Research And Development Of Borehole Shearing Test Equipment And Test Application

Drilling sampling and laboratory test is an important way to obtain the shear strength index of underground soil in the field of geotechnical engineering investigation in China.The weakness of laboratory test relative in-situ test led the researchers focused on development of the shear strength in-situ test method.Among all in-situ shearing test,the borehole shear test is one of the important methods.This method upon launch was brought to the attention of the relevant researchers,but the application of this method in our country is still in its infancy,in view of the test method,test principle and test equipment is less,besides our country related specification is not covered.Based on the Mohr-Coulomb strength criterion and the basis of summarizing the relationship between yield and destruction of soil,the theoretical foundation borehole of the soil shear failure in borehole shearing test is established through a point in the soil shear stress limit equilibrium.According to elastic theory,analysis of borehole shear test of drilling bit and the shear cutter tooth stress state of soils,show that the shear failure is located near the borehole wall.According to the borehole shear test method and the existing research results,summarizes the parts and components of borehole shearing test equipment.Based on the specific conditions of geotechnical engineering investigation in China,borehole shear equipment is processed,after assembly and test shows the applicability of the equipment.According to indoor direct shear test rules at the same time,combining with the existing study,suggest borehole shear test procedures and related parameters.On this basis,borehole shearing test was take respectively in gongyi pingdingshan and indoors field,after that the site soil was sampled and used in indoor direct shear test.The test and study show that borehole shear test can effectively carry out,test result is believable in well holeformation conditions.Meanwhile the linear correlation coefficient of shear strength is relatively high than indoor test in a relatively homogeneous at the same time complete smooth borehole wall condition.The borehole shearing test shear force changes with the shear process grows slowly in initial stage and growth expand in medium-term,later growth decrease and slightly drop after peak.The whole process is similar with indoor direct shear test.Test results show that the correlation coefficient of shear strength of borehole shear test is bigger than laboratory test and shear strength index is smaller.Among the index the internal friction angle is more close to the index from indoor direct shear test.Overall study shows that the borehole shear test compared with traditional shear testing method is more rapid,efficient,clean and has a higher correlation,So borehole shearing test has a high applicable value in engineering testing field.