Advanced Triaxial Testing Of Soil And Rock Issue 977 Pdf


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advanced triaxial testing of soil and rock issue 977 pdf

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Citation: Don J. DeGroot, Melissa E.

A saturated non-cohesive soil can exhibit features typical of both solid or liquid phases, depending on circumstances or the history of loading.

The role of pore water in the mechanical behavior of unsaturated soils

Impact of methods used to reconstitute tailings specimens on the liquefaction potential assessment of tailings dams. The aim of this research is to investigate the liquefaction susceptibility of silt sandy mining tailings by experimental laboratory techniques. The main aspect analyzed is how techniques of sample reconstitution impact the results obtained in static undrained triaxial tests.

Different methods of sample preparation are reviewed, such as moist tamping MT , air and water pluviation, and a newly developed one called the Slurry Deposition SD method.

This research highlights the importance of the "fabric" or particle structural arrangement associated with the various specimen preparation techniques when liquefaction potential assessment is of concern.

Two series of undrained static triaxial tests were performed on specimens prepared according to MT and with SD techniques on specimens in the loose and very loose state. Results have demonstrated that MT specimens have shown the whole spectrum of liquefaction resistance total liquefaction, limited liquefaction, and no liquefaction on increasing density, while the SD campaign has shown only liquefaction resistance even in the overlapping intermediate densities with the MT series, where the latter has shown liquefaction, although limited.

This scientific study critically discusses the risk of taking laboratory results of replicated soil elements that may not correspond to the reality. Laboratory tests play an important role in understanding the mechanical response of geomaterials. For this purpose, testing undisturbed samples obtained from field investigations is considered more appropriate for studying natural soil behavior, since it allows the structure of soil particles in situ, stress field, depositional history, etc.

However, the use of reconstituted samples of granular soils for laboratory testing has gained widespread acceptance in the past for a number of reasons, including Khalili and Wijewickreme, :. The use of reconstituted samples for liquefaction potential assessment of tailings deposits as proposed by this research can be easily justified by all three of these reasons. In addition, most of our fundamental understandings of the liquefaction phenomena in sands has been derived from controlled laboratory studies.

However, previous articles on this issue have shown that each sample preparation method renders a specific fabric, which may result in distinct stress-strain characteristics and responses Vaid and sivathayalan, ; Carraro and Prezzi Sample reconstitution methods, such as moist tamping MT , air pluviation AP and water pluviation WP are the most widespread methods in laboratory routines.

In addition, Slurry Deposit SD is a newly developed preparation technique, derived from WP, which has been considered to yield the most realistic results for natural alluvial soils, and tailings deposits formed by disposed slurries. Table 1 summarizes the methods, their characteristics and applications. Soil liquefaction is one of the geotechnical engineering phenomena that has been researched for decades. Its consequences can be catastrophic, whether caused by dynamic or static loading.

To this day, most research has been directed to the phenomenon occurrence under dynamic conditions, performed mainly in countries with constant records of seismic events. However, static stress-strain analyses of this mechanism of failure has recently received more interest especially in the context of tailings dam collapse disasters, such as Fundao TSF, in , in Southeastern Brazil.

This article deals exclusively with static liquefaction. Silty sand liquefaction is known to be affected by the following factor: fines content, confining stress, test specimen preparation method, and dry density Monkul and Yamamuro Table 2 presents a summary of main research findings on liquefaction resistance while investigating those factors. Experimental work comprised of performing two series of isotropic undrained consolidated static triaxial tests CIU on specimens prepared using either a moist tamping or slurry deposition technique, variable density or void ratio , at 50 kPa and kPa confining effective stress.

Material used in the study was silt-sandy tailings with non-plastic fines, from iron ore flotation processes, collected at a mine site in the Quadrilatero Ferrifero, in the State of Minas Gerais. Indexed property tests on this material rendered a mass density of 2.

Microscopic mineral analysis identified quartz, hematite and goethite. Soil elements were recreated in the lab for the triaxial tests, firstly using the moist tamping technique MT with undercompaction, as suggested by Ladd , in order to improve specimen uniformity.

Triaxial tests performed with specimens prepared according to the MT technique initially followed a two-fold saturation procedure. First of all, they were submitted to a low hydraulic gradient flux outside the triaxial chamber using differential elevation heads between a water source and the specimen.

