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Tensile cracking in clay is an important phenomenon that affects the strength and permeability of clays in many facilities, such as dams, embankments and landfill liners, as well as being a precursor to slope failures in the natural terrain. This study investigates the stress-strain criteria for cracking in clays by performing four-point bending te...
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... material chosen, E-grade kaolin, is well characterised and has a liquid limit of 51%, a plastic limit of 30%, and a saturated permeability of the order of 10 À9 m/s ( Barker, 1998). The values of critical state para- meters of E-grade kaolin clay acquired from various sources in the literature are summarised in Table 1. The water retention curve for E-grade kaolin is given by Rabozzi (2005); it shows an air entry suction of 250 kPa. ...
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Citations
... Indirect methods modify the sample loading method, utilizing splitting, bending, and other approaches combined with theoretical formulas to calculate tensile strength. Representative tests include radial splitting (Brazilian splitting) tests (Frydman 1964;Festugato et al. 2018;Sobhan and Mashnad 2002), axial splitting tests (Fang and Chen 1972;Kim et al. 2007;Liang et al. 2014), and three-point bending tests (Narvaez et al. 2015;Thusyanthan et al. 2007). The Brazilian splitting method, characterized by its straightforward sample preparation, simple testing methodology, and stable results, is widely applied in measuring the tensile strength of soils . ...
Landslides, ground fissures, and soil collapses are common natural disasters frequently associated with the tensile strength of loess. However, due to measurement difficulties, previous studies have often overlooked the tensile failure characteristics and processes of loess. This paper utilizes electrical resistance and Digital Image Correlation (DIC) technologies to investigate the changes in electrical resistance and surface strain fields during the Brazilian split test on remolded loess under various dry densities, moisture contents, and loading methods. The experimental results indicate that an increase in dry density and a reduction in moisture content decrease the tensile strength of loess. Cracks appear and electrical resistance begins to increase after reaching the peak load. The tensile strength under platen loading is lower than that under loading disc application, and the latter is not suitable for soils with high plasticity. Borehole water injection reduces the tensile strength and peak displacement of high moisture content soil samples, whereas for low moisture content samples, the peak displacement remains unchanged after water injection, but the tensile strength decreases. The failure stages of loess in the Brazilian split test are divided into four phases: stress adjustment contact phase, elastoplastic deformation phase, tensile cracking phase, and residual deformation phase. The angle between the load–displacement curves before and after the peak load is proposed as a criterion for determining brittleness.
... A large number of laboratory experiments have been conducted to study the development and mechanism of soil desiccation cracking (Velde 1999;Thusyanthan et al. 2007;Tang et al. 2011;Xu et al. 2022). Desiccation crack formation and morphology are related to various factors, including the mineral composition and fabric of soil, layer thickness and size, atmospheric temperature, and relative humidity (Cui et al. 2005;Romero 2013). ...
As a common natural phenomenon in clayey soil, drought-induced desiccation cracks impose danger to soil structures by degrading soil mechanical strength and hydraulic properties. In this study, through a series of field tests, we evaluated the effect of microbially induced calcite precipitation (MICP) technology on the suppression of desiccation cracks in field clayey soil and examined the impacts of MICP treatment methods (two-phase and one-phase methods) and cementation solution (CS) concentrations (0.5 and 1.0 M) on soil desiccation cracking behaviors and soil microstructure variation. The results revealed that MICP is capable of suppressing desiccation cracks in field soil. The surface crack ratio, average crack width, total crack length, and average crack depth decreased with the increase of treatment cycles and CS concentration. The two-phase MICP method performed better on soil crack suppression than the one-phase MICP method. Further CaCO 3 distribution and soil microstructure characterizations indicated that the CaCO 3 crystals generated by the MICP process contributed dominantly to the soil crack suppression by filling crack space, bonding soil particles, and reducing soil water evaporation. This study demonstrates that MICP is expected to serve as an eco-friendly and sustainable technology for soil desiccation crack suppression at the field scale.
... With macroscopic cracks in the soil, the external load will lead to stress concentration at the crack tip, which can be analyzed from the perspective of material fracture [5]. Since the introduction of fracture mechanics theory into geotechnics, extensive attention has been paid to crack propagation in rock-like materials. ...
