A CURVED REINFORCED CONCRETE BEAM MEHTOD FOR CALCULATING INITIAL CRACK SPACE IN THE LINING OF PRESSURE TUNNELS

The space between cracks in the concrete lining of pressure tunnel has an important effect on the crack opening. The practical results of four prototype water pressure tests indicate that less initial cracks, of relatively larger spacing, would be triggered under critical internal water pressure as compared to that of reinforced concrete members in structural engineering. A curved reinforced beam method is presented for the determination of initial crack space in the lining of pressure tunnels, which, as a simple approach, can consider the effects of lining curvature, reinforcement ratio, the internal water pressure, as well as the normal and tangential reaction forces by the surrounding rock mass. A comparison is also made between the proposed method and the theory of a bending beam on elastic foundation, and the advantages and disadvantages of both methods are discussed. A field case of a pressure tunnel is analyzed and the predictions by the two methods compare favorably and are basically in agreement with the actual cracking behavior in the lining. Moreover, the occurrence of further cracking under increasing water pressure can be determined by the proposed method.