Guangzhou metro line 8 north extension of the entry and exit section of the tunnel through two lines

Recently, as the cutter head of the shield tunneling machine on the outgoing section of subway line 8 gradually emerges from the water, the tunnel on the northern extension of the inbound and outbound section of subway line 8 has been completed with two lines.

High geological risk

High construction difficulty

Line 8, north extension period of cables in and out of the line segment is train in and out of the hushan car depot, among them into the period of line length of about 712 meters, the section of line tunnel span about 650 meters, 1.3-12.4 meters depth, maximum longitudinal grade 34 ‰, the minimum turning radius of 250 meters, slope, curvature have reached the limit of the shield tunnel construction, is a typical shallow buried, small radius and large gradient of shield tunnel. The tunnel body is located in the area with strong karst caves. 

In addition, geological risks such as upper soft and lower hard stratum and liquefied sand stratum also pose high challenges to construction.In addition to the geological challenges, the construction also faced a complex ground environment. In the construction of the short access line of several hundred meters, the shield tunneling machine shall successively pass through the sewage treatment station, inverted suction rainbow sewage box culvert, bafang logistics park south gate bridge, baiyun lake diversion canal, xijiang diversion pipe, south China rapid viaduct, etc. The above risk points were continuously arranged, and the cumulative impact length reached 301.2 meters, accounting for up to 46.4% of the whole section.

Come across pine pile group

Take initiative to clean up problems

In the tunneling of the shield tunneling machine, pine piles were also encountered. The cutter disc could not effectively chop up the pine piles, and a large amount of pine was overpiled into the soil bin, resulting in frequent blockage of the mud water circulation system, which easily caused grouting and settlement on the ground. To this end, the subway builders removed and cut the mud and water pipes, and carried out the cleaning in the way of "surgery" to ensure the smooth tunneling of the shield tunneling machine.

For this reason, subway builders strictly implement the acceptance system of major risk source nodes. During the period of penetrating serious and large risk sources and buildings, the system of round-the-clock rotation is implemented and 2-hour monitoring frequency is generally adopted. Meanwhile, experts are stationed at the site to focus on key points and key points to ensure safe and stable tunneling.

The water out of the hole

Ensure construction safety

Due to the complex geology and ground environment at the tunnel exit of shield tunneling machine, subway builders decided to adopt the underwater receiving method after comparing the conventional receiving method and steel sleeve receiving method. The receiving well is backfilled with active water and mud, and the penetration can be controlled by the balance of water and soil pressure inside and outside the receiving well. Under the condition of the balance of water and soil pressure, the shield tunneling machine is pushed into the receiving well safely, which greatly reduces the influence of the shield tunneling machine on the surrounding environment.

By controlling the water level in the process of receiving, revealing the knife dish couple, both to prevent groundwater from crisis occurs through a circle of open hole, and to observe the knife dish like regular reception mode of accurate position, realize accurate schedule control and flexible emergency management, under the condition of "visualization" to implement security.

Up to now, the north extension of line 8 has completed 78% of the civil works and 93% of the cars in baiyun lake. Among the 15 stations, 13 main structures have been capped and transferred to electromechanical engineering, and the construction of subsidiary structures has been promoted, and 2 are under construction. Of the 15 sections, 8 have been through the double line, 7 civil construction, baiyunhu depot access line tunnel through.