Characterization of Soft Soil Strength Properties and Settlement Behavior

Catchment-scale spatial variability of soil properties and implications on site-specific soil management in northern Ethiopia

The unconfined compressive strength is the most widely used parameter to measure the strength of the subgrade or foundation soil for cohesive soils. Due to its time-consuming and cost-effective nature, most of the time-correlation equations have been used to correlate unconfined compressive strength with compaction parameters and soil index properties. The current study was conducted in Burayu town where fifty soil samples were collected and experimental geotechnical soil tests were carried out based on the American Society for Testing and Materials (ASTM) standards. The correlation and regression analyses were done using the experimental results obtained for unconfined compressive strength (UCS) and compaction characteristics. The regression analysis resulted in a fair coefficient of correlation of 0.61 and 0.78 for single linear regression of UCS with maximum dry density (MDD) and optimum moisture content (OMC), respectively, while R2 = 0.83 for multiple linear regression analysis of UCS with MDD and OMC. After further emphasis, the equation developed using multiple linear regression (UCS = −3105 + 1625 MDD + 40.9 OMC, R2 = 0.83) which was chosen as a prediction equation. After validation of the established model using control tests, the statistical regression analysis shows that the correlation is 97% accurate in the UCS determination for multiple regression analysis. This implies that the established model could be used to predict the UCS in the study area.

Assessing wheat spatial variation based on proximal and remote spectral vegetation indices and soil properties

This study explores the mechanical properties and micromechanisms of sulfuric saline soil from Kashi, Xinjiang, modified using various types and contents of eco-friendly or recycled natural fibers. The unconfined compressive strength (UCS), shear strength, and micromorphology of fiber-reinforced soils were systematically analyzed through experimental methods, including unconfined compression tests, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR). Results demonstrated that incorporating natural fibers significantly enhanced the soil's mechanical performance. For instance, UCS increased by 2.11 times with 6% rice husk fiber and by 2.8 times with 4% jute fiber (40mm length) compared to ST. Similarly, 15mm sisal fiber at 2% content improved UCS by 2.48 times, while palm fiber (1.5%, 20-40mm) enhanced UCS by 2.13-2.29 times. Optimum moisture content (OMC) and maximum dry density (MDD) varied depending on fiber type and content, with the highest MDD (1.97 × 103kg/m3) observed at 0.6% coconut shell fiber content. Wet-dry cycle tests revealed that fiber reinforcement effectively reduced strength loss, and dissolution coefficient analysis confirmed improved resistance to saline soil degradation. These findings highlight the potential of natural fibers as a sustainable and environmentally friendly solution for stabilizing saline soils in arid regions, offering improved durability and reduced ecological impact.

The application of alkali-activated slag (AAS) cementing material to the curing of soft soil foundations has a good engineering application prospect and is economical and environmentally friendly. In this study, three different activators (Na2O·nSiO2, NaOH, Ca(OH)2) were used to alkali-activate slag powder to solidify and improve soft soil in inland port areas. In order to explore the mechanical properties and strength formation mechanism of AAS-solidified soil under different activators, mechanical properties, and microscopic tests were carried out. Firstly, with unconfined compressive strength as the evaluation index, an orthogonal test of three factors, such as the type of activator, the amount of activator, and the amount of slag powder, was designed. Then, the unconfined compressive strength, resilience modulus, shear strength, and compression modulus of AAS-solidified soil were tested with the three activators under optimal dosage. Finally, phase composition, SEM-EDS, TG-DTG, and FT-IR analyses were carried out with the three AAS-solidified soils. The results show the following: (1) The factors affecting the unconfined compressive strength of AAS-solidified soil are ordered as follows: the type of activator > the amount of activator > the amount of slag powder. In addition, the optimal factors were as follows: activator type: Na2O·nSiO2; amount of activator: 3%; and amount of slag powder: 20%. (2) In considering the macroscopic mechanical properties, the effect of the activator is Na2O·nSiO2 > NaOH > Ca(OH)2, and the Na2O·nSiO2 AAS-solidified soil has good early strength. (3) The hydration products of AAS are mainly C-A-S-H gel, N-A-S-H gel, and C-S-H gel, which increase the strength and cohesion of solidified soil. The results show that AAS-solidified soil with 0.7-modulus Na2O·nSiO2 as the activator has good engineering characteristics and can be used for curing soft soil foundations.

