Study on mechanical features of pit support system with bi-directional adjustable internal support

In order to overcome the shortcoming that foundation pit support system can only passively bear earth pressure and cannot realize active adjustment, this paper proposed a novel internal support axial force servo system, and conducted a scaled model test with a geometric scaling ratio of 1:25 to investigate the influences of surface surcharge, active adjustments of internal strut position and length on mechanical features of the diaphragm wall support system with a dimension difference between long and short sides. The experimental results show that the mechanical features of long and short sides of the diaphragm wall are different under various surface surcharge conditions, the maximum change in horizontal displacement and support force on long side of the diaphragm wall is 2.79 times and 1.84 times of that on short side, there is an obvious size effect. Moreover, the active adjustment of height and length of internal strut can affect the mechanical behavior of the support system, the elongation of inner struts by -1 mm ∼ 3 mm can change the earth pressure behind the diaphragm wall by -77.37 % ∼ 1046.73 %, and influence the axial force of internal support by -32.09 % ∼ 308.54 %. The finite element analyses indicated that the regularity results of the experiments are applicable to different structural stiffness, soil distribution and pit dimension conditions of the support system.