Çatlaklı kaya kütlesi dayanımının sürekli yenilme durumunda üç eksenli deneylerle araştırılması
Investigation of the strength of the fractured rock mass by triaxial tests in case of continuous failure
Yazar: HASAN MERT ÖZKARSLI
Danışman: DOÇ. DR. YILMAZ MAHMUTOĞLU
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Jeoloji Mühendisliği Ana Bilim Dalı / Jeoloji Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Jeoloji Mühendisliği = Geological Engineering ; Maden Mühendisliği ve Madencilik = Mining Engineering and Mining ; İnşaat Mühendisliği = Civil Engineering

Özet:
Çalışmada, çatlaklı kaya kütlesi dayanımının sürekli yenilme durumunda üç eksenli deneylerle araştırılması amaçlanmıştır. Bu amaçla, tane sınırları önceden ısıl bir işlem sonucunda örselenmiş ve kısmen koparılmış Muğla-Kavaklıdere mermeri çatlaklı kaya için model malzemesi olarak seçilmiştir. Başlangıçta, farklı sayıda periyodik ısıl döngüye sahip örnek kategorilerinde ısıl işlem sonucu oluşan fiziksel değişiklikler belirlenmiş, daha sonra aynı örnek kategorileri için mekanik deneyler uygulanmıştır. Sürekli yenilme durumunda üç eksenli deneylerden her bir örneğin yenilme sonrasındaki dayanımlarına karşılık gelen yenilme zarfları normal gerilme düzleminde (σ1, σ3) çizilerek elde edilmiştir. Çalışmanın son bölümünde elde edilen deneysel sonuçlar uygulamada kabullenilmiş Hoek-Brown yenilme ölçütü ile karşılaştırılmıştır. 
Deneysel çalışmalar, farklı sayıda ısıl işlem döngüsüne tabi tutulan 6 ayrı örnek kategorisi üzerinde gerçekleştirilmiştir. Deney malzemesinin tane (kalsit minerali) sınırlarını açmak, örnek dokusunu çatlaklı kaya dokusuna benzetmek için uygulanan ısıl işlemde, maksimum sıcaklık diferansiyel termal analiz (DTA) sonuçlarına göre 400 ⸰C ile sınırlandırılmıştır. Deneylerde standart boy/çap oranına sahip silindirik örnekler kullanılmıştır. Deney örneklerinin alt ve üst yüzeyleri arasında paralellik sağlanmış ve parlatılarak pürüzsüz hale getirilmiştir. Üçer numuneden oluşan 6 örnek kategorisinden 5'i farklı sayıda 24 saatlik ısıtma-soğutma döngüsüne tabi tutulmuştur. Orijinal örnek kategorisi A, diğer örnek kategorileri ise sırasıyla B, C, D, E ve F olarak adlandırılmıştır. A grubu örnekler herhangi bir ısıl işleme tabi tutulmamıştır. Diğer örnek kategorileri (B, C, D, E ve F) ise farklı sayıda ısıl işleme maruz bırakılmıştır. 
Isıl işlem sonucunda deney örneği kategorilerinin dokusal ve fiziksel özelliklerinde oluşan değişiklikler rutin deneylerle belirlenmiş ve değerlendirilmiştir. Bu değerlendirmeler sonucunda tane sınırlarında oluşan kalıcı fissürlerin genişliklerinin ve sıklıklarının ısıl işlem döngüsü sayısına bağlı artış gösterdiği belirlenmiştir. Ayrıca, kaba taneli Muğla Mermeri'nden oluşan deney örneği kategorilerinin kuru birim hacim ağırlığı, doygun birim hacim ağırlığı,  görünür porozitesi (gözeneklilik), kapiler su emmesi, sonik hızları, boşluk oranı, yoğunlukları gibi fiziksel özelliklerindeki değişiklikler belirlenmiş ve yorumlanmıştır. 
Yukarıda değinilen bazı deneyler doygun koşullarda tekrarlanmış ve elde edilen sonuçlar irdelenmiştir. Aralarındaki farklar karşılaştırılmıştır. Aynı örnekler üzerinde mekanik deneyler son aşamada uygulanmıştır. Sürekli yenilme durumunda üç eksenli deneylerden elde edilen ve yenilme sonrası durumu temsil eden dayanım zarfları Hoek-Brown yenilme ölçütü ile karşılaştırılmış, benzerlikler ve farklılıklar tezin son bölümünde tartışılmıştır. Üç eksenli deneyler sonucunda, özellikle ısıl işleme tabi tutulan örneklerin tümünde yenilmenin taneler arasında geliştiği, örneklerde doku yenilmesinin oluştuğu görülmüştür. Ayrıca, düşük çevre basınçları altında, yenilme zarflarının eğiminde önemli artışın olduğu belirlenmiş, bu durum sığ derinliklerde kaya kütlesi dayanımını içsel sürtünme açısı tarafından denetlendiği anlaşılmıştır. Dayanım zarfı üzerinde, farklı çevre basıncı aralıklarına karşılık gelen kısımlar için kesme mukavemeti parametreleri Mohr-Coulomb eşitlikleri yardımıyla belirlenmiş ve çevre basıncına bağlı değişimleri ortaya konmuştur. Sonuç olarak, çatlaklı kaya kütlesi dayanımlarının tanımlanmasında kullanılan kesme mukavemeti parametrelerinin (içsel sürtünme açısı ve kohezyon) sabit birer değer olarak alınmasının doğru olmayacağı, bu büyüklüklerin çevre gerilmesinin fonksiyonu olarak değişeceği belirlenmiştir.

Abstract:
Studies on the design of underground and aboveground structures, rock mass and rock failure criteria are of great importance. As a matter of fact, in order to make the design, it must be analyzed correctly and data must be taken from the experiments correctly. For this reason, one of the reasons affecting the process of rock mass failure is the state of the rock mass being intact or fractured rock. Today, studies on the behavior of fractured rock masses have aroused curiosity in the community. The reason for this is that problems arise before and after geotechnical studies. Both experimental and theoretical approaches on these issues have an important effect on the decision phase against these problems. The Mohr-Coulomb criterion, which has been used in the past and is currently used for some practical solutions, cannot fully explain the failure process in multibody, namely fractured rocks. These issues were expressed in the 1970s.
Both in the world both in Turkey theorems related to the failure behavior of the rock mass in the 1970s and began to be raised prior year. Until the 1970s, the necessary information about the failure behavior of fractured rocks was not at the desired level. After these years, these behaviors were tried to be explained by Mohr-Coulomb's criteria, albeit partially, but there were still deficiencies in terms of applicability. In the 1980s, the Hoek-Brown failure criterion was an important gain for that period in terms of both applicability and practical solutions. The Hoek-Brown failure criterion is an empirical approach, making it more effective than other criteria in terms of applicability. On the contrary, between 1980-1988, according to the criteria proposed by Hoek-Brown, σ1 found the curvature of the stress and the shear strength with the greatest principal stress and σ3 the smallest principal stress. In the 1990s, some changes were made and they emphasized that the "m" and "s" parameters were also important.
Between 1997 and 1999, an important change was made and the concept of GSI started to be discussed. During these years, GSI, internal friction angle, deformation and cohesion parameters were developed. In 2002 in the world and many of the researchers and academics in Turkey have made updates to Hoek-Brown failure criterion. The distortion factor "D" has started to be talked about this year. GSI has updated the blocks, SRC and the number of volumetric joints and the massive rock group have been added to the block. The importance of this year is that the changes and updates made this year are still valid today. Finally, the Hoek-Brown failure criterion, updated in 2018, was tried to be explained with an approach based on bayes statistics, that is, the method of probability and frequency. As a result of the advancement of technology and the positive progress in this direction in academic studies, it is essential that there are changes, developments and updates in studies related to this innovation criterion.
The Hoek-Brown failure criterion is an empirical criterion, and its usability is high compared to other criteria in terms of its applicability especially in fractured rocks. In this respect, in the thesis, the continuous failure of fractured rock samples has been investigated by triaxial strength tests, and the aim is to compare the data obtained with this purpose with the Hoek-Brown failure criterion in the literature.
Firstly, in this study, it is aimed to investigate the strength of fractured rocks by triaxial tests in case of continuous failure. For this purpose, the Muğla-Kavaklıdere marble, whose grain boundaries were previously damaged by a heat treatment and partially detached, was chosen as the model material for the fractured rock. Initially, physical changes resulting from heat treatment were determined in sample categories with different number of periodic thermal cycles, then mechanical tests were applied for the same sample categories.
The failure envelopes corresponding to the strength after failure of each sample from the triaxial tests in the case of continuous failure were obtained by drawing in the normal stress plane (σ1, σ3). The experimental results obtained in the last part of the study were compared with the Hoek-Brown failure criteria accepted in practice.
