| Subsea faults,fracture zones and other fault structures are important geological features that can cause water inrush from subsea tunnels.Excavation of subsea tunnels will disrupt the original state of these fracture structures,creating pathways for seawater to connect,potentially leading to incidents of water inrush from subsea tunnels.As the scale and complexity of underwater tunnel construction continue to increase,the encountered engineering geological conditions are becoming increasingly challenging.For example,the ongoing construction of Second Jiaozhou Bay Subsea Tunnel,will traverse major fault structures such as the Cangkou Fault Zone.Due to tectonic forces,the tunnel site may experience earthquakes of magnitude 6 to 7 within the next 100 years,with a maximum magnitude reaching 7.5.The nearby areas would be subjected to an intensity of IX on the seismic intensity scale.Consequently,the construction risk of the subsea tunnel will be further exacerbated.Ensuring the construction and operational safety of subsea tunnels when crossing the unfavorable geological section,particularly under the influence of dynamic forces like earthquakes,poses a significant scientific challenge in the secure development of subsea tunnels.Therefore,it is of great theoretical significance and significant engineering practical value to conduct studies on the disaster mechanism,gain in-depth understanding of the seepage evolution laws of water-rich fractured rock masses,and establish scientific prevention and control methods.Based on the aforementioned issues,this study employs theoretical analysis,numerical simulation,laboratory experiments,and model tests as research methods to investigate the disaster mechanism of water inrush during the construction of subsea tunnels when crossing large fault zone,particularly water-rich fracture zones,under the influence of dynamic forces such as earthquakes.This study analyzes the internal structural patterns of subsea faults and the groundwater migration patterns,explores the seepage evolution laws of fractured rock masses under different seismic action,elucidates the response characteristics of multiple physical fields during the water inrush process of underwater tunnels under seismic action,and reveals the dynamic water inrush mechanism when traversing water-rich fracture zones.and then,the engineering application study was performed based on Second Jiaozhou Bay Subsea Tunnel.The research works and main achievements of this study are as follows:(1)The internal structural patterns of subsea fault zone were analyzed,and the groundwater migration patterns were studied for univariate fault structure model,binary fault structure model,and ternary fault structure model.Additionally,a disaster model for underwater fault zone was constructed.An analysis was conducted on the impact of fault zone scale(including fault width,dip angle,and seawater coverage),fault zone properties(rock properties,permeability),and fault zone activity(fault slip,seismic activity)on engineering construction.Quantitative criteria were proposed for evaluating these factors.The interval hierarchy analysis method,fuzzy comprehensive evaluation method,and relative advantage analysis method were employed to establish a risk assessment methodology for water inrush when subsea tunnels crossing water-rich fault zone.The water inrush risk level was analyzed for the crossing of the Cangkou Fault Zone by Second Jiaozhou Bay Subsea Tunnel.These findings lay a foundation for the study of water inrush when subsea tunnels crossing water-rich fault zone.(2)Based on the stress-permeability coupling tests of fractured rock,the stress paths under dynamic loads such as earthquakes were analyzed.Simplified stress paths were derived and used as the basis for conducting stress-permeability tests under cyclic loading.The influence of dynamic parameters,such as dynamic load amplitude and frequency,on the permeability of fractured rock was investigated.A characterization relationship between the permeability of fractured rock and dynamic parameters was established.During the application of dynamic loads,the variation in dynamic load amplitude has a significant effect on the increase in permeability.Once the frequency reaches a certain level,the fracture distribution within the fractured rock mass does not continuously change.The permeability of the rock mass tends to gradually stabilize in the later stages of the cyclic process.By incorporating the Weibull distribution,the constitutive model for the damaged fractured rock based on the D-P criterion was modified.The evolution patterns of parameters Fo and m during the cyclic loading phase were analyzed concerning the dynamic load amplitude and frequency.This elucidates the response mechanism of damage and permeability in fractured rock under seismic action.(3)Based on similarity theory and orthogonal experiments,a fluid-solid coupling similar material was developed.Through sensitivity analysis,the influence of the components of the similar material on the physical and mechanical properties was studied,and the proportioning of the similar material for the fractured rock in Second Jiaozhou Bay Subsea Tunnel,was determined.A model test system for dynamic water inrush in subsea tunnels crossing waterrich fracture zone was developed.Experimental investigations were conducted to study the distribution of the seepage field in water-rich fracture zone rock masses under different seismic action and the dynamic-seepage evolution during tunnel excavation.The water inrush process during the crossing of water-rich fault zone by subsea tunnels under various seismic intensity conditions was analyzed.The research revealed the variations in stress,acceleration,hydraulic pressure,and water inflow in water-rich fracture zone rock masses under different seismic action.(4)The catastrophic characteristics of dynamic water inrush for subsea tunnels crossing water-rich fault zone were analyzed.Taking into account the relationship between the dip angle and strike of the fault zone and the position of the subsea tunnel,a mathematical model was generalized for dynamic water inrush for subsea tunnels crossing water-rich fault zone.By combining the seepage caused by the far-field hydraulic head and the seepage caused by the hydraulic head of the water-rich fault zone,the total seepage flow for subsea tunnels crossing water-rich fault zone was calculated.By utilizing the principle of mirror image method,the potential function for subsea tunnel crossing the water-rich fault zone was determined.Furthermore,simulations of the water inrush evolution process at an engineering scale were carried out,revealing the mechanism of dynamic water inrush for subsea tunnels crossing water-rich fracture zones.(5)To address the issue of subsea tunnel water inrush caused by seismic action during the subsea tunnel crossing water-rich fracture zones,research is being conducted based on the Second Jiaozhou Bay Subsea Tunnel.The engineering geological conditions of the site for the Second Jiaozhou Bay Subsea Tunnel,including topographic and geomorphological features,geological structures,formation lithology,and hydrogeology,have been investigated through literature research and geological surveys.Based on the proposed generalized model and numerical analysis methods for dynamic water inrush in subsea tunnels,this study predicts the amount of water inrush in the Second Jiaozhou Bay Subsea Tunnel crossing the fault zone.It also analyzes the evolution patterns of the stress field and seepage field in the subsea tunnel under different seismic actions.To further control the risk of water influx in underwater tunnels,a refined detection method is proposed through the fusion of multiple geophysical data and joint inversion.An advanced reinforcement plan is suggested to effectively reduce the degree of tunnel structural damage and enhance its seismic safety.Additionally,partitioning drainage measures are proposed based on the internal structural characteristics of the Cangkou fault zone,dividing it into different structural zones for targeted prevention and drainage.This study provides crucial assurance for the safe construction of the Second Jiaozhou Bay Subsea Tunnel crossing the Cangkou fault zone. |
PDF Full Text Request