The concept of wall deflection path and reference envelope is introduced herein for evaluating performance of diaphragm walls. It has been found that, at a given site, wall deflection paths, which are plots of maximum wall deflections versus depths of excavation, converge to a narrow band as excavation goes beyond a depth of 10 m or so. The reference envelope of wall deflection paths characterizes performance of diaphragm walls. It, however, should be noted that inclinometer readings must be interpreted with care and corrections must be made to account for toe movements, if any. Based on the data obtained for deep excavations carried out in recent years, reference envelopes are established for the T2, TK2, and K1 zones and they can be used to evaluate the performance of individual walls.