Effect of embedment on consolidated undrained capacity of skirted circular foundations in soft clay under planar loading

Abstract

The effect of foundation embedment ratio and soil–skirt interface roughness on the consolidated undrained capacity of skirted circular foundations under planar loading in normally consolidated clay has been investigated through coupled three-dimensional finite element analyses. Results are presented as failure envelopes, and changes in shape and size of the normalized vertical–horizontal–moment (VHM) failure envelopes are described as a function of relative magnitude and duration of applied preload. Results show that embedment ratio and interface roughness affect the load distribution within the soil mass, but that consolidated undrained capacity under planar loading scales proportionately with the (unconsolidated) undrained capacity of the foundation. This latter feature enables the results to be neatly synthesized into a relatively straightforward method for use in engineering practice for prediction of gain in undrained VHM capacity due to preload and consolidation.

Consolidated undrained capacity of shallow foundations subjected to self-weight and horizontal in-service loading

“…Stress and strength factor f σ f su for critical state interpretation, equation 1Loading direction counterpart. This trend is consistent with that observed for skirted circular foundations preloaded under self-weight conditions only (Vulpe et al, 2016b).…”

“…quantify the increase in consolidated undrained uniaxial vertical capacity of surface foundations following vertical preloading and consolidation (equation 1). The framework was successfully applied to predict gains in consolidated undrained vertical, horizontal and moment uniaxial capacity of skirted circular foundations (Vulpe et al, 2016a(Vulpe et al, , 2016b)…”

“…Failure envelopes in normalised horizontal and moment load space (HM) for rough skirted foundations with d/D = 0•25 under unconsolidated undrained (UU) (Vulpe, 2015) and consolidated undrained consolidations (Vulpe et al, 2016b and current study) are compared in Fig. 9.…”

“…The deep sea architecture is generally constructed well in advance of commencement of hydrocarbon reserves extraction operations, leaving sufficient time for the excess pore water pressure generated under the low self-weight of the structure to dissipate. The effect of self-weight (vertical) preloading and consolidation on the undrained capacity of shallow foundations has been previously investigated (Bransby, 2002;Zdravkovic et al, 2003;Chatterjee et al, 2014;Gourvenec et al, 2014;Feng & Gourvenec, 2015;Fu et al, 2015;Vulpe et al, 2016aVulpe et al, , 2016b but the effect of in-service horizontal loading on the undrained response of shallow foundations has not been previously considered. The pipeline expansion/contraction loading is cyclic and the soil consolidates following each cyclic loading event until a critical state is reached.…”

Vertical cyclic loading response of shallow skirted foundation in soft normally consolidated clay

“…Consolidated soil strength, s u (consolidated) is considered here to account for the increase in su during the waiting period under the monotonic vertical stress. The value of su (consolidated) is estimated based on a theoretical framework, verified by back-calculating s u values from uplift resistance in centrifuge uplift tests of a shallow skirted foundation (d/D = 0.2) in lightly over-consolidated kaolin clay following preloading and consolidation (Li et al 2015), and numerical results reported by Vulpe et al (2017) for a monotonic vertical stress q V/qV,ult = 0.2 and T = 0.04 (Figure 8).…”