This external saturation, although necessary and common in laboratory routines, was not very effective, since in the end, the Skempton B parameter was below 0. Secondly, specimen saturation was pursued by backpressure incremental steps with the triaxial cell already assembled. This time the procedure was effective, although extremely slow, taking days to finish, and requiring high back pressure values, approximately kPa.

The specimens were then isotropically consolidated under a confining effective stress of 50 kPa or kPa. For the undrained shearing phase CIU , a shear rate of 0. Field soil elements were also recreated using the reconstitution technique for sandy soils with slurry deposition fines SD , as suggested by Carraro and Prezzi , with some modifications and additions of Wang et al.

The main materials and equipment used in this preparation were: a cylindrical acrylic tube After specimen preparation, SD specimens for triaxial tests were also saturated following similar laboratory techniques as described for MT samples.

In this case, as expected, the initial percolation at low gradient rendered Skempton B values approximately 0. Saturation was then completed by applying backpressure steps.

The desired saturation, that is, B values around 0. The specimens were then isotropically consolidated under 50 kPa or kPa stress. The undrained test shear rate was set at 0.

The main results of this research are related to the analysis of CIU triaxial tests performed on the silt sandy tailings, whose specimens were prepared according to the moist tamping MT and slurry deposition SD methods. The goal was to attempt to verify the impact of these specimen reconstituting techniques on liquefaction susceptibility. Figures 1 and 2 show CIU tests results for MT test specimens plotted in terms of stress path p' x q according to the MIT convention ranging from low 1.

Figure 3 replotted all 50 kPa tests together, and also one kPa test. At low densities Figure 1 , a complete liquefied state is reached, differently from the intermediate range where a limited liquefaction state is observed also in Figure 1 , 1. For the test with the highest specimen density Figure 2 , high liquefaction resistance is configured. Briefly, the increase in density produces a change from contractive, softening liquefiable behavior, to a dilating and hardening liquefaction resistant pattern, including an intermediate state of slight softening limited liquefaction.

It is further noted that for the kPa confining effective stress test Figure 3 , although it is performed on a low density 1. All of this corroborates previous studies, with influence factors density and confining stress playing important roles on liquefaction resistance Yamamuro and Lade, Figure 4 shows CIU tests results plotted in terms of stress path p' x q for SD test specimens with densities between 1.

The same behavior was observed in all four tests, regardless of the density difference or the confining stress. Firstly, stress paths rise, bending slightly to the left, generating low positive excess pore pressure, and then, as the deformation increases, the trajectory turns to the right, climbing the same slope, generating large values of negative excess pore pressure during shear, and revealing a dilating and hardening behavior. It is interesting to note that at large deformations, the stress paths of all tests overlap, characterizing a limit state of resistance critical state strength parameters.

Observing Figure 5 , there are apparently different and conflicting behaviors for the same soil element recreated according to different methods, MT and SD.

First, it is possible to obtain specimens with liquefaction behavior by the MT method for low density 1. For intermediate densities 1. The SD, with lower density 1. In Figure 6 , it can be seen that the two specimens show resistance to liquefaction, have hardening with deformation, and are dilating.

These characteristics are more noticeable with the specimen prepared by MT. It can be concluded that regardless of the reconstituting technique, the same behavior is observed with increased density.

Until the present, discussions on liquefaction susceptibility have focused on reconstitution techniques and specimen densities without referring the latter to material limits item 3. Results in Figure 7 suggest several things, for example, that it is possible to achieve higher void ratios than the maximum considered. Another interesting matter is that all liquefaction, limited liquefaction or liquefaction resistance behaviors happened for specimens presenting relative densities in the range of loose, very loose and beyond.

One can consider that sand soils with high fines content may need different limit standards in order to make comparisons with the copious literature on liquefaction susceptibility that relates it to relative density. Even having resolved this issue, there still remains the question why SD specimens have not shown liquefaction.

This research does not examine that aspect, but it endorses the previously mentioned idea that the static liquefaction condition may be achieved simply by bringing the material into a non-stable state high pore pressure for example in which its resistive force is reduced sufficiently to allow static conditions to produce static liquefaction.

Such type of pre-triggering mechanism can be caused by, e. The present research established an experimental program to assess the mining tailings liquefaction potential through isotropically consolidated undrained triaxial tests.

