Determination of Deformation Distribution around Modified Horseshoe Cross-sectional Tunnels in Weak Rock Mass

Year 2021, Volume: 21 Issue: 4, 934 - 944, 31.08.2021

Alaattin Sakcalı

https://doi.org/10.35414/akufemubid.935746

Cited By: 1

Abstract

Characterization of deformations occurring in the rock mass around the tunnel after tunnel excavation can be used as an auxiliary tool for support design. After the tunnel excavation, the deformations in front and behind of the tunnel face in perpendicular direction can be determined with the longitudinal deformation profile (LDP). There are equality proposals by considering the effects of different parameters for the establishment of the LDP in the literature. These equations are proposed for circular section tunnels by assuming that tunnel excavation is carried out under hydrostatic conditions. The highway tunnels in Turkey are generally opened with modified horseshoe cross-section and difficulties are encountered in precisely predicting deformations around the tunnel face. It is possible to analyze the deformations in the rock mass around the tunnel by numerical modeling. In this study, the most preferred modified horseshoe cross-sectional tunnels of 2 different sizes in highway tunnel excavation in Turkey are discussed. The tunnel excavations to be opened in the weak rock mass in the determined sections were modeled with FLAC3D based on finite difference method. In addition to the tunnel opened under hydrostatic conditions, non-hydrostatic conditions were also evaluated. The tunnels in the determined sections for conditions with horizontal stress / vertical stress ratio (k-value) between 0.5 and 2 were modeled as unsupported. The deformation distributions obtained from the model and the deformation values recorded in the points determined with an angular change of 15⁰ from the roof to the base were examined. With this study, it is concluded that numerical modeling can be a good auxiliary tool in determining LDP in tunnel excavations with non-circular (modified horseshoe cross-section).

Keywords

Deformation distribution, Modified horseshoe cross-sectional, Numerical modelling, Tunnel

Zayıf Kaya Kütlelerinde Açılan Modifiye At Nalı Kesitli Tünellerdeki Deformasyon Dağılımının Sayısal Modelleme ile Belirlenmesi

Abstract

Tünel kazısı sonrası tünel çevresindeki kaya kütlesinde meydana gelen deformasyonları karakterize etmek tahkimat tasarımı için bir yardımcı araç olarak kullanılabilmektedir. Tünel kazısı sonrası tünel aynasına dik doğrultuda aynanın ön ve arkasındaki deformasyonlar uzunlamasına deformasyon profili (Longitudinal Deformation Profile (LDP)) ile belirlenebilir. Literatürde farklı parametrelerin etkileri de göz önünde bulundurularak LDP’nin oluşturulmasına yönelik eşitlik önerileri vardır. Bu eşitlikler hidrostatik koşullarda tünel kazısı gerçekleştirildiği varsayımı yapılarak dairesel kesitli tüneller için önerilmiştir. Türkiye’de karayolu tünelleri genellikle modifiye at nalı kesitli açılmakta olup tünel aynası çevresindeki deformasyonların tam olarak tahmin edilmesinde zorluklarla karşılaşılmaktadır. Tünel çevresindeki kaya kütlesindeki deformasyonları sayısal modelleme ile analiz etmek mümkündür. Bu çalışmada, Türkiye’de kara yolu tünel kazılarında en çok tercih edilen 2 farklı boyuttaki modifiye at nalı kesitli tünel ele alınmıştır. Belirlenen kesitlerde zayıf kaya kütlesinde açılacak tünel kazısı sonlu farklar yöntemine dayalı FLAC3D ile modellenmiştir. Hidrostatik koşullarda açılan tünelin yanı sıra hidrostatik olmayan koşullar da değerlendirilmiştir. Yatay gerilme / dikey gerilme oranı (k-değeri) 0,5 ile 2 arasında değişen koşullar için belirlenen kesitlerde tüneller tahkimatsız olarak modellenmiştir. Modelden elde edilen deformasyon dağılımlarına ve tavandan tabana doğru 15⁰’lik açısal değişimle belirlenen yerlerde kaydedilen deformasyon değerleri incelenmiştir. Bu çalışma ile, dairesel olmayan (modifiye at nalı kesitli) tünel kazılarında LDP’nin belirlenmesinde sayısal modellemenin iyi bir yardımcı araç olabileceği sonucu elde edilmiştir.

Keywords

Deformasyon dağılımı, Modifiye at nalı kesit, Sayısal modelleme, Tünel

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