Geometric Defect Detection Of Rock Specimens And Its Influence Of Uniaxial Compression

Uniaxial compression of rock specimens test is one of the basic tests of rock mechanics characteristics.Rock test result is influenced by the precision of rock specimen,mainly including the non-parallel end faces,the verticality of the end face and the axis,and the diameter error.The non-parallel degree of the end surface includes the top surface convexity,the existence of the groove and the partial tilt,and the perpendicularity of the end surface and the axis means the tilt of the end surface and the axis.Developed a measuring instrument for measuring geometrical defects in cylindrical rock specimens.The influence of geometric defects of rock specimens on its mechanical properties was studied through uniaxial compression test and numerical simulation.The main contents are as follows:(1)A geometric defect detector for cylindrical rock specimen is developed based on the Laser displacement sensor.The main measurement principle of the instrument was designed,the design process was introduced,and the hardware of the instrument was designed including the establishment and processing of the SCM control system,power drive system and instrument support model.According to the detection principle of the instrument,the algorithm for calculating flatness and perpendicularity is derived,and the program is programmed,and then the corresponding control and data processing program is developed.(2)The uniaxial compression test of rock specimens with geometric defects was carried out.5 different groups of rock specimens with defects are designed and processed,namely,the middle uplift of the top surface,the eccentric protruding of the top surface,the local warping,the groove of the top surface and the inclined specimen.Uniaxial compression tests were carried out on the processed rock specimen group,and the acoustic emission technology was applied to monitor the failure process of rock,and the acoustic emission characteristics of the specimens with defective rock under uniaxial compression were obtained.The uniaxial compression test results show that the influence of the middle part of the top surface convex defect on the rock strength is larger,the average uniaxial compressive strength of rock as the standard 64%,and the eccentric convex defect of rock uniaxial compressive strength weakened obviously,the average compressive strength as the standard rock 33.8%,uplift failure mode from the specimen group by convex influence,mainly for the convex part of the specimen cracking caused by the formation of wedge failure;local tilt specimen group average compressive strength and standard rock group is close to the failure form and standard of rock is similar to that of the top surface tilting angle is large,the top surface of the sliding surface damage form to the top surface of the lower side overturning trend;top surface groove specimen group,the top and the press in the test head between do not apply lubricating oil to form a ring to the top surface of the hoop force,there is no damage near the top surface groove Tilt;specimen group average uniaxial compressive strength of rock strength as the standard 93.3%,tilt angle is small,the failure mode and the standard of rock is similar to that of large inclination,a larger wedge after the destruction of the middle part of the formation of rocks,extending the bottom and the two rupture is the word "V" shape.According to the data detected by acoustic emission,the acoustic emission events are more dense when the rock is near damage.(3)Numerical simulation of defective rock samples based on RFPA3 D software was carried out.The load is conveyed by loading the cover to simulate the actual loading plate.Three typical forms of unilateral parallelism are designed: the end point of the single point(center or eccentric),the end of the groove and the side of the single side tilt.Different inclinometer rock specimen were designed for the vertical dimension of the end face and the axis.Numerical simulations show that: when raised part exist in center,the raised part forms a dense core,it shows wedging effect when the raised part is higher.when raised part exist in one side,Rock samples show eccentric shear.Stress concentration and produce local damage occurs on the cocked side.When groove exist in center,the stress of the rock specimen is shifted.Stress concentration occurs on both sides of the groove,when the groove diameter is larger.