Karst Hydrogeological Characteristics In The Slope Zone Of The Plateau In Northeastern Yunnan And Its Influence On Tunnel Engineering

The northeast plateau slope zone is located in the transition zone between the Sichuan Basin and the Yunnan-Guizhou Plateau.The terrain is strongly cut,forming a characteristic canyon landform.The carbonate rocks in the zone are widely distributed,and the lithofacies are complex and variable.The karst development characteristics,karst hydrogeological structure,karst water flow system model,karst water source and water-rock interaction in the background are of great significance for engineering construction.Since the implementation of the western development strategy,the construction of railways and highways in Southwest China is in full swing.This zone is the only way to pass through Sichuan,and it is very important to understand its karst hydrogeological conditions and its impact on tunnel engineering.It is especially important for the construction of traffic engineering to provide scientific basis for predicting and preventing karst water inrush diseases.The paper uses hydrological geological survey statistics and analysis method,system analysis method,hydrogeological section method,rock and mineral identification method,gis three-dimensional data extraction method,hydrogen and oxygen isotope method,by referring to the relevant information in the southwest region and combining the special geological environment background of the slope zone.Hydrogeological reversal simulation method,fuzzy mathematics and other technical methods,from the karst development characteristics,clarified the karst aquifer system and karst water flow system in the study area,and on this basis,discussed the tunnel sag under different karst hydrogeology conditions.The problem of water inrush prediction and evaluation,and achieved the following main results and conclusions:?1?According to the macro-geological background of the study area,combined with the development characteristics of karst landform types of each soluble rock group,the main controlling factors of karst development characteristics are analyzed.The karst development intensity and spatial distribution characteristics are affected by lithology and structure.The segmentation effect of the water system is obvious,that is,the influence of the deep cut valley and the shallow cut valley on the development characteristics of karst?2?By analyzing the medium type and spatial distribution characteristics of the soluble rock aquifer group,and according to the karst aquifer group,the characteristics of the aquifer,the geological structure and the karst hydrodynamic conditions,the pure layer is gently pleated and the uniform anticline is multi-layered.Five karst hydrogeological structures and their main features of uniform multi-layered,fractured and anticline-fracture composite multi-layer.?3?The study area is divided into two primary karst water systems,six secondary karst water systems and 14 tertiary karst water systems,and its main features are expounded.The HI value of each basin was calculated by the area-elevation geomorphological cycle theory.The results show that most of the rivers in the region are in strong years.Four kinds of karst water flow system models of deep valley type,shallow cut valley type,deep cut valley-deep cut valley type and around-axis rotation-shallow cut valley type are proposed,and the characteristics of karst hydrodynamic cycle are expounded.?4?The coupling relationship between karst hydrogeology structure and karst water flow system model is analyzed.The results show that when the karst hydrogeology structure is controlled by the deep-cut valley flow system model,it is easy to form a medium type based on the pipeline network,and when controlled by When the shallow valley water flow system mode is adopted,it is easy to form a medium type mainly based on a fracture network.?5?The control effect of karst hydrogeological structure on karst water inrush is reflected in the water inrush mode,while the karst water system model affects the development depth and integrity of karst hydrodynamic zoning,which in turn affects tunnels at different zoning locations.On the basis of this,the main controlling factors of four types of karst water inrush disasters are proposed,including topography,stratum lithology,geological structure and karst hydrodynamic zoning.?6?The calculation method of water inrush under different karst hydrogeology conditions in the plateau slopes of northeastern Yunnan is proposed.The karst hydrogeological structure under the influence of the deep-flow river flow pattern is mainly based on pipeline network medium.It is advisable to adopt non-deterministic method,ie karst The karst hydrogeological structure under the influence of shallow cut valleys is mainly based on the fracture network medium,and the deterministic method should be adopted,that is,the calculation of the water inrush.?7?The groundwater runoff modulus method and groundwater hydraulics method were used to calculate the karst water inrush from the Xiaocaoba tunnel through the T₁y limestone.The normal water inflow was predicted to be 1047.6m³/d and 563.3m³/d,respectively.The fuzzy comprehensive evaluation method was used to evaluate the risk of karst water inrush from the tunnel through the P₁m limestone.The seven stages of predicted hazard levels are IV,I,I,I,I,I and IV.