Study on characteristics of pile–net composite foundation at 500 kV substation in China

The overall requirements of substation engineering are very high, and the differential settlement control of substation engineering is relatively strict. On the soft foundation of the tidal flats at the Zhenhai 500 kV substation in China, a field test was carried out to study the working characteristics of the pile–net composite foundation during the soil filling and consolidation stage. Variation laws of the settlement, earth pressure, pile–soil stress ratio, geogrid tension and axial force of pile were obtained and analysed. When the height of the filled soil increased to 2 m, a plane of the equal settlement was formed. Because of the soil arch effect, the earth pressure on the pile top was always higher than that between the adjacent piles. The pile–soil stress ratio rapidly increased from 1.2 at the stage of soil filling to 6.0 at the initial stage of consolidation. The ability of the geogrid to transfer the load was limited, and the soil arch effect was the main reason that the load was transferred to the pile top. Due to the lateral negative friction resistance of the pile in the shallow soil, the axial force of the pile first increased and then decreased along the depth.