In order to study the influence of stress path on the true triaxial macroscopic and mesoscopic deformation characteristics of rocks, a calibrated granular flow numerical specimen was established using the discrete element method, and the loading planes were selected as meridian plane, <i>π</i>-plane and the fixed-axis plane. Numerical experiments with different stress paths were conducted on the numerical specimen to analyze the true triaxial deformation evolution of rocks from the macroscopic and mesoscopic viewpoints, and the numerical simulation results were compared with the D-P yield criterion to verify the correctness of the results. The research results showed that:for the same stress increment, the anisotropy of strain increment was the lowest when loading along the meridian plane, and the stress reached the yield plane fastest when loading along the <i>π</i>-plane, resulting in the largest strain increment and the two-way unloading in fixed-axis plane produced the largest strain increment in all stress path loading processes. The elastic-plastic deformation characteristics were analyzed using the relative imaging of stress space and yield surface, defining deformation anisotropy parameters; the correlation between stress and strain increment paths was quantitatively analyzed at the mesoscopic view level, and it was concluded that the number of contact force chain transformations and strain increment deflection angle were negatively correlated, and the numerical model produced the largest number of microcracks with the most obvious internal damage when loaded along the <i>π</i>-plane, and the smallest number of microcracks with the least internal damage when loaded along the fixed-axis plane.

Based on a shield tunnel with a small turning radius project, the stratum deformation characteristics caused by the construction of shield tunnel with a small turning radius and the influence law of tunnel buried depth on stratum deformation were studied through analyzing on-site measurement and numerical simulation. The results showed that the on-site measured data were consistent with the simulation results. The shallower the tunnel was buried, the smaller the surface deformation was. The overbreak made the surface deformation inside the curve larger and caused the centerline of the sedimentation tank to offset to the overbreak side in the meantime. The horizontal deformation characteristics of the strata on both sides of the curve were significantly different from those of the linear tunnel. The stratum on the inner side was disturbed more seriously, which should be paid enough attention to. The influence law of tunnel buried depth on the horizontal deformation of stratum on both sides of the curve was different: the shallower the tunnel was buried, the greater the horizontal deformation of the strata inside the curve was and the smaller that outside the curve was.

The research preliminarily demonstrated the feasibility of building natural gas storage in abandoned salt caverns in Tai'an from the geological point of view. According to the characteristics of high-proportioned interlayers in Tai'an salt mine, a new model of underground space utilization of salt cavern—the model of sediment interspace utilization(Tai'an model)was put forward. The feasibility of building gas storage using abandoned salt caverns was analyzed from two aspects of stability and permeability. The permeability, porosity, scanning electron microscope(SEM)results of the interlayer and the thickness of the top retained salt layer were used to demonstrate the sealing performance. The stability of salt cavern gas storage was demonstrated by the proportion of sediment filling and the distribution of surrounding faults. Based on the investigated salt mining information, the preliminary analysis showed that the short-term potential gas storage scale could reach 1.86 billion cubic meters, and the long-term potential gas storage scale could reach 7.5 billion cubic meters.

In order to explore the impact of slurry pressure-balanced(SPB)shield tunneling on the ground response in high water pressure environment, this research systematically analyzed the ground stability subject to continuous excavation of SPB shield tunnel considering different overlying water heights and permeability coefficients by means of refined three-dimensional finite element numerical models. The evolutions of seepage and displacement fields at different stages of underwater shield tunneling, including shield placement, continuous excavation and stoppage, were obtained. It was found that for tunneling project in soft soil areas such as Shanghai, 40 m could be regarded as the threshold value distinguishing high and low water pressures. The seepage and deformation fields would show different evolution laws between cases with the water head higher than this threshold and cases with the water head lower than this threshold, and the difference could be more obvious in low permeable stratum. Seepage led to the change of ground's excess pore water pressure field, which further affected the ground displacement field. The largest deformation at the excavation face with seepage effect was about 1.4 times of that without seepage effect. The ground deformation under high water pressure condition was affected by the seepage effect, while the ground deformation under low water pressure condition was dominated by tunneling parameters, such as the grouting pressure. The aforementioned observations could provide useful guidance for the safety control of underwater shield tunneling.

