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Water is generally recognized as the cause of most geotechnical failures or poor performance. This is because water affects both sides of the stability equation. It increases the loading and reduces effective strength.
In addition, flowing water adds seepage forces as well as increases the potential for migration of particles causing either a loss of volume and/or changes to the gradation and consistency of the soil. Volume changes can cause settlement of the soil supporting a structure. Change in the material gradation (typically increasing the silt and clay size particles) can cause a change in the soil behavior. Increasing the percentage of fine-grained soils can reduce the permeability and strength of the soil.
Fortunately, there are several approaches to manage water and its impact on structures:
- Drain the water
- Use filters to allow flow without particle migration
- Impede the flow
- A combination of these options
These approaches can and have been done by using natural materials that are designed to function for the given criteria. For instance, to prevent flow we utilize a very fine plastic clay which has very low permeability to act as barriers. We can also use a series of soil layers of different gradations to act as a graded filter which would be designed to allow flow while retaining fine particles from migrating. Utilizing natural materials for these applications works well but they tend to be time consuming and challenging to construct.
Geosynthetics have been designed and manufactured to perform these functions and meet specific design requirements. For example, there are liner systems, geotextiles (woven and non-woven), drainage nets/cores and several composite type products available. The quality control as related to the desired hydraulic performance can be much more reliable compared to field installation which require specific gradations and thicknesses that need to be uniform for the extent of the design area.
Geosynthetics are easier to install and require less volume and space. From a constructability and schedule perspective, the use of geosynthetics is more practical which can also relate to lower overall project cost.
For pavements, water is one of the most damaging factors that cause early failure and/or maintenance. The pavement foundation support is very sensitive to changes in moisture and gradations as discussed above. When the pavement foundation support is lower than required the damage caused by vehicles significantly increases. Once the pavement foundation starts seeing distress due to the loading, the repair solution will most likely include reconstruction down to the subgrade. This can be very time-consuming and expensive.
Geosynthetics can play an important role in protecting the pavement foundation from this type of damage. Geotextiles can be used to separate and filter fine-grained materials while allowing excess pore-pressure to dissipate. Edge drains and/or geomembranes can be used to limit the water from entering or to provide an adequate flow path out of the embankment. Geosynthetics are generally easy to design and install and will address the design criteria efficiently. In the pursuit of longer pavement life, using geosynthetics to address water and its impacts is low hanging fruit.
A new approach which can be used to transport water across the pavement section has been used for several years. This technique allows water entering the pavement section vertically from the surface or water flowing up do to excess pore pressure to have a flow path outside the pavement section. Dr. Jie Han at the Department of Civil, Environmental, and Architectural Engineering at the University of Kansas, delivered the 2025 Burmister Lecture at Columbia University on September 30, 2025, on this topic. This is currently a topic of interest and research.
For additional information:
- National Highway Institute (NHI) Courses:
- Geotechnical Aspects of Pavements No. 132040
- Geosynthetic Course No. 132013
- Geosynthetic Design & Construction Guidelines, FHWA-NHI-07-092
- AASHTO Course – Geosynthetic Materials: Fundamentals
- Liu, H., Han, J., Al-Naddaf, M., Parsons, R.L., and Kakrasul, J.I. (2022). “Field monitoring of wicking geotextile to reduce soil moisture under a concrete pavement subjected to precipitations and temperature variations.” Geotextiles and Geomembranes, 50(5), 1004-1019.
- Zaman, W., Han, J., Kabir, M., Parsons, R., 2024. “Laboratory evaluation of wicking geotextile for moisture reduction in silty sands at different fines contents.” Geotextiles and Geomembranes, 52(2024), 1180-1190.
- Zhang, X., Presler, W., Li, L., Jones, D., Odgers, B., 2014. “Use of wicking fabric to help prevent frost boils in Alaskan pavements.” Journal of Materials in Civil Engineering. ASCE 26 (4), 728–740.
Daniel Alzamora, P.E., is a contributing editor for Geosynthetics and has spent more than three decades in the geosynthetics industry in both the public and private sector.