Concreted-in 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. A free length of 15 feet is normally required for fully-integral abutments; however, shorter free lengths may be acceptable provided a flexure check 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 or Class B modified concrete shall be used in the rock socket. Placement of concrete shall be 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-in piles are used, the piles are to comply with AASHTO M160 and M270, Grade 50.
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 126.96.36.199 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 188.8.131.52 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.
Please see the Technical Engineering Memo - Concreted-in Pile Substructures
for additional information.