Analysis of Construction Monitoring and Control of Tunnels Crossing Broken Faults and Water-rich Geology

In view of the poor geology such as tunnel engineering crossing faults or passing faults, the construction of surrounding rock and support is complicated. During construction, it is necessary to ensure the stability of the surrounding rock and supporting system, and ensure the timing of the secondary lining construction. For this reason, through the analysis and processing of monitoring data, the law of stratum change is mastered, and the supporting parameters and construction methods are adjusted and revised at the same time, so as to provide the best information for the tunnel surrounding rock and supporting lining construction.

Deformation Characteristics of the Surrounding Rock of a Six-Lane Multiarch Tunnel under Different Excavation Conditions

Highway tunnel plays an increasingly prominent role in the development of high-grade highway traffic in mountainous countries or regions. Therefore, it is necessary to explore the deformation characteristics of the surrounding rock of a six-lane multiarch tunnel under different excavation conditions. Using the three-dimensional indoor model test and finite element analysis, this paper studies the dynamic mechanical behavior of a six-lane construction, reveals the whole process of the surrounding rock deformation process of class II surrounding rock under different excavation conditions, and puts forward the best construction and excavation method. The results show that the maximum displacement rate of excavation scheme III is the largest, and the maximum displacement rate of excavation scheme I is basically the same as that of excavation scheme II. Therefore, in terms of controlling the displacement rate of the surrounding rock, the effect of excavation scheme I is basically the same as that of excavation scheme II, while that of excavation scheme III is poor. In terms of construction technology, scheme II is simpler than scheme I and can ensure the integrity of the secondary lining. Therefore, in class II surrounding rock of the supporting project, it is recommended to adopt scheme II for construction.

Mutual influence of long-span urban highway tunnel and rail transit construction

In order to analyze the mutual influence between the long-span highway tunnel and urban rail transit tunnel that is constructed at proximity, this paper established 3D finite element models based on Chongqing Zengjiayan Tunnel and the Metro Railway Line 9 and Line 10 projects to calculate and analyze the secondary lining stress, distribution and change law of deformation of Zengjiayan Tunnel and the Metro Railway Line Tunnel. The results show that: (1) The main risk of the Zengjiayan Tunnel is that the tunnel body might displace in the excavation and the surrounding rock stress could possibly change. The forces undertaken by the main structure of the cross-section are calculated and analyzed based on the shallow buried tunnel. Accordingly, the horizontal and vertical displacement limit and relative displacement meet the relevant specification; (2) Zengjiayan Tunnel over the lobby of Liyuchi Station, a transitional station of Line 9 and Line 10. The main risk is the displacement of the transitional channel in the excavation and changes in the stress on surrounding rocks, but the risk of self-structure excavation and support is under control.

Stress-Strain Calculation Method of Composite Lining considering the Creep Characteristics of Tunnel Surrounding Rock

Tunnels are generally designed for a sustained usage of 80 to 100 years, during which the safety of tunnel structures must be guaranteed. A common supporting form utilized in contemporary tunnel engineering is composite lining. To derive applicable parameters of the supporting form and therefore ensure the long-term safety of the tunnel structure, it is imperative to determine the extra acting force exerted onto the composite lining by the creep of the rock surrounding the tunnel and to calculate the stress-strain characteristics of composite lining. In the current study, this paper proposes an approach termed surrounding reinforcement, which is based on the homogenization method. Specifically, this paper defined the bolt force as the internal force of the surrounding rock, analyzed their viscoelastic-plastic properties using the unified strength theory, and derived an equation for calculating the stress-strain relationship of the composite lining. To further validate the method in tunnel structures, this paper applied the derived equation to a representative instance. The results of this paper show that the initial support force has also increased during the creep process of the surrounding rock, indicating that engineers should pay close attention to the coordination between the strength of initial support and the secondary lining and thus ensure an optimal distribution of the pressure from the surrounding rock when designing composite lining tunnel within weak strata. This paper proposes that the initial support not only would guarantee the tunnel safety during the construction stage but also could cooperate with the secondary lining to brace the stress caused by the creep, ensuring that the supporting structure stays stable across the whole period of tunnel operation. This paper provides an alternative to previous methods that is more comprehensive, with simpler calculations, and more applicable to the composite lining supporting design within weak strata.

