Latest ArticlesIn order to characterize the distribution law of active earth pressure with depth for a circular platform foundation pit under transient infiltrations, this study derived the slip line equation for the active earth pressure of circular platform foundation pits. The derivation was based on the strength equation of generalized effective stress for unsaturated soils and matric suction under transient infiltration conditions. Subsequently, the differential iterative method was adopted to obtain the slip line solution of active earth pressure for circular platform foundation pits under transient infiltrations. Last, the accuracy of the obtained slip line solution was verified, and an influencing factor analysis was conducted. The results indicate that the obtained slip line solution, compared with the existing solutions, can reasonably account for comprehen-sive influences of transient infiltration（time, infiltration ratio, nonlinear profiles of suction stress）, soil types（sand, silt, clay）, foundation pit model parameters（wall dip angle, wall-soil friction angle）, and the circumferential stress coefficient on the active earth pressure of foundation pits. The accuracy of the obtained slip line solution of active earth pressure under specific reduced conditions is demonstrated by comparing it with the slip line solution of circular platform foundation pits in saturated soils（when suction stress is zero）, and the limit equilibrium solution of plane retaining walls under transient infiltrations（when the radius of foundation pit tends to infinity）reported in the literature. The influence of time and infiltration ratio on the value and distribution of active earth pressure is most pronounced for foundation pits in clay, followed by foundation pits in silt. However, it is negligible for foundation pits in sand, which is caused by nonlinear profiles of suction stress for different soils. The active earth pressure of foundation pits decreases significantly with the increase of wall dip angle, wall-soil friction angle and circumferential stress coefficient, while its distribution and change with depth are closely related to soil types.
To explore the plantar pressure characteristics of flat-footed amateur runners when running on different sports surfaces.
We selected 15 individuals using the foot print method and Novel emed ® Amateur runners with flat feet diagnosed by 3D foot scanning（arch index≥0.6）and 15 normal foot controls. Using the Pedar-X 1.0 plantar pressure testing system, the maximum plantar pressure, contact area, peak pressure, pressure time integral, and total force impulse were synchronously collected while the subjects completed multiple straight-line running tests on three surfaces at a self-paced speed（4-6 m/s）. The differences between the groups were compared through repeated measurement variance analysis.
The pressure in the heel area（M3）and midfoot area（M2）of the flat-foot group was significantly higher than that of normal feet（P<0.05）, and the pressure in the anterior lateral area（T3）was significantly lower than that of normal feet（P<0.05）. The contact area of the entire sole of flat feet was larger than that of normal feet（P<0.05）, with the most significant difference in the midfoot area（M2）（P<0.01）. The difference in elastic surface was slightly reduced but still significant. The normal foot in the forefoot area（T1-T3）was significantly higher than that in the flat foot area（P<0.05）, and the pressure on the flat foot in the middle area（M2）of the plastic track was nearly 4 times higher than that of the normal foot（P<0.01）. The pressure time integral and total impulse of flat foot M2 were significantly higher than those of normal foot（P<0.01）, while the anterior lateral area（T3）was significantly lower than that of normal foot（P<0.05）.
When running with flat feet, the plantar pressure shows the characteristics of“overload in the midfoot area and insufficient force on the anterior lateral side”. The hard ground intensifies the instantaneous impact, and the elastic surface amplifies the accumulated load. It is suggested that flat-footed runners prioritize choosing a moderately elastic surface and pairing it with arch support equipment to reduce the risk of injury.
To improve the quality and efficiency of the mesh in the finite element model of the knee joint by using the cell-based smoothed finite element method（CS-FEM）.
The gradient smoothing technique is introduced on the basis of the traditional finite element method, and CS-FEM is used to mesh the finite element model of the knee joint, and to compare which of the two methods（traditional finite element method and CS-FEM）is more accurate for the experimental data of the previous study.
CS-FEM is more accurate and reduces the complexity of meshing than the traditional finite element method, and reduces the number of cells, making the solution process more efficient.
The conventional FEM methods offer high computational accuracy and stability when dealing with relatively simple geometries and linear materials due to their wide application and maturity. However, in biomechanical simulation of complex structures and nonlinear materials, CS-FEM provides higher computational efficiency and accuracy by optimizing meshing and reducing stress concentration. Therefore, CS-FEM is expected to be more widely used in the modelling of knee joints and other complex bio-logical structures in the future.
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