Organic soil is widely recognized for its low shear strength and high compressibility, which pose challenges for construction projects. One of the most commonly used methods for enhancing the mechanical properties of soil is chemical stabilization using various additives. In this study, the undrained shear strength of organic soil from Quito, Ecuador, with an average organic content of 43.84%, was reinforced using 0.5, 1, 3, and 6% nanosilica. A series of tests, including Atterberg limit, specific gravity, compaction, and unconfined compression tests, were conducted on specimens cured for 28 days. The results indicate that increasing the nanosilica content leads to higher plasticity, lower maximum dry density, and higher optimum moisture content. In addition, the modulus of elasticity and undrained shear strength improved. The optimal nanosilica content was found to be 1%, resulting in a 211.28% increase in the undrained shear strength. The mechanisms of soil improvement driven by the chemical interactions between nanosilica, mineralogical components (analyzed via XRD), and soil organic matter are discussed in detail.

This study investigates the effectiveness of deep soil mixing (DSM) in enhancing the strength and modulus of organic soils. The research evaluates how varying cement types, binder dosages, water-to-cement (w/c) ratios, and curing durations affect the mechanical properties of two different organic soils that were used; natural soil from the Golden Horn region of Istanbul with 12.4% organic content, and an artificial soil created from a 50/50 mixture of Kaolin clay and Leonardite, which has an acidic pH due to high organic content. The specimens were cured for four durations, ranging from seven days to one year. The testing program included mechanical testing; Unconfined Compression Tests (UCS), Ultrasonic Pulse Velocity (UPV) measurements, and chemical analyses; XRay Fluorescence (XRF) and Thermogravimetric analyses (TGA). The UCS tests indicated that higher binder dosages and extended curing durations significantly improved the strength. Higher w/c ratios resulted in decreased strength. Long curing durations resulted in strength values which were four times the 28-day strength values. This amplified effect of strength gain in longer durations was evaluated through Curing time effect index, (fc). The results were presented in terms of cement dosage effect, effect of cement type, effect of total water/cement ratio (wt/c), standard deviation values, E50 values and curing time effect index (fc) values respectively. Results of UPV tests were used to develop correlations between strength and ultrasonic pulse velocities. Quantitative evaluations were made using the results of XRF and TGA analyses and strength. Significant amount of data was produced both in terms of mechanical of chemical analyses.

Arctic permafrost soils contain a vast reservoir of soil organic carbon (SOC) vulnerable to increasing mobilization and decomposition from polar warming and permafrost thaw. How these SOC stocks are responding to global warming is uncertain, partly due to a lack of information on the distribution and status of SOC over vast Arctic landscapes. Soil moisture and organic matter vary substantially over the short vertical distance of the permafrost active layer. The hydrological properties of this seasonally thawed soil layer provide insights for understanding the dielectric behavior of water inside the soil matrix, which is key for developing more effective physics-based radar remote sensing retrieval algorithms for large-scale mapping of SOC. This study provides a coupled hydrologic-electromagnetic framework to model the frequency-dependent dielectric behavior of active layer organic soil. For the first time, we present joint measurement and modeling of the water matric potential, dielectric permittivity, and basic physical properties of 66 soil samples collected across the Alaskan Arctic tundra. The matric potential measurement allows for estimating the soil water retention curve, which helps determine the relaxation time through the Eyring equation. The estimated relaxation time of water molecules in soil is then used in the Debye model to predict the water dielectric behavior in soil. A multi-phase dielectric mixing model is applied to incorporate the contribution of various soil components. The resulting organic soil dielectric model accepts saturation water fraction, organic matter content, mineral texture, temperature, and microwave frequency as inputs to calculate the effective soil dielectric characteristic. The developed dielectric model was validated against lab-measured dielectric data for all soil samples and exhibited robust accuracy. We further validated the dielectric model against field-measured dielectric profiles acquired from five sites on the Alaskan North Slope. Model behavior was also compared against other existing dielectric models, and an indepth discussion on their validity and limitations in permafrost soils is given. The resulting organic soil dielectric model was then integrated with a multi-layer electromagnetic scattering forward model to simulate radar backscatter under a range of soil profile conditions and model parameters. The results indicate that low frequency (P-,L-band) polarimetric synthetic aperture radars (SARs) have the potential to map water and carbon characteristics in permafrost active layer soils using physics-based radar retrieval algorithms.

In recent years, biopolymers have been widely used in soil, but few concentration on the application of biopolymers in the organic soil. In this work, the potential using locust bean gum for improving the physical characteristics of the organic soil has been fully evaluated, while the Atterberg limit test, unconfined compressive strength test, and unconsolidated undrained shear test were conducted. In addition, the mineral composition and micro-mechanisms have been analyzed by X-ray diffraction tests, Fourier transform infrared spectra tests, and scanning electron microscopy tests. And we found that locust bean gum could increase the liquid limit and plastic limit of the organic soil, and enchance the compressive strength and shear strength. The increase in soil cohesion with locust bean gum content was more pronounced than the increase in internal friction angle. And as the curing time progresses, locust bean gum gradually transformed from a hydrogel state to a high tensile strength biofilm or flocculent gel matrix, which enhanced the bonding force between soil particles, thus increasing the strength of the specimens, which can be validated by the scanning electron microscopy observations, in which the porosity of soil was significantly reduced. We believed that this work could provide an ecological, economical and practical insight dealing with the engineering project constructions in the organic soil area.

