Yumuşak kil zemin üzerine inşa edilen yol dolgularında EPS geofoam ve geogrid kullanımının dolgu deplasmanlarına etkisi
The effect of the usage of EPS geofoam and geogrid on embankment displacements in highway embankments constructed on soft clay soil
Yazar: EKİN KENDAL DUMAN
Danışman: DOÇ. DR. MÜGE BALKAYA
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Geosentetikler, son yıllarda inşaat sektöründe büyük ilgi gören ve önemi gittikçe
artan malzemelerdir. Geotekstiller , geomembranlar, geogridler, geonetler, hücresel
dolgu sistemleri (Geocell), geofoam, geokompozitler, geoboru, geotüp ve geosentetik kil kaplamaları içinde barındıran geosentetikler geleneksel malzemelerle birlikte kullanılmaktadır.
Geosentetiklerin kullanım alanları, teknolojik gelişmelerle birlikte ortaya çıkan yeni
malzemelerle her geçen gün artmaktadır. Günümüzde hızlı bir şekilde degişim ˘
ve gelişim gösteren malzemelerin başında gelen geosentetik malzemeler, geoteknik
mühendisliği alanında da sıklıkla tercih edilmektedir. Fabrika koşullarında üretilen bu malzemeler, zemin ile birlikte kullanılarak geoteknik projelerin hayata geçirilmesinde önemli bir rol almakta, geleneksel yöntemlerle kıyaslandığında maliyetleri de düşürerek hızlı, kalıcı ve estetik bir çözüm sunmaktadır.

Yol inşaatlarında, yol güzergahının belirlenmesi, yolun geometrisi, kullanım
amacı, hizmet süresi, kamulaştırma sorunları, artan arazi maliyetleri, güzergahtaki
zeminin yapısı gibi birçok faktörden etkilenmektedir. Tasarlanan yol güzergahı
üzerindeki problemli zeminler, projenin gerçekleştirilmesinde önemli sorunlara yol
açar. Bu sorunlar çogunlukla geleneksel ve pahalı zemin iyileştirme yöntemleri kullanılarak aşılmaya çalışılmaktadır. Geleneksel yöntemlerin aksine, geogridlerin
yol inşaatlarında kullanımıyla yolun taşıma gücü arttırılıp, oturma miktarı azaltılırken, geofoam malzemelerin kullanımıyla da zemin üzerine gelen yük azaltılır ve zeminde çok daha düşük oturmalar gözlenir. 

Bu yüksek lisans tez çalışmasında, 3 farklı yükseklikte, 2 farklı eğimde, sadece dolgu malzemesi kullanılarak, geogrid ve dolgu malzemesi kullanılarak ve EPS geofoam kullanılarak oluşturulan karayolu dolgusuna ait stabilite ve maliyet analizleri incelenmiştir. Plaxis 2D programı kullanılarak modellenen ve analiz edilen karayolu dolgusu modelleri, şev stabilitesi, düşey ve yatay deformasyonlar, gerilme artışları, boşluk suyu basıncı değişimleri ve maliyet konularında karşılaştırılmıştır. Elde edilen sonuçlara göre geogrid kullanımının sadece dolgu malzemesi kullanımına göre şev stabilitesine büyük katkılar sağladığı, EPS geofoam kullanımının diğer iki yönteme göre oturma, şev stabilitesi ve inşaat süresinin kısaltılması noktalarında tasarlanan karayolu dolgusu üzerinde büyük etkilerinin olduğu görülmüştür. Sonuç olarak, yol dolgularında geogridlerin ve geofoam malzemelerin kullanımıyla daha uzun ömürlü ve daha güvenli  bir yol elde edilmesinin ve yol dolgusunun daha kısa sürede inşa edilmesinin mümkün olabileceği görülmüştür.

Abstract:
Geosynthetics are materials that have attracted great interest and increasing importance in the construction industry in recent years. Geosynthetics including geotextiles, geomembranes, geogrids, geonets, geocells (cellular filling systems), geofoam, geocomposites, geopipes,  geotubes and geosynthetic clay liners are used together with traditional materials. Geosynthetic materials have filtration, drainage, protection, separation, insulation, filling and reinforcement functions. The usage areas of geosynthetics are increasing day by day with new materials emerging with technological developments. Geosynthetic materials, which are one of the most rapidly changing and developing materials today, are frequently preferred in the field of geotechnical engineering. Geomembranes are used for insulation in solid waste storage areas, acid ponds and tunnels, roofs and foundations due to their impermeable properties. Geogrids are utilized in highways, reinforced wall applications. Geocells are applied in erosion control, slope stability and erosion control. Geofoams are used on highways, behind retaining walls, on buried pipelines, while Geotubes are used in breakwater applications in harbor projects and in dredging activities for river or lake bottom mud. These materials, which are produced under factory conditions, play an important role in the realization of geotechnical projects by being used together with the ground, and offer a fast, permanent and aesthetic solution by reducing costs compared to traditional methods.

