Mechanism Study On Coulomb’s Theory Of Earth Pressure And Its Engineering Application

Coulomb’s theory of earth pressure remains one of the main methods of calculation of earth pressure, and is widely used in engineering. However, with the development of science in civil engineering and the improvement of security requirements to civil engineering, the traditional earth pressure theory has not been able to meet the design and calculation of earth pressure problems, the study on earth pressure theory has always been an active topic in the field of civil engineering. According to current research on Coulomb’s earth pressure, this thesis discusses and studies Coulomb’s earth pressure calculation method from the view of basic mechanics methods and mechanical phenomena. The research work of this thesis can be summarized as follow:1. With the analysis of mechanical characteristics of the limiting equilibrium soil wedge behind the retaining wall, especially with a further study of the force between the soil wedge and retaining wall, some modifications to traditional Coulomb’s theory of earth pressure are presented.(1) Considering that it is not necessary for the force (which is defined as earth pressure) between the wedge and the retaining wall surface acting on the wedge to be on the point of sliding or to be in a condition of limiting equilibrium, the direction of the earth pressure can not be determined, but it must be limited in an allowed range according to the friction angle. Therefore, the active earth pressure is defined as the maximum value of the force within the allowed range, and the passive earth pressure will be the minimum value of the force within the corresponding allowed range.(2) This paper also considers that the soil wedge and the retaining wall are two different objects, and the soil wedge is formed only because of the potential failure surface of the soil itself, in other words, it is not necessary for the force between the wedge and the wall surface to achieve a critical state. Indeed, the force between the wall surface and the soil wedge is equivalent to the force that an object (retaining wall) acts on another object (soil wedge), and even if the soil wedge slides along a failure surface, the two objects do not need to slide each other along their contact surface.(3) The formulas of the new defined active earth pressure are derived and an approximate solution is presented for the passive earth pressure calculation. Examples prove that the results of the works in this paper are significantly different from the classic Coulomb’s theory.2. Considering that the traditional Coulomb’s theory of earth pressure is not satisfied with the balance of torque, a strict static equilibrium calculation method is studied.(1) The analytical formulas of soil pressure are derived under the condition of earth wedge static equilibrium of torque.(2) By establishing the model of different types of retaining wall, and using the Matlab software for the analytical formulas caculation, the magnitude of the thrust is solved for various inclining angle of the sliding surface of the soil wedge. The maximum magnitude of soil pressure is searched out in the allowed range of angle of the thrust direction. Then the sliding surface is obtained as well.(3) The results is obtained that the inclining angle of the surface of backfill slope have an effect on the calculation results of earth pressure.3. Engineering examples are studied by the finite element method, with the comparison to the results of traditional Coulomb theory, modification’s theory method and the strict static equilibrium method. The results show that both the modification’s method and the strict method are more reasonable than the traditional theory, and demonstrates the significance of this study both in theory and in engineering.