Geohazard Assessment And Construction Controlling Technology Study Of High-risk Krust Tunnel

As a common of geological disasters, Karst has produce great harm during tunnelexcavation process. Based on the high-risk karst as the object of study, through fieldinvestigations, theoretical studies, laboratory experiments and numerical simulationsthe development pattern and risk assessment of karst, karst disaster research andconstruction influence, different types of karst disaster control and so on were studied.(1)On the bases of engineering and hydrogeology survey in the study area, find outthe route area landform, stratum lithology, structure unit, and divided the whole routeinto three hydrogeology unit, according to the distribution and the history of the karst,and characteristics of groundwater. The karst development is most obvious of which isI-1-2Daguan water unit, I-1-3Dazhai water unit and II-1-3Shuoluohe water unit,most of them are development in P Maokou Formation and T in Jialingjiangformation.(2)According to surface karst features and excavation exposed in the karst tunnelarea, Xuda railway engineering’s karst geological hazard was caused by suddenlykarst water and karst caves instability. On the foundation of karst developmentfeatures of the tunnel and karst geological hazard category five classification system,and by doing risk level prediction and evaluation to the whole line of the main karsttunnel, we can conclude that Xianrendong and zhongba tunnel is high karst risktunnels.(3)Through the study of karst geohazard development regulation, the cave which tobe detected is filled with mud in vertical direction. According to the features of thistype of karst geohazard, and analyzed the adaptability of different detection methods.①Tunnel Seismic Prediction(TSP) detection range is long and it can distinguish themacro risks, but cannot distinguish crushing and intercalated gouge in low velocityzone;②Ground Penetrating Radar(GPR) detection range is short and the rear of thereflector is unreliable, but the first reflection interface is clear.③Radon measuring method on the ground detection range is wide and the effect isacceptable, but affected by the weather condition and karst extension directionobviously. (4)Using forward modeling, inversion interpretation and excavation validatedmethods to study different scale, shape and filling material in vertical mud-filling cave,and including the following several parts:①By forward modeling method, building model to obtained reflection graph fordifferent scale vertical mud-filling cave, and proposed by using a two positive andone negative reflected wave to determine the top of the karst cave boundary, andadopting the sidewall multiple interference method and radius of curvature method tojudgment the scale of the karst cave;②Collect data on the spot, through the inversion of the frequency, wavecharacteristics to determine the filling material, and forward simulate common sceneempty karst cave covered with mud in the spot to empty karst cave to compare theresponse feature of the both, and from the reflection type, frequency and energy threeaspects to compare it.(5)On the basis of summarize the type and category of the karst cave filling material,and according to the actual condition of the Xianrendong tunnel, we calculate that thesafety thickness is over3.5meters. In the study of various types of support measuresand their combination effect, using the umbrella arch, steel pipe shed, and small ductto joint support the large mud-filling cave. After validate near construction to otherconstruction that is adjoin the karst cave,we prove that if the cave of Xianrendongtunnel is proceed in integrity rock, the effect to the above Xihu tunnel is less, but oweto the existence of the karst system, causing the deformation and cracking.(6)Through the analysis of concealed karst cave of underground river tunnel, andaccording to the theory of beam bending, shearing estimate, and combined with theactual operation load of the Xianrendong tunnel.According the conceal river’s featurerevealed by Zhongba, putting forward the Release power and reduce pressure,grouting reinforcement and comprehensive treatment treatment measures.