All posts tagged Retaining Walls in San Francisco

Retaining Walls in San Francisco? Watch Closely When El Niño Starts Up Again

El Niño

Effects of El Niño on San Francisco retaining walls

When El Nino hit this year, you may have been looking forward to it. After all, it’s rain – albeit a lot of it – on ground that badly needs the moisture. What you may not have expected, and what some homeowners obviously didn’t expect, is the strong storm taking down the San Francisco retaining walls that hold the hilly landscape at bay.

A lot of the problems we’ve had here in San Francisco this year have been small compared to the two Bay Area homes affected by sliding hillsides at the end of January. However, retaining walls failed all over the city because of the rains. -And now the El Nino, although it’s one of the strongest in history, is on pause.

Rather than breathe a sigh of relief that everything held, now is the time to really take a look at your property. If you have retaining walls (and what San Francisco property doesn’t?), you need to have them checked to make sure they’re still doing their jobs correctly.

Why Do San Francisco Retaining Walls Fail in Rain?

It’s often believed that San Francisco retaining walls fail because of the pressure of all that earth being held back. After all, the Bay Area is just one big hill, right?

That’s far from the truth, however. It’s actually water – not dirt – that is the biggest culprit for knocking down retaining walls. More specifically, it’s water combating a wall with improper, or no, drainage.

When a retaining wall has proper drainage, water slowly seeps out, keeping pressure on the wall down to manageable levels. Without that drainage, however, water builds quickly behind the wall, causing hydrostatic pressure.

Hydro means water, and static means non-moving. So hydrostatic pressure is the pressure against the wall caused by standing water. To understand how this principal works, you can take a full cup of water and stick your finger in it. The pressure of the water against your finger is hydrostatic pressure.

The resulting additional weight of the water against the wall – with no outlet because of poor drainage – causes structural damage. In some cases, it causes cracks or buckles as the water forces its own seep holes into the wall. In other cases, it brings the retaining wall down, along with the soaked ground behind it.

Is Your Retaining Wall Failing?

Is there a way you can tell if your retaining walls are… well, retaining? Are they doing their job? Luckily, your wall doesn’t have to be horizontal to tell if it needs repair. Here are a few warning signs that your retaining wall may not stand up much longer:

  • Non-weeping weep holes – If your retaining wall has little holes in it, and those holes aren’t seeping after a rain (particularly a heavy rain), this is a sign that the drainage behind the wall is either inadequate or blocked.
  • Pregnant walls – If your retaining wall looks pregnant about a third of the way up, this is a sign that it may not hold much longer. Another good hard rain may be all it will take to knock the wall down.
  • Cracking walls – If your retaining walls have cracks, especially if the cracks are deep, long or wide, it’s a good indication that they need repair.

Repair or Rebuild Your Retaining Walls?

If your in San Francisco retaining walls are showing one or some of the signs above, it’s time to have them inspected by the professionals. However, none of these signs are definitive signs of doom; it may not take a complete rebuild to fix the problem. Luckily, there are several ways to repair a retaining wall without starting from scratch.

Tamate Landscaping will work with you to develop the best plan for your landscape and budget, whether it’s repair, renovate or rework. Contact us at 415-265-2697 for a free estimate.

Retaining Walls: 3 Types to Hold Back Those California Hills

Multi Terraced

Tamate Retaining Wall

In the landscaping world, retaining walls have the major purpose of providing stability to the earth, preventing erosion and the movement of soil. With San Francisco’s hilly grounds, retaining walls are an essential part of almost any household, apartment complex and business. Mud slides, ground seepage, crumbling dirt trying to take over your backyard – these structures are a barrier in the constant battle between man and nature.

Because of the ongoing war with gravity these structures are built to be burly and unstoppable. However, contrary to popular belief, these carefully engineered systems can also be aesthetically stunning. Not only do they hold back Mother Nature, but they also offer pragmatic benefits towards embellishing your home, such as providing privacy to your outdoor living areas and increasing the value of your home (which is a great return on investment, by the way).

Normally, retaining walls use their own mass, backfill anchoring systems to fend off the terrain behind it. They’re most commonly made with offset cinderblocks, angled stones, heavy blocks, wood or reinforced concrete frames, and then filled or backfilled. The fill source can be from just as many materials as the wall itself, but it has to have the necessary physical properties to act as a resistance to the natural earth pressures.

Types of Retaining Walls (and Examples of Landscape Projects You Might Use Them for)

When you think “retaining walls”, you may picture the oh-so-popular gray, imposing hunk of concrete. There are several types, however, and each one has a better use compared to another. For instance, a gravity wall (which you’ll read about shortly) is great for short terraces, but not so great for retaining walls over four feet.

Gravity Retaining Walls are the oldest type of retaining wall, and are built to be bottom-heavy. Fatter at the bottom than they are at the top, they’re often built to lean against the ground they’re holding up. It takes math and a ratio to get them set right, but these walls are great for short terraces. At four feet tall or less, they won’t require mortaring or steel reinforcements.
An example of gravity retaining walls is this multi-terraced retaining wall and drainage project below.

Example of Gravity Retaining Walls

Cantilever Retaining Walls can hold a significant amount of dirt, and are good for tall slopes. They have a horizontal base that extends out to the back, and often to the front as well. For a cantilever wall to last and not come down eventually, it needs reinforcements (often steel) and some form of water drainage.

While a retaining wall with weep holes or a drainage system doesn’t very aesthetically pleasing, you’d be surprised to find out how beautiful it can be. Tamate Landscaping often uses stone facing and caps to turn a plain wall into a perfect backdrop for an Asian garden, or stucco covering to blend in with the Californian landscape like we did in Glenn Park. Click the link to read more about this retaining wall project.

Example of Cantilever Retaining Walls

Steel H Beam and Plank Retaining Walls are sturdy structures, and great for soft soil areas. They consist of beams driven into the ground at spaced intervals. Only about one third of the beams are above ground, with the rest below. They can be made out of steel, wood, concrete, or a mix, as we did in this Buena Vista retaining wall project in 2013. We buried the steel beams, then used treated wooden planks for the wall material.

Example of Steel H Beam and Plank Retaining Walls

Now that you are a pro at retaining walls you can consider having one built. These walls have been around for years and continue to offer myriads of solutions and aesthetic landscaping additions. Take care of the evil slouch in the yard where you wanted to build a pool but never got around to it. Beautify the atmosphere of your home in the back yard, front yard or all the way around the house.

Call Tamate Landscaping at 415-265-2697 to discuss your landscaping project. Find out how a retaining wall can beautify your view.