In this study, a modified maximum tangential stress criterion by considering T-stress and uniaxial compression tests have been utilized to theoretically and experimentally reveal the fracture initiation mechanism of a center-symmetric closed crack in compacted clay. The results show that wing cracks occur in the linear elastic phase of the stress-strain curve. In the plastic phase of the stress-strain curve, the wing cracks extend gradually and the shear cracks occur. The crack initiation stress and peak stress of compacted clay first decrease with the rise in pre-crack inclination angle (β = 0°–40°), and then increase with the rise in pre-crack inclination angle (β = 50°–90°). When the pre-crack inclination angle is relatively small or large (β ≤ 10° or β ≥ 70°), the crack type is mainly tension cracks. Secondary shear cracks occur when the pre-crack inclination angle is 10°–80°. When the dimensionless crack length is larger than 0.35, the crack types include wing-type tension cracks and secondary shear cracks. The experimental results were compared with the theoretical values. It was found that the critical size rc of compacted clay under compression-shear loading was 0.75 mm, smaller than the value calculated by the empirical formula (12 mm). The MTS criterion considering T-stress can be used to predict the compression-shear fracture behavior of compacted clay.
... Generally, there are three frequent indirect tensile test methods: the split tensile test (Brazilian test) (Festugato et al. 2018;Frydman 1964;Ismaiel 2006;Munkholm and Kay 2002;Sobhan and Mashnad 2002). The beam bending test (Narvaez et al. 2015;Thusyanthan et al. 2007). Unconfined penetration test (Fang and Fernandez 1981;Kim et al. 2012), and the axial fracturing test (double-punch test) (Fang and Chen 1972;Kim et al. 2006;Liang et al. 2014). ...
This research presents a modified numerical simulation approach for predicting approximate values of unsaturated soil parameters with low water content. In order to understand how unsaturated soils behave and to create the soil–water characteristic curve, the suggested model attempts to predict the following parameters. First, the relationship between the water content and the matric suction in terms of particle separation distance. Secondly, the relationship between the effective stress parameter χ and the filling angle θ when the separation distance between soil particles is taken into account. Thirdly, the relationship between suction stress and filling angle θ, in terms of particle separation distance. Fourthly, the effect of particle separation distance on the curve of tensile strength in terms of the degree of saturation. The updated model assumes that all the particles are equally dispersed spheres of the same size. In this study, the updated model is exclusively applied to simple cubic packing order with zero contact angle. The model may also be used to predict matric suction, effective stress parameter, suction stress, and tensile strength while combining experimentally determined soil properties. This removes the requirement for sophisticated measuring devices or specific test procedures to illustrate how the separation distance affects the behavior of unsaturated soils. Compared to the experimental data, our model has shown positive results. In this paper, all curves have been programmed using MATLAB.
... Except for the water content, the tensile strength is affected by the mineral type and content, particle size, bulk density, stress state, etc. [52][53][54]. Such factors affecting cracking need to be studied further. ...
Natural fractures in shale have been commonly recognized as a vital factor in shale gas production. Diagenetic shrinkage fracture is an important type of natural fracture; however, its formation mechanism and prediction remain largely unexplored. Given the similarity between diagenetic shrinkage fractures and desiccation cracks, the influence of smectite, kaolin, quartz, and feldspar on shrinkage fractures were investigated using the physical simulation experiment of desiccation in this study. Here, water evaporation, surface cracks initiation and propagation processes were monitored during the whole desiccation. The morphological characteristics of cracks patterns were quantitatively described. Diagenetic shrinkage fractures of transitional shale with different minerals were observed using SEM. The results show that the development and morphology of cracks are affected by the mineral composition, and the sediments with higher clay content tend to form more complex fracture networks. We further propose a morphological prediction model for cracks and compare this model with diagenetic shrinkage fractures under SEM. We found that the effects of mineral composition on both were similar, with more well-developed diagenetic shrinkage fractures in those clay-rich samples. Taken together, this study implies the feasibility of using physical simulation experiment of desiccation cracks to invert diagenetic shrinkage fractures and provides new insights into the mechanism and development regularity of diagenetic shrinkage fractures.
... Many experimental studies have been carried out to explore the deformation characteristics and cracking behaviors of clayey soil, which can be categorized as tensile tests, Brazilian tests, and beam bending tests (Ziegler et al. 1998;Kim et al. 2007;Thusyanthan et al. 2007;Lin, Xiong, and Yan 2016;Wong, Wan, and Wong 2017). The four-point bending test is a frequently used method to study the mechanical behavior of concrete. ...
... Furthermore, the procedure was also utilized to evaluate the enhancement of geotextiles and chemical additives on the strength and other properties of soils (Viswanadham, Jha, and Pawar 2010;Tang et al. 2012;Anggraini et al. 2017). Using this loading form, Thusyanthan et al. (2007) explored the strength of materials criteria for crack initiation in compacted clay. ...
... The technique based on closerange photogrammetry and particle image velocimetry (PIV) has achieved wide application in geotechnical testing. For instance, in the compacted beam bending tests conducted by Thusyanthan et al. (2007), the PIV analysis was employed to capture the strain profiles of the clay surface. This photograph-based technique can provide planar deformation information on the soil surface. ...
Understanding the mechanical characteristics of clayey soil is critical to estimate the stability of clay-related geotechnical engineering works. However, the distributed information of the internal deformation of clay is hard to capture through traditional methods. In this paper, a set of four-point bending tests were performed on a compacted clay beam instrumented with fiber optic strain sensors to investigate the flexure and cracking behaviors. The optical frequency domain reflectometry technique with high spatial resolution and precision was employed to establish a distributed strain sensing (DSS) system in this study. The results show that the DSS system exhibits a high accuracy in the collection of the clay deformation in terms of compression, tension, and cracking. The comparison of the internal strain profiles with the observation of particle image velocimetry analysis system verifies the feasibility of fiber optic sensing technology in the quantitative assessment of clay deformation. The performance of fiber optic sensors in the rebound deformation and creep deformation monitoring was preliminarily issued in the study. In addition, the progressive failure on the fiber–soil interface was analytically studied to evaluate the deformation compatibility between the fiber and surrounding clayed soil. The conclusions drawn in this paper can help to guide the state interpretation of clayey soil instrumented with fiber optic sensors.
... In comparison, the flexural strength is significantly higher than the references on other liner construction materials. For example, the hydrostatic resistance for PVC plastic liners used for pond sealing typically ranges from 0.4 to 1.0 MPa (Stabnikov et al. 2011), and 0.03 MPa for 8-cm-thick consolidated clay (Thusyanthan et al. 2007). The density of calcium carbonate content distribution of the bioslurry layer is shown in Fig. 3(b), where the calcium carbonate content increment is relatively uniform as the density of all samples increased from 0.14 g=cm 3 to the range of 0.27 to 0.31 g=cm 3 . ...
This paper presents a methodology to construct a water pond in sand using bioslurry layer via the microbially induced car-bonate precipitation (MICP) process. Bioslurry is calcium carbonate crystals containing high-urease active bacteria cells, allowing further microbially induced calcium carbonate precipitation when introducing cementation solutions (urea and calcium ions). With the effect of a top sand layer, the daily seepage rate of the water pond was dramatically reduced to 3 mm=day through four rounds of treatments with 1.6 M of cementation solution. In this way, a bioslurry-based waterproofing layer was formed for the construction of a water pond. Due to the bonding strength gained from calcium carbonate crystal precipitation, the flexural strength of bioslurry layer was in the range of 3.6-4.2 MPa. This is sufficient to support the hydrostatic pressure and avoid bending for water pond. With the low seepage rate and high flexural strength, the proposed bioslurry layer is a promising method for the construction of a fishpond in sand; other potential applications include stabilization of sand dunes and concrete healing.
... Cohesive soils manifest limited, if not negligible, tensile strength so they are subject to the formation of cracks (Porbaha & Goodings, 1997;Thusyanthan et al., 2007). Tension cracks forming in geo-reinforced slopes have been reported in experiments in geotechnical centrifuges (Porbaha & Goodings, 1997;Suah & Goodings, 2001) and in post-earthquake field observations (Ling et al., 2001). ...
... Here cracks are assumed to pre-exist the formation of the shear log-spiral failure since there is abundant experimental evidence showing that crack formation in cohesive soils is a brittle phenomenon (e.g. Thusyanthan et al., 2007), unlike the log-spiral part of the slope failure mechanism where failure is in shear and ductile. This implies that stress redistribution can be assumed only along the log-spiral part of the mechanism, with the crack to be assumed opened by the time the progressive ductile failure along the log-spiral part of the mechanism reaches the crack. ...
