Coupling effects of interfacial friction and layer thickness on soil desiccation cracking behavior

Piles are critical structural elements that often face lateral loads from various sources, including moving vehicles on bridges, wind, waves, slope movement, and seismic activities. These lateral loads can cause substantial bending moments and lateral deflections in piles, which can compromise the structural integrity of the foundation. The point of fixity is a widely used concept in the design of laterally loaded piles, providing the necessary rigidity to withstand these forces and minimize deflections. While several analytical methods have been developed to determine the point of fixity in single-layered soils, their effectiveness and applicability in multilayered soils remain less certain. This study investigates the validity of two commonly used analytical methods, Broms method and Kocsis method for determining the point of fixity in multilayered soils. The depth of fixity was estimated using average soil properties and compared against results obtained from more advanced approaches, including finite element modelling and p-y curve analysis, which consider distinct properties of individual soil layers. A comprehensive parametric study was also conducted to examine the influence of various factors, such as soil type, soil layer thickness, pile diameter, magnitude of lateral and axial loads, and pile embedment length, on the point of fixity. The comparison revealed significant differences between the analytical methods, particularly in the context of predominantly cohesive soils. The Broms and Kocsis methods estimated the depth of fixity to be between 1.0 and 2.0 times the pile diameter below the ground surface, while the p-y curve and FEA methods yielded slightly more conservative values, ranging from 1.0 to 1.5 times the pile diameter. In predominantly cohesionless soils, the estimated fixity depths were more consistent across all methods, varying between 1.0 and 1.5 times the pile diameter below the ground surface. These findings highlight potential limitations in the applicability of traditional analytical methods to multilayered soils and underscore the importance of refining these approaches for more accurate and reliable design. The parametric study further revealed that for long (flexible) piles, the depth of fixity is generally not significantly affected by factors such as surrounding soil type, layer thickness, axial load, and pile length. However, pile diameter and lateral load were found to have a substantial impact on the depth of fixity, with the effects varying depending on the analytical method employed and the soil's cohesive or cohesionless nature. Interestingly, the study also found that, even in single-layered soils, the Broms and Kocsis methods could yield results that significantly deviate from those obtained via p-y curve analysis. This discrepancy underscores the necessity for further detailed studies, including experimental work with instrumented pile tests, to enhance the accuracy and reliability of these methods. Overall, the study suggests that the point of fixity in predominantly cohesive soils ranges from 0.5 to 2.5 times the pile diameter below the ground surface, whereas in predominantly cohesionless soils, it ranges from 0.5 to 2.0 times the pile diameter.

A framework for evaluating deformation-based basal heave stability is proposed in order to distinguish between the different responses under freely developed and prohibited basal heave failures. In the case of freely developed basal heave failure, the maximum deformation values occur at the center point of pit bottom, whereas this is not the case for the prohibited basal heave failure. The critical thickness of soft soil layer between the end of supporting structures and the top of hard stratum is about 0.3B (B = excavation width), beyond which the freely developed basal heave failure arises. In situations otherwise, the prohibited basal heave failure occurs. The failure probability of basal heave failure at the center point increases significantly as B ranges within a limited value; then, it begins to decrease or to vary slightly at a certain value under a given thickness of soft soil layer. If the thickness of soft soil layer is so sufficiently large that freely developed basal heave failure occurs for any of B, the failure probability of basal heave failure at the center point increases as B increases. The selection of the optimum monitoring points for basal heave stability is recommended to account for the weights in the contribution to the basal heave deformations of the influencing factors such as excavation width and thickness of soft soil layer. The proposed framework is applicable to basal heave reliability analysis for braced excavations where deformation values are focused.

A temperature-dependent model for tensile strength characteristic curve of unsaturated soils

In this paper, a dual-frequency permafrost active layer thickness (ALT) retrieval algorithm is presented wherein P-band AirMOSS and L-band UAVSAR data are used to retrieve the layered soil dielectric constants and layer thicknesses. Using the known radar calibration accuracy, radar sensing depth is defined to help understand the limit of radar backscatter sensitivity to subsurface soil conditions and used as a consistency check when determining ALT. Retrieved maps of soil dielectric constants and layer thicknesses show high spatial correlation with the vegetation type and organic layer thickness. It is shown that the retrieval accuracy for ALT is between 5 cm and 14 cm when the ALT is smaller than the sensing depth.

