The Technology Investigation On Pull-out Cone Penetration Test

In recent years,the scale of development and utilization of marine resources has gradually expanded,and the demand for offshore infrastructure and energy facilities has increased.Static cone penetration test(CPT)is the most mature and convenient method in situ test.Because of the complexity of the marine environment,such as rough waves,deep seawater,complex marine sediments,CPT has unstable test data,lack of counterforce and easily breakoff rod problems in practical ocean engineering application.CPT which made in foreign countries is more advanced;in the meantime it needs to rely on large exploration vessel and advanced test technique and it costs too much to purchase equipment and prospect.Pull-out cone penetration test which is proposed by Yangtze River Scientific Research Institute can also reflect the properties of soil by relation curve of pull-out resistance along with depth of stratum.This technique can be used to solve the deficiencies of traditional CPT in offshore engineering.In order to promote the application of the new in-situ test method in practical engineering,the most urgent problem is to find out the mechanical mechanism of pull-out CPT.In this paper,according to the theory and research method of the traditional CPT,put the pull-out CPT as the research object,it founds some rules about the mechanical mechanism of pull-out CPT by theoretical and experimental methods.The main contents and results are as follows:(1)Collect and summarize the development of the equipment,testing technology and mechanics mechanism of CPT.The comparison of the working mechanism of traditional CPT and pull-out CPT provides the theoretical support for the pull-out CPT mechanism study.In meanwhile,make experimental program by referring to the research methods of CPT.(2)Obtain the relation curve of pull-out resistance and relative density of sand or compaction of clay by the model device for pull-out CPT.Analyzed the variation of the relation curve and figure out the relationship between pull-out resistance and density or the degree of compaction.This experiment proved that pull-out resistance has the similar rules with traditional CPT,and the relationship between pull-out resistance and relative density or degree of compaction has a high fitting degree.(3)Obtain the shear strength parameters of the soil used in model test by axial compression test.Matching the shear strength parameters with pull-out resistance can figure out that it has a positive correlation between the pull-out resistance and internal friction angle or cohesive force.(4)Carry out some in situ test,such as traditional CPT,pull-out CPT and pressurement test respectively.Based on the comparison of the relation curves of test metrics along with depth of stratum testing by these three kinds of in situ technologies,it can be found that the variation tendency of pull-out resistance is similar with the metrics of traditional CPT and pressurement test.This conclusion proves that it is feasible to evaluate the properties of soil by pull-out resistance of pull-out CPT.