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.

Hydromechanical Simulation of Tunnel Excavation in Rock Considering a Nearby Karst Cave

Tunnel excavation tends to be affected by karst cavities in karst areas. Some cavities that are at low risk of causing safety issues without treatment tend to be ignored in the design and construction of tunnels to reduce costs. It is necessary to gain a better understanding of the effect of such a cavity on the seepage around a tunnel, the deformation of the surrounding rock, and the stress of the tunnel lining. In this paper, a two-dimensional rock-tunnel hydromechanical model with a karst cave was established with FLAC3D finite difference software to simulate the tunnel excavation with the consideration of seepage. Numerical simulations were performed to analyze the deformation of the surrounding rock, the seepage field of the surrounding rock, and the stress of the tunnel lining, and the results were compared for scenarios when the karst cave is at different locations relative to the tunnel. These results can provide a reference for the design and construction of tunnel engineering in rock with karst caves.

A Case Study of Thaumasite Sulfate Attack in Tunnel Engineering

There existed ever-increasing structural diseases in the Dugongling tunnel after the completion of the construction. Systematic research was carried out based on the information of tunnel engineering geology, disease development, mineral composition of surrounding rock and concrete, and laboratory tests. Results showed that (1) the concrete structure from the Dugongling tunnel suffered from a typical thaumasite sulfate attack (TSA); (2) tunnel diseases developed under the influence of multiple geological factors such as groundwater, karst, gypsum bearing stratum, and geological tectonics. Groundwater aggravated the appearance of engineering defects of various geological factors and accelerated the softening and swelling of surrounding rock. Moreover, the additional load of supporting structure increased, and the concrete structure was prone to sulfate attack; (3) the development of tunnel diseases showed long-cycle and large-scale characteristics, and the types of diseases are heterogeneous. The tunnel diseases develop rapidly in the third year after the construction. The structure collapse disease, one of the most serious diseases of tunnel lining, occurred in the fifth year after construction; and (4) according to the conditions of TSA, technical treatment measures were proposed. These measures included blocking the flow of CO 3 2 − , improving the impermeability of concrete structures, and decreasing the diffusion of external ions and groundwater. This work provides a solution for the treatment of similar tunnel disease and mechanism analysis.

Research on the Interaction Mechanism between Landslide and Tunnel Engineering

The landslide at the entrance of a railway tunnel is large scale, and serious diseases are prone to appear under natural disasters, which threaten the safety of the tunnel. According to its characteristics, on-site long-term monitoring experiments and numerical analysis were carried out, and the mechanism of interaction between landslide and tunnel engineering was analyzed. The results show that under the impact of rainfall and earthquake, the original internal stress balance in the landslide body is disturbed, leading to the increase in landslide thrust and damage of the tunnel lining. Simultaneously, the excavation of the tunnel can slack the surrounding rock to increase the landslide thrust and make the landslide be finally formed; this landslide conversely acts on the tunnel, resulting in deformation and destruction of the tunnel. During the monitoring, under the influence of rainfall and earthquake, the stress of the secondary lining was continuously increased by 25%. Tunnel construction caused a maximum deformation of 30 mm in the antislide pile at a distance of 2.12 m, and the slope and the tunnel were also affected. Under extreme conditions such as rainfall and earthquake, shear failure occurred at the vault, bottom, and waist of the right-line tunnel located at the junction of soil and rock; at this time, the tensile strength of the tunnel reached 93.8% of the limit value of concrete, which seriously affected the safety of the tunnel. As for the weakened tunnel structure, measures such as dense planting and strengthening of concrete strength should be adopted to enhance the safety of the tunnel structure.

A Novel Excavation and Construction Method for an Extra-Long Underwater Tunnel in Soft Soils

The cut-and-cover technique is widely used in the field of tunnel engineering owing to its simple construction technology, high working efficiency, and low cost. However, the safety of the foundation pit and the environmental impact during excavation are of great concern, especially for tunnels that pass through lakes and/or rivers. In this paper, a novel excavation and construction method is presented for the Taihu tunnel, which is the longest lake-crossing tunnel in China. In this method, a cofferdam of double-row steel sheet piles (DSSPs) was designed in order to divide the overlying excavation into several closed zones. During the construction, four zones were regarded as a unit, and different construction steps were carried out simultaneously in each zone. Therefore, an assembly line for the tunnel excavation was established to accelerate the construction speed. The most distinctive advantage of this method is that the excavation did not cut off the normal flow of the lake water and the shipping routes, with low environmental impact. To investigate the tunnel deformation during excavation, a finite element analysis combined with field monitoring data was adopted, indicating that the magnitude of the tunnel deformation was notably less than those reported from other excavation projects. Moreover, the effect of groundwater on the piles and the safety of the foundation pit was revealed using numerical modelling. This study provides a new idea for the design and construction of tunnel engineering, especially for extra-long underwater tunnels in soft deposits.

Intelligent rating method of tunnel surrounding rock based on one-dimensional convolutional neural network

Accurate prediction of surrounding rock grades holds great significance to tunnel construction. This paper proposed an intelligent classification method for surrounding rocks based on one-dimensional convolutional neural networks (1D CNNs). Six indicators collected in some tunnel construction sites are considered, and the degree of linear correlation between these indicators has been analyzed. The improved one-hot encoding method is put forward for transforming these non-image indicators into one-dimensional structural data and avoiding the sampling error in the indicators of surrounding rock collected in the field. We found that the 1D CNNs model based on the improved one-hot encoding method can best extract the features of surrounding rock classification indicators (in terms of both accuracy and efficiency). We applied the well-trained classification model of tunnel surrounding rock to a series of expressway tunnels in China, and the results show that our model could accurately predict the surrounding rock grade and has great application value in the construction of tunnel engineering. It provides a new research idea for the prediction of surrounding rock grades in tunnel engineering.