Abstract
Waste-rock material used in underground backfill mining has a granular texture and acquires non-linear deformation characteristics when compressed. The deformation modulus of waste-rock measured by a laboratory compression test is significantly different from the true deformation modulus in the field, due to the complete confining effect of the loading steel cylinder. In this study, we performed a series of laboratory-based compression tests on waste-rock samples. The results showed that lab-acquired deformation modulus variations of waste rock could be divided into three stages: slow increase, accelerated increase, and rapid increase. We also measured the true deformation modulus of backfill waste rock by conducting a field test in gob areas of the Tangshan coal mine, China. The hardening process of backfill waste rock during the field test was analyzed, and could be divided into four stages: roof contact, rapid compression, slow compression, and long-term stable. With the increase of axial strain, the lab- and field-measured deformation moduli of waste rock both increased exponentially. A correction parameter was proposed to investigate the relationship between the field-generated true deformation modulus and the lab-tested deformation modulus. The correction parameter k positively correlated with the axial strain, in the form of an exponential function. The magnitude of k was between 0.5616 and 0.6531.
Highlights
In recent years, backfill mining methods have developed rapidly around the world [1–4], among which waste-rock backfill mining has become increasingly popular in the Chinese coal mining industry [5–7]
The bearing capacity of backfilled waste-rock in gob areas is influenced by its deformation modulus
It is of great significance to accurately and efficiently evaluate the deformation modulus of backfill waste-rock material in underground backfill mining
Summary
Backfill mining methods have developed rapidly around the world [1–4], among which waste-rock backfill mining has become increasingly popular in the Chinese coal mining industry [5–7]. The bearing capacity of backfilled waste-rock in gob areas is influenced by its deformation modulus. Using a self-designed bidirectional loading test system for granular materials, Li et al [29] investigated the influence of lateral stress on the compaction deformation characteristics of crushed waste-rock samples. While most compression tests are carried out under complete confinement conditions (zero lateral strain), this is not a common boundary condition of field waste-rock in a gob area [30–32]. The lateral boundary condition of waste-rock in a gob area is significantly vague and difficult to be represented exactly in a laboratory compression test. Measuring the true deformation modulus of backfill waste-rock in gob areas is difficult, due to the complicated field conditions. The true deformation modulus of backfill waste rock in gob areas was measured during a field test performed in the Tangshan coal mine in China. The feasibility and effectiveness of the correction parameter with axial strain were discussed
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