Research On Dynamic Characteristics Of Impact Compaction On Silt Subgrade And Mechanism Analysis In The Yellow River Flood Area

The subgrade was one of the important components of the road, which bore the load transferred from the road. The uniformity and stability of the subgrade directly affected the performance of the road. Effective compaction could obviously improve the strength and stability of the subgrade. At present, vibrating compaction or static compaction was often used for the subgrade compaction. This compaction method had the advantages of uniform compaction and easy control of compaction quality. But its compaction energy was small, thickness allowed of the layer was small and construction efficiency was slow. It was not applicable to the engineering with short construction period. The soil in the Yellow River flood area was mainly silt and silt clay, whose pore ratio was large, moisture content was high, compressibility was large. How to compact quickly and effectively was a key and difficult problem.. Impact roller compaction was more and more applied in road engineering because of its large compaction energy, high construction speed, high compaction efficiency, low cost, larger range of moisture content allowed and the soil below the compaction layer was still reinforced.Impact roller compaction started lately and it was applied to subgrade construction especially less in the Yellow River flood area. The dynamic stress propagation law, the reinforcement mechanism and the influence scope of the impact roller compaction was not yet clear, which had seriously affected the deep research and development of the technology. Relied on Jinan-Dongying expressway in construction, the soil properties of the subgrade filling material in the Yellow River flood area, the compaction effect, the dynamic stress propagation law and the reinforcement mechanism was analyzed through laboratory tests, field tests and numerical simulation. The main conclusions were as follows:(1) Through the comparison and analysis of the impact compaction effect of 4 kinds of silt soil subgrade with different loose paving thickness, it was obtained that impact compaction of silt soil was used for embankment area, but was not used for roadbed area, and applicable range of moisture content could be relaxed appropriately. According to different loose paving thickness, that the compaction degree increment of the final 5 times was less than 1% corresponding to the compaction times could be as effective compaction times.(2)According to the principle of economic efficiency, the process parameters of impact compaction on subgrade applied to the Yellow River flood area recommended for the YCT-25 type impact roller:The optimum loose thickness was 0.8m. The moisture content range allowed was ωop-5%≤ω≤ωop+4%. The optimum rolling speed was 10-12km/h. The optimal rolling pass number was 20.(3) The impact load was Instantaneous. The dynamic stress produced by two successive impact was not superimposed obviously. The peak value of dynamic stress had hysteresis along the depth direction. The peak value of dynamic stress at certain depth of the roadbed increased first and then decreased in the process of impact compaction on loose subgrade. The dynamic stress on both sides of the impact point at any depth was approximately symmetrical along the longitudinal direction. The dynamic stress at the front of the impact point was greater than the dynamic stress after the impact point. The vertical dynamic stress, the lateral dynamic stress and the vertical displacement of the soil varied similarly along the depth, and there were obvious inflection point of them. The inflection point of the same variable was basically the same. Based on the above, a simplified model of dynamic stress distribution in soil when impact compacted was presented. The theoretical influence depth was about 3.7m and the radial effective range was about 1m for the YCT-25 type impact roller.(4) The impact compaction process of silt soil could be divided into 4 stages from the macroscopic perspective. It was loose soil stage (absorbed energy)â†'dense soil stage (transfer energy)â†'plate formation stage (diffusion energy)â†'plate down stage (loose zone thickening); It could be divided into 4 stages from the microscopic perspective. It was inputing dynamic load, vibration propagation and medium motion.The research results could provide practical engineering data for the establishment of the relevant standards and norms of the impact roller compaction on subgrade, provide the basis for the process parameters selection of the impact roller compaction on the silt subgrade in the Yellow River flood area, contribute to the theoretical research and development of the impact roller compaction, had significant engineering significance, social and economic benefits. The prospect was very broad.