It is very important to get the accurate calculation of pit-excavation volume in many civil engineering projects. There have been common drawbacks to earlier methods of ground profiling, such dealing with sharp corners or the grid points any two straight lines. There are several papers of using spline surfaces to obtain more accurate calculations of the earthwork. In this paper, we propose an algorithm of finding a spline surface without boundary conditions which interpolates the given data and an appropriate method to calculate the earthwork. We present some computational results showing that our proposed method provides good accuracy.