By César Roldán Acosta
The strategic geographical location of the state of Mexico forces a constant interaction with the economic activities of Mexico City. For this reason, it is critically important to keep the roads linking several towns throughout the state in good condition. The Secretaría de Comunicaciones y Transportes (SCT) directs the strategies for the construction of new roads as well as the conservation of federal roads, reviewing their situation to keep them in optimal condition.
Ecatzingo, where this project is located, is in the southeastern part of the state, bordering the states of Morelos and Puebla. This municipality has grown rapidly in recent years, requiring the creation of new highways to access the municipal headquarters.
One of these new access roads required the construction of an embankment to cross a gorge 30-feet (9.2-m) high and 131-feet (40-m) long. The timing of the job was important, as it had to be completed in less than one month—including the land preparation work.
Initially, the SCT engineers proposed building the embankment using a reinforcement system with galvanized steel meshes and finished with concrete tablets manufactured on-site.
The contractor reviewed various retaining wall systems. The systems had to comply structurally with the project, but above all, they needed to be efficient enough to manufacture and install in a short time, a difficult undertaking with numerous tablets.
The technical department from the company ML Ingeniería proposed using mechanically stabilized earth (MSE) walls with polyester geogrid covered with PVC and changing the finishing from tablets manufactured on-site to shotcrete simulating such tablets. The wall design took into account the geometry; considering an inclination of 78º with respect to the horizontal, structural factors would be required for the SCT office to accept the design.
After several meetings with the engineers justifying the change of system and demonstrating the performance of the earth retaining walls reinforced with geogrids, the project was accepted.
A reinforcement of 73,356 pound-force/foot (100 kN/m) geogrid was used for the construction of the first layers of the wall, and 44,254 pound-force/foot (60 kN/m) geogrid was used to complete the upper layers.
The drainage system to avoid hydrostatic pressures was based on transversal pipes dispersed along the face of the wall, and the use of sacks filled with the same embankment material as lost formwork was proposed to give the design alignment: 5V:1H.
Once the embankment was finished, an electro-welded mesh was placed on the entire face of the wall to receive the shotcrete.
The contractor was able to finish the wall in the established time, and the SCT was satisfied with the system, especially with the finish that replicated the appearance of concrete tablets without the additional expense of manufacturing and installing them.
César Roldán Acosta is the commercial manager for ML INGENIERIA in Mexico City, Mexico.
Figure courtesy of the author.
SIDEBAR: Project Highlights
Earth retaining walls reinforced with geogrids
Location: Ecatzingo, Edo Mex, Mexico
Design Engineering: ML INGENIERIA by Jose Luis Esparza
Geosynthetics products: ACE GG100-I, ACE GG-60-I”
Geosynthetics Manufacturer: ACE Geosynthetics