Abstract: The pipe curtain method applied in shallowburied underground structures has many disadvantages, such as failure coordination of pipe curtain segments and lowsupport efficiency. Therefore, a novel structure called the underground bundled integrated tunnel (UBIT) based on transverse prestress is proposed. This structure uses rectangular pipes as the supporting structures; the pipes are connected using a lock catch and concrete by applying tensioning transverse prestress, thus forming an integrated stress body. To further investigate the influence of the arrangement of unbonded tendons on the mechanical properties of the UBIT, bending and shear tests were conducted, and the quadratic and doublelinear arrangements of the unbonded tendons are comparatively analyzed. The following results were obtained. (1) The crack load and failure mechanism of the bond interface are not affected by the linear arrangement of the unbonded tendons. (2) The ultimate bending moment bearing capacity of the joints under the quadratic arrangement is 1.4~1.6 times that of the double linear arrangement when the joints are opened and under the same prestress. (3) In the shear test, when there is no opening or dislocation of the joint, the application of prestress can be regarded as an external horizontal force. The shear stiffness of the joint increases with the horizontal force, and the quadratic arrangement is 7%~9% more in shear stiffness than that of the joint in the doublelinear arrangement under the same horizontal force. (4) The actual stress of the structure possesses a composite state of bending and shearing, and joint cracking causes a significant decline in the shear capacity of the structure.

Key words: bundled integrate structure, prestress tendons; bending test, shear test, mechanical property