Pile end-bearing capacity in crushable sands

Abstract

The occurrence and formation of crushable soils is a widespread phenomenon. Warm tropical seas give rise to deep deposits of biogenic skeletal sediments in coastal shelf areas, or exposed granitic intrusions are subjected to deep weathering resulting in decomposition. The end-bearing capacity of piles in crushable soils is important for the design of foundations in these diverse soils, but the analysis of foundations in these soils is problematic due to their compressibility and highly curved Mohr–Coulomb failure envelopes. The use of the spherical cavity expansion method offers potential for a better prediction of end-bearing capacities by taking into account soil crushability and the decrease of friction angle with increasing mean normal stress. A formula relating end-bearing pressure to the pressure to expand a cavity and the soil secant friction angle has been developed, which refines and simplifies Vesic's original equations. However, the actual model pile settlement ratio at which the predicted cavity expansion values were reached increased with soil crushability and decreased with increasing relative density. A simple linear relationship has been proposed between a soil compressibility index Cp and the pile settlement ratio at which the bearing capacity predicted by the theoretical cavity expansion method is mobilized. KEYWORDS: calcareous soils: laboratory tests; model tests; offshore engineering; piles; sands. Les sols compressibles sont des formations très répandues. Its se forment dans les mers chaudes tropicales qui favorisent le dépôt de sédiments biogéniques profonds dans les zones de plate-forme côtière, ou proviennent de l'altération profonde de granites intrusifs affleurants se traduisant par une décomposition du matériau. La capacité portante en pointe des pieux devient done un paramètre primordial pour la conception de fondations dans ce type de sols. Toute analyse de fondations dans ce type de sols pose cependant des problèmes en raison de la compressibilité et des enveloppes de rupture de Mohr–Coulomb très incurvées de ces sols. La méthode par expansion d'une cavité sphérique est susceptible de permettre une meilleure prévision de la capacité portane en pointe puisqu'elle prend en compte la compressibilité du sol et al diminution de l'angle de frottement lorsque la contrainte normale moyenne augmente. Une équation, plus simple que les équations de Vesic, a été établie entre la pression en pointe, la pression d'expansion d'une cavité et l'angle de frottement tangential du sol. Cependent, avec notre modèle de pieux actuel, les valeurs de tassement, correspondant aux valeurs prévisionnelles de l'essai d'expansion de cavité, augmentent avec la compressibilité du sol et diminuent lorsque la densité relative augmente. On propose une relation linéaire simple entre l'indice de compressibilité Cpdu sol et le tassement des pieux pour lequel la capacité portante prevue par la méthode d'expansion d'une cavité théorique est mobilisée.

Particle breakage during cyclic triaxial loading of a carbonate sand

“…The engineering behaviour and properties of the material have been examined in detail by a number of researchers (e.g. Houlsby et al 1988;Golightly 1989;Coop 1990;Coop & Lee 1993;Yasufuku & Hyde 1995;Hyodo et al 1998;Coop et al 2004;Tarantino & Hyde 2005;Qadimi & Coop 2007). There is some variability among the particle size distributions ( Figure 1) and index properties (Table 1) reported in the literature.…”

Interpretation of Cone Penetration tests in Cohesive Soils

“…After Vesic, significant progress was made in developing cavity expansion solutions by adapting improved soil stress-strain models and yield criteria in both clay and sand (Cater et al 1986, Yu and Houlsby 1991, Salgado et al 1997, Salgado and Randolph 2001. More specifically, many researchers have related limit pressure solutions to practical values, such as pile end bearing or cone resistances (Randolph et al 1979, Salgado 1993, Yasufuku and Hyde 1995, Salgado and Randolph 2001). All cone factors N k derived from cavity expansion solutions depend on the rigidity index I r of soil.…”

Breakage of an artificial crushable material under loading

“…: detrimental clogging and formation damage near petroleum wells [12], permeability losses around perforations [10,31], impaired fluid conduction owing to particle crushing in locations adjacent to testing penetrometers and friction fatigue around piles [42], and crushing-induced instability transitions in highly stressed soil masses adjacent to or located within geotechnical structures, for instance filters for large dams [19]. [44] and [35] have discussed the effect of soil crushing on pile end bearing capacity while, more recently [22] examined the effect of particle crushing on the capacity of driven piles; Zheghal [45] studied the role of grain crushing in road construction; [29] reported that grain crushing within the failure zone is responsible for the rapid long run-out motion of landslides and sturzstroms, as observed in physical experiments in a geotechnical drum centrifuge by [16].…”