The uplift load capacity of an enlarged base pier embedded in dry sand

Abstract

The purpose of this research is to determine the capability of (and the factors which affect the performance of) an enlarged base pier in resisting uplift capacity. Experiments were conducted in the reinforced bin box of an enlarged base pier with a shaft diameter ranging from 30 to 50 mm, base diameters between 75 and 150 mm and base angles of α = 30°, α = 45°and α = 60°. Tests were conducted in both loose and dense sand packing. A failure mechanism was studied in a glass box for loose and dense sand packing. A dry sand with a unit weight of γ d = 14.80 kN/m 3 and γ d = 17. 0 kN/m 3 was achieved for loose and dense packing, respectively. Increasing the bell angle and shaft diameter would result in a decrease of the net uplift capacity and failure displacement. This is due to the reduction in the amount of the sand column above the bell that resists the uplift of the pile. Failure displacements at a constant base diameter generally increased considerably with the increase of the embedment ratio but decreased with the increment of the sand density. It is thus apparent that the shaft diameter, bell diameter and bell angle are geometric factors which, together with the embedment ratio and the sand density, should be taken into account in the design of enlarged base piers.

Comparison of Uplift Capacity and Nonlinear Failure Surfaces of Single‐Belled Anchor in Homogeneous and Layered Sand Deposits

“…In the present study, it is observed that, when β increased from 45 to 63°and from 63 to 72°, almost all the values of uplift capacities decreased by maximum 10% and by 17 to 22%, respectively, in both the types of sand deposits. e similar pattern in behaviour of uplift capacity was noticed by Nazir et al [8,34] for small bell angles up to 60°installed in homogeneous dry cohesionless soil in conventional test by Advances in Civil Engineering Table 4: Values of experimental uplift capacities in S I and S II /S I (Q u (S I ) and Q u (S II /S I )), analytical uplift capacities in S I and S II /S I (Q u.anlyl. (S I ) and Q u.anlyl.…”

“…Matsuo [24] reported that, due to uplift of anchor, earth pressure within the wedge altered from semiactive condition to passive condition. Failure surface mechanism in homogeneous sand deposit was reported by Dickin et al [3,8] by using semicylindrical modelling. Sakai and Tanaka [23] explained that development of shear band indicated the localized deformation in layered sand.…”

“…e overburden pressure becomes significantly larger when stronger sand of increasing thickness is overlying comparatively weaker sand of fixed thickness, so Q u (S II /S I ) is higher than Q u (S I ) for the same model. ere has been a general trend to gradually decrease in both [2,4,7,8,34,36] in dry sand observed that uplift capacity was considerably decreased by higher diameter ratios in homogeneous sand deposit. In the present study, increasing thickness of overlying stronger sand in layered sand deposit is responsible for higher value of Q u (S II /S I ) than Q u (S I ) in the same model.…”

“…It has been explored from the experimental data presented in Table 4 [2,29,36] in case of plate anchors [7,8,34] for belled anchors had noticed that uplift capacity was significantly increased by higher embedment ratios in homogeneous sand deposit. Higher embedment ratio involves larger overburden pressure on same anchor base irrespective of the type of sand deposit.…”

“…Belled anchor piles may be attractive and economy-friendly alternative to resist resultant pull-out forces in foundation design, but its uplift capacity has yet not been fully investigated. e uplift capacity is influenced by embedment depths, sizes of diameter, and bell angles as observed by Dickin et al [2][3][4][5][6][7][8], but these studies are carried out on homogeneous sand only. Few field tests on belled anchors were reported by Adams and Radhakrishna [9] and Ismael and Kylm [10].…”