This paper proposes a semi-analytical solution for one-dimensional consolidation of viscoelastic unsaturated soil considering a variable permeability coefficient under exponential loading. The governing equations of excess pore air pressure (EPAP) and excess pore water pressure (EPWP) were acquired by introducing the Merchant viscoelastic model. By employing Lee's correspondence principle and the Laplace transform, the solutions for EPAP and EPWP were derived under the boundary conditions of the permeable top surface and impermeable bottom surface. Crump's method was then used to execute the inverse Laplace transform, yielding a semi-analytical solution in the time domain. Through typical examples, the dissipation of EPAP and EPWP and the change of the average degree of consolidation over time under the influence of different elastic moduli, viscoelastic coefficients, and air-to-water permeability ratios were studied. The variation of the permeability coefficient and its influence on consolidation were also analyzed. The findings of this research show that the consolidation rate of viscoelastic unsaturated soil is slower than that of elastic unsaturated soil; however, an acceleration in the consolidation of the soil is observed when changes in the permeability coefficient are considered. These discoveries enhance our comprehension of the consolidation behaviors exhibited by viscoelastic unsaturated soil, thereby enriching the knowledge base on its consolidation traits.

A unified approach for solving the one-dimensional consolidation equation is introduced for the first time in geotechnical engineering. The one-dimensional consolidation partial differential equation is solved through a combined approach employing the complementary functions method (CFM) and Laplace transform. Using the coded program prepared in the FORTRAN, various time-varying loads are applied to different soil types to obtain the response of excess pore water pressure. The comparison demonstrated an excellent agreement, thus proving the effectiveness, applicability, and capability of the proposed approach in solving the governing canonical equations. The study's findings reveal that sand soil (high permeability) exhibits a less pronounced cyclic response under various cyclic loads compared to other soil types, whereas clay soil (low permeability) exhibits significant periodicity in its response. The investigation into the effect of soil properties on one-dimensional consolidation indicates that the dissipation of excess pore water pressure occurs relatively quickly in the case of highly permeable soils and gradually slows down as the soil permeability decreases. Due to the lower permeability of clay soil, the full dissipation of excess pore water pressure takes a much longer time compared to other soil types. Consequently, this process occurs over a more extended period in clay soil.

This study introduces a novel methodology to address consolidation under long-term cyclic loading. The approach simplifies analysis by neglecting cyclic load induced fluctuations and by decomposing the cyclic load into a static load and a vibratory load without net tensile or compressive tendency over time. One-dimensional vibration consolidation tests are proposed to investigate the consolidation behavior of normally consolidated soil under vibratory loading. These tests yield a normal vibration consolidation line, which visually represents the consolidation effect of a given vibratory load on normally consolidated soil under different consolidation pressures. Based on these test results, a mathematical model is developed. This model incorporates a constitutive relationship that accounts for both the decrease in effective stress due to the structural damage caused by the vibratory load and the increase in effective stress due to the compression of the soil skeleton. The governing equation, with void ratio and effective stress as dependent variables, comprehensively describes the state change process of soil elements during vibration consolidation. Numerical solutions are then employed to analyze this process in detail.

In uncoupled consolidation analysis, settlement and pore water pressure are solved independently, whereas in coupled analysis, they are solved simultaneously to ensure continuity (i.e., the volume change in soil due to compression must equal the water volume change caused by dissipation). This study investigates the coupling effects of soil deformation and pore water pressure dissipation in the back analysis of soft soil settlements. It further evaluates the suitability of both coupled and uncoupled constitutive models with different types of monitoring data, providing practical guidance for selecting consolidation models and achieving reliable long-term predictions. The one-dimensional governing equations for soft soil consolidation, incorporating prefabricated vertical drains and creep deformation, are first reviewed. A case study of a trial embankment in Ballina, New South Wales, Australia, is then used to demonstrate the impact of coupling effects and monitoring data on settlement predictions. The results show that considering coupling effects not only improves long-term settlement predictions but also reduces uncertainties in the updated soil parameters, especially when both settlement and pore water pressure data are used.

A few recent studies introduced natural rubber latex (NRL) as a stabilizer for improving the mechanical properties of soil such as ductility, compressive and tensile strengths, durability, etc. However, none of these studies addressed the effect of NRL treatment on swelling and compressibility of soil. The present study investigates the effect of NRL treatment on swelling and compressibility characteristics of three soils of different plasticities by conducting oedometer tests. Untreated and NRL-treated samples of the selected soils were prepared with the same soil dry density. For preparing treated samples, in place of water, NRL was added to soil. The results of one-dimensional swelling-compression tests demonstrated that in low and medium plastic soils, NRL treatment increased the swelling potential marginally, whereas it considerably reduced the swelling in the high plastic soil, which is expansive in nature. NRL did not cause any changes in the swelling pressure of medium plastic soil. At the same time, it brought about a considerable drop in the swelling pressure of high plastic soil. In the consolidation tests, a decrease in compressibility, quantified in terms of compression index, was observed in all soils after NRL treatment. The resilient nature of rubber content caused an increase in the recompression index in all treated samples. A reduction in the coefficient of consolidation was observed in NRL-treated soils. The study concludes that despite the high deformability of rubber, NRL treatment does not negatively affect the swell-compression behaviour of soils. Besides, the treatment effectively controls the swelling and compression of highly compressible soil.

