Experimental Investigation on Monotonic Shear Resistance of Granular Material: Effect of the Reconstitution Method and Other Parameters (original) (raw)
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Geologia Croatica, 2011
The effects of confi ning pressure, relative density and sample preparation methods on the shearing strength of Chlef sand were studied. Results are presented of drained and undrained monotonic triaxial compression tests, performed on samples with initial densities of 0.29 and 0.80, under initial confi ning pressures ranging from 50 to 200 kPa. Specimens were prepared by two depositional methods; dry funnel pluviation and wet deposition. There was a marked dif ference in the undrained behaviour, even though the density and stress conditions were identical. The soil fabric was responsible for this result. The results also indicated that at low confi ning pressures, the specimens reconstituted by the wet deposition method exhibited complete static liquefaction, (zero effective confi ning pressure and zero stress dif ference). As confi ning pressures and densities were increased, the effective stress paths indicated increasing resistance to liquefaction by showing increasing dilatant tendencies. The same trends were observed in drained tests results in the form of an increase in the volumetric strain and the rapid transition from the contractancy phase to the dilatancy phase.
Acta Mechanica Sinica, 2011
This paper describes the results of an experimental study on the undrained shear behaviour of loose sand collected from the location close to the epicenter of the recent Chlef (Algeria) Earthquake (October 10, 1980). The study focuses on the effects of the mode of the soil deposition on the liquefaction resistance of the Chlef sand. For this purpose, the results of undrained monotonic triaxial compression tests performed on samples with initial density of 0.29 under initial confining pressures ranged from 50 kPa to 200 kPa are presented. The specimens were prepared by two depositional methods namely dry funnel pluviation and wet deposition. It was found that there was a marked difference in the undrained behaviour of sand in terms of maximal deviatoric stress, peak strength, residual strength and excess pore water pressure, even though the density and stress conditions were identical. The conclusion was that the soil fabric was responsible for this result. The results indicated also that at low confining pressures, the specimens reconstituted by the wet deposition method exhibited complete static liquefaction (zero effective confining pressure and zero stress difference).
Geotechnical and Geological Engineering, 2020
This paper presents a laboratory investigation on soil densification effect on the behaviour of Chlef sand (Algeria). The study is carried out via a series of monotonic and cyclic tests in drained and undrained conditions using the triaxial apparatus. It's conducted in three stages: the first consists on the study of the sand behaviour under monotonic loading in drained conditions. Effects of the confining pressure and of the relative density Dr on the sand's shear strength are observed. In the second step, the undrained behaviour of the studied sand under monotonic loading is studied, and finally the last step deals with the sand undrained behaviour under cyclic loading. In each step, sand samples with different values of relative density that are ranging from loose, medium and dense state are tested (Dr = 10%, 15, 18%, 50%, 65% and 80%). The obtained results show a significant upgrading of the mechanical properties of the sand samples proportionally to the densification rise. The aim of the study is to highlight the improvement that can bring soil densification process on the behaviour of Chlef sand, and therefore its use as a soil reinforcement technique to solve soil deformations in the study area, which is a prone zone to seismic risk.
Experimental Study of Undrained Shear Strength of Silty Sand: Effect of Grading Characteristics
2010
The liquefaction susceptibility of saturated medium sand-silt mixture samples is evaluated by monotonic undrained triaxial laboratory tests that were carried out on reconstituted specimens at various relative densities (Dr = 17 and 91%) and a constant confining pressure (3'= 100 kPa). The test results were used to conclude on the effect of grading characteristics and other parameters on the liquefaction resistance of the sand-silt mixtures. The test results indicate that the undrained shear strength at the peak can be correlated to the coefficient of uniformity (Cu) and the average diameter (D50). Indeed, they decrease linearly with the increase of the uniformity coefficient and decrease of the average diameter. It is found that a relationship between the static liquefaction resistance and any of the diameters (D10 or D50) and the coefficient of uniformity (Cu) would be more realistic than to build a relation between the coefficient of gradation (Cc) and the static liquefaction resistance.
