Modernisation of a railway tunnel for high speed. Case study Romania Carmen BUCUR Prof. PhD. Eng. Technical Univ. of Civil Eng. - Dep. Mechanics of Structures Bucharest, Romania Carmen Bucur, born 1951, received her civil engineering degree from Technical University of Civil Engineering Bucharest Romania in 1974 and PhD in 1994 Doru ZDRENGHEA Eng. Chief of Tunnels Department Institute of Railway Studies and Design Bucharest, Romania Doru Zdrenghea, born 1969, received his civil engineering degree from Technical University of Civil Engineering Bucharest Romania in 1996 Ionuţ MOISE student master degree - Technical Univ. of Civil Eng. Bucharest, Romania Ionuţ Moise, born 1979, will receive his civil engineering degree from Technical University of Civil Engineering Bucharest Romania in 2003 Summary Three of the ten European transport corridors cross Romania due to its geographical position: Corridor IV Helsinki bough IVC, Corridor VII Danube, Corridor IX Helsinki, fig. 1. The structure dealt with in the present study is a single track tunnel on corridor IV Helsinki, between Bucharest and Braşov. The article will present the way in which the above mentioned tunnel will be rehabilitated with a view to two objectives: to increase the travelling speed and to make seismically calculus. Keywords: Tunnel, rehabilitation, high speed 1. Introduction On the railway component of IVC branch, on Curtici-Arad-Sighişoara-Braşov-Bucureşti-Constanţa route of 880 km total length, 24% of the total traffic of Romanian Railway is running. The studied structure is single track tunnel, called Predealul Mic track I situated on - Bucureşti Braşov railway line, between Predeal and Timişu de Sus, (fig. 1, fig. 5). This railway is part of European networks of AGC, AGTC, TER Agreements (European lines E56 and E54). The modernising project of substructure aims is achieve 160 km/h maximum speed. The main works categories which are to be executed on Bucureşti Braşov line section refer to embankments (3678 mil. m 3 ), embankments reinforcement (10 km), bridges works (0.40 km), tunnels works (1.20 km) etc. The works have to be carried on during 2000-2003, [1]. For several years an intense activity to adopt technical regulations in accordance with European recommendations has been going on in our country. Such regulations as the clearance ones for high speed traffic or anti-seismic calculations are in final stages of carrying out. 2. Description of the studied structure The tunnel crosses the Carpathians and it is situated on Piatra Mare s western side, fig.1. The Predealul Mic track I tunnel has been used since 1940, in 1965 it was electrified and in this period of 62 years no major intervention occurred. At present, in the tunnel the goods trains run at a speed of 40 km/h, and passenger trains at a speed of 65-70 km/h. The rehabilitation intends to increase the speed to 100 km/h. The tunnel is situated at an approximate 1000 m height, it is 128 m long and its maximal covering is of 26.17 m. The cross section of the tunnel has the classical horseshoe shape, made up of concrete, its intrados lined with stone rubbles for protection, fig.2.
The mountain mass tunnelled is composed of argillaceous slates very folded and faulted. Fig. 1 Romanian map the Corridors Fig. 2 Existing transversal section 3. Technology for the achievement of the new transversal section of the tunnel The tunnel has been the object of a complex technical expert appraisal. Samples have been used to determine the phisico - mechanical characteristics of the ground, concrete, reinforcement. For the concrete, non-destructible tests have been performed. These tests demonstrated that the main structure is generally good. To inscribe the rated G.C. clearance of obstacle [2] the solution of lowering the levelling with 0.60 m has been adopted. This could be made by replacing of the existing tunnel basement, fig.2. Taking into consideration that the lateral pressures are not high, it resulted a straight tunnel basement of 0.60 m thickness also. Its lower part will be at 0.10-0.15m above the inferior level tunnel foundation, fig.3. As Bucuresti - Predeal railway has two tracks, the works of rehabilitation, reinforcement, tightness, hydroinsulation etc and of tunnel basement restoration are to be made with total track lock. The new tunnel basement will be executed on alternating cuts of 4.0-6.0 m. To reduce the maintenance and operation expenses, they propose to give up the ballast prism and to pay special attention to concrete pouring and to track adjusting for inscribing on the designed levelling. Fig. 3 New transversal section 4. Calculation model The calculation model is composed of two dimensions finite elements in plane state of deformation. From the tunnel axis-laterally and bellow, a zone of massif of 5 diameters has been considered. Above the tunnel, the maximum covering of 26.17 m has been considered, fig.4. The general size of model (63x56m) assure the elimination of perturbations created by the kinematic consequences
from the outline. The connections from the model outline are realised so that they model the ground continuity. So in the model points, on vertical sides, rigid connections on horizontal direction have been introduced and also elements with elstic behaviour on vertical direction. On inferior horizontal side, rigid connections have been introduced on vertical direction. The choice of finite elements size have been made so that all materials composing the tunnel and ground could be modelled. The strengthening structure has been divided in a finer network aiming to obtain a better accuracy of the stress state in this one. The masses taken into consideration correspond to strengthening structure, ground and 20% of the standard convoy. Fig. 4 Calculation model The physical - mechanical, static and dynamic characteristics of ground and of structural concrete are determined by the technical expert appraisal. 5. Seismic calculation From seismic point of view, this area is affected by earthquakes from Vrancea region, fig. 5. The tunnel is placed in 7 1 seismic zone (with a return period of 50 years). When it was designed, the tunnel has not been verified from seismic point of view. 5.1 Dynamic characteristics of the structure 20 modes of vibration have been determined, reaching out a modal mass participation ratio of more 98% on the two directions of motion. Fig. 5 Romanian seismic map The fundamental mode (T 1 = 0.38s) is represented by the vibration on vertical direction which entails the whole assembly structure-ground, fig 6. Mode 2 (T 2 = 0.32s) is the vibration on horizontal direction, entailing the structure ground assembly, fig. 7. Mode 3 (T 3 = 0.27s) is a torsion vibration entailing mainly the massif, fig. 8. Mode 4 (T 4 = 0.21s) is represented by a vibration on vertical direction but with displacements of opposite direction on the massif and structure. In table 1 are presented dynamic characteristics and the modal mass corresponding to the first 3 modes of vibration. Table 1 Dynamic characteristics Mode Period (s) Direction Modal mass Fundamental 0.38 Vertical 67 % 2 0.32 Horizontal 83 % 3 0.27 Torsion -
