Research on Slope Adjustment Design Method Ensuring Standard Geometric Shape and Position Construction of Circular Tunnel Drainage Ditches

［Objective］ Prior to track laying in a circular subway tunnel, if the clearance under the tracks is insufficient, it will prevent drainage ditches from being constructed according to standard geometric shapes and positions. The smooth slope treatment in gentle interval slope section is prone to water accumulation, and special designs for the track bed structure and drainage ditches may result in tortuous ditch paths, which can also lead to poor drainage and have a certain impact on the track bed structure strength. Therefore, a slope adjustment design is required to ensure that circular tunnel drainage ditches can be constructed according to the standard geometric shape and position. ［Method］ Based on a single hole single line circular tunnel with an inner diameter of 5 400 mm and a lateral drainage ditch of the long sleeper monolithic track bed, to ensure the drainage ditch being constructed according to the standard geometric shape and position, calculation formulas for the minimum track clearance required are proposed respectively for straight and curved sections, where the actual measured tunnel deviation direction is consistent with the designed offset deviation direction, and for curved sections where the actual measured tunnel deviation direction is opposite to the designed offset deviation direction; slope adjustment is optimized within the allowable range of the clearance on the track. To verify the reliability of the proposed slope adjustment design method, the clearance under the track after slope adjustment is compared with the minimum clearance under the track required to ensure that drainage ditches being constructed according to the standard geometric shape. ［Result & Conclusion］ Verification results of the engineering case show that after optimizing the slope adjustment, the track is properly raised, and the clearance under the track meets the minimum clearance required for drainage ditches construction according to the standard geometric shape and position. Thus, the drainage ditches can be constructed according to the standard geometric shape and position, with the slope of the drainage ditch bottom consistent with the slope of the track surface, and the drainage is smooth, which verifies the reliability of the proposed slope adjustment design method.