The construction parameter optimization research of the double-side heading method usually adopts single factor analysis, which has certain limitations. The research took the Wulidian Subway Station Tunnel Project as the research background, which is one of the first phase projects of Chongqing Rail Transit Line 9. The radius of temporary support, the thickness of the middle rock wall, and the excavation footage were used as influencing factors, and the maximum vertical displacement of the vault and the maximum horizontal displacement of the side wall were used as the calculation indicators. The finite difference software FLAC^3D was used to carry out multi-factor numerical simulation analysis. The results showed that the optimal combination of construction parameters obtained by multi factor analysis were that temporary support radius was 23.0 m, medium rock wall thickness was 9.0 m and excavation footage was 0.75 m; the optimal combination obtained by the back analysis of regression method based on the results of multi factor analysis that temporary support radius was 24.0 m, medium rock wall thickness was 8.0 m and excavation footage was 0.8 m. By comparing the maximum vertical displacement of the arch crown and the maximum horizontal displacement of the side wall of the three groups of optimal construction parameters, it was concluded that the construction parameters obtained by regression back analysis based on the results of multi factor analysis have more advantages.

To improve the accuracy of information acquisition, the density-based spatial clustering application with noise(DBSCAN)algorithm was improved based on 3D point clouds. The k-nearest neighbor algorithm and the evaluation criterion based on density ratio S were used to divide the point cloud regions with different densities in order to set parameter ε and analyze the point cloud normal vector adaptive. The angle threshold T of normal vectors was introduced to determine the points belonging to the same plane and the points belonging to the same plane were displayed with the same colour. This paper discussed the influence of different parameter combinations on the identification results and enabled a fast analysis of rock joints. The research results could provide a reliable application method for efficient measurement of discontinuity information.

Jiaxing City's extraterritorial water distribution project(Hangzhou direction)long-distance shield tunneling underneath 2 roads of the Shanghai-Kunming railway Upstream Line, 17 roads and turnout area of Hangzhou North Depot, 11 roads of Departure Yard of Qiaosi Marshalling Stationas section road Interchange project. The stratum and engineering building environment are complex, and the deformation control requirements are very high. Based on this case, the method of field test and finite element simulation were used to discusse the railway deformation law and safety control measures in the process of shield tunneling through large railway hub. The results indicated that the numerical model results matched the monitoring data well, which calculated by Mohr-Coulomb model for deep buried tunnels in soft soil layer. It was recommended that the buried depth of the tunnel should not be less than 35 m when the shield passed through the turnout area; the analysis on the relationship between different loss ration and the maximum settlement of subsidence bed traversed by a shield tunnel revealed that the maximum settlement of the subsidence bed had a linear relationship with the formation loss. The recommended loss ratio of a shield tunnel passing through the turnout area should be no more than 0.3%.

A similar physical model test was established to study the static response of the ground penetrating shield technology(GPST)tunnel with multiple working conditions. Based on similitude ratio theory, the mechanical state of the prototype tunnel was reproduced by controlling the layered soil modulus and prototype field equivalent and ensuring the cross-sectional and longitudinal stiffness of the shield tunnel after assembling. The diameter distortion, joint deformation, and earth pressure of the model under gravity and overload were tested, therefore, the static response characteristics of the GPST tunnel were investigated. The results showed that with the increase of burial depth from -0.5D to 0.5D, the tunnel diameter deformation gradually changed from "vertical egg" to "horizontal egg", and reached the maximum value when the burial depth was -0.1D. Besides, the overall trend of the longitudinal joint opening was positively correlated with the diameter deformation, and the horizontal earth pressure of the structure could be approximated to triangular distribution.

