Excavation of the foundation pit of the main envelope structure of Dongsha Station on Guangzhou Line 10

Spring breeze brings warmth to the Pearl River. In only 20 days after the resumption of work, the 127th diaphragm wall was successfully completed for the Dongsha Station of Line 10 in Guangzhou by wiping off the adverse effects from Coronavirus epidemic and conducting scientific planning and meticulous organization. The Dongsha Station has thus become the first station with its main envelope structure completed on the whole of Line 10 of Guangzhou, marking the entry into the stage of the foundation pit excavation being started.

Dongsha Station is the 17th station of Guangzhou Line 10 (non-interchange station). It is located on the south side of Cuiyuan Road in Liwan District, Guangzhou City. It runs east-west along Cuiyuan Road, with the entrance and exit of Dongxin Expressway on the west and Guangzhou Ring Road on the south. The city expressway connects Daganwei Station in the east and Guanggang Xincheng Station in the west. The station is an underground two-story island platform with shield wells at both ends. It is 326 meters long, the standard section is about 20 meters wide, and the excavation depth is about 20 meters. 

Well-organized management and strict process control to ensure safety in construction

According to reports, the north side of Dongsha Station is close to the 220kv high-voltage line, which is parallel to the foundation pit in an east-west direction. The horizontal projection line is 0.05 to 3.95 meters away from the side of the envelope and the vertical direction is 16 to 21 meters away from the ground, posing great challenges to the on-the-spot reinforcement cage hoisting. According to the JGJ46-2005 “Technical Specifications for Safety of Temporary Electricity on Construction Sites”, the horizontal and vertical distance of 220kv high-voltage line is 6m as the safety distance. The length of the reinforcement cage of the diaphragm wall of building envelope on the north side ranges between 20.435 meters ~ 22.905 meters. In order to meet the safe construction distance under the high-voltage line, the constructor installed height-limiting facilities under the high-voltage line along the east-west direction of the station to ensure that the equipment is operated outside the safe distance of 6 meters on the high-voltage line. With the height limitation taken into consideration, the management team of the second work area of Guangzhou Line 10 decided to use the reinforcement cage of the continuous wall in the form of section hoisting for construction. In order to ensure that no errors would occur when the reinforcement cage was hoisted in sections, the technical department formulated a rigorous and thorough construction plan. During the manufacturing process, the construction quality of the reinforced joints was being brought under strict control. The hoisting process ensured the precise positioning of the steel cage, and the joint work was being well done to ensure the joint pass rate to reach 100%. 

According to information, the development of soft soil (sludge) in the construction area of the station, the formation of the continuous wall groove protection wall was prone to collapse, shrinkage and other risks, the construction of the diaphragm wall and the foundation pit support were much more difficult. In order to ensure the safety of foundation pit construction, the management team of the second working area reasonably planned and formulated a targeted plan, started technical exchanges with the slot machine manufacturers in advance, and customized the low-headroom slot machine grab, and the diaphragm walls were reinforced with agitating piles to prevent collapse of the ground and the collapse of the ground during the process of groove formation. The foundation pit adopted an 800cm thick underground continuous wall as an enclosing structure and a water-stop curtain, with three supports inside. The groove forming machine and the pile driving machine were adopted for the continuous wall to form the groove, thus greatly improving the groove forming efficiency. At the same time, through the reasonable site layout, the steel cage processing shed was as close as possible to the diaphragm wall. The jib crane was quickly hoisted into sections and concrete was poured to ensure the construction quality of the continuous wall and to improve the construction efficiency. 

Consolidating the safety protection to push ahead the next-step project construction in an orderly way

After the outbreak of the Coronavirus epidemic, the second construction area of the Guangzhou Metro Line 10 has kept a firm grip on epidemic prevention and control as well as on resumption of work. They actively responded to the call for “work resumption and complement”, scientifically and meticulously studied the resumption plan, contacted the construction team, machinery, and materials in advance, meticulously organized daily construction and production, and took 14-day quarantine and blood antibody testing among all returning workers. They also strengthened the daily management and control of the workers to ensure safety and smooth work resumption.

In order to ensure the safety in construction during the possible rainy and typhoon-inflicted days when excavatig the foundation pit, the second construction area of Guangzhou Line 10 compiled the "Construction Plan for the Rainy Season", "Emergency Plan for Typhoon Prevention", and " Emergency Plan for Excavation of the Foundation Pit" in line with the characteristics of the Dongsha Station. Temporary typhoon prevention measures were mapped out for the construction site, and 2 drainage ditches were set within the site to ensure smooth drainage during the rainy season. Sufficient and reliable emergency materials were furnished for the construction site.