Noise Attenuation Due to Vegetation

Transcription

1 Noise Attenuation Due to Vegetation Vasile BACRIA Politehnica Univesity of Timisoaa, Bd. M.Viteazu,1, Timisoaa, Nicolae HERISANU Politehnica Univesity of Timisoaa, Bd. M. Viteazu, 1, , Timisoaa, Abstact: - It is well-known that noise deceasing techniques ae based on two types of methods: one active and anothe passive. The latte often employs the vegetation which is planted foming geen potection zones aeas. In this pape we pesent some consideations concening noise attenuation due to vegetation, emphasizing some elements which influence it. The elucidation of these elements has been done by measuements. The esults of measuements wee pocessed, analysed, intepeted and compaed with the admissible values defined by standads. Keywods: - noise, attenuation, passive method, vegetation 1. INTRODUCTION The poblem of noise and vibation attenuation eceived in the last yeas an inceasing impotance and became an issue of lage impotance. This is due to the multiplication of noise souces and also to the inceasing of thei powe, which lead to a noisy life climate. In the same time, it was poved that noise and vibation have injuious effects on human s health and advesely influence the woking efficiency. The noise and vibation affect the human s health pemanently, eveywhee they ae encounteed. That is why attenuation measues intended to decease the noise and vibation levels should be taken in all woking domains in ode to ensue human potection against these noxious factos. At intenational level thee ae developed standads which limit the noise level and human exposue to noise. In ou county, the foundations of a lage action concened with noise and vibation contol has been set few decades ago [1]. In this pape we pesent some consideations about noise deceasing though passive methods, especially noise attenuation due to vegetation. Theefoe we identified the elements which influence it and thei effects. The elucidation of these elements has been done though measuements. 2. NOISE SOURCES The noise is geneated by souces fom industial equipments, building sites, spots activities on stadiums, maket activities, disco-clubs, oad, ail and ai taffic and so foth. The noise geneated by these souces has noxious effects upon people s life and activity. It has specific souces, levels and chaacteistic specta. Measuements should be pefomed in ode to detemine the chaacteistic levels and specta and fo identification of specific souces. Measuements pefomed in industial halls emphasize the weekly aveage and daily values of the equivalent noise the wokes ae exposed to. These values, pesented in Table 1, exceed the admissible limit fo daily exposue in the woking place, established at 87 db [2], [3]. Table 1. Equivalent noise levels Measued place L eq [db] Weaving station Running hall fo intenal buning engines Spinning station 90.6 The noise popagates outside the industial hall and affects the envionment. Within constuction sites thee ae pesent vaious machines and equipments such as excavatos, bulldozes, canes, concete mixes, tucks, tactos, moto pumps, and so foth. The noise geneated by these ones oiginates in the mechanical, electomagnetical, aeodynamical and hydostatical pocesses which aise duing the woking egimes. Thus, the causes of noise appeaance duing the mentioned pocesses ae the shock inteaction of two o moe bodies, the fiction of inteacting sufaces, the aeodynamical tubulences, the foced oscillations of igid bodies, RJAV vol X issue 1/ ISSN

