Unconsolidated Research Articles

FEM Analysis on Isotropic Consolidation of Unsaturated Soils Using Ceramic Disks and Microporous Membrane Filters for Suction Control

Abstract Microporous membrane (MM) filters with a significantly thin thickness have recently been used as an alternative to ceramic disks for matric suction control in the axis-translation technique for element tests on unsaturated soils. Although researchers have highlighted some discrepancies in test results when ceramic disks and MM filters are used, the mechanism leading to these discrepancies has not yet been clarified. In this study, suction-controlled triaxial tests were first conducted on unsaturated completely decomposed granite using two filters. Then, it is natural to believe that the different thicknesses of ceramic disk and MM filters may significantly influence the suction equilibrium process of specimens. To clarify this issue, soil-water-air coupled finite element modeling was performed to simulate the consolidation process in triaxial tests as an initial/boundary value problem. In the numerical calculation, the influence of the void ratio on the water retention curve (WRC) of soil was properly considered by adopting a deformation-dependent WRC model. In particular, the ceramic disk and MM filter, along with the specimens, were modeled, and their differences in thickness were considered. The calculated results show that a nonuniform distribution of suction occurred in the ceramic disk, leading to greater drainage discharge of the specimens. In other words, the influence of the thickness difference between the MM filter and ceramic disk cannot be neglected. However, regardless of whether ceramic discs or MM filters are used, the uneven distribution of the state variables in the specimens may occur in the triaxial tests for unsaturated soils, which emphasizes the importance of assessing the soil tests using the present axis-translation technique as initial/boundary value problems.

Evaluation of the Effects of Climate Change and Environmental Parameters on Evaporation and Settlement of Unsaturated Soil

Evaluation of the Effects of Climate Change and Environmental Parameters on Evaporation and Settlement of Unsaturated Soil

Understanding and mitigating settlement in gypseous soils: A comprehensive study on the role of saturation and soil stabilization techniques

This study examines the influence of saturation levels and soil additives on the load-settlement properties of gypseous soils, a significant geotechnical concern in regions like Iraq. The study analyzes the deficiencies of conventional oedometer testing, which often fail to adequately represent the true unsaturated conditions prevalent in these soils. The research investigates the impact of varying matric suction (Ψ) values on the compressibility of untreated, cement-treated, and CKD-treated gypseous soils. A modified oedometer apparatus, engineered to control and quantify matric suction, was used to replicate diverse moisture conditions. The experimental program investigated soils with varying gypsum contents (8.8%, 12.66%, and 30%), reflecting the diversity of gypseous soils seen in the field. The findings demonstrate that increased saturation levels significantly enhance settling in gypseous soils. As matric suction increases, settlement is markedly reduced due to elevated soil suction pressure and enhanced effective stress. The findings underscore the importance of unsaturated conditions in improving the load-bearing capacity of these soils. The study illustrates the advantageous impacts of cement and CKD treatments in reducing settling. The effectiveness of these methods is particularly apparent in partially saturated environments, emphasizing the need of including matric suction into design considerations. This research improves understanding of the complex behavior of unsaturated gypseous soils. The findings have practical importance for geotechnical engineering, including foundation design, ground improvement methods, and the development of effective solutions for settlement issues in areas with high gypsum concentrations.

Isolation and characterization of a resistance Bacillus subtilis for soil stabilization and dust alleviation purposes

Dust poses environmental, geological, health, and economic concerns, and microorganisms can help mitigate these adverse consequences by improving soil properties. Microbial calcium carbonate precipitation (MICP) has been found to be an efficient strategy for increasing soil strength, reducing soil porosity, and preventing erosion; however, severe environmental conditions such as pH and high temperatures may impede this process. To identify the best strain for MICP, 60 bacteria strains were obtained from arid soils using the enrichment culture technique. They were tested for the capacity of calcium carbonate deposition and biocement synthesis in stress environments. Phenotypic characterization indicated that the majority of the bacterial isolates were gram-positive and rod-shaped, with strong catalase and oxidase enzyme activity. Furthermore, MALDI-TOF MS identification revealed that the isolates were from the Bacillus and Pseudomonas genera. Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used to analyze the microstructures and composition of bacterial cement. The results represented that B. subtilis isolate S56 has a higher production yield and forms distinctive calcite crystals as a result of fast urease synthesis. B. subtilis isolate S56 can be applied in situ to reduce soil erosion and dust pollution. This study reveals the potential of the B. subtilis S56 strain for soil consolidation and dust prevention in harsh environments and has the prospect of promoting its application in desertification control and ecological restoration.