Monitoring of drying-induced volume shrinkage and desiccation cracking in clayey soils is of great importance in geological and geotechnical engineering. Compared with conventional strain monitoring methods providing discrete measurements, the Brilliouin optical time domain reflectometer (BOTDR) technique enables continuous measurement of the distributed strain generated along optical fibers. In this study, a physical model test is conducted to investigate the feasibility of monitoring drying-induced soil shrinkage and desiccation cracking using BOTDR. Three optical fibers with different surface protections (thermoplastic polyester elastomer (TPEE) jacket, nylon jacket, and acrylate coating) are tested and compared. Experimental results validate that BOTDR is applicable for the direct strain monitoring of desiccation cracking soils. Monitored strain values are strongly influenced by water content, soil cracking, and fiber types. The strain measured by the optical fiber reaches only several micro strains when the soil is over-saturated, gradually increases with the decreasing water content and the increasing soil-fiber interfacial shear stresses, and drops rapidly after the occurrence of decoupling between fiber and soil resulting from the mature development of desiccation cracks. The optical fiber with acrylate coating is not suitable because of its fragility and the poor interfacial coupling with the soil. Optical fibers covered with TPEE jacket or nylon jacket are both applicable for soil strain monitoring, with the former one more sensitive to water content variations. The study is the first attempt to apply the BOTDR technique for the direct and continuous monitoring of drying-induced soil shrinkage and desiccation cracking process. It is expected bring new insights into the fundamental understanding of volumetric shrinkage and desiccation cracking in clayey soils.

This article focuses towards the newer manufacturing technique 3D Printing (3DP). The objective of this work is the mechanical characterization (flexurel properties) of materials produced by 3D printing based on fused filament fabrication with fused deposition modeling (FDM). The materials chosen are a polylactic acid (PLA). This paper described the effect of different layer thickness of PLA by 3D printing on flexural properties.Additive manufacturing, also known as 3D printing, is a common material extrusion process using (bio) polymers PLA. The study begins from manufacture the solid 3D model based on the ASTM standards for flexural properties test of the material using Three-point bending method. Three-point bending test was conducted with Tensilon Universal Testing Machine – AND RTF-2410 with a 100kN load cell, specimen shape and size according to standard size ASTM D 790. The result shown that the layer thickness had an effect on flexural strengths of PLA samples. The maximum flexural strengths from Lt = 0.4 to 0.5mm were significantly increase. Moreover, it is worth nothing that ductility decreased as layer thickness increased. According to test result that the maximum flexural strength occurred at 0.5 mm layer thickness with 59.6 MPa and the minimum flexural strength occurred at 0.1 mm layer thickness with 43.6 MPa. The higher layer thickness tended to promote higher strength. The thicker layer is the stronger layer bond in holding the load bending. In this study the thicker layer have tendend to shown a 90-degree delamination fracture and the thinner layer have tendend to shown a 45-degree delamination fracture according to the direction of printing is ± 45°.

Black soil has good properties and high fertility. Understanding the spatial distribution of black soil layer thickness is of great significance in promoting regional agricultural development, ecological environmental protection, and soil erosion control. However, traditional soil investigation methods often fail to provide detailed soil thickness information. This study focuses on a small watershed in Northeast China’s black soil region. By integrating topographical parameters and vegetation-climate indicators, random forest and kriging methods (classical bayesian, ordinary, and simple) were used to estimate the spatial distribution of thickness of black soil layer. An integrated evaluation framework was developed by combining RUSLE-derived erosion estimates with black soil layer thickness, systematically incorporating both external erosive forces and inherent soil erosion resistance attributes. The results show that the random forest model outperformed the kriging models, with smaller RMSE (34.05 cm) and larger R² (0.57), especially when handling nonlinear, high-dimensional data. The predicted thickness of the black soil layer ranged from 16.2 cm to 107 cm, with a mean of 48.31 cm, closely matching the measured value of 48 cm. Elevation (EL) was found to be the most significant factor affecting the thickness of black soil layer. Soil erosion risk assessment revealed that areas with no risk and low risk accounted for 21.91% and 62.21%, respectively, while medium and high-risk areas made up 15.87% and 0.01%. No-risk areas were soil accumulation zones, while low-risk areas were mainly sloped farmland, where measures like terracing, adjusting crop ridge directions, and planting pedunculated vegetation were recommended. Medium- and high-risk areas should be addressed by returning farmland to forests and implementing engineering practices. This study offers a reference for thickness of black soil layer estimation and provides valuable insights for soil erosion risk management.

