Wall (1 of 2) (IMAGE) University of California - San Diego Caption Engineers tested two types of retaining wall systems -- one without a sound barrier (foreground) and one with a sound wall (background) during a series of rigorous simulated earthquake tests at UCSD's Englekirk Structural Engineering Center, which has the largest outdoor shake table in the world. Credit UC San Diego Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.