Earthmoving operations are a major part of many civil engineering works and as such they present an ideal opportunity for improved estimation forecasts and efficiency. This paper presents a computer simulation model which is based on the assumption that an earthmoving cycle can be broken down into its component parts which can be represented by Erlang probability distributions. Such a distribution can be generated on a computer and incorporated into a discrete-event simulation program. The development of the model and of a program to carry out simulation runs is described. The importance of model validity is discussed; results from a simulation cannot be relied upon if the model does not actually agree with the real system. The results of a validation exercise are shown which compares system output data (obtained from actual contracts in the UK) and model output data. Simulation output data is also shown in a graphical form which is intended to ease the use of the model on a site basis.