The Application And Study Of Geophysical Methods On Testing Superficial Fractures At Yungang Grottoes

China has a long civilized history more than 5000 years. Yungang Grottoes isimprinting and witness of historical track that Buddhism had been spread to the east.It embodies the process of nationalization and secularization about Buddhism Statuein China, it is a beginning of grottoes art with Chinese characteristics, and it is themost valuable historical and cultural heritage. Under the influence of different variousnatural and human factors, grottoes and statues have been affected very seriously bycomplicated and various diseases, especially the rock fractures with differentdevelopment degrees, cross-cutting and transfixion, which do not create conditions offormation and aggravation for other diseases, but also will directly affect the integrityand stability of the stone relics. There is an important practical significance to carryout protection research, repairing and strengthening based on the comprehensivedetection about superficial fracture disease of the rocks and the distribution charactersthrough nondestructive testing.In the paper, through indoor simulations, ultrasonic method and groundpenetrating radar were used for qualitative analysis and quantitative calculation aboutthe depth and width of the regular simple single fracture model, according to finitedifference, forward modeling with Res2dmod simulation software had been donethough contributing fracture models with different sizes, the anomalous character anddistribution regularity about different size fractures were known through the modeltest and forward modeling in the different geophysical fields. On the basis of indoorsimulations, comprehensive test and study on the superficial fractures of sandstoneoutcrops was mainly carried out by geophysical methods which combined with othernondestructive testing methods, qualitative and quantitative analysis about differentfracture indexes were finished at Junzhuang, Beijing. As a guide, comprehensive testusing the same methods for the superficial fractures with different developmentcharacteristics and scales had been done according to the test conditions at YungangGrottoes. The anomalous character and distribution regularity of fractures werequalitatively analyzed, and the fracture indexes about width, depth and others were quantitatively analyzed based on the test results. For the purpose of test, ultrasonicmethod, micro-electrodes resistivity method and ground penetrating radar wereapplied for testing the grouting fractures, and the effect of strengthening wasevaluated through comparing and analyzing the differences of abnormality.Objective analysis and evaluation on various nondestructive testing methodsfrom different aspects, ultrasonic method has obvious advantages on detectingfractures and grouting effect, there has relation between the amplitude of abnormalchanges and depth of fracture. For greater measurement error that caused by the affectof grounding resistance, inversion results of micro-electrodes resistivity method cannot reflect fracture abnormality well. The hyperbola abnormality of fracture can bereflected through ground penetrating radar, and the strength of reflection signal hasrelation with the width of fracture. Quick testing methods can quantitatively measurethe geometric parameters of fractures conveniently and fast. In contrast, close-rangephotography method does not only automatically figure out geometric parameters toreconstruct fracture after image processing, but also complete three-dimensionaldescription of fractures combined with their depth, which is a non-destructive testingmethod with great potential. The detection scheme and method system have beeninitially established on the basis of scientific classification about non-destructivetesting method and technology, which can provide technical basis for fracturedetection and grouting effect evaluation on the surface of stone relics.