# Applicability Study on Modified Argillaceous Slate as Subgrade Filling for High-Speed Railway
###### Abstract  
Modifying weathered argillaceous slate (WAS) to fill the subgrades of high-speed railways not only leads to obvious environmental benefits but also significantly saves natural resources. Previous studies have used several additives together with cement/quicklime. Using cement/quicklime as an additive would also improve the strength of weathered soft rock. Therefore, cement/quicklime can be used effectively as a sustainable solution. To illustrate the feasibility of cement/quicklime in WAS improvement, the mineral components and physical, mechanical and hydraulic characters for cement/quicklime-modified WAS were investigated via laboratory test. The dynamic behaviors were then analyzed by establishing a 3D vertical coupling dynamic model and performing dynamic triaxial tests. After mixing cement/quicklime, the following was proved: (1) The particles were coarsened, the content of kaolinite and amorphous phase increased, and the content of muscovite decreased, resulting in weakened hydrophilicity, reduced plasticity and enhanced water stability; (2) Mechanical and deformation characters were enhanced, reflecting an unconfined compression strength of quicklime/cement-modified soil greater than 0.5 MPa and elastic deformation for the subgrade of less than 0.1 mm; (3) For the quicklime-modified WAS, the dynamic strength was below the allowable value, and the sample disintegrated in water in 2 min, indicating it to be unsuitable for subgrade filling in HSR; (4) For cement-modified WAS, the water stability and dynamic strength were improved greatly, as well as the static strength. The sum of results highlights that 5% cement-modified WAS is recommended for filling subgrades of HSR for comprehensive factors. argillaceous slate; unconfined compression strength; dynamic response; water stability 202212222022202220222022202220  
A/B-group filling (well-graded coarse-grained soil with less than 30% fine-grained soil) has been suggested to fill the bottom of the bed and the subgrade for HSR [3,4]. However, a large amount of C-group filling, namely weathered argillaceous slate (WAS), is exposed along the Wuhan-Guangzhou HSR, most of which is waste residue from railway cutting and belongs to soft rock. This is not suggested to fill the bottom of the bed and the subgrade directly in HSR [5, 6, 7]. If it can be modified to be used, it will protect the environment and save considerable investment. In order to improve the mechanical properties of WAS, researchers have proposed the use of many kinds of stabilizer such as cement, lime, etc. [8, 9, 10], which are illustrated in Table 1. In these stabilizers, cement is widely used to improve soil's strength properties; however, cement is one of many reasons for the CO\({}_{2}\) emissions mentioned in [8]. Quicklime can permanently stabilize fine-grained soil, which chemically combines with water and improves soil workability and short-term strength. Lime modification works best in clay soils, as presented in [14]. Sand is also used to improve soft rock, through improving its graduation. In recent years, the use of soft rock has been investigated through experiments, modeling and other methods. Some researchers studied the feasibility of modified soft rock as subgrade material by experiments [21, 22]; [PERSON] and [PERSON] [15] and [PERSON] et al. [23] studied the effect of lime on some physical and geotechnical properties of Igumale shale and phylllites clays by indoor tests. The cement-modified method was studied by [PERSON]