What are the foundation design methods of natural foundation?

Above the foundation are the walls and columns of the superstructure, and below the bottom of the foundation is the foundation soil. The foundation bears the action of the superstructure, exerting pressure (base pressure) on the foundation surface, and at the same time, the foundation surface produces reaction force (base reaction force) on the foundation. They are equal in size and opposite in direction.

The upper load and foundation reaction force borne by the foundation should meet the equilibrium conditions. Foundation soil produces additional stress and deformation under the action of foundation pressure, foundation produces internal force and displacement under the action of superstructure and foundation reaction, and foundation and foundation interact and restrict each other. In addition, besides the load, the foundation is also closely related to its ability to resist deformation or displacement. Moreover, the foundation and foundation are also related to the load and stiffness of the superstructure, that is, the foundation, foundation and superstructure influence and restrict each other. Under the comprehensive influence of load, displacement and stiffness of each part, the parts they are used to connect or contact generally remain connected or contacted, and the displacement at the bottom of the wall column, the displacement of the foundation there and the settlement of the foundation surface are consistent, which meets the deformation coordination conditions. The above concept can be called foundation-foundation-superstructure interaction. In order to simplify the calculation, in engineering design, the superstructure, foundation and foundation are usually calculated separately: the bottom of the superstructure is regarded as a fixed bearing or a fixed hinge bearing, and the relative displacement of the end of each wall column under load is not considered, and the internal force is analyzed accordingly; For foundation and foundation, it is assumed that the foundation reaction and foundation pressure are distributed in a straight line, and the internal force and settlement of foundation are calculated respectively. This traditional analysis and design method can be called conventional design method.

This design method is feasible for high-stiffness foundation and superstructure with uniform wall and column layout, symmetrical acting load and similar size on good homogeneous foundation. In these cases, the results calculated by conventional design methods are not much different from the analysis of foundation-foundation-superstructure interaction, which can meet the requirements of structural design reliability and have been tested by a large number of engineering practices. Generally speaking, the foundation pressure is not distributed in a straight line (or plane), which is related to the nature of soil, the size and stiffness of foundation and load. Under the conditions of weak foundation, large plane size of foundation and uneven load distribution of superstructure, the settlement and stress of foundation will be affected by foundation and superstructure, and the internal force and displacement of foundation and superstructure will also be adjusted. If calculated by conventional methods, the displacement at the bottom of the wall column, the deflection of the foundation and the settlement of the foundation are all different, and the deformation of the three is uncoordinated and unrealistic. Moreover, the additional internal force of superstructure and the change of internal force of foundation caused by uneven settlement cannot be considered in structural design, so it is unsafe.

Only by analyzing the interaction of foundation-foundation-superstructure can the design be carried out reasonably, thus reducing the cost and preventing the building from being damaged. At present, the research work in this field has made progress. According to some measured data, people can analyze the interaction of some structural types, foundation forms and foundation conditions with the help of computers, and apply the results or concepts of interaction analysis to engineering practice.