Some additional capacity for the Public Works Department has been added, to help maintain our roadway systems and to minimize the damaging effects from sediment transport.
In our research to find the best tool to clean sediment from existing roadway culverts, we recognized an opportunity to buy a more versatile piece of equipment. Most culvert cleaning systems rely on augers to push or pull accumulated sediment from the pipe. But another technique involves jetting the pipe with water under pressure.
A frequent problem we experience in BSL is the washing away of silt and sediment when we excavate into the clean beach-like sands that are so prevalent (often called sugar sands), or erosion that results when an embankment of soil without vegetative cover is exposed to rainfall. Our stormwater ditch systems provide a good example of this erosion, with many of our driveway culverts partially or half-filled with material that has been washed in from the upstream side. We cannot stop all such movement of silt, but it would be nice to improve the function and stability of culverts and ditches.
There are many methods for reducing silt transport, including erosion control blankets, rip-rap (stone), the use of check dams across ditches, placing sod, or articulated concrete blocks and mats. However, long term control is best achieved by a good stand of grass or other vegetation where the resulting root mat infiltrates the soil and interlocks the material, thereby restricting transport.
So how do we start to grow grass in difficult areas, often without an organic soil layer at the surface?
The answer is a “hydro-seeding” unit, which is commonly observed on DOT projects where large scale embankment projects are seeded by Contractors. For BSL we purchased a smaller unit, but the concept is the same.
The Turf Maker has an internal auger, engine and pump system that enables us to mix seed, fertilizer, and mulch with water, and also with a special “tack” type material that helps the mixture adhere to the surface.
Once the components are mixed together, they are sprayed hydraulically on the ground, and before you know it these sandy areas grow grass! The mulch component is intended to hold the moisture in the mix, protect the mix from sun and bird feeding, and also prevent erosion of the seeded area.
Now here is the really great “extra” benefit!
By fabricating steel rods and specially shaped nozzles we can fill the unit tank with water alone, and then use the hydraulic system to spray pressurized water inside any clogged culvert. With different fittings we can either spray the material forward or work it backwards until most or all is removed and the pipe is free flowing.
This gives us the added benefit of using the machine for both: 1) placing seed and creating grass cover, or 2) cleaning culverts with water pressure.
Pavement Spray Patching
As described by a previous article, poor performance of paved roadways is usually the result of inadequate or non-suitable base materials. When moisture is trapped beneath pavements, and support issues are worsened by repetitive freeze-thaw cycles (in the winter season), potholes often can form. Well constructed and properly sized gravel sub-base layers that are free-draining will minimize this possibility, but unfortunately in BSL many of our roads were created a long time ago and without long-term performance as a goal. Some of our roads have limited base materials, and also a thin layer of asphalt pavement.
Under such poor circumstances the only long term solutions tend to be quite expensive. One includes the removal and replacement of road pavement surfaces and its sub-base materials (full-depth replacement). When underlying soils are of suitable gradation, another option involves grinding up the road in place, adding gravel or admixtures to reinforce the new base, and then overlaying this with new pavement (known as base reclamation). Unfortunately just overlaying a poor road with new pavement does not work if the base materials are inadequate, since those same problems will reflect up through the new pavement typically within a couple of seasons.
So with our limited budget and the need to pave new roads each year, what can we do to maintain the use of our older roads? Patching potholes has been our approach, and when done correctly this is the way to make spot repairs. However, the only patches that last have been constructed by an outside contractor as a vendor, since they have the tools, the staff and experience to place hot asphalt emulsion. Our Public Works staff has been limited to placing cold patch material, which will not last as it does not knead or mesh with the surrounding pavement, and is typically not placed over a gravel base.
Our contractors have done a fine job in the past, but this work requires a significant expenditure each year as the number of our potholes increases. Would it not be better if Public Works could patch the problems with something more permanent?
The answer is a truck-mounted machine with an aggregate hopper (for stone) and a heated emulsion tank that will enable a two-man crew to safely repair potholes with a more permanent patch. Using a pressurized nozzle with compressed air, the operator of this equipment can between layers of stone and emulsion to create a patch that is typically stronger than the surrounding pavement.
In addition to our potholes, many of the roads in BSL have edge conditions that are broken or missing, This is sometimes due to inadequate gravel support at the edge, the way the pavement was originally formed, or the lack of proper drainage. The “Spray Patch Process” can also address the repair of these edge conditions, as well as certain patterns of pavement cracking.
Most exciting is that we will be able to control the schedule of repair, and not wait for a large number of holes to appear before retaining a contractor. This process will help us improve road safety in BSL, as we minimize the number of potholes and broken edge conditions.
This unit will more than pay for itself as we use it for many years to come, and it should be operational by late August or early September.
We still ask you to help us by notifying your Public Works Department when potholes are observed and become a nuisance. We appreciate this assistance and encourage you to bring these to our attention.
If you have any questions about this article, please contact the City Engineer at 910-363-0025