In vast areas of rich frozen soil, the intense heat exchange between the hot oil pipeline and surrounding soil results in the continuous melting of permafrost under the pipeline and the continuous sinking of the pipeline. Moreover, the settlement rate and depth of the pipeline are also different due to the influence of ice content and the thickness of rich frozen soil layer. Therefore, in this paper, based on the field measured data, by adopting the method of numerical simulation, the temperature rise process of the soil around the pipeline under the condition of different subsidence rate and different thickness of rich frozen soil layer is studied. The results show that with the increase of the thickness of the frozen soil layer, the degradation depth of the upper limit of the artificial frozen soil in the lower part of the pipeline increases gradually. Under the same thickness of the frozen soil layer, the influence of the settlement rate of the pipeline on the upper limit of the artificial frozen soil in the lower part of the pipeline mainly concentrates on the initial operation stage of the pipeline; with the increase of the thickness of rich frozen soil layer, the upper limit difference of artificial frozen soil under different settlement rates of pipelines at the same time increases gradually. Of different sedimentation rate and the rich soil layer under the condition of ice -6 m depth of geothermal heating process monitoring, the geothermal heating process can be divided into three stages: melting stage (I), rapid heating stage (II), slow heating stage(III). With the increase of the settling depth, the duration of the phase I and II is significantly reduced, the heating rate is significantly promoted, the duration of phase III is increased significantly and the heating rate is gradually reduced.

Slope instability due to rainfall infiltration constitutes major natural disasters in many tropical countries covered by residual soil. In these types of soils, groundwater table usually exist at considerable depth with significance thickness of unsaturated soil above water table. Negative pore water pressure or matric suction exist in the unsaturated soils and contributes additional shear strength to the soil. However, the matric suction reduces due to rainfall infiltration and invariably reduces the additional shear strength provided by the matric suction. The principle of capillary barrier is amongst the methods employed to reduce infiltration of rainfall into unsaturated soil and the infiltrating water into the system is stored in the upper (fine-grained) soil layer. Therefore, this paper highlights the effect of different thickness of fine-grained soil layer on performance of a modified capillary barrier system using numerical modelling approach. The capillary barrier was constructed from residual soils and subjected to three different rainfall intensities of 1 hour, 24 hour and 7 day. The thickness of fine-grained soil layer was varied from 0.1 m to 0.3 m while the coarse-grained soil layer and the unsaturated drainage layer were maintained as 0.3 m and 0.1 m respectively. The results shows that 0.3 m thick fine-grained soil layer is more effective in preventing breakthrough occurrence in case of capillary barrier without unsaturated drainage layer. However, when the capillary barrier was modified with gravel as unsaturated drainage layer, 0.1 m thick fine-grained soil layer was sufficient to prevent breakthrough occurrence for 1 hour and 24 hour rainfall intensities. In the case of 7 day rainfall intensity, breakthrough occurred after 4th day of rainfall infiltration in all the varied thicknesses of the fine-grained soil layer. Therefore modified capillary barrier with unsaturated drainage layer enhance the performance of capillary barrier system by transporting the infiltrating water before breakthrough occurrence. Similarly, it helps in reducing the thickness of fine-grained soil layer.

The present paper develops a constitutive model for the elastic modulus and energy loss of CNT-based polymeric composites. In this study, a close-packed lattice consisting of seven nanotubes in hexagonal arrangement is used to model single-walled carbon nanotubes often found in rope-like bundles in polymers. The composite is described using a multi-phase system composed of a resin and bonded and debonded nanotube ropes. The concept of stick-slip motion caused by frictional contacts is proposed to describe the load transfer behavior among the nanotubes and between the nanotube ropes and resin. A micromechanical model is developed to describe inter-tube and tube/resin frictional motions. Modulus change and energy dissipation due to the stick-slip interfacial load transfer are determined. The developed method is used to analyze composites with aligned nanotube ropes. The analytical study shows that mechanical properties can be significantly affected by adding small fractions of carbon nanotubes in polymers. The elastic modulus and loss factor are both strain-dependent. Also, to show the inter-tube sliding effects due to nanotube aggregation, results obtained for the composites filled with well-dispersed nanotubes and nanotube ropes are compared.

The effect of interfacial friction on adhesion was studied by using a model system, in which a thin strip of silicone elastomer was peeled from a PDMS (poly(dimethylsiloxane)) treated glass slide. The fluorescent particle tracking method revealed that the elastomer stretches and slides on glass well before the crack faces open up. Interfacial energy dissipation due to friction, which is the product of the slip displacement and the interfacial shear stress, is found to be a significant contributor to the total fracture energy at various peel configurations. These results suggest that interfacial sliding may provide a mechanism for energy dissipation in the fracture of asymmetric interfaces.

