When a force is applied to soil or sand, the particles rearrange themselves to form a denser packing, resulting in increased strength. This phenomenon is known as soil densification. However, the exact mechanism by which repeated striking enhances soil densification was not well understood.
To investigate this, the IIS research team conducted a series of experiments using a specially designed impact testing machine. They dropped a steel ball from different heights onto a sand sample and measured the force required to penetrate the sand. The team observed that the penetration resistance increased with the impact energy, indicating that the sand became stronger as it was struck harder.
To gain insights into the underlying mechanisms, the team performed further experiments using high-speed cameras and X-ray computed tomography (CT) scanning. The high-speed camera recordings revealed that the impact of the steel ball generated high-speed shock waves that propagated through the sand. These shock waves induced particle rearrangement and densification, resulting in increased soil strength.
The X-ray CT scans provided detailed images of the sand sample's internal structure before and after impact. The images confirmed the rearrangement of sand particles and showed the formation of denser regions within the sample. These denser regions contributed to the overall increase in soil strength.
The team's findings provide valuable insights into the behavior of soil and sand under repeated impact loading. Understanding this mechanism is essential for designing and optimizing structures that interact with soil or sand, such as foundations, embankments, and road bases. By considering the effects of repeated impact loading, engineers can ensure the safety and integrity of these structures in various applications.
The research findings are published in the prestigious journal "Nature Communications" and represent a significant advancement in our understanding of soil mechanics and geotechnical engineering.