Due to its significant deficiencies such as low permeability, low bearing and shear strength, and excessive compressibility, soft soil is one of the most problematic types of soil in civil engineering and soil stabilization can be considered a suitable technique for pavements. This study investigates the use of ground granulated blast slag (GGBS) and cement kiln dust (CKD) as stabilizers for soft soil. Thus, this study involves two optimization stages; in the first stage, GGBS was incorporated into 0%, 3%, 6%, 9%, and 12% by the weight of cement to obtain the optimal percentage, which was 6%. Then, the optimal GGBS was blended with CKD in a binary system at 0%, 25%, 50%, 75%, and 100% by the dry weight of the soil. The testing program used in this paper was Atterberg limits with compaction parameters to investigate the physical properties and unconfined compressive strength (USC) at 7 and 28 days to examine the mechanical characteristics. In addition, the microstructures of the soil specimens were tested at 7 and 28 days using scanning electron microscopy (SEM). The findings reveal that the binary system enhanced the physical and mechanical properties of the soft soil. The optimum binder achieved in this study was 6% (25% GGBS and 75% CKD), which generates an increase in strength of about 3.3 times in 7 days, and of 5.5 times in 28 days in comparison to the untreated soil. The enhancement was attributed to the formation of the hydration products as approved by SEM. Consequently, in the case of soft subgrade soils, this technique can increase the pavement’s bearing capacity and performance.

In this study, a laboratory investigation was conducted to examine the performance of TerraZyme on different soil types. Laterite and kaolin were treated with 2% and 5% TerraZyme to determine changes in the soils’ geotechnical properties. The obtained results were analysed and investigated in terms of compaction, Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR). The changes in geotechnical properties of the stabilised and unstabilised soils were monitored after curing periods of 0, 7, 15, 21 and 30 days. Changes in compaction properties, UCS and CBR were observed. It was found that laterite with 5% TerraZyme gave a higher maximum dry density (MDD) and decreased the optimum moisture content (OMC). For kaolin, a different TerraZyme percentage did not show any effect on both MDD and OMC. For strength properties, it was found that 2% TerraZyme showed the greatest change in UCS over a 30-day curing period. The CBR value of stabilised kaolin with 2% TerraZyme gave a higher CBR value than the kaolin treated with 5% TerraZyme. It was also found that laterite treated with TerraZyme gave a higher CBR value. Lastly, it can be concluded that TerraZyme is not suitable for stabilising kaolin; TerraZyme requires a cohesive soil to achieve a better performance.

Soft marine soil deposit is distributed under the sea with many special properties. This type ofsoil is rarely researched in Vietnam because of the difficult geotechnical investigation under the sea level.In this paper, the experimental laboratories were performed to investigate the geotechnical properties ofsoft marine soil at Chan May port, Vietnam. The field investigation results indicate that the thickness ofsoft soil varies from a few meters to more than ten meters. Soft soil has a high value of water content,void ratio, and compressibility and a low value of shear strength. The compression index has a goodrelationship with water content, liquid limit, and dry unit weight. The unit weight, shear strength, and preconsolidationpressure increase with the increase of depth. These results show that the soil in the studyarea is unfavorable for construction activities.

