Concreted piles are used when structures sensitive to vibration are within 75 feet of pile driving. In addition, concreted piles are used when the minimum pile driving lengths - either 15 feet for integral, or 10 feet for semi-integral abutments - cannot be obtained due to shallow bedrock. Free-length of 15 feet is normally required for fully-integral abutments; however, shorter free-lengths may be acceptable provided the flexure check discussed below is performed. Semi-integral abutments do not require free-length and can either be placed directly on rock using concreted-in piles, or isolated using a sand cushion that is at least 1 foot thick, depending on the bearing demand and the effect of the horizontal loading on the foundation.
Class DC concrete is tremied around the piles, in accordance with Section 625 of the WVDOH Standard Specifications. The concrete is to be placed to the top of rock socket elevation, as determined by the minimum free-length, and as shown on the plans. When concreted piles are used, the piles are to comply with AASHTO M160 and M270, Grade 50. Mini-Sid and CSL testing are waived unless the Engineer elects to have this testing performed. Pile alignment must meet our Specifications and the piles must be braced to prevent movement during concreting. Shear studs, when required in the plans, are to be welded onto the outside of the flanges at about 1-foot intervals. The zone above the top of the concrete is to be backfilled with clean, dry sand to provide the required free-length. The rock socket should be concreted within 24 hours of excavation for claystone, shale, mudstone, and siltstone.
Concreted-in piles are to be designed for a minimum of 36-inch diameter pre-drilled holes. The rock socket length must be a minimum of 3 feet. The Geotechnical Engineer is to provide end bearing, side resistance (when needed), and associated resistance factors for the concreted-in piles in accordance with the Drilled Shafts procedure detailed in the “Drilled Shaft Guidelines” found at Drilled Shaft Guidelines
. When the structural capacity of the pile controls, a resistance factor of 0.6 can be used. When the geotechnical resistances controls, the factors of 0.45 and 0.55 are to be used for the end bearing and side resistance, respectively.
When fully-integral piles have less than 15 feet of free length, the combined axial and flexure loading must be analyzed in accordance with section 220.127.116.11 of LRFD. The Geotechnical Unit will accept Lpile analysis showing that the total pile stress is not exceeding 45 ksi in the strength limit state in lieu of the section 18.104.22.168 analysis. A free-head (or partially fixed up to fully-fixed, if embedded 3 feet into the cap) can be modeled using the anticipated thermal movement.