Introduction of H2Ri Wicking Fabric and prove of subsurface drainage concept
H2Ri wicking fabric is a recently developed type of wicking fabric is made of special hydrophilic and hygroscopic 4DG™ Fibers with multichannel cross-sections. The multichannel cross-section has one of the highest available shape factors and has the greatest number of channels per fiber, which give the wicking fabric great potential for maximizing capillary action and water transport in an unsaturated environment. The specific surface area of the wicking fabric is 3,650 square centimeters per gram, and it has a permittivity of 0.24 per second, which is equivalent to a flow rate of 611 liters per minute per square meter.
A layer of the proposed geotextile is installed at the bottom of the base layer. The geotextiles are partially exposed to the atmosphere with a length of 1-2 meters at both sides of the embankments. Due to its hydrophilic and hygroscopic nature, the wicking fabric can absorb water from the surrounding soils inside the embankment. As discussed previously, the suction gradient induced by RH difference provides the driving force to wick the water out of the pavement structure to the embankment, and finally the water will be vaporized into the air at the exposed surface via evaporation process. Different from the granular or conventional geotextile drainage system, the new geotextile builds up a liquid connection between the inside and outside of the pavement structure for continuous water removal even under low RH (high suction) conditions. Compared with the amount of water needed to saturate the Earth's atmosphere, the amount of water in the pavement structure is very small. Therefore, the surrounding air provides unlimited driving force and the wicking process will continue until the soil near the wicking fabric is dry and cannot provide sufficient water supply. By adopting the geotextile, the pavement post-compaction water content is expected to be at least maintained at optimum level, or can be further reduced to a lower level. As long as the pavement water content is controlled within a relative low level, the soil stiffness can be ensured at designed value and the rutting depth is also within acceptable range. Thus the pavement long-term performance is improved.
Conceptual Subsurface Drainage Design
TENCATE GEOSYNTHETICS (North America) reported that the new geotextile could transport water to a distance of 1.83 m within 16.5 h with zero hydraulic gradient (Figure 2a) and wick water to a height of 0.25 m within 2 h during capillary rise test (Figure 2b) (under room temperature and RH less than or equal to 40%).
Horizontal Wicking Length Test (Zero Hydraulic Gradient)
Vertical Wicking Height Test (Anti-Gravitational Force)
Water Infiltration Test for H2Ri Geotextile and Conventional Geotextiles
Test Results for Initially Saturated Sand
Case 1: Coldfoot, AK
The road experienced extreme cold temperature and the adjacent ice-rich FS (frost susceptible) soil made the frost heave problem even worse. A 12-mile test section (half of the road length with geotextile and the other half without geotextile) was constructed in 2012, which aimed at mitigating the frost heave issue and preventing ice lenses formation. The shoulder was damp and the road surface was in dry condition. In addition, the road surface was smooth without any soft spots observed. Since this project was newly operated, close monitoring is required to further evaluate the overall roadway performance for the long-term. However, preliminary observation already proved the drainage efficiency of the new geotextile to wick water out of the pavement structure.
Test Section at Coldfoot, AK
Case 2: St. Louis County, MO
A new bridge was being constructed over the Missouri River where saturated soil conditions required the need to remove water from under the pavement section at the bridge approaches. This was a design build project where the Missouri DOT encouraged the design/build teams to explore new and innovative technologies to solve the challenging site conditions. The geotechnical engineer contacted TenCate Geosynthetics to explore the utilization of the TenCate Mirafi® H2Ri high strength wicking geotextile. The objective of using the product was to remove water from underneath the pavement section. The design build team had originally designed a pavement section that included a concrete section over 4" of road base aggregate, 4" layer of drainable aggregate and a prepared subgrade. The inclusion of Mirafi® H2Ri geosynthetic by the design engineer was intended to replace the 4" of drainable base, thus providing equivalent capabilities within the section while reducing overall costs. The high modulus geosynthetic, which provided excellent confinement and separation, allowed for an overall 2" reduction in aggregate base material along with the ability to wick water from under the pavement. The water was able to exit the Mirafi® H2Ri through a combination of day lighting the material onto roadway shouldersor into french drains.
H2Ri Geotextile Installation
Prior and After a 1/4" Rainfall Event
H2Ri Performance after Installation