A road-cut excavation started by mechanical means for the construction of Zonguldak- Amasra-Kurucasile highway between km 26+590 and km 26+700 at Zonguldak province of Turkey in 2014. The road-cut excavation was in close proximity to a masonry-lined 76- year-old railway tunnel in service and to residential buildings. Slope instabilities in the form of plane failure occurred, and thus, risk of toppling of excavators arose due to adverse rock mass conditions. Therefore, the excavation method was required to be changed to cautious bench blasting. In this paper, we present the cautious blast design approach and ground vibration monitoring and control. We carried out a series of test blasts, using limited charge amounts varying from 0.5 kg to 4.6 kg, together with ground vibration monitoring. We determined the safe amount of charge per delay for full-scale blasts as a function of distance using the attenuation equation derived from test blast results. During the full-scale blasts, the peak particle velocities (PPVs) recorded at the wall of the railway tunnel varied from 4 mm/s to 77 mm/s, whereas the PPVs recorded at the ground next to the buildings varied between 4 mm/s and 16.3 mm/s. No damage has been observed, and the tunnel is in service and the buildings are still in use.

INTRODUCTION

The General Directorate of Highways, Turkey, started a road-cut excavation for the construction of Zonguldak-Amasra-Kurucasile highway between kilometres 26+590 and 26+700. A mechanical excavation method was selected, since the slope to be cut was in close proximity to a masonry-lined 76- year-old railway tunnel in service and to residential buildings (Figure 1 and 2, Bilgin and Dagasan, 2014). The road-cut slope was designed such that it consists of a different number of benches at various cross-sections (Figure 3).

The rock formations at the site mainly consist of alternating layers of sandstone, claystone, and siltstone with frequent sandy limestone, and limestone layers. Typical rock mass and material properties determined by Mega Engineering and Consulting Ltd. (2014) are given in Table I. Typical bedding plane orientation is 065/46.

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