The effect of tamping conditions and sample preparation on undrained shear strengths of a non-plastic sandy silt tailings

2021 ◽  
Author(s):  
David Reid ◽  
Riccardo Fanni ◽  
Peter DiDonna
Keyword(s):  
Critical State ◽  
Triaxial Compression ◽  
Engineering Practice ◽  
Compression Tests ◽  
In Situ Testing ◽  
Sandy Silt ◽  
Direct Simple Shear ◽  
Lead Zinc ◽  
Increased Strength

A series of direct simple shear (DSS) tests were carried out on a non-plastic sandy silt lead-zinc-silver tailings to develop a relationship between undrained shearing behaviour and density, where in situ testing had identified contractive behaviour. The critical state line was also obtained through triaxial compression tests to enable the DSS tests to be viewed in a critical state framework and allow comparison with in situ testing. It was found that the gravimetric water content (GWC) used to tamp the specimens had a significant effect on the resulting undrained strengths when attempting to achieve dense states - with higher GWC giving lower strength at a given density than a lower GWC. Intact and slurry deposited (SD) samples were also tested to access denser states without inducing tamping-related stresses. These showed a more consistent trend with the loose-tamped specimens, and with other data from the literature. Plausible explanations as to the causes of the increased strength of dense-tamped samples were obtained through estimating potential preconsolidation stresses and “locked in” horizontal stresses that may occur from dense tamping. The importance of these observations on the development of density - strength profiles in engineering practice was outlined.

scholarly journals The mechanics of subglacial sediment: an example of new “transitional” behaviour

2010 ◽  
Vol 47 (7) ◽  
pp. 775-790 ◽  
Author(s):  
Fatin Altuhafi ◽  
Béatrice A. Baudet ◽  
Peter Sammonds
Keyword(s):  
Critical State ◽  
Triaxial Compression ◽  
Interesting Case ◽  
Strain History ◽  
Compression Tests ◽  
Specimen Density ◽  
The Difference ◽  
Triaxial Compression Tests ◽  
Normal Compression

A series of isotropic compression tests and drained and undrained triaxial compression tests have been performed on glacial sediment from Iceland. Langjökull sediment, which is well graded, is thought to have reached a critical grading during deposition and transportation. Multiple parallel normal compression lines (NCLs) were found, but a unique critical state line (CSL) could be identified. This is unlike other so-called “transitional” soils, whose grading varies between reasonably well graded to gap graded, which tend to have distinct NCLs and critical state lines depending on the specimen density. It is thought that in the case of the Langjökull sediment studied, its particular strain history that involved incessant shearing during deposition accounts for the difference in behaviour. This provides the interesting case of a soil that has been crushed to a critical grading in situ, which depends on the mineralogy of the grains, which was then sampled and tested. Despite the unique grading, samples with a range of different void ratios can be prepared and the combination of grading and density seems to set a fabric that cannot be changed by compression, resulting in multiple parallel NCLs. At the critical state, however, the fabric has been destroyed and the CSL is unique.

Investigations geomecaniques des emplacements de tunnels en rocher sur l'ile de Montreal

1976 ◽  
Vol 13 (4) ◽  
pp. 481-497
Author(s):  
D. E. Gill ◽  
G. Ballivy
Keyword(s):  
Triaxial Compression ◽  
Site Investigation ◽  
Compression Tests ◽  
Testing Program ◽  
Boring Machines ◽  
Permeameter Tests ◽  
Usual Site ◽  
Full Face ◽  
École Polytechnique

Due to the extent of projects of the Montreal Urban Community involving rock tunnelling, the possibility of using full face boring machine had to be considered. The usual site investigation techniques had to be revised. The main purpose of this paper is to describe, discuss and illustrate the new investigation techniques.Problems related to geology that might be encountered with full face boring machines are reviewed and the various investigations which lead to a better geomechanical knowledge of tunnel sites are presented. The diamond drilling program and the aspects which need to be stressed in the reports are discussed.The laboratory testing program includes splitting tests, uniaxial and triaxial compression tests, and modified Handewith punching tests. In situ testing program comprises Ménard pressio-permeameter tests, Goodman jack tests, and borehole punching tests performed with an apparatus developed at Ecole Polytechnique de Montréal.

