Norton Air Force Base  required, like so many public buildings in California, to upgrade for earthquake compliance.  This was accomplished by installing multiple shear walls with an independent foundation from the existing spread footing columns which supported the two story concrete waffle floor type of buildings. 

The project design engineer was Sverdrup, which specified MICROPILES for the foundation support for the shear walls.  Groupings of two and three micropiles was used on each end of the 20 long pile caps.  These micro piles extended 50 feet below the existing grade.  RQ Construction, which specializes in government facilities, selected August Construction for the installation of the micro piles. August Construction used a Davey Kent 525 rotary percussion rig to access under the 17 foot headroom

 (after pile cap excavation) in order to drill the 10 inch nominal diameter micropiles using a Titan 103 rod (hollow tendon which is used to drill while grouting to flush the cuttings, and then left in the hole to act as the reinforcing steel).  The drilling was very difficult in the rocky and caving soil, but far easier than if a conventional pile had been designed (2-3 foot typically).  The obvious advantage of the micropile design was the use of a small diameter and a single rod design.  Additionally, with the use of the Titan hollow bar, there was no need to case the caving soils because the grout acted as the flushing medium to keep the hole open, while conditioning the hole. The Titan rod was coupled in 10 foot sections and had a plate with a nut on top and bottom of the plate.  The rod was bonded to the soil using Neat cement (water and cement without aggregate).

The testing program required 2 micropiles in compression and 2 in tension.  The bearing length of the micro piles was from 18 to 23 feet in a sandy, gravel and cobble matrix about 25 feet below grade level.  That proved to be an exceptionally good  soil for bonding, and the piles easily achieved 400 kips (kip = 1,000 lb) in tension and compression.  The top of the micropiles was designed with a 20 foot steel structural pipe collar (8" diameter). 

Pictured is John Chambers from the Corp of Engineers (left) and Glen Fraser of the Byerly Group overseeing the test for one of five ultra-high capacity micropiles.  Two micropiles were TESTED to 400 kips compression (pictured) and two for tension loads, per each building.  Due to the sandy - coble matrix of the soil, the capacity achieved far exceeded the capacity of the steel (400 kip test loads).