Experimental Study On The Rapid Acquisiti On Of Rock Strength Based On Self-made Portable Point Load Instrument

The point loading index(PLI)has a unique advantage which can determine the uniaxial compressive strength(UCS)of the rock indirectly.Based on the demand of the quick acquisition of rock strength and the parameters of rock mass structure in-situ,a unique in-situ point load portable instrument was innovated in this study.Combined with the experimental research,theoretical analysis and engineering application,a series of tests which is aimed at the common igneous rock,metamorphic rock and sedimentary rock,were conducted to obtain the corresponding uniaxial compression strength by the point load test of the irregular specimens in the field.Firstly,as summarized at the beginning of section 2,the author introduced that the existing rock point load instrument cannot meet the requirements of the portable and intelligent field test instruments.Several improvement ideas were investigated,and multi-functional portable point load device design was completely designed.Including the frame system,loading system,measurement system and electrical integration.Secondly,many researchers have investigated the relationship between PLI and UCS through various rock types with different sizes.It is found that the current research results are limited by four factors,such as anisotropy of rock materials,data fuzzy correspondence,heavy equipment and lack of experimental verification.In this study of section 3,we used point load portable instrument for isotropic rock-like material,for different grade,different sizes,one to one correspondence of point load index and the corresponding relations between uniaxial compression strength test researches.It is proved that the principle of size effect can be used to establish the correlation between point load strength index and uniaxial compression strength.At the same time,the irregular point load test of quartz schist,diorite and marble is carried out.The experimental data is subject to normal distribution,and the size effect can be used to unify the standard equivalent size.Using statistical analysis method to establish the related transformation formula,the result indicates the feasibility of homemade portable rock point load instrument.Finally,combining with the New Jing-Zhang Railway tunnel project in Badaling.In the section 5,according to the selection of irregular specimens,the uniaxial compressive strength of different rocks were rapidly measured and estimated in-situ through self-made portable point load instrument.Test results show that,the experimental data can provides reference for classification adjustment and engineering design change of surrounding rock.