Genleştirilmiş polistiren (EPS) köpüğün geoteknikte kullanılması
Use of expanded polystyrene (EPS) foam in geotechnical engineering
Yazar: HULUSİ HAKAN KİRİŞ
Danışman: DOÇ. DR. İSMAİL HAKKI AKSOY
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Zemin mekaniği ve geoteknik mühendisliğinde, hafif dolgu malzemesi kullanımı önemli bir yere sahiptir. Yumuşak zeminler üzerine teşkil edilecek dolgularda, istinat yapılarının arka dolguları ve şev stabilitesi gibi uygulamalarda çeşitli hafif dolgu malzemeleri kullanılarak güvenli ve ekonomik tasarımlar yapılabilmektedir. Günümüzde uçucu kül gibi atıkların tek başına ya da çeşitli karışımlarla geoteknikte tekrar kullanılması, problemin çözümü ve çevresel sorunların önüne geçilmesi açısından önemli bir yer oluşturmaktadır.
Genleştirilmiş polistiren (EPS) köpük, hafif dolgu malzemesi olarak 1972'den beri geoteknik mühendisliğinde kullanılmaktadır. Çok düşük birim hacim ağırlığı sayesinde inşaat mühendisliğinin çeşitli uygulamalarında geleneksel yöntemlere alternatif olarak ekonomik ya da ergonomik çözümler sunabilmektedir. İlk olarak Norveç'te dolgu malzemesi olarak kullanılan EPS köpük, düşük yoğunluğunun yanı sıra inşaat aşamasında kolay uygulanabilmesi ve hızlı imalat süresi sayesinde dünyanın çeşitli yerlerinde kullanılmaya başlanmıştır.
Herhangi bir hafif dolgu malzemesinin kullanımında, maliyet/performans açısından en iyi sonucu alabilmek için malzeme özelliklerinin bilinmesi gereklidir. EPS köpük, üreticiler tarafından çeşitli fiziksel özelliklerde imal edilir. Bu malzemelerin fiziksel ve mühendislik özellikleri çeşitli şartnameler ile verilmektedir. Ancak statik ve dinamik yükler altındaki davranışının daha iyi anlaşılması için araştırmacılar tarafından çeşitli deneylere tabi tutularak farklı kullanım alanları için malzeme davranışı elde edilmiştir. Ayrıca geoteknikte kullanımı kısmen yeni sayılabilecek bu malzemenin kısa ve uzun vadeli davranışı gözlenerek çeşitli uygulamalarda zamana bağlı performansı takip edilmektedir. Günümüze kadar yapılan gözlemler EPS köpüğün uzun yıllar dayanımını koruyabildiğini göstermektedir.
Günümüzde EPS köpük, bloklar, daneler ve sıkışabilir tabakalar halinde çeşitli geoteknik uygulamalarında kullanılmaktadır. Taşıma gücü düşük ve oturma potansiyeli olan zeminler üzerine dolgu teşkil edilmesinde, dayanma yapılarına gelen yanal itkilerin azaltılmasında, kayma/heyelan riski olan şevler üzerine dolgu teşkil edilmesinde, kaymış olan şevlerin stabilitesinde, gömülü borular/menfezler üzerinde düşey basınçları zeminde kemerlenme etkisi oluşturarak azaltmada, şişen zeminler nedeniyle oluşacak şişme basıncının engellenmesinde, sismik etkiler nedeniyle oluşabilecek kuvvetlerin sönümlenmesinde ve yüzen adalar teşkil edilmesinde başarılı olarak kullanılmaktadır.
Bu tez kapsamında; öncelikle taşıma gücü hesabı, oturma hesabı ve yanal toprak basıncı kavramları ve bazı hafif dolgu malzemeleri incelenmiş, EPS köpüğün geoteknik mühendisliğinde kullanımı araştırılmıştır. EPS'nin tarihçesi, fiziksel ve mühendislik özellikleri, kullanım alanları ve vaka geçmişleri literatürde taranmıştır.

Abstract:
Using light fill material in soil mechanics and geotechnical engineering has had a significant role for the purpose of practical applications in various construction projects in recent decades. Utilizing different types of light fill materials provides great benefits by means of reliability and economy, mainly for the fills that have to be applied on soft foundation soil, backfill placed behind the retaining structures and for the slope stability issues. It is an important aspect in nowadays that reusing some waste materials such as fly ash either solely or with various compositions in geotechnical applications can bring unquestionable advantages both in solving problems easily and regarding environmental issues.
