Friday, 2 December 2016

Historical Background of Roadway Construction for Transportation Engineers


Throughout history, humans have constantly been inventing new ways of travel. The oldest mode of travel was by foot but eventually evolved to using animals to help carry both people and materials. When motorized vehicles came along, people realized the dire need for a hard surface to accommodate wheels, which would make traveling smoother. 

These surfaces were constructed in a large scale during the period of the Roman empire with the earliest construction techniques birthing “Roman roads.” The Romans, who are considered to be the pioneers of road construction, developed roads in many directions, mainly for military operations. 

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The Romans’ Roadway Construction Technology

During the Roman civilization, many roads were built by stone blocks of considerable thickness. Generally, the total thickness of the road was as thick as 0.75 to 1.2 meters. 

Overall, the required layer thickness of each course of the material depends on the average traffic load. Structural number and layer thickness calculation problems are reviewed in FE exam review courses

When examining Roman roads, the cross section typically has a trench of width equal to that of the carriage way. When constructing a road, the trench was excavated up to a depth until a hard stratum was reached. One or two layers of large foundation stones were laid with lime mortar at the bottom, creating a thickness of 10-20 cm for the bottom layer. Vertical curbstones were placed along the edges of the pavement. Then, a second layer of large, broken stones, which were mixed with lime motor, was laid over the bottom course up to a thickness of 25 cm to 40 cm or more depending on the requirement. The wearing course of roadway consisted of dressed large stone blocks set in lime motor at the top; the thickness of wearing course varied from 10 cm to 15 cm. This technique of construction was much stronger than that was required for animal-drawn carts during those days. Pavement design and construction is an interesting topic for professional civil engineers who are engaged in highway engineering infrastructure development projects. Fundamentals of Engineering exam certification will authenticate the design and construction process of roadways.

Roadway Construction Technology Improvement Methods 

  • Tr├ęsaguet construction technique 
Pierre Tr├ęsaguet, a French Engineer in the 1700s, developed a new method of construction, which greatly enhanced the roadway system. The system he created allowed the road to sustain less wear than the prior system of constructing roads. His method involved a layering system with both small and large stones. When constructing the road, the subgrade was prepared, and a layer of large foundation stones were laid on edge by hand. The corners of these heavy foundation stones were hammered, while the interstices were filled with smaller stones. Broken stones were placed to a thickness of about 8 cm and were compacted. The top wearing course was made of smaller stones and compacted to a thickness of approximately 5 cm at the edge and gradually increased toward the center. The shoulders were also provided with a cross slope to drain the surface water to the side drain.

  • Macadam construction 
John Macadam developed an entirely new method of construction compared to previous methods. His method included adding multiple steps during pavement construction, such as preparing a subgrade with a cross slope of 1 inch up to the desired width, then compacting it to the required density. Broken stones of high strength passing through a 5-cm size sieve were placed and compacted to a uniform thickness of 10 cm throughout the width of the pavement. The second layer of 3.5 cm stones were placed and compacted to a thickness of 10 cm. The top layer consisted of stones less than 2 cm and were placed and compacted to a thickness of 5 cm. These techniques provided a wide scope of ideas for recent highway engineering projects. Most of the transportation engineering related topics are reviewed in FE and PE exam prep courses for civil engineers.

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