Vibrationsdämpande markfilter för reduktion av markvibrationer vid sprängning i bergtäkter

Projektet som presenteras i denna rapport har studerat möjligheterna att dämpa markvibrationer från sprängningar med hjälp av luftfyllda hål i berg. Principen är att förändringen i materialparametrar mellan berget och luften i hålen skapar reflektion av vibrationerna. Teoretisk och praktisk litteratur visar på möjligheten att skapa destruktiv interferens mellan de olika reflexerna som kan styras till att dämpa markvibrationerna. Detta projekt har utfört praktiska fältförsök i full skala för att utreda om tekniken är möjlig att använda kring bergtäkter. De utförda provningarna i verkliga miljöer visar på att det finns möjligheter att dämpa markvibrationer genom att skapa ett metamaterial som består av borrade hål i berg. Störst effekt får man om man kan skapa tillräckligt stora hål jämfört med vibrationens våglängd. Genom att välja rätt geometri, d v s håldiameter och borrplan, kan man välja vilka frekvenser där vibrationen ska reduceras. I de praktiska försöken som genomförts i detta projekt har det visats att man kan simulera stora hål genom att borra mindre hål tätt samman inom en cirkel. Detta är ett mycket viktigt resultat då de relevanta våglängder i bergtäktsammanhang är långa, vilket kräver stora håldiametrar. De simulerade stora hålen i Glimmingen visade på en potentiell dämpning av vertikala vibrationshastigheter med omkring 50 % i frekvensbanden 100-125 Hz. Detta är stora sänkningar som bör undersökas vidare om de kan realiseras praktiskt vid befintlig bergtäkt. Vid bostäder som ligger nära bergtäkter är det vanligt att vibrationshastigheterna har högst värden vid ca 30 – 40 Hz, vilket medför att de simulerade hålen skall vara 2 – 3 gånger större än de som borrades i Glimmingen. Detta medför grupperingar av borrhål inom cirklar som är omkring 3 m i diameter. Vidare visade de praktiska försöken att effektiviteten av ett sådant filter måste utvärderas med mätningar i samma punkter före och efter ett filter har konstruerats. Annars finns risk att man attribuerar vågdämpnings- och eventuella vågförstärkningseffekter som sker i berget till filtret. Kort sagt, filtrets effektivitet utvärderas felaktigt. Innan metoden med markfilter av borrhål kan användas som ett praktiskt hjälpmedel att minska markvibrationer kring bergtäkter måste ett designverktyg skapas som kan hantera alla platsspecifika variabler

The failure of traditional traffic noise control for quiet areas

One can consider the acoustic soundscape as consisting of two parts the direct acoustic soundscape and the diffuse acoustic soundscape. This fact has important consequences when attempting to change the acoustic soundscapes. The traditional approach to control traffic noise by means of noise barriers or change of traffic distribution is only valid for the areas directly exposed from sources (direct acoustic soundscape). These areas will experience a certain decrease of sound pressure levels when applying these noise control measures. However there will be a lower limit for reduction due to the presence of a diffuse acoustic soundscape. To control/modify such a diffuse acoustic soundscape has been shown very difficult by traditional means of noise control. Main characteristic of diffuse acoustic soundscapes is the presence of a multitude of sources, distributed over a wide area contributing evenly to the acoustic soundscape in a certain areas. Screening will only lead to a redistribution of sound, however consequences of such a redistribution will not be recognised in a diffuse sound field. Absorption has been identified as a main parameter to control diffuse acoustic soundscapes. Reducing sound pressure levels in shielded areas such as inner-yards can only be achieved by adding acoustically absorbing areas along the transfer path between source and receiver, but especially inside the inner-yard. Redistribution of traffic flow has been shown to have a tremendous effect on the directly exposed side, but only a small effect in shielded areas

Reduction of physiological stress by urban green space in a multisensory virtual experiment

