Experimental Study on the Mechanical Properties of Steel Wedge Active Node in Braced Excavation Engineering

To study the mechanical characteristics of active nodes in excavation engineering, single axial compression tests on the nodes that were taken as specimens at the Beijing subway construction site were conducted in laboratory.The bearing capacity, stress distribution and failure mode of the specimens were obtained from the tests. Based on the experimental results, the stiffness, bearing capability and deformation capability in the key positions of the four specimens were analyzed. Results indicate that:1) For the specimens in the same group, both the yield load and the stiffness of the specimen with the unidirectional wedge are smaller than that of the specimen with the bidirectional wedge and for the specimens in different groups, and both the yield load and the stiffness of the specimens in 3 groups are quite different. 2) The maximum micro strain of the single-box active node occurs at the contact position between the movable end and the steel wedge, the micro strain of fixed end is very small. The maximum micro strain at the fixed end is about 1/50 of the active end, which is about 1/40 of the steel wedge, but the maximum micro strain of the double-box active node occurs at the side wall of the movable end box. 3) The failure mechanisms of single-boxactive node show that the rib in the middle position is pressed to yield and the welding seam between the rib in the middle position and the channel is cracked due to shear force action and those of double-box active node show that the rectangular-ambulatory-plane section of the movable end is yielded and the lateral walls of the movable end are in buckling damage.