Polimerlerle katkılı yüksek plastisiteli bir kilde donma-çözülme çevrimlerinin gerilme-şekil değiştirme davranışına etkisi
Effect of freeze-thaw cycles on the stress-strain behavior in a high plasticity clay treated with polymers
Yazar: HALİL ARDA SARIGÖL
Danışman: PROF. DR. AYKUT ŞENOL
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: İnşaat Mühendisliği = Civil Engineering
Dizin: Killi zeminler = Clay soils

Özet:
Günümüzde artan nüfus ve ihtiyaçlar sonucu mevcut yerleşim alanlarının yerine yeni yer arayışı olmuştur. Yeni yer arayışı kavramı beraberinde birçok probleme neden olmaktadır. Şehirlerin genişlemesi ve bunun sonucu büyük yapı ihtiyacı en belirgin problemlerden biri olmaktadır. Şehirleşmede yapılaşmanın neredeyse imkansız olduğu yerlerde yeni yapı ihtiyacı sorununu doğurmaktadır. Bu nedenle, geoteknik mühendisliğinin en önemli problemlerinden biri de problemli zeminler ve bu zeminler üzerine inşa edilen yapıların projelendirmesi olmuştur. Soğuk iklim bölgelerinde yer alan zeminler tekrarlı ve mevsimsel donma ve çözülme etkisiyle mühendislik açısından inşaat mühendisliğinin son zamanlarda ortaya koyduğu problemlerden biri olarak görülmektedir. Soğuk iklim bölgelerinde bulunan zeminlerde bulunduğu bölgenin iklim koşulları değerlendirildiğinde birbirini takip eden tekrarlı donma ve çözülme davranışları zeminin geoteknik özelliklerini büyük oranda değiştirebilmektedir. Soğuk iklim bölgelerinde siltli ve killi zeminlerde inşa edilen yol inşaat dolgularında ve karayolu yapılarında donma ve çözülme etkisi sonrası ortaya çıkan hasarın erken önlenmesi ve buna bağlı olarak oluşacak maddi kayıpların da tolere edilebilmesi sağlanacaktır. Ortaya çıkan bu problemler doğrultusunda zeminlerde katkı maddesi kullanılarak zeminlerin mühendislik özelliklerinin iyileştirilmesi irdelenmelidir.
Bu yüksek lisans tez çalışması kapsamında, polipropilen (PP) ve homopolimer polipropilen (HPP) fiziksel katkı malzemeleri ile yüksek plastiseteli kilin farklı sayıda donma-çözülme çevrimlerinde gerilme-şekil değiştirme davranışını araştırmak için serbest basınç deneyleri gerçekleştirilmiştir. Bu amaçla, yüksek plastisiteli kil zemin malzemesinin sınıfı belirlenmiştir. Akabinde, CH7 kilinin optimum su muhtevası ve kuru birim hacim ağırlık değerleri belirlenmiştir. Belirlenen optimum su muhtevası değerinde hazırlanan CH7 kilinin D-Ç deneylerine tabi tutulmadan önce serbest basınç deney aletinde serbest basınç mukavemeti belirlenmiştir. Daha sonra, CH7 kil numunesinin ağırlıkça %0.5, %1.0, %1.5 oranlarında PP ve HPP katkılı karışımlarının su muhtevası ve kuru birim hacim ağırlıkları belirlenmiştir. Ardından, donma-çözülme çevrimleri öncesi katkı malzemelerinin yalın kilin serbest basınç mukavemetine etkisini incelemek için CH7 kilinde uygulanan sürece benzer şekilde optimum su muhtevalarında hazırlanan numunelerin gerilme-şekil değiştirme davranışı ve serbest basınç mukavemetleri incelenmiştir. Donma-çözülme çevrimlerine maruz kalmayan CH7 kili, PP ve HPP katkılı hazırlanan numunelerin serbest basınç dayanımları ile gerilme-şekil değiştirme davranışları belirlendikten sonra, numuneler 1, 3, 5, 10, 20 donma-çözülme çevrimleri sonunda serbest basınç deneyi gerçekleştirilmiştir. CH7 kili, PP ve HPP katkılı hazırlanan numunelerin tüm çevrimler sonunda D-Ç etkisinin numunelerin serbest basınç dayanımı, gerilme-şekil değiştirme davranışı ve malzeme davranışları incelenmiştir.
