Citation for published item:ysmnD eF F nd foltonD wF hF @PHHSA 9imple plstiityEsed predition of the undrined settlement of shllow irulr foundtions on lyF9D q¡ eotehniqueFD SS @TAF ppF RQSERRUF Further information on publisher's website: httpXGGdxFdoiForgGIHFITVHGgeotFPHHSFSSFTFRQS Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. A kinematic plastic solution has been developed for the penetration of a circular footing into an incompressible soil bed. In this solution, the pattern of deformation around the footing is idealised by a simple plastic deformation mechanism. Strain-hardening behaviour and nonlinear stress-strain characteristics are incorporated. This application is different from conventional applications of plasticity theory as it can approximately predict both stresses and displacements under working conditions. This approach therefore provides a unified solution for design problems in which both serviceability and safety requirements are based directly on the stress-strain behaviour of the soil. The design strength that should limit the deformations can be selected from the actual stressstrain data recorded from a carefully specified location, and not derived using empirical safety factors. The validity of this design approach is examined against nonlinear finite element analyses and field measurements of foundations on clay under short-term loading.

Citation for published item:ysmnD eF F nd wirD F tF nd foltonD wF hF @PHHTA 9yn the kinemtis of Ph tunnel ollpse in undrined lyF9D q¡ eotehniqueFD ST @WAF ppF SVSESWSF Further information on publisher's website: httpXGGdxFdoiForgGIHFITVHGgeotFPHHTFSTFWFSVS Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. A kinematic plastic solution has been developed for ground movements around a shallow, unlined tunnel embedded within an undrained clay layer. In this solution, the pattern of deformation around the tunnel is idealised by a simple plastic deformation mechanism. Within the boundaries of the deformation mechanism, the soil is required to shear compatibly and continuously with no relative sliding at the boundaries. The soil is regarded here as a rigid plastic (Tresca) material. Peck (1969) summarises the most important requirements for successful design and construction in tunnels as stability, control of ground movements, and performance of linings. This paper aims to provide a simple theoretical framework for assessing the first two requirements for tunnels constructed in clays. This paper is concerned only with construction effects in clays that are presumed to remain undrained. The upper and lower bound theorems of plasticity (Drucker et al., 1952) offer a rigorous and powerful technique for estimating the collapse loads. Davis et al. (1980) derived plasticity solutions employing kinematic upper bounds and statically admissible lower bounds for planestrain circular tunnels and for a two-dimensional idealisation of the tunnel heading stability in clays with constant shear strength. To obtain an upper bound to the collapse load, they developed a number of deformation mechanisms in which the soil moves as rigid blocks sliding relative to each other with displacement discontinuities at their boundaries. Davis et al. (1980) found that the three-variable and the fourvariable mechanisms shown in Figs 1(a) and 1(b) give the lowest (i.e. the most critical) upper bounds. Sloan & Assadi (1993) developed extensive sets of upper bound and lower bound solutions for plane-strain tunnels in soils whose undrained strength varies with depth. Significant improvements on the upper bound solutions were achieved by using a more complex seven-variable mechanism ( Fig. 1(c)). Sloan & Assadi (1993) also improved both upper bound and lower bound calculations using numerical limit analysis. In this technique, rigorous upper and lower bound collapse loads are found numerically by linear programm...

SUMMARYThis paper presents 2D and 3D upper bound solutions for the problem of tunnel excavation in soft ground. The solution invokes the use of incompressible flow fields derived from the theory of elasticity and the concept of sinks and sources. Comparison is made with previously published results. For some geometries the current calculation results in lower (better) upper bound values; however, the results were generally close to previously published values.

Geotechnical design engineers used to rely on arbitrary rules and definitions of "factor of safety" on peak soil strength in limit analysis calculations. They used elastic stiffness for deformation calculations, but the selection of equivalent linear elastic models was always arbitrary. Therefore, there is a need for a simple unified design method that addresses the real nature of serviceability and collapse limits in soils, which always show a nonlinear and sometimes brittle response. An approach to this method can be based on a new application of the theory of plasticity accompanied by the introduction of the concept of "mobilizable soil strength." This approach can satisfy both safety and serviceability and lead to simple design calculations within which all geotechnical design objectives can be achieved in a single step of calculation. The proposed method treats a stress path in an element, representative of some soil zone, as a curve of plastic soil strength mobilized as strains develop. Designers enter these strains into a plastic deformation mechanism to predict boundary displacements. The particular case of a cantilevered retaining wall supporting an excavation in clay is selected for a spectrum of soil conditions and wall flexibilities. The possible use of the mobilizable strength design (MSD) method in decision-making and design is explored and illustrated.Résumé : Les ingénieurs géotechniciens avaient l'habitude de se fier dans leurs calculs d'analyse limite à des règles et définitions arbitraires du « coefficient de sécurité » basées sur la résistance de pic du sol. Ils utilisaient la rigidité élas-tique pour les calculs des déformations, mais la sélection de modèles équivalents élastiques linéaires était toujours arbitraire. En conséquence, on a besoin d'une méthode simple et unifiée de conception qui traite de la nature réelle de la praticabilité et des limites d'effondrement des sols, qui montre toujours une réponse non linéaire et parfois fragile. Une approche à cette méthode peut être basée sur une nouvelle application de la théorie de plasticité accompagnée de l'introduction du concept de « résistance mobilisable du sol ». Cette approche peut satisfaire tant la sécurité que la praticabilité, et peut conduire à des calculs simples de conception dans lesquels tous les objectifs de conception géotech-nique peuvent être atteints au cours d'une étape unique de calcul. La méthode proposée considère un cheminement de contrainte dans un élément représentatif d'une certaine zone de sol, comme étant une courbe de résistance plastique du sol mobilisée à mesure que les déformations se développent. Les concepteurs entrent ces déformations dans un méca-nisme de déformation plastique pour prédire les déplacements aux frontières. Le cas particulier d'un mur de soutène-ment en porte-à-faux retenant une paroi d'excavation dans l'argile a été choisi comme éventail des conditions des sols et de la flexibilités du mur. On explore et illustre l'utilisation possible de la méthode de calcul de la résistance mobilisable...