Colloidal gels under shear: Strain rate effects

A wide range of industrial applications, on land and offshore, require the solution of time domain problems and an associated understanding of rate effects in clay soils. In recent decades many researchers have examined the correlation between shear strength of soils and variation of shear strain rate and it is generally accepted that the strength increases by 1-5% for each order of magnitude increase in shear strain rate. This paper discusses the effects of penetration rate on the penetration resistance (qc) by using cone penetration test (CPT) test setup. The research had been conducted at RECESS and cone penetration test were used in three selected range of rate which were 0.5 cm/s, 1cm/s and 5cm/s. In addition, Mackintosh probe testhad been considered as comparison with CPT test for the unconfined compressive strength. The result shows different penetration rate influenced the soil shear strength. For the slowest rate (0.5 cm/s), the shear strength was approximately 0.15% less compared to the standard rate (2 cm/s). However, for the highest rate (5 cm/s), the shear strength was 0.22% more than the reference rate (0.5 cm/s). In conclusion, it is suggested that the RECESS clay soil influenced by the rate effect and in agreement with previous research findings.

Download Full-text

Strain-Rate Effects in the Propagation of Torsional Plastic Waves

Journal of Applied Mechanics ◽

10.1115/1.3625202 ◽

1966 ◽

Vol 33 (4) ◽

pp. 917-923 ◽

Cited By ~ 73

Author(s):

W. E. Baker ◽

C. H. Yew

Keyword(s):

Strain Rate ◽

Shear Strain ◽

Cross Sections ◽

Pure Copper ◽

High Rate ◽

Strain Rate Effects ◽

Rate Dependent ◽

Dependent Theory ◽

Lower Strain ◽

Rate Effects

A new method was developed for determining the dynamic stress-strain relationships of materials subjected to high rate of torsional loading. In addition, an investigation of propagation of torsional plastic waves in a long tube was conducted. Commercially pure copper was used throughout both investigations. In the material property studies, shear strains up to 20 percent and shear strain rates to 2100/sec were obtained. The results indicated that copper exhibits significantly lower strain-rate effects than those previously obtained by the longitudinal loading method. In the studies of plastic wave propagation, shear strain-time records at several cross sections along the tube were compared with computed results obtained from the strain-rate-independent and strain-rate-dependent theories. It is concluded that the computed results based on the strain-rate-dependent theory give better agreement with the experiments.

Download Full-text

Integration of Viscoplastic Effects in a One-Dimensional Constitutive Model for Ground Response Analysis

Canadian Geotechnical Journal ◽

10.1139/cgj-2019-0717 ◽

2020 ◽

Author(s):

Samuel Yniesta ◽

Mallak Janati-Idrissi

Keyword(s):

Strain Rate ◽

Stress Component ◽

Response Analysis ◽

Shear Strain Rate ◽

Ground Response ◽

Ground Response Analysis ◽

Strain Rate Effects ◽

One Dimensional ◽

Rate Effects ◽

Modulus Reduction

During an earthquake, strain-rate effects affect both the stiffness and damping behaviour of soils, yet existing constitutive models for ground response analysis are typically formulated within a rate-independent framework. In this paper, a one-dimensional viscoplastic stress-strain model is presented to introduce strain rate effects in ground response analysis. Its constitutive equations are based on a model that uses a cubic spline fit of the modulus reduction curve and a coordinate transformation technique to match any input modulus reduction and damping curve. A viscous stress component is added to model the effect of strain rate on the mechanical behaviour of soils using a single input parameter. The model is able to reproduce the linear increase in shear strength with the logarithm of shear strain rate, and allows to introduce viscous effects in 1D ground response analysis with control over damping and modulus reduction behaviour. The model is implemented in a software for ground response analysis and used to predict the results of a centrifuge test modeling one-dimensional wave propagation. The results show that the model predicts accurately the amplification and attenuation of shear waves, in a context where strain rates impact significantly the response of the model.

Download Full-text

Characterization of the Solid-Fluid Transition of Fine-Grained Sediments

Volume 7: Offshore Geotechnics; Petroleum Technology ◽

10.1115/omae2009-79738 ◽

2009 ◽

Cited By ~ 3

Author(s):

Nathalie Boukpeti ◽

David White ◽

Mark Randolph ◽

Han Eng Low

Keyword(s):

Shear Strength ◽

Yield Strength ◽

Strain Rate ◽

Shear Strain ◽

Water Content ◽

Strength Parameter ◽

Shear Strain Rate ◽

Fine Grained ◽

Rate Effects

Characterization of the strength of fine-grained sediments as they evolve from an intact seabed material to a remolded debris flow is essential to adequately model submarine landslides and their impact on pipelines and other seabed infrastructure. In the current literature, two distinct approaches for modelling this material behavior have been considered. In the soil mechanics approach, fine-grained soils are characterized by the undrained shear strength, su. The critical state framework proposes a relation between su and the water content, or void ratio of the soil. In addition, rate effects and strain softening effects are described by multiplying a reference value of su by a function of the shear strain rate or the accumulated shear strain respectively. In the fluid mechanics approach, slurries of fine-grained material are characterized by a yield strength and a viscosity parameter, which describes the change in shear stress with shear strain rate. Empirical relationships have been proposed, which relate the yield strength and the viscosity to the sediment concentration. This paper demonstrates that the two modelling approaches are essentially similar, with only some formal differences. It is proposed that the strength of fine-grained sediments can be modelled in a unified way over the solid and liquid ranges. To support this unified approach, an experimental campaign has been conducted to obtain strength measurements on various clays prepared at different water content. The testing program includes fall cone tests, vane shear tests, miniature penetrometers (T-bar and ball) and viscometer tests. Rate effects and remolding effects are investigated over a wide range of water contents spanning the domains of behavior that are usually defined separately as soil and fluid. The present paper focuses on analyzing the results of fall cone, vane shear and viscometer tests. Analysis of the results shows that the variation in shear strength over the solid and liquid ranges can be described by a unique function of water content — suitably normalized — for a given soil. Furthermore, the effect of strain rate and degree of remolding can be accounted for by multiplying the basic strength parameter by appropriate functions, which are independent of the current water content.

Download Full-text