Dinamik özellikleri belirlenen sıkıştırılmış killi kalın bir zemin tabakasının tek boyutlu sismik yer tepki analizleri
1D ground response analyses of compacted soil with dynamic properties measured in laboratory
Yazar: CEREN AYDIN
Danışman: PROF. DR. RECEP İYİSAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Deprem, yerkürenin iç yapısında oluşan kırılmaların meydana getirdiği titreşimlerin
kaya, zemin gibi ortamlardan geçerek yeryüzünde oluşturduğu sarsıntılar olarak ifade
edilebilir. Titreşimlerin yeryüzüne ulaştıkları hali gerçekleşen kırılmanın tipi,
uzunluğu, magnitüdü gibi deprem kaynaklı parametrelere bağlı olsa da dalgaların
içlerinden geçtikleri ortamların özelliklerinden de etkilendikleri bilinmektedir. Yerel
zemin etkisi olarak adlandırılan bu etki zeminlerin tekrarlı yükler altında sahip olduğu
gerilme şekil değiştirme davranışı, doğal periyot, topoğrafya gibi özelliklere bağlı
olarak deprem dalgalarının her bir ortam için farklı şekilde değişmesine sebebiyet
verir. Sismik aktivitelerin yüksek olduğu bir kuşak üzerinde yer alan ülkemiz için
depremleri oluşturan dalgaların, yapıların ve temellerinin inşa edildiği zemin ortamına
ulaştığındaki özellikleri ve yıkıcılıkları üstyapıda meydana gelecek hasarların
sebebiyet vereceği can ve mal kayıplarının yaşanmasında etkili olmaktadır. Bu nedenle
deprem gibi dinamik yüklerin zemin davranışına olan etkisi oldukça önem
taşımaktadır. Tekrarlı yüke maruz kalmış zeminin davranışının belirlenmesinde
yapılan dinamik analizlerde zeminin gerçeğe en uygun şekilde modellenmesi elde
edilecek sonuçların değerlendirilmesinde büyük bir öneme sahiptir. Dinamik yükler
altındaki gerilme şekil değiştirme özelliklerinin laboratuvar ve arazi deney yöntemleri
ile bulunmasıyla yapılan analizlerin doğruluğu ve güvenirliliği artmaktadır. Özellikle
farklı gerilme durumları ve değişen çevrimsel yükün etkisinin incelenebildiği,
oluşabilecek drenajın kontrol edilebildiği laboratuvar deneyleri bu özellikleri bulmada
arazi deney yöntemlerine göre öne çıkmaktadır. Zeminin arazide sahip olduğu ortamın
bir, iki, üç boyutlu olarak modellenebildiği programlarla gerçekeltirilebilen analizler
neticesinde zemin yüzeyinde meydana gelecek yatay yer değiştirmeler, oturmalar,
tepki spektrumları, maksimum yer ivmesi değerleri, spektral büyütmeler, kayma
deformasyonları belirlenebilmektedir. Elde edilen sonuçların değerlendirilmesiyle
inşası planlanan yapı depreme dayanıklı olarak dizayn edilebilmektedir. Analizler
arasında zemin modelinin bir boyutlu olarak oluşturulduğu tek boyutlu analizler
pratiklik açısından öne çıkmaktadır. Tek boyutlu analizlerin gerçekleştirilmesinde
kullanılan yöntemler zeminin tekrarlı yükler altında sahip olduğu gerilme şekil
değiştirme davranışını belirleyen dinamik özelliklerin farklı kabullere dayandırıldığı
doğrusal, eşdeğer doğrusal ve doğrusal olmayan olarak üçe ayrılmaktadır. Laboratuvar
ve arazi deneyleri ile belirlenen dinamik özellikler kayma modülü ve sönüm oranı
olarak adlandırılmaktadır. Dinamik özelliklerin her bir tabaka için deprem hareketi
sırasında sabit kabul edildiği doğrusal yöntem, zeminin tekrarlı yük altında değişen
rijitlik ve sönüm oranını modelleyemediğinden tercih edilmemektedir. Kayma modülü
ve sönüm oranının zamana ve de oluşacak deformasyona bağlı değişimini dikkate alandoğrusal olmayan yöntem birçok parametre gerektirmesinden ötürü karmaşık bir
yöntem olmaktadır. Dinamik özelliklerin başta kabul edilen değerlerin oluşacak
deformasyona göre iteratif şekilde elde edildiği eşdeğer doğrusal yöntem ise pratikliği
sebebiyle yaygın olarak kullanılmaktadır.