This paper investigates the anisotropic characteristics of Champlain marine clay soil using a combination of laboratory techniques. A modified oedometer cell with a piezoelectric ring actuator technique was used to measure shear wave velocity during consolidation stages. The axisymmetric design of the oedometer allowed for the determination of shear wave velocity in both the vertical and horizontal planes. The preliminary findings reveal that the sensitive marine clay is inherently anisotropic, with lower preconsolidation pressure for horizontally consolidated specimens and faster propagation of shear waves in the plane parallel to the bedding layer. High-precision strain gauges integrated into the consolidation ring were used to evaluate horizontal stress during the one-dimensional consolidation test. The ability to determine mean effective stress enables the normalization of shear wave velocities using this stress, providing more coherent empirical correlations in terms of shear wave velocity. Scanning electron microscopy was used to examine the microstructure of clay specimens, providing qualitative and quantitative insight into the restructuring and reorientation of clay platelets under consolidation stress. The consistency of the results through both micro and macro-scale analyses confirms the reliability of the experimental approach, highlighting its potential for future studies on the anisotropy of Champlain marine clay fabrics.

Layered unsaturated soils exhibit complex mechanical and physical properties. Owing to the roughness between unsaturated soil interfaces and the presence of irregularly distributed micro-pores, this study explores the laminar flow of pore water and counter-cyclonic flow of pore air through these channels at low velocities. In response to the complex consolidation behavior of unsaturated soils influenced by the flow and air contact resistance, an improved model is developed. The model incorporates the flow contact transfer coefficient (R-omega), flow partition coefficient (eta(omega)), air contact transfer coefficient (R-a) and air partition coefficient (eta(a)). Semi-analytical solutions for pore water pressure, pore air pressure and settlement in layered unsaturated soils are derived by employing the Laplace transform and its inverse transform. The rationality of the model is validated through comparative analysis with existing solutions. Analysis of the improved model yields critical insights: the presence of flow and air contact resistance leads to the development of relative pore pressure and air pressure gradients at interfaces, which diminishes the influence of the permeability coefficients of the water phase (k(omega)) and air phase (k(a)) on the consolidation process. Moreover, neglecting the flow and air contact resistance effects may lead to an overestimation of settlement.

Xanthan gum (XG) is an eco-friendly biopolymer with potential applications in soil amendment. However, in acidic soil environments, the pyruvate groups and glycosidic bonds in XG molecules tend to hydrolyze, thereby weakening the efficiency of soil improvement. In this study, the feasibility of utilizing alkaline Class-F fly ash (FA) to assist XG in reinforcing acidic soils was evaluated through proctor compaction, unconfined compression, and one-dimensional consolidation. With the decrease of pore fluid pH values, the beneficial effect of FA on the reinforcing efficiency of XG seemed to grow. As a result, the soil with the strongest acidity (pH = 3) had even higher strength and lower compressibility than the neutral soil that was treated under the same condition. The improvement in both mechanical strength and compressibility of acidic soils might be caused by the crossing-linking of XG molecular strands and the mitigated hydrolysis of XG hydrogels due to the presence of FA. Based on the findings, it is suggested to use FA in combination with XG for treating the acidic soils and use XG alone for treating the neutral soils. The research outcomes will promote the reuse of solid waste Class-F FA in sustainable geotechnical engineering practices, e.g., biopolymer-based soil amendment in acidic soils.

This study shows the influence of the inclusion of abaca fiber (Musa Textilis) on the coefficients of consolidation, expansion, and compression for normally consolidated clayey silt organic soil specimens using reconstituted samples. For this purpose, abaca fiber was added according to the dry mass of the soil, in lengths (5, 10, and 15 mm) and concentrations (0.5, 1.0, and 1.5%) subjected to a curing process with sodium hydroxide (NaOH). The virgin and fiber-added soil samples were reconstituted as slurry, and one-dimensional consolidation tests were performed in accordance with ASTM D2435. The results showed a reduction in void ratio (compared to the soil without fiber) and an increase in the coefficient of consolidation (Cv) as a function of fiber concentration and length, with values corresponding to 1.5% and 15 mm increasing from 75.16 to 144.51 cm2/s. Although no significant values were obtained for the compression and expansion coefficients, it was assumed that the soil maintained its compressibility. The statistical analysis employed hierarchical linear models to assess the significance of the effects of incorporating fibers of varying lengths and percentages on the coefficients, comparing them with the control samples. Concurrently, mixed linear models were utilized to evaluate the influence of the methods for obtaining the Cv, revealing that Taylor's method yielded more conservative values, whereas the Casagrande method produced higher values.

Volcanic eruption at La Palma island (Tajogaite, 2021) has produced tons of volcanic ash as natural sediments spread all around the island covering existing crops, roads, embankments, buildings, etc., by that way producing damage to environment. For the rehabilitation and reconstruction of island, and its application to adjacent areas, it is practical and economical to employ these volcanic ashes as construction material being encountered in abundant volume, and by that way could be considered as a resource material instead as a waste material, reducing necessary volume of landfills for its deposition. This paper defines the investigation of chemical, mineralogical and geotechnical properties of these deposited materials for its possible reuse by that way providing solution for its recovery. These young volcanic ashes are studied in its fresh natural state, prior to consolidation and cementation has taken place for its chemical, mineralogical and geotechnical characterization. Volcanic ash of Tajogaite is of a poorly graded sandy nature having difficulties for its compaction, having low improvement of relative density by the application of standard compaction methods. Mineralogy analysis indicates it is rich in silica, iron, calcium and alumina oxide, although being necessary the addition of mineral additives for its alkali-activation. Geotechnical characteristics of different samples vary depending on the sampling site, being resistance parameters determined by direct shear test (friction angle 30 degrees degrees to 34 degrees) degrees ) and deformational properties defined by one-dimensional consolidation test considered low values as of loose sand materials (deformation modulus range from 20 to 40 MPa).