This paper presents an experimental study aimed at assessing the suitability of rice husk ash (RHA) treated black cotton soil as a barrier in Municipal Solid Waste (MSW) containment facility. Laboratory tests were conducted on black cotton soil treated with 5, 10 and 15% RHA at moulding water contents of 2 and 4% on both wet and dry sides of optimum moisture content (OMC) using British Standard Heavy (BSH) compactive effort. Index properties, hydraulic conductivity (k), volumetric shrinkage strain (VSS), and unconfined compressive strength (UCS) tests were conducted on all the samples. The results obtained indicated that the soil was classified as A-7-5(18) according to the American Association of States Highway and Transport Officials (AASHTO) classification system and Silt of high plasticity (MH) in accordance with the Unified Soil Classification System (USCS). It was observed that addition of RHA was accompanied with decrease in the plasticity index from 24 to as low as 3%. An improvement in the moisture-density relationship of the soils showed an increase in Maximum Dry Density (MDD) from 1.46 to 1.52 Mg/m3 as well as a decrease from 24.5 to 21.2% in OMC. The increase in RHA contents up to 10% brought about an improvement in the strength of the soil specimens by almost 332.4kN/m2 at 2% on the dry side of OMC. The VSS decreases with increase in RHA content to achieve the minimum shrinkage strain of 4.1% at 5% RHA treatment.

This work investigates the behavior of a silty clay stabilized with 3, 6, 9, and 12 % of ground granulated blast-furnace slag (GGBS), respectively, and 1 % of quicklime used as an activator. The influence of the composite (Quicklime - GGBS) on the immediate behavior of the silty clay is studied by examining the Atterberg limits, the maximum dry density, the optimum moisture content, and the immediate bearing index. The evolution, at different curing periods (1, 7, and 28 days), of the mechanical characteristics of the treated soil, namely unconfined compressive strength, cohesion, and internal angle of friction is also studied. The increase, up to a dosage of 9%, of the GGBS content, leads to an increase in the optimum moisture content, the immediate bearing index, the unconfined compressive strength, and shear strength parameters. Paradoxically, a decrease in the plasticity index and the maximum dry density was observed.

Soft soil is widely distributed in Vietnam, especially in the coastal area. In engineering practice, soft soil cannot be used to build any construction and needs to be improved or treated before building construction. In addition, Vietnam has many pig‐iron or thermal power plants, which annually produce a huge amount of granulated blast furnace slag (GBFS). Thus, the use of this material for soft soil improvement needs to be considered. This paper presents experimental results on the unconfined compressive strength (UCS) of three Vietnam’s soft soils treated with Portland cement and Portland cement with ground granulated blast furnace slag (GGBFS). Binder dosage used in this study is 250, 300, and 350 kg/m3 with the three different water/cement ratios of 0.8, 0.9, and 1.0, respectively. The research results showed that the UCS of soil‐cement mixtures depends on soil type, water/cement ratio, cement type, and binder content. Accordingly, the unconfined compressive strength increased with the increase of binder contents, the decrease of the natural water content of soft soil, water/cement ratios, and clay content. The highest value of UCS of treated soils was found for the soil at Site II with the Portland cement content, cement GGBFS, and water/cement ratio of 873 kg/m3, 2355 kg/m3, and 0.8, respectively. Besides, for all the three soils and two binder types, the water/cement ratio of 0.8 was found to be suitable to reach the highest UCS values of treated soil. The research results also showed that the UCS of treated soil with cement GGBFS was higher than that of treated soil with Portland cement. This indicated the effectiveness of the use of Portland cement with GGBFS in soft soil improvement. There is great potential for reducing the environmental problems regarding the waste materials from pig‐iron plants in Vietnam and the construction cost as well.

Crude oil and petroleum products can pollute soils during refining, transportation and operation processes. Because of physicochemical effects and reactions between these fluids and soils, geotechnical behavior and properties of soils change. Since these changes are mostly adverse, improvement and treatment of contaminated soils and sediments are necessary in many geotechnical projects and works. In present research, using lime as a traditional additive and nanosilica is considered for treating of gas oil contaminated clay. The polluted specimens were prepared by mixing the soil with gas oil in amounts of 0, 3, 6 and 9% by dry weight. The contaminant increased liquid limit (LL) and plastic limit (PL), and reduced maximum dry density (MDD) and optimum moisture content (OMC) of the soil. Unconfined compressive strength (UCS) of the soil showed an initial increase in 3% of contamination and then a decrease for the heavily contaminated samples (i.e., gas oil content greater than 3%). After adding 0, 1, 2 and 3 weight percent of lime and nanosilica, both independently and together; LL, PL, OMC and UCS of the samples increased and MDD of the treated soils decreased. Compared with lime and nanosilica, the mixture of them was considered more efficient in improving the UCS. By adding 3% of nanosilica-lime mixture and increasing curing time, considerable UCS gains occurred.

