Experimental and numerical study of dynamic compressive stress wave propagation across geological lithological layers

Abstract

This experimental and numerical study examines the propagation of dynamic compressive stress waves within geological lithological layers. In contrast to conventional split Hopkinson pressure bar (SHPB) systems, this research employed a custom-designed electromagnetic pendulum impact testing (EPIT) system. The electromagnetically controlled EPIT system was developed to allow precise and consistent repetition of impact tests at varied speeds. The EPIT system was integrated into a modified SHPB apparatus, featuring an extended length of up to 3 m and using rock bars exclusively, rather than conventional steel bars. Three types of modified SHPB configurations-single-rock-bar, double-rock-bar, and triple-rock-bar systems-were analyzed. Testing was conducted on limestone, marble, and sandstone specimens, each measuring 1 m in length and 0.05 m in diameter. Results indicate that sandstone exhibits the highest peak compressive strain and attenuation rate along the propagation path, distinguishing it from the behaviors observed in limestone and marble. The dynamic response characteristics of each rock layer are affected by the source of dynamic load, the inherent properties of the rock layer, and the properties of subsequent layers. A significant negative correlation was found between the average compressive strain amplification ratio and density (\(\rho \)) ratio (\( R = -0.92 \)). Ratios of elastic modulus (\( E \)), P-wave velocity (\(v_p\)), and wave impedance (\(Z_w\)) also notably influence compressive strain amplification (\( R = -0.85, -0.86, \) and \( -0.85 \), respectively). The UCS ratio has the least impact on strain amplification (\( R = -0.7 \)). Additionally, the pattern of stress attenuation was effectively described using a combination of power and Gaussian functions.