A rational approach is presented for evaluating differential settlement of structures at nuclear power plants where settlement monitoring and the associated documentation are important. In nuclear plants, allowable differential settlement is governed by the necessity to prevent architectural and structural damage, equipment malfunction, touching of adjacent buildings during an earthquake, and damage to buried utilities. Measurements of actual settlement of the plant should be taken on a regular basis from start of construction and compared with the allowable values. A description is given of methods for calculating allowable values for differential settlements, and a comprehensive program for obtaining actual settlement data at a nuclear site is outlined. The ratio of measured to allowable differential settlement at which remedial action may be required is discussed. A case history of differential settlements at a nuclear plant is presented. The settlement patterns exhibited by the major structures can be correlated with foundation conditions at the plant site. Measured differential settlements are small, generally less than 0.25 inch, compared with values of allowable differential settlement which are mainly greater than 0.75 inch
