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23-535: The tunnel consists of two traffic tubes carrying two lanes each. The original tunnel tube, which opened for traffic on the 27 September 1981, is 9.1 meters (30 ft) wide and 5,062 m (16,608 ft) long. The second tunnel tube, opened for traffic on the 13 September 2024 is 5,634 m (18,484 ft) long. It is the third longest in Croatia after the Mala Kapela and Sveti Rok tunnels. Construction on

46-431: A "design as you go" approach, by providing an optimized support based on observed ground conditions. More correctly it can be described as a "design as you monitor" approach, based on observed convergence and divergence in the lining and mapping of prevailing rock conditions. It is not a set of specific excavation and support techniques. NATM has seven elements: Based on the computation of the optimal cross section , only

69-429: A thin shotcrete protection is necessary. It is applied immediately behind the excavated tunnel face to create a natural load-bearing ring and minimize the rock's deformation. Geotechnical instruments are installed to measure the later deformation of excavation . Monitoring of the stress distribution within the rock is possible. This monitoring makes the method very flexible, even if teams encounter unexpected changes in

92-547: Is also provided to ensure continuous operation of the tunnel. Traffic is regularly counted and reported by Croatian Motorways Ltd, operator of the A1 motorway and the tunnel, and published by Hrvatske Ceste. Substantial variations between annual ( AADT ) and summer (ASDT) traffic volumes are attributed to the fact that the motorway carries substantial tourist traffic to the Dalmatian Adriatic resorts. The traffic count

115-424: Is generally thought to have helped revolutionise the modern tunneling industry. Many modern tunnels have used this excavation technique. The Sequential Excavation Method is very cost effective, even in karst conditions. The NATM integrates the principles of the behaviour of rock masses under load and monitoring the performance of underground construction during construction. The NATM has often been referred to as

138-599: Is partly caused by an increased use of the tunneling method in the United States, particularly in soft ground shallow tunnels. Other designations are seen for this modern tunneling style; Sequential Excavation Method (SEM) or Sprayed Concrete Lining (SCL) are often used in shallower tunnels. In Japan, the terms Centre Dividing Wall NATM or Cross Diaphragm Method (both abbreviated to CDM) and Upper Half Vertical Subdivision method (UHVS) are used. The Austrian Society of Engineers and Architects defines NATM as "a method where

161-484: Is performed using analysis of toll ticket sales. New Austrian Tunnelling method The new Austrian tunneling method ( NATM ), also known as the sequential excavation method ( SEM ) or sprayed concrete lining method ( SCL ), is a method of modern tunnel design and construction employing sophisticated monitoring to optimize various wall reinforcement techniques based on the type of rock encountered as tunneling progresses. This technique first gained attention in

184-470: Is the longest tunnel in Croatia. The tunnel is geographically located between the villages of Jezerane and Modruš (although it cannot be accessed from the villages directly), and between Ogulin and Brinje motorway interchanges. The tunnel passes through the Mala Kapela mountain in the northeast-southwest direction. The first tunnel tube through the Mala Kapela mountain was completed in 2005, and

207-511: Is the only suitable road between Istria and the rest of Croatia for vehicles over 5 tonnes. In 2022 more than 1.94 million vehicles passed through with AADT of 5,326 and ASDT of 7,361. In a 2004 traffic safety test by ADAC , the Učka Tunnel shared the last place with Tuhobić Tunnel , also from Croatia, being classified as a high-risk transportation utility. In 2008, the Tuhobić Tunnel

230-576: The geomechanical rock consistency, e.g. by crevices or pit water . Reinforcement is done by wired concrete that can be combined with steel ribs or lug bolts, not with thicker shotcrete. The measured rock properties suggest the appropriate tools for tunnel strengthening, where support requirements can traditionally be estimated using the RMR or Q System. Since the turn of the 21st century, NATM has been used for soft ground excavations and making tunnels in porous sediments . NATM enables immediate adjustments in

253-506: The 18 September 2023. It was opened to traffic on 13 September 2024, slightly later than originally planned. In the existing tunnel tube, upgrades of the emergency and signalization systems are ongoing. Mala Kapela Tunnel Mala Kapela Tunnel ( Croatian : Tunel Mala Kapela ) is the most significant structure on the Croatian A1 motorway route. As it is 5,821 metres (19,098 ft) long (northbound tube), Mala Kapela Tunnel