2 the action of vaiable electomagnetic foces (especially at electical opeated goups), the vibation of oad o membane-shaped pats, pulsating pessue in hydostatic opeated devices. Measuements pefomed at 2 metes distance fom the wall of a building nea the constuction site emphasized values of the equivalent noise level of db, which ae highe than the admissible limit established at 50 db [4]. The chaacteistic noise levels on the building sites duing the day ae situated between db fo fequencies between Hz. Also the pesence in the uban taffic of a lage numbe of tams, tucks, tains and tactos contibute to an inceasing noise level. The deteioated state and the natue of the oad supestuctue favoued highe values of the noise level poduced by diffeent types of vehicles, in tems of the speed. Measuements pefomed in 119 points located nea oad o ail taffic in Timioaa City eveal that in 95 of the measued points (79.83%), the equivalent noise level exceeds the maximum values allowed by STAS concening Uban acoustics. This ovetaking is of db. The taffic intensity anged fom 9 veh/h to 2681 veh/h and the vehicle speed was found to be between km/h [5]. The admissible limit of the noise level measued at 2 m distance fom the building wall, which is set at 50 db, was in geneal exceeded with db. The noise levels geneated by tains measued at the ailway zone limit exceed the admissible limit with db. At the Timioaa Aipot the noise levels exceeds the admissible limit with 7 db [5]. An inceased noise level is pimaily due to the vehicles, tains and aiplane taffic, to the change of diection, to the vehicle passing ove the tam ails as well as to the acceleation and beaking. Duing the displacement of vehicles, in the coido steets, an inceased noise level is poduced also by the supeposition of the eflected wave on the diect one. A high degee of technical deteioation of some vehicles is an impotant facto that inceases the noise poduced by the oad taffic. Because in the majoity of the points whee measuements wee taken the admissible limits ae exceeded, it is necessay to decease the noise whethe by active o passive methods. 3. ATTENUATION DUE TO VEGETATION In ode to educe the noise in Timioaa City, on many steets, the supestuctue of the unways was impoved. Many cossing wee modenised and semaphoes wee installed. One-way taffic was imposed fo some oad thooughfaes, the speed of vehicles was limited and on many steets wee installed physical speed limites. It was eliminated the pesence in taffic of heavy tucks in the cental aea of the City. In some aeas it was esticted the access of cetain categoies of vehicles. In the N-E zone of the City has been activated the ing-oad which ediect the heavy taffic in this diection. The effects of the implementation of these measues on noise eduction wee evaluated though new measuements. Analysing the data of these measuements one can obseve that by implementing the above mentioned noise deceasing methods, it was obtained indeed significant eductions of the noise levels, but in some cases, the admissible limits established by STAS ae still exceeded. In these cases, othe acoustical aangements on the thooughfaes ae needed to be designed and implemented in ode to diminish futhe the noise geneated by tanspotation means. An attenuation of the noise level in the uban envionment can be obtained by inceasing the distance between the inhabited aeas and the unway o by ceating potection aeas (geen aeas). The level of noise changes once with the distance fom the souce; it decays once with aising the distance. The noise level L n aound the buildings situated at a distance n fom the unway fo point souces and fo souces disposed in succession at a distance s, fo n s/2 is given by the elation [6] L L7 20k n n s (1) 7 and fo n> s/2 0.5s L L k k n n 7 20 s lg lg (2) 7 0.5s and fo geometical souce L L7 10k n n s (3) 7 whee L 7 epesents the noise level measued at 7.5 m distance fom the axis of the unway, k is a coefficient with given value (table 2) and k s is a coefficient elated to the featue of the gound. Figue 1. Noise popagation in fee space Concening the coefficient k s, the following values ae consideed: 0.9 fo asphalt, 1 fo gound and 1.1 fo tuf. RJAV vol X issue 1/ ISSN

3 Table 2. Detemination of the coefficient k s [m] k s [m] k The distance s fo the tanspot fluxes is detemined with the elation v s 1000 t (4) N whee v t is the speed in km/h, and N the taffic intensity in vehicle/h. Also the tees, bushes and tufs contibute to sceening noise souces. The pope attenuation in these cases, as well as fo the sufaces coveed with tuf is detemined depending on fequency and length of the coveed zone with the help of the diagam fom fig.2 [1]. Attenuation constant [db/100m] Fequency [Hz] Figue 2. Noise attenuation due to vegetation An assessment of noise popagation and attenuation due to geen zones could be done using the schemes pesented in figues 3 and 4. An assessment of the noise popagation in the cases when it is due only to pemanent taffic could be accomplished using Eqs.1-3, whee beside the suface coefficient k s it is intoduced also the geen zone coefficient k gz. It is ecommended to use the following values of the coefficient k gz [6]: k gz =1.5 fo potection zones made of planted tees with dense cown, with bushes on the peimete; k gz =1.2 fo plantations of wood-pak type having aveage thickness and with bushes. Figue 4. Noise popagation scheme fo multiple geen sceen Noise popagation though geen zones must be assessed with the help of the following fomulas [6]: - fo point souces: Z L n n L7 20lg 1. 5Z Bm (5) fo a ange of souces in cases n s/2 o fo a geometical souce: Z L n n L7 10lg 1. 5Z Bm (6) fo a ange of souces in case n >s/2: 0.5s L n n L7 20 k lg lg 7 0.5s (7) Z 1.5Z B m 1 whee is the specific absoption of acoustic powe chaacteistic fo plantations (table 3) and Z is the numbe of component elements in the geen zone. Table 3. Acoustic powe absoption by plantations [6] Fequency Boadband [Hz] aveage eduction Reduction of the acoustic pessue level Type [db/m] Pine Bushes of pines Fi-tees Dense boadleaved tees Dense hedge Figue 3. Noise popagation scheme though potection geen zones In the following we pesent the esults obtained by measuements. In figs.5-7 ae pesented the time-histoy of the noise level, the spectal distibution of the noise and the statistical distibution at 7 =7.5 m fom the axis of the fist unway and in figs.8-11 the same types of RJAV vol X issue 1/ ISSN