A Numerical Analysis of the Role of Pile Foundations in Shaft Sinking Using the Vertical Shaft Sinking Machine (VSM)

The use of the Vertical Shaft Sinking Machine (VSM) for shaft construction marks a significant advancement in modern technology and is recognized as one of the leading techniques in the field. However, much of the existing research focuses on mechanical and technical challenges, often overlooking the effects on surrounding soil and the structural integrity of shafts. This study demonstrates that increasing pile diameter by 20% improves load-bearing capacity by 15% and reduces soil settlement by 12%, though these improvements come with higher construction costs. Additionally, larger diameters improve lateral stability, but excessively long piles lead to diminishing returns. To address the limited research on reinforcement design in soft soils, a series of numerical models were employed to investigate the effects of pile spacing, length, and diameter on surrounding soil behavior. This in-depth analysis aims to provide a scientific foundation for optimizing VSM technology in caisson pile foundations, particularly in soft-soil conditions.

Bearing Characteristics of Deep Cement Mixing Integrated Drilling, Mixing and Jetting Piles Based on Numerical Simulation

The Deep Cement Mixing Integrated Drilling, Mixing and Jetting (DMJ) technique has been developed through the installation of high-pressure spray holes at the mixing blades, with the objective of enhancing the bearing capacity of deep-mixed piles in the Yellow River floodplain. In order to enhance the bearing capacity of the foundation, variable-modulus piles and capped piles were incorporated within the DMJ piles. Engineering applications have demonstrated that DMJ piles can effectively address the issue of foundation reinforcement in the Yellow River floodplain region, minimize the wastage of cement, and reduce the environmental pollution associated with waste slurry. Nevertheless, a comprehensive study of the relevant factors is still lacking in the available literature. This study addresses this gap by conducting a numerical simulation of these two types of DMJ piles based on the preliminary field test data, with the objective of analyzing both the single-pile-bearing characteristics and the composite foundation-bearing characteristics. Furthermore, the study seeks to optimize the DMJ pile’s structure based on the simulation results. The findings demonstrate that the premature failure of a single pile during the bearing process can be averted if the modulus of the pile core reaches a minimum of 0.3 GPa or if the pile cap thickness exceeds 1 m. The utilization of large-diameter drilling, stirring and spraying piles can markedly enhance the bearing capacity of the composite foundation and mitigate the differential settlement of pile and soil. The spacing of the pile has been identified as a significant factor influencing the differential settlement of pile and soil. Consequently, this study also examines the impact of pile spacing on the differential settlement of piles and soil.

A Study on the Influence of Hydraulic Compactor Reinforcement on the Force Law of an Independent Foundation Under a Column and Its Safety Standard

Due to the complexity of the actual geotechnical environment, the backfill compaction design theory and calculation method are not reflected in the current specification. Therefore, in order to investigate the effect of the hydraulic compactor on the foundation structure during the treatment of the backfill of an independent foundation under a column, the Menard formula was modified. At the same time, relying on an independent foundation project under a column in Jinan, the dynamic model of compactor tamping backfilling soil was established. The applicability of the calculation formula is verified by simulating the single-point multiple tamping on the backfill directly above the foundation tie beam, and the influence law of two factors, the thickness of the backfill and the tamping energy, on the force of the foundation tie beam is elucidated. The results show that after reaching the optimum number of tamping, the cumulative soil settlement and the effective reinforcement depth of tamping show a stable trend, and their simulation results are in good agreement with the analytical solution, which provides a supplement to the relevant safety standards. At this critical point, the force on the tie beams peaked and showed up and down fluctuations under the subsequent ramming action. The tamping action of the compactor has a significant effect on the structural forces within the effective reinforcement range, and there is a negative correlation between the magnitude of the structural forces and the thickness of the backfill. According to the numerical calculation results to choose the best construction programme, the on-site monitoring shows that under 42 KJ tamping energy and 1.5 m single backfilling thickness, the tie beam reinforcement stress reaches 18.5~55.5% of the specification warning value, which meets the safety standard. The research results of this paper can provide important guidance for the hydraulic tamping treatment of an independent foundation backfill project.