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276-458: The 1960s based on the work of Ladislaus von Rabcewicz , Leopold Müller , and Franz Pacher between 1957 and 1965 in Austria. The name NATM was intended to distinguish it from earlier methods, with its economic advantage of employing inherent geological strength available in the surrounding rock mass to stabilize the tunnel wherever possible rather than reinforcing the entire tunnel. NATM/SEM

299-525: The construction details, but requires a flexible contractual system to support such changes. NATM was originally developed for use in the Alps, where tunnels are commonly excavated at depth and in high in situ stress conditions. The principles of NATM are fundamental to modern-day tunnelling, and NATM fundamentally involves specifically addressing the specific soil conditions being encountered. Most city tunnels are built at shallow depth and do not need to control

322-492: The northbound tube is 5,821 metres (19,098 ft) long, while the southbound one is somewhat shorter, as it is 5,780 metres (18,960 ft) long. The tunnel tubes are excavated 25 metres (82 ft) m apart, and are linked by 6 vehicle passages and 14 pedestrian passages. The tunnel comprises 7.7 metres (25 ft) wide carriageways, permitting driving speeds of up to 100 km/h. The tunnel features an autonomous drainage system channeling water accumulating during cleaning of

345-620: The original tunnel tube began in 1978, and at the time of opening it was the longest road tunnel in Yugoslavia. The toll is part of the rest of the closed toll collection system in use on the Istrian Y. The shortest possible journey through it costs EUR 4,50 for a class I vehicle. It is rated Class D/E under the ADR treaty for hazardous materials transportation , and vehicles transporting restricted goods must be pre-arranged and escorted. It

368-451: The release of in situ stress, as was the case with the original NATM in the Alps. Projects in cities place a higher priority on minimizing settlement and so tend to use different support methods from the original NATM. That has led to a confusion in terminology in that tunnelling engineers use "NATM" to mean different things. New terms have arisen, and alternative names for certain aspects of NATM have been adopted as its use has spread. That

391-425: The safety requirements, had to be modernized by 30 April 2014. For certain tunnels, as it is the case of Učka’s tunnel, that period could be prolonged by five years (until 30 April 2019). However, due to the lack of upgrade to the tunnel, this obligation was not met. As such, the government of Croatia accelerated the works. In June 2011, BINA Istra announced that design documents were being prepared for construction of

414-408: The second tunnel tube of the Učka Tunnel, and that construction was scheduled to start in mid-2012, estimating its completion in 2015. However, this construction never started. It was transferred to be part of the wider Istrian Y upgrade plan, as part of the 2B2-1 phase. The excavation of the second 5.63 km (3.50 mi) tunnel tube started on 17 December 2020 and was officially completed on

437-426: The surrounding rock or soil formations of a tunnel are integrated into an overall ring-like support structure. Thus the supporting formations will themselves be part of this supporting structure." Some engineers use NATM whenever they propose shotcrete for initial ground support of an open-face tunnel. The term NATM can be misleading in relation to soft-ground tunnels. As noted by Emit Brown, NATM can refer to both

460-442: The traffic, regulated from traffic control centres along the A1 motorway. Electronic equipment of the tunnel allows radio reception of two UHF radio frequencies ( HR1 at 92.1 MHz and HR2 at 98.5 MHz) as well as use of cell phones. Electrical power is supplied to the tunnel through one 35 kV switching station at each end of the tunnel and 8 distribution switching stations in the tunnel itself. A backup electrical power supply

483-438: The tunnel, as well as seeping water and liquids spilled in accidents or used for firefighting. The tunnel was executed using New Austrian Tunnelling method , by means of drilling and explosive blasting. Numerous caves, caverns and other speleological structures were found during the construction, but all of those were addressed successfully. The tunnel is equipped with variable traffic signs in order to ensure enhanced safety of

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506-448: Was used for both directions of traffic until the second tube was completed in 2009. The tunnel is tolled within the A1 motorway closed toll collection system . There are no other toll plazas related to use of the tunnel. The northern portal of the tunnel is located at elevation of 562 m.a.s.l. , while the southern one is found at 575 m.a.s.l. The tunnel tubes are not equally long -

529-702: Was widened to four lanes. However, no improvements were made to the Učka Tunnel, causing a demonstration clogging the traffic at a tunnel entrance by Istrian bikers . More serious implications of the tunnels lack of safety were seen in October 2019, when the European Commission recalled Croatia on their obligations to comply with the minimum safety requirements set out in the Tunnel Safety Directive . Tunnels already in operation on 30 April 2006, and that were not already in accordance with

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