Chemical grouting has been widely used to ensure the stability and durability of built structures by enhancing the engineering properties of soils. The objective of this study was to investigate the effect of a newly developed acrylate-cement grout, composed of component A (acrylic polymer, catalyst, and hardener) and component B (cement) having mixing ratios varying from 0.5% to 2% of the total weight, on the unconfined compressive strength of silty sand. Three series of laboratory tests (gel time, expansion ratio, and unconfined compression strength) were carried out on reconstituted soil samples with a void replacement ratio of 80% and 100% by acrylate-cement grout. The results showed that the optimum cement ratio of the chemical grout was 1.5% based on the unconfined compressive strength and the elastic modulus for the silty sand with grouting.

Even a small amount of settlement is critical in the operation of high-speed railways. Recently, in Korea, additional settlement was observed at many sites of high-speed railways after the construction of concrete tracks including sites where ground improvement methods were applied. Among 1,118 observing sites, 95 sites experienced the settlement exceeding the control limit of high-speed railways. The present work described factors causing additional settlement in high-speed railways. Geological features, embankment height, layer thickness, ground improvement method, groundwater drawdown, compaction of frozen soil, and dynamic loading by train operation were selected as the potential factors of the additional settlement. Analysis results showed that high settlement was measured in concrete tracks that were constructed over alluvium and biotite granodiorite layers (85.76%) and the settlement increased according to the increase of the embankment height and the thickness of the subgrade layer. In 92.63% of high settled sites, a sudden increase of settlement caused by groundwater drawdown was observed during the dry season as well. Also, compaction of the embankment during winter and dynamic loading by train operation increased the settlement to a certain degree.

In South Korea, Honam High-Speed Railway has a relatively large residual settlement issue and high fines content has been pointed out as one of the causes. Design guidelines regulate not to use soils containing fines content higher than 25%. However, there is no background information on the effect of fines content on settlement. Therefore, this paper aims to investigate compressional behavior according to fines content using sand and kaolinite. Oedometer test results showed that the compression index is lowest with fines content of 15% to 20% at which the mixture produced maximum density. The optimum fines content for inducing low settlement would be 15% to 20% for the sand–kaolinite mixture. Transition fines content (TFC), which shows sand-like to claylike behavior, was observed to have between 21% and 26% of fines content. Critical fines content (fcrit) where a minimum void ratio occurs was estimated as 21.67%. These behavioral changes appear when fines content is greater than the optimum fines content. SEM also shows that the kaolinite particles were overlapped, creating flat surfaces with a fines content higher than 30%, and showing clay-like behavior. Based on the analysis results, engineers can simply identify the behavior of embankment materials to ensure optimum fines content and consequently minimize long-term settlement potential.