Study On Geological Characteristics And 3d Geological Modeling Of Xinchang Underground Laboratory Site

After more than 30 years of research in high-level radioactive waste disposal,China has initially identified Xinchang block as the recommended site of underground laboratory.On the one hand,it is necessary to make full use of the existing data to express all kinds of geological phenomena accurately and intuitively to reproduce the spatial distribution of geological units and their mutual relations.On the other hand,it is possible to mine hidden geological information to facilitate geological analysis and engineering decision-making,which is very important in the research phase of underground laboratory.On the basis of fully collecting the existing data,the geological characteristics of Xinchang?focus on the fracture characteristics?were studied in detail by means of supplementary geological survey,comprehensive geophysical exploration,borehole survey,and 3D geological modeling.A three-dimensional geological model of Xinchang URL site was established,and the engineering analysis application was carried out based on the model.The main conclusions are as follows:?1?The strata exposed on the north and south sides of Xinchang block are mainly AnChD,Chxs,J,K₁xn and Q.Among them,AnChD and Chxs Group are the surrounding rocks of the granite in this area.The J and Q are covered on the granite.The body of granite is distributed in EW direction.The granie units from north to South is:Hongliujingnanshan unit?Pt₂²H?gneissic granodiorite,Xinchang unit?O₁X?monzonitic granite,Jijinggou unit?O₁J?granodiorite and Yuanyanggou unit?Pt₂²Y?gneissic monzonitic granite.The total area of the granite unit is about 100 km²,and the average thickness of the rock mass is about 2000 m.The thickness of rock mass increases gradually from west to East and from north to south.?2?The faults in Xinchang area can be divided into three groups:NE direction,NW direction and EW direction.Compressive and compressive-torsional faults tend to strike EW and extend about 2-3 km in depth,which is consistent with the strike of strata.They are large faults with controlled significance in the area,cutting the Mesozoic and its previous strata and rock mass,with multiple periods of activity.Under the control of EW strike faults,tensional and tension-shear fault along NE and NW strike are generated in the Xinchang block,which are the secondary fault associated with EW strike faults.The length of these faults are about 2 to 5 km,and the inclination angle are about 50°to 80°.?3?The Xinchang site is located in the“tectonic safety island”,which is between F6 and F7 in the EW direction,and the clamping sites of the F31,F32,F33,F34 and F32-1.The length of these faults is more than 3km,and the thickness is about0.80³.56 m.The shallow thickness of the fault is relatively large and the thickness gradually decreases toward the deep part.The faults are tensional or torsional in nature,and fault rocks are siliceous,calcareous or argillaceous breccia.The rock above the hanging wall and below thefootwall is intact,and the crack is not developed.?4?Based on the three-dimensional visualization technology,the comprehensive three-dimensional geological model which can truly reflect the deep geological environment characteristics of underground laboratory site has been established.We used the multi-condition constrained geological modeling method and combined the multi-information of surface geological survey,geophysical investigation,borehole exposure and borehole comprehensive survey to build the model.The spatial distribution and interrelationship of faults are mainly described,and the deep extension and morphology of faults are effectively controlled in Xinchang site.?5?A series of visualization analysis applications are carried out by using the 3D geological model of Xinchang rock.Based on the comprehensive consideration of the topography,geomorphology,fault structure,geological characteristics,research purposes,construction difficulty and other factors in the vicinity of the candidate site,a batch of 600 m inclined holes were designed to expose the deep geological characteristics of the fault and the effect seems good.The location and main structure layout of the underground laboratory site were also initially determined.It has practical engineering guiding significance for the subsequent engineering design and excavation of the underground laboratory.?6?According to the characteristics of granite sites and the special requirements of underground laboratory sites on geological conditions,the methods and means used were systematically summarized on the basis of the previous research on the geological characteristics of sites.Based on the key issues such as the scale and integrity of deep rock mass,as well as the fault distribution and characteristics of candidate sites,the evaluation method of geological characteristics of underground laboratory sites is proposed.