Penetration mechanism of CPT probe in the dense sand assisted by ultrasonic vibration

The cone penetration test (CPT) is widely used because of its minimal soil disturbance, simplicity, low-cost and dual functionality for exploration and testing. However, conventional CPT technology encounters significant difficulty in dense sands, which limits its applicability. To address this challenges, a novel ultrasonic-assisted CPT probe was developed based on an ultrasonic-vibration drilling technique, a series of penetration tests were performed in sand with relative densities ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) ranging from 30 % to 90 % to quantify the effects of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> </mml:math> and ultrasonic vibration on penetration resistance and particle breakage. Besides, the particle breakage mechanism of sand and interaction between probe and sand under ultrasonic vibration were revealed. The results showed that the penetration load increases with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> </mml:math> . Ultrasonic vibration effectively reduced the penetration load, however, the reduction decreased from 60 % to 18 % as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> </mml:math> increased from 30 % to 90 %. As <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>D</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> </mml:math> increases, particle breakage around the cone tip becomes more pronounced, with a higher breakage rate closer to the cone tip. Under the ultrasonic-static coupling, particle breakage was mainly caused by ultra-high-frequency impacts between particles and the cone tip, particles collided with each other, vertical and shear stress around the probe, The stress state of the sand and soil around the ultrasonic CPT probe was divided into five regions. This study introduces a novel ultrasonic vibration CPT probe, quantifies its penetration benefits in the dense sand, and reveals the particle breakage mechanisms under the ultrasonic-static coupling. The investigation will provide insights for applications of CPT in dense sands.