Road landslides typically occur due to the loss of stability in a slope caused by weak backfill and/or excessive loading from the combination of heavy, saturated soils within the materials that make up the slope.
A slope is considered stable when the shear strength of the soil is greater by a factor of safety than the driving force (weight of the backfill) downslope along the projected minimum slip plane. In the case where the driving force exceeds the shear strength of the backfill material, the slope will fail and slide downward.
Because TDA is lightweight and permeable, it is effective in reducing excessive loading on an unstable slope. An added benefit, TDA's high permeability permits drainage through the various layers and can dramatically reduce the potential hydrostatic pressures that promote slope stability.
In landslide repair projects, TDA is typically designed using alternating layers of TDA and soil. There are several key advantages to designing a slope with a TDA backfill:
It is less than half the weight of soil, so the driving force causing a potential landslide is significantly reduced.
The internal shear strength of TDA is greater than soil, further increasing the resistance to the overlying driving force.
Using a TDA backfill design results in a more stable slope as compared to a soil backfill design.
Designs using TDA as an alternative backfill can achieve the needed factor of safety values with much less excavation and engineered backfill.