It was driven by the challenge of searching for the most adequate specimen reconstitution method that could make it possible to produce soil elements with a similar structure, as in tailings dam deposits, such as those found in mines in the Quadrilatero Ferrifero of Minas Gerais, Brazil. The literature review carried out indicated that the Moisture Tamping MT specimen reconstitution method is not the appropriate way to replicate soil elements formed under an alluvial environment and hydraulic fills, as is the case of mining tailings deposits.

In such conditions, the Slurry Deposition SD specimen method seems to render the best results. It has been observed that material density greatly influenced the results for very loose soil specimens, since a small difference in this index property was enough to manifest different behaviors in the MT campaign, as total liquefaction lower density and non-liquefaction higher density. On the other hand, the SD technique showed dilating behavior, a characteristic that corresponds to liquefaction resistance, in all possible experimental densities, even in the overlapping range with the MT series.

This research has shown how fabric, resulting from different specimen preparation, can affect liquefaction assessment. Unfortunately, scientific research based on laboratory tests cannot exactly replicate all possible and existing situations in the field; however, the SD technique may offer an appropriate method for studying fluvial or hydraulic fill deposits in the future.

All specimens tested were prepared with relative densities in the range of loose and very loose and even beyond categories according to the Brazilian ABNT standards for dry densities limits. This finding generates several questions, for example, if the maximum and minimum void indexes found are true for this material, which does not seem to be the case. If they are not, what would actually be the range of relative density for the tested specimens.

In addition, how logically and consistently the relative density compactness would relate to the mechanical response of these soils.

It is fair to say that laboratory testing of representative samples is a valid resource. Research has been used to understand soil liquefaction susceptibility, although some intangible factors may limit its conclusiveness. This research has shown how fabric resulting from different specimen preparation can affect that phenomenon assessment.

MB Slurry deposition method for reconstituting specimens for triaxial and consolidation tests. A new slurry-based method of preparation of specimens of sand containing fines. Geotechnical Testing Journal , v. Liquefaction and cyclic deformation of sands: a critical review.

Buenos Aires, v. New slurry displacement method for reconstitution of highly gap-graded specimens for laboratory element testing. The effect of gradation and fines content on the undrained loading response of sand. Vancouver, Canada: University of British Columbia, Master of Applied Science.

LADD, R. Preparing test specimens using undercompaction. A sample preparation method and its effect on static and cyclic deformation-strength properties of sand.

Advanced Triaxial Testing of Soil and Rock

A series of triaxial tests were performed on specimens made of Toyoura sand having different dry densities. Based on these static and dynamic measurements, we discuss the following aspects: 1 the difference among the three types of dynamic measurements, 2 the relationships between the dynamic and static measurement results and 3 the effects of stress stateinduced anisotropy and dry densities of the specimens. Tatsuoka, S. AnhDan, J. Koseki, T.

Advanced triaxial testing of soil and rock

A38 A. Would you like to tell us about a lower price? If you are a seller for this product, would you like to suggest updates through seller support?

Donaghe, Ronald C. Chaney, and Marshall L. Silver, editors I I! Silver, editors. Includes bibliographies and index.

Geology and engineering properties of sensitive Boston Blue Clay at Newbury, Massachusetts

Deformation and failure of soils are governed by the stresses acting on the soil skeleton. The isotropic stress acting on the soil skeleton can be divided into two components. One is the stress component which is transmitted through the soil skeleton. The other is the internal stress component which does not contribute to equilibrium with a given external force.

Impact of methods used to reconstitute tailings specimens on the liquefaction potential assessment of tailings dams. The aim of this research is to investigate the liquefaction susceptibility of silt sandy mining tailings by experimental laboratory techniques. The main aspect analyzed is how techniques of sample reconstitution impact the results obtained in static undrained triaxial tests. Different methods of sample preparation are reviewed, such as moist tamping MT , air and water pluviation, and a newly developed one called the Slurry Deposition SD method. This research highlights the importance of the "fabric" or particle structural arrangement associated with the various specimen preparation techniques when liquefaction potential assessment is of concern. Two series of undrained static triaxial tests were performed on specimens prepared according to MT and with SD techniques on specimens in the loose and very loose state.

Donaghe, Ronald C. Chaney, and Marshall L. Silver, editors I I! Silver, editors. Includes bibliographies and index.

Series: ASTM special technical. A38 Would you like to tell us about a lower price?

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STP Advanced Triaxial Testing of. Soil and Rock Robert T. Donaghe, Ronald C. Chaney, and Marshall L. Silver, editors I I! ASTM.

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