Strengthening of foundations with micro piles is progressively being used due to major advantages that this technique can be adopted with limited space availability for execution and with less disturbance to the nearby existing structures/foundations. Current codes do not present specific design and detailing guidelines for this retrofitting situation. In one project, the process plant building is being presently operated with a 20Ton (T) capacity Electric Overhead Travelling (EOT) crane. Since the existing crane had served its design life, owner decided to install a new 25T capacity crane. To carry the new increased loads, retrofitting of foundations for few columns was required for higher loading. In this case, micropiles are designed to underpin the existing foundations for upgrading load bearing capacity of the existing foundations. The work was to be done keeping the plant in running condition and no civil construction work for foundation jacketing is allowed inside the building. Micro piles were chosen for underpinning the foundations by installing adjacent to the existing raft outside the building and connecting the two rafts. Hollow TITAN bar has been used as the reinforcement as well as grouting facilitator and no other separate casing was required for constructing the micro piles. This solution achieved the objective of in-situ strengthening of foundations to carry the higher column load without need for foundation jacketing.
Subjects: process plant, EOT crane, micropile, foundation underpinning
Author: Runu Dutta, Anup Kumar Mandal, Ph.D., Biswajit Das and Manos De