Research On Rapid Testing Technology Of Subgrade Construction Quality Based On PFWD

Subgrade construction quality is one of the important factors affecting the long-term performance of pavement structure.At present,deflection,compactness and resilient modulus are the main control and acceptance indexes of sub grade construction quality in China,but there are some shortcomings in the traditional testing methods.For this reason,relying on the construction project of Chang-Lin(From Changzhi to Linfen)Expressway in Shanxi Province,the thesis will carry out a comparative research between PFWD(Portable Falling Weight Deflectometer)and other conventional testing technologies for establishing their corresponding correlations to test and evaluate the subgrade construction quality in rapid and reliable way.1)According to the actual situation of the support project,the soil tests about subgrade filler were carried out.The results show that both the plain soil and the lime soil meet the requirements of performance and bearing capacity in the relevant technical specifications.2)The characteristic analysis of the PFWD device show that,compared with the traditional methods,the PFWD test method is more rapid,reliable,convenient and economic etc.When the PFWD is applied to the site rapid test of subgrade construction quality,the repeated test times should generally be controlled within 3 groups at the same testing point.Otherwise,the variation coefficient is too large due to the uneven compaction of sub grade,which makes the test results unstable.Meanwhile,the influence depth of impact load of PFWD meets the control requirements of compaction layer thickness.3)Through the correlation analysis of test results of deflection between the PFWD,the Benkelman Beam and the FWD show that there are good correlations of power function between all kinds of deflection.The correlation of deflection tested with the PFWD 10kg hammer is more obvious,which can be used as a rapid testing and evaluating index of deflection for the subgrade construction quality.Through the correlation analysis of modulus between the PFWD,the bearing plate,the Benkelman Beam and the FWD show that there are good correlations of power function between all kinds of modulus,and all the correlations are obvious.The results indicate that the PFWD modulus can be used as a rapid testing and evaluating index of modulus for the subgrade construction quality.The correlation analysis between the PFWD modulus and the compactness of sand replacement method show that there are obvious correlations between the PFWD modulus tested with 15kg hammer on the plain soil subgrade or 10kg hammer on the lime soil subgrade and the corresponding compactness respectively,which can be used as a rapid testing and evaluating index of compactness for the subgrade construction quality.4)According to the evaluation standards of deflection and compactness of subgrade construction quality,the above empirical formulas were applied to convert and obtain the corresponding control standards of the PFWD test indexes.The standards were applied to the subgrade construction control in the support project.The results show that the PFWD can effectively test and evaluate the subgrade construction quality in rapid and reliable way.In conclusion,the research results in the thesis can provide a scientific reference for the popularization and application of the rapid test technology of subgrade construction quality based on PFWD.