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When a loose sand specimen is loaded under an undrained condition, it may become unstable. The instability conditions may be specified by an instability line determined using undrained tests. However, the instability behavior of sand has seldom been studied under plane-strain conditions. Experimental data obtained under both triaxial and plane-stra...
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... Significant strain softening was observed after the peak without any localized deformations. It was also established by Chu and Wanatowski (2008) that there is a unique relationship between the slope of the instability line normalized with the slope of the critical state line. ...
The influence of effective confining pressure on Chang Dam soil obtained from the Kutch region in India is explored in a flexible boundary plane strain apparatus. The boundaries of the apparatus were relatively flexible along the two loading directions. The test setup offers the advantage of measurement of strains and stresses along the principal loading and lateral direction. Consolidated undrained tests were performed for sand at four effective confining pressures. The applicability of instability criteria based on the second-order work is examined for Chang Dam soil. Furthermore, the instability onset indicated by the evolution of lateral strains is almost coincident with the second-order work criterion. However, the global stress-strain response does not depict unstable behaviour. The dilatancy angle decreases non-linearly with the stress ratio. The stress ratio at phase transformation is observed to be a function of the state with varying effective confining pressures.
... Previous researches indicate that coal ash may manifest cyclic liquefaction (Boominathan and Hari 2002;Mohanty et al. 2010b;Zand et al. 2009). Although numerous research has been carried out to investigate the cyclic instability behaviour of sands (Andrade et al. 2013;Castro 1975;Chu and Wanatowski 2008;Ishihara 1993;Lade 1994;Yang 2002) and silty sands Baki et al. 2012;Chiu and Fu 2008;Rahman et al. 2014) under triaxial loading condition; such investigation has been somewhat relatively brief for coal ash. Previous relevant research (Chattaraj and Sengupta 2017;Hwang 2002;Jakka et al. 2010;Mohanty et al. 2010a;Mohanty and Patra 2016;Nong et al. 2022;Yoshimoto et al. 2014;Yoshimoto et al. 2006;Zand et al. 2007;Zand et al. 2009) on coal ash under triaxial testing mainly investigated cyclic strength behaviour, and thus, stress-strain and ESP plots were not presented in many cases. ...
Cyclic liquefaction of granular materials may be triggered in two major forms: cyclic instability and cyclic mobility. Under a load-controlled condition, cyclic instability manifests as a "run-away" flow-like failure. Previous research indicates that coal ash may manifest cyclic liquefaction. Although numerous research has been carried out to investigate cyclic instability behaviours of sands and silty sands in triaxial testing; investigation has been somewhat relatively brief for coal ash, and mainly focused on cyclic strength behaviour (i.e. cyclic mobility). Numerous research in linking static and cyclic liquefaction for clean sands and sand with fines are available in the literature, however, whether this is the case for coal ash is yet to be investigated. Thus, the objective of this study is to evaluate the cyclic instability triggering mechanism for loose coal ash corresponding to monotonic test under triaxial loading condition, and to identify and compare differences in linking onset of cyclic instability for coal ash in relation to sands and sand with fines/silty sand.
... The shear strength and dilation of sandy soils are affected by their confining pressure and density (Charles and Watts 1980;Fukushima and Tatsuoka 1984;Been and Jefferies 1985;Kolymbas and Wu 1990;Chu 1995;Guo 1998, 1999;Li and Dafalias 2000;Lancelot et al. 2006;Varadarajan et al. 2006;Chakraborty and Salgado 2010;Cinicioglu and Abadkon 2015;Chen and Zhang 2016b;Esposito and Andrus 2017;Giampa and Bradshaw 2018), particle size and gradation (Al-Hussaini 1983;Muir Wood and Maeda 2008;Vangla and Latha 2015;Amirpour Harehdasht et al. 2017;Yang and Luo 2018;Deng et al. 2021), the addition of fines to the sand matrix (Salgado et al. 2000;Ni et al. 2004;Yang et al. 2006;Murthy et al. 2007;Carraro et al. 2009;Rahman et al. 2011;Yang and Wei 2012;Rahman and Lo 2014;Wei and Yang 2014;Chen and Zhang 2016a;Ng et al. 2017;Xiao et al. 2017aXiao et al. , 2017bHassan et al. 2022;Yilmaz et al. 2023), the addition of coarse aggregates to the soil