In most parts of the U.S. you don't have to look far to find failed or failing retaining walls. They can lead to callbacks, unhappy customers, and even worse, damage to property or even serious injury. Catastrophic failure (walls tipping over completely) is unusual, partly because the process often progresses slowly and corrective action is usually taken before the catastrophe can occur. But that's not always true. One rainy afternoon in about 1960, the harmless-looking wall in Figure 1 suddenly and spontaneously tipped over. Fortunately my three sisters and I were inside playing Monopoly instead of out playing in the yard. The shock of the impact of five tons of masonry against our house, followed by twenty tons of mud,