CH7 kilinin endeks özellikleri ve kıvam limitleri, optimum su muhtevası ve kuru birim hacim ağırlığı belirlenmiştir. Belirlenen optimum su muhtevasında serbest basınç deneyi için 3 adet özdeş numune hazırlanmıştır. CH7 kiline ait numunelerin donma-çözülme çevrimlerine maruz kalmadan önceki serbest basınç dayanımı belirlenmiştir. Artan donma-çözülme çevrimleri sonucunda CH7 numunelerin serbest basınç mukavemetlerinde azalma gözlenmiştir. 20. D-Ç çevrimi sonrası CH7 numunelerin %88'lik azalma gözlenmiştir.
PP katkılı hazırlanan numuneleri için benzer aşamalar uygulanmıştır. Ağırlıkça %0.5, %1.0 ve %1.5 oranlarında PP katkı CH7 kili karışımları için optimum su muhtevaları belirlenmiştir. Ağırlıkça %1.0 PP katkılı numunelerde yapılan serbest basınç deneyi sonucunda %24'lük bir mukavemet artışı meydana gelerek PP katkılı karışımlar içerisinde en yüksek mukavemet artışı belirlenmiştir. Artan D-Ç çevrimleri sonucunda PP katkılı numunelerin serbest basınç dayanımlarında azalma gözlenmiştir. D-Ç çevriminden sonra %0.5 PP, %1.0 PP ve %1.5 PP katkılı karışım numunelerinin serbest basınç mukavemetlerinde sırasıyla %76, %75 ve %83 azalma gözlenmiştir.
HPP katkılı hazırlanan numuneleri için de benzer aşamalar uygulanmıştır. Ağırlıkça %0.5, %1.0 ve %1.5 oranlarında HPP katkı CH7 kili karışımları için optimum su muhtevaları belirlenmiştir. Ağırlıkça %1.5 HPP katkılı numunelerde yapılan serbest basınç deneyi sonucunda %11'lik bir mukavemet artışı meydana gelerek HPP katkılı karışımlar içerisinde en yüksek mukavemet artışı belirlenmiştir. Artan D-Ç çevrimleri sonucunda HPP katkılı numunelerin serbest basınç dayanımlarında azalma gözlenmiştir. 20. D-Ç çevriminden sonra %0.5 HPP, %1.0 HPP ve %1.5 HPP katkılı karışım numunelerinin serbest basınç mukavemetlerinde sırasıyla %84, %81 ve %85 azalma gözlenmiştir.
Son olarak bütün serbest basınç deneyleri sonuçlarına göre, PP katkılı numunelerin serbest basınç değerleri HPP katkılı numunelerin serbest basınç değerlerinden daha yüksek olduğu görülmüştür. Ayrıca, elde edilen sonuçlara göre, numunelerin gevreklik indeksi değerleri hesaplanmıştır. Buna göre, CH7 kilinin gevreklik indeksi katkı ilaveli numunelere kıyasla artmış ve bütün D-Ç çevrimlerindeki numuneler karşılaştırıldığında CH7 numunelerin gevrek davranış gösterdiği, katkılı numunelerin ise gevreklik indeksinin azaldığı ve sünek davranış gösterdiği gözlenmiştir. Elde edilen bulgular, zemin iyileştirmesinde kullanılan PP ve HPP katkılı malzemelerin donma-çözülme çevrimlerinden sonra serbest basınç dayanımında gözlenen farklar için açıklayıcı bir öğe olabilir.