Bu çalışmada yüksek enerji ile sıkıştırılarak oluşturulmuş mühendislik dolgusunda
yapılan sondaj çalışmasından elde edilen numunelerin geoteknik malzeme ve dinamik
özellikleri laboratuvar deney yöntemleri ile belirlenmiştir. Sondaj numunelerinin
özelliklerini belirlemede ilk olarak elek ve hidrometre deneyleri yapılarak malzemenin
kaba ve ince dane oranı tespit edilmiştir. İnce daneli malzeme olduğu anlaşılan
numune üzerinde Atterberg limit deneyleri yapılarak zemin sınıfları belirlenmiştir.
Numunelerin mukavemet parametreleri belirlemek için serbest basınç deneyleri
yapılmış ardından konsolidasyon deneyleri yapılarak yük altında sıkışma davranışı
incelenmiştir. Yapılan piknometre deneyleri ile özgül ağırlık değerleri belirlenmiştir.
Çalışmanın amacı kapsamında sıkıştırılmış dolgu zeminin dinamik özellikleri dinamik
basit kesme deneyi ile belirlenmiştir. Geoteknik malzeme özellikleri belirlenen
numuneler tabakalara ayrılmış ve dinamik özellikler olan kayma modülü ve sönüm
oranının kayma deformasyonları ile değişimi elde edilmiştir. Türkiye Bina Deprem
Yönetmeliği kapsamında incelenen dolgu numunelerinin laboratuvar deneylerinden
elde edilen drenajsız kayma mukavemeti yardımıyla hesaplanan kayma dalgası hızı
kullanılarak zemin sınıfı belirlenmiştir. Deprem yönetmeliğinde de önerildiği gibi
sahaya özgü tek boyutlu dinamik analizler Deepsoil V6.1 programı kullanılarak
yapılmıştır. Yapılan analizler sonucunda 11 adet deprem kaydı kullanılarak
yönetmelik ve tehlike analizlerinden elde edilen yatay tepki spektrumları
karşılaştırılmıştır. Dinamik analizler bölümünün diğer bir kısmında ise değişen
spektral ivmelere sahip 18 adet kuvvetli yer hareketi kaydı kullanılarak sıkıştırılmış
zeminlerin dinamik tepkileri kayma deformasyonu, yatay deplasman, PGA,
büyütmeler ve hakim periyot değerlendirilerek incelenmiştir.

Abstract:
Earthquakes could be expressed as the vibrations caused by the ruptures in the inner
structure of the earth. Even though it is known that the properties of waves reached
ground surface could be affected by the earthquake source characteristics such as
magnitude, type and length of the rapture they were also influenced by soil layers
which they travel through. Therefore two seismic waves which are created by the same
source with the same characteristics could have completely different shapes when they
arrive ground surface due to the distinct properties of soil layers they pass through.
This effect, which is called as a site effect, causes the earthquake waves to change
differently for each medium depending on the properties of sites under dynamic
loading such as stress-strain behavior, natural period and topography. Since our
country has a high seismic activity, the characteristic and destructiveness of the waves
at the ground surface are one of the most important topics in the evaluation of
earthquake effects in terms of loss of life and property. For this reason, the effect of
dynamic loads such as earthquake is vital on stress-strain, bearing capacity and
settlement behavior of soils. The dynamic properties which determine the stress-strain
the behavior of soils under cyclic loading called shear modulus and damping ratio are
determined by both laboratory and field experiments. Since the laboratory experiments
such as dynamic simple shear test have the ability to create various loading, stress and
drainage conditions comes to the forefront when field tests are considered. Dynamic
analyzes have an important role in determining the behavior of the soil subjected to
dynamic load. Horizontal displacements, settlements, response spectra, amplification,
shear deformations that may occur on the ground surface by earthquake loading could
be obtained from the numerical analyzes that can be performed in one, two or three
dimensional according to their sufficiency to modeling of real site conditions. With the
results obtained, the planned construction can be designed as earthquake resistant.
Among the analyzes methods, one-dimensional analyzes, in which the soil model is
formed as layered horizontally comes forward in terms of practicality. The methods
used to perform one-dimensional analysis are divided into three as linear, equivalent
linear and non-linear procedure in which the dynamic properties that define the stress-strain
behavior of the soil under repetitive loads is based on different assumptions.
The linear method which dynamic properties are considered constant during the
earthquake loading for each layer is not preferred since it is not able to model the soil
stiffness and damping ratio that varies under repetitive load. The nonlinear method,
which takes into account the change in shear modulus and the damping ratio due to
time and deformation is a complicated method because it requires many parameters.
The equivalent linear method, in which the dynamic properties are obtained as a results
of iterative procedure of initial shear modulus and damping ratio according to the shear
strain induced in soil is widely used in terms of practicality.

