Various measures to prevent retaining wall distress and failures shall be taken for safety and stability. Methods to prevent distress in retaining wall is discussed.
There are various construction, design, and detailing reasons that influence retaining wall safety and stability. On the other hand, there are convenient measures or methods by which retaining wall problems can be decreased and prevent the retaining wall distress.
In the following sections, techniques which are employed for declining or avoiding retaining wall instability and distress are explored and it is worth mentioning that these measures are not applicable for walls that are wore down almost entirely.
Measures to Prevent Retaining Wall Distress and Failures
Following are the methods to prevent failure and distress in retaining walls:
- Redeem surface drainage problems
- Reduce retaining wall height
- Use tie backs
- Extend the footing
- Remove and replace backfill materials
- Reinforce the front of the wall
- Add a key
- Use cantilevered soldier beams
- Get a building permit
- Push it back to plump
- ‘Tear down that wall’
- An exotic solution
Redeem Surface Drainage Problems
Replacing backfill materials or reaching to the drainage system at retaining wall base is uneconomical. Therefore, it is recommended to prevent accumulating water at the back face of the wall by re-grading backfill material surface or constructing small concrete culvert to divert water and direct it away from the backfill.
Moreover, increasing number of weep holes might be another mitigation strategy, even though it can be objectionable aesthetically. Furthermore, in most cases, it is feasible to solve drainage issues by just closing active drainage systems.
Reduce retaining wall height
There are number of options that can be used in the case where reducing soil pressure is required for example decreasing retain earth height by re-grading backfill earth surface, and landscape changing or pressing down drainage culvert at the wall back face.
These techniques may decline retained earth height to a satisfactory level depend on as-built capacity of the retaining wall.
Use tie backs
Tie backing retaining wall can be used as mitigation method for situations that stem wall overstressed extremely. Holes are drilled at the back of the wall and tie back is installed that exceeds the backfill failure plane.
It is necessary to reanalyze wall shears and moments due to changing restrains.
This method is considered undesirable aesthetically due to the appearance of tie back anchors on the exposed face of the wall or using tie back the surface with concrete block.
Extend the footing
Footing toe extension decrease soil bearing pressure significantly. The soil is excavated and concrete is poured after the required amount of extension is determined and the footing could be deepened for a key if required.
The bond between new and existing concrete is created by drilling hole in existing concrete then place epoxy dowels to withstand computed pullout and consequently transfer shears and moments.
Remove and replace backfill materials
This solution is employed when backfill soil is saturated and cannot be mitigated from the surface. Crushed rock is a choice that might be used to replace backfill earth and well-functioning of the drainage at wall base should be assured.
Reinforce the front of the wall
The base thickness is increased to reinforce the front of the wall through placing concrete and tapering to an extent that thickening is no longer required. This method improves compression strength only therefore shear transferring at the interface should be tackled as well. Interface shear can be transferred by fixing dowel pins.
Add a key
deepened key provision in front of the existing footing may solve retaining wall sliding problems and increase passive resistance.
Use cantilevered soldier beams
Soldier beams are installed in the holes that are drilled on the footing heel and tied to the wall to transfer loads. The beams are spaced at specified distance along the horizontal span of the wall. Moreover, how long the distance between the wall and soldier beams is controlled by footing heel.
Get a building permit
There might be no obvious distress in the retaining wall but an observant building inspector found that a permit, which happens when new building or addition is constructed on a property, was not issued. When retaining wall’s plan is available, it is necessary to prove computations with signature of an engineer.
One of mitigation techniques which are discussed in this article is used to solve an overstress if the calculation could not be justified.
In case of lacking wall construction plane, it is necessary to find out how the retaining wall constructed. This might be carried out by probing and testing to specify toe and heel dimension of the footing, bar spacing and location, and testing core sample to determine material strength.
Back calculate the design to the actual retaining wall capacity and consequently checking retaining wall adequacy. Form this it becomes obvious the importance of getting permit and it might avoid expenses in the future.
Push it back to plump
This method is not advised but it is feasible to carry out successfully when the wall lean out is around 2.5 cm or 5 cm. the likelihood of executing this technique successfully related to certain conditions for example the backfill material has not been placed, retaining wall height, and with the above fixes.
Factor such as bumping the wall and using machine compactor near the wall might be lead to wall plump out. There are discussions about this method but it can be executed properly with considerable attention. In most cases, it may be needed to remove great amount of the backfill earth to avoid problems.
‘Tear down that wall’
When the retaining wall is in severe conditions and it seems that none of the above solution is feasible to rehabilitate the wall, then it may be more economical demolishing and reconstruction the wall will be the best solution.
Utilization of this option is strongly supported if new condition arises for instance need for higher wall or a preference for another construction material.
An exotic solution
There are exceptional site conditions that can be tackled with specific economical method. In this case engineers can come up with very clever and unique idea to solve the problem and prevent demolition and rebuilding the retaining wall.