Interpretation of Impact Penetration Measurements in Soft Clays

Aubeny, Charles; Han, Shuai

doi:10.1061/(asce)1090-0241(2006)132:6(770)

Cited by 70 publications

(46 citation statements)

References 12 publications

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“…Regarding the soil as a grid of several, very thin layers of particles, the penetration can be viewed as a sequence: (1) The probe hits the upper layer, (2) the load per unit area or pressure on the soil exceeds the bearing capacity, (3) the upper layer fails and the probe hits the next layer, and so on. Thereby, the derived sediment resistance force for each layer is the maximum resistance force the sediment can exhibit until it fails and the probe continues penetrating (Aubeny and Shi 2006). This means that the bearing capacity can be expressed by the sediment resistance force:…”

Section: Dynamic Penetrometermentioning

confidence: 99%

“…Regarding the probe as a single particle in equilibrium (after reaching the terminal velocity in the water column), the sediment exerts the sediment resistance force F sr against the probe and decelerates it (Aubeny and Shi 2006):…”

Section: Dynamic Penetrometermentioning

confidence: 99%

“…Instruments frequently used for geotechnical in situ tests are dynamic penetrometers (consider the use of, e.g., Stoll and Akal 1999;Stoll et al 2004;Aubeny and Shi 2006;Stegmann et al 2006a, b;Kopf et al 2007;Stegmann and Kopf 2007;Stark and Wever 2008;Stark et al 2009a). Many of the coastal areas investigated in these studies consist mainly of sand.…”

Section: Introductionmentioning

confidence: 99%

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Geotechnical Properties of Sandy Seafloors and the Consequences for Dynamic Penetrometer Interpretations: Quartz Sand Versus Carbonate Sand

et al. 2011

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The societal usage of coastal zones (including offshore wind energy plants, waterway deepening, beach conservation and restoration) is of emerging importance. Sediment dynamics in these areas result in sandy deposits due to strong tidal and wave action, which is difficult to simulate in laboratory geotechnical tests. Here, we present data from in situ penetrometer tests using the lightweight, free-fall Nimrod penetrometer and complementary laboratory experiments to characterize the key physical properties of sandy seafloors in areas dominated by quartzose (North Sea, Germany) and calcareous (Hawaii, USA) mineralogy. The carbonate sands have higher friction angles (carbonate: 31-37°; quartz: 31-32°) and higher void ratios (carbonate: 1.10-1.40; quartz: 0.81-0.93) than their siliceous counterparts, which have partly been attributed to the higher angularity of the coralderived particles. During the in situ tests, we consistently found higher sediment strength (expressed in deceleration as well as in estimated quasi-static bearing capacity) in the carbonate sand (carbonate: 68-210 g; quartz: 25-85 g), which also showed a greater compressibility. Values were additionally affected by seafloor inclination (e.g., along a subaqueous dune or a channel), or layering in areas of sediment mobilization (by tides, shorebreak or currents). The study shows that the differences in in situ measured penetration profiles between carbonate sands and quartz sands are supported by the laboratory results and provide crucial information on mobile layers overlying sands of various physical properties.

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Section: Dynamic Penetrometermentioning

confidence: 99%

Section: Dynamic Penetrometermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Geotechnical Properties of Sandy Seafloors and the Consequences for Dynamic Penetrometer Interpretations: Quartz Sand Versus Carbonate Sand

et al. 2011

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“…Liyanapathirana, 2009;Sheng et al, 2009;Carter et al, 2010). The method has also been employed for the analysis of FFPs (Aubeny & Shi, 2006;Abelev et al, 2009). The analysis of dynamic penetration is probably one of the most sophisticated and challenging problems in computational geomechanics.…”

