Here are some key features and functions of retaining walls:

1. Erosion Control: Retaining walls help prevent soil erosion by stabilizing slopes and retaining the soil in place. This is particularly important on steep terrain or areas prone to erosion due to water runoff or other environmental factors.
2. Supporting Slopes: Retaining walls provide structural support to vertical or near-vertical slopes, preventing them from collapsing or slumping. They can be used to create level terraces or platforms on hillsides, allowing for more usable space.
3. Landscaping: Retaining walls are often used in landscaping to create visually appealing terraced gardens, flower beds, or seating areas on uneven terrain. They can add dimension and interest to outdoor spaces while also serving a practical purpose.
4. Water Management: Retaining walls can help manage water runoff and drainage by redirecting water away from structures or controlling its flow down slopes. Properly designed retaining walls can mitigate soil erosion and reduce the risk of water-related damage.
5. Property Boundaries: Retaining walls are sometimes used to define property boundaries or provide separation between different areas of a landscape. They can create a clear delineation between neighboring properties or designate specific zones for different purposes.
6. Materials and Construction: Retaining walls can be constructed using various materials, including concrete, stone, brick, timber, or modular blocks. The choice of material depends on factors such as aesthetics, structural requirements, cost, and environmental considerations.
7. Design Considerations: The design of retaining walls involves careful consideration of factors such as soil type, slope angle, groundwater levels, drainage requirements, and anticipated loads. Proper engineering and construction techniques are essential to ensure the stability and longevity of the retaining wall.
8. Permits and Regulations: In many areas, the construction of retaining walls may require permits or approval from local authorities. Building codes and regulations dictate specific requirements for the design, construction, and placement of retaining walls to ensure safety and compliance with local standards.

Common types of retaining walls:

1. Gravity Retaining Walls: Gravity retaining walls rely on their own weight and mass to resist the pressure exerted by the retained soil. They are typically made of heavy materials such as concrete or stone and are suitable for low to medium-height applications where soil pressures are moderate.
2. Cantilever Retaining Walls: Cantilever retaining walls are reinforced concrete structures that use a horizontal footing and a vertical stem to resist soil pressure. They employ the principle of leverage, with a portion of the wall extending backward (into the retained soil) to counteract the pressure exerted by the soil. Cantilever walls are suitable for medium to high retaining wall heights.
3. Sheet Pile Retaining Walls: Sheet pile retaining walls are constructed using interlocking steel, vinyl, or wood sheets that are driven into the ground to create a barrier against soil movement. They are commonly used in waterfront applications, temporary shoring, or areas with limited space for excavation.
4. Anchored Retaining Walls: Anchored retaining walls incorporate cables or tendons that are anchored into the soil or rock mass behind the wall to provide additional lateral support. They are often used in situations where conventional gravity or cantilever walls are not feasible due to high soil pressures or space constraints.
5. Gabion Retaining Walls: Gabion retaining walls are constructed by filling wire mesh baskets with stones or other durable materials and stacking them to create a retaining structure. Gabion walls are flexible, permeable, and can adapt to ground movement, making them suitable for a variety of soil conditions.
6. Reinforced Soil Retaining Walls (Mechanically Stabilized Earth Walls – MSE): MSE walls consist of alternating layers of compacted soil and reinforcement materials, such as geogrids or geotextiles, to create a stable retaining structure. They are cost-effective, flexible, and can accommodate settlement and differential movement.
7. Segmental Retaining Walls (SRW): Segmental retaining walls are constructed using interlocking concrete blocks or precast concrete panels. These walls are versatile, easy to install, and available in a variety of shapes, sizes, and textures, making them suitable for both residential and commercial applications.
8. Timber Retaining Walls: Timber retaining walls are built using pressure-treated timber planks or logs stacked horizontally to create a retaining structure. They are commonly used in landscaping and residential projects for their natural appearance and affordability.

Each type of retaining wall has its own advantages, limitations, and suitability for specific site conditions and project requirements. The selection of the appropriate retaining wall type depends on factors such as soil characteristics, site constraints, aesthetic considerations, budget, and engineering requirements.

Situations and entities that may require retaining walls:

1. Homeowners: Homeowners may need retaining walls to address sloping terrain on their property. Retaining walls can help create level areas for landscaping, gardens, patios, or driveways. They may also be used to prevent soil erosion, stabilize slopes, or manage water runoff.
2. Land Developers: Land developers often use retaining walls in residential, commercial, or industrial projects to prepare land for construction. Retaining walls can help optimize land use by creating level building pads, roadways, or parking areas on uneven terrain.
3. Civil Engineers: Civil engineers design and implement retaining walls as part of infrastructure projects such as highways, bridges, railways, and water management systems. Retaining walls are used to stabilize embankments, protect roadways from landslides, and control erosion along waterways.
4. Landscapers and Architects: Landscapers and architects incorporate retaining walls into landscape designs to create visually appealing terraces, gardens, and outdoor living spaces. Retaining walls can enhance the aesthetics of outdoor environments while providing functional benefits such as soil retention and erosion control.
5. Property Owners in Flood-Prone Areas: Property owners in flood-prone areas may use retaining walls to protect their homes and structures from flooding and soil erosion. Retaining walls can help redirect water flow, stabilize riverbanks, and prevent damage to property during heavy rainfall or flooding events.
6. Coastal Communities: Coastal communities often use retaining walls, seawalls, and revetments to protect shorelines from erosion, storm surges, and tidal forces. These structures help prevent coastal erosion, preserve beaches, and safeguard coastal infrastructure and properties.
7. Environmental Restoration Projects: Retaining walls are sometimes used in environmental restoration projects to stabilize slopes, control erosion, and rehabilitate degraded landscapes. They play a role in habitat restoration, watershed management, and soil conservation efforts.
8. Commercial Property Owners: Commercial property owners may install retaining walls to maximize usable space, create parking lots, or accommodate building expansions on sloping terrain. Retaining walls can enhance property value and improve the functionality of commercial developments.

Overall, retaining walls are needed by a diverse range of individuals, organizations, and communities to address soil stability, erosion control, land development, and infrastructure needs in various settings and environments. They serve a critical role in shaping the landscape, protecting property, and enhancing the resilience of built environments against natural forces and environmental challenges.