Interpretation of T-bar penetrometer tests at shallow embedment and in very soft soils

White, David; Gaudin, Christophe; Boylan, Noel; Zhang, Hongjie

doi:10.1139/t09-096

Cited by 157 publications

(44 citation statements)

References 11 publications

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“…This not only allows the fully remoulded soil strength to be quantified, but provides a basis for 0 0·0 0·2 0·4 0·6 0·8 1·0 0·0 0·2 0·4 0·6 0·8 1·0 1·2 Experience with a dual pore pressure element piezoball Colreavy, O'Loughlin and Randolph making corrections to the net resistance, accounting for changes in soil buoyancy and load cell changes associated with the changing acceleration field in the centrifuge (Sahdi et al, 2014;White et al, 2010). Typical piezoball and T-bar cyclic remoulding data are provided in Figure 6.…”

Section: Cyclic Remoulding Testsmentioning

confidence: 99%

Experience with a dual pore pressure element piezoball

Colreavy

O’Loughlin

Randolph

2016

International Journal of Physical Modelling in Geotechnics

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Piezoballs, which are full-flow ball penetrometers incorporating pore pressure measurements, are an attractive soft soil characterisation tool as they allow measurement of the intact and remoulded strength and the consolidation coefficient in a single test. The merit of full-flow penetrometers as a reliable tool that is superior to the cone in quantifying the strength of soft clay is gaining acceptance. Much of the recent focus on piezoballs has been on the pore pressure measurement location. Prompted by recent studies that highlight the merit of measuring pore pressure concurrently at more than one measurement location, this paper considers a new centrifuge-scale piezoball, with simultaneous pore pressure measurement at the equator and mid-face positions. Results from centrifuge tests in normally consolidated kaolin clay form the basis for the examination and yield coefficients of consolidation that are consistent with values derived using a number of different methods. Although the mid-face position appears to be the more sensible pore pressure measurement position for dissipation tests, consideration of the values measured at both positions provide strong indications of the drainage response during penetration that is shown in the paper to be important for deriving coefficients of consolidation from subsequent dissipation phases.

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Section: Cyclic Remoulding Testsmentioning

confidence: 99%

Experience with a dual pore pressure element piezoball

Colreavy

O’Loughlin

Randolph

2016

International Journal of Physical Modelling in Geotechnics

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“…Merifield et al, 2009;White et al, 2010;Chatterjee et al, 2012;Zhou et al, 2013). An alternative approach to derive this multiplier directly, is to consider the work required to lift the soil that is displaced by the incrementally advancing ball.…”

Section: Experimental Procedures Preparation Of Clay Specimenmentioning

confidence: 99%

“…This is critical for the design of almost all shallowly embedded offshore infrastructure (Puech et al, 2010) including subsea pipelines, steel catenary risers and mudmats. Large-deformation finite-element (LDFE) analyses on a T-bar (White et al, 2010;Tho et al, 2012), spudcan (Hossain et al, 2005) and ball penetrometer (Zhou et al, 2013) have shown that the transition depth from N b-shallow to N b-deep is dependent on the dimensionless strength ratio s u /c9D, where c9 is the effective unit weight of the soil and D is the diameter of the penetrometer. Higher strength ratios are associated with a delay in the transition to a steady N b-deep .…”

Section: Introductionmentioning

confidence: 99%

“…Higher strength ratios are associated with a delay in the transition to a steady N b-deep . Correlations for the transition depth and N b-shallow have been derived and, in the case of the T-bar and ball, a basis for correcting penetration data within the shallow zone has been proposed (White et al, 2010;Zhou et al, 2013). However, from the perspective of a spherical penetrometer, which is the focus of this paper, the range of strength ratios previously examined (s u /c9D52?95-44?25 (Zhou et al, 2013)) is narrower than the range that is of practical interest for offshore problems.…”

Section: Introductionmentioning

confidence: 99%

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Strength assessment during shallow penetration of a sphere in clay

