A theoretical solution for the progress of consolidation of a saturated soil layer subjected to cyclic loading is obtained.Consolidation, proceeding inwards from the drainage face, is slower than consolidation under an equivalent sustained loading because positive and negative pore-water pressures, produced during the loaded and unloaded portion of the cycle, cause flow of water from and into the soil. An equilibrium, or finalized, consolidation ratio is reached which is dependent on the pattern of loading cycle; it is not possible to reach 100% consolidation under cyclic loading.
Repeated and sustained loading tests on undrained samples of normally consolidated lacustrine clay are used to prove the existence of a relationship between pore water pressures and axial strains.The behavior of the clay is studied by investigating the pore pressure and strain responses under repeated loading, and comparing them with the responses from the more usual sustained loading. Samples under repeated loading fail at a stress below the compressive strength of the material as obtained from a standard strength test.It has been shown that, for a repeated stress level below a critical value a non failure equilibrium state is reached, closed stress-strain hysteresis loops occur and the soil behavior is essentially elastic. For a repeated stress above the critical value, the effective stress failure envelope is reached and each loading cycle leads to further nonrecoverable deformations and ultimate failure.The pore pressures and axial strains produced by loading may be divided into recoverable and nonrecoverable components; both components of pore water pressure are linearly related to the axial strain provided the sample is not close to failure and there is a gradual increase in axial strains and pore pre~sures with time. This relationship is explained by a simple mechanistic picture.The pore pressures due to the application of a shear stress may be considered as a combination of an elastic recoverable component, due to the elastic response of the soil grain structure, and a plastic nonrecoverable component due to a partial collapse of the grain structure with subsequent transfer of stresses from the failed grain contacts to the pore water. There are coresponding axial strains occurring due to the elastic response of the soil grain structure and the partial collapse of the structure.Experimental proof of the pore pressure versus strain relationship is presented by means of a series of loading tests on normally consolidated lacustrine silty clay samples tested under undrained triaxial conditions. Des essais non draines de changernent a charge constante ou alternee sont utilises pour demontrer l'existence d'une relation entre pressions interstitielles et deformations axiales.Le comporternent de l'argile est etudie, par observation des variations de pressions interstitielles et des deformations sous I'infiuence de charges alternees et par comparaison de ces variations avec celles qui :;e produisent dans les essais classiques ii charge constante, Les echantillons soumis a des charges alternees atteignent la rupture pour une contrainte inferieure it la resistance en compression du rnateriau telle qu'obtenue a partir d'essais standards.II a cte etabli que, pour un niveau de contrainte alternee 'inferieur it une valeur critique, un etat d'equilibre stable est atteint auquel correspondent des courbes effort-deformation en forme de boucles d'hysrerisis ferrnees et un cornporternent essentiellernent elastique du sol. Pour une contrainte alternee superieure a la valeur critique, I'enveloppe de rupture en contraintes effe...
= cohesion strength when the major principal stress at failure is inclined at angle i to the vertical (Fig. lb) = principal cohesion strengths in the horizontal and vertical directions respectively (Fig. 1 b) = vertical height of an embankment = critical height of an embankment = length AA' in Fig. l a = angle of rotation of major principal stress from vertical, measured clockwise (Fig. Ib) = angle between failure plane and the plane normal to the direction of the major principle stress which inclines at angle i with the vertical direction (Fig. la) = angular parameters of an embankment, Fig. l a x l , C L~ = depth factor of the slope, Fig. l a *a&, = angular variables of a log-spiral curve, Fig. l a 8111 = angle of a log-spiral curve, see Fig. l a 9 = friction angle of soil ro,ql,r(0) = length variables of a log-spiral curve R = angular velocity V(0) = discontinuous velocity across the failure plane Ns = stability factor Y = unit weight of soil K = degree of anisotropy = C,/C, z = ordinate measured from top of slope C = horizontal cohesion strength at the level of the toe (Fig. lc)
The paper is divided into two parts. The first part deals with the systematic program of measurements undertaken on an open braced cut in dense sand at the Greenway Pollution Control Centre in London, Ontario. In the second part, the experimental data are analyzed and a new solution is presented based on Dubrova's analysis, which related qualitatively and quantitatively the active earth pressure distribution to the mode of deformation of a retaining structure.The roughly L-shaped excavation measured 68 × 42 ft (20.7 × 12.8 m) for the longest leg, the other leg was 30 × 23 ft (9.1 × 7.0 m). The temporary bracing system consisted of interlocking steel sheet piles (Larssen IIIN), and wales and struts from wide-flanged steel sections. The maximum depth of the cut was 50 ft (15.2 m) below ground elevation of 722 ft (220.1 m). The soil consisted of fine uniform dense sand having a relative density varying from medium to very dense. The natural water level was approximately 20 ft (6.1 m) below the ground surface prior to construction.The instrumentation program was carried out during the 6-month construction period (January–June 1964) and consisted of measuring: (1) The strut loads with a mechanical strain indicator (Whitmore gauge) over 8 in. (20.3 cm) gauge lengths, (2) The deformation of the north wall in a horizontal and a vertical plane, (3) The water levels and water pressures from borehole and standpipe observations, and (4) The active and passive earth pressures over the cut with 'Geonor vibrating-wire pressure transducers mounted flush on two adjacent sheet piles of the north wall.Field and laboratory tests supplied the necessary soil data.Comprehensive measurements of this kind in deep cuts in sand, prior to this London investigation, had only been made in Berlin, Munich, and New York. But at London, for the first time the actual distribution of earth pressures in sand were measured on a full-scale braced wall.The analysis of the experimental data showed that the earth pressure distribution can be approximated by the extended Dubrova’s solution. The agreement between the total active earth pressure obtained from the pressure cells and the corresponding Coulomb values varied from excellent (upper bound) to good (lower bound).An experimental relationship between the horizontal soil strain and the variation of K-values over the depth of the cut was established.The different theories for predicting Ko-values do not seem to apply to over consolidated dense sand deposits. The experimental Ko-values, rather, agree with other published experimental values for similar soils.The strut load readings were somewhat erratic, not necessarily corresponding to the excavation progress. The total strut loads were lower than the corresponding forces from the earth pressure cells or the corresponding Coulomb values.
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