Effect of support system type on boundary displacement of tunnel in soft soil

For many years, the rockbolt and shotcrete lining have been an integral part of the supporting structure system to reducing tunnel boundary displacement. Theirs various characteristics, such as length, diameter, distribution technique for rockbolt and the thickness of the shotcrete lining are critical in describing their role in this field. A parametric study conducted by a numerical finite element technique called Plaxis 2D, to investigated the effects of different bolt and lining parameters on the maximum boundary displacement of tunnel in soft soil type. Bolt's parameters were available in five diameters of 16, 22, 25, 28, and 32 mm and selected four lengths 3, 4, 5, 6 m. The lining changeable parameter was only its thickness by taking four different thicknesses of 30, 35, 40, and 50 cm. It was noticed that sidewall displacement is greater than the crown displacement. The maximum displacements were about 1656 mm and 1280 mm at sidewall and crown respectively, when no bolt was used which are reduced by 31% and 26.64% when a 3 m bolt with a diameter of 32 mm has been used. Bolt diameter performs better at longer lengths, while the boundary displacement at 3 m bolt length is often smaller than other lengths. The performance of the lining was much better than bolt effect. It's reduced the displacement at sidewall (for lining of 50 cm thickness) from 1656 mm to only 50 mm which is mean 97% reduction and also shows a 98.4% reduction for crown displacement.