The distribution law of fluid flow in natural fissures was obtained by simulating the fluid flow in the rock fissures of the fault fracture zone. Based on the theoretical analysis, the velocity distribution model of wedge-shaped flow field was established. It was found that the location of the fracture mainstream zone could be expressed by the maximum inscribed circle of the fracture section. Computed tomography(CT)was used to reconstruct the natural fracture of the dielectric skeleton of the fault, and the maximum inscribed circle of the fracture was calculated by MATLAB to estimate the permeability of the fracture. The correlation between the results to calculate the fracture permeability obtained by the maximum inscribed circle method and the hydraulic diameter method was 0.976, which indicated that it was feasible to calculate the fracture permeability by the maximum inscribed circle of the fracture section instead of the hydraulic diameter.

Aiming at the selection of ventilation modes during the construction of a large underground cavern storage, according to the ventilation design of a large underground cavern storage, on the basis of comparing the advantages and disadvantages of the extraction type, the press-in type and the mixed type ventilation mode, and according to each ventilation mode calculate the air volume according to the method was calculated, and the ventilation mode of each stage of the construction of the large underground cavern storage was determined. A Ventsim numerical simulation model for ventilation of a large underground cavern storage was constructed, and numerical simulations were conducted to study the dynamic evolution law of wind flow in a large underground cavern storage with different ventilation modes in different construction stages, and the differences in different construction stages were analyzed. The ventilation effects of the ventilation methods were compared and analyzed, and the ventilation methods in different construction stages were optimized. The numerical simulation results showed that the optimal ventilation mode in the first construction stage was press-in ventilation, the optimal ventilation mode in the second construction stage was mixed ventilation, and the optimal ventilation mode in the third and fourth construction stages were extraction ventilation. At the same time, it was verified that the effect of wind resistance, air volume and air network efficiency of each ventilation method in different construction stages was optimal, which provided a scientific basis for the ventilation design of large underground water-sealed caverns during the construction period.

Based on random field theory, finite element numerical analysis and Monte-Carlo stochastic simulation method, the influence of spatial variability of geotechnical parameters on land subsidence was investigated. The spatial variability of the internal friction angle was focused as the representative, and the effects of the coefficient of variation, horizontal correlation distance and vertical correlation distance of the internal friction angle were systematically studied. It was found that the larger the coefficient of variation was, the higher the dispersion degree of land subsidence curve was; compared with the results of deterministic analysis, the ground subsidence of the stochastic analysis considering the spatial variability of geotechnical parameter was greater; the offset distance of settlement center was affected by horizontal and vertical correlation distance, and the former had greater influence; when cavern was large enough, the influence of cavern on land subsidence was stronger than that of spatial variability of geotechnical mechanical parameters.

Aiming at the water inrush disaster that was easy to occur during tunnel construction, the internal law of tunnel water inrush was analyzed through the statistics cases of tunnel water inrush. The water inflow in tunnels during construction was predicted by using the methods of long short-term memory neural network(LSTM), Elman neural network and multiple linear regression based on partial least square respectively, and compared with the actual water inflow, then the optimal method for predicting the tunnel water inflow was obtained. The results showed that water inrush accidents were more likely to occur in shallow-buried, long tunnels and extra-long tunnels, and in fault, karst and soluble rock strata. By comparing the prediction results of three different models with the water inflow during tunnel construction, the LSTM model had higher accuracy in predicting the water inflow in tunnels during construction.

In order to study the damage mechanism of shield segment structure of shield tunnel with small curvature radius, based on practical engineering cases, a fine lining segment model considering segment joints and inter-ring joints was established to reveal the segment damage mechanism in the construction stage of shield tunnels with small curvature radius. The results showed that the axial force, shear force, positive bending moment and Mises stress of the segment all peaked at the inner and outer arch waists when the shield tunnel with small curvature radius was constructed in the turning section. The arch waist position of segments were more likely to be damaged during the excavation process. When the rectification angle of the jack thrust increased, the overall tunnel deviated to the outside. The outer side of the shield tunnel waist was more obviously affected, since the offset of outer arch waist was significantly larger than that of inner arch waist. The numerical simulation was consistent with the field observation of segment damage, which could provide reference for practical engineering.

There were many conflicts with existing traffic lines in the process of expansion. Taking the overburden capacity expansion of a highway tunnel in southeast China as an example, the influence of the newly increased overburden load on the safety of underpass tunnel structure was studied. The leachate level height and the physical and mechanical parameters of the overlying waste were obtained through experiments. The finite element models of different dangerous tunnel sections were established to analyze the structural deformation and internal force changes of the tunnel, and the vault settlement, bearing capacity and cracks were checked. The upper limit of the thickness of the overlying waste on each tunnel section during the subsequent expansion of the landfill was proposed. The results showed that the actual leachate level and the physical and mechanical parameters of the overlying waste had the most significant effects on the tunnel structure after the landfill expansion. Within the design range, the influence of the thickness of the overlying waste on the settlement and bearing capacity of the tunnel vault was not significant, and the cracks of the tunnel structure usually played a controlling role.

