Study On The Statistical Law Of Shear Characteristics Of Rock Mass Discontinuities Based On The Number Of Effective Samples

Natural irregular structural planes are widely distributed in the engineering rock mass,causing the discontinuity,anisotropy and non-uniformity of the rock mass,and affecting the strength and stability of the engineering rock mass.The shear characteristics of rock mass structural plane is an important factor affecting the stability of engineering rock mass.This paper conducts research on the statistical law of the shear strength of structural planes at a series of scales,combined with the PFC2 D numerical simulation software to statistically analyze the size effect change law of the shear characteristics of rock mass structural planes.It also evaluates the selection of representative samples of structural planes from the perspective of quantitative and qualitative analysis.The main contents and conclusions are as follows:(1)As there is lack of reasonability on determining the number of samples required for statistical measurement of structural surface roughness coefficient(JRC),a method for determining the number of effective samples required for statistical measurement of structural surface roughness coefficient based on the principle of simple random sampling is proposed,and the number of effective samples required for statistical measurement of structural surface shear specimens is determined by this method.Taking the natural slate structural surface in Changshan County as the research object,it is found that the number of statistical measurement samples corresponding to the series-scale structural surface is different,and the effective sample number will decrease as the sample size increases.This research method can improve work efficiency for engineering rock mass measurement,and is of great significance for the accurate acquisition of structural surface mechanical parameters.(2)As it is difficult to carry out multiple tests on natural irregular structural planes,a numerical calculation model for direct shear tests of rock mass structural planes is proposed.The meso-parameters of the calculation model are calibrated according to the macro-mechanical parameters obtained from laboratory experiments.Use the obtained mesomechanical parameters to establish a direct shear model of the rock mass structural plane.Taking the dynamic shearing process of a 10 cm structural plane as an example,it is found that many cracks appear around the joint during the loading process,and they are mainly concentrated in the joint bulge.According to the development process of cracks,it can be roughly divided into three stages,namely,stress growth zone,stress reduction zone and stress stable zone.At the same time,the correlation analysis between the shear strength and roughness of the structural surface is carried out,and the peak shear strength of ten groups of natural irregular structural surfaces and the fluctuation of the JRC curve can be found.JRC is consistent,indicating that PFC2 D can visually and clearly show the shear characteristics of rock joints,and can better predict the shear strength of joints.(3)To study the influence of size on the shear characteristics of rock mass structural planes.Combined with the PFC2 D numerical simulation software,the direct shear test of the structural surface under a series of sizes was carried out,and the distribution law of shear characteristics of rock mass structural planes was obtained.The distribution of shear characteristics of structural planes of the same size shows that the peak shear strength,shear stiffness and peak shear displacement of the structural planes all approximately obey the normal distribution,and have a certain degree of skewness.The overall appearance is a positively skewed distribution with the tail lengthening to the right.The distribution law of the shear characteristics of a series of size structural planes shows that there is an obvious size effect in the shear characteristics of the structural plane.The specific manifestation was: as the sample size increased,both the peak shear strength and shear stiffness of the structural surface decrease,while the peak shear displacement increases.Then,the empirical formula for the shear strength of rock mass discontinuities to inversely calculate the JRC value,and compare and analyze it with the JRC of the original rock discontinuity.Observing the changing trend of the two under the series size,we can see that the numerical simulation results are in good agreement with the engineering measured results.(4)In order to study the sampling location of representative samples of rock mass structural planes,a representative evaluation method of structural plane sampling using shear strength and roughness coefficient is proposed as the research method respectively.The selection of representative samples of structural planes using shear strength as a research method is mainly through quantitative analysis by Dice similarity measurement method to screen out the most representative samples.The representative evaluation of structural plane sampling using roughness coefficient as a research method can be realized by Dice similarity measurement method and multi-attribute decision-making method based on linguistic cube hesitant fuzzy sets(LCHVs).For structural surfaces with good exposure conditions,quantitative analysis can be performed by Dice similarity measurement method to determine representative samples of structural surface roughness coefficients.In view of the complex geological environment,the multi-attribute decision-making method of LCHVs can be used to qualitatively analyze the surface undulations of multiple sets of structural planes to determine the most characteristic structural plane samples.This research method can provide a reference for the selection of representative samples of structural planes during actual engineering site measurements.