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.

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.

Spherical glass beads weaken the influences of particle morphology, surface properties, and microscopic fabric on shear strength, which is significant for revealing the relationship between macroscopic particle friction mechanisms and the particle size distribution of sand. This paper explores the shear mechanical properties of glass beads with different particle size ratios under different confining pressures. It obtains the particle size ratio and fractal dimension D through an optimal mechanical response. Simultaneously, we explore the range of the fractal dimension D under well-graded conditions. The test results show that the strain-softening degree of R-s is more obvious under a highly effective confining pressure, and the strain-softening degree of R-s can reach 0.669 when the average particle size (d) over bar is 0.5 mm. The changes in the normalized modulus ratio E-u/E-u50 indicate that the particle ratio and arrangement are the fundamental reasons for the different macroscopic shear behaviors of particles. The range of the peak effective internal friction angle phi is 23 degrees similar to 35 degrees, and it first increases and then decreases with the increase in the effective confining pressure. As the average particle size increases, the peak stress ratio M-FL and the peak effective internal friction angle phi first increase and then decrease, and both can be expressed using the Gaussian function. The range of the fractal dimension D for well-graded particles is 1.873 to 2.612, and the corresponding average particle size (d) over bar ranges from 0.433 to 0.598. Under the optimal mechanical properties of glass beads, the particle size ratio of 0.25 mm to 0.75 mm is 23:27, and the fractal dimension D is 2.368. The study results provide a reference for exploring friction mechanics mechanisms and the optimal particle size distributions of isotropic sand.

The changes in the mechanical properties of collapsing walls under the influence of natural factors in the hilly area of southern China need to be determined. We systematically studied the influence of the interaction of dry density rho (1.0, 1.1, 1.2, 1.3, 1.4 g/cm(3)) and moisture content omega (0.05, 0.1, 0.15, 0.2, 0.25 g/g) on the stability of four soil layers in a collapsing wall. The soil cohesion decreased with increasing soil depth. The cohesion force initially increased and then decreased with increasing omega and increased with increasing rho; the internal friction angle was mainly affected by omega and decreased with increasing omega. The cohesion could be used to effectively characterize the stability of the collapsing wall. The shear strength index was modeled based on interaction between the dry density and moisture content (R-2 > 0.95). The optimal combination of moisture content and dry density was obtained, and the collapsing wall was in the most stable state at a moisture content of 0.12-0.19 g/g and a dry density of 1.40 g/cm(3). Based on the analysis of the critical height and safety factor (FS), the FS values of the sandy layer (C) was 0.53 and 0.57 for omega values of 0.25 g/g and 0.05 g/g, respectively. In the alternating process of soil wetting and drying, the basic properties of the soil changed; caused traceback erosion, and thereby affected the stability of the collapsing wall. Our study provides a theoretical basis for the investigation of the factors influencing the stability of collapsing walls. (c) 2023 International Research and Training Center on Erosion and Sedimentation, China Water and Power Press, and China Institute of Water Resources and Hydropower Research. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY

Soil organic matter (SOM) usually occurs in mineral-associated or particulate forms, with significant variations in the physical and chemical properties among different forms of organic matter. In soil mechanics, there has been focusing on the influence of SOM content on the macroscopic engineering properties of soil. To date, limited knowledge exists regarding the influence of SOM occurrence form on soil engineering properties. In this study, soil samples with different SOM contents w(u) were manually prepared, and the contents of various occurrence forms of SOM were measured using Fu's method. Direct shear tests were conducted under drained and undrained conditions to elucidate the variation in ultimate shear strength and shear strength parameters with SOM content w(u), while also examining the impact of SOM occurrence form on the shear strength of organic soil. The experimental outcomes are as follows. The internal friction angle undergoes a notable decrease with increasing w(u) under undrained conditions, which can be categorized into three distinct stages: a significant decline (Stage I), a transition phase (Stage II), and a stable change (Stage III). w(u) corresponding to the endpoint of stage I approximates the threshold w(u,2), suggesting that the pronounced reduction in internal friction angle with w(u) augmentation primarily occurs in organic soils dominated by mineral-associated SOM. Stage III emerges approximately after w(u) > 25%. Under drainage conditions, the internal friction angle diminishes with w(u) augmentation, yet its variation is independent of the occurrence form of SOM. No discernible correlation exists between cohesion of organic soil and occurrence form of SOM under drained and undrained conditions. Mechanism analysis reveals that mineral-associated SOM facilitates lubrication and diminishes friction between soil particles under undrained conditions. When the content of particulate form SOM reaches a critical threshold, the mechanical properties of the soil transforms from a frictional material to a colloidal material. Nevertheless, under drainage conditions, SOM's susceptibility to compression results in the soil skeleton ultimately comprising primarily mineral soil particles, regardless of SOM content or occurrence form.

The mechanical properties of agricultural materials influence not only the loads occurring inside agricultural silos, but also the design of several types of post-harvest machinery. The loads generated by these materials inside silos can be predicted with silo calculation methodologies from their mechanical properties. It has been known for many years that these properties are highly dependent on the moisture content of the material. However, to date, there are not many studies focused on its determination. The goal of this research is the determination of the internal friction angle, apparent cohesion, angle of dilatancy and apparent specific weight of maize when different moisture contents are applied. The equipment used for this study consisted mainly of direct shear and oedometer assay apparatus. The maize samples used were moistened using a climatic chamber. Moisture contents applied to maize samples ranged from 9.3% to 17.4%. Results similar to those provided by other authors were obtained for the internal friction angle, apparent cohesion and apparent specific weight. On the other hand, the values obtained for the dilatancy angle of maize as a function of moisture content could not be compared because nothing has been published so far. The values obtained for this parameter overlap with those published for this material under ambient conditions. In addition, for the samples tested, these results did not allow confirming the existence of a direct relationship between the dilatancy angle and the moisture content. Finally, the increase in moisture content led to an increase in apparent specific weight, which differed from that published in the literature. The values provided here can be used for the optimization of storage and handling structures for granular agricultural materials.