Does Retaining Wall Need Drainage? Here's What You Need to Know

After months of decision-making, you finally had that beautiful retaining wall that mirrors Albuquerque’s desert mirage built. For sure, you’re feeling proud of the outcome. And you are confident that it will hold and grow old with you. But just a few years of getting battered by frequent afternoon monsoon rain, you start noticing something weird - your wall has cracks, and it is bucking! What could be the problem? It’s supposed to last 50 years or so!

Well, let me ask you: Does your retaining wall have proper drainage?

If you are not sure and are wondering if it even needs one, this is the best time to understand why drainage matters, what happens when a retaining wall has poor drainage, and what you can do to fix it.

Everybody wants a picture-perfect backyard retreat. But instead of giving you peace of mind, cracks snaking across the wall's surface will instantly give you a headache. Worse, if it starts leaning forward, the structure is in big trouble.

But what brought on those cracks? And why is it leaning? Well, the most likely culprit is improper drainage. All retaining walls require adequate drainage systems to make them safe and sturdy.

• Hydrostatic Pressure: Without proper drains, water that gets trapped behind the wall will have nowhere to go. Without an outlet and water just building up, it will start relentlessly pushing against the wall. When that happens, it will put immense pressure on it causing it to crack. Add more water and it will start weakening the structure, causing the structure to bow.
  
  
• Erosion: This is a silent killer. With an improper drain system, the soil behind gets washed away. This leaves the structure vulnerable to collapse as it lost its integral support from the back.
  
  
• Foundation Problems: Excess moisture is no friend to foundations. This is like a domino effect once erosion sets in. With the structure near your house, erosion can undermine the foundation and leave you with expensive repair bills.
  
  
• Freeze-Thaw Cycle: Here in Albuquerque, things are even more complicated. Besides summer monsoons, winter’s freeze-thaw cycles create subterranean pressures that drainage struggles against. With a poor system, water behind the facade gets trapped in cracks and then ice up. This ice expands and exerts even more stress on the structure. On top of that, the cold air in winter builds up pressure in cracks and fissures, resulting in bigger ones.
  
  
• Mold and Mildew Growth: Sedentary water is like a beacon to mold and mildew. It’s like a welcome invitation to those health hazards. Once inside, mold eats away at the materials, while mildew stains and weakens surfaces.

This chain of dominoes doesn’t end there, either. Your failing retaining wall can start a rotating piñata of cracked walkways and sidegrade shifts in your patio. You’ll also have to worry about sluggish watercourses in your yard and compromised sewer and water lines underground.

Here in Albuquerque, geographical and climatic factors challenge the basic sense of drainage design.

This salty-crusty calcium carbonate makes Albuquerque soil unique. Since it is dense, it acts like a barrier that prevents water from freely flowing. In a sense, drainage is anathema; you have to have a system that can ‘handle’ the hardpan.

For caliche challenges, your Albuquerque block wall contractor might suggest:

• Specially Perforated Pipes: Other drainage systems make use of specially perforated pipes designed to effectively penetrate the caliche layer to capture water and carry it away.

• Deep watercourse trenches: Consider digging deeper trenches to reduce the flow of the water so it can percolate down through the caliche to collect and flow away.

• Gravel: What kind of gravel to use? Larger size and highly open-graded (more rocks with 80 percent or more area). Water can flow through any size of rock if it is open-graded. Even with caliche, open-graded gravel will allow water to flow when embedded in the gravel.

Caliche doesn’t have to be a dealbreaker. Understanding that caliche is a reality here in Albuquerque and working with an experienced concrete contractor, you can design a system that combats the challenge and keeps your wall in tip-top shape.

Albuquerque’s dry climate is sneaky. It lulls you into a false sense of security, then out of nowhere, a monsoonal downpour deluges your yard with a torrent of water that your troughs must handle in one season. Then the freeze-thaw will follow, creating another set of problems. When water seeps into cracks, it then freezes and expands. When it thaws it will then exert pressure on the whole house. 

Good drainage is a balancing act for monsoon chaos and winter ice. So, if you are still asking if you need drainage pipe for wall drainage, the answer is a resounding YES!

• Standing water: If puddles are forming in a low spot next to your retaining wall, the outcome is never good. Water build-up signals that water isn’t draining and is accumulating pressure behind it, ready to cause a problem.
  
  
• Bowing or Leaning: Has your once-proud retaining wall become a hunchback? A bowed-out structure is a very clear sign of trouble. When bowed, it is literally leaning outward at an angle because the forces acting on its back side are greater than those pushing in. In many cases, water pressure is causing the problem.

• Shut off the source: If the house can still get back on track, identify the source of the extra water and turn it off. It could be faulty pipes, the downspout’s routing, or clogged gutters.

• Secure the area: If the structure is collapsing, keep people and pets away from the area. If possible, move patio furniture or grills away from the area temporarily. 

• Call for backup: Don’t open it up yourself unless the lean is minor. Call a foundation engineer robust enough to work on retaining walls and drainage – someone who is also licensed in contracting. 

The assessor will evaluate the extent of the damage and the effectiveness of the drainage system: what type of soil it rest upon; is the slope of the terrain steep or shallow; and how does the water run off?

Depending on the situation, repairs might involve:

• French Drain installation: An excavation of gravel topped with a perforated pipe running under a building, downhill from the foundation that takes in and diverts water cast to the wall) remains the go-to recourse for resolving this issue.

• Repair existing weep holes: The weep holes on your existing stucco might need to be cleaned and enlarged for water to run off properly. Digging the slope back from the wall will lessen water pressure.

• Wall Repair might be required: The extent of the cracks and the degree to which the wall leans or tilts will affect whether repair is appropriate and if so, what treatment is most likely to help; materials and methods can vary a great deal depending on the particular structure.