Çevresel koşulların yol üstyapısına etkisi

Abstract

ÇEVRESEL KOŞULLARIN YOL ÜSTYAPISINA ETKİSİ ÖZET Yol üstyapısının tasarım, yapım ve işletme aşamasında etkili çevresel faktörler; ısı, su (nem), yağış, don, buzlanma, kuvvetli rüzgarlar vb. yolu kullananlar açısından büyük tehlikeler yaratırlar. Trafik kazalarının da meydana gelmesinde büyük etkisi olan bu faktörler üç aşamada da (tasarım, yapım, işletme) titizlikle incelenmelidir. Gerekli önlemlerin alınmadığı durumlarda trafik kazaları kaçınılmaz olup, yollarda oluşacak hasarların onarımı da kaynak israfına neden olacaktır. Çalışma dört bölüm halinde sunulmuştur. İlk bölüm; yol üstyapısının tasarım aşamasında dikkate alınan çevresel etkenlerdir. Bu bölümde sıcaklık, su(nem), don ve buzlanma faktörlerinin yol üstyapısının tasarımını nasıl etkiledikleri anlatılmıştır. Drenaj ve çeşitleri, taban zemininin şişmesi, zeminlerin sıkıştırılmasında su (nem) etkisi, Kaliforniya taşıma oranı ve su (nem) etkisi ile geçirimli kaplamalar ve su ilişkisi, genleşme katsayısı ve elastisite modülü - sıcaklık ilişkisi, asfalt betonuna ve beton plaklara sıcaklığın etkileri, don çözülmesi ve kabarması, taban zemini, kaplama tabakası ve don ilişkisi ile soğuk bölgelerde yol üstyapı tabakalarının tasarım yöntemleri belirtilmiştir. Çevresel etkilerin şiddeti arttıkça yolların tasarımı da zorlaşmaktadır. En önemli aşama olan bu bölümde yapılacak hatalar ileride telafisi imkansız zorluklara neden olacaktır. ikinci bölüm; yol üstyapısının yapım aşamasında etkili çevresel faktörlere ayrılmıştır. Su(nem), sıcaklık ve don etkileri incelenmiştir. Yol altyapısı, alttemel, temel ve kaplama tabakası yapımında suyun etkileri, zeminin sıkıştırılmasında optimum su oranının önemi, suyun eritici özellikleri, sıcaklığın asfalt malzeme üzerindeki etkileri, beton plaklarda yol yapımı sırasında sıcaklık farklılıkları yüzünden oluşan gerilmeler, soğuk havada beton ve betonun korunması ile soğuk bölgelerde yol üstyapı tabakalarının yapımı konularına değinilmiştir. Yapım aşamasının da en az tasarım aşaması kadar önemli olduğu vurgulanmıştır. XİİÜçüncü bölümde; işletme aşamasında çevresel etkenler ve bakım, onarım çalışmaları incelenmiştir. Yolların ömürleri bu son aşamanın titizlikle yürütülmesiyle uzayacaktır. Bu bölümde yağmur, dolu, sis, rüzgar, don ve buzlanma etkileri ile mücadele yöntemleri anlatılmıştır. Ulaşımda kaynak israfı ve çevrenin tahrip edilmemesi için kar çitlerinin kullanılması anlatılmıştır. Ayrıca tuz kullarak kar ve buzlanma ile mücadelenin kötü etkileri üzerinde de durulmuştur ve tuzun sadece gereken yerlerde gerektiği kadar kullanılabilmesi için bazı teknoloji ve yöntemler önerilmiştir. Yol planlamasının yapılabilmesi, kötü hava şartlarında trafik akışının sağlanabilmesi, meteorolojik gözlem yapılabilmesi ve gerektiğinde de sürücülerin uyarılması için ölçüm, işaret ve sinyalizasyon aygıtları için yer seçiminde sis potansiyeli indeksi, meteorolojik radarların kullanımı anlatılmıştır. Son olarak da çevresel etkenler sonucu rijit ve esnek yol üst yapılarında oluşan hasarlar ve bunların onarımı ile ilgili bilgi verilmiştir. Son bölüm olan dördüncü bölümde ise çalışma sonunda ulaşılan sonuçlar ve öneriler verilmiştir. X111

