The research results of this project belong to the field of civil construction.
With the rapid development of underground space development and utilization in soft soil areas such as Shanghai, during the construction of underground projects, engineering precipitation inside the foundation pit will inevitably induce surface deformation in local areas around the pit. While the latter threatens the safety of buildings (structures) around the pit, it will also aggravate the existing regional land subsidence in soft soil areas, seriously affecting the building environment and the safe operation of the entire city. This project adopts the method of recharge of surface water outside the foundation pit to control the change of groundwater level around the pit to achieve control of land settlement induced by project precipitation. After years of joint research by industry, academia and research, the following innovative results have been achieved:
1. Calculation theory of land settlement induced by engineering construction based on the integration of pumping and irrigation. Classical elastic-plastic theories of soil mechanics (including the Cambridge Model) assume elasticity as the stress-strain relationship of soil during unloading and reloading. However, in fact, plastic strain will also occur during this process; and once normally consolidated clay enters the unloading and reloading process, it will be in an overconsolidated state, that is, plastic strain will also occur in the overconsolidated state. During foundation pit construction, the formation deformation caused by the fluctuation of shallow groundwater level (dry-wet (suction) cycle) caused by pumping-(recharge) is essentially a unloading and loading process. In response to this problem, the Cambridge model of the lower load surface was introduced for the first time, combined with the soil-water characteristic curve and the water-soil coupling theory, and focused on analyzing and simulating the change laws of the seepage field and stress field of the foundation pit, forming an engineering construction based on the integration of pumping and irrigation. Calculation theory of induced ground settlement.
2. Recharge and formation deformation monitoring technology. In view of the difficulty in implementing recharge in soft soil formations, patented technologies such as "a sealing device for relief wells with micro-confined water in foundation pits","decompression and dewatering in interfering formations in foundation pits" and "foundation pit dewatering automatic control system" have been developed to improve recharge efficiency, achieve timeliness and effectiveness of recharge, and accurate on-site control of the precipitation process; On-site monitoring technology for ground settlement induced by underground engineering construction based on integrated control of pumping and irrigation has been formed.
3. Integration and demonstration of technology for preventing and controlling land subsidence induced by engineering construction based on the integration of pumping and irrigation. For the first time, it integrated engineering dewatering within foundation pits and ground settlement prevention and control technologies based on the integrated concept of pumping and irrigation, compiled enterprise specifications, and successfully applied them to Shanghai Shengda foundation pit dewatering and No. 3 Huaihai Middle Road foundation pit dewatering demonstration project, University of Macau Hengqin Island Cross-Harbour Tunnel and other major engineering practices, revealing the quantitative relationship and linkage laws between groundwater level changes and ground settlement during the recharge process. It solves the problems of controlling precipitation and ground deformation in case projects, and provides a demonstration for controlling land settlement induced by underground engineering construction in soft soil areas.
This project has obtained a total of 7 authorized national patents; 17 publicly published papers, including 2 papers included in SCI and 7 papers included in EI; and 1 standard/guide was compiled. The project results have been successfully applied in Shanghai, Macau and other places, achieving direct economic benefits of approximately RMB 230 million. With the promotion of this complete set of technology on a larger scale, it will surely produce greater economic and social benefits.
The results have been accepted and evaluated by famous experts: they are generally at the international advanced level, and some key original technologies are at the international leading level. The "Science and Technology Project Consultation Report"(No. 20141349) issued by the Shanghai Science and Technology Novelty Search Consulting Center of China Academy of Sciences, a national-level science and technology novelty search unit, concludes: "Many core technologies of this topic have been patented, and the overall technology has reached the international advanced level." The results have also greatly promoted the development of disciplines and technological progress in the industry, and comprehensively improved the company's independent innovation capabilities, the level of technical equipment integration, and the core competitiveness at home and abroad.