The super-span hyperboloid dome has the characteristics of large section, low flat rate and complex contour. To solve the problems of low construction efficiency, high construction risk, and inconvenient construction equipment, the construction technology of super-span hyperboloid dome cave storage was studied. A method combining engineering investigation, numerical calculation and on-site monitoring was adopted. The geological situation and design overview of the project were introduced, the overall construction sequence and subsection excavation plan were given, combined with the design characteristics, the corresponding key technologies were summarized, and the rapid construction technology suitable for the super-span hyperbolic dome cavern was proposed. The following conclusions were drawn: the rapid construction technology researched in this research was applied to the site to achieve a monthly excavation volume of 9 600 m³. Shotcrete had high flatness and no water leakage. The on-site stress and deformation monitoring showed that the structure was stable under stress, with small deformation and good supporting effect, which could provide valuable experience for similar projects.

The large finite element analysis software MIDAS/GTS was used to numerically simulate the whole process of excavation and support of a single tank chamber of an underground oil and gas storage tank in Jiangxi, focusing on the analysis of the displacement field, stress field and plastic zone distribution characteristics of the surrounding rock after the excavation of the tank chamber was completed, and to study the influence of the central rock column reserved for the excavation of the dome on the vertical displacement of the surrounding rock at the center of the vault and the horizontal displacement of the surrounding rock at the foot of the vault. The research showed that the maximum vertical displacement of the surrounding rock occured in the vault and the bottom plate, the maximum sinking of the surrounding rock in the vault reached 12.71 mm, the maximum uplift of the surrounding rock in the bottom plate reached 17.96 mm, the maximum horizontal displacement occur in the side wall of the tank chamber, which was 1.99 mm, the distribution of the plastic zone near the foot of the dome was obvious, the overall deformation of the surrounding rock was not large, the displacement field, stress field and plastic zone characteristics basically met the stability requirements of the tank chamber. The center rock column reserved for dome excavation had almost no effect on the horizontal displacement of the surrounding rock during the excavation and support of the dome, and had a certain limiting effect on the sinking of the surrounding rock in the center of the vault, but after the removal of the center rock column, the displacement of the surrounding rock in the center of the vault changed abruptly to almost the same as the solution without the center rock column, and the basic contribution to limiting the overall vertical displacement of the surrounding rock after the excavation and support of the tank chamber was completed was not significant; In the case of better surrounding rock conditions, the dome excavation could be considered as a whole, without reserving the central rock column, which could save the construction cost and also meet the stability requirements of the surrounding rock.

For the purpose of researching the influence of seawater environment on the viscosity of cement sodium silicate(C-S)grout, the study tested the time-varying characteristics of grout viscosity under different water-cement(W-C)ratio, C-S volume ratio and grouting conditions(fresh water and seawater)by laboratory test method. The results showed that the viscosity of C-S grout could be divided into initial stage and rising stage under fresh water environment. In seawater environment, grout viscosity could be divided into three stages: initial stage, stable stage and rising stage. W-C ratio and C-S ratio directly affected the duration and viscosity of grout in each stage. Due to the complex ionic composition of seawater environment, the viscosity of grout rose to a certain level in a short period of time before entering a stable period of viscosity. Based on the test results, some suggestions were put forward for the construction of grouting in the unfavorable geological body of submarine tunnel, and the research conclusions had certain promoting significance for the safety construction of submarine tunnel.

Based on the deep foundation pit project of Yellow River Tunnel in Jinan, this paper studied the deformation rules of ultra-deep foundation pit in considering seepage and not seepage.The numerical simulation results were compared with the field measured data, and the final seepage hazard mode to the excavation of the ultra-deep foundation pit in the silty clay formation was mastered. Mohr-Coulomb model was modified for soft clay and clay. For soil with higher friction coefficient like sand, the Mohr-Coulomb model was adopted.The main 15 stages of foundation pit excavation under seepage were simulated, and the influence of foundation pit excavation on the surface settlement, the horizontal displacement of the underground continuous wall, and the influence on the bottom uplift of the foundation pit were finally analyzed. It was found that the seepage greatly affected the deformation of the foundation pit, which was greater than the posterior deformation value when the seepage was not considered. In the site construction, if the deep foundation pit design was conducted without considering the seepage action, it would cause great judgment error and make the project have great safety risks. The study in this paper provides empirical guidance for similar engineering.