Effects of Aggregate Particle Size on the Pavement Performance of Improved Filler Soil

In the context of sustainable civil infrastructure development, the reuse of waste soft soil with high moisture content as engineered fillers presents both environmental and economic advantages. However, critical technical challenges exist during the stabilization and modification processes of waste soft soil, i.e., a large number of soil aggregates with diameters much larger than 10 mm and difficult to sieve are prone to occur, thereby which seriously hinders its large-scale and efficient application as a filling material resource. To overcome this limitation, this study investigated the feasibility of expanding the particle size of aggregates in improved filler soil during the modification process. A series of laboratory tests were carried out, including the unconfined compressive strength test, water stability test, California bearing ratio test, and resilient modulus test, to investigate the influence of soil aggregate particle size and curing agent dosage on the road performance of modified filler soil. Based on the experimental results, a calculation formula for the theoretical dosage of curing agent required for the preparation of improved filler soil with the target particle size aggregates was derived, which provided theoretical reference values for the mix proportion design and optimization of modified filler soil in engineering applications. At the same time, pilot tests were conducted to simulate the on-site conversion of a large amount of waste soft soil into modified filler soil under actual working conditions, and the operation effect and application potential for the filler pilot system were evaluated. The laboratory test results indicate that the increase in the maximum particle size of the aggregate will have a negative impact on the road performance of the improved filler soil. To ensure the road performance of improved filler soil, the maximum particle size of aggregate can be appropriately expanded by controlling the dosage of curing agent. If the maximum particle size of the aggregate is expanded to 25-30 mm, the dosage of curing agent is recommended to be controlled at about 4%. Under higher dosage of curing agent, the maximum particle size of aggregate should be controlled at 20 mm below. According to the derived formula, it is calculated that when the soil was completely wrapped by the curing agent, the theoretical dosage of the curing agent required when the maximum particle size of the aggregate is expanded to 15, 20, 25, and 30 mm is 6.63%, 5.87%, 5.10%, and 4.13% respectively. These values exhibit a high degree of consistency with the results obtained from laboratory test. The pilot test results demonstrate that the filler pilot system can effectively improve the production efficiency and is suitable for handling large quantities of waste soil materials on site, exhibiting better adaptability for larger particle size aggregates. Although samples produced via secondary lime mixing treatment of waste soft soil with high moisture content using the filler pilot system show lower CBR and rebound modulus values than those produced by manual mixing treatment, they can all satisfy the specification requirements. In conclusion, the study suggests that when improving waste soft soil with high moisture content through secondary lime mixing under the premise of meeting the specifications of subgrade fill materials, appropriately relaxing the particle size of aggregates sieving and optimizing the dosage of curing agent in combination with theoretical calculation can significantly enhance the treatment efficiency of waste soft soil and the production capacity of soil materials, which can provide a reference for the application of improved fill soil in engineering practice.