EUROPEAN CIVIL ENGINEERING, ARCHITECTURE AND MANAGEMENT
www.eceam.eu
Volume 2023
ISSUE 1
Part 2
VIBRATION FROM THE RAILS IN THE SOFIA METROPOLITAN
Prof. PhD. Eng. Stoyo Todorov
University of Architecture, Civil Engineering and Geodesy, Sofia
Bulgaria, Sofia 1164, 1 HristoSmirnenskiblvd.
E-mail: stoyo_fte@uacg.bg

Abstract:
    The metro in Sofia started operating 25 years ago. The vibrations in the rails are produced by the interaction of the rolling stock and the rails. Vibrations cause noise (20-20000 Hz) and vibrations (0-15 Hz), imperceptible to the human ear, in the environment. They reach residential and public buildings near the route. Their spreading depends on the environment. In solid materials, building structures, rock formations, etc., their distribution is greater than in loose soils, porous materials, etc. If the track is on aartificial facilities or passes over land, the vibrations from passing metro trains may increase. When the train accelerates and stops at a station, in addition to vertical vibrations, longitudinal and transverse vibrations are generated. They increase the overall effect with a longitudinal component.

Резюме:
    Метрото в София започва работа преди 25 години. Вибрациите в релсите се получават от взаимодействието на подвижния състав и релсите. Вибрациите причиняват шум (20-20000 Hz) и трептения (0-15 Hz), недоловими от човешкото ухо в околната среда. Те достигат до жилищни и обществени сгради в близост до трасето. Разпространението им зависи от околната среда. При твърди материали, строителни конструкции, скални образования и т.н., разпространението им е по-голямо, отколкото при несвързани почви, порести материали и др. Ако трасето е на изкуствено съоръжение или преминава наземно, вибрациите от преминаващите метровлакове може да се увеличат. При ускоряване и спиране на влака на спирка, освен вертикалните се генерират надлъжни и напречни вибрации. Те увеличават общия ефект с надлъжна компонента.

Keywords:
    railwaytrack, railsvibration

Introduction

   When rolling stock interacts with the rails in the metro, noise and vibrations occur. They arise due to:
    - The normal sinusoidal movement of the axles;
    - Acceleration and stopping of the train at the stations, due to an increase in the longitudinal component;
    - Ground passage of the metro and artificial facilities - bridges and overpasses.
Vibration spreading is damped in elastic materials, loose soils and porous materials. In continuous environments, dense materials, bedrock, facility structures, propagation is stronger. In the case of a weldless track, worn rails and unregulated temperature gaps, the vibrations are amplified. The normal movement of the colossus is sinusoidal, due to the clearance between the distance between the rails and the flanges of the wheels. It also generates vibrations. Vibrations are amplified with unsupported track, wider gauge, one-sided or two-sided rail dips, etc.

A metro has been operating in Sofia for 25 years. This improved the general urban development plan and the transport master plan. Plots near metro stations have become attractive for development. In the area of Musagenitsa quarter, where the metro runs above ground, the vibrations are felt. Most of the facility after Musagenitsa in the direction of Mladost 1 fig. 1. It turned out that, from an advantage, the metro turns into a nightmare for some of the people who bought properties in close proximity to it [1].

New buildings are being built next to the metro, but with their accommodation, the owners understand that they have a problem. When the metro line is above ground, the problem is noise. And when the building is next to the tunnel or an artificial facility, they are also tormented by vibrations.

These problems are relevant for the first metro line in the Iztok district between "Interpred" and G. M. Dimitrov Blvd., and in Musagenitsa before the Mladost 1 district [1].

Fig. 1 Scheme of the metro in Sofia

The problem also arises further from the metro line, when the train moves on the bridge over Vartopo Park. There are also problems in the area of Andrey Sakharov Blvd., Mladost quarter, Plovdivsko Pole St., Dianabad quarter, etc.

