Every transportation challenge revolves around the aspect of the land development process that causes the most headaches – water.

Whether it is the water itself (i.e., stormwater) or its aftermath (erosion control), potential problems need to be addressed before, during, and after the design and construction of land development projects – including the transportation components.

One of the increasingly popular solutions to development challenges is the use of geosynthetics.

Multitude of Uses
Geosynthetics are now commonly used for reinforcement, confinement, and stabilization in a variety of applications. Over a half-dozen applications, from improving road drainage and filtration to pavement restoration and reinforcement to stabilizing retaining and embankment structures, are illustrating beneficial results from geosynthetics – not to mention stormwater management and erosion control implementation.

Geosynthetics provide methods to increase the long-term durability of projects by reducing the frequency of maintenance and repair.

Geosynthetics are also used in landscaping and architectural projects. Steep slopes and retaining walls, otherwise thought unlikely to be feasible, can be stabilized using geosynthetics, allowing for additional options and avoiding the expensive cut-and-fill routine that is often suggested in these situations.

”Geosynthetics have become a standard of practice in many transportation applications for the various DOTs and these techniques are translating to the land development arena.” said Fred C. Chuck, P.E., Transportation Market Manager with MIRAFI Construction Products.  “The drainage function of geosynthetics are used in land development projects to improve the longevity of drainage systems.  Geosynthetic improvements over the years, in subgrade stabilization and base reinforcement, can now help developers complete their roads on time and provide additional life to their pavements.”

Subgrade Applications
In Temecula, California, water from the irrigation of orange groves combined with low lying areas bordering Sandia Creek Road was causing major rutting and potholes.

Petra Geotechnical, the project engineering firm, determined that geosynthetics would be needed to provide both reinforcement and separation. A woven polypropylene material was selected for its high tensile strength that contains uniform openings for filtration yet is recognized for high soil confinement. The goal was to separate the base material from the fine-grained soils within the subgrade while increasing the bearing capacity of the base material. Its use eliminated the need for over-excavation, especially in softer fill areas.

In another California project, the Los Angeles Department of Water & Power needed its contractor, Barnard Construction Company, to construct a water pipeline throughout the Owens Valley dry lakebeds to make a future irrigation system possible.

The contractor could not attain the minimum required 90% relative compaction of the subgrade and Boyle Engineering determined that the main access roads were also to receive a six-inch layer of aggregate – compacted to 95% relative compaction. The use of 300,000 square yards material in the construction enabled the contractor to construct up to 1,000 linear feet of berms and/or access roads a day. Following the creation of a stable working surface, trenching equipment was brought in to begin the pipeline excavation.

Reinforcement of Base Layers
In northern Kansas City, Missouri, Zona Rosa Development had designed a large commercial retail center. With precipitation always providing a potential delay of the project’s development, it was determined by the engineer (TranSystems/Walton Construction) and contractor (Hanrahan Asphalt Paving) that a rock base and an initial asphalt layer were needed during construction. The challenge, of course, was to provide heavy truck traffic access without causing damage to the pavement so that the final asphalt-leveling course could be applied without extensive repairs to the initial layers.

A geosynthetic grid (BasXgrid® 11) would be used to prevent rutting and other types of road failure. After preparing the subgrade, the geogrid was installed and followed by 6-8 inches of base rock. An initial asphalt course was then installed on the base rock.

After the construction of the buildings was completed, the final asphalt layer was laid down without any repairs to the initial course.

Admittedly, there was an initial cost incurred by utilizing the geogrid, but delays due to difficulty in accessing the site were eliminated and there were no repairs needed to any damaged asphalt during or following construction.

Water, expected to be ever present due to continuous irrigation of lawns and landscapes in a new residential development in Laguna Hills, California, caused some concern for the project owner, William Lyon Homes. The developer’s private
consulting engineer, Goffman, McCormick & Urban, Inc., wanted to ensure that potential problems related to the unknown moisture content of the subgrade and the minimal structural design of the pavement (per city minimums) were mitigated in the design phase.

Therefore, the engineer recommended that the subgrade soils be moisture conditioned to at least 2% over optimum content and compacted to a minimum of 90% relative compaction. After the utilities were installed and the subgrade was completed, All-American Asphalt applied the material and six inches of base material was bottom dumped and leveled. (The ability to bottom dump the base course directly on the fabric helps to reduce the cost of installing the base material.)

