Research On Engineering Applications Of Self-drilling Little Pipe-shed For Deeply-buried Large Cross-section Tunnel With Soft Rock

It has always been a difficult problem in the engineering field to constructing a tunnel in soft rock. With the recently large scale construction of high-speed railway in western region, it appeared an increasing number of cross-section tunnel in soft rock featured with extremely complicated geographical conditions, which makes the ongoing innovation of construction techniques of soft rock tunnels an urging need. Based on the Dadushan tunnel of Hu-Kun passenger dedicated line, which is still under construction, this paper did a research on the engineering applications of self-drilling little pipe-shed (type of T76S) for deeply-buried large cross-section tunnel with soft rock ground. The main work and results are listed as follows:(1) Made a study on the construction techniques and efficiency and supporting features by site investigation and subsequent summarizing. It shows that self-drilling little pipe-shed is a new kind of pipe-shed technique that incorporating drilling, grouting and supporting. It effectively overcomes the many negative problems of the traditional pipe-shed like hole-collapsing and hole-blocking and the existing of vulnerable link. Moreover, it has the advantage of simple and reliable techniques, high efficiency and good supporting effect.(2) Calculated the force load of self-drilling little pipe-shed in deeply-buried soft rock ground by theoretical analysis method and studied on appropriate design schemes of self-drilling little pipe-shed for Dadushan tunnel. Carried out site monitoring of structural steel arch stress and early supporting-surrounding rock contact pressure of typical cross-section of pre-supporting length with self-drilling long pipe-shed to test and verify if the scheme can meet the structural demand.(3) By comparing the site monitoring deformation of similar layers of surrounding rock of different pre-supporting length, comprehensively analyzed the deformation control effect of self-drilling little pipe-shed on surrounding rock of deeply-buried large cross-section tunnel with soft rock. The results show that the tunnel excavated with two-step and core-soil-preserved method has deformation mainly caused by the rheological deformation of the surrounding rock after the excavation of upper step while the special effect contributes little to it. Self-drilling little pipe-shed has an obvious effect on the deformation of the surrounding rock and its largest role played in the deformation control is the improvement of the properties of the surrounding rock ahead of the vault and tunnel face as well as the controlling of the rheological deformation of the surrounding rock.(4) By summarizing civil projects with application of pre-supporting pipe-shed on tunnel collapse treatment, analyzed the functional regime of pre-supporting pipe-shed in collapse treatment for deeply-buried tunnel. Aimed at the collapsing condition of deeply-buried length with soft rock of Dadushan tunnel, analyzed the collapse reason and made a comparison of pre-supporting schemes and excavating methods. The given solution achieved impressive effect on collapse treatment by using self-drilling little pipe-shed and small grouting pipe-shed on pre-supporting and applying the3-step-7-procedure method and mechanical-manual-excavating method.