With the country proposing the strategy of developing the western region, Urumqi's economy has continued to develop rapidly in recent years, and transportation supply has seriously lagged behind transportation demand. The traffic volume borne by the outer ring line has far exceeded the original design forecast traffic volume and actual bearing capacity, resulting in multiple road sections, overpass nodes, and ramp entrances and exits have become frequent congested sections and nodes. In order to alleviate the current traffic congestion in Urumqi and meet the functional requirements of the outer ring expressway network, it is necessary to renovate and expand the existing outer ring road. The Yashan Tunnel was set up in the original outer ring line crossing the Yamarik Mountain. The current Yashan Tunnel is a separated two-way four-lane tunnel. The Yashan Tunnel is 445 meters long and the clear tunnel distance is about 28 meters. The outer ring expansion line needs to cross the Yamarik Mountains near the existing Yashan Tunnel. It has a two-way four-lane scale and a speed of 80km/h. The concealed excavation section of the proposed Yashan Tunnel adopts the form of a double-arch tunnel, and the open-excavation section adopts the form of a box structure. The proposed tunnel is located above the existing tunnel, with a minimum horizontal clear distance of about 1m and a minimum vertical clear distance of about 9.6m from the existing tunnel. It belongs to a parallel small clear distance double-arch tunnel. The proposed Yashan Tunnel has a total length of 345 meters, including a double-arched mountain tunnel of 155 meters and an open-cut tunnel of 190 meters. The existing Yashan Tunnel within the scope of project impact is a plain concrete structure.
Based on the research background of the newly built Yamalik Mountain Double Arch Tunnel on the "Tian-shaped" Expressway Network in Urumqi City, this project conducts systematic research on the design and construction methods of the Yashan Double Arch Tunnel in the newly built shallowly buried weak and fractured surrounding rock with existing tunnels parallel to small clear distances, the impact of large-area unloading of the open-cut tunnel, and the control technology of micro-vibration and weak blasting, and has achieved the following innovative results:

1. Through the comparison and selection of multiple schemes, the tunnel direction was optimized, a shallow-buried multi-arch tunnel scheme that penetrated the existing tunnel was proposed, the structural type and structural design were optimized, and the construction control standards were clarified.
2. The three-pilot tunnel method and the middle pilot tunnel step method are systematically compared and analyzed, and the middle pilot tunnel step method for multi-arch tunnels in shallowly buried weak and fractured surrounding rock is recommended, and the construction process and process parameters are optimized.
3. An optimal control method to control bottom bulge and deformation of existing tunnels during large-area unloading construction in open-cut sections is proposed.
4. The optimized blasting method and construction process parameters for tunnel construction are proposed, which control the vibration impact on the existing tunnel, ensure project safety, and improve construction efficiency.
   This project has completed the general report of "Research and Application on Key Technologies for the Design and Construction of the New Yamarik Mountain Double-Arch Tunnel and the Existing Tunnel Parallel to Small Clear Space on the" Tianzi "Expressway Network in Urumqi City", obtained the unloading construction control technology at the top of mountain tunnels, completed the design and construction guidelines for small clear distance, microearthquakes and weak explosion of existing tunnels used to guide this construction, and obtained reasonable construction methods for new multi-arch tunnels parallel to the existing tunnels. Accepting one invention patent and one utility model patent, and publishing 5 domestic core journal papers. The research results are innovative, advanced and practical.
   The research results of this project will first be directly applied to the design and construction of the new Yashan Tunnel in the expansion and reconstruction project of the "Tian-shaped" expressway road in Urumqi City (Phase II) to ensure the smooth and safe construction of the tunnel, ensure the normal use of existing tunnels, and provide technical support and experience accumulation for the design and construction of similar close-distance tunnel reconstruction and expansion projects in the future. The relevant research results obtained and engineering measures taken can be promoted and applied in similar engineering practices in the future.