Influence of generalized initial state and principal stress rotation on the undrained response of sands

2002 ◽  
Vol 39 (1) ◽  
pp. 63-76 ◽  
Author(s):  
S Sivathayalan ◽  
Y P Vaid
Keyword(s):  
Principal Stress ◽  
Strain Softening ◽  
Principal Stresses ◽  
Initial Stress State ◽  
Stress Rotation ◽  
Bedding Planes ◽  
State Strength ◽  
Major Principal Stress ◽  
Undrained Strength ◽  
Static Shear

The dependence of the undrained behaviour of sand on the initial stress state and the orientation of principal stresses with respect to the bedding planes is assessed under generalized loading paths using hollow cylinder torsional shear tests. The undrained tests were carried out using displacement-controlled loading to confidently capture the post-peak strain-softening response. Undrained behaviour of sands under identical initial states is shown to be dependent on the direction of principal stresses, during and prior to undrained shear, in relation to the direction of bedding planes. The minimum undrained strength of the strain-softening sand is found to be highly influenced by the initial stress state (confining stress, direction of principal stresses, and static shear), even though the friction angle mobilized at the instant of minimum strength is unique. A mere rotation of principal stresses at constant deviator stress alone can lead to a strain-softening response that may culminate in limited or unlimited flow deformation. The susceptibility of sand to liquefaction due to stress rotation increases as the direction of the major principal stress approaches the orientation of the bedding plane. The potential for flow deformation is strongly dependent on the direction of the major principal stress in relation to the bedding planes, and the steady state strength is not uniquely related to the void ratio alone.Key words: liquefaction, hollow cylinder torsion test, principal stress direction, static shear, steady state strength, minimum undrained strength.

scholarly journals Influence of principal stress direction on the stress-strain-strength behaviour of completely decomposed granite

2010 ◽  
Vol 8 (1) ◽  
pp. 79-97 ◽  
Author(s):  
Md. Kumruzzaman ◽  
Jian-Hua Yin
Keyword(s):  
Principal Stress ◽  
Hollow Cylinder ◽  
Principal Stress Rotation ◽  
Strength Parameters ◽  
Principal Stress Direction ◽  
Stress Rotation ◽  
Strength Behavior ◽  
Major Principal Stress ◽  
Decomposed Granite ◽  
Completely Decomposed Granite

The measurement and study of the stress-strain-strength behavior of soils in general stress states involving principal stress rotation are necessary and valuable. To investigate the strength behavior under principal stress rotation, a series of undrained tests on compacted hollow cylinder specimens of completely decomposed granite (CDG) was carried in hollow cylinder apparatus. Tests were conducted using constant inside and outside pressures and maintained a fixed angle of rotation of principal stress with the vertical (?). Seven different angles of major principal stress orientations were used to cover the entire range of major principal stress directions from vertical to the horizontal. Two different confining stresses were used to find out the variations of the experimental results. It is observed that the deviator stresses as well as excess pore pressures decrease with the angle ?. It is also observed that specimens were getting softer with the increase of ?. The results also show a significant influence of principal stress direction angle on the strength parameters. It is found that the angle ? is related to the occurrence of cross-anisotropy and the localization which resulted in a pronounced influence on the strength parameters of the CDG specimens.

The Nerlerk berm case history: some considerations for the design of hydraulic sand fills

1991 ◽  
Vol 28 (4) ◽  
pp. 601-612 ◽  
Author(s):  
Jean-Marie Konrad
Keyword(s):  
Steady State ◽  
Large Scale ◽  
Void Ratio ◽  
Strain Softening ◽  
Back Analysis ◽  
Confining Stress ◽  
Hydraulic Fill ◽  
State Strength ◽  
Undrained Strength ◽  
Unique Relationship

Back-analyses of recent large-scale slides during the hydraulic placement of an articial sand island at the Nerlerk site (Beaufort Sea) using different methods have resulted in contradictory conclusions with respect to the state of the fill. All the interpretation methods assume a unique relationship between steady-state strength and void ratio. This assumption is, however, not verified, since steady-state strength depends also on effective confining stress. This paper presents the results of a back-analysis at the Nerlerk site using a modified concept proposed by the author which isbased on nonunique values of steady-state strength for a given sand. It is established that the density conditions at Nerlerk, on average at a relative density of about 40%, and the initial stress conditions are conducive to strain softening, with a steady-state strength corresponding to the minimum strength defined by the LF line. For Nerlerk sand,the minimum undrained strength is about 18% of the steady-state strength determined with conventional methods using high confining stresses. The Nerlerk berm failures were thus "liquefaction" slides induced most likely by progressive straining. Key words: sand, undrained, strength, steady state, hydraulic fill.

