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An Experimental Study of Rock Strength with Shallow Openings Under Uniaxial Compression

Moataz A. Al-Obaydi(1*), Thamer M. Al-Noori(2), Sinan K. Al-Azawi(3)

(1) University of Mosul, Iraq
(2) University of Mosul, Iraq
(3) University of Mosul, Iraq
(*) Corresponding author



The stability of rock mass with openings near the ground surface is an important issue in shallow underground structures. An experimental work has been carried out on limestone rock samples with openings in order to examine the effect of very shallow openings on the peak strength ((f) of the rocks under an uniaxial compression load. Many parameters have been studied comprising the number of openings, the cover thickness (H), the clear spacing between openings (S), and the alignment of the opening. The strength of rock mass ((f) decreases as the number of openings increases. The presence of one opening in rock results in a reduction of (f by 46.7, 50.0, 58.5, and 62.8% for D/H= 1.0, 1.6, 2.5, and 5.0 respectively. For rock with two openings with D/S=1, the reductions in (f are 67.6, 70.5, 74.7, and 77.1% and 56.7, 58.6, 63.8, and 66.2% for horizontal and vertical alignment respectively. No further reductions in (f have been found with three openings. (f is reduced when the cover thickness (H) and the spacing between openings decrease. Openings with horizontal alignment have showed less strength ((f) and higher displacement than the ones with vertical alignment. The concentration of tangential stress increases at the sidewall of the openings for rocks with two openings and remains almost constant for rock with three openings. Increases in stress concentration ratio are associated with increased spacing and cover thickness. The horizontal alignment of the openings shows higher stress concentrations that increase by about 1.6 times with an increase in D/S from 1 to 5.
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Hollow Rock; Rock Strength; Shallow Opening; Tunnel; Underground Structures

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