Fig. 6 Mode 1 Fig. 7 Mode 2 Fig. 8 Mode 3 5.2 Spectral response The study aims to obtain the seismic response by spectral analysis. The spectrum used is the designing spectrum of technical regulation [4] corresponding to the seismic zone where the tunnel is placed. Considering the dynamic sensitiveness of the structure, the spectrum has been considered successively in three situations of action, meaning: (1) on vertical direction (2) a horizontal direction and (3) at 45 0. The mechanical characteristics for the spectral response are presented in table 2. Mechanical characteristics Max displacement of assembly (m) Stresses (kn/m 2 ) Table 2 Mechanical characteristics Spectral action on Spectral action on Spectral action at 45 0 vertical direction horizontal direction Vertical 0.02 Vertical 0.0002 Vertical 0.014 Horizontal 0.004 Horizontal 0.012 Horizontal 0.008 Maximum Max. = 682.0 Max. = 160.0 Max. = 484.0 Maximum Maximum Min. = 25.7 Min. = 1.98 Min. = 31.2 Minimum Max. = 99.4 Max. = 20.3 Max. = 77.7 Minimum Minimum Min. = (-) 90.6 Min. = (-) 20.4 Min. = (-) 43.5 In table 3 are shown the displacements in vertical direction and the maximum stresses from spectral load in some characteristic points of the strengthening structure. Table 3 Spectral action on vertical direction Displacement Stresses Point position /value (m) (kn/m 2 ) Intrados key 0.0132 5.71 Mid basement 0.0129 217.0 On horizontal Left 0.0131 73.0 at maximum span Right 0.0131 73.0 In fig. 9,10,11 and 12 maximum and minimum stresses are presented in case of spectral action on vertical direction in the assembly ground - structure, and also in structure.
Fig. 9 Maximum spectral stresses assemble Fig. 10 Maximum spectral stresses structure Fig. 11 Minimum spectral stressess assemble Fig. 12 Minimum spectral stressess - structure (obs.: Unlike fig. 11 the colours presented in this figure were differently chosen) 6. Static calculations The make some comparisons, the results of static calculations are to be presented. The actions considered are those of the structure weight, ground and 20% of the calculation convoy (corresponding to the masses of dynamic model). In table 4 are presented various mechanical characteristics for the static response. In table 5 are shown the displacements in vertical direction and the maximum stresses from the static load in some characteristics points of the strengthening structure.
Table 4 Mechanical characteristics static calculations Mechanical Value characteristics Max displacement of assembly (m) Vertical direction = (-) 0.047 Horizontal direction = ± 0.007 Maximum Max. = (+) 422 Stresses (kn/m 2 ) Minimum Min. = (-) 168 Max. = (+) 74 Min. = (-) 1390 Table 5 Point position Displacement Stresses (m) (kn/m 2 ) Intrados key 0.0366 11.89 Mid - basement 0.0360 306.0 On horizontal left 0.0366 300.0 at max span right 0.0364 300.0 7. Comments The period of the fundamental vibration mode places the assembly structure-ground in the rigid behaviour zone. The structure has the same sensitiveness both on vertical and horizontal directions. The period of mode 2 decreases related to the fundamental mode period with 16%. The periods of mode 2 and mode 3 are different with the same percent. The contribution of the first two modes in seismic response is predominant. The maximum structural response is appropriate to the spectral action on vertical direction. The following commentaries concern the results in case a spectral action on vertical direction. - The spectral displacement of the assembly on vertical direction represents 44% of the appropriate static displacement. In the studies characteristic points the percent is 36%. - On the symmetry axis between the key section and the basement, the relative spectral displacement is only 0.3 mm; on the horizontal direction where the tunnel has the maximum span, the relative spectral displacement is almost zero (0.08 mm). Between de key section and the basement on the symmetry axis the relative static displacement is only 0.6 mm. On the horizontal direction where the tunnel has the maximum span, the relative static displacement is of 0.1mm. - The maximum spectral stresses are 1.62 times higher than the appropriate static ones. The minimum spectral stresses are in reverse ratio, namely the static stresses are of 15.34 times higher than the spectral ones. 8. Conclusions 1. The carrying out of the transversal section according to the European recommendations and redimensioning of the tunnel basement for the new stresses, will allow the increasing of the circulation speed through the tunnel up to 100 km/h, meaning the double of the existing speed. 2. From dynamic point of view, the structure-ground assembly has a rigid behaviour; the assembly sensitiveness existing both on vertical and horizontal directions. 3. The relative displacement of the sections on vertical direction (key-basement) and horizontal direction (max-span) of the strengthening structure are reduced and can be taken over by the concrete flexible deformation. 4. Except the tunnel basement, the rest of the strengthening structure verified to the new stresses doesn t require the adjustments. References [1] G. DRAGOMIR European transport corridors. Romanian railway substructure modernising projects for Corridor IV Helsinki Romanian Railway Revue no. 1-2 / 2000, pp 3-7. [2] *** UIC 502, 504, 505 [3] *** Romanian technical regulation 4392 / 1984 [4] *** Norms for anti-seismic designing of road and railway tunnel 1997