mixture (Simoni and Houlsby 2006;Li 2013;Li et al. 2013;Wei et al. 2018;Shi et al. 2021), the addition of biotreated bonds (Wu et al. 2021a;Xiao et al. 2021bXiao et al. , 2022aXiao et al. , 2023aWu et al. 2023), particle shape (Cho et al. 2006;Yang and Wei 2012;Li et al. 2013;Wei and Yang 2014;Altuhafi et al. 2016;Gong and Liu 2017;Kandasami and Murthy 2017;Keramatikerman and Chegenizadeh 2017;Zhao and Zhou 2017;Alshibli and Cil 2018;Jiang et al. 2018;Zhou et al. 2018;Gong et al. 2019;Guida et al. 2019;Xiao et al. 2019a, b;Chen et al. 2021;Liang et al. 2022;Wang et al. 2022), interparticle friction, particle roughness (Cavarretta et al. 2010;Koval et al. 2011;Dai et al. 2016;Alshibli et al. 2017;Wu et al. 2017;Tovar-Valencia Ruben et al. 2018;Guida et al. 2019; Thakur Mohmad and Penumadu 2021), particle breakage (Muir Wood and Maeda 2008;Yao et al. 2008;Daouadji and Hicher 2010;Bandini and Coop 2011;Alikarami et al. 2015;Liu et al. 2017;Xiao and Liu 2017;Karatza et al. 2018;Yu 2019;Ciantia and O'Sullivan 2020;Zhang and Luo 2020;Xiao et al. 2022bXiao et al. , 2022cXiao et al. , 2023b, loading mode (i.e., load-controlled shearing for prefailure instability and deformation-controlled shearing for prefailure strain softening) (Chu et al. 1993;Chu and Leong 2001;Chu and Wanatowski 2009), stress and/or strain path (Tatsuoka et al. 1986;Lam and Tatsuoka 1988;Chu et al. 1992Chu et al. , 1993Hanna 2001;Alshibli et al. 2003;Wanatowski and Chu 2007;Chu and Wanatowski 2008;Arda and Cinicioglu 2021;Shi et al. 2022), and drainage conditions (Chu and Lo 1994;Yamamoto et al. 2009;Chu et al. 2012;Zeybek and Madabhushi 2019). ...
... This highlights the effect of fabric anisotropy, i.e., as the degree of relative fabricinduced anisotropy increases (from TC to TE), the instability stress-ratio decreases. Of final note, the results presented for the triaxial compression tests on compressional consolidated specimens in Figures Figure 4 and Figure 5 are consistent with previous experimental studies (Chu and Wanatowski 2008;Kato et al. 2001;Yang et al. 2021). ...
... The effect of cross-anisotropy on the stress-strain-strength behavior of soils cannot be fully investigated in a triaxial testing apparatus as this device cannot apply principal stress rotation or shear at principal stress angles relevant to below-slope stress conditions. Testing with a rotation of the principal stress angle from 0°to 90°h as been carried out by several researchers in cyclic triaxial from an initial isotropic condition (e.g., the early work of Seed and Lee 1966;Tori et al. 1986), while the instability of sands has been investigated under the constant shear drained stress-path in triaxial compression (e.g., Chu, Leroueil, and Leong 2003), the plane strain biaxial device (Wanatowski 2005;Chu and Wanatowski 2008;Wanatowski and Chu 2012) and triaxial extension (Dong et al. 2016). However, while these tests allow some aspects of anisotropy to be investigated, they do not produce realistic stress conditions for below-slope locations. ...
The determination of the critical state locus (CSL) via triaxial testing has become a key input to the current state of practice to characterize the liquefaction susceptibility of tailings. However, an accurate estimate of void ratio is required to infer the CSL and allow correlation of the expected in situ state to element laboratory testing. This is an issue of particular importance for the loose moist tamped specimens generally used for CSL testing, which undergo significant volumetric collapse during saturation—a volume change that is difficult to measure using conventional test techniques. The torsional shear hollow cylinder (TSHC) device has been adopted in the past to investigate the effect of cross-anisotropy on the strength of soils, although studies on tailings in the TSHC are limited. The void ratio in previous TSHC testing programs appear to have been based on initial dimension measurements, with or without the adoption of internal instrumentation. However, as silty sands and sandy silts prepared in a loose state experience collapse during saturation, this may introduce an unquantifiable error in void ratio if the initial dimensions method is adopted and volumetric change due to saturation is not properly considered. A procedure is proposed in this paper that provides simple steps and calculations to enable the determination of void ratio in the TSHC apparatus in specimens that undergo significant volumetric collapse on saturation. This method is potentially more accurate than methods based on initial dimensions measurements to infer void ratio and does not require costly internal instrumentation.