Although stress is an increasing global health problem in cities, urban green spaces can provide health benefits. There is, however, a lack of understanding of the link between physiological mechanisms and qualities of urban green spaces. Here, we compare the effects of visual stimuli (360 degree virtual photos of an urban environment, forest, and park) to the effects of congruent olfactory stimuli (nature and city odours) and auditory stimuli (bird songs and noise) on physiological stress recovery. Participants (N = 154) were pseudo-randomised into participating in one of the three environments and subsequently exposed to stress (operationalised by skin conductance levels). The park and forest, but not the urban area, provided significant stress reduction. High pleasantness ratings of the environment were linked to low physiological stress responses for olfactory and to some extent for auditory, but not for visual stimuli. This result indicates that olfactory stimuli may be better at facilitating stress reduction than visual stimuli. Currently, urban planners prioritise visual stimuli when planning open green spaces, but urban planners should also consider multisensory qualities

A laboratory study on the effects of wind turbine noise on sleep: Results of the polysomnographic WiTNES study

Study Objectives: Assess the physiologic and self-reported effects of wind turbine noise (WTN) on sleep. Methods: Laboratory sleep study (n = 50 participants: n = 24 living close to wind turbines and n = 26 as a reference group) using polysomnography, electrocardiography, salivary cortisol, and questionnaire endpoints. Three consecutive nights (23:00-07:00): one habituation followed by a randomized quiet Control and an intervention night with synthesized 32 dB LAEq WTN. Noise in WTN nights simulated closed and ajar windows and low and high amplitude modulation depth. Results: There was a longer rapid eye movement (REM) sleep latency (+16.8 min) and lower amount of REM sleep (-11.1 min, -2.2%) in WTN nights. Other measures of objective sleep did not differ significantly between nights, including key indicators of sleep disturbance (sleep efficiency: Control 86.6%, WTN 84.2%; wakefulness after sleep onset: Control 45.2 min, WTN 52.3 min; awakenings: Control n = 11.4, WTN n = 11.5) or the cortisol awakening response. Self-reported sleep was consistently rated as worse following WTN nights, and individuals living close to wind turbines had worse self-reported sleep in both the Control and WTN nights than the reference group. Conclusions: Amplitude-modulated continuous WTN may impact on self-assessed and some aspects of physiologic sleep. Future studies are needed to generalize these findings outside of the laboratory and should include more exposure nights and further examine possible habituation or sensitization

Sounds of Nature in the City: No Evidence of Bird Song Improving Stress Recovery

Noise from city traffic is one of the most significant environmental stressors. Natural soundscapes, such as bird songs, have been suggested to potentially mitigate or mask noise. All previous studies on masking noise use self-evaluation data rather than physiological data. In this study, while respondents (n = 117) watched a 360\ub0 virtual reality (VR) photograph of a park, they were exposed to different soundscapes and mild electrical shocks. The soundscapes-"bird song", "bird song and traffic noise", and "traffic noise"-were played during a 10 min recovery period while their skin conductance levels were assessed as a measure of arousal/stress. No significant difference in stress recovery was found between the soundscapes although a tendency for less stress in "bird song" and more stress in "traffic noise" was noted. All three soundscapes, however, significantly reduced stress. This result could be attributed to the stress-reducing effect of the visual VR environment, to the noise levels being higher than 47 dBA (a level known to make masking ineffective), or to the respondents finding bird songs stressful. Reduction of stress in cities using masking with natural sounds requires further studies with not only larger samples but also sufficient methods to detect potential sex differences

Mjuka eller hårda data för bedömning av järnvägars bullerstörning

Viljan att vistas utomhus minskar med ökande trafikstörning mätt i dB. Men störningarna är inte bara relaterade till ljudnivån utan störningarna ökar ju torftigare utemiljökvaliteterna är (Mistraprojektet Ljudlandskap för bättre hälsa). Det bör betyda att förbättring av mjuka kvaliteter torde minska störningarna av buller. Utbyggnaden av Södra stambanan genom Åkarp i Burlövs kommun har blivit ett mycket omdiskuterat projekt. Det beror sannolikt på kombinationen av att trafikbelastningarna spränger tidigare kända ramar och att gängse beräkningsmodeller och bedömningskriterier inte hunnit anpassa sig till så stora volymer, samtidigt som forskningen kring buller/hälsa och miljömedicin gått framåt och gör anspråk på ny bedömningskriterier. Förändringar är på väg. EU föreskriver nya beräkningsmetoder, men varje medlemsland får fortfarande använda sin gamla metoder. Denna artikel tar upp några av de frågeställningar som utkristalliserats från kommunens sida i samband med järnvägsutredningen för Södra stambanan mellan Malmö-Lund