4 diagams ae obtained at a distance n =20 m behind the geen sceens pesented in fig.3. Figue 5. Time histoy of the noise level at 7.5 m distance fom the axis of the fist unway Figue 9. Spectal distibution of the noise behind the geen zone Figue 6. Spectal distibution of the noise at 7.5 m distance fom the axis of the fist unway Figue 7. Statistical distibution of the noise at 7.5 m distance fom the axis of the fist unway Figue 10. Statistical distibution of the noise behind the geen zone These measuements have been taken using as a noise souce the oad taffic having an intensity of 1752 vehicle/h. In this case it is obtained a noise attenuation of 5.9 db. The potection geen zone was epesented by a dense wood fomed of tees, bushes and hedge. In the figues ae pesented the time histoy of the noise level, the spectal distibution of the noise and a statistical distibution at 7 =7.5 m distance fom the axis of the fist unway while in figues the same type of diagams ae obtained at a distance n =30 m behind the geen zone compounded of multiple tee-sceens. Figue 8. Time histoy of the noise behind the geen zone Figue 11. Time histoy of the noise at 7.5 m distance fom the axis of the unway RJAV vol X issue 1/ ISSN

5 Figue 12. Spectal distibution of the noise at 7.5 m distance fom the axis of the unway Figue 13. Statistical distibution of the noise at 7.5 m distance fom the axis of the unway Figue 16. Statistical distibution of the noise behind the geen zone As in the pevious case, the noise souce used fo ecoding these measuements was epesented by the oad taffic having an intensity of 1440 aut/h. In this case, it was emphasised a noise attenuation of 16.5 db. The potection geen zone has been compounded of multiple geen sceens located as follows: the fist sceen B 1 =5 m made of geen fence and bushes and othe two tee sceens having B 2 =8 m and B 3 =8 m espectively. These geen sceens wee sepaated by the empty zones A 1 =3 m and A 2 =6 m. The esults of the measuements taken in case of two geen sceens ae pesented in figues 17-19, whee we pesent the time histoy of the noise level, the spectal distibution of the noise and the statistical distibution ecoded at 7 =7.5 m fom the axis of the fist unway while the same types of diagams ae pesented in figues coesponding to the distance n =30 m behind the above descibed geen zone. Figue 14. Time histoy of the noise behind the geen zone compounded of multiple tee-sceens Figue 17. Time histoy of the noise at 7.5 m distance fom the axis of the unway Figue 15. Spectal distibution of the noise behind the Figue 18. Spectal distibution of the noise at 7.5 m geen zone distance fom the axis of the unway RJAV vol X issue 1/ ISSN

6 compounded by two geen sceens: a fist sceen made of hedge and bushes having B 1 =5 m and a second sceen made of tees having B 2 =22 m, sepaated by an empty zone A 1 =3 m. Fom the above esults of measuements one can be obseved the efficiency of the vegetation on deceasing the phonic pollution. 4. CONCLUSIONS Figue 19. Statistical distibution of the noise at 7.5 m distance fom the axis of the unway Figue 20. Time histoy of the noise behind the geen zone compounded of two tee-sceens Figue 21. Spectal distibution of the noise behind the geen zone The noise souce used fo ecoding these measuements has been epesented by the oad taffic having an intensity of 1656 aut/h. In this case the noise attenuation emphasized by measuements was of 5.8 db. The potection geen zone was Deceasing the noise due to vegetation poduces a diminution of the degee of phonic pollution and also a diminution of the pecentages of distubed people. The vegetation has also a positive effect on the olfactoy, visual and sound comfot. The choice of geen zone type depends on the degee of phonic attenuation desied. Using vegetation to phonic attenuation contibutes also to the embellishment of the landscape. Vegetation is vey useful fo people s life and health; even it is viewed as a means fo noise eduction. REFERENCES [1] Gumzescu M., Stan A., Wegene N., Mainescu V., Contol of noise and vibations, Technical Publishing House, Buchaest, 1964 (in Romanian) [2] *** Geneal noms fo wok potection, National Institute of Reseach and Development fo Wok Potection, Buchaest, 2002 (in Romanian) [3] Bacia V., Toade M., Heianu N., Opiescu C., Ciupa V., Fiat C., Consideations concening noise attenuation in uban envionment, Poceed. IX-th Symp. Acoustics and Vibation of Mechanical Stuctues, Timioaa, May, 2007, p.7-12 [4] Bacia V., Heianu N., Deceasing the noise level on a constuction site, Session of Scientific Communications of depatment of Technical Mechanics, SIMEC 2011, Buchaest, p.15-22, 2011 [5] Heianu N., Bacia V., Toade M., Popa-Radovan S., Investigation of the noise pollution in an uban aea, WSEAS Tansaction on Systems, vol.5(7), 2006, pp [6] Iudin E.Ia., Isolation against noise, Technical Publishing House, Buchaest, 1968 (in Romanian) RJAV vol X issue 1/ ISSN