In road constructions, the determination of the road route is affected by many factors such as the geometry of the road, the intended use, the service period, expropriation problems, increasing land costs, and the structure of the soil on the route. Problematic soils on the designed road route cause significant problems in the realization of the project. These problems are often overcome by using traditional and expensive ground improvement methods. In contrast to the traditional methods, the use of geogrids in road construction increases the bearing capacity of the road and reduces the amount of settlement, while the use of geofoam materials reduces the load on the ground and much lower settlements are observed.

In this master thesis, a highway embankment with 3 different heights (6m, 8m, 10m) and two different slope (3/1, 5/2) to be constructed on a soil profile with low bearing capacity and groundwater level close to the surface was modeled using EPS geofoam, geogrid and only embankment material without any improvement method and analyzed with Plaxis 2D program. The analyzed highway embankment models were compared in terms of slope stability, vertical and horizontal deformations, stress increases, pore water pressure changes and cost. According to the results obtained, the safest and most economical method among 3 different construction methods was investigated. In the analyses performed with Plaxis 2D program, the model type was Plane Strain and a triangular finite element mesh with 15 nodes (mesh size: very fine) was selected and SI unit system values were used. Since the system is symmetrical, only half of the system was modeled while generating the analysis models. The highway, which is planned to be built according to the standards prepared by the General Directorate of Highways for highways, is a 6-lane highway with a lane width of 3.75m with three departures and arrivals. The road width is 30m in total, including a 6m shoulder and 1.5m guardrail. The soil materials were defined in Plaxis 2D program as Mohr Coulomb soil model, which provides a relatively faster solution compared to other soil models. The constructed soil is a soft clay layer and the groundwater level is 1.5 m below the ground surface. The groundwater level is assumed to be constant throughout the embankment construction and road usage. A recommended traffic load of 30 kN/m2 was selected and applied as a static load in the analysis. The analysis model, which was constructed with the staged construction option, was left to consolidate for a certain period of time after each filling step. As consolidation boundary conditions, the symmetry axis was kept closed and the other directions were left open. The analysis model was analyzed under a traffic load of 30 kN/m2 for 100 years of road use. 

In the geogrid reinforced road embankment construction option, two-way geogrids were selected and geogrid placement distance was taken as 50 cm in all analyses. In order to see the effect of geogrid placement distance on slope stability, geogrids were placed at a distance of 1 and 2m and analyzed. 3 different geogrid placement distances were analyzed and the results were compared.

In the highway embankment construction option with EPS Geofoam, EPS Geofoam with 4 different densities was used in the analysis to investigate the effect of EPS Geofoam density variation on the highway embankment. EPS Geofoam placement distance was chosen as 1m and unlike the other 2 construction options, EPS Geofoam was analyzed without consolidation.

As a result of all the analyses and the data obtained, slope stability could not be provided and failure occurred in the construction option using only embankment material among the 3 different construction options. In the other construction option, geogrid reinforced road embankment and EPS Geofoam filled road embankment construction, slope stability is ensured in the system and no failure occurs. The results obtained are compared for the 6m high geogrid reinforced road embankment and EPS Geofoam filled road embankment models with 3/1 slope.

When the analysis results are analyzed in terms of total deformations, it is seen that the biggest deformations in the Y and X axes occur in the geogrid reinforced embankment option.
It is seen that with the use of EPS Geofoam in the highway embankment, a 60\% decrease in vertical displacement and a 24\% decrease in displacement is achieved compared to the use of geogrid+fill material. 

In the construction option using EPS geofoam, it is seen that with the use of higher density EPS Geofoam, the displacements in the Y axis of the system decreased, but the displacements in the X axis remained almost the same value.

When the 2 different construction methods are evaluated for the pore water pressure values, the maximum pore water pressure Pmax value occurs in the middle of the soft clay layer where the maximum pore water pressure occurs in the construction option with geogrid+fill material. 
The use of EPS Geofoam has a significant effect on the occurrence of pore water pressure and leads to the occurrence of pore water pressure at lower values compared to the use of geogrid+fill material. In the use of EPS geofoam, there is a slight increase in the pore water pressure Pmax value with the increase in density.


Although failure occurred in the construction option using only embankment material, when this option was compared with the other 2 methods in the cost calculation, it was calculated that the highest cost among the 3 different construction options occurred in the use of EPS Geofoam and the lowest cost occurred in the construction option using only embankment material.
The increase in the density of EPS geofoam leads to an increase in costs.

When 2 different construction options are evaluated in terms of construction time, the use of EPS geofoam allows the targeted project to be completed in a shorter time compared to the use of other geogrid+fill material. The use and application of EPS geofoam will contribute to the completion of the projects in a shorter time as it is easier to apply than the use of geogrid and does not include process steps such as supply, compaction and consolidation of the embankment material.

It was observed that the use of geogrid contributes more to the slope stability of the system compared to the use of only embankment material, while the use of EPS geofoam has great effects on the designed road embankment in terms of settlement, slope stability and shortening the construction period compared to the other two methods.
In conclusion, the use of geogrids and EPS geofoam materials in road embankments can provide a longer lifetime and a safer road and the road embankment can be constructed in a shorter time.