Engineering geology characterization of lacustrine overconsolidated clays in an alpine area of Italy

2000 ◽  
Vol 37 (6) ◽  
pp. 1241-1251
Author(s):  
R Meriggi ◽  
P Paronuzzi ◽  
L Simeoni
Keyword(s):  
Triaxial Compression ◽  
Mechanical Resistance ◽  
Compression Tests ◽  
Stress History ◽  
Depositional Processes ◽  
Geotechnical Characteristics ◽  
Lithostratigraphic Units ◽  
Overconsolidated Clays ◽  
History Of

This study reports the main geotechnical characteristics of the Steggio Clay unit, a lacustrine sequence located in a valley of the Veneto Piedmont area (northern Italy). Analyzing the variations of overconsolidation pressure with depth, and the compressibility characteristics of natural, swelled, and reconstituted samples, one can hypothesize about the existence and influence of swelling processes on the stress history of the deposit. The yield pressures, determined by oedometric tests for the various lithostratigraphic units, are compared with the preconsolidation pressures deduced from the geological analysis, and a reduction in apparent preconsolidation pressures is evident in the upper layers. Comparing the natural water content of each stratigraphic unit with that of the overconsolidated and normally consolidated states, it can be seen that the same layers are softened. These phenomena could have been caused by swelling induced by erosion of the overlying deposits, sliding of glacial masses, and unloading due to deglaciation. The results of undrained consolidated triaxial compression tests indicate that the variations between the parameters of mechanical resistance of some lithological units can be attributed to the different values of the void index, Ivo, corresponding to the lithostatic in situ stress.Key words: overconsolidated clays, stress history, swelling, intrinsic characteristics, post-depositional processes, glaciation.

Mobilized strength components of Athabasca oil sand in triaxial compression

1999 ◽  
Vol 36 (4) ◽  
pp. 718-735 ◽  
Author(s):  
Ron CK Wong
Keyword(s):  
Critical State ◽  
Triaxial Compression ◽  
Shear Banding ◽  
Shear Bands ◽  
Compression Tests ◽  
Oil Sand ◽  
Shear Dilation ◽  
X Ray Imaging ◽  
Microscopy Techniques ◽  
Triaxial Compression Tests

Dense uncemented Athabasca oil sand specimens exhibit unusually high peak strength, dilation with severe softening, and residual strength in drained triaxial compression tests. Computer tomography scanning, X-ray imaging, and scanning electron microscopy techniques are used to examine the microstructural features of the sheared specimens, such as interlocked structure, shear-banding pattern, and porosity distributions inside and outside shear bands. The characteristics of these microstructural features are used to explain the macrodeformation responses observed in the triaxial compression tests. Mobilization of strength components derived from interlocked structure, dilation, rolling, and critical state are analyzed for pre-peak, post-peak softening, and residual states.Key words: oil sand, interlocked structure, shear dilation, shear band, critical state.

scholarly journals Relationship between monotonic and cyclic behavior of saturated soft clay in undrained triaxial compression tests

2021 ◽  
Author(s):  
Tingyu Wu ◽  
Jie Han ◽  
Yuanqiang Cai ◽  
Lin Guo ◽  
Jun Wang
Keyword(s):  
Cyclic Loading ◽  
Triaxial Compression ◽  
Soft Clay ◽  
Cyclic Behavior ◽  
Triaxial Tests ◽  
Engineering Practice ◽  
Compression Tests ◽  
Cyclic Tests ◽  
Saturated Soft Clay ◽  
Triaxial Compression Tests

Cyclic loading-induced deformation of soil is a common problem in the engineering practice. In the current practice, however, monotonic triaxial tests are more commonly used in the practice, due to the availability of apparatus and ease of operation. Thus, it will be very useful and practical if the monotonic triaxial tests can be used to evaluate the behavior of soil under cyclic loading. This study aims to find an explicit relationship between monotonic and cyclic behavior of saturated soft clay. Six monotonic and nine cyclic triaxial compression tests were conducted on undisturbed saturated soft clay under an undrained condition. The test results showed that the monotonic and cyclic tests shared the same stress-strain surface in a three-dimensional space p^'-q-ε_a. It is also found possible to evaluate the effective stress states of cyclic tests at two specific numbers of cycles, using corresponding monotonic tests. Based on these two findings, a simple procedure was then proposed to predict the peak axial strain for the saturated soft clay under different cyclic loadings based on the monotonic tests and only one cyclic test, which was further verified against more test data from the previous literature.

