To investigate the behavior of X-section cast-in-place concrete piles (XCC pile), a series of static load tests for piled foundation are conducted on the basis of a soft soil reinforcement engineering for a sewage treatment plant in the north of Nanjing, China. The testing results are presented in load-settlement curves, pile-soil stress ratios, distributions of skin friction (side friction) and axial force, and load-sharing between side resistance and end-bearing capacity. Comparative analysis between an XCC pile and a circular section concrete pile (circular pile) with the same cross-sectional area indicates that the XCC pile with its increased perimeter can improve the vertical-bearing capacity by 20% because of the larger skin friction. Also, the XCC pile shows increasing pile-soil stress ratio and reduces settlement. The existing design standards for traditional piles can be referenced by the XCC pile composite foundation, because the axial force and skin friction distribution are the same as...

The dynamic behavior of calcareous sand at high strain rates (HSRs), which is relevant to mining industry, aircraft wheel loading, and pile driving, is still not fully understood. To investigate the effects of the moisture content, 34 HSR tests and 26 low strain rate (LSR) tests were conducted on calcareous and silica sands using the split Hopkinson pressure bar (SHPB) technique with a rate ranging between 100 s⁻¹ and 10⁴ s⁻¹ and using a mechanical testing and simulation (MTS) apparatus with a rate ranging between 10⁻⁵ s⁻¹ and 10⁻¹ s⁻¹, respectively. It is found that the compression of unsaturated sand is almost larger than that of dry sand because the compressibility of particles and effective confining pressure change with moisture content. The dynamic stress–strain curve of unsaturated silica sand moves upward with moisture content at HSRs, but that of unsaturated calcareous sand is insensitive to moisture content. Compared with silica sand, calcareous sand reached its optimum capacity for energy absorption at lower stresses and energies. The energy absorption of unsaturated sand decreases with an increasing moisture content, while its transmitted load increases. To improve the cushioning properties of sand, a moderate water content is proposed.

When applying axial load on piles subjected to negative skin friction (NSF), the yielded NSF is gradually eliminated. The process is notably influenced by the tip location (Y) and still a lack of understanding. This paper reports three‐dimensional numerical simulations with tip locations Y = 1.00 pile diameter (D), 0.25D, 0.00D, and −1.00D. It is found that, against expectations, the dragload and NSF are not proportionally related to the tip location. When maximum dragload (P_max) is eventually eliminated due to an axial load, there is also a negative crest of the skin friction, indicating that NSF still exists based on the criterion of the dragload reduction. The side resistance of the piles with Y = 1.00D and 0.25D is almost fully mobilised, which is demonstrated by the increment of end resistance that greatly increases with the larger axial loads. However, the side resistance of the piles with Y = 0.00D and −1.00D has a potential capacity to carry more loads with continued displacement since the increment of end resistance increases almost linearly with axial load. Therefore, when designing the pile foundation, the inclusion of the NSF should be governed by the amount of axial load to be resisted.