... One area that has not received sufficient attention in the context of CSD triggering is the potential effects of crossanisotropy on η IL , as nearly all CSD elements tests carried out have been in either triaxial or plane strain devices under compression loading conditions (e.g. Chu & Wanatowski, 2008;Wanatowski et al., 2010), thus with direction of the major principal stress relative to the vertical axis (α) of 0°. Two exceptions are the triaxial extension CSD tests of Dong et al. (2016) and the direct simple shear (DSS) CSD tests of Reid & Fourie (2019) and Riveros & Sadrekarimi (2021). ...
... The distinction above is required as the code implemented in the software to target a specific stress-path controls q 13 and not q as discussed subsequently. Nevertheless, the η IL is calculated in this study from the octahedral deviator stress, consistently with current practice involving non-axisymmetric conditions (Chu & Wanatowski, 2008;Wanatowski et al., 2010;Jefferies et al., 2019;Reid et al., 2022b;Shuttle et al., 2022). ...
Results of torsional shear hollow cylinder (TSHC) tests carried out on a reconstituted sand maintaining a constant direction of major principal stress relative to the vertical axis (α) and intermediate principal stress ratio (b) during shearing are presented. Tests were undertaken following the constant shear drained (CSD) stress-path, which simulates stress conditions under a rising phreatic surface. The test programme was complemented by undrained TSHC tests to provide further insight on the behaviour of the sand when sheared under a range of α values. Various reconstitution methods (i.e., moist tamped (MT), dry pluviated (DP) and wet pluviated (WP)) were included to examine the effects of fabric on CSD triggering. Only MT and DP specimens could be prepared loose enough to exhibit liquefaction behaviour, hence the focus of this study was on these preparation methods. The programme indicated that the instability stress ratio (η IL ) under the CSD stress paths decreases as α increases, suggesting that cross-anisotropy strongly influences the shearing behaviour of sands under this trigger mechanism. Additionally, the DP sand showed a greater decrease of η IL with increasing α compared to the MT sand, consistent with other studies examining the effect of fabric and preparation methods on inherent anisotropy. The results of this study suggest that ignoring the effect of cross-anisotropy on the CSD trigger mechanism will lead to unconservative slope stability assessments.
... In contrast, Kato et al. (2001) using anisotropically consolidated specimens of Toyoura sand subjected to undrained triaxial compression loading, suggested that the slope of the instability line did not vary significantly with respect to the initial anisotropic consolidation. Beyond the triaxial conditions, Chu and Wanatowski (2008) performed plane strain tests on Changi sand to understand the conditions for flow liquefaction. An instability line was established, which was dependent on the state parameter defined by Been and Jefferies (1985). ...
... An instability line was established, which was dependent on the state parameter defined by Been and Jefferies (1985). Chu and Wanatowski (2008) also suggested that a normalization of the instability stress ratio ( ) by the stress ratio at the critical state ( ) provides a unique relationship in terms of the initial state parameter. Using this relationship, the instability conditions Lade (1999). ...
... The results presented for the triaxial compression tests on compressional consolidated specimens in Figs. 16 and 17 are consistent with previous experimental studies ( Kato et al., 2001;Yang et al., 2021;Chu and Wanatowski, 2008). ...
Previous experimental studies have shown that the onset of instability in sands under undrained loading is affected by the initial state (i.e., void ratio and confinement), intermediate stresses, and fabric anisotropy. These experimental results have motivated numerical studies that investigate the conditions for instability triggering; however, most efforts have been focused on triaxial conditions, mainly addressing the role of state with few notable exceptions that extend to a multiaxial setting incorporating fabric anisotropy. In this study, we use the relatively new anisotropic critical state theory (ACST) to investigate the onset of instability in sands under undrained loading considering the role of state, multi-axial loading, and fabric anisotropy. We use the ACST-based SANISAND-F constitutive model to extend a previously established stability criterion and take into account the effect of fabric anisotropy in a multiaxial setting. The analytical instability criterion is derived from the fabric-dependent constitutive equations, and predicts the plastic modulus and the flow stress ratio at the instability point. The derived criterion highlights the benefits of the ACST framework in incorporating fabric and anisotropy effects. Lastly, we show that the stress ratio at the instability onset is not significantly affected by the extent of anisotropic consolidation.
... After the initiation of static liquefaction, the static shear stress can be the driving force of flow slides (Ishihara 1993). Furthermore, the statically sustained shear stress can result in instability of soils, leading to a runaway type of soil collapse (Chu and Leong 2001;Chu and Wanatowski 2008). ...