Superstructure of the Sofia metro

The superstructure for the metro is a classic ballast less construction. Analyzes, measurements and experiments have been done repeatedly, but the problem of vibration and noise has not been finally solved. The metro train has a table that is elastically suspended from the bogies. The wheel axles are spring-suspended to the bogies fig. 2, similar to the scheme shown in [2]. Which means that in addition to the normal vertical, longitudinal and transverse loading, a dynamic component also appears during movement. The interaction of the wheels with the rails is elastic because the wheel and the rail are elastic steel elements. The construction of the upper building is a Winkler beam on an elastic base. The rail is supported by two-block sleepers, and between them there is an elastic rubber pad. Transverse elasticity (rotation) of the knot is achieved with an elastic clamp of the joint. In our country it is SKL 14 or SKL 21 [3]. The two-block traverse, compared to the monoblock B-91, also has some elasticity. The two blocks can be rotated. The two blocks can be rotated independently within the reach of the rubber boot. The rails are welded lengthwise and work as long welded rails [4]. The streel elements between the blocks is also elastic.

Fig. 2 Dynamic model of the vehicle-railway interaction [2].

Under the sleepers there is a rubber boot fig. 3. The concrete is poured to the edge of the boot. The rubber boot makes it possible to replace single sleepers. Some elasticity is guaranteed under load. In fig. 3 can see the placement of an additional elastic pad in the rubber boot of the two-block sleepers [5, 6].

Fig. 3 Rubber boot and additional elastic pad on the sleepers [5, 6]

Under the superstructure, concrete is poured next to the tunnel structure. No resilient element is provided between the precast concrete and the structure of the tunnel or artificial facilities.

Technical requirements for the implementation of the above construction

The metro rails are bearing and contact. The supporting rails are type 49 E1 with volume hardened heads, without holes and without edge hardening, hardness R = 350 НВ, according to BDS EN 13674-1:2004 +A1:2008 fig. 4.

Fig. 4 Carrier rail type 49 E1 and contact rail

The smallest production length of rails is 25 m, and the smallest length of an inserted piece of rail around the points of connection of individual construction sections or switches is 6m[7]. Before commissioning, the heads of the rails are ground. Guideless track is made with aluminium-thermite welds or by methods that guarantee a weld strength of 100% of the strength of the rail steel. The inclination of the rail’s inwards to the axis of the road should be 1:40, which should be provided by the inclined upper surface of the two-block sleepers or by the fasteners.

Rail fasteners are SKL14 [3] fig. 4, two-block reinforced concrete sleepers DT-M for ballastless railway fig. 5. The rail fasteners of the rails to the sleepers must comply with EN13481-5:2012 for the requirements for fasteners and those of BDS EN 50122-1:2004 for the electrical insulation of the rails in relation to the rest of the structure.

Fig. 5 Type fastening SKL 14 for two-block sleepers DT-M

The fastening system of the rails for the sleepers must be elastic - type W14 or W21[8]. The latter is interchangeable with the W14 system with the differences that the elastic clamps SKL14 are replaced by longer ones, resp. the more resilient SKL21 (in the stations areas) and hard plastic under-rail pads are replaced with highly resilient closed-cell rubber. No changes to the outline of the upper surfaces of the sleepers are necessary. In places, the elastic clamp is W21. It is similar to W14, but more elastic.

Contact rail fig. 4 provides the power supply to the traction electric motors of the rolling stock with direct electric current with a voltage of 825 V. The transmission is carried out by means of sliders touching from below on the head of a contact rail.

In a straight section and a curve with a radius R≥1200 m, the traverse grid must have a density of 1680 tr/km. Every second traverse must have a metal connecting profile fig. 6.

Fig. 6 Two-block sleepers Sateba and DT-M

In curves with R<1200 m and their adjacent transition curves, the density ofsleepers should be 1840 tr/km fig. 7, and all sleepers must have a metal connecting profile. Rubber boots and pads for the two-block sleepers, for ballastless track. The solid concrete enclosing the tracks up to the edge of the traverse boots is of at least B30 class.

