In-situ measurement of stress of rebars in shaft lining during drilling sinking

The stress-measuring scheme of rebars in the shaft lining of auxiliary shaft of Wenjiazhuang Iron Ore Mine during drilling sinking is introduced, and the variation of the measured stresses is discussed. The results show that the rebars bear compressive stress during drilling sinking, the compressive stress of the tangent-directional rebars is greater than that of the vertical one, and the variation phases of the stresses correspond to the sinking phases. During the floating and dropping phase, the stress curves present 'bilinear' feature. During the water-adding phase, the compressive stress of the tangent-directional rebars decreases and that of the vertical one increases. During the first grouting phase, the compressive stress decreases significantly, and some rebars even bear tensile stress. During the sequent three grouting phases, the compressive stress increases first, then partially recovers. During the drainage phase, the compressive stress of the tangent-directional rebars increases and that of the vertical one changes little. During the additional grouting phase, the compressive stress increases first, then partially recovers a less part as compared to the preceding grouting. When the sinking is completed, the maximum compressive stress of the rebars reaches the yield stress of 41%. This installation stress should be considered when designing the shaft lining.