Insights from the numerical analysis of axially loaded piles in liquefiable soils

Axially loaded piles in liquefiable soils can undergo severe settlement due to an earthquake event. During shaking, the settlement is caused by the decreased shaft and tip capacity from excess pore pressures (ue) generated around the pile. Post shaking, soil settlement from the reconsolidation of liquefied soil surrounding the pile results in the development of additional load (known as drag load), causing downdrag settlement of the pile. Estimating the axial load distribution and pile settlement is essential for designing and evaluating the performance of axially loaded piles in liquefiable soils. In practice, a simplified neutral plane solution method is used, where the liquefied soils are modeled as a consolidating layer without considering the effect of ue generation/dissipation. A TzQzLiq analysis models the load and settlement response of axially loaded piles in liquefiable soils by accounting for the effect of excess pore pressure (ue) generation/dissipation on the shaft and tip capacity. This paper presents the deficiencies of the simplified neutral plane method in predicting the drag load as well as the downdrag settlement by comparing it with the TzQzLiq analysis validated with hypergravity model tests. The results show that the drag load and the downdrag settlement predicted by the neutral plane method might be over- or under-estimated depending on the pile load, the rate of ue dissipation, and the soil settlement. For the cases studied, it was found that most of the pile settlement occurs during shaking due to the decrease in the pile's tip resistance from the development of ue in the soil surrounding it. While large drag loads develop during reconsolidation, the resulting downdrag settlement is small. While the neutral plane method generally predicted a downdrag settlement comparable to that of the TzQzLiq analysis, it overpredicted drag load and could not predict co-seismic settlement. Finally, the study advocates for the development and use of a displacement-based procedure (accounting for all the mechanisms occurring during and after an earthquake event) such as based on TzQzLiq analysis in accurately evaluating the performance of the pile (i.e., the pile settlement and the maximum load), thus providing an overall safe, efficient, and optimized design.

Coupled filtration–consolidation model for vacuum-preloaded soft ground

The widespread utilisation of vacuum-assisted prefabricated vertical drains for managing clayey soft ground has led to the development of numerous consolidation models. However, these models have limitations when describing the filtration behaviour of soil under conditions of high water content, without the formation of a particle network. To address this issue effectively, in this work, based on the compressional rheology theory, a two-dimensional axisymmetric model incorporating the compressive yield stress Py(ϕ) and a hindered setting factor r(ϕ) was developed to couple the filtration and consolidation of soil under vacuum preloading. A novel approach for determining the unified ϕ–Py–r relationships was introduced. The equation governing such fluid/solid and solid/solid interactions was solved using the alternative direction implicit method, and the numerical solutions were validated against the one-dimensional filtration cases, three-dimensional laboratory model tests and large-scale field trials. Further parametric analysis suggests that the radius of the representative unit and r(ϕ) exclusively affect the dewatering rate of the clayey slurry, while the gel point and Py(ϕ) influence both the dewatering rate and the final deformation.

Coupling effects on class C predictions of soft soil settlements

AbstractIn 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.

Long-term effect of soil settlement on lateral dynamic responses of end-bearing friction pile

This paper presents a closed-form solution to evaluate the lateral dynamic responses of pile foundation adjacent to superficial surcharge. The equilibrium equation of soil is analyzed using continuum solutions, and the Euler-Bernoulli beam theory is employed to model the pile. The consolidation settlement of surrounding soil induced by the superficial surcharge is determined by Terzaghi's consolidation theory. The lateral soil resistance is formulated using potential functions, and the dynamic responses of the end-bearing friction pile are subsequently obtained by considering the vertical load and skin friction. Our results are compared with analytical approaches from previous literature to validate the effectiveness of the present solution. The evolutions of lateral dynamic responses of pile foundation are systematically analyzed. It is suggested that the superficial surcharge influences the distribution of skin friction of the pile foundation, thereby altering its lateral dynamic responses. This phenomenon does not manifest immediately but demonstrates significant long-term effects during the consolidation settlement of surrounding soil.

