Treatment and Effect of Loess Metro Tunnel under Surrounding Pressure and Water Immersion Environment

Abstract

It is possible to pass through a collapsible loess stratum during metro tunneling. When the surrounding potential water sources with pressure are induced by external influences, the tunnel structure will be influenced in the affected area of loess collapsibility. To deal with the water inrush disaster of the tunnel in a collapsible loess stratum, the mechanism of grouting diffusion in the loess stratum is analyzed. It is found that the main influencing factors of the grouting effect are the radius of the grouting ring and the permeability coefficient of the grouting ring. Then, based on the water inrush section of a metro tunnel in Xi’an city, China, the treatment effect of the project is compared and analyzed through field tests, field monitoring, and finite element simulation. The results show that the water pressure at the measuring point of the tunnel vault is reduced by 4 MPa; the maximum and the minimum principal stresses at the top of the segment lining increased by 34.9 kPa and 8.8 kPa, respectively, which is less than the increase without grouting; and the maximum displacement of the surrounding rock is reduced by 19 mm. The plastic area produced by local water source infiltration is about 62% of that before grouting. The treatment measures of grouting in the tunnel are safe and effective. This study is of valuable meaning for the treatment of water inrush disaster of a loess tunnel under the water environment.

Review of Application and Innovation of Geotextiles in Geotechnical Engineering

“…In addition to the above several fiber materials, there are an army of fiber materials, which have the possibility of being used as high-performance geotextile raw materials, among which the most desirable one is nanofiber. Nanofibers are one of the most advanced materials, which can be easily designed into high-performance materials with unique performance, and can greatly enhance the performance of existing geotextiles [128][129][130][131].…”

New Construction Technology of a Shallow Tunnel in Boulder‐Cobble Mixed Grounds

“…Compared with the CD method, the Support system e original design adopted Φ4.2 m long 42 small conduit, system bolt was 3.5 m long D25 grouting bolt, I20a steel spacing was 0.75 m, reserved deformation was 12 cm, and C25 reinforced concrete was used as secondary lining. (2) Later stage support was strengthened, leading small conduit was changed to double layer, length was adjusted to 1.2 m and 2 m, steel frame spacing was 0.5 m, and feet reinforcement bolt group was changed to double group.…”

“…e grounds consisting mainly of boulders soil and cobble soil are called BCM grounds. At present, most of the pervasive BCM grounds are formed in the Quaternary [1][2][3][4][5][6] and are widely distributed in some valleys of Beijing, Changsha, Chengdu, Lanzhou, and Tibet ( Figure 1). BCM grounds are composed of granules consisting of boulders and cobble, coarse sand, and some clay.…”

Thermal Conductivity Characteristics of Thermal Insulation Materials Immersed in Water for Cold‐Region Tunnels

“…erefore, the thermal conductivity of ice-containing thermal insulation Note: RSD is the relative standard deviation, which can be used to analyze the accuracy of the results. materials is greater, worsening the effect of thermal insulation materials [46][47][48][49][50][51][52][53].…”