Vízügyi Közlemények, 1935 (17. évfolyam)

Kivonatok, mellékletek - Kivonat a 3. számhoz

I. THE CLASSICAL THEORY OF EARTH PRESSURE. By Prof. DR. J. JÁKY. (In the Hungarian text, pages 352—390.) The problem of earth pressure is still an unsolved question oftechnical mechanics. It is true that practically sufficient solutions are known as to the magnitude of the pressure, but there is great uncertainty as to how its direction lias to be taken. A perfect mathematical solution is still wanting. The present study clears up the subject, and on the basis of a curved sliding slope gives a definitive solution for soils without cohesion. I. History of the Earth Pressure Theories. The fundamental principles of the classical theory of earth pressure were laid down by Charles Coulomb, the great French physicist, in 1773. In his proposition, the computation of earth pressure on retaining walls is a simple static problem, because he neglects the assumption of deformations. Coulomb'

s theory assumes that (1) the sliding slope is a plane ; (2) when sliding ensues, in the sliding plane T=N . tgrp, where cp is the angle of internal friction ; (3) among the infinitive many plane sections starting from the base-point A, the actual sliding plane cuts that ABC J earth wedge which exerts a maximum pressure E on the retaining wall (fig. 1). In this way •— supposing that the pressure is of horizontal direction — the value of earth pressure is defined by equation 2, and the resultant pressure attacks the back of a retaining wall in the lower third point. Later investigators, disciples of Coulomb, have also generalized this solution of earth pressure for the case when the resultant pressure passes under any S angle, i. e. when friction is also acting on the back of the wall. Figure 2 shows this case (Poncelet'

s graphic method, Rebhann's theorem, Culmann'

s hyperbola, Möllens rule as to the direction of pressure, etc.). But this generalisation infringes the third law of equilibrium of forces, because the three forces E, G, and R do not pass through one point. The importance of the direction of the earth pressure has been pointed out by M u e l ler Breslau, and in figure 3 we show the different stresses and dimensions of wall, which result from the variation of the stress with t) angle. The value of earth pressure scarcely changes with !) angle, but the magnitude and point of application of the resultant pressure change all the more, as do the stresses in the wall and subsoil.