Recently, supplementary geological exploration for boulders in the shield tunneling sections between Shuping and Pingdong on the Fuzhou Metro was carried out, aiming to provide “minimally invasive diagnosis and treatment” for shield tunneling and clear obstacles such as boulders. The supplementary exploration is expected to be completed this weekend. This exploration adopted the microtremor detection method. Compared with traditional geophysical methods, it is a green, environmentally friendly, energy-saving detection method with stronger anti-interference capability and higher detection accuracy.

　　“Pulse diagnosis and treatment” for geologically complex bid sections

　　According to reports, the Shuping section (Shudou Station to Pingshan Station section) and the Pingdong section (Pingshan Station to Dongjiekou Station section) belong to Civil Engineering Bid Section 04 of Metro Line 1. Due to factors such as archaeological excavation at Pingshan Station, the relocation and modification of multiple “110 kV” power lines at Shudou Station, and the underpass beneath the dormitory and office buildings of the Provincial Department of Agriculture, Bid Section 04 has become a controlling node project of Metro Line 1. The construction period has been delayed by a full year, making it one of the most difficult bid sections to construct along the entire line.

　　According to Cheng Ting, head of the supplementary survey project, in order to ensure normal operation of the shield machine, detailed exploration of the geological conditions in the section is required before shield tunneling construction. “In 2010, we arranged a large number of boreholes on both sides of Line 1 and successively carried out preliminary survey work and detailed survey work.”

　　Preliminary and detailed surveys found that the Shudou Station—Pingshan Station—Dongjiekou Station section is located beneath Hualin Road and Guping Road, roughly bounded by the Shudou River. The metro shield tunnel on the east side mainly passes through soft soil strata, while the tunnel on the west side mainly passes through slope residual soil, completely and strongly weathered soil, and protruding hard rock. For shield construction, boulders and strata with uneven hardness and softness are all “cancers” affecting shield tunneling.

　　Wang Lianjiang, deputy manager of the project department for Bid Section 04 of Metro Line 1, told reporters that Fuzhou’s geological conditions are inherently complex, and the Shuping and Pingdong sections can be said to have the most complex geological conditions along the entire Metro Line 1. Flowing-state silt plus hard rock further increases construction difficulty. “What is being carried out within the enclosure this time is special supplementary exploration for boulders. ‘Pre-detection + micro-blasting’ is also a common treatment method in the world at present.”

　　Microtremor detection takes the lead in “scanning”

　　Cheng Ting introduced that this supplementary exploration adopted the latest microtremor detection method. Compared with traditional geophysical methods, microtremor detection is a green, environmentally friendly, energy-saving detection method with stronger anti-interference capability and higher detection accuracy. This exploration work is mainly divided into two steps: first, a set of sensors is installed on the ground directly above the shield tunnel to receive natural vibration data of underground rock and soil masses within a certain range, and the collected data are analyzed point by point indoors to delineate anomalous areas; second, further drilling work is carried out for the anomalous areas, and rock and soil cores within the tunnel body range are extracted to determine whether boulders exist.

　　According to detection results, there are currently 12 suspicious points where boulders may exist in the Pingdong section, and 1 confirmed boulder location in the Shuping section. Microtremor detection is still continuing. After the location and size of the boulders are determined, micro-blasting will be used for treatment. “Microtremor blasting does not affect the ground and can also reduce the risks of shield construction,” Cheng Ting said. Boulders are like stones in the human body; “after scanning, ‘stone removal’ is carried out inside the body.”

　　Supplementary exploration work will end this weekend

　　It is understood that this supplementary exploration has set up a total of 32 supplementary survey boreholes along the Hualin Road and Guping Road sections. Each borehole has a diameter of 110 millimeters and a depth of about 30 to 40 meters. The required time is 2 to 3 days, and this work can be completed this weekend. “Although the exploration holes are small, in order to prevent pedestrians and motor vehicles from passing between the enclosures and causing traffic hazards, the method generally adopted is to connect adjacent survey points with enclosures,” Cheng Ting said.

　　To reduce the impact on citizens’ travel, the supplementary exploration work is scheduled to carry out drilling point construction on non-motorized vehicle lanes from 10 p.m. Monday to Friday, and concentrated drilling point construction on motorized vehicle lanes from 10 p.m. Friday to 6 a.m. Monday.

　　Shield machine from Pingshan to Dongjiekou Station to launch next month

　　Pingshan Station of the metro has a total length of 173 meters and a width of 22 meters. The archaeological work at Pingshan Station was fully completed on January 25 this year and has been handed over to the project department for continued construction. At present, all work is progressing steadily. “About 130 meters in length has been excavated so far, and the width and depth have been fully excavated. Earthwork progress is about 75% complete. After the length is excavated, the concrete pouring stage can begin,” Wang Lianjiang introduced. At present, the main structure construction of the entire station has been completed by 40%. The first shield machine from Pingshan Station to Dongjiekou Station is expected to launch in mid-May, and the main structure will be completed in August this year.

　　Construction progress at Shudou Station is also proceeding as planned. The distance from Shudou Station to Pingshan Station is 1 kilometer. At the end of June, the shield machine from Shudou Station to Pingshan Station will be able to launch. It is understood that the construction section of Shudou Station is divided into 3 sections. The 80-meter section east of Wusi Road has been fully completed. The section currently under construction is the 130-meter section west of Wusi Road. The section between Hualin Road and Wusi Road is planned to start construction around October this year. “The main structure of the entire Shudou Station can be completed by June or July next year, and the section tunnel construction will be carried out in coordination,” Wang Lianjiang said.