A Diamond Pier foundation code inspection may take place at any time during or after installation and may be combined with the structural framing inspection as each jurisdiction warrants. The top ends of all pins should be accessible for measuring pin lengths.
Pin Length Inspection
Diamond Pier foundations are designed to be inspected from above grade after they have been installed. An inspection plug must be installed at the lower (driven) end of the pin to keep soils from moving up inside it and to allow a tape measure to be slid down from the top of the installed pin to verify its length (see “Install Inspection Plugs in Pins”).
NOTE: The Diamond Pier foundation is a shallow bearing technology and does not require “refusal” or “friction” resistance, or the professional installation monitoring or special inspection typically associated with conventional vertical or battered piling.
NOTE: If framing members will be too close to the top of the concrete head to allow the tape measure to be inserted, then the inspection should be done before the framing is in place. Also, if inspection plugs have been unintentionally forgotten, then the pins can be twisted or jacked out with a pipe wrench to verify their length (see “Removing Pins”). They can then be redriven into the same soil cavity. If a plug has been removed to facilitate driving in an obstructed condition (see “Encountering Obstructions,” page 13), be sure to note or mark the location of this pin for the inspector. Pins are to be their full specified length without joints or coupling (length tolerance is ±1/2").
Bearing pins provided with the piers are schedule 40 galvanized pipe, Grade A electric resistance welded, with no threads. This also can be verified from above grade; with the pin cap removed, the weld can be verified on the inside wall of the pin, and the wall thickness can be checked. If the wall thickness is thinner than specified, the pins have been substituted with a lower schedule pipe or conduit and must be replaced with the properly specified pipe—1" nominal schedule 40 pipe has a wall thickness of 0.133" (just over 1/8"), 1-1/4" nominal schedule 40 pipe has a wall thickness of 0.140". The wall thickness tolerance is ±12%.
Concrete Head Integrity
If the “INSTALLATION INSTRUCTIONS” (page 8) are properly followed, the concrete heads should be level, and they should not have structural cracks as a result of improper handling or pin driving. (Surface spalls or chips may occur during driving or handling, but these are not structural, and will not affect the concrete head.) A structural crack is a fissure running internally into the head. It is perpendicular to the outer face of the head and runs inward to its core. This can weaken the strength of the pier head and/or allow water to penetrate and cause freeze/thaw problems in the concrete. If a concrete head has a structural crack, it should NOT be patched. It must be removed and replaced.
If a concrete head is more than 5 degrees out of level, the symmetry of the pin pairs may be compromised, and the head should be removed and correctly reinstalled.
The piers must not be overloaded. The total load on any specific pier is based on the individual tributary loads of the structure, supported by the corresponding post or beam connected to the pier. If you are not capable of properly calculating allowable loads, have the loading and capacities verified by your local building department or an independent registered design professional.
The total load calculated for a post or beam connected to the pier (also known as the “support column”) is based on a combination of the live load (snow, people, furnishings, etc.) and the dead load (weight of structure itself). The live load and dead load requirements are provided by your local bulding department; loads are specified in pounds per square foot (psf). A determination must be made as to what portion of the floor area is supported by a single support column. A design professional should be able to make this determination. Once the proper area for the single support column is determined, multiply the area (A) supported by the required loads (in psf) to determine the total tributary load (in pounds) for the single pier:
(A) x (psf) = Total Tributary Load
This value should not exceed the published capacity of the Diamond Pier model and corresponding pin length intended for use.