Purpose of Retaining Walls
Retaining walls support and stabilize excavations, foundations, slopes, and embankments. They are designed with factors of safety for sliding, overturning, foundation bearing capacity, active loading, and extreme events.
Why Retaining Walls Fail
Despite their robust construction, retaining walls can fail due to combinations of:
- Insufficient drainage that allows water to accumulate behind the wall and results in deformation, cracks, tilting, erosion, and loss of backfill.
- Degraded foundations that allow the wall to tilt or slide.
- Increased loads from traffic or new construction that exceed the limits of the original design.
- Aging of the wall from weathering, erosion, freeze-thaw cycles, and corrosion of anchors.
Visual Signs of Defective Retaining Walls
Periodic inspections of retaining walls are usually mandated by federal, state, or local authorities. Defects that may indicate the need for monitoring or repair include:
- Visible changes in the tilt of the wall or differential tilt of adjacent panels.
- Wall face has vertical cracks or spalling.
- Joints are misaligned or separated, possibly leaking water or backfill.
- Tension cracks or settlement of soil at the top of the wall.
- Settlement or heave of the soil at the bottom of the wall.
- Gap between soil and the backside of the wall.
- Lateral cracks in pavement or walkways at the top of the wall.
- Blocked drainage channels and outlets, or excessive ponding of water over backfill.
Prioritizing Monitoring & Repair
There are federal, state, and local requirements for inspection of retaining walls and condition categories that prioritize monitoring:
Legal and Regulatory Requirements: Some jurisdictions require regular inspections and condition assessments for retaining walls of certain heights or in specific locations.
Walls with a higher risk of failure and more significant consequences are top priority. This includes walls near critical infrastructure, populated areas, or in areas prone to natural hazards.
- Walls affected by new construction. Monitoring is usually required as part of the permitting process.
- Walls subject to heavy rainfall or seismic activity require more frequent monitoring.
- Older walls known to be in poor condition or nearing the end of their design life may require more immediate and continuous monitoring.
Parameters for Automated Monitoring
The main parameters for monitoring walls are lateral displacement and tilt. Other parameters include loads on anchors, pore-water pressure, and subsurface displacements.
AMTS systems monitor prisms fixed to the wall and reveal changes in tilt, lateral displacement, and settlement.
Tiltmeters are fixed to directly to the wall and are useful for detecting differential tilt of adjacent panels.
Shape Arrays are installed on the backside of the wall or on slopes above the wall to monitor lateral displacement of soil.
Anchor load cells or strain gauges monitor anchor performance.
Piezometers monitor pore-water pressure.
Crackmeters can monitor movement at joints.
Related: Monitoring Excavations
GeoCloud Automation operates 24/7 to transfer monitoring measurements from the project site to secure project web sites. GeoCloud automation features wireless data acquisition, web-based data management, and dedicated website access to alerts, graphs, and reports.