Roads and highways are often taken for granted, and perhaps one of the only times you actually consider a road is if it’s closed due to construction or a traffic accident. For most of us, driving on roads and highways is a routine, like sleeping and eating.
Although most people don’t think twice about the roads and highways that they utilize daily, a lot of thought goes into planning, designing and constructing roads and highways, and it is quite an undertaking. Many considerations must be taken into account. One consideration is slope stabilization and to understand the environment in which the road or highway is built.
While it would be great if all roads and highways were built on flat ground in a straight line, that just isn’t the case. The earth contains natural peaks and valleys, and highways and roads are built over these. Many roads and highways are built on some type of slope or angle. Slope stabilization assesses the environment under which the road or highway is built to measure how much movement and stress the road can take before it collapses or fails. Slope failure is a common occurrence that happens near roads and highways, and various methods are used to repair or prevent this. However, these methods could use improvements because many of the solutions are not long-term, are very costly and deteriorate over time. In March 2011, a study was conducted by the Texas Department of Transportation and civil engineers from University of Arlington and Jackson University that utilized a new method for slope stabilization. Using recycled plastic pins by Bedford Technology, the group carefully followed the project from installation to finished product and over a period of five years, monitored the results of this innovative construction material.
Before we dive into that, let’s discuss more traditional slope stabilization methods.
Slope Stabilization Solutions
Slope failures are caused by erosion, heavy or consistent rainfall, earthquakes, hurricanes and human disruption like construction projects near or on the slope itself. The effects of slope failure include structural damage, collapsed soil and ground, and erosion. All of these effects, if severe enough, can cause the road or highway to collapse.
Once slope failure has occurred, many factors influence the solution including soil composition, amount of rainfall, likelihood of natural occurrences like hurricanes, earthquakes, etc. and budget. These are a few of the most common types of slope stabilization methods.
Drainage – This method includes an underground system that releases pressure build up in or on the slope. Drainage plans should channel water away from the slope without causing erosion.
Retaining Walls – These walls are designed to keep soil and rock in place to stabilize slopes around the construction site. Keep in mind that retaining walls can be customized to suit your specific project, but might require additional permits, depending on height and city standards.
Sheet and Friction Piling – Sheet pilings, typically made of steel, vinyl or wood planks, are driven into the ground. This method is commonly used in soft soil. Friction piles are driven into the ground towards the layer of earth that bears the weight and stress. Friction piles installed can also be used to form retaining walls. If these pilings are made of traditional wood, over time the exposure to moisture from the soil will cause it to break down.
BioTechnical Slope Stabilization – This method uses plants, trees and other vegetation to stabilize the soil. Tree and plant roots can stabilize the soil which prevents erosion and it can act as a natural drainage system by slowing down the water flow.
While all of these methods are being utilized and meant to be long-term solutions, depending on the construction material, can break down over time. Before you know it, you’re back to the drawing board to find another solution. To truly find the best solution, it’s important to understand the causes and effects of slope failure and to determine the best method based on the environment. Engineers have been looking for a new construction material solution to help make these projects last. A new potential method was introduced using recycled plastic pins. A large study was conducted and published based on the results.
Testing, Testing, 1…2…3…
In March 2011, members from the Department of Civil Engineering at Jackson State University and the Department of Civil Engineering at the University of Texas at Arlington conducted a study using recycled plastic pins in an area along Highway 287 in North Texas with the TXDOT to test this material as a possible solution to slope failure.
The test included three 50 ft. slope sections that were stabilized using the recycled plastic pins. There were also two control areas without reinforcement that were compared against the areas with the RPPs. The sites were then monitored for the next five years.
The Results Are In!
Starting with installation of these pins, the results were already favorable. The machine used to install these pins was able to maintain balance over the slope which reduced labor and equipment cost and time. Not to mention, the average installation time for a 10ft. long RPP was 4 minutes, and a total of 100-120 RPPs could be installed in just one day.
Next was the RPP performance results. A topographic survey was conducted and monitored on a monthly basis to determine the settlement of the crest of the slope. Inclinometers were also installed and monitored on a bi-weekly basis to determine the movement of the angle of the slope over a period of time. In the areas that did not have the RPPs, significant settlement at the crest of the slope, 38 cm was recorded, whereas the incremental settlement in the areas with the pins was less than 3.75 cm.
Based on the results, the overall performance of recycled plastic pins was far superior than the control sections. The recycled plastic pins were manufactured out of FiberForce® by Bedford Technology and provide a cost-effective and sustainable solution to help mitigate the slope failure problem.
Recycled Plastic Pins by Bedford Technology
Cost-effective and sustainable solutions are our bread and butter; recycled plastic is at our core. The material is cost-effective and durable because unlike traditional slope stabilization materials, it will not mold, rot or deteriorate. It also is impervious to insect and pest damage, so when it is underground, it will not become a new home for a family of termites. The material is also manufactured from household products like laundry detergent bottles and milk jugs, so it stays out of the landfill and reduces waste.
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