Effect of grading characteristics on the undrained shear strength of sand: review with new evidences
Arabian Journal of Geosciences, 2012
In this paper, the shear strength of saturated pure sand and sand-silt mixture is evaluated by monotonic undrained triaxial tests that were carried out on reconstituted specimens at same relative densities and a constant confining pressure (σ 3 0300 kPa). The test results were used to conclude on the effect of low non-plastic contents (0-20 %) and grading characteristics on the liquefaction resistance of the sand. The test results indicate that the undrained residual strength reduced with the increase of non-plastic fine content. Also, shear strength of gap-graded sand mixed with low non-plastic fine content increases with decrease in effective size (D 50). In other words, in this state, we can use the D 50 as a parameter to control of silty sand's undrained resistance. Besides, the undrained residual strength of pure sand specimens with same effective size increases due to increase of coefficient of uniformity (C u).
Post-liquefaction deformation and strength characteristics of sand in torsional shear tests
Soils and Foundations, 2021
The estimation of strength deterioration with the increase in the undrained cyclic shear-induced strain in liquefiable soils is an important topic in geotechnical earthquake engineering that is still poorly understood and needs to be properly addressed. In this paper, in an attempt to provide new insights into this topic, the post-liquefaction undrained strength and deformation of Toyoura sand were investigated through a series of laboratory tests performed by using a large-strain torsional shear apparatus. In the tests, simple shear conditions were reproduced on a medium-size hollow cylindrical specimen to apply stress conditions that soil experiences in the field during earthquakes. Specimens prepared by the air-pluviation method were first liquefied by applying a constant amplitude undrained cyclic shearing to induce a target cyclic shear-induced damage strain (c D). The tests were terminated at different amplitudes of c D and subsequently loaded monotonically in undrained conditions to obtain stress-strain and excess pore water generation responses. The test results indicate that the post-liquefaction monotonic loading (ML) stress-strain behavior of sand can be divided into three regions, namely Region 1, 2 and 3. The sand behavior changes to strain-hardening from essentially zero strength and stiffness from Region 1 to 2. While Region 3 marks the beginning of strain-softening state in the sand. It is found that the strain localization is associated with the transition of sand behavior from strain-hardening to strain-softening state. It is proposed that the sand undrained strength in monotonic shearing is the true representation of specimen response until the state of uniform deformation is maintained, based on the sudden drop of the differential stress (r d = r 0 v-r 0 h). The test results also revealed that there is a progressive degradation in the shear strength with the increase in the amplitude of c D. A correlation depicting the degradation ratio (s d) with the increase in the c D is proposed. This correlation can be used to estimate the degree of degradation with the increase in the applied c D , and it is valid for different density states, confining stresses and cyclic stress ratios.
Geologia Croatica, 2011
This laboratory investigation has been conducted to elucidate how the fi nes fraction affects the undrained residual shear strength and liquefaction potential of sand-silt mixtures (Algeria). A series of monotonic and cyclic undrained triaxial tests were carried out on undrained, reconstituted, saturated samples of sand with varying fi nes content ranging from 0 to 50%. These were undertaken in order to evaluate the effect of the fi nes fraction on the undrained residual shear strength and liquefaction potential of loose, medium dense, and dense sand-silt mixtures (D r = 17%, 53%, 62% and 91%), under an initial confi ning pressure of 100 kPa. The results of the monotonic tests indicate that the stress-strain response and shear strength behaviour is controlled by the percentage of the fi nes fraction and the samples become contractive for the studied relative density (Dr = 17% and 91%). The undrained residual shear strength decreases as the gross void ratio decreases, and the fi nes content increases up to 30%. Above this level of fi nes, it decreases with increasing gross void ratio. Moreover, the undrained residual strength decreases linearly as the fi nes content and the intergranular void ratio increase. Cyclic test results show that for the studied amplitude, the increase in fi nes content leads to an acceleration of liquefaction. The liquefaction resistance decreases with the increase in gross void ratio and the loading amplitude.