The effects of different fiber lengths on the unconfined compressive strength and microstructure of cemented aeolian sand reinforced with hybrid fiber

Soil reinforced with fiber can make use of the advantages of different lengths of fibers, and the strength and ductility of the soil are improved. The different lengths of fibers and cement were used to reinforce the aeolian sand from the Hotan-Ruoqiang Railway to meet the requirements of surface filler of the railway subgrade bed. The effects of different polypropylene fiber lengths on the unconfined compressive strength (UCS) and microstructure of samples that were cemented aeolian sand reinforced with hybrid fiber (CASRHF) cured on the seventh day. They were studied by the UCS and scanning electron microscope (SEM) tests. The total fiber content of two different lengths of hybrid fibers that reinforced cemented aeolian sand was 8‰ and 10‰. Fibers with different lengths of 3, 6, and 12 mm were used in the test and mixed according to the ratio of 1∶3, 1∶1, and 3∶1. Cylindrical specimens with diameter and height of 50 mm were made by hammering method. The specimens were placed in a standard curing room and then placed in a universal testing machine for the UCS test. Finally, the compressed specimens were sampled for the SEM test. The results show that the peak stress, residual stress, and ductility index of the samples which were cemented aeolian sand reinforced with different length hybrid fiber are significantly higher than those of the samples with single fiber length, while the pre-peak stress growth rate and post-peak stress decay rate are significantly reduced. The UCS of CASRHF samples increases by 12%～46% compared with that of single fiber samples. The UCS of CASRHF samples increased by 10%～13% when hybrid fiber content increased from 8% to 10%. The ductility coefficient of CASRHF samples increases with the content of 12 mm long fiber. The pore orientation probability entropy (POPE) of CASRHF samples with 3 mm fiber and 12 mm fiber increases with the proportion of 12 mm fiber, while the porosity and average pore abundance (APA) are opposite. The UCS of CASRHF samples is negatively correlated with porosity and APA. The research results are valuable in the design and construction of railway subgrade bed filling in the Aeolian sand area. © 2024, Central South University Press. All rights reserved.