Numerical solutions for strain-softening surrounding rock under three-dimensional principal stress condition

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sheng Yu-ming ◽  
Li Chao ◽  
Xia Ming-yao ◽  
Zou Jin-feng
Keyword(s):  
Finite Element ◽  
Principal Stress ◽  
Stress Condition ◽  
Strain Softening ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Strength Criterion ◽  
Surrounding Rock ◽  
Flow Rule ◽  
Finite Element Software

Abstract In this study, elastoplastic model for the surrounding rock of axisymmetric circular tunnel is investigated under three-dimensional (3D) principal stress states. Novel numerical solutions for strain-softening surrounding rock were first proposed based on the modified 3D Hoek–Brown criterion and the associated flow rule. Under a 3D axisymmetric coordinate system, the distributions for stresses and displacement can be effectively determined on the basis of the redeveloped stress increment approach. The modified 3D Hoek–Brown strength criterion is also embedded into finite element software to characterize the yielding state of surrounding rock based on the modified yield surface and stress renewal algorithm. The Euler implicit constitutive integral algorithm and the consistent tangent stiffness matrix are reconstructed in terms of the 3D Hoek–Brown strength criterion. Therefore, the numerical solutions and finite element method (FEM) models for the deep buried tunnel under 3D principal stress condition are presented, so that the stability analysis of surrounding rock can be conducted in a direct and convenient way. The reliability of the proposed solutions was verified by comparison of the principal stresses obtained by the developed numerical approach and FEM model. From a practical point of view, the proposed approach can also be applied for the determination of ground response curve of the tunnel, which shows a satisfying accuracy compared with the measuring data.

Numerical modelling of the crack-pore interaction and damage evolution behaviour of rocklike materials with pre-existing cracks and pores

2020 ◽  
pp. 105678952098387
Author(s):  
PLP Wasantha ◽  
D Bing ◽  
SQ Yang ◽  
T Xu
Keyword(s):  
Principal Stress ◽  
Damage Evolution ◽  
Shear Failure ◽  
Mechanical Response ◽  
Distribution Patterns ◽  
Stress Distributions ◽  
Compressive Stresses ◽  
Major Principal Stress ◽  
The Right ◽  
Macroscopic Failure

The combined effect of pre-existing cracks and pores on the damage evolution behaviour and mechanical properties of rocklike materials under uniaxial compression was numerically studied. Simulations of cracks and pores alone showed that increasing crack length and pore diameter decrease uniaxial compressive strength (UCS) and elastic modulus. Subsequent simulations considered two types of combinations of pre-existing cracks and pores – two cracks either side of a centric pore, and two pores either side of a centric crack – and the distance between cracks and pores was changed. In the case of two cracks at either side of the pore, UCS increased only slightly when the distance between the cracks and pore was increased. This was attributed to the more profound effect of the presence of the pore on UCS, and was confirmed by the progressive crack development characteristics and the major principal stress distribution patterns, which showed that the cracks initiated from the tips of the two pre-existing cracks made little or no contribution to the ultimate macroscopic failure. In contrast, models with two pores at either side of a centric crack showed a marked dependency of UCS on the distance between the pores and the crack. Cracks propagating from pre-existing pores made a greater contribution to the ultimate macroscopic failure when the pores were close to the centric crack and the effect gradually diminished with increasing space between pre-existing pores and the centric crack. Major principal stress distributions showed an asymmetric mobilisation of compressive stresses at the right and left sides of the two pores, favouring macroscopic shear failure when they were close to the centric crack which had led to a lower UCS. Overall, this study presents some critical insights into crack-pore interaction behaviour and the resulting mechanical response of rocklike materials to assist with the design of rock structures.

Assessing the undrained strength cross-anisotropy of three tailings types

2022 ◽  
Vol 12 (1) ◽  
pp. 1-24
Author(s):  
D. Reid ◽  
R. Fanni ◽  
A. Fourie
Keyword(s):  
Principal Stress ◽  
Stress Ratio ◽  
Additional Data ◽  
Layered Materials ◽  
Engineering Practice ◽  
Published Data ◽  
Shear Tests ◽  
Undrained Strength ◽  
Cross Anisotropy ◽  
Current Engineering

The cross-anisotropic nature of soil strength has been studied and documented for decades, including the increased propensity for cross-anisotropy in layered materials. However, current engineering practice for tailings storage facilities (TSFs) does not appear to generally include cross-anisotropy considerations in the development of shear strengths. This being despite the very common layering profile seen in subaerially-deposited tailings. To provide additional data to highlight the strength cross-anisotropy of tailings, high quality block samples from three TSFs were obtained and trimmed to enable Hollow Cylinder Torsional Shear tests to be sheared at principal stress angles of 0 and 45 degrees during undrained shearing. Consolidation procedures were carried out such that the drained rotation of principal stress angle that would precede potential undrained shear events for below-slope tailings was reasonably simulated. The results indicated the significant effects of cross-anisotropy on the undrained strength, instability stress ratio, contractive tendency and brittleness of each of the three tailings types. The magnitude of cross-anisotropy effects seen was generally consistent with previous published data on sands.

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