J & J Nevada - Seismic Retrofit & Tenant Improvement with Micropiles
J & J Nevada was a project involving a seismic retrofit and tenant improvement to an existing warehouse in Sparks, Nevada. Additional truck docks were required to be installed, changing the structural characteristics of the tilt up concrete building. The installation of a moment frame on the interior of the structure required some relatively high loads to be addressed in tension and compression at specific locations. VersaGrade was contacted early in the design phase to help determine the best foundation system to address these loads.
Originally built in 1979, the warehouse was constructed for General Motors Corporation as a parts distribution center. The 634,000 Square Foot facility included dozens of truck dock openings and an interior railroad spur for the unloading of train cars inside the building. The soils are predominately Alluvium of the Truckee Meadows, consisting of pebble to cobble sand, silty sand, and sandy silts overlain by scattered, well rounded volcanic & granitic cobbles. Due to the rocky nature of the site and limited soils investigations, VersaGrade concluded that the use of Micro Piles would be the best system to meet the required loads. Pile groups of 3-4 would be necessary to achieve the 140 Kip allowable loads at specific points along the perimeter foundation.
VersaGrade, Inc. was awarded the subcontract to install 40mm Contech Systems Micro Piles along with a custom Ram Jack bracketing system. K2 Structural Design & Ram Jack Engineering were contacted to help design the bracket that would carry a 35 kip allowable capacity (70 Kip Ultimate) in tension and compression for each pile. Each bracket was designed to work on shear strength alone, and attach directly to the tilt up panels themselves as there were no footings to attach to in some locations. Six each 7/8” diameter epoxy doweled bolts (per bracket) were used to secure the brackets to the face of the concrete tilt-up walls. A 5 ½” diameter x 8’ long steel guide sleeve was then inserted through the brackets and set to elevation. After bracket installations were complete, VersaGrade installed Contech 40/16 Micro Piles with a 4” carbide cutting bit down through each guide sleeve. The Micro Piles were installed to an average depth of 21’. One of the challenges of the project was higher than expected grout usage during the Micro Pile installation due to unconsolidated material and fissures. Some piles took in excess of 35 cubic feet of grout to complete.
VersaGrade used a Komatsu PC-160 Track-mounted hydraulic excavator with an Excavator Mount TEI 350 Rock Drill and ChemGrout CG600 Batching Plant for the Micro Pile installations.
Total No. of Contech Micro Piles and Ram Jack Custom Brackets installed: 14