对库仑土压力理论的若干修正

库仑土压力理论至今仍是计算土压力的重要方法而被人们所熟知。通过分析库仑土压力的墙后土楔体的受力特点，特别是深入研究了土楔体与墙的作用力关系，对库仑土压力理论给出了一些修正。认为土楔体和挡土墙之间的作用力（即定义的土压力），并非一定要达到极限状态，所以不能确定土压力的作用方向，但土压力的作用方向必须在其允许的角度范围之内。所以，认为库仑主动土压力为作用方向角度变化范围内的最大值，库仑被动土压力为作用方向角度变化范围内的最小值。对于墙后土楔体，认为墙体和土楔体是两个不同物体，土楔体的形成是因为土中产生潜在破裂面，而原库仑土压力理论要求墙体与土之间也达到临界状态是不必要的。墙体对土楔体的作用力（即土压力）实质就是相当于一物（墙）施加于另一物（土楔体）的力，即使土楔体滑动了，两物之间也并非要滑动。推导了主动土压力计算公式，给出了被动土压力的近似计算方案。算例证明，计算结果与原库仑理论有明显不同。该研究对库仑土压力的修正和求解值得引起重视。

Modifications to Coulomb’s theory of earth pressure

Coulomb’s theory of earth pressure is still playing an important role in calculating soil earth pressure and is well known all the world. By analyzing the mechanical characteristics of the limiting equilibrium soil wedge behind the retaining wall, especially the force between the soil wedge and retaining wall, some modifications to traditional Coulomb’s theory of earth pressure are presented. Considering that it is not necessary for the force (which is defined as earth pressure) between the wedge and the retaining wall surface 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 is the minimum value of the force within the corresponding allowed range. 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. As a matter of fact, the force between the wall surface and the soil wedge is equivalent to the force exerted on an object (soil wedge) by another object (retaining wall); 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. The formulas of the modified active earth pressure are derived and an approximate solution is presented for the passive earth pressure calculation. Examples prove that the results of this study are significantly different from the classic Coulomb’s theory. The works of modifying Coulomb’s theory of earth pressure deserve much more attention.