Mustafa KANIK, Zülfü GÜROCAK

Kazı Derinliğinin Püskürtme Beton Dayanımı Üzerindeki Etkisi: Sayısal Bir Yaklaşım

Uygun ve güvenilir destek sistemlerinin seçimi, tünelcilikte maliyet ve güvenliği etkileyen en önemli faktörlerden birisidir. Farklı araştırmacılar tarafından önerilmiş olan görgül kaya sınıflama yöntemleri destek tipinin seçiminde büyük kolaylık sağlamaktadır. Bu konuda kullanılan diğer bir yöntem sayısal analizlerdir. Görgül olarak elde edilen destek tipinin sayısal olarak da analiz edilmesi sonucunda daha güvenilir ve ekonomik destek tipi belirlenebilmektedir. Bu çalışmada, farklı kaya sınıfları için RMR89 tarafından önerilen püskürtme betonun dayanımı ile kazı derinliği arasındaki ilişkileri incelemek amacıyla Sonlu Elemanlar Yöntemi (FEM) kullanılarak sayısal modellemeler yapılmıştır. Modellemelerde, Zayıf, Orta ve İyi kaliteli kaya sınıfındaki kaya kütleleri ve farklı kazı derinlikleri dikkate alınmıştır. Kazı derinliğinin artması bağlı olarak, destek sisteminin yenilmeden çalışabilmesi için püskürtme beton dayanımının ne kadar olması gerektiği araştırılmıştır. Yapılan analizlere göre püskürtme beton dayanımının 30 MPa alınması durumda, İyi kaliteli Kaya sınıfında 450 m, Orta kaliteli Kaya sınıfında 310 m, Zayıf kaliteli Kaya sınıfında ise 200 m kazı derinliğinde püskürtme betonda yenilmeler meydana gelmektedir. Bu derinliklerden sonra destek sisteminin duraylı kalabilmesi için püskürtme beton dayanımının artırılması gerekmektedir. Püskürtme beton dayanımı 40 MPa’ya çıkarıldığında, İyi kaliteli Kaya sınıfında 530 m, Orta kaliteli Kaya sınıfında 420 m ve Zayıf kaliteli Kaya sınıfında ise 260 m kazı derinliğine kadar destek elemanlarında yenilme meydana gelmemektedir. İyi kaliteli kaya sınıfında 20 MPa dayanımlı püskürtme beton için yapılan analizlerde, 410 m örtü kalınlığına kadar destek sisteminde yenilme meydana gelmemektedir. Bu çalışmadan elde edilen sonuçlar, kazı derinliğinin artması sonucunda, destek sistemlerinin yenilmemesi için püskürtme beton dayanımın artırılması veya bir alt kaya sınıfı için önerilen destek sistemlerinin seçilmesi gerektiğini göstermektedir.

Anahtar Kelimeler:

Kazı derinliği, RMR sınıflama sistemi, Püskürtme beton dayanımı, FEM analizi

Effect of Excavation Depth on Shotcrete Strength: A Numerical Approach

Choosing appropriate and reliable support systems is one of the most important factors affecting cost and security in tunneling. The empirical rock classification methods proposed by different researchers provide great convenience in selecting the support type. Another method used in this regard is numerical analysis. With the aid of the numerical analyses, analyzing the support system empirically obtained helps to determine more reliable and economic support types. In this study, numerical models were developed using Finite Elements Method (FEM) to investigate the relationship between the strength of shotcrete and the excavation depth for the different rock classes proposed by RMR89. Different excavation depths for Weak, Fair and Good rock masses are taken into account in the modeling. Depending on the increase in depth of excavation, it has been researched how much the strength of the shotcrete must be so that the support system can continue to support without being yielded. According to the evaluated models, when the shotcrete strength is assumed as 30 MPa, the elements of shotcrete was started to yielded at 200 m depth for the weak rock mass, 310 m depth for the fair rock mass and 450 m depth for the good rock mass. After reaching the mentioned depths, it is necessary to increase the strength of the shotcrete in order to keep the support system stable. Once the shotcrete strength is increased to 40 MPa, there was not failure in the support elements up to the excavation depth of 530 m in the good rock mass, 420 m for fair rock mass and 260 m for the weak rock mass. The support system was determined stable up to 410 m overburden in the evaluated analyses for 20 MPa strengthen shotcrete. In this study, it is revealed that, the increase in depth of excavation indicates that the strength of the shotcrete must be increased to avoid instabilities of the support systems or that the support systems recommended for a lower rock class should be selected.

Keywords:

Excavation depth, Numerical modeling, RMR classification system, Shotcrete strength,

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