# Applicability Study on Modified Argillaceous Slate as Subgrade Filling for High-Speed Railway
###### Abstract
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Additives** & **Reference** & **Findings** \\ \hline \multirow{4}{*}{Cement kiln dust} & [9] & CKD can be an effective additive as it improves soil strength significantly \\ \cline{2-3}  & [1] & (1) \\  & (2) & Adding CKD decreases the swelling ratio. \\ \hline \multirow{4}{*}{Lime and cement} & [10] & (1) \\  & (2) & Adding CKD reduces the cost of pavements by USD 25.875 per square meter. \\ \cline{2-3}  & [12] & (1) \\  & (2) & Addition of lime/cement has noticeable impact on the geotechnical, textural and mineralogical characteristics of mountain soil. \\  & (2) & Satisfactory strength can be achieved with the addition of 5\% additives to the soil mixture. \\ \cline{2-3}  & [11] & (1) \\  & (2) & The mechanical properties of the modified filler are greatly improved. \\ \cline{2-3}  & [11] & (2) \\  & (2) & There is the best mixing ratio. \\ \cline{2-3}  & [12] & (1) \\  & (2) & Hydraulic and mechanical properties were improved. \\ \cline{2-3}  & [13] & (1) \\  & & the unconfined compressive strength of cement-modified red sandstone increases with the increase in cement content, curing age and compactness. \\  & (2) & There is an optimal lime content in the strength of lime modified red sandstone. \\ \hline \multirow{2}{*}{Lime} & [14] & There is optimal lime content to improve the characters of red sandstone residual soil. \\ \cline{2-3}  & [15] & All aspects of the improved filler have been better improved. \\ \hline \multirow{4}{*}{Lime, cement and fly ash} & [16] & (1) \\  & (2) & Cement has the greatest influence on the shear strength and compressive modulus of \\ \cline{1-1}  & & remolded red sandstone samples. \\ \cline{1-1}  & (2) & Loess has a significant influence on the compaction effect of remolded red sandstone soil. \\ \hline \multirow{4}{*}{Water-resistant polymer cement base} & [17] & The micro strain phase produced by polymer cement reinforced soil is three times higher than \\ \cline{1-1}  & & that of pure cement reinforced soil, showing good fatigue resistance. \\ \hline \multirow{4}{*}{Lime, cement and fly ash} & [18] & (1) \\ \cline{1-1}  & (2) & The modifier can greatly improve its bearing capacity and compressive strength, and its \\ \cline{1-1}  & & disintegration resistance and water stability are also improved. \\ \cline{1-1}  & & Among them, when the mixing ratio of cement-modified soil is 5\%, the improvement \\ \cline{1-1}  & & effect is the best, and adding an appropriate amount of fly ash also improves the \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Similar studies on adding additives to improve the properties of kinds of soil. [PERSON] [24] regarding the field performance of weathered phyllite as a subgrade material for highways, and was also investigated by [PERSON] et al. regarding expansive soil [25]. Moreover, [PERSON] studied the characterization of the geomechanical and water-vapor-absorption properties of deep soft rocks [26]. Modeling is another means of studying the feasibility of modified soft rock as subgrade material [27]. [PERSON] investigated the influence of cement-fly ash-gravel pile-supported approach embankments on abutment piles in soft ground [28]. [PERSON] et al. (2013) performed a numerical analysis to study the mechanical properties of soft soil beneath approach embankments [29]. From the analysis above, it is clear that most previous studies were about the performance of modified soft rock for highways. There is little research aimed at using WAS as the subgrade-filling material for HSR. Moreover, the post-construction settlement can not exceed 15 mm due to the high requirements of deformation control of the HSR subgrade; whether modified WAS can be used in the bottom bed or subgrade in HSR requires further research. Based on the experiences of Japan, Europe and China, soft rock can be used as subgrade filling for HSR through modification, and must meet some requirements [30; 31].