The 2 x 1 km Lorca twin-tube tunnel in the region of Murcia is on the Mediterranean motorway A-7 between Murcia and Almeria in Andalusia. It crosses the hillside under Lorca Castle. Opened in 1988, it has a daily traffic of 30,500 vehicles. In 2006, it was rated "very poor" by the EuroTAP (European Tunnel Assesment Programme) tests.
The EuroTAP audit listed the following deficiencies: insufficient lighting, no radio signal coverage throughout all the length, no automatic detection of the problems in case of use of emergency telephone or extinguishers, no emergency lights, emergency call telephones not working during the test, no drainage systems for toxic or flammable liquids, no automatic fire alarm system, no escape exits, radio communication between safety teams is impossible, and absence of emergency safety drills or simulation exercises.
The tunnel is currently subject to refurbishing works to equip it with state-of-the-art security systems. The improvements under way comply with Royal Decree 635/06 of 26th May, 2006 on the minimum safety requirements in road tunnels across the country.
In January 2007, the Ministry of development awarded a joint venture of Probisa, Obras Subterráneas, Murtrafic and Electromur (the last two companies being part of Grupo Etra) the refurbishing works of the tunnel. Visit www.probisa.com, www.obrassubterraneas.es and www.grupoetra.com
Because the average daily traffic in both bores is very high, it is necessary to maintain fully operational the four lanes throughout the day and do the works at night.
Construction and fit-out of cross passages
Construction began in March 2007 and slowed down during the summer months to avoid disruption to road users, and during Christmas, the two periods of the year which the highest traffic through the tunnel.
The works mainly include the construction of two cross-passages between the existing tunnels with a 2.5 m radius semicircular vault and 2 m-high walls. The north cross-passage is 193.7 m long while the south cross-passage is 182.8 m long. These crosscuts will enable rescuers to act in situation of emergency and evacuate quickly people injured in an accident. In addition, they will provide access to fire fighters in case of fire.
The south cross-passage, which connects the north tunnel with outside, has been completed on 24th January, 2008. Then work proceeded in the north cross-passage, which will connect the two paralle tubes. This was due to complete in February.
Due to the hardness of the ground, the drill-and-blast method has been used. A jumbo drill rig drilled the blast holes in which the explosive was introduced. Fourty blasts using Goma 2 Eco explosive supplied by Maxam sufficed to hole through the south cross-passage. The detonations took place every day early in the morning. Each day, a unique blast was carried out and the construction of the south cross-passage required only 40 days. Visit www.maxam-corp.com
During the soft controlled blasts, delay blasting has been employed. This technique triggers the explosives in a staggered manner some milliseconds one after the other to increase efficiency. Each blast requires quantities of explosive much lower than what is normally used to construct open air roads.
To speed up construction and shorten the time frame for works, and given the heterogeneousness of the material to excavate, a mixed excavation method has been utilized. It consisted in using a roadheader when the ground permitted and blasting in harder ground.
The vibrations and acoustic wave produced by each blast have been closely monitored by means of a seismometer placed near the walls of the Lorca Castle, listed a cultural asset of national interest. The castle is relatively nearby the north cross-passage. In this way, it has been possible to make sure that the vibrations and acoustic wave generated by the explosives, and supervised by the authorized control body, were very under the exposure levels set for the buildings around the project.
In the last days of drilling of the south cross-passage, the impact on nearby houses was also controlled to verify that these vibrations had been much under the limits set by law as for the blast effects on buildings in the vicinity of the works.
The cross-passages will be equipped with fire protection. Four reversible fans will be installed in the northern cross-passage and two (not reversible) in the south, as well as motorized fire-break doors. Besides, they will be signalled with photoluminescent exit signs, guide lines with photoluminescent painting and dynamic variable message panels in the accesses to each of them.
The cross-passages will also be fitted with electrical supply, normal and emergency fluorescent lighting, emergency waymarkers to guide in case of fire, and there will also be luminous signposting, access control and a CCTV system with fixed video cameras. A comprehensive public address system is also planned, with loudspeakers and amplifiers, as well as SOS stations.
Safety equipment in the main tunnels
Safety will also be improved in the main tunnels. The fire protection installations will be upgraded or modernised by adding portable fire extinguishers, fire hydrants, fire detection system with thermal sensitive cable and a push-button warning network, installed along the full tunnel length, as well as photoluminescent signage.
Other improvements will concern the lighting, with the installation of normal and emergency fluorescent lighting and emergency waymarkers in case of fire. There will also be luminous signage and access control, CCTV with fixed video cameras, public address system with loudspeakers and amplifiers as well as SOS stations for aid in case of incidents. The closed circuit television (CCTV) system will be wired with monomode optical fibre.
The electrical supply involves the extension of the existing power transformer centres, the construction of technical rooms to house the electrical and control equipment, and the installation of three sets of Uninterruptible Power Supply (UPS).
Finally, the ventilation will consist of four new fans in one of the two bores. It was also deemed convenient to complement all the equipment and installations with the construction of two heliports, one at each tunnel mouth and their construction has already ended. 21/08.
