Proceedings of DFI-India 2018: 8th Conference on Deep Foundation Technologies for Infrastructure Development in India, (DFI)
Use of Socketed Micro Piles for Excavation Support in Heterogeneous Fill Material
Shuvranshu K. Rout, Manos De, Anup K. Mandal and Biswajit Das
Micro piles are extensively used in various forms with different applications starting from foundation support to landslide mitigation. The present case study highlights a unique experience of socketed micro piles which are subjected to high traffic load and at the same time providing support to shallow excavations. The shallow excavations were required to construct structures like pipe and duct supports / trestles for new power plant inside steel plant premises. Most of the structures were coming in between vicinity of existing building foundation and adjacent plant main road. Open excavation with slope or elaborate excavation support system were not feasible due to space, time and cost constraints. Also, the depth of new foundations could not be reduced in the varying depth of heterogeneous fill material. The heterogeneous fill material comprised of mostly slag, fly ash, concrete debris, broken bricks, loose soils and boulders. The underlying highly weathered mica schist layer or virgin soil layer was most suited for placing the new foundation. Therefore, micro pile option was explored considering availability of small drilling equipment, readily available materials and resources. Steel pipe along with reinforcement rods with cement-sand grout were used for making the micro piles. Wagon driller was used to drill holes for 150mm diameter micro pile. These micro piles were socketed inside the weathered rock layer or grouted slag filled zones. Given the highly variable thickness of heterogeneous fill material above weathered mica schist rock, the lengths of the micro piles above the bond zone were varying significantly. Often these lengths also varied with the depth of highly weathered mica schist rock layer. The field experiences in these conditions are demonstrated with supported reverse design analysis to ascertain the desired safety against uncertainties.
|article #3184; publication #1050 (India2018)|