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.

The Effect of Polymer Elastic Particles Modified with Nano-Silica on the Mechanical Properties of Oil Well Cement-Based Composite Materials

“…However, all these polymer particles need to be hydrophilically modified, mainly due to the hydrophobic groups on the surface of the polymer particles, which have a lower interfacial adhesion force and lower co-crosslinking level. When applied to water-based mixed systems, this can cause a decrease in the stability, strength, toughness, and other physical properties of the mixed system [ 12 , 13 , 14 , 15 ]. Cheng et al [ 16 ], He et al [ 17 ], and Zhong et al [ 18 ] found that unmodified rubber powder cannot be dispersed when soaked in water, and when added to cement-based composite materials, its compressive strength is low, which can easily lead to a poor stability of the cement paste and the deterioration of its mechanical properties.…”

Experimental Study on Silt Soil Improved by Microbial Solidification with the Use of Lignin

“…The unconfined compressive stress–strain curve can be obtained through the unconfined compressive strength test; the triaxial compression stress–strain curve can be obtained from the triaxial compression test, which generally has three stages: linear elasticity, yield, and ductile flow. Scholars have added soil conditioners to improve soil strength in their research on soil improvement experiments, including poly-Lys [ 65 ], foaming agents [ 66 , 67 ], reactive magnesium oxide [ 68 ], bentonite [ 69 , 70 ], cement [ 71 , 72 , 73 ], fiber [ 74 , 75 ], polyacrylamide [ 76 , 77 ], and quicklime [ 78 , 79 , 80 ]. The improvement effects using different contents of modifiers have been discussed, and the overall strength has improved; however, the production of soil modifiers such as cement and lime causes great pollution to the environment.…”