Abstract:
Nowadays, as a result of increasing population and needs, there has been a search for a new place to replace the existing settlement areas. The concept of searching for a new place causes various problems. The expansion of cities and the consequent need for large buildings are one of the most obvious problems. The fact that the resources are limited and the needs are unlimited creates the problem of new building needs in the places where it is almost impossible to build in the urbanization. Therefore, one of the most important problems of geotechnical engineering has been the design of problematic soils and the structures built on these soils. Although swelling and collapsing soils are seen as problematic soils, soils in cold climatic regions are seen as one of the recent problems of civil engineering in terms of engineering with the effect of repetitive and seasonal freezing and thawing. When the climatic conditions of the region are evaluated on the soils in cold climate regions, successive freezing and thawing behaviors are observed. This situation is able to change the geotechnical properties of the soil. Especially in silty and clay soils that can retain a high amount of water in their content, as the water in its content turns into ice during the freezing process, ice lines are formed on the soil as a result of the increase in volume, the void ratio increases and the strains occur in the thawing process on the soil. Due to seasonal behavior changes in soils located in cold climate regions, important situations such as bearing capacity, settlement problem and swelling potential occur. It will be ensured that the damage caused by freezing and thawing in highway embankments and highway structures built on the silty and the clayey soils in cold climates will be prevented early and the financial losses that will occur as a result can be tolerated. In line with these emerging problems, improvement of the engineering properties of soils by using additives should be examined.
Within the scope of this research, the unconfined compressive strength tests were performed to investigate the stress-strain behavior of the high plasticity clay with the polypropylene (PP) and the homopolymer polypropylene (HPP) additives in the different number of freeze-thaw cycles. For the purpose, the classification of testing soil was determined by performing the sieve analysis, the hydrometer and the Atterberg limits tests. Determined high plasticity clay was named CH7 in this research by being a relevant part of the main research. It is a continuation of previous studies conducted to examine the effect of freeze-thaw effect on different engineering properties of the soil. Then, the optimum water content and the maximum dry unit weight values of CH7 clay were determined in the Harvard miniature compaction test device. The unconfined compressive strength of the CH7 clay, which was prepared at the determined optimum water content, was determined in a unconfined compressive test device before it was subjected to freeze-thaw tests. Then, the water content and the dry unit weights of the mixtures with PP and HPP additives at 0.5%, 1.0%, 1.5% by weight of the CH7 clay sample were determined. The stress-strain behavior and the unconfined compressive strength of the samples prepared at the optimum water contents (similar to the process of plain CH7 clay) were examined in order to determine the effect of additives on the compressive strength of the natural clay before freeze-thaw cycles. After the determination of unconfined compressive strength and stress-strain behavior of the PP and the HPP added samples of CH7 clay, which was not exposed to freeze-thaw cycles, the unconfined compression tests were performed on the samples prepared with and without additives at the end of 1, 3, 5, 10, 20 times of freeze-thaw cycles. The unconfined compressive strength, the stress-strain behavior and the material behavior of the samples were investigated by the freeze-thaw effect of the mixture samples prepared with PP and HPP at the end of all cycles.
First of all, the grain size distribution and the Atterberg limits tests of CH7 clay were determined. According to the consistency limit tests, the liquid limit, LL = 60%, the plastic limit, PL = 22%, the plasticity index and PI = 38% were determined. The results of the compaction test in the Harvard miniature compaction test device were determined as wopt=20% and γdry,max=17.30 kN/m3. Three identical samples were prepared for the unconfined pressure test at the determined optimum water content. Accordingly, the unconfined compressive strength of the samples of CH7 clay before exposure to freeze-thaw cycles was determined as 217 kN/m2. CH7 samples were subjected to freezing at -23±2 ºC for 24 hours in each cycle. Then, at the end of 24 hours, the samples were taken out of the freezer and thawed in a desiccator at +23±2 ºC. The 24-hour freezing and 24-hour thawing processes were determined as a freeze-thaw cycle, respectively, and 1, 3, 5, 10 and 20 freeze-thaw cycles were applied to the samples.
