In this paper, the pile-soil interaction of the pile foundation of an inclined straight alternating group in a liquefiable site under a seismic load was studied through the form changes to the pile cap within the inclined straight alternating group. Based on an analysis of the soil acceleration, hole pressure ratio, horizontal displacement of the pile body, vertical displacement of the pile body and bending moment of the pile body, the dynamic characteristics of the pile soil at the free site are studied with two layers of liquefiable soil. The results show that the sand layer can amplify seismic waves under a seismic load, so the soil acceleration under the pile foundation model of the high-rise pile cap group is slightly greater than it is for the low-rise pile cap model; then, the pore pressure ratios at the monitoring point in the low-rise pile cap and high-rise pile cap pile foundation models present certain fluctuations. The analysis of the pile displacement and the bending moment shows that the pile foundation from the high-rise pile cap group can resist the seismic load better than the pile foundation from the low-rise pile cap group.

In ocean engineering, pile sliding often occurs in the driving process of large‐diameter pipe piles and will affect the engineering quality, so accurate pile sliding interval is necessary. According to the stress situation of steel pipe pile out of actual engineering, the causes of pile sliding are analysed. Using the static equilibrium equation, the mud depth at which the pipe pile may slip is calculated. The influence of pile siding friction was considered when calculating the second pile sliding, and the pile siding friction is divided into three influential areas. Using integrating method, the work done by pile resistance is calculated. Combined with the working principle and power principle, the energy transformation equation of the pipe pile in the process of sliding is obtained, and the sliding length and interval of the pile are calculated. A comparison between the measured results and the real case calculation was conducted using this new method. The comparison indicated that the total relative errors in pile sliding interval are 8% to 16%, and the new method has high accuracy. The results of the new method are in accord with the measured data, which can provide a reference for predicting the interval of pile sliding in the project.

In this paper, the pile‐soil interaction of a low‐rise pile cap foundation of an inclined straight alternating pile on two or three layers of a soil liquefaction site under seismic load is studied. By inputting the 0.5 g El Centro seismic wave in FLAC^3D, the pile‐soil interaction rule of the pile foundation of the inclined and straight pile groups of the low‐pile cap under seismic action is simulated. By analyzing the soil acceleration, the pore pressure ratio, the horizontal displacement of the pile body, the vertical displacement, and the pile body bending moment, the law of pile‐soil interaction between the pile and soil when the lower part of the pile is embedded in the clay layer is studied, and the low‐rise pile cap inclined straight alternating group pile foundation on the two‐layer soil and the three‐layer soil free field is compared and analyzed. The results show that, under seismic load, the maximum acceleration of soil mass in the two‐layer soil and three‐layer soil model is discrete, and the pore pressure ratio of sand soil increases from bottom to top. By analyzing the displacement and bending moment of pile body, the bending moment at the joint between the pile cap and the top of pile body is the largest and the most vulnerable to damage. The maximum value of pile displacement and bending moment in the three‐layer soil is less than the maximum value of the two‐layer soil, indicating that the pile group foundation in the three‐layer soil free site model is safer.

To study the force and deformation characteristics of subsea mudmat-pile hybrid foundations under different combined loads, a project at a water depth of 200 m in the South China Sea was studied. A numerical model of a subsea mudmatpile hybrid foundation is developed using the numerical simulation software FLAC3D. The settlement of the seabed soil, the bending moments of the mudmat, and the displacements and bending moments along the pile shaft under different load combinations, including vertical load and horizontal load, vertical load and bending moment, and horizontal load and bending moment load, are analyzed. The results indicate that settlement of the seabed soil is reduced by the presence of piles. The settlement of the mudmat is reduced by the presence of piles. Different degrees of inclination occur along the pile shaft. The angle of inclination of pile No. 1 is greater than that of pile No. 2. The dip directions of piles No. 1 and No. 2 are identical under the vertical load and bending moment and are opposite to those under the other combined loads. The piles that are located at the junctions between the mudmat and the tops of the piles are easily destroyed.

For the study of interaction between piles‐soil‐structure with different caps, the FLAC3D finite difference software was used as the research tool, and dynamic load was El Centro seismic wave. The numerical model of obliquely pile groups of the pile‐soil‐structure with low cap and high cap was established, respectively. The variation of pore pressure, the moment, the displacement of piles, and the displacement of pier was analyzed. The results indicate that under the action of earthquake, the distribution of pore water pressure in the soil layer increases gradually from top to bottom. The instantaneous negative value of partial soil due to shear dilation occurs at the peak of vibration acceleration. The middle area of the pile foundation in sandy soil is prone to liquefaction. In the same model, the maximum bending moment of inclined piles is greater than that of vertical piles. The vertical displacement of the vertical piles is a constant value along the depth, while the vertical displacement of the inclined piles is changed along the depth of the buried piles. In the high cap model, the horizontal displacement of the inclined piles is no longer monotonous along the burying depth, and the maximum value occurs in the sand soil layer. The vertical and horizontal displacements of the inclined piles and vertical piles in the high cap model are obviously greater than those of the low cap model. The maximum horizontal displacement of the pier of the two models occurs at the same time.