In order to fully study the research progress of the delimitation of deep and shallow loess tunnels, the research status of the delimitation of deep and shallow loess tunnels was described from four aspects: theoretical research, numerical simulation, model test and actual measurement analysis. The results showed that: the theoretical research was mostly based on the study and analysis of the changes in surrounding rock pressure and deformation pressure with the buried depth of the tunnel, and the best limit value was found in the changing rules; the numerical simulation was mostly to study the deformation and settlement laws of tunnels with different buried depths, the results were relatively intuitive, and the tunnel force and deformation could be analyzed intuitively; the model test was mainly to carry out the gravity similar simulation test on different buried depth tunnels, which could analyze the force status of the actual project; the actual measurement analysis was based on the on-site statistical results for analysis, according to experience, the boundary value of the depth of the tunnel was delineated. Based on the analysis of the four methods of dividing the depth of the loess tunnel, the factors considered when dividing the boundary between deep and shallow burial was summarized, and the problems in the existing research such as the inaccurate division of the buried depth of the tunnel and the large range of the obtained buried depth were pointed out. In combination with the engineering characteristics of the loess tunnel, it was suggested to use the improved XIE Jiaxiao Maximum Method to calculate the depth and shallow burial limit of the loess tunnel.

Based on statistical analysis of mechanical characteristics of secondary lining for 28 monitoring cross-sections of 13 loess tunnels in the literatures, the population distribution characteristics of the contact pressure between primary support and secondary lining, and their relationship with their classification grade, buried depth and excavation span of tunnels were studied. Through the statistical analysis of in-situ monitoring data of the contact pressure, the variation law with time-change and the spatial distribution law were studied. The research results showed that the contact pressure of the tunnel increased with the increase of the buried depth and the excavation span, and its time history experienced a process of first increasing to the peak value and then decreasing for a period of time, and then continuously increasing and tending to be stable. The contact pressures around the tunnel circumference gradually increased from the crown→the arch shoulder→the arch waist→the arch foot. The research conclusion of this paper has some reference value in analyzing the pressure mechanism of loess tunnels and perfecting the design method of supporting structure.

Based on a highway tunnel in loess with high water content under construction, the crown settlement and horizontal convergence of the tunnel were monitored and discussed, the causes of tunnel deformation were analyzed, and the corresponding control measures were proposed. The crown settlement was larger than the horizontal convergence of tunnel. The tunnel deformation was greatly affected by rainfall, and its stability time was basically 35 d. The tunnel deformation was roughly divided into three stages: the rapid development stage, the continuous development stage, and the stable stage. With the excavation of the upper, middle, and lower benches, the crown settlement and horizontal convergence of tunnel changed greatly. After each construction step was completed, the supporting measures such as lock-foot anchor were taken in time. Early closing of the invert could effectively control the tunnel deformation. The tunnel deformation was consistent with the exponential function rule and could be predicted by the law of exponential function. It was recommended to use arch-foot steel pipe piles and curtain grouting in the construction of water-rich loess tunnels to effectively control water leakage and large deformation of surrounding rocks.

In order to study the rapid construction technology of the single-side heading method, the proposed three-lane highway rock-soil mixed tunnel that in the Dashuidong Village Highway Section in Laizibao Township, Yuzhong County, Lanzhou City, Gansu Province were based on to study the method. The overlying stratum of the tunnel site is the Quaternary Upper Pleistocene aeolian loess(Q^eol₃), and the underlying bedrock is the precambrian Gaolan Group hornblende schist(AnC-gla). The MIDAS/GTS finite element software was used to compare the single in the sidewall pilot method, the partition wall was optimized for half-width construction. Through two-dimensional numerical simulation, the structural force characteristics and displacement change law of the optimized single sidewall pilot method and the optimized single sidewall pilot method were compared. The results showed that: the force of the supporting structure at each stage under the two construction methods was similar. The final settlement and convergence were also the same; after the optimization of the construction method, the displacement law during the construction process was similar and both it could meet the requirements of construction stability, and the optimized single-wall pilot method had more advantages in terms of construction schedule and economic benefits.

In view of the current engineering problems of large deformation, easy collapse in the construction of watery and large-span loess tunnel, combined with the results of on-site curtain grouting test and indoor test for the watery and large-span Yima No. 1 loess tunnel of the Yinchuan-Xian High-Speed Railway, and then the application effects of surrounding rock reinforcement and stability improvement of loess tunnels was analyzed. The results showed that the curtain grouting pressure showed a four-stage change trend of “rapid increase-slow increase-slight decrease-sharp increase” with the grouting time. The curtain grouting in the cave could effectively fill the pores in the loess layer in the grouting range, compress and compact the soils, slow down the permeability of the loess, reduce the water content of the surrounding rock, and significantly improve the physical and mechanical properties of the surrounding rock within the grouting range. The average increased in physical and mechanical parameters could be up to 10%-35%. The curtain grouting could effectively reduce the deformation of the surrounding rock in the cave by about 20% to 70%, and could alleviate disasters such as slippery soils on the face of the tunnel and collapse of the vault. Through the curtain grouting, the self-stability of the excavation surface was enhanced, the plasticity of the surrounding rock was improved, and the strength and overall stability of the surrounding rock was improved. The research results not only guided the on-site construction, but also provided a basis for optimizing the support system of the loess tunnels, which could provide reference significance for the construction of similar characteristic tunnels.