A Parametric Method to Synthesize Wind Turbine Sounds

The annoyance to wind turbine sound is today well known. There is no doubt that increased sound pressure level causes in general an increased annoyance. However, when it comes to additional descriptors of the wind turbine sound, such as e g equivalent frequency spectrum or amplitude modulation, there is no consensus on what parameters that are most important. In the research project Wind Turbine Noise Effects on Sleep (WiTNES) there was a need for 8 hour long sound signals from wind turbines that were completely free of extraneous sounds. Recordings from reality are difficult to maintain free from disturbances. Instead a parametric synthesis method was developed that is capable of creating wind turbine sounds of arbitrary length. The sounds can be designed in terms of equivalent frequency spectrum, what frequency bands that have amplitude modulation as well as frequency dependent amplitude modulation strength and variation. Recordings of wind turbine sounds at immission distances from different wind turbine types were used to find relevant values for the parameters. This paper describes the synthesis method and some examples of input parameters

Prediction and Optimisation of Traffic Noise. A Study on Noise Barriers and Shielded Areas

The main contribution of noise levels in cities is today road traffic. The strongest source for all road vehicles is most often the tyre-road contact. This source position close to the ground is fortunate with respect to secondary noise abatement measures, such as absorbing road surfaces or noise barriers. The first part of this thesis deals with noise reduction possibilitiesusing optimised surface treatments on the ground and on noise barriers, with special attention to low-height barriers. The insertion loss can be significantly improved through optimisation. The amount of improvement depends on barrier geometry, the impedance of the surrounding ground and on the frequency. The largest improvements can be found at low frequencies, but siginificant improvements can also be found at 1 kHz, where the traffic noise spectrum is strongest. A specialized surface on the road and a 1 m high barrier gives 7 dB better insertion loss than a rigid barrier of equal geometry when weighted with a representative traffic noise spectrum. The second part of this thesis studies noise in cities, where a many sources distributed over a large area are responsible for the total noise level. The noise levels on the silent side is in focus, which due to shielding has lower noise levels than the directly exposed side. Two new methods which are suitable for silent side calculations over large areas are presented.The main contribution to the noise level on the silent side is found to propagate over the rooftops of surrounding buildings and not around them. The noise abatement possibilities in cities are then studied using these models with respect to two features: 1) An increased absorption, and 2) A modified vehicle flow distribution. Both features show a promising noise reduction potential. A reduction of 10 dB may be possible on the silent side through increasing absorption. A traffic concentration to few streets gives larger areas with low levels than an evenly distributed vehicle flow. The amount of reduction is however dependent on the street grid geometry and the existing vehicle flow

Subjective evaluation of footstep noise on lightweight structures - Design of laboratory experiments

Footstep noise in dwellings with a lightweight structure is often perceived as more disturbing than footstep noise in a house with a heavyweight structure for an equal weighted impact noise level measured using a tapping machine. This is still the case when extending the frequency range down to 50 Hz. Many studies have been done on the subject during the latest decades, but no clear conclusion exist on all aspects of the subjective evaluation mechanisms involved with footstep noise. This paper presents the main findings from a literature survey on subjective aspects of footstep noise, low-frequency hearing, laboratory experiment design and annoyance studies in dwellings. The paper also presents the design of coming laboratory experiments on subjective evaluation of footstep noise within the AkuLite project, and some initial findings on acoustic characteristics of footsteps on both lightweight and heavyweight structures