The semi-circular bending (SCB) using a split Hopkinson pressure bar system appears to be a promising method for measuring dynamic flexural strength of rock materials due to its distinct advantages. The quasi-static analysis is adopted for determining the dynamic flexural strength, of which several vital prerequisites have not been thoroughly examined yet. In this study, dynamic flexure tests regarding dynamic force equilibrium, interfacial friction effects, and energy partitioning are numerically investigated based on discrete element method (DEM) modeling. Results show that by virtue of the ramped wave loading, the force equilibrium of the specimen can be effectively achieved and the rupture is precisely measured to synchronize with the peak force, both of which guarantee the quasi-static data reduction method employed to determine the dynamic flexural strength; while the opposite occurs for the test under a rectangular wave loading. Furthermore, dynamic flexural strengths obtained by the numerical SCB tests exhibit approximately linear rate dependence that is identical with the experimental results. The interfacial friction, which is found to significantly influence the measuring results for rather high loading rates, contributes to enhancing the rate dependence of flexural strength and must be taken into account in dynamic flexure tests. In addition, energy partitioning is first numerically performed in the dynamic SCB tests and the nominal fracture energy manifests an S type of rate dependence with loading rates.

Red clay is susceptible to cracking in desiccating environments, with resulting crisscrossing cracks that compromise the soil structure and increase the likelihood of geological hazards. To investigate the dynamic mechanism of the initiation and propagation of soil desiccation cracks under natural hygrothermal conditions, a desiccation test was conducted on a red clay slurry using three-dimensional digital image correlation (3D DIC) technology. The evolution behaviour of desiccation cracks was analysed, and the dynamic relationships between moisture content, displacement field, strain field, and soil desiccation cracking were explored. The test results showed that the Atterberg limits of red clay are correlated with desiccation cracking. Cracks tend to initiate in areas where tensile strain is concentrated or significant displacement differences exist. Following crack initiation, the surrounding strain and displacement fields redistribute, influencing the propagation direction, development rate, and morphology of subsequent cracks nearby. Additionally, the relative displacement and strain at the edges of cracks are related to the crack propagation direction. Earlier crack initiation usually corresponds to a larger relative displacement and strain at the crack edges, while the displacement and strain at the soil clod centre are typically smaller than those at the crack edges. DIC technology can quickly and accurately obtain dynamic information about displacement and strain fields, providing feasible technical support for analysing the dynamic mechanism behind soil desiccation cracking. It has potential value in engineering hazard prevention and sustainable development.

This paper considers a piezoelectric ceramic layer with a surface electrode. It focuses on the effect of the layer thickness on the electrode tip fields. A closed-form solution for the electromechanical fields at the electrode tip is obtained and is expressed in terms of the applied electric field intensity factor, which can be obtained exactly for infinite layer thickness and numerically for finite layer thickness. The stress, electric displacement, and electric field are plotted to show the effect of layer thickness. It is found that the stresses and field intensities at the electrode tip can be reduced considerably by decreasing the thickness of the piezoelectric layer, confirming the previous finding. The paper also gives a solution for two identical and collinear surface electrodes. The relative distance between the electrodes is observed to have significant influence on the electromechanical field in the piezoelectric layer.

The effects of desiccation cracking in clay soils on geotechnical constructions are substantial. This study investigates the viability of utilizing Enzyme-induced calcite precipitation (EICP), a bio inspired approach, as a potential solution for addressing desiccation cracking in fine-grain soils. For the EICP technique, crude soybean extract is employed for the purpose of urea hydrolysis. Multiple fluid samples, including a control sample, a cementation solution containing 1 M urea, 0.675 M CaCl2, and 4 g/L milk, along with various concentrations of enzyme solutions (3–80 g/L), were tested for the study. To evaluate the surface cracking patterns, the method involved constant monitoring and photo recording using a high-resolution camera aided by image processing software. The results showed that fine-grain soils improved from increased calcite precipitation and decreased desiccation cracking intensity when the EICP method was used. Cementation and enzyme solution with low concentrations (3 g/L and 10 g/L) had similar effects on crack remediation, suggesting a modest influence. In contrast to the sample treated with water, the crack network remained unaltered in this case. CaCO3 precipitation within the void area kept the crack network in place even as the void thickness decreased at increasing enzyme concentrations (30 g/L, 50 g/L, and 80 g/L). Wetting and drying cycles were found to decrease the crack ratio, crack width, and crack length in the EICP-treated sample, particularly under higher concentrations of urease enzyme. Lower enzyme concentrations of 3 g/L and 10 g/L have minimal impact on crack remediation but effectively inhibit new crack formation. Furthermore, higher enzyme concentrations result in calcium carbonate precipitates, forming a soil crust and increasing surface roughness. The study aims to enhance understanding of the EICP methodology and to provide novel perspectives on potential uses for soil enhancement.