Deformation measurement and analysis of tunnel backfill in High Intensity Heavy-Ion Accelerator Facility

High Intensity Heavy-ion Accelerator Facility (HIAF) was constructed by Institute of Modern Physics, Chinese Academy of Sciences. Spanning over 2 km in total length, the beam line is situated 12.6 m below ground level in the accelerator tunnel. The extensive spatial configuration of the installation structure poses challenges for installation and collimation, necessitating accurate civil construction. The purpose of this paper is to investigate the impact of tunnel deformation on particle accelerators by examining the deformation of the tunnel in HIAF. This analysis is crucial to guarantee the seamless installation of the subsequent accelerator. This paper proposes a method for monitoring tunnel backfill deformation. The method involves establishing a common reference point in the tunnel using a reserved intervisible hole. It combines underground laser tracker measurements with ground total station measurements to create a secondary control network based on the primary control network in the tunnel. The primary control network of the park and the secondary control network of the tunnel measure the coordinates of the common reference points at the intervisible holes. The deformation of the tunnel is then determined, showing close alignment with the data from the second-level collimation control network before and after the tunnel backfill. A comparison of the measurement results from the two methods reveals a measurement deviation of less than 0.5 mm. Additionally, the maximum deformation in the tunnel's horizontal plane is less than 10 mm. Based on the measurement results of tunnel deformation, the deformation of the tunnel backfill primarily occurs in the direction of the tunnel alignment, specifically within the expansion deformation joints of the tunnel.