Aug 30, 2010

Retaining Wall Repair needed quickly in Ann Arbor

Repair of Landscape Wall

We were needed recently to repair a Retaining Wall in Ann Arbor that was beginning to collapse. The corner of this retaining wall was beginning to separate and slide off it's bottom foundation. The homeowner had recently noticed further gapping of the blocks and leaning of the wall towards his front walk.  Time was of the essence and the modular retaining wall needed total reconstruction.

The homeowner was frustrated because the original landscape architect & contractor would not properly address the issues regarding this landscape retaining wall.  Because of my 27 years experience constructing & repairing modular retaining wall systems, I had some theories as to the reason this block wall had drastically settled.

From my visual inspection, I had noticed that the 90 degree corner of this retaining wall had failed miserably and some lower modular blocks had "slid" off the ones below them. This particular retaining wall system is Fendt's Keystone Old World Country Manor and requires a fiberglass pin system to hold the structure together.  These modular retaining wall blocks also have a hollow center that requires to be filled with gravel.

I had concluded from my visual inspection that these  2 key factors contributed to the failure of this retaining wall system.  As we disassemble this landscape wall, my conclusions were accurate. See the pictures to the right to see the poor installation of these retaining wall blocks.

The corners of modular retaining wall systems are the most important part of any large landscape walls.  They require extra reinforcement because the brunt of hydro static pressure & gravity can compromise the weakest part of any retaining wall construction. This retaining wall lacked the basic requirement of fiberglass pins to help secure the blocks in place. The landscape contractor choose to just "glue" the corner blocks. The result was a lower landscape block "sliding" off the foundation block below and allowing the pressure to push the retaining wall out.

As we tore down the complete wall due to excessive gapping, leaning, & settling, we also observed that none of the block's hollow centers & gaps were filled with gravel.  Filling all voids in a modular retaining wall system is required to give the wall additional mass.  Landscape wall systems are engineered with minimum specifications to help insure long-term performance. This particular retaining wall failed to meet 2 key installation specifications.

We disassembled the entire retaining wall from the top down. We re-leveled and recompacted the gravel base, reinstalled the bottom blocks to the correct level, and reconstructed the modular retaining wall blocks one-by-one, using the correct number & location of fiberglass pins and filled all voids with gravel. The finishing touch was to re-cap the wall and touch up the surrounding landscape.

We paid special attention to the corner of this retaining wall.  We replaced the small blocks the past contractor used and used the larger blocks in the retaining wall system so we could properly pin the units. We also constructed the corner using the "log cabin" method of overlapping the corner units as each row was stacked, pinned, filled, and backfilled. 

This retaining wall repair situation is very common in Ann Arbor. The landscape architect & contractor had a good design and good use of product, but the execution of installing was poor.  It does take some expertise & experience installing modular retaining wall systems properly. This particular landscape wall construction should have started and constructed from the corner out. It only took "one" block to slide out and destroy the performance of this very popular retaining wall application.