PILED-RAFT FOUNDATIONS IN BELARUS-Paper

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The article examines piled-raft foundations as a way to improve foundation capacity and reduce construction costs in Belarus. Unlike conventional pile foundations, a load-bearing raft transfers part of the building load directly to the soil, potentially allowing fewer or shorter piles.<br /><br />The author reviews previous research and reports laboratory, model-scale, and field tests conducted by Belorussian National Technical University. Tests show that soil beneath the raft, including soil between piles, contributes substantially to load resistance. Raft contribution generally increases as pile length decreases, pile spacing increases, and foundation settlement grows. Field tests in Minsk found that rafts increased bearing capacity by approximately 30–103%, depending on raft size and soil conditions. In one case, combining a raft with tapered piles increased capacity by 30% beyond the improvement achieved by widening the pile feet.<br /><br />The article presents calculation methods for ultimate vertical load and settlement. The load capacity is treated as the combined resistance of the pile group and raft. Settlement includes the pile group’s settlement and additional settlement caused by stresses beneath the pile tips.<br /><br />The research supports the use of short, vibro-compacted tapered piles with bearing rafts, particularly where relatively firm soil occurs near the surface or filled ground can be improved through compaction. In a church project in Minsk, the proposed foundation used 285 short tapered piles alongside existing piles; the raft carried about 40% of the load. The solution nearly halved foundation costs compared with a design using 480 long driven piles.<br /><br />Overall, raft–soil interaction can increase foundation capacity by roughly 10–100% and reduce costs by 30–50% in suitable conditions. Performance depends on soil conditions, soil preparation and compaction, pile geometry and spacing, raft dimensions, and applied load.

Keywords

piled-raft foundations

foundation capacity

load-bearing raft

soil-structure interaction

Belarus construction

tapered piles

pile spacing

bearing capacity

settlement analysis

foundation cost reduction