Effects of soil moisture content and installation method on ultimate bearing capacity of pile in unsaturated silty sand

• The load-bearing capacity of piles is mainly influenced by the matric suction in unsaturated soil. • Changes in matric suction can significantly alter pile performance. • Two pile installation methods ("with" and "without" displacement) were tested in a lab. • Experiments were conducted at five different moisture levels. • Results indicated a peak in the bearing capacity curve, with increases in capacity being more evident in the "non-displacement" method. The load-bearing capacity of a pile embedded in unsaturated soil depends mainly on the matric suction present in the soil. Changes in this parameter directly influence pile performance. This study examined how the pile installation method and variations in soil moisture content affect matric suction and, in turn, the ultimate bearing capacity of a pile in unsaturated silty sand, including shaft, end, and total resistance. An instrumented pile installed with two methods, with displacement and without displacement, was placed in a laboratory chamber. To assess the effect of moisture variation, or in other words, matric suction changes, both installation methods were tested at five moisture levels. The results showed that the relationship between pile bearing capacity and matric suction reaches a peak rather than rising continuously. Under optimal matric suction, the bearing capacity of this soil reached values up to 4.5 times those in saturated conditions and 1.3 times those in dry conditions. This increase appeared stronger for the non-displacement method. Attention to matric suction effects in the design of foundations in unsaturated soil can reduce the required number and size of piles, resulting in lower construction costs and shorter project timelines.