Section: Introductionmentioning

confidence: 99%

Dynamic analysis of a smooth penetrometer free-falling into uniform clay

Nazem¹,

Carter²,

Airey³

et al. 2012

Géotechnique

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The finite-element analysis of free-falling objects penetrating soil deposits is one of the most sophisticated and challenging problems in geomechanics. A robust numerical method will be described here for dealing with such complex and difficult problems. The approach is based on the arbitrary Lagrangian-Eulerian (ALE) method of analysis, the main features and challenges of which are described briefly in the paper. The ALE method is then employed to perform a parametric study of a perfectly smooth penetrometer free-falling into a uniform layer of clay, which deforms under undrained conditions. The effect of the mechanical properties of the clay soil on the penetration characteristics is presented, and an approximate, closed-form expression is derived for the dynamic penetration factor, N dp : Comparisons are made between the deduced values of N dp and published values of the conventional cone factor, N c , and comparisons are made with experimental data to validate the approach.KEYWORDS: numerical modelling; offshore engineering; shear strength; site investigation; soil/structure interaction L'analyse aux éléments finis d'objets en chute libre péné-trant dans des dépôts de sol est un des problèmes les plus sophistiqués et difficiles de la géomécanique. La présente communication décrit une méthode numérique robuste pour résoudre des problèmes aussi complexes et difficiles. Cette approche est basée sur la méthode d'analyse Lagrangien-Eulérien arbitraire (ALE), dont les principaux problèmes et caractéristiques sont décrits brièvement. On utilise ensuite la méthode ALE pour effectuer une étude paramétrique d'un pénétromètre parfaitement lisse tombant dans une couche d'argile uniforme, qui se déforme dans des conditions non drainées. On présente l'effet des propriétés mécaniques du sol d'argile sur les caractéris-tiques de pénétration, et on dérive une expression à forme fermée pour le facteur de pénétration dynamique N dp : On effectue des comparaisons entre les valeurs déduites de N dp et des valeurs publiées du facteur de cone N c , pour procéder ensuite à des comparaisons avec des données expérimentales pour valider cette approche.

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“…Also, cohesionless soil strengths were studied by NFESC using a calcareous sand site off the coast of Key West, FL and a denser quartz/mineral sand off the coast of Biloxi, MS (Orenberg, 1996). In the Gulf of Mexico, reasonable values for the undrained shear strength of soft clays were obtained using the acceleration measurements of an expendable penetrometer (Aubeny and Shi, 2006). Although there are current algorithms for predicting dynamic penetration of the seafloor already in use, recent experiments have indicated that these algorithms tend to under-predict the penetration of objects which are larger than three inches in diameter.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Diameter on Dynamic Seabed Penetration

Ortman¹

2008

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REPORT DOCUMENTATION PAGE Form Approved OMB No. 074-0188Public reporting burden for this collection of information is estimated to average 1 hour per response, including g the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. 12b. DISTRIBUTION CODE13. ABSTRACT (cont from p. 1) have indicated these algorithms tend to under predict the penetration of objects which are larger than three inches in diameter. To improve the current algorithms, a numerical and experimental study of the seabed penetration event was conducted. A computational analysis of the seabed penetration problem was conducted using the LS-DYNA finite element analysis (FEA) code. LS-DYNA was used to model the experiments, and then the model predictions were compared with experimental results. The penetration depths predicted by the model showed good agreement with experimental results for cohesionless soils. Using the USNA Oceanography Research Vessel (YP-686), three and nine inch penetrometers were repeatedly dropped off the stern and allowed to free fall to the seabed. An accelerometer attached to each penetrometer measured acceleration output beginning before release and continually throughout the drop. By integrating the acceleration data twice, the penetration depth could be calculated. Using this experimental data and equations available in the Handbook for Marine Geotechnical Engineering, new values were calculated for the strain rate factors of objects larger than three inches in diameter. AbstractAn accurate estimate of the undrained shear strength of seabed sediments is critical to the design of foundations and anchors of offshore structures. Naval mine warfare and undersea salvage also depend on the prediction of seafloor embedment depth, which is primarily a function of sediment strength. Direct measurement of in-situ sediment strengths in the offshore environment is often difficult using conventional methods, especially where depths prohibit the use of divers. Sediment core samples can be analyzed using various laboratory methods, including tri-axial and vane-shear testing, but sample disturbance during collection may introduce inaccuracy into these measurements.Dynamic soil penetrometers have been increasingly employed in recent years to profile seafloor sediment strength. These penetrometers are normally deployed from the sea surface, with either the velocity or acceleration measured throughout the fall to the seafloor. Total embedment and undrained shear strength are estimated from the resulting measured velocity profile, using an algorithm first described by True and later refined by Rocker in the Handbook for Marine Geotechnical Engineering.The method in the Handbook is a quasi-static approach, where work done on the penetrometer is calculated at each time step, and subtracted from the total kinetic energy before advancing to the next step. The empirical strain rate factors used in the calculations to modify the ...

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Interpretation of Impact Penetration Measurements in Soft Clays

Cited by 70 publications

References 12 publications

Geotechnical Properties of Sandy Seafloors and the Consequences for Dynamic Penetrometer Interpretations: Quartz Sand Versus Carbonate Sand

Geotechnical Properties of Sandy Seafloors and the Consequences for Dynamic Penetrometer Interpretations: Quartz Sand Versus Carbonate Sand

Dynamic analysis of a smooth penetrometer free-falling into uniform clay

The Effect of Diameter on Dynamic Seabed Penetration

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