Fig. 7 Distribution of two-block sleepers DT-M before and after concreting

In the platform sections of the metro stations, the construction of the railway track for the second metro line is non-sleepers - fastening system 336 [9], anchored on continuous reinforced concrete beams along the length of the tracks fig. 8. The schemes for the distribution of the fastener 336[4] are the same as for the traverse structure. Stationary lubricators are installed in the track construction in the direction of train movement before each curve with radius R≤650 m.

The minimum height for the construction of the railway track from the head elevation of the rail HER to the bottom elevation of monolithic concrete is a minimum of 600 mm. When connecting new tracks to those in operation, this height is allowed to be reduced or increased, incl. using trackless track constructions.

All cross lines in the strap and hand are cast from manganese steel (13Mn) with a minimum tensile strength of 1800 N/mm2 and a hardness of not less than 320 HB.

The type of rails from which the switches are made must match the type of rails of the tracks they connect. All arrows in the project must be equipped with hydraulic arrow turning machines and built-in locks. Dimensionally, the automatic machines must fit completely into the gauge of the arrows at the tips of the tongues.

Fig. 8 Type fastening system 336 [9]

Vibrations from the rails

Vibrations of the rolling stock when passing along the rails have a frequency of 1 to 20 Hz. Frequencies from 20 to 20,000 Hz are perceived as noise. At each of the transitions, as given in fig. 1 an elastic element or an elastic pad can be placed. The elastic clamp W 14 can be replaced with W 21 [8].

Fig. 9 Elastic pad under the single supports of the rail [6]

Another solution is presented in fig. 10. The elastic pad here is under the rubber boot [10]. It is a matter of calculations and selection what it should be, of what material and how to produce it.

Fig. 10 Additional elastic pad under the rubber boot of the sleepers [10]

Looking at fig. 2 has another possibility to reduce the spread of vibrations. Between the enclosing concrete and the structure of the tunnel or facility.

Conclusions

    The review of the situation and analysis of the problems leads to some conclusions, conclusions and proposals for a solution:
    - The vibrations of the rails caused by the movement of metro trains is a problem that can and should be solved. Many solutions are known in world practice and some of them are successfully implemented in the Bulgarian metro. There are also additional possibilities by placing additional elastic elements in the area between the individual elements of the railway structure and the structure of the tunnel or facility.
    - In the area of facilities, it is necessary to make measurements in order to determine the nature of transmission of vibrations and mark measures.
    - In the area of stations, it should check the influence of the variable longitudinal forces from braking and acceleration of the train on the vibrations during

Literature

[1]      Terziyska S., Nobody wants apartments meters from the metro, in "24chasa", 09/08/2010, https://www.24chasa.bg/
[2]      Coenraad Esveld , Modern railway track, MTR- productions , ISBN 90-800324-3-3, Netherland, 2001
[3]      Vossloh, Fastening system, edition VT/04, 08=2004, www.vossloh.com
[4]      Nitova D. "Safety of the railway at high temperatures" - magazine "Railway Transport" no. 9/2008
[5]      Brochure Elastic Solutions for use in the Railway Superstructures EN.pdf, www.getzner.com
[6]      Elastic insertion pads for sleeper boots EN.pdf, www.getzner.com
[7]      Nitova D. "Defects in the elements of railway switches", Scientific journal Mechanics Transport Communications, vol. 12, issue 3/3, 2014 International scientific conference of VTU "T. Kableshkov"
[8]      Vossloh, System W14/ W 21 with tension clamp SKL14 / Skl 21, www.vossloh.com
[9]      Vossloh, System 336 Highly elastic rail fastening for metro – the ribbed base plate solution for slab track, www.vossloh.com
[10]   Case Study Elasticity for the Slab Track in the Gotthard Base Tunnel, (CH) EN.pdf, www.getzner.com macia/zahranicna-politika
Last update: 1.2023 ©2023 Zdravko Rusev EUROARCH, All author (Kvetoslav Kmec, SK) rights reserved.