In this study, firstly the geotechnical and dynamic properties of the soil samples which
obtained from the boring in the engineering fill which was constructed with high
compaction energy was determined by laboratory test at Prof. Dr. Kutay Özaydın Soil
Mechanics Laboratory. After the determination of the physical and dynamic properties
of soil samples, engineering fill was modeled with the usage of the data obtained from
test results by Deepsoil V6.1 in order to perform ground response analyzes.
In line with the thesis purposes, sieve and hydrometer analyzes were conducted to
determine the granulometry of the compacted soil. From the results of the experiments,
it was obtained that soil sample has coarse grain material varying between 7-28% and
fine grain material changing between 72-93% by sieve analysis. It was stated that soil
samples attained from drilling highly consist of fine grain material.
After the determination of the percentage of fine grain material, Atterberg Limits tests
were carried out on soil samples to know the relationship between soil's water content
and consistency. From the result of Casagrande Liquid Limit tests, it was observed that
liquid limit (LL) is changing between 38-80% for compacted soil while the results of
plasticity limit tests indicate soil's plasticity limit (PL) is between 22-26%. With the
evaluation of the test results, soil classification has been made according to the Unified
Soil Classification System (USCS). It was concluded that the soil samples used in this
study were low plasticity clay (CL), high plasticity clay (CH) and low plasticity silt
(ML). To better understanding of the consistency of samples liquidity index (LI) and
consistency index (CI) were calculated according to experimental results and the natural
water content (wn). It was found that liquidity index (LI) is between -1 and 0 while
consistency index (CI) is between 0.9 – 2. Both of the indexes indicated that soil
samples are in the hard-stiff state.
Pycnometer tests were carried out to define specific gravity. It was seen that values are
varying between 2.66 and 2.75 compatible with fine-grained soil's specific gravity.
In order to determine the shear strength of soil samples, unconfined compression tests
were performed. It was calculated that unconfined compressive strength (qu) for soil
samples except T5 was bigger than 400 kPa which is convenient with the liquidity and
consistency index results since they correspond hard consistency.
From the results of consolidation test the preconsolidation pressure (Pc') was
determined between 200 - 400 kPa. It was also observed during the experiment that
heave pressure (Pheave) that soil sample had varying approximately between 50-200
kPa. The compression index was defined for soil samples in a range of 0.0685 -0.0959.
After the determination of the geotechnical and physical properties of samples
dynamic simple shear tests were conducted to define the shear modulus (G) and
damping ratio (ξ) change. The experiments were carried out with sinusoidal
waveforms with 1 Hz loading frequency. Before starting to dynamic experiment
program, with the tentative test it was seen that calibration of the test apparatus should
be done since each type of materials such as soft clay, loose sand, dense sand, stiff clay
requires different calibration factors suggested by test apparatus. Following the
tentative tests the experiment device has operationalized. Since the aim of this thesis
was to perform ground response analyzes with the dynamic properties of soil samples,
engineering fill was divided into six layers which are called T1 for the 0-12m, T2 for
12-24 m, T3 for 24-36 m, T4 for 36-48 m, T5 for 48-60 m and T6 for 60-75 m. Stress-controlled cyclic simple shear tests were conducted with a different cyclic stress ratio
(CSR) values to define the relationship between shear strain induced in the soil sample
and the shear modulus for soil layers consisted of different elevation depth. With the
evaluation of the hysteretic curves obtained from test results the variation of the
damping ratio with shear strain also determined by soil samples at different depth.
Since the materials investigated through thesis were clayey soils it was observed that
the change in the dynamic properties is highly dependent on plasticity characteristic
of soils rather than normal stress applied to it. As a result of tests and calculations, six
different shear modulus and damping ratio curves were obtained. By the evaluation of
the dynamic simple shear and consistency tests, empirical correlations have found
between the shear modulus, consistency limit and plasticity index for shear strain values
bigger than 10-3. Since the numerical analyzes require normalized shear modulus
degradation (G/Gmaks) to determine the dynamic response, shear wave velocity has
been predicted by the correlations in the literature and the Earthquake Regulation for
Turkey. Obtained shear wave velocities were used to calculate the maximum shear
modulus (Gmaks) which corresponds small strain range.
Thereafter one-dimensional ground response analyzes were performed by Deepsoil
with the using normalized shear modulus- shear strain, damping ratio- shear strain
curves procured by dynamic simple shear tests. Within the scope of analyzes eighteen
strong ground motion data with different PGA values (0.1g, 0.2g, 0.3g, 0.4g) and
various Arias Şiddeti values were used to obtain horizontal displacements, shear
strains, amplifications, peak ground accelerations and response spectrum of the soil profile
by dynamic loading.
