The shield-tunnel engineering of this section is mainly made of geological substances of sandstone formation (Danawan section) and cobblestone formation (Zhongli section). Considering the geological conditions and the construction environment for the location, two shielded-type shield-tunneling models were utilized. As for the measurements of the components, the outer diameter of the shield-tunneling machine is φ6,240㎜, the length of the shield-tunneling machine is 13.29 m, the outer diameter of the segment is φ6,100㎜ and inner diameter of the segment is φ5,600㎜.
The current construction progress has completed a total of 792 meters of southbound tunneling from Laojie River Station (A22) to Huanbei Station (A21). The shield-tunneling construction of this section was launched on May 20, 2016 and has completed equipment transfer on Jul. 23, 2016, entering the formal tunneling phase. At last, the tunneling operations reached A21 Station on Dec. 22, 2016; the average shield-tunneling rate was 4.8 meters per day.
Due to a stratum of muddy sandstone at the southbound 175 to 325-meter section between A22 Station to A21 Station, the tunneling rate dropped significantly to an average of about 2 meters per day. Following, the team would continue to try and adjust the way of tunneling and gradually improved and tunnel through the difficult strata. In addition, the monitoring data along the road were all normal. Subsequently, the construction team will improve the maintenance frequency of machinery and equipment and the establishment of muddy sandstone tunneling management mechanism to maintain the construction quality and progress.