The right picture of Hejianlan expressway Shaxi Tunnel runs smoothly.

Heqing County to Jianchuan County to Lanping County expressway

Shaxi branch line project

Shaxi Tunnel on the right runs smoothly.

Shaxi tunnel is located in Shaxi branch line of Jianchuan county, which is a separated tunnel with poor geology and shallow buried depth. The picture on the right is 730 meters long. The whole tunnel is V-class surrounding rock, and the maximum buried depth is only 60.7 meters. The terrain is undulating, surrounded by villages and farmland. The surrounding rock in the tunnel is weak, with low strength and poor self-stabilization ability. It is the tunnel with the worst geological conditions and one of the most difficult tunnels in the eyes of experts.

The tunnel is constructed according to the standard of two-way four-lane expressway, with a design speed of 80km/h, a right width of 730m and a maximum buried depth of 60.75m m. The terrain in the area is steep and the terrain gradient changes greatly, with a maximum relative height difference of 77.7m m. ..

Since entering the tunnel in April, 2020, the strength of the soil has been greatly weakened due to the thin tunnel cover, loose soil, irrigation of farmland above the top of the tunnel and infiltration of rain in rainy season. According to the surrounding rock conditions of the tunnel and the results of advanced geological prediction, measures such as strengthening advanced support with φ89 middle pipe shed, adding φ89 large lock feet, adjusting the use of I22b initial support arch frame to strengthen initial support, increasing the reserved settlement, shortening the connecting time of working procedures and shortening the safety step were taken. However, deformation, cracking and settlement of initial support still occur from time to time, which seriously restricts the construction period.

Under the complicated geological conditions, the general contractor He Jianlan sent special personnel to guard the site successively, and urged the work area to organize the construction in strict accordance with the principles of "pipe advance, strict grouting, short footage, strong support, early closure and diligent measurement" to ensure safe construction and escort the smooth penetration of the tunnel.