Study On Evaluation Method For Compaction Quality Of Continuous Compaction Control Of Railway Subgrade

As is the foundation of track structure, the subgrade is supposed to provide a more smooth and stable support for the upper structure of the high speed railway. The construction quality of the subgrade plays an important role in the structural performance of the subgrade-track system. The roller-integrated compaction measurement is capable of monitoring the compaction quality of the whole compaction layer in the real time. During the QC/QA of the subgrade, besides the selection of the fillers and control of the vibration parameters, the accurate evaluation of the compaction quality is significantly important for quality assurance.Although the existing specification has made regulation for subgrade compaction quality control standards and quality assessment.Thus there are some limitations when applying the traditional specification in practical engineering, the quality of the foundation filling could not be appropriately controlled. In order to control the compaction quality more reasonably, the study on developing a systematic continuous compaction quality evaluation is still a new issue.In this paper, based on tests in Loudi, Shaoshan, Zhijiang of Shanghai-Kunming high-speed railway, the applicability of the foundation compaction quality continuous detection is verified through field tracing and analysis of theoretical model in this trial.And based on this, through quantitative studies on the influence factors and detection depth of compaction quality continuous detection, new method for correlation check and compaction degree evaluation is developed. The innovative research results could be concluded as follows:(1)Before the continuous check on High-speed railway subgrade compaction quality, the applicability of compaction quality continuous detection is verified by trial in Shanghai-Kunming high-speed railway of Hunan section.The results show that the stability of the compaction quality testing equipment, the sensitivity of the compaction quality continuous detection index and the accuracy of test results all meet the requirements.(2)Concerning the previous studies which could not quantitatively analyse the vibratory compaction technology parameters on the influence degree of continuous compaction measured value, the vibratory compaction technology parameters are taken as the factors; the orthogonal experiment for the analysis of variance is carried out, which quantifies the influence degree of the amplitude, excitation frequency, roller speed and driving direction on CMV. Through the variation of CMV, the combination of the vibratory compaction technology parameters which makes sure the stability of continuous compaction measured value is determined. Based on the steady-state CMV,a regression model is established to correct the CMV under the condition of the other vibratory compaction technology parameters.(3)By setting the CFG pile foundation and coarse-grained soil foundation, the check depth of vibratory roller is studied according to comparisons between the variation of each filling layer between CFG pile foundation and coarse-grained soil foundation and analysis on the result of the correlation verify on the CFG pile foundation. By setting pressure boxes in the coarse-grained soil foundation, the effective influence depth of vibratory roller is analyzed according to the trend of earth pressure of each filling layer. The results show that the check depth and the effective influence depth of the vibratory roller is about 1.5m.(4)Concerning the deficiency on correlation verify and the differences in detection area between continuous check and regular check about compaction quality in the<Technical Code for Continuous Compaction Control of Fill Engineering of Railway Earth Structure>, new linear fitting for correlation verify is suggested corresponding to the angle of the check area. And the correlation verify trial based on test in Shanghai-Kunming high-speed railway Zhijiang test section verifies the applicability and superiority of new linear fitting and the precision of correlation verify compared with the point to point fitting in the code.(5)Concerning the existing compaction degree indicator that do not consider the effect of weakness area and discrete spatial distribution on the evaluation result, the area effect coefficient are determined, and the spatial distribution coefficient based on the nearest neighbor distance method, the comprehensive evaluation index is suggested to evaluate the compaction degree.