Cat® RM500 Rotary Mixer stabilizes Sahara haul route
Tamanrasset, Algeria, was established centuries ago along the trans-Saharan trade routes. The routes evolved into the Trans-Sahara Highway, and Tamanrasset remains a key outpost today. It is an oasis where citrus fruits, apricots, dates, figs and other produce are grown.
It’s also a key oil center, with several large facilities located nearby. A single clay road serves as a pipeline from the facilities, connecting them to the Trans-Sahara Highway.
The clay road was in need of repair. It came as no surprise given the pounding of both the heavy trucks that use the road, as well as the sun. Temperatures in the desert city of about 70,000 are among the highest ever recorded. Highs have hit 47.4º C (117º F) in both July and August. The average temperature in July is 35.9º C (97º F).
The baked clay can become brittle as the heavy trucks travel the roads. Yet the road also experiences extreme temperature changes over the course of the year, with average lows falling to 6.4º C (44º F) in January. Those on the jobsite believe that the temperature fluctuations likely had as much to do with the deterioration of the road as did the heat itself.
The Project
The soil road desperately needed repair. Cost was a key consideration, so the decision was made to go with stabilization. A Cat® RM500 Rotary Mixer was the machine selected for the job by Chebli & Tellawi Corp., the contractor handling the work.
The project called for all 50 km (31 miles) of the connecting road to be stabilized by the RM500. The road was to be stabilized at a width of 9 m (30') and a depth of 20 cm (7.9"). Plans also included the use of a special bonding material to strengthen the road that leads to the oil facilities.
Getting Started
The work began in February. Preparations had to be made before the RM500 could make a pass.
First, a dozer made a very rough grading pass. This work mostly required removal of large stones that had been brought to the surface by the heavy trucks and temperature fluctuations. The dozer also cleared larger chunks of broken clay.
A water truck then sprinkled the roughly graded surface. Next, the RM500 made a stabilizing pass. Ahead of the RM500 was a truck containing the bonding material. A hose connected the rotary mixer and the truck that contained the binding agent. The emulsion was mixed with the soil in the mixing chamber of the RM500.
The bonding agent is made from calcium and lignin, a complex polymer extracted from paper pulp. Lignin is environmentally friendly, as it is a natural fiber found in trees and plants.
The bonding agent was chosen because of its fit with the existing clay road. The agent helps make clay more elastic, preventing material from breaking loose. The organic binding agent also facilitates compaction.
A motor grader then made a finished grading pass, followed by a soil compactor.
The Challenges
Hitting the deadline was crucial to the project. Inefficiencies associated with the work would have cost the oil industries time and money. Once the work was started, it had to be completed in a hurry.
Weather also added time pressure. The project started in February, when the average temperatures range from 7.5-20.6º C (46-69º F). But the likelihood of a heat wave increased with every passing day.
Another challenge was that the operators had never previously worked on a rotary mixer. The speed of the project increased quickly as the crews grew in experience. At the beginning, the crew was stabilizing 58 m (190') per day. By the middle of the project, the pace was 600 m (1,968') per day.
By the conclusion of the project, crews reached a working speed of 1200 m (3,936') per day.
It was a substantial increase and showed how quickly operators can adjust to the new machine and bring productivity to the worksite.
The durability of the machine also impressed Chebli & Tellawi Corp., as did the productivity. Operators, meanwhile, appreciated the sight lines around the machine. “We are impressed by the visibility,” said one operator.