Songgang Station of Shenzhen Metro Line 12 Phase II Project and the existing wind pavilion section of Line 6 were taken as the research background. The parameters of the advanced support of horizontal jet grouting pile under the condition of marine strata were analyzed by three-dimensional finite difference software FLAC^3D. Based on the analysis and comparison of the surface settlement and displacement results of tunnel excavation under this stratum condition, it was concluded that the stability of surrounding rock during tunnel excavation of marine silt layer was affected by horizontal jet grouting piles with different lengths, section sizes and insertion angles. The results showed that compared with the reinforcement without horizontal jet grouting pile, the surface settlement with horizontal jet grouting pile was reduced by 64.8%. With the increase of the section size of horizontal jet grouting pile, the surface settlement decreased gradually. With the increase of the length and insert angle of horizontal jet grouting pile, the surface settlement increased gradually. In order to find the optimal construction method of horizontal jet grouting pile, the settlement changes of 125 kinds of horizontal jet grouting pile under different supporting conditions were compared and studied, and the economic cost and construction safety were considered comprehensively. It was concluded that the length of horizontal jet grouting pile was 10 m, the pile diameter was 600 mm, and the intercalation angle was 1°, which had the best control effect on the surface settlement deformation of marine silt texture layer. At the same time, Pearson correlation analysis was conducted on the influence of pile length, pile diameter and extrapolation angle of horizontal jet grouting pile on the surface settlement by using IBM SPSS software, and the conclusion was drawn that the influence of pile diameter on surface settlement was greater than that of pile length and greater than that of extrapolation angle.

In order to study the influence of different forms of defects on the stress of lining structure, through the model test, different forms of defects were simulated, and the changes of bending moment, axial force and safety factor at different parts of lining structure were analyzed. The results showed that the defects at the connection between the side wall and the inverted arch increased the bending moment and axial force at the middle of the lining arch waist and the inverted arch, and decreased the bending moment and axial force at the vault. According to the different forms of defects, the effects on different parts of the lining were different. When there were only concrete shrinkage defects or unconnected steel defects, the main influence parts of lining structure were haunch and side wall. When the two defects coexisted, the middle part of vault and inverted arch would also be greatly affected. The influence of concrete loose defects on the safety factor of lining structure was generally greater than that of unconnected defects of steel bars. The main influence areas were arch waist and side wall. When the two defects coexisted, the safety factor at the middle of arch waist and invert decreased obviously, which was 52.03% and 32.40% respectively. The effect of defects on the safety factor at the middle of the hance and inverted arch was greater than that at the vault and side wall. During construction, the quality of concrete pouring here should be strictly controlled to ensure the strength after forming, and the pouring thickness can be appropriately increased to make it have a higher safety reserve.

A large-section rectangular pipe-jacking tunnel in Shenzhen passed through the bridge pile foundation of an interchange ramp with only a distance of 0.8 m, and down-traversed multi-purpose networks for underground pipelines with only a distance of 3 m. Relying on the tunnel project, the design of the segment of the rectangular pipe-jacking tunnels with large sections and the complex condition was studied in detail. A design flow of the design of the segment of the rectangular pipe-jacking tunnels with large sections and a complex condition was proposed. The design elements of the segment configuration of the rectangular pipe-jacking tunnels with large sections were analyzed. The configuration of the segment was designed. Then three working conditions, including the lifting of the segments, the construction pushing condition, and normal service conditions, were assessed using numerical analysis to determine the dimension of the structures. The joints of the segments, longitudinal connections, reserved holes and so on were specially designed considering the properties of the project with large sections, deep-covered soils and high water pressure. Based on the case investigation, contrastive analysis and practical verification, the paper drew the conclusion that the proposed design flow and the design elements were much helpful for the design of the rectangular pipe-jacking tunnels with large sections in complex condition.

In view of the road diseases that occurred during the operation of the Shiyan to Tianshui Expressway, such as road cracks, bulges, kick drums, etc, the reinforcement measure using pile-plate composite structure replacing of invert was proposed, comprehensively considering of many factors such as tunnel geology, hydrology, lining structure, disease situation, construction conditions, disposal period, project cost, etc. Using finite element numerical simulation calculation, and getting through the comparison and analysis of on-site test data, the results showed that the reinforcement schemes based on pile-plate composite structure replacing invert could better control tunnel settlement and deformation, reduce road settlement diseases, ensure tunnel operation safety, and provide reference for the treatment of similar operating tunnel diseases.

Relying on the Hongshengsha-Yufengwei Section Tunnel Project of the second phase of Guangzhou Metro Line 7, this paper used the particle swarm optimization random forest method(PSO-RF)to establish a sealed cabin pressure prediction model in the dual-mode shield soil pressure boring mode. Through the correlation analysis of shield boring parameters, the tunneling parameters that had a great influence on the pressure of the sealing chamber were screened out, including screw speed, screw torque, cutterhead speed, propulsion speed, penetration degree, cutterhead torque, and total thrust, and the screened tunneling parameters were used as the input parameters of the prediction model, and the pressure of the sealing chamber was used as the output parameter of the model to predict the pressure of the sealing chamber. The results showed that the random forest PSO-RF prediction model improved by particle swarm algorithm could effectively predict the pressure of the dual-mode shield sealed cabin, and compared with the traditional neural network prediction model, the PSO-RF model had higher prediction accuracy, the average absolute error was within 10%, and the predicted value and the actual goodness-of-fit R2 were 0.901 4, which was significantly superior to the BP neural network in terms of prediction accuracy and generalization ability of the model.