The theoretical analysis of the mechanism on the new shield tunnel crossing the existing subway tunnel was carried out, the 15 project instances and the corresponding measured data of new shield tunnels crossing the existing metro was collected and counted. The results showed that the uplift and settlement deformation of the existing subway tunnel were easily caused by new shield short-distance crossing, the maximum vertical displacement was mainly concentrated in the range of ±5 mm, and the deformation of the existing subway tunnel was closely related to the clearance between the two tunnels, reinforcement and soil conditions. Based on the project of Hangzhou Metro Line 2 closely under-crossing Metro Line 1, the deformation of existing subway tunnel during the whole process of shield tunneling was deeply discussed. Meanwhile, the combination of pipe shed and rotary jet reinforcement below existing Metro Line 1 could effectively reduce the deformation of the existing subway tunnel. In the process of crossing construction, the shield construction parameters should be adjusted in real time through the measured deformation data of the existing subway tunnel, so as to ensure the safety of the new shield tunneling.

The construction of overlapping shield tunnels with small net distance is a typical problem, especially in soft soil layer. In order to solve the construction problem of the overlapping shield tunnel of Wuchang Vehicle Base in Hangzhou Metro Line 5, the mutual disturbance influence of construction sequence on the deformation of the soil and the structure of overlapping tunnels was studied using the methods of numerical analysis and field monitoring. The result showed that the construction sequence of lower tunnel ahead of upper tunnel was better than that of upper tunnel ahead of lower tunnel. The influence of the former on the deformation of the soil and the structure of overlapping tunnels was less than the latter; secondary grouting reinforcement and moving support trolley could effectively reduce the deformation of the soil and tunnels. The construction sequence of lower tunnel ahead of upper tunnel was used to carry out the construction of overlapping tunnels.

Three normally-adopted schemes highway tunnel with a parallel pilot tube were taken to formulate their corresponding smoke spreading in the main tunnel and pilot tube by using the fire simulation software FDS to establish a local tunnel model. The analysis results showed that: soon after the fire was confirmed, jet fans should be turned off to induce the smoke spread freely to both sides. As a result, the stratification phenomenon(smoke gathered in the tunnel vault)caused by the buoyancy of the smoke could facilitate the escape and evacuation of occupants on both sides of 2.5 m above road surface. Until all the occupants had evacuated to the pilot tube, then the air flow with critical air velocity should be yielded to drive the smoke to one side. It was suggested that the direction of smoke exhaust should be consistent with the normal operation ventilation direction. The research conclusions is conducive to compiling fire emergency plan of similar projects.

In order to study the influence of long-distance and small-spacing pipe gallery excavation on the deformation of shield tunnels, relying on the common construction project of Shenzhen Metro Line 12 pipe gallery, numerical simulation software was used to simulate the comprehensive pipe gallery excavation to study the influence of different excavation length of pipe gallery on shield tunnel under the working condition of excavation width of 10.5 m and the excavation depth of 6.5 m. The influence of different excavation steps, embedded depth of bored piles and thickness of grouting layer on tunnel deformation were studied to provide technical guidance for the subsequent construction of the integrated pipe gallery. The results showed that: the deformation of the tunnel below the excavation of the comprehensive pipe gallery increased with the increase of the excavation length, when the excavation length was 3 times greater than the excavation width, the influence of the excavation length on the tunnel could be ignored; the smaller the step of the bunker excavation was, the smaller the tunnel deformation after the completion of the excavation of the pipe gallery; there was an optimal thickness of the grouting layer and grouting pile embedment depth, beyond the optimal value, the tunnel deformation was basically unaffected by it.

According to the hard rock stratum of Qingdao subway tunnel, the prestressed anchor rod, instead of the traditional hollow grouting anchor rod, was used for active support of the arch and side wall of the underground excavation station. The grid spacing and shotcrete thickness was optimized. The excavation of large section tunnel in grade Ⅳ surrounding rock in step method was realized. The numerical analysis and monitoring measurement results showed that the support scheme was safe and feasible. The construction methods of the underground excavation station and the air duct was compared and analyzed. Combined with the active support technology, the technology of construction through air duct was optimized, the upper half section of the duct was expanded and section steel frame supporting conditions was reserved. The construction in step method was realized, with clear force conversion, which was safe, efficient and convenient.