Fixing existing retaining walls with Tieback Anchors
Many existing concrete and wood retaining walls around the Puget Sound area are failing. You see these concrete walls cracked, bowing, and tipping from the soil loads on them. The wood wall will be seen not only to tip or bow, but many also begin to rot as old RR ties or other treated wood beams reach their life expectancy. All of these walls fail because they were not built in a properly engineered way to work as structural Retaining Walls.
Permanently stabilize Failing Concrete Walls
A. Short Concrete walls
Small concrete walls 4 ft. to 5ft high or less can often be permanently supported in place by coring a hole ( usually around 12 in. diameter) through the wall and then installing a Tieback Anchor which goes in several feet, sloping down through the loose soils which are loading the wall and down into strong bearing soils. These Tieback Anchors are usually Helical Tieback which can penetrate the hard clay or very dense sands which generally constitute the bearing soil layers which are a cohesive formation that does not move or slide. The densest of these soils layers in this area is Glacial Till, which were fine silts that were compacted by the Glaciers into a very hard, rock like formation. Where Glacial till is the bearing soil layer Injection Boring Anchors must be used for Tiebacks. Injection Boring Anchors allow penetration into hard layers that would resist a Helical Tieback Anchor. After the Tieback Anchors are in place the shaft of the Anchor is adapted into threaded bar that extends out though the wall. A large steel plate with a hole in the center for the Anchor rod can then be placed against the wall. Large Anchor nuts and Wedged bearing washers are then used to secure the plate tight to the wall. Many of the short walls we Tieback in the greater Seattle area are walls along a sidewalk or Alley right-of-way. The Municipalities in this area have allowed me to put Tieback Anchors to stabalize these walls even if they exist in a non-conforming state (in or protruding into a city owned street, sidewalk, or alley right-of-way). When that is not the case the ends of the anchor rods with the washers and nuts are visible on the outside of the plate. We have also developed a method of making the connection to the plate inside of the wall for the locations where the city does not want protuberances into the right-of-way that could be dangerous. In those applications the plate are connected to a apparatus that allows the Anchor to connect to the plate inside the wall and all that is visible outside is the large steel plate with a small steel plate tacked over the hole where the connection is made. We have included pictures of both applications in this section.
B. Tall Concrete walls
Many taller concrete walls are also failing and many of these are not only in front or rear yard but on side yards separation neighboring properties which are at different elevations. These larger concrete walls can also be Tied-Back in a similar manner except that the Tieback Anchors must be connected to vertical and sometimes horizontal steel walers which extend the holding capacity of the Anchor over a larger area than could be supported with just a steel plate. For old concrete walls the Cities require that the Tieback anchors are attached to supporting steel pieces with no more than 4 ft. spans vertically or horizontally. This is because un-reinforced or under reinforced concrete can only span 4 ft. and most old failing walls either have no structural rebar or an insufficient amount. We have also included photos of a wall with Tiebacks and a steel waler grid.
C.Wood Retaining walls
Tipping wood walls happen when the wall was not structurally designed to hold the soil loads on them. If the Timbers of the wall are still in good shape, holes for Tieback Anchors can be cut through the wall, Tiebacks installed to bearing soil and Vertical steel walers can be used to secure against the wall. In this repair method the quality and strength of the timbers ( which are till the horizontal members of the wall) determine along with the soil load how far apart you can place the Tieback Anchors. The load capacity of the Tiebacks Needed will be determined by the wall height and the soil loading above the wall. Often the timber walls also have rotting timbers. In this instance we can install new Timbers between the new vertical steel walers and fill the space between the new wall and old wall with draining pea gravel. We have included some structural details of this repair method as well as pictures of what the new wall in front of the old looks like. By making the vertical walers straight and the height of the walers slightly above the old wall height these new walls look plumb and the soil behind them hides the old wall.
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