Currently, the Jinan Shunhe Viaduct South Extension Phase II project has fully commenced, primarily in the form of underground roads. Among the four construction inclined shafts set up, two at Ma'anshan Park and Shunyu Road have already started excavation.

  The entire Phase II project mostly adopts blind excavation: during construction, dynamic monitoring is carried out on the ground roads and buildings on both sides. Since the underground tunnel of the Shunhe Viaduct South Extension Phase II project is located 8 meters below the road, non-blasting blind excavation with tunneling machinery is mostly used throughout the project. At the same time, dynamic monitoring of the ground roads and buildings on both sides is implemented during construction to ensure the safety of the entire project and surrounding structures.

     
Excavator Tunneling for Jinan Shunhe Viaduct South Extension Phase II Underground Project

    It is understood that currently, tunnel excavation in China also mostly uses this type of tunneling machine. The machine relies on multiple drill bits rotating at high speed at the front to break the rock wall, and then an excavator is used to dig out the crushed rock. "Because the No. 1 inclined shaft is on the side of the Ma'anshan mountain, mostly rock with hard soil, under smooth conditions, using the tunneling machine, it can advance about 1 meter per day," said a relevant person in charge.

     Tunnel excavation adopts the "three-in-two" method: first excavate the middle, then the sides, advancing a section every 50 meters. After the inclined shaft is dug through to the main tunnel area, the construction team will use the "three-in-two" method for tunnel excavation. Ultimately, an underground expressway with two tunnels will be built. "The excavation method for the main tunnel is relatively complex. First, reserve a cross-section of about 3 tunnels, then excavate the middle tunnel first. After about 50 meters, build a concrete partition wall in the middle, and simultaneously support the entire tunnel face to prevent danger. This partition wall will be the middle partition wall after the two tunnels are completed," introduced the project manager. This method of first excavating the middle, then fixing, then excavating the sides can better ensure the quality and safety of the entire tunnel project. After building the 50-meter middle wall, excavate one side of the main tunnel, and after about 50 meters of depth, excavate the other side of the main tunnel.

Excavator Tunneling for Jinan Shunhe Viaduct South Extension Phase II Underground Project

    The excavation of the main tunnels on both sides is also not simple. "A tunnel cannot be excavated all at once; otherwise, if a collapse occurs during construction, it would be irreparable. Therefore, for a single tunnel face, we also adopt a method of excavating in small sections. First, excavate the upper part, then immediately install temporary support. Then excavate the other side of the upper part with support. In this way, a tunnel is divided into several small blocks for excavation. This will not extend the construction period and can maximize safety and quality," introduced the relevant person in charge.

     It is reported that the deepest buried depth of No. 1 inclined shaft can reach 19.3 meters, with a total length of about 90 meters, of which about 44 meters is blind excavation. During blind excavation, the impact on road traffic is relatively small. The construction period of No. 1 inclined shaft is expected to last about 3 to 4 months.

    Maximize reduction of traffic pressure: 4 inclined shafts are constructed in phases, and later excavation can proceed in 6 directions for the entire underground tunnel project. From Ma'anshan intersection southward, from Qilishan intersection northward, No. 1 inclined shaft at Ma'anshan Park and No. 2 inclined shaft at Shunyu Road intersection will excavate towards both ends. 4 inclined shafts and 6 excavation directions will maximize the project progress.

    In addition, the excavation of inclined shafts also depends on the specific conditions of the construction section. Since the entire Phase II project does not involve demolition, whether the road has the conditions for excavating inclined shafts is crucial. "Currently, the first to start is No. 1 inclined shaft. After the entire underground road project is completed, the inclined shafts will be used as emergency evacuation passages for the underground tunnel," said the relevant person in charge.

    The inclined shafts and underground road project are mostly blind excavation, but open excavation is still needed to assist in the early stage of construction. Therefore, to avoid affecting traffic, the four inclined shaft openings will be constructed in phases. Currently, only No. 1 and No. 2 inclined shafts have started.

    At the same time, both Ma'anshan intersection and Qilishan intersection are open excavation. Once construction starts, the relevant roads will be closed. Therefore, phased and staggered construction is an important measure to reduce traffic pressure and ensure road passage.

    The deepest part of the rail transit tunnel can reach more than 20 meters underground.

    Compared with municipal tunnels, rail transit underground tunnels are higher in depth, precision, and cost. Taking Rail Transit Line R1 as an example, the average cost per kilometer of the underground part is as high as over 700 million yuan, and the deepest part can reach more than 20 meters from the ground.

   In appearance, unlike the usual rectangular cross-section of municipal tunnels, the cross-section of rail transit tunnels is circular, which depends on the construction equipment for the underground section of rail transit—the shield tunneling machine. This is a large machine with a cylindrical appearance that can excavate tunnels underground, supporting formation pressure and advancing in the strata.

   The relevant person in charge stated that in terms of excavation depth, taking a standard 2-level platform as an example, the top of the section connected to such a platform is 10-12 meters from the ground, and generally the outer diameter of the tunnel is 6.4 meters, meaning the bottom of the tunnel is about 16-18 meters from the ground. If it is a 3-level platform, the top of the section is 15-18 meters from the ground, and the bottom depth can reach more than 20 meters.

   Industry insiders revealed that the cost of the underground part of Line R1 averages more than 700 million yuan per kilometer.