Experimental studies were carried out on six different sample categories that were subjected to different numbers of heat treatment cycles. In the heat treatment applied to open the grain (calcite mineral) boundaries of the test material and to simulate the sample texture to the fractured rock texture, the maximum temperature was limited to 400 0C according to the results of differential thermal analysis (DTA).
Cylindrical specimens with standard length/diameter ratio were used in the experiments. Parallelism was provided between the lower and upper surfaces of the test samples and they were polished and smoothed. Five out of six sample categories consisting of three samples were subjected to different number of 24-hour heating-cooling cycles. The original sample category was named A, while the other sample categories were named B, C, D, E and F, respectively. Group A samples were not subjected to any heat treatment. Other sample categories (B, C, D, E and F) were subjected to different number of heat treatments.
Changes in textural and physical properties of the test sample categories as a result of heat treatment were determined and evaluated by routine experiments. As a result of these evaluations, it was determined that the width and frequency of permanent fissures formed at the grain boundaries increased depending on the number of heat treatment cycles. In addition, the changes in the physical properties of the test sample categories consisting of coarse grained Muğla Marble such as dry unit weight, saturated unit weight, apparent porosity, water absorption, capillary water absorption, sonic velocities, void ratio and densities were determined and interpreted.
Some experiments mentioned above were repeated under saturated conditions and the results obtained were examined. The differences between them have been compared. Mechanical tests were applied on the same samples at the last stage. Strength envelopes obtained from triaxial experiments in case of continuous failure and representing the state after failure were compared with Hoek-Brown failure criterion, similarities and differences were discussed in the last part of the thesis.
In thin section samples, it was determined that fracture development after heat treatment was high in all samples except A group sample, and the fracture development of F group samples, which were exposed to heat treatment the most, was the highest. In addition, it was observed that 99% of calcite minerals in CaCO3, the chemical composition of the marble sample, were affected by heat treatment and degraded.
In addition, apart from heat treatment, grain size difference in physical properties (coarse and fine) is an important factor in fracture formation. While the porosity, water absorption and fracture formation were more common in the physical experiments of the coarse grained samples, these were observed less in the fine grained samples.
As a result of physical experiments, A group samples were not subjected to heat treatment in any way, so density, porosity, water absorption, micro-fracture development were less common than other groups. In the samples subjected to heat treatment, the water absorption, micro fracture formation, porosity of the samples, which were mostly heat treated according to the degree of heat treatment, increased the parameters listed here.
One of the important inputs regarding the strength and fractured of the samples after heat treatment is the ultrasonic wave velocity test. While the ultrasonic wave velocity classification of the samples before the experiment was high-speed and intact rock, after the experiment, that is, after the heat treatment, the ultrasonic wave velocities of the samples were found to be very low speed and fractured rock and the wave velocities were noticeably reduced in the experiments.
In the mechanical experiments, it was determined that the samples subjected to uniaxial compression test were affected by the processes in heat treatment and other physical experiments and accordingly decreased from group A to group F. Accordingly, uniaxial compression strength, modulus of elasticity and deformation modulus decreased according to the duration of heat treatment. As a result of the triaxial compression test, it was determined that σ_c decreased from A group samples towards F group samples.
As a result of the triaxial experiments, it was observed that in all the samples that were subjected to heat treatment, the defeat developed between the grains and the tissue regeneration occurred in the samples. In addition, under low environmental pressures, it was determined that there was a significant increase in the inclination of the failure envelopes, and this situation was found to be controlled by the internal friction angle at shallow depths. The shear strength parameters for the parts on the strength envelope corresponding to different environmental pressure ranges are determined with the help of Mohr-Coulomb equations and changes depending on the ambient pressure are revealed. As a result, it was determined that it would not be correct to take the shear strength parameters (internal friction angle and cohesion) used in defining the fractured rock mass strengths as a constant value, and these sizes will change as a function of the environmental stress.
We can come to the following conclusion about the values found. When the GSI value increases, the internal friction angle increases and the cohesion value decreases. Increasing the GSI value indicates that the rock has a intact structure or has very few fractures, a low GSI value indicates that the strength of the specimens becomes susceptible to cracks and fractured development increases. It also shows that under low environmental pressures, it was determined that there was a significant increase in the inclination of the failure envelopes, and this situation was found to be controlled by the internal friction angle at shallow depths.