For deep, loose sandy deposits under a proposed heavy structure where liquefaction is a concern, which ground improvement technique would an expert typically recommend to densify the soil?

For deep, loose sandy deposits under a proposed heavy structure where liquefaction is a concern, an expert would typically recommend Vibro-compaction, also known as Vibro-flotation, to densify the soil. Vibro-compaction is a ground improvement technique that directly densifies loose granular soils in situ, meaning in their original place. The process involves inserting a high-energy vibrator, called a vibroflot, deep into the ground. A vibroflot is a specialized probe containing an eccentric weight that generates powerful horizontal vibrations. As the vibroflot penetrates the soil, often aided by water jetting or air flushing, its vibrations cause the surrounding loose sand particles to rearrange into a much denser configuration. Water or air flushing helps lubricate the soil particles, facilitating their rearrangement, and often carries fine particles to the surface, further improving the soil structure. The vibroflot is then systematically withdrawn, creating a densified column of soil. This process is repeated on a grid pattern across the site, resulting in widespread densification of the deep sandy deposits. This densification is crucial because liquefaction is a phenomenon where saturated, loose granular soil temporarily loses strength and behaves like a liquid due to increased pore water pressure, typically induced by seismic shaking. By densifying the soil, its relative density—a measure of how compacted a granular soil is compared to its loosest and densest possible states—is significantly increased. Denser sand has a higher resistance to the cyclic shear stresses caused by earthquakes, meaning it is less prone to collapse of its soil structure and subsequent build-up of pore water pressure. This increased density translates to higher shear strength and stiffness, directly mitigating the risk of liquefaction by preventing the sand from losing its load-bearing capacity during a seismic event.