Mortise-tenon and joint-flange assembled foundation has excellent application as a new type of slab concrete assembled foundation, but there is a lack of research on its bearing capacity. In order to explore the mechanical characteristics and bearing capacity of this type of foundation under combined load (uplift-horizontal load), which is different from the traditional cast-in-place foundation, the uplift bearing model of mortise-tenon and joint-flange assembled foundation and the uplift model of cast-in-place foundation with the same specification were established based on the actual geological environment by finite element software. The stress distribution, vertical and horizontal displacements, and uplift and horizontal bearing capacities of the foundations were simulated and calculated. This study found that the bearing capacity of the Mortise-tenon and joint-flange assembled foundation has not been fully utilized. Specifically, the deformation of the foundation mainly concentrates on the main column, and the load is unable to be transmitted to the lower structure through the flange. Under combined loading (uplift-horizontal load), the load-displacement relationship curve can be roughly divided into three stages: linear slow rise stage, plastic accelerated rise stage, and linear failure stage. During the pull-out process, the foundation demonstrates stress characteristics of segmented load transmission. After the concrete upper column yields, the mortise-tenon and joint-flange connection node receives the load transmitted by the upper column, and continues to transmit the load to the lower column of the foundation after the displacement of the node reaches its limit. When the uplift cumulative displacement of the foundation reaches approximately 13 mm and the horizontal cumulative displacement reaches around 10 mm, the foundation reaches its ultimate state. At this point, its ultimate bearing capacity surpasses that of the cast-in-place foundation of the same specification, with significant improvement. The ultimate uplift bearing capacity increases by 33.34%, while the ultimate horizontal bearing capacity increases by 48.09%.

Influenced by the complex geological conditions in mountainous region, micro-pile foundation for transmission line faces the risk of insufficient bearing performance. It is important to study the risk suppression measures of micro-pile foundation and its assessment method to promote the construction of transmission lines in mountainous regions. Firstly, the mechanical simulation model of pile-soil system for the micro-pile foundation is established in this paper, and the field test is carried out to verify the accuracy of the simulation model, thus the ultimate load of the micro-pile foundation is determined according to the current code requirement for maximum displacement in case of damage to the group pile foundation. Secondly, to address the subjectivity of traditional methods, an improved Likelihood-Exposure-Consequence (LEC) method is proposed. Its novelty lies in constructing a quantitative displacement-risk mathematical mapping, directly linking the physical limit state (maximum displacement) to the risk likelihood factor. Thirdly, structural risk reduction measures for the micro-pile foundation using micro-expanded pile foundation and micro-inclined pile foundation are proposed, and the ultimate load of the traditional micro straight pile foundation is used as an excitation to carry out the simulation of the bearing performance of the two improved micro-pile foundations, and the maximum displacements of the two improved micro-pile foundations are calculated. Finally, based on the proposed improved LEC method, the risk values-defined in the LEC framework as the quantitative product of Likelihood ( L ), Exposure ( E ), and Consequence ( C )-and risk classes of the two improved micro-pile foundations are calculated and compared with the conventional micro straight pile. The results demonstrate that the proposed strategies significantly reduce the safety risk class, providing a robust, quantifiable basis for optimizing foundation designs in complex mountainous terrain.

To balance the requirements of structural safety and economic efficiency in transmission tower design, this study proposes a structural optimization method based on an Improved Sparrow Search Algorithm (ISSA). Specifically, the methodology integrates Circle chaotic mapping to initialize the sparrow population distribution, followed by the introduction of a firefly perturbation strategy. This strategy updates the sparrow positions derived from the basic algorithm, thereby enhancing the algorithm’s ability to escape local optima. Based on these enhancements, a mathematical model for structural optimization is established with the primary objective of minimizing the total weight of the tower. The penalty function method is employed to handle constraints, while the finite element method is utilized for internal force analysis. To verify the effectiveness of the proposed approach, a typical cat-head transmission tower is selected as a case study. The optimization results obtained from the ISSA are compared with those produced by the Daoheng software, demonstrating a weight reduction of 3.79%. These findings indicate that the ISSA effectively improves the optimization performance and provides an efficient solution for the preliminary sizing design of transmission towers.