关键词: 非对称基坑, 双环梁支撑, 数值模拟, 冗余度

Abstract: A case study is conducted on a foundation pit project in Beijing, China, to address the continuous failure caused by partial failure of ring beam support system in asymmetric foundation pit. Further, the evolution law of surface settlement, horizontal displacement of diaphragm wall and internal forces (bending moment and axial force) of supporting structure is investigated using threedimensional finite element simulation and field monitoring methods. The numerical simulation results are in good agreement with the field monitoring results. The collapse resistance of asymmetric doublering beam supported structure is analyzed using the method of "removing the rod" for different Angle bracing schemes. Finally, the strength redundancy and stiffness redundancy of each support are calculated using redundancy theory. The results show the following: (1) The surface settlement at the middle height is affected by both soil height and boundary distance, and the closer the distance, the greater is the influence. (2) With the excavation depth of foundation pit, the horizontal displacement of diaphragm wall presents a bow shape distribution, and suddenly changes at the supporting position. The displacement change speed is affected by the depth of foundation pit on both sides and the supporting system. (3) The axial force and bending moment of each part of the large ring beam in asymmetric foundation pit gradually increase with the dispersion degree of the excavation sequence, and the dispersion degree of the member redundancy of each part of the ring beam also increases. (4) The dispersion degree of bracing internal forces positively correlates with the span and excavation depth of the foundation pit. Increasing the transmission path can effectively alleviate the dispersion of internal forces. However, when the transmission path increases to a certain extent, the relief effect weakens. (5) The position of the Angle braces has a great influence on the internal force distribution of the entire support system, and the absolute value of the strength redundancy tends to 1 when the middle Angle braces fail. (6) The middle Angle brace has the greatest effect on the collapse resistance, while the shortest Angle brace has the least effect on the stiffness.

Key words: asymmetric foundation pit, doublering beam support, numerical simulation, redundancy degree