Morton

O’Loughlin

White

2014

Géotechnique Letters

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Strength interpretation from the measured penetration resistance of full-flow penetrometers, such as the T-bar and ball, is generally based on a constant bearing capacity factor associated with a deep flow-round mechanism. This approach may underestimate the strength of near-surface sediments, which is becoming increasingly important for the design of offshore infrastructure such as pipelines, steel catenary risers and mudmats. This paper describes a series of centrifuge experiments designed to capture the change in the capacity factor of a ball penetrometer during shallow penetration. A rigorous consideration of soil buoyancy is provided. This is an important consideration in soils with a higher strength to self-weight ratio because a cavity is formed by the passage of the ball and remains open to greater depths. The depth at which a full-flow mechanism develops is related to the dimensionless strength ratio, expressed as the ratio of the undrained shear strength to the effective unit weight and penetrometer diameter. This observation forms the basis for proposed formulations that describe the evolution of the bearing capacity factor with depth for different dimensionless strength ratios. These formulations can be used to determine more accurately the undrained shear strength of near-surface soil over the range of dimensionless strength ratios that is of interest to offshore applications.

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“…Modeling techniques have been developed to simulate dynamic lay embedment and monitor the development of the pipe embedment with variation of pipe self-weight, horizontal cyclic amplitude and cyclic number (Gaudin and White, 2009). Innovative soil characterization tools, such as the T-bar and ball penetrometer (Randolph et al, 2005), testing procedures, such as the monitoring of load cell drift and cyclic sequences (Randolph and White, 2008a) and results interpretation, such as the treatment of shallow and buoyancy effects in the interpretation of T-bar tests (White et al, 2010a) and the assessment of post-remolding consolidation (White & Hodder 2010) have also greatly benefitted from the outcomes of centrifuge observations.…”

Section: Centrifuge Modelling Of Pipe-soil Interaction Geotechnical Cmentioning

confidence: 99%

Centrifuge Modeling to Support the Design of Subsea Pipelines

Gaudin

White

2012

GeoCongress 2012

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Offshore geotechnical engineering is characterized by unusual soil and loading conditions, a continuously moving frontier resulting in the requirement for innovative geotechnical solutions, and the very high cost associated with in-situ soil characterization and field testing in remote and deep oceans. As a consequence, offshore engineering practice has probably benefitted more from centrifuge modeling than other domains of geotechnical engineering, since the first offshore projects performed in 1973. After a brief overview of the role and contribution centrifuge modeling has had on offshore geotechnics, the paper illustrates the influence centrifuge modeling in recent years in improving the understanding of subsea pipe-soil interaction, to assist the development of guidelines and recommendations for practitioners, and in being used to design subsea pipelines in offshore Australia. CENTRIFUGE MODELLING IN GEOTECHNICS Role and contribution of centrifuge methodsThe role and contribution of centrifuge modeling to the design of offshore structures and the understanding of offshore soil-structure interaction has been addressed successively by Murff (1996), and more recently Gaudin et al. (2010). A short summary of the roles of centrifuge modeling in offshore geotechnics practice is presented here:1. Provide performance data to calibrate analytical or numerical models. Centrifuge modeling provides homogeneous and well characterized soil conditions, known boundary conditions, accurate measurements of parameters and repeatable testing conditions, offering reliable performance data for a given idealized problem which can be used to calibrate analytical and numerical models. 2. Providing qualitative insights into soil-structure interaction and mechanisms. This aspect is particularly important when novel concepts or unusual conditions are encountered. Understanding the structure behavior, observing the failure mechanism taking place, is a pivotal step into the development of sound design methodology. 3. Validate the structure design for a particular site or a specific design approach. By allowing the use of natural soils, sampled in-situ, by applying complex loading sequences directly relevant to design and by using a models replicating precisely prototypes, centrifuge modeling offers a valuable tool to validate or justify specific offshore structures.

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Interpretation of T-bar penetrometer tests at shallow embedment and in very soft soils

Cited by 157 publications

References 11 publications

Experience with a dual pore pressure element piezoball

Experience with a dual pore pressure element piezoball

Strength assessment during shallow penetration of a sphere in clay

Centrifuge Modeling to Support the Design of Subsea Pipelines

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