Influence of silt size and content on liquefaction behavior of sands

2011 ◽  
Vol 48 (6) ◽  
pp. 931-942 ◽  
Author(s):  
Mehmet Murat Monkul ◽  
Jerry A. Yamamuro
Keyword(s):  
Void Ratio ◽  
Triaxial Compression ◽  
Relative Size ◽  
Silty Sand ◽  
Engineering Practice ◽  
Compression Tests ◽  
Confining Stress ◽  
Liquefaction Potential ◽  
Fines Content ◽  
Triaxial Compression Tests

This study investigates the fines content influence on liquefaction potential of a single base sand mixed with three different essentially nonplastic silts through strain-controlled monotonic undrained triaxial compression tests. Confining stress (30 kPa) and deposition method (dry funnel deposition) were kept the same, while fines content was varied, to solely focus on how different silts and their contents influence the undrained response of the sand under comparable conditions. It was found that if the mean grain diameter ratio (D50-sand/d50-silt) of the sand grains to silt grains is sufficiently small, the liquefaction potential of the sand increases steadily with increasing fines content for the studied range (0%–20%). As D50-sand/d50-silt increases, the liquefaction potential of the silty sand might actually be less than the liquefaction potential of the clean sand. Test results also revealed that commonly used comparison bases (i.e., void ratio, intergranular void ratio, relative density) are not sufficient for assessing the influence of fines on liquefaction potential of silty sands. Finally, relative size of the silt grains should also be considered in geotechnical engineering practice in addition to content and plasticity of fines to characterize the influence of silt on liquefaction potential of sands.

Behavior of a Sandy Silt Reinforced with Discontinuous Recycled Fiber Inclusions

2000 ◽  
Vol 1714 (1) ◽  
pp. 9-17 ◽  
Author(s):  
J. J. Murray ◽  
J. D. Frost ◽  
Y. Wang
Keyword(s):  
Shear Strength ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Value Added ◽  
Strength Loss ◽  
Dry Density ◽  
Compression Tests ◽  
Maximum Dry Density ◽  
Deformation Response ◽  
Sandy Silt

Laboratory compaction and triaxial compression tests were performed to assess the compaction characteristics and load deformation response of a sandy silt reinforced with randomly oriented recycled carpet fibers. Discrete, randomly distributed fiber inclusions significantly increase the peak shear strength, reduce the postpeak strength loss, increase the axial strain to failure, and, in some cases, change the stress-strain behavior from strain softening to strain hardening for a sandy silt. Fiber inclusions also impede the compaction process, causing a reduction in the maximum dry density of reinforced specimens with increasing fiber content. The strength losses associated with in-service saturation are significantly reduced with fiber reinforcement. It is suggested that large volumes of recycled waste fibers can be used as a value-added product to enhance the shear strength and load deformation response of soils.

Undrained triaxial strength and stress–strain characteristics of a glacial till soil

1988 ◽  
Vol 25 (3) ◽  
pp. 428-439 ◽  
Author(s):  
J. H. Atkinson ◽  
J. A. Little
Keyword(s):  
Critical State ◽  
Soil Mechanics ◽  
Triaxial Compression ◽  
Practical Importance ◽  
Small Strain ◽  
Compression Tests ◽  
Triaxial Strength ◽  
Current State ◽  
Boulder Clay ◽  
Triaxial Compression Tests

Undrained triaxial compression tests were carried out on reconstituted and nominally undisturbed tubed samples of a lodgement till from the Vale of St. Albans in Hertfordshire, England. The soil is a matrix-dominant, chalky boulder clay of Anglian age with little discernable engineering fabric. Electron microscope observations showed the presence of crystalline calcite in tube samples.The test results were examined within the general framework of critical state soil mechanics using normalizing procedures to take account of the different states and stress histories of the samples. These analyses demonstrate the practical importance of accounting for the current state and stress history in the interpretation of soil test data.The present results form a self-consistent pattern of behaviour. Differences between reconstituted and tubed samples were found only at small strain and may be attributed to cementing in tubed samples, which is broken down during reconstitution and during relatively large straining in recompression and shearing. Key words: boulder clay, cemented soil, critical state, shear strength, soil mechanics, stiffness, till, triaxial test.

