| The Danxiashan Global Geopark is famous for its landform and landscape of "colors like Lilium concolor Salisb,as bright as the clouds ".The formation is based on the red clastic rocks of the Late Cretaceous Danxia Formation,which is several kilometers thick,gradually formed erosive landforms characterized by red cliff landscapes.The determination of the mechanical strength index parameters of the stratum rock mass is of great significance for the calculation and analysis of the stability of the dangerous rock mass in the scenic spot and the safety evaluation of the tourist routes in the scenic spot.In this paper,the dangerous rock mass of Danxia Mountain is taken as the research object,and the correlation between the strength index parameters and the rebound number is studied by using an N-type Schmidt hammer with an impact kinetic energy of 2.207 J.The in-situ rebound test and sonic velocity test of sandstone,conglomerate,and glutenite rock bodies of the Bazhai and Jinshiyan sections exposed in the Late Cretaceous Danxia Formation in the Danxiashan Global Geopark were conducted.The indoor mechanical strength test was carried out for drilling and coring the rock mass at the in-situ test point.The correlation between rock mass rebound value and strength index was analyzed by fitting exponential and linear functions,and the relationship with the highest fitting correlation was selected as the basis for quickly and nondestructively measuring the strength index of dangerous rock mass in Danxia Mountain landscape using a rebound meter.The conclusions reached are as follows:(1)Conduct on-site investigations and review of relevant materials,analyzed the causes and influence factors of dangerous rock masses.The development of dangerous rock masses in the scenic area is mainly affected by joint cutting,differential weathering,unloading,gravity and flowing water.There are differences in material composition and cementation form among sandstones in different regions of danxiashan,which leads to different rock strength indexes of the same lithology.(2)Through the field rebound test,the relationship between the rebound value of the rock mass and the number of bounces was analyzed,and it was found that the curve of the rebound value of the Danxia rock mass and the number of bounces showed an increasing trend of fast first and then slow,and finally stabilized.The rebound values of sandstone,conglomerate,and glutenite in the study area ranged from 31.3 to 40,22.4 to 38.4,and 26.4to 41.5,respectively.(3)Through the mechanical strength test of the rock mass,it is concluded that the compressive strength range of the rock mass in Danxiashan area is 6.84 MPa to 56.00 MPa;the tensile strength ranges of sandstone,conglomerate,and glutenite are 0.21 MPa to 0.77 MPa and 0.48 MPa to 0.69 MPa,0.48 MPa to 0.77 MPa.(4)By comparing the results of in-situ tests and laboratory tests of rock masses,it is found that the changes in the strength index parameters of the rock masses in Danxia Mountain are similar,and the conglomerate and sandy conglomerate of the Jinshiyan section<Bazhai section < The trend of conglomerate and glutenite in the section <Bazhai section>.(5)By analyzing the correlation between the rebound value and the strength index of the landscape rock mass,the linear and exponential functions are used for fitting analysis.The wave velocity of the rock mass is linearly related to the rebound value,and the compressive strength value of the rock mass and the rebound value It has a linear correlation with a correlation coefficient of 0.87.By comparing and verifying with the formula given by the predecessors,it is found that the formula given in this paper is more accurate.Danxia Mountain sandstone and conglomerate's tensile strength value and rebound value have an exponential and linear correlation,respectively.It is more scientific and reasonable to use the rebound value to determine the strength indexes of the rock mass. |
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