Bridging system for freight railway complex

Project description

As part of the project carried out in the city of Zaragoza in advance of EXPO 2008, it was decided to construct a large logistic centre on the outskirts of the city, so as to relieve the central stations of a major part of the railway cargo traffic.  The new railway complex extended into an area measuring  1,000,000m2 that cut through a zone which was prone to the appearance of sinkholes.

Solution

In the project phase and to solve this problem, it was decided to sanitize the entire area concerned. This decision called for removal of such a large volume of earth that it was dismissed at the execution phase.  To implement a proper design, the baseline data from different geotechnical studies conducted in the zone were used. The maximum diameter of the expected hole was one meter and it was estimated that a filling with a maximum height of 2.6 meters would go on top of these cavities. British standard BS 8006:1995 was used to implement the design.  The resulting design resistance was around 200 kN/m for a uniaxial bridging effect (load transfer in a longitudinal direction) allowing for a deformation of less than 5% for definitive bridging in the event of breaking. The geogrid is endowed with these properties; it is made of polyvinyl alcohol (PVA) and polyamide and has an elastic modulus in excess of 4000 kN/m.

Benefits

The advantage conferred by this design method resided in its capacity to predict surface settlements based on deformations in the geogrid.