Kireç ile stabilize edilmiş bentonitin kür süresinin mukavemet üzerindeki etkisi
Curing time effects on the bearing capacity of stabilized bentonite with lime
Yazar: SELDA GHABAEE
Danışman: DOÇ. DR. AYKUT ŞENOL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Bu yüksek lisans çalışmasının amacı problemli zeminlerin katkı malzemeleriyle iyileştirilmesinin araştırılmasıdır. Bu çalışmada, bir bentonit kilinin, yüzeysel zemin iyileştirmesi kapsamında, kireç katkısı ile taşıma gücünün arttırılmasına yönelik bir deneysel çalışma yapılmıştır. Laboratuvar çalışmaları 2014 yılında İstanbul Teknik Üniversitesi, Ord. Prof Dr. Hamdi Peynircioğlu Zemin Mekaniği Laboratuvarı'nda gerçekleştirilmiştir. Bentonit üzerinde gerçekleştirilen Granülometri analizi ve Atterberg deneyleri sonucunda zemin sınıflandırılması yapılmış ve yüksek plastisiteli kil (CH) olarak belirlenmiş ve modifiye edilmiş, minyatür Harvard kompaksiyon aleti ile farklı su muhtevalarında hazırlanan numunelerin optimum su muhtevaları ve maksimum kuru birim hacim ağırlıkları belirlenmiştir. Katkısız bentonit numune üzerinde yapılan serbest basınç deneyi ile, bentonitin taşıma gücü belirlenmiştir. Katkısız zemine, kuru zemin ağırlığının % 3, % 6 ve % 9'u oranlarında kireç              eklenerek homojen olarak karıştırıldıktan sonra, serbest basınç deneyleri için numuneler hazırlanmıştır. Hazırlann numunelere, 7, 14 ve 28 günlük kür süresinde bekletildikten sonra serbest basınç deneyi gerçekleştirilmiş ve mukavemetleri belirlenmiştir. Deneysel çalışmaların sonucunda, yüksek plastisiteli bentonitin mukavemeti farklı yüzdeler ve kür süresinde arttırdığı saptanmıştır.

Abstract:
With the increasing of population and the reduction of available land, more and more construction of buildings and other civil engineering structures have to be carried out on weak soils. These types of soils, can be found in every country and are a worldwide problem that possesses various challenges for civil engineers. With increasing water content, they exhibit excessive volume changes, resulting in large horizontal and vertical stresses to the structures located or buried in these regions.  Weak soils undergo large amounts of volume changings due to seasonal moisture changes. These changes of volume, lead to cracking and buckling of the structure built on the weak soils and result in damages annually. The high cost of repairing damaged structures, has drawn attention to the need for more reliable investigation of these soils and new methods to eliminate, or at least reduce, the effect of soil volume change on the integrity of structures.
Owing to such soil of poor shear strength and bearing capasity, a great diversity of ground improvement techniques such as soil stabilization and reinforcement are employed to improve engineering properties of soil, thereby enhancing the reliability of construction. The most common method to minimize this effect, is to replace these types of soils around the proposed structure with soils with better engineering properties. For the cases, needing larger volume of replacement, either sidewalls or the foundations must be designed to cater for the anticipated pressures or a suitable improvement technique shall be applied in place. Stabilization of weak soils is an alternative method for geotechnical engineers considering the economics of construction with such soils. Mechanical stabilization, such as  compaction, is an option; however many engineers have found it necessary to alter the physicochemical properties of weak soils in order to permanently stabilize them. 
For solving problems of weak soils, it is necessary to stabilize them with any of additive substance such as lime, gypsum etc. After stabilization, soil properties such as bearing capacity and shear strength are altered, and stability of soil is increased. While planning for treatment of weak  soils with chemical additives, it is important to kept in mind that how much addition of additive would be economical to get higher strength. It is necessary to keep the cost of chemical treatment as much as low without compromising with the strength.
Chemical stabilization with lime has been proven to be useful in decreasing the volume change of weak clayey soils. Clay particles have a large specific area and electrical forces acting on the surface of the particles, are more influential than gravitational forces. The term specific surface area, refers to the area per unit mass of soil and is usually expressed as m2/g. There is strong evidence in the literature that shows that specific surface area may be the most important contributing factor that controls the engineering behavior of fine-grained soils.
Natural clay deposits can have a wide range of total surface area, since the combination of external and internal surface areas may change simply because of the mixed layer minerals that may exist and the variations in clay mineralogy. Additionally, the clay mineral fraction which is part of the overall grain-size distribution can vary greatly. Consequently, the type of clay mineral present in soil is of major importance in determining the effect of specific surface area, on soil properties. In present research bentonit is used which is a kind of caly that contains high percent of montmillillonite mineral. The volume change of Montmorillonite occurs due to the poor bond between the stacks of sheets forming the mineral. High osmotic pressure develops, and water molecules are absorbed causing the mineral composition to break into 0.1 angstrom thick structural units resulting in the swell of the soil. This cause the bentonite to have a high value of water content.
Soil stabilization with additive chemicals is happened because of chemical reactions.  The chemical reaction occurring between lime and soil is quite complex. The hydrated lime reacts with the clay minerals and permanently transforms them into a strong cementations matrix. 
The stabilization apparently occurs as a result of two processes; In one process, a base exchange occurs with the strong calcium ions of lime replacing the weaker ions such as sodium on the surface of clay particle. Also, the additional non-exchanged calcium ions may be adsorbed so that the total ion density increases. The net result is low base-exchange capacity for the particle with a resulting lower volume change potential. In other process, a change of soil texture through flocculation of the clay particles takes place when lime is mixed with clays. As the concentration of lime is increased, there is a reduction in clay content and a corresponding increase in the percentage of coarse particles. The reaction results in improving the bearing capasity and workability.
In this thesis, an experimental research that, within the scope of the soil stabilization, bentonite that is a high plasticity clay type, contributed with the lime to increase the bearing capacity, is represented. The Laboratory tests had been performed in the Istanbul Technical University of Ord. Prof. Dr. Hamdi Peynircioğlu Soil Mechanics Laboratory. The index properties and compaction parameters of bentonite and bentonite-lime mixture were determined. The bentonite has been classified as a high plasticity clay by completing the granulometric analysis and the Atterberg limits. To get the same energy from Harvard miyature compaction as standard proctor compaction, some calibirtions have done on the Harvard compaction device  then the optimum water contents and the maximum dry unit weights of the plain bentonite prepared with the different water contents in miniature Harvard compaction device were determined. In addition to the plain soil, rates of 3%, 6%, 9% of lime-clay mixture containing lime by weight of dry soil, had been prepared. The prepaired  samples, after 7, 14 and 28 days curing time, had been executed to the unconfined compression test. 
As a result of the experimental research, it had been determined that the prepared mixtures increased the unconfined compression strength of high plasticity bentonit clay with different percentages and different curing time. As the lime percentage and curing time increases, more improvment on bearing capasity is achieved.