Abstract
A dynamic constitutive model of tensile and compressive damage was constructed on the basis of the ZWT and statistical damage models, particularly by introducing the maximum tension and maximum shear stress criteria to solve the failure problem of the surrounding rock mass caused by deep excavation unloading. A shock compression and splitting test of sandstone specimens under different strain rates were performed by using a split Hopkinson pressure bar (SHPB). The constitutive model was developed again by LS-DYNA for the secondary numerical impact compression and split test of sandstones. Results demonstrated that the constructed dynamic constitutive model of tensile and compressive damage could considerably simulate tensile and compressive stress-strain relations and failure features of sandstones well. Lastly, the constitutive model was applied to conduct a numerical study on damage distribution and failure laws of the surrounding rocks at Gaochou Roadway, Luling Mine under cyclic excavation unloading. Results showed that the unloading failure of surrounding rocks has significant accumulation effects, and the accumulated damage on the floor is larger than those on the roof and roadway walls. The maximum breaking and damage depths are 0.4 m and 5.31 m, respectively. Circumferential damage showed an “umbrella-shaped” distribution pattern. With respect to trend, the damage accumulation effect at the rear part of the excavation face is stronger than that at the front part and the maximum influence distance is 6.4 m. However, the influencing degree of the accumulation effect attenuates gradually as advancing into the excavation face. The reliability of the numerical simulation is verified by combining the test results of the field geological radar on the roadway roof.
Highlights
With the increase of coal resource mining depth in China, the coal rock advancing and mining environment in deep areas are more complicated than those in shallow areas [1]
In a deep environment, such operations as roadway excavation and face mining destroy the balance of the original stress field, and rock units on the excavation face are under a stress state of a three-directional compressive one-way unloading [2, 3]. e result is in the frequent occurrences of the surrounding rock cracking and peeling. e research on dynamic unloading has attracted considerable attention
Zhai et al [11] proposed a dynamic model of viscoelastoplastic damage, and its applicability was verified by the split Hopkinson pressure bar (SHPB) experiment of two rock materials
Summary
With the increase of coal resource mining depth in China, the coal rock advancing and mining environment in deep areas are more complicated than those in shallow areas [1]. A numerical model based on bond-based Peridynamic theory was proposed by Ai et al [10] to simulate crack propagation and dynamic mechanical properties of coal under the SHPB test This model failed to consider the rate effect of rock materials. Zhu and Tang [19] constructed a dynamic constitutive model of rock damage based on the maximum tension stress criterion and MohrCoulomb criterion, with consideration to the tensile properties of rock materials. This model had difficulty in reflecting the prepeak mechanical properties of rocks because it was constructed based on the elastic constitutive theory. This constitutive model was applied to a deep roadway excavation project, and the reliability of the research results was verified by field measurement. is study provides a constitutive theoretical basis for studying the dynamic mechanical properties of rock masses and presents beneficial references to study the dynamic excavation unloading of deep rock engineering
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