This paper reviews the behaviour of reinforced embankments on soft ground. Case of the Almere test embankment is used as an example to demonstrate the key function of reinforcement in improving the performance of embankments on soft foundation. The effects of partial drainage are summarized for reinforced embankments and contrasted the results from undrained analyses to highlight the effect of partial consolidation during construction. Effects of the interaction between reinforcement and prefabricated vertical drains (PVDs) are presented. It is concluded that the combined effects of partial consolidation provided by PVDs and the tension mobilized in reinforcement can substantially increase the stability of an embankment on a given soft soil. This paper also provides brief explanation of a recent design approach for embankments on soft soil, considering the combined effect of reinforcement and PVDs. Effects of the creep/relaxation characteristics of geosynthetic reinforcement and rate-sensitive nature of soft cohesive foundation soil are discussed. It is shown that time-dependent nature of geosynthetics and foundation can decrease the failure height of a reinforced embankment. Also, the long-term performances of a reinforced embankment can vary significantly depending on the soil and reinforcement characteristics. The results suggest the need for care when the foundation soil is rate-sensitive.

The strength characteristics of two genetically different shales treated with both Rice Husk Ash (RHA) and Coconut Husk Ash (CHA) was evaluated to elucidate responses and effects, examine effectiveness of the additives with a view to ultimately provide economically viable and environmental friendly options for modification and hence stabilization. 2 to 20 % by weight of both RHA and CHA were separately added to Okitipupa (SW) and Enugu (SE) shales with the subsequent determination of Plasticity Index (PI), Maximum Dry Density (MDD), Optimum Moisture Content (OMC), Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR). RHA and CHA were found to possess pozolanic properties such that their addition to shale in modest amounts (not more than 10 % by weight) has beneficial effect on the strength characteristics. Addition of RHA produced shales with reduced PI, higher UCS, increased MDD and more pronounced reduction in OMC when compared with the CHA stabilized shales. However in general, addition of 10 % RHA and 6–10 % CHA brought about optimal effect on the geotechnical properties of shales and as such can be regarded as the optimum content. These materials can thus serve as suitable alternatives to modify and stabilize problematic shale and hence help reduce construction costs, environmental hazards and ultimately bring about shales with improved geotechnical properties.

Chemical stabilization is extensively employed to enhance the physical and mechanical properties of problematic soils. For instance, there are various types of chemical additives in liquid and powder forms. One of the potential bio-polymer stabilizer is Xanthan Gum which has widely been employed due to the environmental issues and the effect of land desertification. This research is devoted to studying the effect of Xanthan Gum on the strength improvement of lateritic soil. The lateritic soil sample is provided from the hilly area at Universiti Teknologi Malaysia. The physical and engineering tests on untreated and treated samples were conducted according to BS1377:1990. The Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) were determined using the compaction test results. Then, MDD and OMC are used for the Unconfined Compressive Strength (UCS), and direct shear tests sample preparation. The lateritic soil was mixed with different percentages of Xanthan Gum including 0.5%, 1.0% and 1.5% of the soil mass and cure for 3, 7 and 14 days. It was found that the UCS and direct shear strength parameters of cohesion and internal friction angle improve with the curing duration. The Field Emission Scanning Electron Microscopy (FESEM) shows the generation of new cementitious products as a result of the reaction between Xanthan Gum and lateritic soil. New generated products fill the porous areas within the soil particles, leading to a continuous soil structure. Therefore, stronger and denser soils are provided as the pore space is reduced.