The changing strength of carbonate silt: parallel penetrometer and foundation tests with cyclic loading and reconsolidation periods

Abstract

This paper describes a centrifuge study using novel penetrometer tests (T-bar and piezoball) and model foundation tests to explore through-life changes in the strength of a reconstituted natural carbonate silt. The test procedures include episodic cyclic loading, which involves intervals of pore pressure dissipation between cyclic packets. These loads and the associated remoulding and reconsolidation cause significant changes in the soil strength and foundation capacity. Soil strength changes from penetrometer tests differed by a factor of 15 from the fully remoulded strength to a limiting upper value after long-term cyclic loading and reconsolidation. For the model foundation tests, the foundation capacity of a surface foundation and a deep-embedded plate were studied. The soil strength interpreted from the measured foundation capacity varied by a factor of up to three due to episodes of loading and consolidation, with an associated order of magnitude increase in the coefficient of consolidation. The results show a remarkable rise in soil strength over the loading events, and provide a potential link between changes in soil strength observed in penetrometer tests and the capacity of foundations, allowing the effects of cyclic loading and consolidation to be predicted.

A cyclic p-y model for the whole-life response of piles in soft clay

“…The net result is a rise in strength and stiffness, and a reduction in the sensitivity observed in each packet. This trend matches published results from various model testing studies of lateral pile behaviour (Zhang et al 2011, Doherty et al 2019, Guevara et al 2020, Lai et al 2020 as well as analogous studies of cyclic T-bar penetrometer tests (White & Hodder 2010) or plate anchor loading (Zhou et al 2020).…”

“…The same process of cyclic softening followed by consolidation and strengthening has been recognised in the behaviour of pipelines, foundation and anchors on soft clay seabeds, and has been captured by simple design-focused models based on critical state soil mechanics (e.g. Boukpeti and White 2017, Cocjin et al 2017, DNV-GL 2019, Zhou et al 2020. The purpose of this paper is to outline a model for the lateral p-y response of piles that captures these same underlying mechanisms.…”

“…The parameter values are listed in Table 1 and are based on the theoretical consideration given earlier in the paper, with minor modifications to improve the match with the experimental data. The adopted initial sensitivity, S t0 , is from cyclic T-bar testing of carbonate silt reported by Zhou et al (2020). The predicted evolution of cyclic secant stiffness is shown in Fig.…”

A Framework for Mooring and Anchor Design in Sand Considering Seabed Trenches Based on Floater Hydrodynamics

“…Thus, a reliability study could generate a better understanding of the results. In addition, for the long-term behavior of anchors, whole-life analyses of the anchors should be considered in the design [48][49][50][51].…”

Effect of Gain in Soil Friction on the Walking Rate of Subsea Pipelines

“…As is evident, throughout a pipeline's operational loading cycle, the surrounding soil could be enhanced during the intermittent periods, such as in the operation and maintenance phases, which is mainly attributed to the occurrence of consolidation in these stages [15,[21][22][23][24]. Hence, reasonable adoption of soil friction in the design of subsea pipelines is necessary in order to capture a reliable estimation of walking rate.…”