Organic soil is usually required to be improved/treated before engineering construction, especially in cold regions due to deterioration introduced by freeze-thaw cycle. In this study, cement-and-fly ash is adopted as agents to stabilise the organic soil. A photogrammetric method is proposed to accurately reconstruct the surface of these cement-and-fly ash-treated organic soils and measure the volume before and after freeze-thaw cycles (F-T-C). Meantime, unconfined compression (U-C) test was performed to evaluate the performance of these specimens after different numbers of F-T-C, and the influence of organic content on soil behaviour was also investigated. These results indicated that an increase in the cement content enhanced the resistance of the organic soils against volume change before and after F-T-C. A proper adoption of cement-and-fly ash significantly improves the unconfined compression strength (UCS) of organic soils subjected to different numbers of F-T-C. The strength of treated organic soil continuously decreased with increasing content of organic. A model was also established to predict soil stress-strain curves with consideration of the number of F-T-C and volumetric changes after the F-T-C.

Organic soil is often encountered in seasonally frozen areas in China. Before construction, the organic soil is required to be treated to improve its engineering performance due to the high moisture content and low bearing capacity. Cement and fly ash were adopted in this study to treat organic soil subjected to natural freeze-thaw cycles. The influences of freeze-thaw cycles on the stress-strain behavior and microstructure of cement and fly ash-stabilized organic soil (C-F-S-O-S) were evaluated using unconsolidated undrained triaxial (U-U), mercury intrusion porosimetry (MIP) and CT experiments. With and without freeze- thaw cycles, results indicate that the specimen with 20% cement and 5.0% fly ash content performed the best in strength and was selected to evaluate the influence of freeze-thaw cycles on C-F-S-O-S mechanical and microstructure characteristics. The strength, elastic modulus (E-M), cohesion, and internal friction angle of the specimen show the largest decrease of 9.27%, 13.97%, 3.45%, 5.19% after the first freeze-thaw cycle and then slow decreased with further increase of the number of freeze- thaw cycles. The strain corresponding to the peak stress increased with increasing freeze-thaw cycles, and the increase was the largest with a value of 10.19% after the first freeze-thaw cycle. Relationships between the number of freeze-thaw cycles and above parameters were established. A generalized model was also established to predict the stress-strain curve of the C-F-S-O-S. The applicability of the proposed model was validated with published experiment data. The specimen porosity increased first (by 11.03%) and then gradually stabilized after a series of freeze-thaw cycles as revealed by the MIP. Consequently, MIP and CT analysis reveals the soil structural variation since the freeze-thaw cycle is the main reason of the reduction of the specimen strength after the freeze-thaw cycle.

Highly organic soil and peat are problematic soils due to their low bearing capacity and high compressibility. In tropical regions, the presence of woody material in these soils often affects the stress-compression and time-compression curves in load-increment consolidation tests, leading to unusual shapes. Consequently, conventional inorganic soil theory and the C alpha/Cc concept are inadequate for analyzing their compression behavior. As an alternative, the Gibson and Lo model can be used to obtain compression parameters from single-load consolidation tests. However, this method introduces considerable discrepancies when predicting the primary settlement. To address this issue, this paper proposes a formula for predicting the primary settlement in highly organic soil and peat in the field, especially in tropical regions. Samples were collected from several locations in Indonesia. The formula was constructed from the stress-strain relationship during the primary compression stage, obtained from numerous single-load consolidation tests. Long-term field settlement is predicted by combining this empirical equation for primary settlement with the Gibson and Lo model for secondary settlement. The proposed formula was verified using field soil monitoring data, demonstrating reasonable accuracy in predicting the primary settlement of highly organic soil and peat.

The impact of storage duration on the geotechnical properties of soils is a recurring issue in the field of geotechnical engineering. Due to the lack of previous research addressing this topic, an experimental study was conducted to evaluate the variation of these properties over time. Undisturbed samples of silty and organic soil from Quito, Ecuador, were obtained. These samples were subjected to unconfined compressive strength (UCS) and moisture content (MC) tests at various intervals (1, 3, 7, 14, 21, 28, and 56 days). Results revealed a significant correlation between MC, UCS, and modulus of elasticity (ME). A progressive increase in UCS and ME was observed as MC decreased, with peak values observed to occur between 20 and 30 days. These findings suggest that matric suction plays a predominant role in increasing cohesion and, consequently, UCS. Therefore, it is concluded that the time elapsed between sample extraction and testing is a critical factor influencing the preservation of MC and, hence, the accurate assessment of the soil's mechanical properties.

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.

One of the issues with clayey soils, particularly those with significant quantities of organic matter, is the creep settling problem. Clay soils can be strengthened using a variety of techniques, one of which is the use of stone columns. Prior research involved foundation loading when the soil beds were ready and confined in one-dimensional consolidation chambers. In this study, a particular methodology is used to get around the model's frictional resistance issue. Initially, specimens were prepared via static compaction, and they were then re-consolidated inside a sizable triaxial cell while under isotropic pressure. With this configuration, the confining pressure can be adjusted, the pore water pressure beneath the foundation can be measured, and the spacemen's lateral border may be freely moved. This paper's important conclusions include the observation that secondary settlement declines with area replacement ratio. Because of the composite ground's increasing stiffness, the length to diameter ratio (l/d) and the stone column to sample height ratio (Hc/Hs) both increase. The degree of improvement varies from 12.4 to 55% according to area replacement ratio and (l/d) ratio.