为克服管幕法钢管节之间无法协同工作、支护效率差等缺点，进一步拓展管幕在浅埋大跨地下结构中的优势，提出一种依托横向预应力的新型地下结构形式——U-BIT束合管幕结构。该工法采用矩形管幕作为支护结构，管幕通过锁扣以及填充混凝土进行连接，并通过张拉横向预应力，使各个钢管之间协同受力，形成受力整体。为进一步研究预应力筋布置线型对束合管幕结构力学机制的影响，结合压弯试验及剪切试验，针对预应力筋二次型及双直线型布置形式进行对比分析。结果表明： 1）预应力筋线型布置不影响结合缝黏结界面的开裂荷载及结构破坏机制； 2）压弯试验中结合缝张开后，张拉相同预应力时，二次型布置下的结合缝极限弯矩承载力是双直线型的1.4~1.6倍； 3）剪切试验中，结合缝未出现张开及错动时，施加预应力可等视为外部施加水平力，而结合缝抗剪刚度基本随水平力线型增长，二次型布置会比相同水平力作用下双直线型结构中结合缝抗剪刚度大7%~9%； 4）结构实际受力是处于压弯剪的复合受力状态，结合缝脱开会导致结构抗剪承载力大幅下降。
The pipe curtain method applied in shallowburied
underground structures has many disadvantages, such as failure coordination of
pipe curtain segments and lowsupport efficiency.
Therefore, a novel structure called the underground bundled integrated tunnel
(UBIT) 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 UBIT, 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.
