GABION RETAINING WALL FAILURES : Decoding the Causes and Consequences !

Retaining walls fail when they can't hold back the weight of the dirt behind them!! As simple & straight as this.

Gabion #retainingwalls have long been favored for their cost-effectiveness, ease of installation, and aesthetic appeal in both residential and civil engineering applications. The failure of retaining wall is categorized as a #geotechnical disaster because it not only causes major economic losses but also some casualties have been reported in the past. However, like any structural system, gabion walls are susceptible to failures, which can have a range of causes and effects. In this article, we will delve into the common reasons behind gabion wall failures, their potential consequences, and strategies for remediation.

Causes of Gabion Retaining Wall Failures:

Poor Design: The main reason for the failure could be the?improper design of the retaining and supporting system.

Poor Foundation Preparation: Inadequate site preparation, such as improper grading or compacting the base soil, can lead to an unstable foundation for the gabion wall.

Hydraulic Pressure: Excessive water buildup behind the wall, often due to inadequate drainage, can increase hydraulic pressure on the structure, causing bulging or displacement.

Erosion: If gabion baskets are not adequately filled with stone, the voids can promote soil erosion through the wall. This can weaken the structure over time.

Settlement: Uneven settlement of the wall's foundation or footing can create stress concentrations, leading to wall deformation or collapse.

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Considering an example of a site:

This is constructed by metal Gabion wall for river embankment of a River to avoid bank erosion and retain the earth fill. Average height is 7m and base width is 7m and length is about 600m as shown in Fig. below.

Observations: Due to lose packing of filled basalt stones bulging of Gabion wall is observed at the top layer of the wall as shown in the image below. Sharp edges of stones has cut the coating, which leads to corrosion of Gabion mesh wire, as shown below.

?Some of the classic observations of failures are-

a.?????? Due to lose packing of filled basalt stones and crushing filled soft stones there is bulging of Gabion wall observed at some locations of the wall as shown in the Image below:

b.?????? The stones used for filling in Gabion are having sharp, which cuts the coating of Gabion mesh, which leads to Corrosion of Gabion mesh wire, as shown in Image.

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Effects of Gabion Wall Failures:

Property Damage: Gabion wall failures can result in damage to nearby structures, roads, or properties, leading to costly repairs.

Erosion and Landslides: Without the retaining wall's support, soil erosion and landslides can occur, causing environmental damage and posing hazards to nearby communities.

Loss of Function: A failed gabion wall can disrupt the intended function of the structure, such as protecting against erosion, retaining soil, or managing water flow.

Safety Risks: Collapsed gabion walls can pose safety risks to people and vehicles in the vicinity.

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Remediation and Preventive Measures:

Proper Site Preparation: Ensure thorough site preparation, including adequate grading, compaction, and soil stabilization, to create a stable foundation for the gabion wall.

Adequate Drainage: Implement proper drainage systems, such as weep holes and geotextile fabrics, to manage water buildup behind the wall and prevent hydraulic pressure.

Regular Inspection: Periodic inspections and maintenance can identify issues early and prevent extensive damage. Replacing deteriorated stones and gabion baskets is essential.

Proper Filling: Ensure that gabion baskets are filled to the required density and maintain the structural integrity of the wall.

Geotechnical Analysis: Conduct a geotechnical analysis of the site to assess soil conditions, evaluate load-bearing capacity, and choose the appropriate gabion design.

Engineered Solutions: In some cases, gabion walls may need to be engineered with additional features such as reinforced concrete foundations, tiebacks, or geogrid reinforcement.

Consult Professionals: Seek the expertise of geotechnical engineers, structural engineers, or gabion wall specialists when designing, installing, or remediating gabion retaining walls.

Suggestions:

To avoid bulging Stones used in Gabion box should be all in size which minimizes the voids and increases the self-weight of gabion, leads to the possible reduction in wall cross-section.

To avoid cutting/corrosion of Gabion wire By proper placing of stones (i.e. sharp edge should not perpendicular/angled) cutting wires and succession corrosion of Gabion mesh get reduced. By proper selection of wire mesh based on design and coating PVC/Zinc to reduce corrosion of Gabion mesh.

To avoid erosion of soft stone Stones filled in Gabion should be tested not only for strength but for weathering action also.

To avoid cracks in backfill The material used in backfill should not be black cotton soil or if used it should be mixed with other materials to minimize the effect of expansion-contraction on Wetting-drying. This will minimize the effect of alteration of backfill pressure on the wall. Backfill should be placed in layers and well compacted. Proper drainage arrangement for percolated water in backfill. Proper design of wall by considering all forces acting on it.

To avoid erosion of foundation soil Wall should be properly embedded in soil (optimum depth of foundation). A concrete/stone blanket on the toe side may provide to avoid foundation soil erosion especially in heavy rainfall and mountainous region.

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In conclusion, while gabion retaining walls offer several advantages, they are not immune to failure. Understanding the causes, effects, and remediation of gabion wall failures is crucial for ensuring the long-term stability and functionality of these structures. By following proper construction practices, conducting regular inspections, and seeking professional advice, the risk of gabion wall failures can be minimized, and their benefits fully realized.

Failures observed in site investigation are mostly due to bulging, corrosion, erosion of filled stone, backfill crack, and foundation erosion. Mostly these failures are due to improper stones and improper filling of stones in Gabion box.

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