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The importance of soil

Thursday, July 16th, 2009

The soil on your site is a critical aspect to your retaining wall project. Among the ways your soils can affect your overall project cost are:

  • Geogrid Requirements
  • Increased Effort to Compact
  • Cost of Importing Additional Material and Removing Existing Soils

A wall built in clay will have an increased need for geogrid when compared to the same wall build on a sandy site. This is because clay will “push” on the wall more than sand. This geogrid will be used to create a mass of soil large enough to overcome these forces.

Clays and silts resist compacting due to the shape of each grain of soil. They to trap water more and make proper compaction more labor intensive. It is important to achieve proper compaction to reduce future settlement and to increase the stability of the reinforced soil mass. To achieve the required compaction, you may need to compact more frequently with smaller lifts of soil, or use specialized compaction equipment.

When your site does not meet the minimum requirements suggested on the Working with Soils page on the Allan Block website, it may be required to remove the existing soil from the site and use select fill for the area within the geogrid. You may also find it necessary to increase the width of your base to compensate for poor soils under the wall.

If you have questionable soils on your site, please visit our website at allanblock.com for suggestions and recommendations. It will also be important that you contact a local engineer for help designing your retaining wall.

Tom

Posted in AB FAQs, Commercial Retaining Walls, Landscape Retaining Walls | 1 Response »
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Finishing your Allan Block Wall with Style

Thursday, April 23rd, 2009

Finishing your Allan Block Wall

Finishing your Allan Block Wall

Landscape design options are endless and finding the right one to fit your landscape can be a lengthy process. When designing your retaining or landscape wall, how you top off or finish your wall can change the look and feel of your landscape. Need some ideas on how to put that finishing touch on your Allan Block retaining wall? You can find some great ideas and instructions on finishing options that are sure to fit the design and style of your landscape on the Allan Block website. So check them out, find one that works for you and be the talk of the neighborhood with your beautiful landscape!

Danelle

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Planning and Estimating your Segmental Retaining Wall

Tuesday, February 17th, 2009
Planning and Estimating

Planning and Estimating

Our backyard wall was going to be a big project for a small backyard. We needed to have a staging plan for all the material, but before that we needed to estimate the project and figure our budget. The first step in building a retaining wall is to make a plan. A good plan will lead to a good project. To start, figure out how much grade change you are working with. In our case we had around 7 ft. We decided to cover this height with two terraced walls. But how tall should each wall be? We decided the lower wall should be about 3 ft tall for easy access for planting and gardening and the upper wall should cover the rest of the grade change and be as close to the property line as possible.

Now that we knew the rough wall height and wall length (property line length) we used the incredibly easy AB Landscape Estimating Tool that we downloaded from allanblock.com. It works in Microsoft Excel which most people have on their computers. When using this great tool, I had to remember to add a little to the wall height for the buried block. You can also use this estimate to calculate the amount of wall rock and infill soil you will need. Don’t forget to consider equipment rental such as a skid steer, plate compactor, diamond saw and maybe even a wet saw for cutting caps at the end. It all adds up and if you plan ahead you will limit the surprises to your budget during the process.

Staging & Site Preparation

Planning and Staging

How about staging the material? I think a lot of do-it-yourselfers like me, forget that with a project of this magnitude you need to store/stage a lot of material. Our project had 23 pallets of Allan Block, 3 truck loads of washed wall rock and 1 truck load of sand, drain piping and geogrid. We also had to have a place to store the spoil, or the earth that we removed

during the excavation of the hillside. This was a huge pile that was there from day one until the end of the project when it was used as topsoil backfill. Because we had a good plan for all the material and spoil, the neighbors were surprised we had space to actually build the wall!

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Do you want to build your own Segmental Retaining Wall?

Wednesday, February 11th, 2009

Curved Walls

Curved Walls

I wanted a nice straight wall, no problems, just stake a working line in the ground and start building. But my wife wanted nice flowing curves. Look who won that discussion! Here are the two Allan Block Europa curved walls we built in our backyard. WE decided that it would add a lot of character to the walls and backyard if they had gentle curves instead of simply two straight walls. In the end, they turned out fantastic and transformed our backyard from a space we didn’t spend much time in to a place we don’t want to leave. The walls are parallel and have symmetrical inside and outside curves from one end of the property to the other, about 90 ft (27.5 m) each. At the center of the yard the walls bow away from each other forming a larger “Eyebrow” that is the centerpiece of the landscaping.

  • How do you start planning and estimating?
  • How do you prepare your site for construction?
  • Where do you store the product as you are building?
  • How do you lay out the leveling pad and start the base course?
  • How do I build a wall with a pattern?
  • Do you have to cut the blocks to make the curves?
  • How do you fit the caps in place?

Wow, there is a lot to consider when you are going to build a wall and this is just a short list. In the next few weeks I will take you through a very detailed, easy to read book that Allan Block has on their website called Landscape Walls by Allan Block. I will do so by telling you the story of my wall construction, starting with a good plan, a sound design and finally with a lot of help from my friends and family, to the building.

We will get down to business with my next blog called Planning and Estimating your Segmental Retaining Wall.

Rich

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Can I Use a Simple Gravity Wall?

Friday, December 12th, 2008

The question often comes up whether a wall can be built by just stacking block using the installation recommendations found on the Allan Block website, or if geogrid reinforcement is necessary behind the wall. Every time this question is asked, four equally important issues need to be addressed: how tall is the retaining wall, what is going to be above the wall, what type of soil will be behind the wall, and what type of block is being used?

To help simplify this decision, take a look at the Maximum Gravity Wall Height Chart on the Allan Block website. This handy chart can give you an idea of the maximum wall height for a variety of situations. The AB Commercial Wall Manual also describes the fundamental principles of gravity walls and how to build them using Allan Block retaining wall blocks.

How tall is the retaining wall?

AB Ashlar Blend Pattern

AB Ashlar Blend Pattern

This is an important question to answer because the taller the segmental retaining wall (SRW), the more soil behind the wall is going to be trying to push the wall forward or tip it over. This is called the wall’s external stability. In order for a gravity wall to work, the weight of the block and crushed stone within the block must be greater than the forces pushing against the wall.

What is going to be above the wall?
It is intuitive that a landscape wall with a level planter bed of flowers above it would have less force pushing on the wall than if you were building a retaining wall to hold up your driveway, but what about a slope above the wall? When your wall has a slope above it, there is more weight above the wall trying to push the wall over. What another wall above, forming a terrace? True, you might only have two 3-foot (0.9 m) walls, but that top wall of the terrace is going to be pushing on the bottom wall. In summary, any time you have a surcharge (some type of additional weight) above the wall, your overall gravity wall height will be reduced.

What type of soil is behind the wall?
Clay soils are going to push against the wall more than granular sandy soils. This is because a typical clay soil has a lower internal angle of friction than a sandy soil. By clicking the link above, the AB Commercial Wall Manual may be reference to learn more about soils and their influence on the wall.

Which Allan Block retaining wall block is being used?
A wall made from AB Stones will tilt into the hill more than a wall made from AB Classic blocks. This is because the AB Stones have a setback of roughly 12-degrees, while the AB Classic has a setback of about 6-degrees. Therefore, under the same conditions, a gravity wall constructed from AB Stones will have greater stability than a wall built using the AB Classic.

Next time you are planning your landscape or retaining wall project, keep these four questions in mind. Then, reference the Allan Block website to assist in designing a gravity retaining wall that you can enjoy for a lifetime.

Tom

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