Study on strength and ultrasonic pulse velocity of cemented aeolian sand backfill under multiple factors using response surface method

Aeolian sand (AS) has been increasingly used to prepare cemented AS backfill (CASB) for coal mining. Although strength is an important determinant of the CASB performance, existing research on the CASB has not addressed the effects of multi-factor interaction and coupling on the uniaxial compressive strength (UCS) and splitting tensile strength (STS). In addition, ultrasonic pulse velocity (UPV) testing, has not been used on the CASB. In the present study, ordinary Portland cement (PO) to fly ash (FA) ratio (PO/FA, x₁), fine particles (total mass of PO and FA) to AS ratio (fine particles/AS, x₂) and solid content (x₃) were considered as factors. The response surface method (RSM) was used for assessing their influence on the UCS, STS and UPV of the CASB, and for analyzing the relationships between the UCS, STS and UPV. The RSM results showed that the UCS, STS and UPV increased with these factors. The interaction terms x₁x₂ and x₁x₃ significantly affected the UPV, and x₂x₃ significantly affected the UCS and STS. The influence surface of the two-factor interaction and a three-dimensional scatter plot of the three-factor coupling were established. The effects of above factors on the strength and UPV were revealed from three levels of "single factor-interaction terms of double factors-coupling effect of three factors". There existed a linear growth relationship between the STS and UCS, and the STS values were primarily distributed within 0.09-0.105 of the UCS values. The strength increased quadratically with the UPV. In conclusion, this study determined the influence rules of the PO/FA, fine particles/AS and solid content on the UPV, UCS and STS, and the relationship among the UCS, STS and UPV.