การเสริมกำลังฐานรากสะพานด้วยเสาเข็มชนิดสปันไมโครไพล์

Abstract

This article demonstrates an approach to reinforce the bridge’s foundations which its safety factor had been reduced to a dangerous level by scouring with spun micro piles. The bridge was built two decades ago at Dong Pa Lan, Mae Fai, Amphoe San Sai, Chiang Mai. The Department of Rural Roads investigated the existing piles’ lengths embedded in the soil using Parallel Seismic Test and then recalculated the capacity of the foundations. The calculation suggested that one of the foundations had a safety factor of 1.04 which was considered extremely dangerous in geotechnical engineering aspect since the typical value used is more than three. A collapse would occur if the bridge was subjected to more scour and traffic without reinforcement. The department examined a few solutions to the problem considering limitations on the construction space, necessity of traffic during the repairing process, cost, and safety for the construction, and then decided to reinforce the foundations with spun micro piles. The process began with pressing the piles around the old foundations to the strong soil layer by using hydraulic jacks. The weight of the superstructure was transferred by temporary steel structures to the new micro piles. The bridge was then lifted a little to pre-load the piles. Finally, concrete columns reinforced with steel tubes were cast to connect the old foundations with the micro piles. The result suggested that the spun micro piles were able to support the weight of the bridge and complied with the design criteria and engineering standards.