... Lade (1992) explained that the potential zone of instability can be defined using the instability line that is determined experimentally by a line connecting the origin and the peak points on the effective stress paths of an undrained tests, as illustrated in Fig. 9(a). Previous studies (Chu and Leong 2002;Chu and Wanatowski 2008) have shown that the gradient of the instability line h IL changes with void ratio as shown in Fig. 9(b). ...
Bio-gelation is a new method for improving the hydraulic and mechanical properties of sandy soil through the production of polymeric gel to fill in the pores of soil. In this paper, a study on the engineering behaviour of loose sand treated using this method is presented. A series of permeability and undrained monotonic and cyclic triaxial tests were carried out on both clean sand and bio-gelled sand. The test results showed that the coefficient of permeability was reduced by 3 to 4 orders of magnitude in the bio-gelled sand samples, and the higher the alginate concentration, the lower the permeability. In the monotonic triaxial tests, sand samples that would have liquefied under static conditions manifested strain-hardening behaviour after treatment. The shear strength of the bio-gelled sand also increased as was indicated by an increase in the slope of the failure line from 1.08 to 1.27. In the cyclic triaxial tests, the number of cycles at failure increased from 183 for clean sand to 485 for bio-gelled sand, and the excess pore water pressure response was also much reduced. The hydrogel produced by the bio-gelation process was stable under both hydrostatic and seepage conditions. The other advantages of the bio-gelation method include 1) the massive formation of hydrogel can be controlled to be 28 hours later after injection, 2) the pH value of soil fluid can be maintained at neutral and 3) it is cost-effective for liquefaction or seepage control for sand compared with other conventional methods.
... The various interpretation methods for liquefaction under monotonic loading, including a steady-state approach and collapse line approach were used to analyze the laboratory test results on the soil mixtures by previous researchers (Wei and Yang 2014;Belkhatir et al. 2011;Amini and Qi 2000). Experimental investigations, including triaxial tests (Thevanayagam 1998;Monkul and Yamamuro 2011) and plane strain tests (Chu and Wanatowski 2008), were performed to investigate the onset of instability in granular materials under different boundary and loading conditions. Over the past two decades, persistent efforts have been made to understand the static liquefaction behavior of silty sands. ...
Liquefaction susceptibility of cohesionless soils is influenced by various factors such as stress state, loading conditions, and shearing modes, and therefore, the implicit assumption of completely undrained shearing modes could pose damaging consequences. In the current research, the effect of stress state and shearing modes on liquefaction response of cohesionless soils was studied under monotonic compression and cyclic simple shear loading conditions. Undrained, drained, and partially drained shearing modes were applied on three different silty sands collected from three different locations of earthquake-prone region of Kutch. The partially drained shearing mode was applied at different effective stress ratios (ESRs) to simulate different stress states. All three silty sands exhibited undrained instability at large ESR values. The effect of cyclic stress ratio (CSR) on liquefaction response of cohesionless soils was also evaluated by conducting cyclic simple shear tests. Soil specimens from all the three locations exhibited liquefaction due to the generation of large excess pore water pressure of greater than 95% of the loss in effective stress. The number of cycles required to initiate liquefaction decreased and the rate of development of pore water pressure increased with the increase in the applied CSR under cyclic simple shear loading conditions.
... Therefore, the characteristics of the shear bands are also related to the types of soils. Because the clays in slopes are under stress conditions very close to plane strain [26,28,29], plane strain compression tests were performed in this study. ...
The formation of the shear band is associated with the failure of soil. However, there has been relatively little investigation on the evolution of shear bands in naturally structured clay with a high sensitivity. In this study, undrained plane strain compression tests, digital image correlation (DIC) analyses, and scanning electron microscopy (SEM) tests were performed to investigate the characteristics of shear bands in naturally structured clay. The basic mechanical properties and stress–strain relationships show that naturally structured clay exhibits a strong structure and high sensitivity. Compared with plane strain compression tests under low confining pressure, more localized shear bands emerge in the specimens during the tests under high confining pressures; however, when the specimens fail, only one shear band is fully developed, and the local deformation in the developed shear band is much larger than those in other localized shear bands. Moreover, the local stress–strain relationships inside and outside the shear band show distinct discrepancies. The SEM results show distinct micro-structures of clays inside and outside the shear band, which are caused by the development of the shear band. The findings in this work provide new insight into the failure of structured clay.