THE EFFECTS OF ENVIRONMENTAL CONDITIONS TO PAVEMENTS SUMMARY Environmental conditions like temperature, water (moisture), rain, ice, strong winds etc. which are effective in designing, costructing and operating pavements cause great dangers for the road users. These factors which are the main cause of traffic accidents should be investigated thoroughly in its three phases (design, construct and operate). If necessary precautions are not taken, the traffic accidents will be inevitable and repairing the damages will be waste of the sources. The study is presented in four sections. The summary of these sections are: Section 1 In this section the environmental factors that are considered in desing phase of the pavements are discussed. In this section it is explained how water (moisture), temperature, freezing and icing effect the design of pavements. These effects are as follows: 1 - Effect of the water. Drainage and kinds: Drainage is an important factor in designing pavements. A good drainage system must be choosen in designing part. In addition it is very important that the drainage system is also appropriate for the environmental factors. XIV. Swelling of the roadbed Swelling happens in roadbed with absorbing the moisture. In AASHTO designing method in order to establish the servicabiiity loss ratio swelling rate constant, potential vertical raising and swelling probability irregulars should be searched.. Effect of the moisture in compacting the soil One of the most important factors in compacting the soil is the ratio of moisture in the soil, or the contents of water in the soil. For all kinds of soils, in a certain compacting energy level, there is a definite relation between the soil's dry unit volume weight and the content of water it bears.. California Bearing Ratio and water (moisture) relation: There is a relation between California Bearing Ratio and water contents. According to this in order to have maximum resistance, the soil should be compacted more than optimum water ratio.. Porous pavements and water (moisture) relation: Since porous pavements have the specifications of clearing rain from the surface in a short time, does not permit reflection, have a high coefficient of sliding friction and resistance, decreases the noise created by the traffic the application of this kind of pavements should start. 2- Effects of the temperature. Thermal coefficient and temperature relation Since expansion and lengthening of the objects does not happen in a free surface, it causes tensions in the object and some cracks may happen.. Affect of temperature to asphalt concrete As the temperature increases the viscosity of the pavement slab decreases and slab deforms very soon due to the weights it bears. As the temperature decreases the XVasphalt slab tries to contract and as a result contracting tension is formed on the slab. As the contracting tension increases the aggregate separates from the asphalt and forms holes.. Heat and elasticity module relation: In order to determine the asphalt concrete thickness elasticity module is used. Elasticity module shows a reverse reaction with temperature.. Influence of temperature to concrete slabs: The temperature difference between the top and bottom of the pavements causes the edges to bend upward at daytime and downward at nights. Because of bending, the edges getting far from the base, the support of base decreases and the bending- contracting influence of wheel loads increase. These tensions are kept in a security limit by making an appropriate seams. 3- Influence of Freezing and icing. De-freezing: In frost susceptible surfaces de-freezing and water that leaves the surface will cause great damages. Traffic will decrease the power of pavements during de-freezing.. Frost heave: Frost heave happens by freezing of the moisture on the subgrade surface and by taking the capillary water around it. Since this difference in the volume is not uniform, there would be bends and fractures on the pavement surface. According to AASHTO design method, to evaluate the frost heave three factors should be considered. These are frost heave rate, maximum potential servicability loss and the probability of frost heave. XVI. Subgrade surface and freezing relation Low temperature to form freezing, existence of subgrade surface water and frost susceptible soils are the three important factors that create freezing influence. In order to take the necessary precautions where those three factors are present, those factors and total pavement thickness, frost penetration depth and excavation-filling specifications should be carefully observed.. Sub-slab layer: It is required to design sub-slab layer when freezing occurred, effects of swelling and shrinking in high volume changeable soils and pumping effect in thin grained soils. Section 2 In this section the environmental factors that influence the costruction of pavements are discussed. The effects of water (moisture), temperature and freezing have been investigated. These are as follows: 1 - Influence of water. Roadbed soil and effect of water Rain waters drain down from the edges of the road and cause changes in the water content of the roadbed soil. These changes in the contents of the water causes roadbed to swell and change its volume and cause swells on the surface.. Effects of water to base and sub-base: On the sub-base part of the pavement a suitable material should be places so that the soil inclined to pumping should be preserved. In construction phase precautions should be taken in order to stabilise the uniformity of the natural surface in composition, density and water ratio. XVll. Pavement surface and the influence of water In concrete casting attention should be given to the ratio of mixing water. Accumulation of rain water collecting in the subgrade should be prevented. The place where asphalt will be layed should be dry. Ratio of moisture should be maximum %2 and temperature should be minimum +7°C.. Specifications that come from the solvent properties of the water: The salts and organic substances that solved with the effect of water give harm to cement and concrete. In addition they cause filling the porous substances and corrosion in iron pipes. 2- Effects of Temperature. Applying bitumen binders and temperature effect: Bitumen material that are used in summer season contract and cause cracks. No matter what the climate conditions are a suitable binder should be chosen.. Concrete pavements and temperature effect: Cracks form in concrete pavements due to temperature differences. Concrete should be preserved to in order not to permit this.. Concrete in cold weather: If concrete is cast in a suitable weather and if most of the heat that outcomes in hardening can be kept in the body, hardening can be maintained in every climatic condition. In preserving time precautions should be taken so that the temperature of the body does not decrease below +15°C.3- Effect of Freezing and icing. Construction with frost susceptible material: In cold climates the damage that frost susceptible material (clay, silt etc.) are the damages formed by the heat of melting ice masses.. Construction with non frost susceptible material: Clean sand and gravel do not form harmful effects to the road during freezing and melting. Dirty particles may form little ice separations and freezing swellings. Section 3 In this section environmental effects in operation phase, maintenance and repair works have been studied. The life of the roads will extend by careful application of this phase. In this section the fighting methods against rain, hail, fog, freezing and icing is explained.. Effect of Rain: Most of the traffic accidents happen in the rain. To prevent these accidents meteorological radars should be used.. Effect of Hail: If hail particles are over 5-10mm the vehicles will go off the road and accidents happen.. Effect of Fog: Fog affecting the vision of the drivers slows the traffic flow and therefore causes accidents by increasing the intensity of the traffic. On roads in every 500 meters a potential fog index should be calculated, fog valleys should be established ^nd fog observation and alarm systems should be installed in these valJeys. XIX. Effect of wind: Although wind is not the main cause of big traffic accidents it can cause problems to high vehicles, bridges, and traffic signs.. Freezing and icing effect: Freezing and icing effect makes roads sliding and causes accidents. By thermal mapping of the roads the icing can be known in advance and accidents may be prevented.. Effect of Snow: Ice layers that form on the road due to winter conditions prevents the traffic to flow securely and fast. Therefore struggle should be given against the snow by forming snow barriers, and cleaning the roads mechanically and chemically. Attention must be shown in salt using. Only enough sait should be poured to necessary places. If there are other opportunities besides salt, like calcium magnesium acetate, it should be used.. Maintenance and repair works: Maintenance and repairs are the only way to extend the roads life and to keep transportation comfort in a certain level. In order to make a proper maintenance the reasons of detonation should be known very good. If on maintenance the reasons of detonating is not known well the same detonation may happen again under the same circumstances. Section 4 In the last part the results of the study and advises are given. XX