Control Technology for Shrinkage Cracks in Concrete Structures of Power Tunnel Pipe Jacking Working Shafts

To address the issues of shrinkage cracks in large-volume concrete during the construction of pipe jacking work tunnels in ultra-deep buried power tunnels—cracks that compromise structural waterproofing and durability—the study examines a pipe jacking project in Nantong City. By combining field monitoring with numerical simulation， the research investigates the formation mechanisms of concrete shrinkage cracks during tunnel construction and evaluates the effectiveness of hydration heat control， volume deformation management， and water cooling systems. Results demonstrate high consistency between numerical simulations and actual monitoring data. During construction， the vertical concrete side walls around the pipe jacking tunnel experienced significant temperature peaks due to cement hydration heat generation， followed by substantial shrinkage deformation caused by combined thermal contraction and hydration-induced self-shrinkage. When this deformation is restrained by the underlying hardened concrete and the adjacent walls， the maximum cracking risk reached 1.17， significantly increasing fracture susceptibility. The addition of 0.2% hydration heat control material reduced temperature peaks by 24.4% and 28-day maximum tensile stress by 43.9%； incorporating 8% expansion agent compensated for shrinkage deformation， lowering 28-day stress by 57%； and installing cooling water pipes reduced temperature peaks by approximately 20% and 28-day stress by 44.3%. These three measures effectively mitigate crack formation in tunnel concrete structures.