Study on mechanical properties and compaction quality evaluation of gravel soil subgrade based on impact load method
LI Mengwei1，2，LU Zheng1，TANG Chuxuan1，2，HU Zhi3，CHAI Shaoqiang4，LIU Yong4
(1. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，China；2. University of Chinese Academy of Sciences，Beijing 100049，China；3. Key Laboratory of Road and Bridge Detection and Maintenance Technology Research of Zhejiang Province，Zhejiang Scientific Research Institute of Transport，Hangzhou，Zhejiang 310023，China；4. No. Seven Engineering Co.，Ltd. of CCCC First Highway Engineering Co.，Ltd.，Zhengzhou，Henan 451450，China)
Abstract：The impact loading method is an approach to evaluate the compaction quality of subgrade by applying impact forces and analyzing the resulting response signals. Studying the response mechanism of gravel soil subgrade under impact loading helps to deepen the understanding of the mechanical properties of such subgrades，as well as enhance the comprehension of the principles behind evaluating subgrade compaction quality using impact loading methods. The real working condition of gravel soil sungrade was fully considered，and a dynamic response model for gravel soil subgrade under impact loading was established using the discrete element method. The model parameters were calibrated through triaxial tests，and the model's validity was verified by field experiments. Subsequently，the attenuation characteristics of dynamic stress in the subgrade under different compaction densities were explored and compared with the results obtained from continuous medium theory. A quantitative model relating porosity to the resilient modulus was further developed. The variations in surface response of the subgrade with changes in its properties were analyzed，and finally，the effects of different impact loads amplitudes and plate radius on the effective detection depth were discussed. It is found that：(1) porosity significantly affects the attenuation of internal dynamic stress in gravel soil subgrade，with faster attenuation observed at lower porosity levels；also，the dynamic stress obtained using continuum medium theory is generally lower，with a maximum difference of over 70%；(2) there is a good linear relationship between porosity and resilient modulus of gravel soil subgrade，validating the feasibility of using the impact loading method to evaluate subgrade compaction quality；(3) the plate radius has a significant impact on the effective detection depth of the impact loading method，with effective detection depths within 0.3 m for plate radii of 0.15 and 0.2 m，and between 0.3 and 0.4 m for a radius of 0.25 m.
