The Stabilizing StormTech Chamber Foundations with StormGrid technical note provides information about foundation performance, design and product specifications.

StormTech Chambers are arch structures that concentrate overburden loads at the chamber bases and the stone columns between chamber rows. A layer of crushed foundation stone beneath the chambers helps to spread these concentrated loads, ensuring they are distributed to an appropriate bearing pressure on the subgrade. The foundation stone thickness for the specific chamber application is based on the overburden loads and allowable subgrade bearing capacity. Placing a StormGrid at the interface of the foundation stone and the subgrade is an innovative approach (patent-pending) to increase load transfer efficiency. This reduces the depth of foundation stone needed to achieve adequate pressure on the subgrade. Figure provided.

It is common practice for geotechnical engineers to place a “Bridging Layer” consisting of high strength materials over weaker materials, such as the crushed stone foundation used by StormTech. For roadways this approach is used to achieve a working surface to support paving operations. Subgrade preparation for shallow foundations also uses this approach to increase bearing capacity and reduce potential settlement. Figures provided.

A design example is explained.

StormGrid stabilized crushed foundation stone installation explains site preparation, placing geogrid, spreading foundation stone, making repairs and cold weather considerations. Foundation stone and StormGrid product specifications are listed.

Subgrade considerations explain bearing capacity, settlement and subgrade saturation. General comments note that Chamber designs do not consider settlement or ground movement tolerance of surface improvements above the chambers. A bearing capacity factor of safety of 2.5 was used in determining the allowable bearing pressure. Geogrid stabilized raft only aids in the increase of the bearing capacity at the base of the chamber. It is assumed that the effect of any net unloading during construction and any wetting of the subgrade soil from water contained in the chambers on the shear strength of the subgrade soil is taken into account in design. Maximum cover heights do not exceed 3.6 m (12’) and applied loads are less than 12,000 per square foot. Scour / erosion and its effect on the performance of stabilized foundation stone is not considered.