Calculations of the bearing capacity of soil masses

Abstract

Calculation of the stress and strain of soil masses (foundations, dams, earth embankments, and slopes) to assure the maximum use of their bearing capacity should be done for any effects on them wlth consideration of the appearance and development of zones of limit stress in the soil. Such a Solution is realized in the mixed problem of the linear or nonlinear theory of elasticity and plasticity using a single model of elastoplastic soil at all loading stages [1]. The corresponding variants of its formulation within the scope of the theory of plastic flow with the use of associated and nonassociated laws for plastic deformations developing in the region of limit equilibrium were examined earlier [2,3]. Realization of the mixed problem and the results of calculations of the stress and strain of earth dams and structures within the scope of the associated model were presented in sufficient detall in articles [4,5]. Also given there with reference to flexible and rigid plates is a detailed comparison of the calculated and experimental results on the values and character of the load--settlement curves, outline of the settlement crater and its change during loading, diagrams of contact stresses, and a number of other quantities.It is shown that the calculated results qualitatively and quantitatively agree well with the data from the instrumental measurements and reliably reflect the behavior of the soils during loading, thereby justifying the use of the associated law in mixed solutions for dense and average-density soils, i.e., for practically the majority of foundations and masses that are encountered. At the same time we note that the solution of the mixed problem in the case of the nonassoclated law of flow obtained for compacted soils showed an insignificant (for dense soils within the accuracy of the calculations) deviation of the results from those obtained on the basis of the associated model of soil [3]. In particular, in the case of plane strain the use of a rate of dilatancy A =(0.5-0.8) sin~, which is characteristic for moderately dense soils, instead of A -sin ~ (associated flow) increases settlements of foundation by not more than i0-15%, i.e., both flow laws give practically the same results. However, the use of the associated law considerably shortens the program an d calculation on a computer and eliminates laborious (we add, quite inaccurate) experiments on measuring the rate of dilatancy, which is an additional parameter of the nonassociated soil model. All this determined the use of the associated law in the examples of applying the mixed problem of plane strain to calculation of the bearing capacity of certain soil masses examined below. We will dwell on the results of this application. Figure i shows for various schemes of foundations the "average pressure --settlement" curves used for determining the values of the limit pressures. In the calculations the state of strain in the foundations was determined from the external load, but in this case the natural stresses o x =~TY, Oy =TY, Zxy =0 from the...

Bearing capacity of sand bases (discussion of construction specifications)

“…An analysis of recent experimental and theoretical works [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] devoted to a study of the stability of sand bases under inclined static loads revealed substantial differences in a quantitative estimation of the bearing capacity of these bases. These estimates in various methods of calculation differed by a factor of 8-10, which forces one to doubt the reliability of their theoretical basis.…”