Biodiversity and Soil Reinforcement Effect of Vegetation Buffer Zones: A Case Study of the Tongnan Section of the Fujiang River Basin

The riparian vegetation buffer zone is an important component of riverbank ecosystems, playing a crucial role in soil consolidation and slope protection. In this study, the riparian vegetation buffer zones in the Tongnan section of the Fujiang River Basin were selected as the research object. Surveys and experiments were conducted to assess the species composition and the soil and water conservation effectiveness of the riparian vegetation buffer zone. There are a total of 35 species, mainly comprising angiosperms and ferns. The dominant species include Cynodon dactylon, Setaria viridis, Phragmites australis, Erigeron canadensis, and Melilotus officinalis. The Patrick richness index (R) and Shannon–Wiener diversity index (H) are more significantly influenced by the types of land use in the surrounding area, whereas the impact on the Simpson diversity index (D) and Pielou uniformity index (E) is comparatively less pronounced. When the root diameter is less than 0.2 mm, the tensile strength of Cynodon dactylon roots is the highest. For root diameters larger than 0.2 mm, Melilotus officinalis roots exhibit the highest tensile strength. The presence of plant root systems significantly reduces erosion, delaying the time to reach maximum erosion depth by 1–4 min, decreasing erosion depth by 9–38 mm, and reducing the total amount of erosion by 20.17–58.90%. The anti-scouribility effect of Cynodon dactylon is significantly better than that of Setaria viridis. The root system notably enhances soil shear strength, delaying the shear peak by 0.26–4.8 cm, increasing the shear peak by 4.76–11.37 kPa, and raising energy consumption by 23.76–46.11%. Phragmites australis has the best resistance to shear, followed by Erigeron canadensis, with Melilotus officinalis being the least resistant. Therefore, to balance the anti-scouribility effect and shear resistance of plant roots, it is recommended to use a combination of Cynodon dactylon and Phragmites australis for shallow-rooted and deep-rooted planting. This approach enhances the water and soil conservation capacity of riverbanks.

Predictive model for shear wave velocity of gravelly soil and its application to liquefaction triggering assessment

Several studies have established empirical correlations between shear wave velocity (Vs) and standard penetration test blow count (SPT-N) for engineering use. However, these empirical correlations cannot be applied to gravel-rich soils since the measured SPT-N is often inflated in gravel. Therefore, an empirical correlation of Vs for gravel is developed in this study using the Engineering Geological Database for the Taiwan Strong Motion Instrumentation Program. The Vs predictive model considers gravel content (GC) and coefficient of uniformity (Cu) in addition to effective vertical stress, void ratio, fines content, plasticity index, and overconsolidation ratio, which have been considered previously. The proposed model indicates that Vs increases with GC and Cu. Moreover, the Vs adjusted for GC can be used with existing Vs -based liquefaction triggering relationships to rationally define the boundary between liquefaction and non-liquefaction case histories with different GCs.

Analytical solution for radial consolidation of combined electroosmosis-vacuum-surcharge preloading considering free strain and cyclic loading

In this study, electro-osmotic consolidation considering smear effect and free strain under cyclic loading was investigated. The analytical solution of radial consolidation of electroosmosis-vacuum-surcharge combined preloading is derived by using the Bessel function and eigenfunction methods. Subsequently, the effectiveness of the proposed method is validated through comparison with existing numerical solutions. Based on the derived solutions, the influence of the smear effect, applied voltage, vacuum pressure, and cyclic loading on soil consolidation characteristics was analyzed. The results showed that the smearing effect slows the rate of consolidation, but the final average consolidation and negative excess pore water pressure are enhanced. Compared with only cyclic loading, the combined effect of electroosmosis, vacuum, and surcharge preloading enables the soil to achieve higher strength and consolidation. When the effect of electroosmosis alone on reinforcing low-permeability soils is not significant, the combination of electroosmosis with vacuum preloading helps enhance the soil reinforcement effect.

Re-examination and analysis of test data on consolidation of soft soils exhibiting creep with different thicknesses

Re-examination and analysis of test data on consolidation of soft soils exhibiting creep with different thicknesses

Water‒soil-air‒plant mutual feedback mechanism under the application of red bed composite polymers.

