摘要:

AbstractThe paper studies certain dynamic characteristics of soil deposits with wave velocities increasing with depth according to (1 + μz)m, wherem= 1, 2/3, 1/2, 1/4 and 0. Analytical solutions are presented for the fundamental periods, mode shapes and amplification functions due to vertically propagating shear waves and the effects of type (m) and rate (μ) of heterogeneity are systematically investigated. The analytical–numerical techniques are used to study the attenuation with depth in a deposit of the vertical and horizontal displacements due to travelling of Rayleigh waves. Differences attributed to different heterogeneities are discussed in connection with the machine isolation problem and the steady‐state vibration technique for soil exploration. Finally, the dependence on soil heterogeneity of the time–distance response curves, obtained during seismic refraction surveys, is graphically illu

ISSN:0363-9061    

DOI:10.1002/nag.1610060103

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractAn analysis is presented of the non‐linear creep effects around a deep circular tunnel driven in ‘squeezing’ ground. The time‐dependent behaviour of the geotechnical medium is described by means of a simple viscoplastic rheological model capable of approximating primary, secondary and tertiary creep behaviours. It is shown that tertiary creep can be allowed for by providing a suitable law governing the variation of some material parameters (such as viscosity) with stresses and strains. The basic operations of the ‘evolutive’ procedure adopted for time integration are outlined. Along each time integration step, quadratic variations of the stress and strain fields and linear variations of the material parameters are assumed. The results of various finite element analyses are presented concerning both lined and unlined cases. For the lined cases, the influence of the liner stiffness and of the time elapsed between the end of excavation and the liner installation is

ISSN:0363-9061    

DOI:10.1002/nag.1610060104

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractIn this paper, the ability of a displacement‐type finite element analysis to predict collapse loads accurately is investigated. For the usual assumptions of ideal plasticity and infinitesimal deformations, attention is focused on undrained geotechnical problems. The theoretical criterion originally developed by Nagtegaalet al.1is applied to each member of the serendipidity quadrilateral and triangular family of elements, up to and including those with a quartic displacement expansion. This method of assessing the suitability of a particular type of element is shown to be valid for any constitutive law which attempts to enforce the constant volume condition at failure, such as critical state type soil models. The method is also generalized to permit an assessment,a priori, of the suitability of any given mesh which is composed of a finite number of elements of the same type. It is postulated that the 15‐noded, cubic strain triangle is theoretically capable of accurate computations in the fully plastic range for undrained geotechnical situations which involve axial symmetry or plane strain. This prediction is verified by a series of numerical experiments on footing problems. Extending the work of Nagtegaalet al.,1it is established theretically that if lower order finite elements are employed rigorously for non‐trivial undrained problems with axial symmetry, then it is impossible to predict the exact limit load accurately, regardless of how refined the mesh m

ISSN:0363-9061    

DOI:10.1002/nag.1610060105

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractIt is commonly accepted that the mechanical behaviour of granular masses is strongly affected by their microstructure, namely the relative arrangement of voids and particles, i.e. the granular fabric. Therefore, parameters which characterize the granular fabric are of paramount importance in a fundamental description of the overall macroscopic stresses and deformation measures. In this paper several measures of granular fabric are introduced for a random assembly of spherical granules, using a statistical approach. In particular, a second‐order symmetric tensor,Fij, emerges from this consideration, which seems to be of fundamental importance for the description of fabric, and which is closely related to the distribution of the contact normals in the assembly. The relation between fabric measures presented here and those discussed by other investigators is also discusse

ISSN:0363-9061    

DOI:10.1002/nag.1610060106

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe notion of overall macroscopic stress in granular masses is examined from a fundamental point of view by a statistical consideration of the contact forces that are transmitted by the contacting granules at the microscale. This examination leads in a natural way to relations between the macroscopic stress and the resulting granular fabric. The overall stresses are expressed in terms of the contact forces in two different but complementary ways: (1) by a statistical averaging over the samplevolumeof contact forces and “branches” which are vectors connecting the centroids of two contacting granules; and (2) by defining the overall tractions transmitted across an interior imagined plane as the sum of the contact forces which represent the mechanical effect of granules on one side of a unit area of this plane, upon those on the other side. Conditions under which the two representations of overall stresses are equivalent, are examined in detail. In addition, explicit results are given, which, define stresses in terms of the fabric and other microstructural characteristics of the granular m

ISSN:0363-9061    

DOI:10.1002/nag.1610060107

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThis paper deals with a numerical formulation of the kinematic limit analysis method. This formulation, based on a finite element discretization, is available for axisymmetric cases. The linearization of the yield Tresca and Von Mises criteria leads to linear programming problems. The velocity fields described here are plastically admissible only on an average. The influence of this approximation is quantified for the triaxial test problem and the stability of circular excavations.

ISSN:0363-9061    

DOI:10.1002/nag.1610060108

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractCollapse loads are overestimated by finite‐element or finite‐difference procedures when the material discretization does not allow locally incompressible plastic flow: for example, constant‐strain triangles or tetrahedra give unacceptable results. The use of different discretizations for the isotropic and deviatoric parts of the strain tensor is advocated for preventing this problem. The technique can be easily implemented in existing two‐ and three‐dimensional computer programs. Its effectiveness is demonstrated by several

ISSN:0363-9061    

DOI:10.1002/nag.1610060109

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractA mapping finite element method is proposed for the solution of elastic problems in two‐dimensions. This method, based on the logarithmic condensation of physical space, is found to give significantly greater accuracy than when the problem is solved in the physical plane using the standard FEM. Logarithmic condensation of space also permits the solution of large aspect‐ratio problems of this type, accurately and economica

ISSN:0363-9061    

DOI:10.1002/nag.1610060110

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

ISSN:0363-9061    

DOI:10.1002/nag.1610060111

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

ISSN:0363-9061    

DOI:10.1002/nag.1610060113

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY