In transparent soil model experiments, fused quartz stands out as the most promising substitute for natural sand. However, there is still a lack of a comprehensive evaluation system to assess the similarity of its mechanical properties to natural sand. Therefore, a similarity evaluation method based on constitutive model simulation is proposed. First, due to the high friction angle characteristic of fused quartz in transparent soil model tests, multiple oedometer compression and shear box tests were conducted on various gradations of fused quartz. Subsequently, a hypoplastic sand model, which is abundant in natural sand data, stable, and has a straightforward calibration process, was then selected for parameter calibration of fused quartz. Finally, the substitutability of fused quartz for natural sand was evaluated by comparing constitutive parameters and shear box simulation, considering factors such as initial void ratio and confining pressure. The results indicate that the hypoplastic sand model accurately captures the shear behavior of fused quartz. Particles with grain sizes ranging from 0.5 to 2 mm weaken the strength of well-graded fused quartz. The findings also suggest that well-graded fused quartz maintains consistent shear behavior with various natural sands. By contrast, the applicability of single-sized fused quartz is limited.

The foundation soil is often over-consolidated due to the change of soil consolidation history in practical engineering. The effect of over-consolidation ratio (OCR) on the mechanical properties and microstructure of silt has not been sufficiently studied especially on the Yellow River alluvial silt. A series of triaxial undrained shear tests and corresponding SEM tests of the Yellow River alluvial silt were then carried out under different confining pressures and OCRs. The stress and strain curves of the silt show strain-hardening characteristics. The hardening characteristics become more significant, and the peak stress increases significantly as the confining pressure and OCR increase. The silt specimens show phase transformation behavior under a normal consolidation state, which is characterized by stages of initial contraction, temporary phase transformation, and later dilation. The silt tends to be more dilative for over-consolidated specimens and the dilation behavior was more obvious with higher OCRs. The deviatoric stress of the silt can be normalized by the consolidation pressure. The normalized undrained shear strength of the silt generally increased with OCR. The cohesion and internal friction angle of the silt increase with OCR increasing which behaved more like the typical clays as it has more silt content and clay content. The apparent porosity decreases and the average shape coefficient increases with the increase of confining pressure and OCR which shows the silt is denser and the grain shape is closer to circular under higher confining pressure and OCR. The relationship between macroscopic strength characteristics and the microscopic apparent porosity is also discussed. It shows that the macroscopic peak strength gradually decreases with the increase of the microscopic apparent porosity. Such behavior is mainly caused by the internal pore volume reduction and the rise in the contact area between soil particles.

In this paper, an extensive series of direct shear box tests (99 tests) were conducted to explore and compare the effects of raw and treated natural fibers, specifically Doum fibers on the mechanical behavior of three categories of sandy soils with distinct mean particle sizes (D50 = 0.63, 1, and 2 mm). Specimens from every soil category, containing 0 to 0.8% raw Doum fibers and 0 to 1% treated Doum fibers in incremental step of 0.2%, were reconstituted at an initial relative density of (Dr = 87 +/- 3%) and subjected to three different initial normal stresses (100, 200, and 400 kPa). The obtained results indicate that incorporating raw or treated Doum fibers improve the mechanical and rheological properties (internal friction angle, ductility, and maximum dilatancy angle) of the tested mixtures up to specific thresholds Doum fiber content (FD = 0.6% and FTD = 0.8% for raw and treated Doum fibers respectively). Beyond these limiting values, the mechanical and rheological properties decreased with further increases in Doum fiber content. Additionally, specimens reinforced with treated Doum fibers exhibit higher shear strength than that of the raw Doum fibers for all tested parameters. Based on the experimental results, it has been found to suggest a reliable correlation between Particle Size Distribution (PSD) characteristics and mechanical properties for all reconstituted specimens. The recorded soil trend is especially pronounced for the mean grain size (D50) ranging between 1 and 2 mm, where a notable increase in shear resistance is noticed. The analysis of the obtained outcome suggests the introduction of new enhancement factors (EF tau peak and EF phi degrees) as useful parameters for predicting the mechanical behavior of sand-fibers mixtures. Furthermore, new relationships have been developed to forecast changes in mechanical properties (peak shear strength, internal friction angle, and maximum dilatancy angle) of the tested mixtures under the impact of the selected parameters (FD/TD, D50, and sigma n).

The number of studies concerning the shear strength of resedimented alluvial soils is extremely limited compared to the studies conducted on fine-grained marine sediments, since alluvial soils are generally tested in remolded or reconstituted state especially in the studies investigating their liquefaction potential. In this study, estimation models were developed to predict cohesion (c) and internal friction angle (phi) parameters of a fine-grained alluvial soil using resedimented samples. A total of 60 undisturbed soil samples were obtained from Bafra district of Samsun province (Turkiye) by core drilling. A cone penetration test with pore water pressure measurement (CPTu) was also carried out alongside each borehole to determine the over-consolidation ratios of the samples. Physical-index property determinations and triaxial tests were conducted on the undisturbed samples. 20 sample sets were created with known physical, index, and strength characteristics. The samples are classified as CH, CL, MH, and ML according to the Unified Soil Classification System, with liquid and plastic limits ranging from 31.6-75% and 19.3 to 33.6% respectively. The c and phi values of the samples varied from 4.1 to 46.1 kPa and 26 to 35 degrees respectively. The samples were then resedimented in the laboratory under conditions reflecting their original in-situ properties, and triaxial tests were repeated. The c and phi values of the resedimented samples ranged from 5.3 to 24.5 kPa and 28 to 32 degrees respectively. The results indicate that the c values of the resedimented samples are generally lower than those of the undisturbed samples, whereas upper and lower bounds for phi values are similar. Multivariate regression analyses (MVR) were utilized to develop estimation models for predicting c and phi using strength and physical properties of 20 soil samples as independent variables. Three estimation models with R-2 values varying between 0.723 and 0.797 were proposed for c and phi which are statistically significant for p <= 0.05. Using artificial neural networks (ANN), the estimation models developed by MVR were replicated to validate the models. ANN yielded very similar results to the MVR, where the R-2 values for the correlations between c and phi values predicted by both methods varied from 0.852 to 0.955. The results indicate that c and phi values of undisturbed samples can be estimated with acceptable accuracy by determining basic physical and index properties of the disturbed samples and shear strength parameters of the resedimented samples. This approach, which enables the reuse of disturbed soil samples, can be used when undisturbed soil samples cannot be obtained from the field due to economic, logistical, or other reasons. Further research on the shear strength parameters of resedimented alluvial soils is needed to validate the estimation models developed in this study and enhance their applicability to a wider range of alluvial soils.

This study investigates the shear parameters of sand modified with varying percentages of Portland cement and polyvinyl alcohol (PVA) fibers. Seventy-two static strain-controlled consolidated-drained (CD) triaxial compression tests were conducted on saturated samples. The study evaluated the effects of various factors, including relative density (50% and 80%), cement content (0%, 2%, and 4%), fiber content (0%, 0.5%, and 1%), and confining pressures (50, 100, 300, and 500 kPa), on the peak and residual shear strength parameters of the samples. The findings revealed that increasing the cement content enhances the peak internal friction angle and peak cohesion, while cementation has minimal impact on residual cohesion and residual internal friction angle. Fiber reinforcement improved peak cohesion, peak internal friction angle, residual cohesion, and residual internal friction angle of the sand. The rate of improvement in peak internal friction angle due to fiber addition decreased with higher cement content and dry density, whereas the increase in peak cohesion was more pronounced at higher cement percentages. Furthermore, the influence of cementation on shear strength parameters was more significant in denser samples. These results provide valuable insights for improving the design methodologies of reinforced soil structures such as retaining walls and foundations.

This study used Persian gum (PG) as a sustainable anionic hydrocolloid to alternative traditional stabilizers to stabilize this soil. For this purpose, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), and direct shear tests were performed after freeze-thaw cycles. The results show that biopolymers can improve UCS by creating stronger bonds between soil particles and effectively reducing the adverse effects of freeze-thaw cycles compared to unstabilized clayey soil. Also, the accumulative mass loss by adding 2% of Persian gum to unstabilized clayey soil decreased by about 70% due to the adhesive property and interaction of Persian gum hydrogel with soil grains. In addition, the moisture loss is reduced with the addition of biopolymer compared to the unstabilized sample. The UPV of the samples under the freezing phase is higher than in the thawing phase. The internal friction angle and cohesion of unstabilized and stabilized clayey soil with 2% Persian gum increased and decreased under freeze-thaw cycles. Overall, the findings show that anionic hydrocolloids such as Persian gum can effectively improve the performance and durability of CH clayey soil under severe freeze-thaw conditions.

The cone penetration tests have been employed extensively in both onshore and offshore site investigations to obtain the strength properties of soils. Interpretation of effective internal friction angle gyp' becomes complicated for cones in silty clays or clayey silts, since the soil around the advancing cone may be under partially drained conditions. Although there exist several robust methods to estimate gyp ' , the pore pressure at the cone shoulder has to be measured to represent the drainage conditions. Many cone penetrometers in practice are not equipped with a pore pressure transducer. Even for a piezocone, the pore pressure recorded in-situ may be unreliable due to the poorly saturated or clogged filter. These limitations prohibit the application of existing methods. Large deformation finite element analyses were carried out within the formula of effective stress to reproduce the cone penetrations under various drainage conditions. The numerical approach was validated against the existing model tests in centrifuge and chamber, with wide ranges of penetration rates and soil types. A backbone curve is proposed to estimate the normalized cone resistance varying with the normalized penetration rate. Based on the backbone curve, a procedure is developed to predict gyp' of cohesive soils under undrained or partially drained conditions, replacing the pore pressure with the normalized penetration rate. The procedure can be used for soils with an overconsolidation ratio no larger than 5.

Residual soil widely distributed in Fujian region has the characteristics of strong structure and easy softening in contact with water, which limits the possibility of its beneficial utilization. This study investigates the impact of humid and hot environment on the strength characteristics of residual soil, and how changes in soil microstructure are correlated with strength attenuation. Residual soil with particle size distribution from gravel to clay was subjected to repeated hygroscopic cycle tests. Subsequently, unsaturated triaxial consolidation drainage shear (CD) and nuclear magnetic resonance (NMR) tests were carried out on the samples undergoing 0-7 hygroscopic cycles, and the damage mechanism of the soil was analyzed from macroscopic to microscopic scales. Results showed that the soil shear characteristics were influenced by the number of hygroscopic cycles and had a correlation with stress level (confining pressure and target suction), the greater the cumulative irreversible deformation and the more pronounced shear dilation characteristics of the soil had after more hygroscopic cycles and higher stress levels. The shear strength index of unsaturated soil after repeated hygroscopic paths presented a decreasing trend, but the attenuation of internal friction angle and suction friction angle was limited, and the average values were 21.3 degrees and 14.7 degrees, respectively. The T 2 spectral distribution curve of soil was a trimodal pattern, and the content of small holes consistently decreasing as the cycling process progressed, while the percentage of macropores increased significantly. In view of the continuous dissolution of soluble minerals and cementing materials and the repeated release of suction in the soil, the internal particles of the soil were gradually loosened. Accompanied by the continuous expansion and penetration of intergranular pores, connecting cracks were ultimately formed. The above fatigue damage to the soil pore structure led to the attenuation of its macro-mechanical properties. Throughout the test, the saturated shear strength of the soil continued to decrease due to the interaggregate connection was always broken, while the destruction of the intergranular connection in the aggregate was relatively slow, and the internal friction angle in the soil implied a slow decrease and even stabilized at a later stage. The research results could provide a useful reference for a deeper understanding of the environmental damage effects on the soil macroscopic mechanical properties.

Shear strength is the key index to determine the stability of a soil slope, and cementation between iron oxide and clay minerals is one of the internal factors affecting soil shear strength; however, the effects of the form of iron oxide on the shear strength of granite-weathered red soil are still unclear. Kaolinite, which is the main clay mineral of granite red soil, was selected as the research object, and the effects of three different forms of iron oxide (hematite: HT, goethite: GT, and amorphous iron oxide: AIO) on the soil microstructure, microscopic quantitative parameters, cohesion, internal friction angle, and shear strength were analyzed by scanning electron microscopy, X-ray diffraction, and the shear strength test. The results revealed that the iron oxide promoted the cementation of soil particles, and the cementation characteristics differed with the different forms of iron oxide. Hematite mainly showed flocculent cementation, poor cementation, and simple soil microstructures. Goethite mainly exhibited acicular cementation and the best cementation effect. The degree of aggregation of the soil particles was increased by the coatings, thus forming larger aggregate particles. The cementation effect of amorphous iron oxide was between those of hematite and goethite but included both the flocculation cementation of hematite and acicular cementation of goethite. Amorphous iron oxide and goethite effectively increased the contact area and friction degree between soil particles, while hematite had the opposite effect. The addition of three kinds of ferric oxide reduced the fractal dimension of soil, increased the apparent porosity, and promoted the irregularity of particles to a certain extent, among which hematite had the most significant growth on the long and short axes of the particles. At a content of 10 g kg-1, the addition of AIO and GT increased the soil cohesion and internal friction angle, and therefore increased the soil shear strength, and it was mainly determined by the soil microstructure: the contact area, apparent porosity, and particle short axis. These results indicated that GT and AIO are the main cementing materials affecting soil mechanical properties, and the transformation of iron oxide should be paid attention to when predicting soil slope stability.

Shape of soil grains has a major role in the characterization of its behavior. This important feature has an appreciable impact on all mechanical properties of granular soils. In order to accurately capture such an important contribution, the grain morphological features should be carefully analyzed and described in a systematic manner. The present study aims to review the literature concerning the qualitative and quantitative characterizations of the soil particle shape and its substantial impact on the mechanical behavior of granular soils. Qualitative characterization of the particle shape involves descriptive assessments of the level of angularity or roundness, such as the terms rounded, sub-rounded, sub-angular, and angular, while quantitative characterization refers to measurable parameters, like aspect ratio, regularity, sphericity, and circularity, which provide numerical data on the shape of soil grains. This study specifically examines the influence of particle shape on the compression characteristics, monotonic shear response, shear strength properties, and critical state behavior of granular soils, as well as the mechanical behavior of soil-solid interfaces and stabilized earthen materials. The potential challenges associated with the investigation of the effect of particle morphology on the mechanical characteristics of granular soils are also summarized, and a roadmap is outlined for future research. The findings of this study show that as the soil grains become more angular, the at-rest coefficient of earth pressure (K0) and the maximum dilation angle ( psi max ) decrease whereas the peak friction angle (phi p), critical state friction angle (phi cs), intercept of critical state line (e Gamma), and slope of critical state line (lambda) all increase. With this broad perspective and in an attempt to put such crucial effects into practice, comprehensive sets of experimental data records are compiled from the previous studies in the literature based upon which new practical machine learning (ML) models are developed for the prediction of various mechanical properties of granular soils by accounting for the substantial contribution of particle shape. The study provides practicing geotechnical engineers with a profound insight into the macro- and micro-scale impacts of grain morphology on the mechanical characteristics of granular soils while offering new horizons in the incorporation of particle shape into predictive models for such properties. With these practical models, engineers can readily estimate the compression and strength-related parameters of granular soils by simply examining their particle shape, grain size distribution, density, and overburden pressure.