Pavement Restoration
New procedures from the use of paving fabrics as an interlayer include a applications of “polymer modified asphalt” as the binder fabric.  

Bradley Road is a heavily traveled arterial in an industrial area of Libertyville, Illinois. The existing pavement was a badly deteriorated full depth asphalt pavement with a PCI rating estimate at less than 10 (scale of 100). The original designs called for patching with full depth asphalt patching. However, because of the high percentage of patching required (40% +) it would have been less costly to reconstruct the entire road. Libertyville Township Highway Department, as with many other municipalities, is facing budget restrictions and had opted for a less expensive solution for the repair of this pavement.

To restore pavement, two inches of the existing surface was milled and patched preceding a leveling course. Heavy duty paving fabrics and a thick asphalt overlay completed the section. Because of the extreme temperature variations in this area (-20ºF to 98º F) a thicker paving fabric (Mirapave® 700) was installed with a polymer-modified asphalt (PG 76-22). The polymer-modified asphalt allows for greater flexibility in the pavement surface under high and low temperature conditions. Studies have shown that modified asphalts improve load-associated fatigue cracking and thermal cracking.

Scott Fisher of Peter Baker & Sons developed the construction sequence, starting with a leveling course to fill in the irregular surfaces of the existing pavement. This was followed by the fabric, installed by Road Fabrics. Two lifts of Illinois Department of Transportation hot mix were applied to finish the project.

John Sikich, president of Road Fabrics, stated that the installation using the modified asphalt tack coat went well with a few minor changes to the installation procedure.

“The modified binder is spread hotter than AC grade asphalt binders and care was taken to install the fabric at the optimum temperature,” explains Sikich. ”In addition, the modified binder set up quicker and allowed construction equipment on the surface with no bleed-through.”

The use of paving fabric with chip seal  resurfacing is becoming  recognized for its contribution to longer pavement life.  Road Fabrics also utilized a paving fabric (Mirapave®) on a chip seal project in Newton, Illinois.
In the instance of Martin Street, a heavily traveled two-lane road exposed to heavy truck traffic and a main detour route, the Jasper County Highway Department decided along with Conor & Conor Engineering, to add a paving fabric to the normal chip seal procedure.

The existing seven-year-old asphalt pavement surface was in relatively good condition but was heavily oxidized and was starting to show signs of fatigue cracking. The inclusion of Mirapave®  500 had several benefits. In addition to improving the performance of the road, it can also increase the chip seal service life by 60%.

The fabric acts as a moisture barrier within the pavement and prevents water from penetrating the roadway, which reduces the deterioration of the subgrade due to saturated conditions. Second, its use improves the bond of the chip seal to the existing roadway and reduces future maintenance needs for the surface.

Asphalt cement (AC) was applied to the existing pavement surface at a rate of 0.79 l/m2 (0.25 gal/yd2). AC placement was directly followed by the installation of the polypropylene paving fabric. AC-25 asphalt cement was applied to the fabric surface at a rate of 0.79 l/m2 (0.25 gal/yd2). The chip seal aggregate, which consisted of a CA-16 graded crushed stone material, was then applied by the County of Jasper using a variable width spreader at a rate of 20 lb/yd2. After the chip seal was placed, a second application of AC-25 and crushed stone was applied. The final step was to compact the finished road surface with a rubber-tired (pneumatic) roller compactor. The entire process took less than a day.

Porous Pavement Too
With the increasing popularity of permeable pavements, it should come as no surprise that geosynthetic products are being utilized here as well.

Whether asphalt, concrete, grass, or paving pavers (stones) are the ultimate top-level surface, geosynthetics are being utilized to provide separation and drainage, while still allowing a permeable surface.

A geotextile, like Mirafi 140N, can be used as a separator between two aggregate layers preventing the finer bedding material from migrating into the larger aggregate below, while allowing free flow of infiltrating water through the fabric.  This system, when used in concert with a porous paver, was put to the test in Palm Desert, CA using a water truck to flood the pavement surface.  The system accepted water at a rate equal to a rain event of 12 inches in one hour.
In addition to aesthetics, best management practices in stormwater management are now incorporating more and more permeable pavement options to mitigate stormwater runoff. Some communities and/or projects grant special environmental credits for sustainability and the promotion of environmental solutions like infiltration rather than collection and distribution for using a permeable system.  SLDT

Mirafi and Miragrid are registered trademarks of Ten Cate Nicolon.