Dynamic Splitting Behavior and the Constitutive Relationship of Frozen Sandstone Containing a Single Fissure

Tao Zhao,Lei Wang,Gengshe Yang,Yuzhe Qiao,Hailiang Jia,Bangbiao Wu

doi:10.1155/2021/6661037

Abstract

Fractured sandstone is widely distributed in mining areas throughout western China where the artificial freezing method is extensively adopted to construct vertical shafts. Blasting and excavation generate stress waves and break frozen fractured sandstone. Among the failure modes of frozen fractured rocks, tensile failure is very common. In this study, the dynamic tensile strength of fractured sandstone samples with four crack inclination angles (0°, 30°, 60°, and 90°) is tested by using a split Hopkinson pressure bar at four subzero temperatures (−5, −10, −15, and −20°C). Accordingly, a damage constitutive relationship that considers the effect of fissure angle and freezing temperature is established. The results show the following: (1) the fissure angle does not significantly affect the dynamic tensile strength of frozen fractured sandstone but mainly affects the failure mode of the sample. (2) The dynamic tensile strength of fractured sandstone has a negative linear correlation with the freezing temperature. (3) When the fissure angle is small, only tensile cracking occurs; when the fissure angle is large, tensile cracking occurs along both the loading direction and the fissure; and shear cracking occurs along the fissure as well. (4) Regardless of the fissure angle, tensile cracking is initiated at the stress-concentration zone and then propagates towards the loading end. Fissure ice provides both resistance to deformation and resistance to crack propagation which affects the crack propagation and coalescence mode. A dynamic constitutive relationship is established by considering the effects of fissure angle and freezing temperature on the dynamic properties of frozen fractured sandstone, which is proven to be highly reliable and provides a reference and basis to study the dynamic mechanical properties of similar rock types.

Highlights

A large number of mine shafts in western China pass through Cretaceous strata. ese strata have a short sedimentation time, containing many macro- and mesoscale fissures, and are in a water-rich state [1, 2]. e artificial freezing method has become the best plan for vertical shaft construction in water-rich soft rock strata [3, 4]. e fractured rock mass is damaged in blasting and excavation by the action of stress waves [5, 6]
Dong et al [15] used a separate Hopkinson pressure bar system to study the fracture behaviors of rock plates containing a single fissure and an ultra-high-speed camera system combined with the digital image correlation (DIC) method was adopted to record the transient fracture process
Split Hopkinson pressure bar where P1 and P2 are the loads on both ends; Es is the elastic modulus of the sample; Ab is the cross-sectional area of the pressure bar; and εI, εR, and εT are the strain values of the incident wave, reflected wave, and transmitted wave as collected by the strain gauge

Summary

Introduction

A large number of mine shafts in western China pass through Cretaceous strata. ese strata have a short sedimentation time, containing many macro- and mesoscale fissures, and are in a water-rich state [1, 2]. e artificial freezing method has become the best plan for vertical shaft construction in water-rich soft rock strata [3, 4]. e fractured rock mass is damaged in blasting and excavation by the action of stress waves [5, 6]. E dynamic mechanical properties of weakly consolidated soft rock under different freezing temperatures were studied using the split Hopkinson pressure bar system, and a dynamic constitutive model considering the temperature effects was established [20, 21]. The SHPB system was used to perform dynamic splitting tests on sandstone samples containing a single artificial fissure filled with ice at different freezing temperatures (−5, −10, −15, −20 °C) and with loading angles (0°, 30°, 60°, and 90°). E reason for adopting samples containing a single fissure is that it will make it easier to acquire the first-order rules of how predominant factors (e.g., loading angle and freezing temperature) affect the dynamic properties of frozen fractured rock. A dynamic constitutive relationship is established by considering the effects of initial multiscale damage and freezing temperature on the dynamic properties of frozen fractured sandstone

Methodology

Results and Discussion

Elastic stage

Constitutive Model