Bir iksa sisteminin iki ve üç boyutlu sonlu elemanlaryöntemi ile çözülmesi ve saha ölçümleri ilekarşılaştırılması
Two and three dimentoned finite elements methodanalyses of a support system and comparison of resultswith on-site instrumentations
Yazar: DENİZ TÜRKMEN YILMAZ
Danışman: PROF. DR. MUSAFFA AYŞEN LAV
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
Dizin: Derin kazı = Deep excavation

Özet:
Artan kentselleşmenin sonucu nüfusun ihitiyaçlarını karşılamak amacı ile konut,
sanayi yapıları, iş merkezleri, spor merkezleri, altyapı projeleri gibi inşaat projelerinin
artmasına yol açmaktadır. Yoğun nüfuslu kentlerde mevcut arsaların kullanımını en
efektif şekilde değerlendirme mecburiyeti doğmuştur. Bu sebeple arazilerin
görünmeyen kısımları da inşaat alanlarına dönüşmüştür. Bu alanlarda açılan kazı
çukurlarını desteklemek amacı ile tasarlanan iksa sistemi yapılırken sisteme etkiyecek
olan toprak ve su basıncının yanı sıra sürsarj basınçlarının hesaplanması
gerekmektedir. İksa sistemine etkiyecek olan yükleri belirlemek için sağlıklı bir zemin
etüdünün yapılması gerekmektedir. Yanlış yapılan zemin etüdleri neticesinde
tasarlanan iksa sistemleri neticesinde çevre yapılarda ve yollarda yapısal hasar
oluşabilmektedir. Oluşan hasarlar izin verilen sınırlar içeresinde kalmadığı takdirde
can ve mal kaybına yol açmaktadır. Tasarımı yapılan iksa sisteminin hesaplanan
yükleri izin verilen deplasmanlar sınırında tasarım ömrü süresince karşılaması
gerekmektedir.
Çalışmanın amacı, aletsel gözlemlerin derin kazılardaki önemi ve faydasının
gösterilmesidir. Bu çalışma da tasarımı yapılmış olan derin kazı sisteminin analizler
sonucu elde edilen deplasmanlarla sahada gerçekleşen deplasmanlarının
karşılaştırılması anlatılmıştır.
Tez kapsamında, İstanbul ili Avrupa Yakası kısmında yapılacak olan bir metro hatına
ait istasyonunun kazı destek sistemi için öncelikle literatürdeki veriler ışığında sahada
yapılan sondaj verilerine göre zemin parametreleri belirlenmiştir. Zemin profili, yeraltı
suyu, sürsarj yükleri ve kesitler belirlendikten sonra PLAXIS 2D ve PLAXIS 3D
yazılımı ile analizler gerçekleştirilmiştir.
Tez çalışmasının birinci bölümünde iksa sistemlerinin öneminden bahsedilmiştir.
İkinci bölümünde ise iksa sistemlerine etkiyen yanal toprak basınçları hakkında bilgi
verilmiştir. Üçüncü bölümde yanal toprak basınçları ve çevresel yükleri sağlıklı bir
şekilde taşımak amacıyla gerekli yatay-düşey destekler anlatılmıştır. Sonraki bölümde
iksa sistemlerinin en önemli bir parçası olan geoteknik enstürümantasyonlar hakkında
bilgi verilmiştir. Tezin beşinci bölümünde sonlu elemanlar yöntemi ve geoteknik
analizlerde kullanılan Plaxis programı tanıtılmıştır.
Tez kapsamında Plaxis 2D ve Plaxis 3D ile yapılan analizler sonucunda elde edilen
deplasmanlar ile sahada gerekli enstürümantasyonlar ile ölçülen gerçek deplasmanlar
karşılaştırılmıştır.
Sonuç kısmında ise metro projesine ait istasyon için yapılan analizlerin sonuçları ile
inklinometre ölçümlerinin karşılaştırılması değerlendirilmiştir. Belirlenen idealize zemin profili için farklı kazı uzunluğuna sahip kazı çukurunun çevre yapıların
oturmasına etkisi incelenmiş ve tez çalışması tamamlanmıştır.

Abstract:
Since the urbanization trend continues to grow throughout the world, so does the need
of construction projects as the ever-growing human population demands and requires
new houses, industrial facilities, social centers and infrastructures. This increase in
demands made it a necessity in central cities for the land to be used as efficient as
possible. As a result, the unseen parts of the land; the underground turned into
construction sites. But making deep excavations in order to make use of underground
areas require additional engineering designs.
When designing a support system for an excavation site, surcharge loads must be taken
into account in addition to earth and water pressure. To determine all loads that will
effect the support system, a healthy soil investigation must be carried out first. Without
the data from a healthy soil investigation, designing a support system might cause
damage to nearby structures and roads. When exceeding the agreeable limits, these
damages can lead to loss of lives or properties. The designed support system is
expected to compensate the loads within agreeable displacement limits as far as the
design life.