Study of Temperature Field Distribution in Topographic Bias Tunnel Based on Monitoring Data

In recent decades, numerous tunnels have been built in the cold region of China. However, the temperature field of topographically biased tunnels in the monsoon freeze zone has not been sufficiently studied. In this study, we monitored the temperature of the surrounding rock in two topographic bias sections of the Huitougou Tunnel and analyzed the results by fitting them to the monitoring results. The results showed that the temperature of the surrounding rock on both sides after tunnel excavation varied periodically in an approximate triangular function. As the distance from the cave wall increased, the annual average temperature of the surrounding rock did not change significantly, the amplitude decreased, and the delay time increased, while the annual maximum temperature decreased, and the annual minimum temperature increased. The heat generated by blasting, the heat of hydration of the primary and secondary lining, and the decorated concrete all caused a significant increase in the temperature of the surrounding rock within 4 m for a short period of time. Both construction and topographic factors led to asymmetry in the distribution of the surrounding rock temperature in different ways. The results of this paper are intended as a reference for other studies on temperature in deviated tunnels.

Mechanical Responses to Different Excavation Methods of Qichongcun Tunnel in Guiyang City, China

The construction method of tunnel has a critical impact on the stress and strain field during excavation. This study simulated the construction of Qichongcun tunnel by applying a different excavation method, including double-sided method, single-sided method, and three-step dynamic balance excavation method. The distribution and variation of the stress, vertical displacement, horizontal displacement of surrounding rocks, and stress of initial and secondary lining were studied. The results showed that large displacement of surrounding rocks would be induced during the construction in three-step method, but the stress of the second lining was small after completion of the construction. The displacement and stress of the three-step dynamic balance excavation method were larger than those of the other two methods, but it still met the requirements of safety.

Analysis of Surrounding Rock Creep Effect on the Long-Term Stability of Tunnel Secondary Lining

The secondary lining failure of deep buried soft rock tunnel often occurs, which is obviously related to the time factor. The formation mechanism of this phenomenon is studied in this paper. Therefore, the combination of in situ stress measurement and neural network inversion is used to analyze the distribution characteristics of in situ stress. At the same time, the creep characteristics of surrounding rock are tested in laboratory, and the key parameters are obtained. Combined with the characteristics of surrounding rock, the calculation model is established by using discrete element simulation technology and considering the joints of surrounding rock. According to the above multiple information, the stress characteristics of the secondary lining in different time periods are analyzed creatively. Finally, the method of setting arch and adding anchor bolt in key parts is proposed, and significant effect results are obtained.

Construction, Monitoring, and Analysis: Guiyang Metro Line 1, China

The Huo-Sha Tunnel of Guiyang Metro Line 1 in China, which runs from the Guiyang Railway Station to the Shachong Road Station, passes through the railway station platform closely. The minimum distance between the vault and the pile foundation is only 2.19 m. The geology is complex, and the settlement control requirements for the oblique sections, platforms, station buildings, pile foundations, and existing buildings are remarkably strict. Comprehensive measures of “super pipe shed support, surrounding rock reinforcement, inverted arch grouting, and lining strengthening are strictly adopted” to prevent the influence of construction on the operation of station buildings and in-service railways, high-speed railways, and other buildings. It also analyzes the changing laws of the existing building subsidence, subgrade settlement, station longitudinal displacement variation, and the development trends of lining safety, stability, eccentricity, compression types, and internal force of the lining. The following results are presented. The Huo-Sha Tunnel is gradually excavated. The roadbed settlement of the Guiyang Railway Station platform gradually increases but does not exceed the existing railway deformation control standards for the subsurface excavation section. The longitudinal distribution of the existing railway settlement is approximately a normal curve after the construction of the secondary lining. This result is consistent with the law of the surface settlement trough proposed by Peck, and the range is between −50 m and 50 m. The stress of the lining is mainly concentrated at the arch waist and the vault, the compression types include large and small eccentric, the axial force value gradually increases symmetrically from the vault to the arch footing, the maximum axial force appears at the arch footing, and all control indicators meet the corresponding control standards. The subgrade settlement of the skew section meets the deformation control standards of the existing railway of the subsurface excavation sections after the stabilization of the secondary lining deformation.