When surface conditions are used to determine bearing capacity, care must be exercised to insure that the soil is homogeneous to a depth of at least twice the width of supplemental footing used to support the concentrated load. Supplemental footing shall be provided to distribute the concentrated loads from the mast and rig support points. The manufacturer's load distribution diagram will indicate these locations. In the absence of a manufacturer's diagram, the supplemental footing shall be designed to carry the maximum anticipated hook load, the gross weight of the mast, the mast mount, the traveling equipment, and the vertical component of guywire tension under operational loading conditions. These footings must also support the mast and mast weight during mast erection.
Wellhead cellars present special foundation considerations.
In addition to the obvious ones such as collecting water and fluids that can seep into the ground, cellars also require unique mast support considerations. These should be analyzed by a qualified person to insure that an adequate mast foundation is provided. External guywires should never be used for plumbing the mast. All guywires, as indicated by the manufacturer's diagram, should be in position and properly tensioned prior to commencing any work. These recommendations should be posted on the mast in a weatherproof container and should state the loading conditions for which they were prepared.