Modelling the responses of Athabasca oil sand in triaxial compression tests at low pressure

1998 ◽  
Vol 35 (2) ◽  
pp. 395-406 ◽  
Author(s):  
Ahmed M Samieh ◽  
Ron CK Wong
Keyword(s):  
Experimental Data ◽  
Critical State ◽  
Triaxial Compression ◽  
Shear Zones ◽  
Shear Loading ◽  
Compression Tests ◽  
Oil Sand ◽  
Surface Plasticity ◽  
Triaxial Compression Tests ◽  
Disturbance Function

Experimental data from drained triaxial compression tests on Athabasca oil sand at low confining pressures ranging from 50 to 750 kPa are presented. The tested specimens exhibited severe strain-softening with significant dilation but did not approach the critical state entirely by the end of the tests due to the formation of localized shear zones. A homogeneous deformational response in which the entire specimen would reach to the critical state was derived from the experimental response and the critical state parameters. A constitutive model is established to simulate both the experimental and homogeneous deformational responses of Athabasca oil sand. The model is based on describing the evolution of internal microstructural changes with shear loading through a scalar disturbance function. The deformational response of the material is expressed in terms of the responses of its reference states, namely the virgin and fully disturbed states, through the scalar disturbance function. The virgin state of the material is modelled by a generalized single surface plasticity model, whereas the fully disturbed state is assumed to be the critical state. The parameters required to define the model were identified and evaluated. Comparisons between the predicted results and experimental data were made for model performance evaluation.Key words: oil sand, disturbance, plasticity, critical state, shear band.

scholarly journals A Piecewise Yield Failure Criterion including the Critical State for Brittle Rock

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Jing Zhang ◽  
Fengyu Ren ◽  
Zhihua Ouyang ◽  
Huan Liu
Keyword(s):  
Principal Stress ◽  
Failure Criterion ◽  
Critical State ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Brittle Rock ◽  
Compression Tests ◽  
Primary Object ◽  
Yield Surfaces ◽  
Yield State

The critical state of rock is an important index for measuring the changes in rock characteristics. However, this state is not unique because of the different researcher assumptions. Based on the theory of the partial differential equation proposed by Vutukuri, according to Mohr’s envelope, a piecewise yield failure criterion (referred to as the Mohr–Wedge criterion), including the critical state for brittle rock, is obtained by introducing the wedge model to solve this equation. The Mohr–Wedge (M–W) criterion consisting of nonlinear and linear components includes the critical state for brittle rock. When the minimum principal stress σ3 is lower than the confining pressure σk, the maximum principal stress σ1 varies nonlinearly with σ3; otherwise, σ1 varies linearly with σ3. This variation conforms to rock deformation features under triaxial compression. In this study, we investigate the rationality of this critical state by an analogy method and illustrate that the critical state mentioned in this criterion is related to the microcracks in the potential failure zone of the rock. Alternatively, the primary object of this study is to reveal the applicability of predicting the yield state for this criterion. The method used in our study is compared to the Mohr–Coulomb (M-C) criterion, the Hoek–Brown (H-B) criterion, and the Exponential (Exp.) criterion by the yield surfaces on the deviatoric plane. Notably, there is a vertex consistent region for the four criteria, but except for this region, the yield state of rock predicted by the four criteria is quite different, depending on the extent of the parameters for the criteria and the magnitude of the slopes of the yield surfaces. The results show that the M-W criterion has certain applicability for predicting the rock yield state by using the multiple data of rock triaxial compression tests in the published literature.

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