Expanded polystyrene (EPS) geofoam is an ultra-light geosynthetic that has been being used since 1972 in geotechnical engineering. It can be used in various civil engineering practices as an alternative to traditional methods as it is a promising material due to its apparent very low unit weight, well-known mechanical behaviour, energy dissipation capability, ease of installation and replacement. Moreover, EPS can also alleviate a lot of engineering concerns since it has sufficient compressive and shear strength to undertake the lateral soil pressures, while it also provide a desirable material-soil stiffness ratio. On the other hand, plenty of experimental work and other mathematical and computer based studies are still being carried on for the sake of understanding the mechanical behavior of the material better, particularly its mechanical behavior under static and dynamic loads. Time dependent behavior of this rather recently used geotechnical material is another focused research field that it is observed by researchers as this material shows a remarkable performance for the long time periods where it was used. Besides all of the advantages that are metioned above, EPS geofoam is also quite preferrable due to its relatively low cost and easy applicability during construction. After its first application in Norway, EPS has been utilized by lots of designers through out the world. The use of EPS geofoam in geotechnical issues in Turkey has a relatively young history, as it has been used almost ten years. Considering the usability of EPS geofoam in various geotechnical practices, it can be stated that the more common use of this material in engineering applications results in noticeable benefits in terms of economy.
The most prominent characteristic of the expanded polystyrene (EPS) geofoam is its unit weight, where its basic engineering properties such as compression resistance, modulus of elasticity, poisson ratio, etc. can change depending on the value of unit weight. On the other hand, the following features also belong to EPS geofoam; due to its light nature, it is quite easy to transport the material from the producer to the site and from one place to another on the site. Its water absorption rate is quite low; where even it is exposed to water for long periods, material's absorbtion percentage by volume does not excess the value 10%. EPS geofoam is chemically stable. Beside that, it does not experience biological deterioration since it does not have any nutritional value. In additon, it has not been observed any adverse effect of EPS geofoam on the environment. The use of EPS blocks over and over again (via its effective durability characteristics) also makes a difference by means of sustainability in engineering practices. Furthermore, if we consider the carbon footprint issue, the use of EPS geofoam prevents the high rates of carbon emission since it reduces the amount of time spent in machinary works.
Beside all of the advantages in the use of EPS geofoam that are mentioned above, this material has some fragilities in some respects that necessitate extra precautions during the operation. For example, EPS geofoam can be harmed by acts of vandalism. Moreover, some additional precautions must be taken for the harmful effects that can be quite problematic for the EPS geofoam material during operation such as fire, ultaviolet light, petro-chemical substances. On the other hand, due to some characteristics that EPS geofoam owns such as low value of unitweight and low value of CBR, requires some extra design considerations. Floating potential must be taken into account where EPS geofoam is considered to be used below the groundwater level since it has a significantly low unit weight value. Also, having possessing a low value of CBR makes it impossible to apply traffic load on the EPS geofoam directly. Actually for the latter case, placing of fine granular layer that enables load distrubition and implementation of reinforced concrete slab on the EPS fill can be a successful configuration to accomodate heavy traffic loads.
It is necessary to know material properties well in use of any light-weight materials to have the best result by means of cost/performance. It is observed by a lot of project executers that using EPS geofoam can be quite profitable compared to traditional use of material in some instances. Actually, in spite of the fact that EPS geofoam block can be considered as a relatively high-cost material alone, it can bring economical gains since it enables the shortening of the project duration without giving any concession in the quality of work done.
EPS geofoam can be produced with various target physical properties depending on its usage purposes. Several specifications have been prepared and developed by different technical organizations for controlling the physical and all other engineering properties of this novel inclusion up to now. Additionally, one can find plenty of academic material and case studies from the site when look at the literature of the subject that have an absolute importance on having a comprehensive insight in the field.
EPS geofoam is used as blocks, granular or compressible layers in geotechnical applications depending on its purpose of use. Some of the basic construction applications and purposes of EPS geofoam are as following: fills on foundation soil that have low bearing capacity and prone to high amount of consolidation settlement, reducing the lateral pressures that affect on retaining structures, fills on slopes having high risk of instability, landslide mitigation by estabilishing the stability for the slopes, protecting pipelines and culverts from potential damage resulting from soil stresses caused by vertical permanent ground displacement or other sources, preventing the stresses occured due to swelling of foundation soil, enhancing the damping behavior of the systems that exposed to seismic activations and finally construction of floating platforms as helicopter runway and docks, etc.
In this thesis, first some general geotechnical engineering concepts such as bearing capacity, settlement calculations and lateral earth pressure are discussed; then, some light-weight fill construction materials are investigated and finally a profound approach focused into expanded polystyrene (EPS) geofoam material concentrated on its brief history, physical and engineering properties, mechanical behavior and also stating usage areas via giving some examples from case studies.