introduction Buoyancy of Manholes concrete pipe The buoyant force acting on a submerged object is equal to the weight of the fluid that the object displaces. Provided that the weight of the object is greater than that of the displaced fluid, the buoyant force will be negated. In most circumstances, buoyancy in manholes is not of concern. However, in cases where the groundwater table is expected to be high, in areas where flooding may be of concern, or a large volume of water is to be displaced by the manhole structure, flotation should be checked. A quick check of the weight of the manhole structure versus the weight of the displaced water will provide a relative indication of the probability of flotation. However, the shear force between the walls of the manhole structure and soil is another important consideration. Your local Lafarge representative is able to perform the necessary analysis to determine the likelihood of manhole flotation, if required. Should flotation be of concern, there are a number of solutions available, the most common of which would be to provide an extended base for the manhole structure as an anchor for the unit. For more information on manhole flotation, please refer to the American Concrete Pipe Association Design Data 41, available at http://www.concrete-pipe.org/pages/design-data-p.html. stormwater treatment technologies box sections manhole and catch basin material LAFARGE PIPE eMANUAL PAGE 41