Where granular materials are not easily available, local cohesive soils are increasingly employed in geosynthetic reinforced soil walls as a cheap and sustainable option. Conventional design methods do not yet account for the beneficial effect of cohesion in reducing the amount of required reinforcement. Similarly, the contribution of the face to stability is rarely accounted for, despite plenty of experimental evidence in its favour. In this paper, a semi-analytical method based on limit analysis is developed for the design of reinforced soil walls in frictional-cohesive backfills accounting for the wall contribution. A parametric analysis was conducted to evaluate the effect of soil cohesion and friction angle, facing batter, block width, location of the reaction force acting on the face, facing-backfill interface friction, facing-foundation interface friction, and reinforcement length. Dimensionless design charts providing the required amount of reinforcement for lengths recommended in design standards are provided for both uniform and linearly increasing reinforcement distributions. It emerges that accounting for the presence of cohesion and the facing element can lead to significant savings in the overall level of reinforcement, and that tension cracks can be particularly detrimental to wall stability for highly cohesive soils so they cannot be overlooked in the design.
... In many geotechnical and geo-environmental engineering facilities such as embankments, dams, and landfill liners, crack in soils is an issue because it adversely affects the strength of soils (e.g., Miller et al., 1998;Alonso, 2021;Menon and Song, 2021). Crack has also been considered as a precursor to natural slope failures (Thusyanthan et al., 2007;Lu and Godt, 2013). The crack-induced strength loss matters because slope stability relies on the tensile strength of soil (Lu and Dong, 2017). ...
Cracks in clay are significant in geotechnical and geoenvironmental engineering (e.g., embankment erosion and stability of landfill cover systems). This article studies the mechanism of nucleation and growth of cracks in clay at the nanoscale through full-scale molecular dynamics simulations. The clay adopted is pyrophyllite, and the force field is CLAYFF. The crack formation in a pyrophyllite clay layer is evaluated under uniaxial tension and simple shear. The numerical results show that cracks in the nanoscale pyrophyllite clay layer are brittle and strain-rate dependent. Small strain rate results in low ultimate tensile/shear strength. As strain rate increases, clay crack shifts from a single-crack pattern to a multiple-crack one. The cracking mechanism is investigated from bond breakage analysis at the atomic scale. It is found that the first bond breakage occurs in the silicon-surface oxygen bond. As a crack propagates, the relative percentage of broken silicon-surface oxygen bonds is the smallest compared to other types of metal-oxygen interactions, demonstrating that the atomic interaction between silicon and surface oxygen atoms is the strongest. To understand the propagation of cracks, we also study the stress intensity factor and energy release rate of pyrophyllite and their size dependence at the atomic scale.
... The testing methods for measuring soil's tensile strength include direct and indirect methods. The indirect tensile-test methods include the split tensile test, the beam bending test and the axial fracturing test [7], [37], and there is a critical water content for the peak load vs. water content curve . The diametric splitting test process can be divided into four stages on the basis of the plotted load-displacement curves: a stress contact adjustment stage (I); stress approximately linear increasing stage (II); tensile failure stage (III); and residual stage (IV). ...
There is a close relationship between tensile strength of soil and crack development, but the tensile stress-strain in full failure process is rarely studied because challenges exist in accurately measuring shear strain using traditional methods. In this paper, we employed a newly developed diametric splitting testing apparatus and particle image velocimetry (PIV) system to study the tensile strength of compacted unsaturated expansive soil with different water contents and initial dry densities. Soil water characteristic curves of compacted expansive soil with different initial dry densities were determined using the filter paper method. Test results show that the tensile strength increases first and then decreases with increasing water content and there is a critical water content for the peak load vs. water content curve. The diametric splitting test process can be divided into four stages on the basis of the plotted load-displacement curves: a stress contact adjustment stage (I); stress approximately linear increasing stage (II); tensile failure stage (III); and residual stage (IV). Under the same water content, the angle between the major directions of the displacement vector and the major crack decreases with increasing the dry density, especially when the fissure appears. Using the particle image velocimetry technique, the displacement and strain during the test process recorded is helpful for better understanding the soil failure mechanism.
