Dynamic mechanical properties and instability behavior of layered backfill under intermediate strain rates

To obtain dynamic mechanical properties and failure rule of layered backfill under strain rates from 10 to 80 s(-1), impact loading test on layered backfill specimens (LBS) was conducted by using split Hopkinson pressure bar system. The results indicate that positive correlation can be found between dynamic compressive strength and strain rate, as well as between strength increase factor and strain rate. Dynamic compressive strength of LBS gets higher as the arithmetic average cement-sand ratio increases. Compared with static compressive strength, dynamic compressive strength of LBS is enhanced by 11% to 163%. In addition, the energy dissipating rate of LBS lies between that of corresponding single specimens, and it decreases as the average cement content increases. Deformation of LBS shows obvious discontinuity, deformation degree of lower strength part of LBS is generally higher than that of higher strength part. A revised brittle fracture criterion based on the Stenerding-Lehnigk criterion is applied to analyzing the fracture status of LBS, and the average relevant errors of the 3 groups between the test results and calculation results are 4.80%, 3.89% and 4.66%, respectively.