Red bed composite polymers composed of weathered red bed soil, adhesive materials, and water-retaining materials have been applied as a new type of material for environmental restoration. However, the promotion and application of this material has been limited by a lack of understanding of its action mechanism in environmental restoration. The objective of this study is to innovatively propose a water‒soil-air‒plant mutual feedback mechanism based on this material. Therefore, water‒soil-air‒plant mutual feedback tests were conducted in this study under 3 initial water contents and 10 red bed composite polymers ratios. Key parameters, namely, water content, soil conductivity, pH, temperature, O2 and CO2 contents, pigeon pea (Cajanus cajan) germination number and plant height were monitored and analyzed. As the results, a mutual feedback mechanism driving water retention, soil consolidation, air retention, and plant rooting was revealed under the application of red bed composite polymers. And, suitable environments and optimal compositions for this material are proposed. The study results provide a theoretical basis for the large-scale application of red bed composite polymers.

Seismic performance and recovery of medical infrastructure in Mexico City related to the September 19, 1985 and 2017 earthquakes

To date, the September 19, 1985 Michoacán (Ms = 8.1) and the September 19, 2017 Puebla-Morelos (Mw = 7.1) earthquakes have been the most devastating seismic events in Mexico City. During the 1985 earthquake, 13 important public hospital buildings collapsed or were demolished and 5800 hospital beds were lost. During the 2017 earthquake, 85 buildings of the medical sector were disturbed, two major public hospital were demolished and 1147 hospital beds were affected. In this paper, the author concentrates both in reviewing what occurred during the 1985 earthquake, and in reporting what it has been observed for the 2017 earthquake. From the structural viewpoint, the observed damage is discussed in relationships to: a) seismic codes, b) spectral demands, b) structural irregularities, c) soil settlements, d) tilting, e) structural pounding and, f) deterioration. The observed damaged inventory is also put into perspective with respect to the approximate number of medical facilities that are available in Mexico City. An instantaneous drop of seismic resilience for this sector is crudely assessed. Finally, the progress on the recovery process or adaptive resilience is discussed. Fortunately, most of the main hospitals in Mexico City were not severely damaged, and that it was why most of them and the hospital bed capacity in Mexico City previous to the 2017 earthquake was able to be recovered on time to attend the Covid-19 pandemic which affected Mexico since early 2020.

Rate effects of cylindrical cavity expansion in fine-grained soil

Soil responds to cavity expansion is inherently rate-dependent, especially in the case of fine-grained soils. To better understand such rate effects, self-boring pressuremeter tests were conducted on Kunming peaty soil within a strain rate range of 0.1%/min to 5.0%/min. The results showed a clear dependence of cavity pressure and excess pore pressure (EPP) on strain rates—both increased with higher rates for a given radial displacement. In light of the experimental results, three cases of cylindrical cavity expansion were investigated using the finite element method and analytical method, partially drained expansion in Modified Cam-Clay (MCC) soil, and undrained and partially drained expansion in elastoviscoplastic (EVP) soil. The EVP behavior was and modeled using the MCC model and the overstress viscoplastic theory. The results indicated that over the strain rate range of 0.0001%/min and 50%/min, the rate response of cavity pressure for the case of partially drained expansion in MCC soil (permeability coefficient ranging from 5×10-6 m/s to 2.5×10-11 m/s) is not obvious, while the EPP response during undrained expansion in EVP soil shows rate-independent. Only the partially drained solution for cavity expansion in EVP soil captured the rate-sensitive responses of both cavity pressure and EPP, confirmed by the pressuremeter tests on the Kunming peaty soil, Saint-Herblain clay, and Burswood clay. This suggests that the rate effect results from a combination of drainage-related and time-dependent soil behavior. Parametric studies further demonstrated that both viscous behavior and the overconsolidation ratio significantly influence cylindrical cavity expansion response, and the drainage conditions during expansion can be assessed using a nondimensional velocity.

One-dimensional consolidation analysis of layered unsaturated soils: An improved model integrating interfacial flow and air contact resistance effects

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 (Rω), flow partition coefficient (ηω), air contact transfer coefficient (Ra) and air partition coefficient (ηa). 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 (kω) and air phase (ka) on the consolidation process. Moreover, neglecting the flow and air contact resistance effects may lead to an overestimation of settlement.

Analytical Solution for 2D Electro‐Osmotic Consolidation of Unsaturated Soil With Non‐linear Voltage Distribution

Analytical Solution for 2D Electro‐Osmotic Consolidation of Unsaturated Soil With Non‐linear Voltage Distribution