It was concluded that the peak ground acceleration through the soil profile was
changing slightly for the various PGA values of input motion. As a reason for this
slight change the uniformity of soil profile (except T5) in terms of shear wave
velocities and dynamic properties could be pronounced with the impedance ratio
which is very close to one. From the results of analyzes for earthquakes with 0.1g input
PGA, the surface PGA values for Coyoto Lake, Darfield New Zealand(14W), Hector
Mine(HBS180), Hector Mine (JTN90), Hollister 04, Landers, Sitka Alaska, Darfield
New Zealand(76W) were found as 0.15g, 0.12g, 0.13g, 0.12g, 0.13g, 0.12g, 0.11g,
0.11g respectively. Earthquakes with 0.2g PGA the surface PGA values for Big Bear,
Basso Tirreno, Anza, Northridge, Parkfield-02 CA(36529360) were found as 0.21g,
0.22g, 0.22g, 0.24g, 0.32g respectively. Earthquakes with 0.3g PGA the surface PGA
values for Iwate, ParkDonna -90 were found as 0.30g and 0.32g respectively. Then the
Iwate and ParkDonna – 90 earthquakes was scaled to 0.4g to observe the effect of
higher PGA values and the 0.31g and 0.38g were found respectively. For Kocaeli
earthquake with 0.4g the surface PGA was found as 0.24g.
The horizontal displacements were found as 0.01m for Big Bear, Anza, Northridge,
0.02m for Coyoto Lake, Basso Tirreno, Darfield New Zealand(14W), Hector
Mine(HBS180), Hector Mine(JTN90), Landers, 0.03m for Hollister 04, Darfield New
Zealand(76W), Parkfield-02 CA(36529360), Parkfield-02 CA(Donna90), 0.07m for
Iwate. For the 0.4g - scaled Iwate and ParkDonna-90 earthquakes the displacements at
surface was found as 0.10m and 0.04m respectively. From the analysis of Kocaeli the
displacement was found as 0.13m at ground surface. It can be said that considering the
shear wave velocities of the input motions, the earthquakes with small PGA and Arias
Şiddeti values also have less displacement values on the ground surface in comparison
with the earthquakes with higher PGA and Arias Şiddeti. However the input motions
with same PGA values could generate various displacement values regarding to their
Arias Şiddeti (While ParkDonna-90 with 0.4g generated 0.04m displacement, Kocaeli
with same PGA and higher Arias Şiddeti generated 0.13m displacement at ground
surface.
Shear strains occurred in the soil profile were evaluated through the results of analyzes.
As it was expected the maximum shear strains were generated between 48-60 m which
corresponds to T5 layer with the lowest shear wave velocity for each strong ground
motion record. The amount of shear strains induced in the soil profile at 5 m depth
(approximately the base of elevation for shallow foundations) were found as 0.0045%
for 0.1g input motion, 0.008% for 0.2g input motions, 0.011% for 0.3g input motion.
Shear strains generated by Kocaeli, Iwate, Parkdonna – 90 were found 0.014 %,
0.018%, 0.022% respectively.From the results of analysis the spectral amplifications was found to be varying between 2.15 and 2.59 at predominant periods between 0.96-1.69 sn.
In the scope of the thesis, the ground response analyzes also performed to base on Turkish
Building Earthquake Regulation (TBDY). The soil classification was made according
to TBDY regarding shear wave velocity for upper 30 m of the soil profile and
determined as ZC ((Vs)30 = 360-760 m/s) type of soil with average shear wave velocity
of 383 m/s. Then a response spectrum was drawn according to the TBDY for ZC type
of soil and earthquake level for DD-2 (with the probability of exceeding the spectral
aspects over 50 years is 10% and corresponding repetition period is 475 years.). It was
seen that the response spectrum obtained from the analyzes and calculated from the
earthquake regulation has dominant periods between 0.09-0.40 sec for both. The
maximum spectral acceleration values were 0.74g for the results obtained from the
regulation and 0.68g for the ground response analyses. The different peak values of
the spectrum drawn using two methods indicate the importance of site-specific
analyzes in determining the response spectrum to be used in the design phase.
In the study, the borehole in the engineering fill field has been utilized. Since the
number of boreholes and the type of engineering fill used is the only one the data obtained
from them remained limited in order to obtain dynamic properties of compacted soils.
By using the samples obtained from the borehole to be carried out in the various engineering fill areas, the correlation and the dynamic property curves suggested by this study are open to be developed.