As a result of the increasing freeze-thaw cycles, a decrease in the compressive strength of the CH7 samples was observed, and the most significant loss of the compressive strength value was 43%, at the end of the 1st F-T cycle, the compressive strength of the samples was obtained as 140 kN/m2. It was observed that the strength loss decreased after increasing cycles. After 20th F-T cycle, 88% decrease was observed in CH7 samples and it was obtained that the unconfined compressive strength decreased to 27 kN/m2. Similar processes were applied for the PP added mixtures. The optimum water contents for PP and CH7 mixtures at 0.5%, 1.0% and 1.5% by weight were determined in the Harvard miniature compaction device. Accordingly, for 0.5% PP additive mixture wopt=22% and γdry,max=17.10 kN/m3, for %1.0 PP additive mixture, wopt=22% and γdry,max=16.70 kN/m3; besides, for %1.5 PP added mixture wopt=22% and γdry,max= 16.70 kN/m3. The unconfined compressive strengths of PP additives mixtures prepared at the optimum water content before freeze-thaw cycles were determined as 245 kN/m2, 268 kN/m2 and 223 kN/m2 for 0.5%, 1.0% and 1.5% PP additives, respectively. As a result of the unconfined pressure test performed on 1.0% by weight PP added samples, a strength increase of 24% occurred and the highest strength increase was determined among the PP added mixtures. As a result of increasing F-T cycles, a decrease was observed in the unconfined compressive strength of the PP added samples. For the samples with 1.0% PP additive, a decrease of 32% occurred after the 1st F-T cycle, and the highest strength loss ratio value was obtained with 183 kN/m2. The unconfined compressive strength decreased from 169 kN/m2 to 110 kN/m2 after the 3rd F-T cycle by realizing a strength loss of 35% in 0.5% PP added samples. Also, it was determined that the unconfined compressive strength decreased from 71 kN/m2 to 38 kN/m2 after the 20th F-T cycle, with a strength loss of 47% in 1.5% PP added samples. After the 20th F-T cycle, 76%, 75% and 83% reductions were observed in the unconfined compressive strength of the mixture samples with 0.5% PP, 1.0% PP and 1.5% PP, respectively. According as CH7 and the PP mixtures, similar processes were applied for the HPP added mixtures as well. The optimum water contents for the HPP additive CH7 clay mixtures at 0.5%, 1.0% and 1.5% by weight were determined in the Harvard miniature compaction device. Accordingly, for 0.5% HPP additive mixture wopt=24% and γdry,max=17.00 kN/m3, for %1.0 HPP additive mixture, wopt=23% and γdry,max=16.90 kN/m3; and, for %1.5 HPP added mixture wopt=24% and γdry,max= 16.00 kN/m3. The unconfined compressive strengths of HPP additives prepared at optimum water content before the freeze-thaw cycles were determined as 225 kN/m2, 226 kN/m2 and 239 kN/m2 for 0.5%, 1.0% and 1.5% HPP additives respectively. As a result of the unconfined pressure test performed on 1.5% by the weight of HPP added samples, a strength increase of 11% occurred and the highest strength increase was determined among the HPP added mixtures. As the result of increasing F-T cycles of the PP added samples, it was observed that the unconfined compressive strength values of the HPP added samples were decreased. While it was determined that the most significant strength losses of 0.5% and 1.5% HPP additive mixtures occurred after the 1st F-T cycle, the most significant strength loss in 1.0% HPP added mixed samples was after the completion of the 20th F-T cycle. The strength losses occurred in 0.5% and 1.5% HPP added mixture samples, 38% and 41%. The unconfined compressive strengths decreased to 138 kN/m2 and 141 kN/m2 after the 1st F-T cycle. For 1.0% the HPP added mixtures, a 39% decrease occurred between the 10th F-T cycle and the 20th F-T cycle and the unconfined compressive strength decreased from 70 kN/m2 to 43 kN/m2. At the end of the 20th F-T cycle, 84%, 81% and 85% reductions were observed in the unconfined compressive strengths of 0.5% HPP, 1.0% HPP and 1.5% HPP added mixture samples respectively.
Finally, as a result of the increase in the additive ratio in the mixture in the PP and HPP added samples, the unconfined compressive strength tests improved the results while it resulted in relatively less improvement in the mixing ratios other than the optimum mixing ratio. It can be expressed by the fact that the additive material is concentrated in the mixture and acts an important role in the compressive strength value. After increased F-T cycles, as a result of the behavior of increasing and decreasing in volume due to the physical behavior of the water in the ground, increased void ratio of soil and random placement of particules after the volume change can be shown as a reason for changing compaction parameters. The findings can be an explanatory element for the differences observed in the unconfined compressive strength of PP and HPP additives used in soil improvement after freeze-thaw cycles.