As one of the problems solved in geotechnical engineering, deep excavations are a
complex topic. This problem incorporates numerous factors which includes several
vertical and horizontal members. The basic logic behind this design is to transfer the
earth and water pressure as well as surcharge loads effecting the system through these
vertical and horizontal members and eventually divert these loads into the soil. While
designing the deep excavation support system, a lateral earth pressure distribution must
be achieved behind the wall in order to determine final wall height and estimate
support loads and bending moment of the wall. Unlike a standard excavation, when
constructing the support system "top-down"; the deformation pattern would become
much more complex and inconsistent with the theoretical Rankine and Coulomb earth
pressure distribution.
The aim of this study is to show the importance and benefit of instrumental
observations in deep excavations. This study contains comparison of a designed deep
excavation support systems displacements and actual displacements seen on site.
Within the study, soil parameters for a deep excavation support system constructed as
a part of subway construction in the European side of İstanbul were determined first.
After determining the soil profile, ground water level, surcharge loads and sections;
analyses were conducted using PLAXIS 2D and PLAXIS 3D software.
The deep excavation system for the station structure will be approximately 21x99m.
In the study area, surface elevations are fixed and the excavation height is 25.40m. The
deep excavation system will be supported internally at 4 different levels. Reinforced concrete elements were preferred as internal support system in the first three levels,
while steel pipe was preferred in the fourth level.
In the first chapter of study, the reasons behind the increased use of deep excavations
and this methods importance in geotechnical engineering were addressed.
Following these details, study continues with earth pressures which is the main factor
behind determining the dimensions of deep excavation support system elements.
Prized scientists in Geotechnical Engineering such as Terzaghi, Peck and
Tschebotarioff proposed various loadings based on the cohesion levels of the soil.
The third section of the study focused on the vertical and horizontal support elements
of the deep excavation support systems. Within the study; bored piles, diaphragm walls
and sheet pile walls were showed as vertical support elements. The comparison and
evaluation of these elements were touched on in details in respect of production
method and difficulties in production. Furthermore; anchorages, soil nails and strut
supports were showed as horizontal support elements. In it a fact that anchorages are
used more often in comparison to soil nails as anchorages provide greater carrying
capacity as a horizontal support element. Whereas the strut supports can also be
preferred as they can be produced a lot faster and are usually required less in number.
Following these details, in the fourth section study focuses on the monitoring of deep
excavation support systems and surrounding structures. It is essential to monitor the
behavior of support systems to ensure the structural safety of deep excavations and
other structures surrounding the excavation site. It is very common to see engineering
applications which show different behavior than their original designs. Because of this,
geotechnical instrumentation holds great importance in all engineering applications.
To this purpose, the respective section of the study shows crack gauges, deformation
measurements, extansometers, piezometers, reflectors and inclinometers in detail.
During deep excavations, high levels of stresses are faced. To compensate these
stresses, diaphragm walls are often preferred as the safest system. The reason behind
this is that diaphragm walls are much more rigid in comparison to pile systems and
that they also allow displacements that will occur during the excavation to be
monitored easily. The most common way to monitor these displacements is with
inclinometers. The deep excavation this study is based on is carried out using
diaphragm walls and struts. The displacements during excavation were monitored with
inclinometers.
The fifth chapter of the study refers to finite elements method and the PLAXIS
software. In principal, finite elements method bears the logic of reaching to the whole
through working on small pieces. In the last century, the fast development of
computers made this method a frequently used supportive element in all engineering
subjects. Today, finite elements method is used in many areas. One of the widely
known software PLAXIS also uses finite elements method logic as its base in order to
solve complex geotechnical problems.
In the analyzes, soil units were modeled using 'Hardening Soil' model, while rock
units were modeled using 'Mohr-Coulomb' structure model, structural elements were
'plate' and struts were modeled using 'node-to-node anchor' elements.
The analyses conducted in two-dimensions and three-dimensions were then compared
to on-site data. The results achieved after this comparison is as follows; The displacement behavior and values obtained in PLAXIS 2D and PLAXIS 3D
analyses were found out to be similar and within close range.
Boscardin and Cording have developed a method for determining damage to existing
structures by angular rotation and horizontal unit deformations. According to this
method, the displacement values obtained as a result of the analyzes were processed
and the effect of displacements on the existing structures were examined and it was
observed that the displacements in the structures remained in the negligible region in
two-dimensional and three-dimensional analyzes.
When the results obtained from finite elements method was compared to actual on-site
data, it was seen that the results from finite elements method were higher in value. It
is believed that the main reason behind this difference is the actual soil parameters are
higher than the parameters taken from literature of which the analyses were based on
or that the soil profile differs.
In respect of displacement behavior, inclinometer results showed similarity to
displacement results obtained through finite elements method.
Internal forces of the diyaphram wall obtained through PLAXIS 2D and PLAXIS 3D
analyses were found out to be similar and within close range.
In the conclusion, the inclinometer measurements and the results of the analyzes for
the station belonging to the subway project were evaluated and compared. For the
idealized soil profile, the effect of excavation with different dimensions on the
settlement of the surrounding structures was investigated and the thesis study was
completed.