not only a retaining wall but space to plant a herbaceous border and on the left, integrated seating.

This kit was designed for a customer. If you need a bespoke design that is for example curved or unique to your garden then just get in touch with us. The WoodBlocX team are happy to draw up and price your design for you (free of charge). Sending a quick sketch via email or by just giving us a call we can help you put your garden thoughts into reality.

* When building on soft ground your kit will include Ground Spikes to secure your structure to the ground - these are 400mm galvanised steel spikes that are installed through the first layer of your design.

** When building on hard ground your kit will include Angle Floor Brackets to secure your structure to the ground - these are galvanised steel L-shape brackets with 4 screws that attach to the first layer of your design. You will need to source a suitable fixing to attach the bracket to your hard ground type.

Our crop protectors are 16mm hollow steel rods with a natural rust finish which are used to create height-adjustable netted growing areas in raised beds (1200mm tall with a 40mm diameter sphere on top). Fixing brackets, adjustable collars and screws included per rod. We DO NOT supply netting.

Your WoodBlocX order will be delivered on a pallet and we can only guarantee kerbside delivery. If you are in a hurry for your WoodBlocX order please contact us (if we can, we will try to speed up your delivery).

You can select an estimated delivery date at checkout. Deliveries can be arranged from Mon to Fri between 9am and 5pm (except Bank Holidays). Saturday delivery slots are currently not available. Tools & liners ordered separately will be charged 12 for Parcelforce delivery so remember to include them with your WoodBlocX order!

We advise choosing a suitable delivery date a few days prior to the date you wish to start your WoodBlocX build just in case your delivery is delayed due to circumstances out of our control. Please DO NOT book a tradesperson to begin work on the day your order is planned to arrive.

When we dispatch your order from our warehouse we will send you full tracking details for your pallet. You will then be called by our delivery partner a few days before delivery to confirm your delivery slot/date.

Using our unique, modular system of interlocking timber blocks, WoodBlocX can be used to create almost any external landscaping structure. From rooftop gardens and retaining walls (max 1m) to street furniture and planters, our professional 3D design team can work closely with you to build a solution that works to your project budget and specification.

WoodBlocX structures are fast to build and require no foundations. Our pressure-treated timber blocks fit together with dowels and require no power tools or specialist skills to erect. Guaranteed for 15 years with fire treatment options, we only use FSC-certified Scottish Pine and are proud to manufacture WoodBlocX from our base in the Scottish Highlands.

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