Study On The Detection Of The Karst Cave And Its Influence On The Stability Of The Surrounding Rock Of The Tunnel

The development of the karst cave is concealed,often hidden around the tunnel,especially the lower concealed karst cave is the most common,and the greatest impact on the tunnel stability.It is difficult to survey the geological conditions such as the location,shape,size and filling of the lower concealed karst cave,and find the convenient and accurate method to determine the karst cave geological information,and then study the influence of the lower cave on the stability of the surrounding rock.Tunnel safety construction operation is of great significance.The main contents of this paper are as follows:(1)Through the study of the regional geological environment of the study area,the influence of the geological structure,meteorological hydrology and lithology on the karst development in the study area is discussed.It is found that the karst cave is more developed in the study area,mostly limestone,some dolomite and marl,and the large cave is mostly buried.The groundwater system is developed.The karst cave is directly or indirectly connected with the underground river.There is flowing groundwater.Underground dark river rock fissure development,most of the cracks for the mud filling.(2)Through the research on the theoretical method of detecting the karst cave of the geological radar,the geological radar detection model test is designed.The waveform characteristics of the typical geological structure of the karst area are analyzed and analyzed by analyzing the waveform characteristics of the radar reflection profile of the experimental results.(1)the level of one side of the geological radar effective detection range for the target of the largest span(2)underground karst cave in the geological radar reflection wave profile,the initial and the final occurrence of the curve of the vertex position is the top and bottom of the karst cave position.The bottom of the karst cave will appear with the karst cave profile similar to the same reflection of the dark area.(3)After the karst cave is filled with clay,the hyperbolic characteristics of the top of the karst cave are not obvious,but it does not affect the hyperbolic characteristics of the bottom of the hole,and the amplitude of the reflected wave is increased.When the water is filled with water,at the interface between the rock mass and the water,the hyperbolic waves show a strong amplitude emission.The high frequency electromagnetic wave energy decays rapidly and the frequency of the reflected electromagnetic wave changes from high to low frequency.(4)The weak facets are shown as continuous hyperbolic layered interfaces in the radar reflections.(3)The geological radar is detected in the study area,and the radar reflection wave profile is analyzed according to the above research law.The parameters such as the height and span of 39 caves in the study area are obtained by combining the drilling data.The stability of the 39 cave roofs in the study area was calculated by using the empirical formula method.(4)By studying the theory of fuzzy function and combining with the characteristics of karst area,a secondary grading factor classification system is established to construct a fuzzy comprehensive evaluation mathematical model for the stability of tunnel surrounding rock.Through the comprehensive evaluation model,the stability evaluation of the lower surrounding rock of 39 tunnels above the proven area of the study area is verified,which proves that the model has high reliability and reliability.And then the stability evaluation of the lower part of the tunnel in the study area is carried out by using the comprehensive evaluation model.Finally,the stability evaluation results of each section in the study area are obtained.The innovation of this paper is:1)In order to study the law of geological radar detection more accurately,the geological model of karst area is designed and fabricated.Through the analysis of the solid model and the waveform characteristics of the reflected wave profile,the reflection profile of the typical geological structure is summarized Waveform characteristics,with a high degree of credibility.2)By studying the principle of fuzzy comprehensive evaluation and selecting the semi-trapezoidal function as the membership function according to the geological characteristics of the karst area,the membership degree of the index factor is determined by the improved gray relational degree method,and the secondary index factor classification system is established,In this paper,a mathematical model of fuzzy comprehensive evaluation of tunnel surrounding rock stability is established.3)Compare the stability judgment results of the empirical formula method and the stability evaluation results of the fuzzy comprehensive evaluation mathematical model.The two methods evaluate the reliability of the results,and consider the more scientific.