Study On Nondestructive Testing Technology Of Loess Foundation Treated By Dynamic Compaction Method Based On Rayleigh Surface Wave Method

Dynamic compaction is an economical and effective foundation treatment method for loess collapsibility.The effect of foundation treatment directly affects the engineering quality.It is very important to realize rapid nondestructive testing of foundation construction quality.Rayleigh wave method is a non-destructive detection method,which has been widely used in the field of road engineering quality detection.The correlation between Rayleigh wave velocity in loess and other physical parameters is still lacking.It is intended to adopt dynamic compaction method for foundation treatment in loess area,and then adopt multi-channel transient Rayleigh wave method for rapid detection after treatment.The detected data can be used for quantitative evaluation of the bearing capacity of loess foundation treated by dynamic compaction method,in order to provide reference for similar projects,and also to verify the provisions of the code.The research content mainly includes:(1)Based on the analysis of the strata that may occur in the loess foundation of expressway after dynamic compaction,the theoretical model of the loess foundation with hard upper and soft lower and soft interlayer in the middle is established.By changing different model parameters and using fast vector transfer algorithm,the theoretical dispersion curve is calculated.The influence of parameter change on phase velocity dispersion curve is analyzed.It is found that the change of shear wave velocity has a significant effect on the phase velocity,and the position of the inflection point is closely related to the thickness of the layer.Through the analysis of the dispersion curve,the principle of layering pavement structure and obtaining the velocity of each layer of pavement is explained.(2)By analyzing the configuration of the field data acquisition system of multi-channel transient surface wave method and the influence of the selection of field data acquisition parameters of multi-channel transient surface wave method on the detection results,a set of field working methods of multi-channel transient surface wave method suitable for different exploration requirements is summarized.(3)Before and after the dynamic compaction,several measuring lines were set to detect the surface waves covering all the test areas.At the same time,the measuring points were selected to carry out field tests such as plate load and standard penetration,and to carry out laboratory soil tests on the soil samples obtained from drilling cores.By comparing the increase value and proportion of wave velocity at different depths,combining with the standard penetration hammer number and physical and mechanical parameters obtained from laboratory soil tests,the influence depth of dynamic tamping treatment of loess foundation at different levels was investigated.(4)The regression relationship between Rayleigh wave velocity and the bearing capacity of foundation is established,and the error value and reliability are analyzed.The regression relationship between Rayleigh wave velocity and compacted degree measured by coring was established,and the comparison between Rayleigh wave velocity and compacted degree measured by coring was made to analyze the error value.According to the regression formula to calculate the bearing capacity and compactness,the contour maps of wave velocity,bearing capacity and compactness were drawn respectively,and the uniformity of dynamic compaction treatment was evaluated according to the contour maps.