Through-wall leakages took place frequently during those excavations in water-rich sandy strata, which often resulted in engineering failures (e.g., global instability of retaining structures and damages to adjacent existing structures) and even injuries and/or fatalities. In spite of this, only few comprehensive studies relevant to this topic have been known in literature to date. During the recent construction of Metro Line 1 in the city of Nantong, China, hundreds of through-wall leaking incidents had taken place, which provided an opportunity for comprehensively investigating through-wall leaking in water-rich sandy strata. First, a database comprised of hundreds of leaking accidents collected in Nantong was built in this study; then, these leaking incidents were classified into three major levels by a descriptive statistics method, i.e., minor seepage without soil loss, massive leakage with a handful of soil loss, and massive through-wall ingress of water and soils. The primary contributory factors of these leaking events included exposure of steel bars of diaphragm wall (DW) panels, local bulging of wall faces, flawed joints of DW panels, and complicated geohydrological conditions. Moreover, the characteristics of these leaking events were examined in terms of their temporal and spatial distributions as well as excavation behaviors. Finally, some practical measures and solutions to deal with potential through-wall leaking incidents during excavations in water-rich sandy strata were proposed.