Today, we are looking at an interesting case study from the field: a collapsed retaining wall at the front yard of a historic property. Work was done to try to stop the destruction of the wall, but it wasn’t enough. The wall was too far gone, and the work was not enough.
We will talk about why a gravel bed was added to the retained ground side of the wall, and alternative strategies That could have been considered.
The outline for today’s article follows:
- How Mortar Joints Deteriorate at Historic Brick walls
- Why a Gravel Fill Alleviates Hydrostatic Pressure at a Retaining Wall
- Alternative Strategies That Should Have Been Considered
How Mortar Joints Deteriorate at Historic Brick walls
Mortar joints in historic brick walls are susceptible to deterioration over time due to various environmental factors, with water being a primary culprit. In the case of the collapsed retaining wall at the front yard of a historic property, the mortar joints on the retained ground side had experienced excessive deterioration that went unmitigated for decades.
The original construction lacked essential waterproofing measures, such as a gravel fill, to facilitate proper water drainage. Without a gravel fill to create a viable path for water with low resistance, the mortar joints faced prolonged exposure to moisture, leading to accelerated deterioration.
The absence of a perforated drain collection pipe further exacerbated the issue, as water could not be efficiently channeled away from the wall. In hindsight, it becomes evident that the original construction missed crucial elements that are now considered standard for preserving the structural integrity of retaining walls. The lack of a gravel fill from the time of the wall’s inception allowed plant roots to propagate excessively, a clear sign that the environment was conducive to unchecked growth.
Why a Gravel Fill Alleviates Hydrostatic Pressure at a Retaining Wall
Gravel fill serves a dual purpose in retaining walls. Firstly, it provides a well-draining medium, allowing water to flow away from the wall’s structure, preventing prolonged exposure and subsequent deterioration of mortar joints. Secondly, the gravel fill discourages the proliferation of plant roots, ensuring that they do not compromise the integrity of the wall over time. The visible presence of plant roots along the edges of the collapsed section serves as a tangible indicator that the original construction did not incorporate a gravel fill, highlighting the missed opportunity for proper water management and root prevention.
A gravel fill plays a pivotal role in alleviating hydrostatic pressure at a retaining wall, acting as a drainage medium to mitigate the impact of water accumulation. Without a proper drainage system, water can accumulate behind the wall, exerting hydrostatic pressure against it. This pressure, resulting from the weight of the water, can lead to structural damage, including mortar joint deterioration and compromised stability.
The diagram below shows the mechanics and the structural engineering elements of a similar typical retaining wall, with similar components but drains designed to actually relieve the hydrostatic pressure more effectively.
The gravel fill creates a path of least resistance for water, allowing it to percolate through the material and move away from the retaining wall efficiently. This drainage mechanism prevents the build-up of hydrostatic pressure, reducing the potential for damage to the wall’s structural components. By offering a permeable layer, the gravel fill aids in the dissipation of water, preventing the adverse effects associated with sustained pressure.
In the absence of a gravel fill, as observed in the case study, hydrostatic pressure remains unmitigated, leading to accelerated mortar joint deterioration and increased vulnerability of the retaining wall. Incorporating a gravel fill from the initial construction phase is a fundamental strategy for preserving the structural integrity of retaining walls and safeguarding against the detrimental effects of hydrostatic pressure over time.
Alternative Strategies That Should Have Been Considered
In hindsight, alternative strategies should have been considered to address the challenges faced by the retaining wall, aside from the partial addition of gravel fill at the top 2 feet of the retained soils. One viable alternative would have been the installation of a comprehensive drainage system incorporating a perforated drain collection pipe along the entire length of the wall’s retained side. This pipe could have been strategically placed at the base of the wall, effectively channeling water away from the structure and preventing hydrostatic pressure buildup. Such a drainage system would have provided continuous and efficient water management, reducing the risk of mortar joint deterioration and structural compromise.
Additionally, the application of waterproofing techniques, such as the use of waterproof membranes or coatings, could have been explored. Waterproofing the retaining wall’s surface would create a barrier, preventing water infiltration and protecting the mortar joints from prolonged exposure. Integrating waterproofing measures into the original construction would have been a proactive approach to enhance the wall’s resistance to moisture-related deterioration.
Furthermore, the consideration of alternative retaining wall materials with inherent resistance to water damage might have been beneficial. Certain composite materials or treated wood designed to withstand moisture and root intrusion could have been explored as alternatives to traditional brick construction, but it is unlikely any solution like that would have really been effective without actually fixing the root cause issue which it that the wall was built in historic times without an actual fully functional passive hydrostatic relief system. Evaluating the specific environmental conditions and tailoring the construction approach accordingly could have offered a more resilient solution, reducing the need for continuous maintenance.
In summary, alternative strategies that should have been considered include the implementation of a comprehensive drainage system, the application of waterproofing techniques, and the exploration of alternative materials resistant to water damage. These alternatives, if integrated into the original construction, could have provided more robust and sustainable solutions to the challenges faced by the retaining wall, preventing the need for subsequent interventions and enhancing the structure’s long-term resilience.
In Upcoming Articles
In upcoming articles, we will discuss how drain systems, like the PVC pipe used at this location can help alleviate hydrostatic pressure build up and the detrimental effect of plant roots once brick joints become excessively deteriorated on the raised ground side of a retaining wall.
Contact us today to learn more.
