Unconfined Compression Research Articles

The geotechnical behavior and microstructural characteristics of the alkaline residue/cement stabilized expansive soil under wetting-drying cycles

In order to explore the geotechnical behavior of expansive soil stabilized by alkaline residue/cement (ARC) under wetting-drying (W-D) cycles, the shrink-swell characteristics, unconfined compressive strength (UCS), compressibility and microstructural characteristics are experimentally investigated in this study. The findings indicate that the incorporation of ARC, particularly with an alkaline residue (AR) content of less than 5%, significantly mitigates the shrink-swell behavior, reduces soil compressibility, and enhances the UCS of the soil. Beyond this threshold, the soil's strength decreases and compressibility increases with increasing W-D cycles. Microstructural analysis reveals the formation of beneficial cementitious products such as C-A-H, C-S-H, and AFt, which contribute to improve engineering performance in the early stages of W-D cycles. Nevertheless, as the W-D cycles continue, these beneficial products diminish, leading to an increase in soil cracks and pores, which indicates a degradation in soil performance. The research posits that ARC can effectively serve as a partial substitute for cement in the stabilization of expansive soils, with the amount of AR within 5%. Despite ARC's environmental advantages as an alternative binder, it may encompass harmful elements. Therefore, a comprehensive environmental risk assessment is essential. Further studies are needed to discern the enduring effects of environmental variables on soils stabilized with ARC.

Innovative Solution for Sulphate Challenges in Lime Stabilisation of Cochin Marine Clays

The current study focuses on the long term strength reduction in lime stabilised Cochin marine clays with sulphate content. By introducing 6% lime and 4% sulphates to untreated Cochin marine clay, the research aims to investigate the effect of sulphates in these clays. Unconfined compression tests were conducted on lime treated clay both with and without additives, immediately after preparation and over 1 week, 1 month, 3 months, 6 months, 1 year and 2 years of curing. Test results indicated that both sodium sulphate and lithium sulphate has a negative impact on the strength gain of lime stabilised clay. To address this issue, Barium hydroxide, in both its pure laboratory form and the commercial product known as "baryta," was incorporated into the lime stabilised soil. The study showed a consistent increase in shear strength with the addition of both barium hydroxide and baryta. When twice the predetermined quantity of baryta was added to lime stabilised clay, it outperformed pure barium hydroxide in terms of strength enhancement. Results of SEM and XRD analysis align with the strength characteristics. The cost-effective use of baryta offers a practical solution to counteract strength loss in lime stabilised, sulphate bearing Cochin marine clays.

Study on the Mechanical Properties of Modified Sludge Soil Based on an SM-C Modifier

The purpose of this study is to solve the problem of the harmless treatment of dredged silt and soil extraction during road construction in lake areas. The silt in the project area is used as the research material to evaluate its engineering applicability as an improved filling material for the roadbed of the lake’s surrounding road. Through indoor pretreatment and a series of mechanical performance tests, including compaction tests, unconfined compressive strength tests (UCS), bearing ratio tests (CBR), triaxial compression tests (CU consolidated undrained), and consolidation tests, we obtained key mechanical parameters of modified sludge soil, such as maximum dry density, optimal moisture content, unconfined compressive strength, bearing ratio, shear strength, and compression characteristics. The research results show that with the increase in modifier dosage, the optimal moisture content of modified sludge soil increases, the maximum dry density decreases, and its compressive strength and shear strength significantly improve. The CBR value also meets the technical requirements of each layer of the roadbed. Specifically, after 7 days of curing, the compaction degree of 10% modified sludge soil can exceed 96%, the unconfined compressive strength reaches 0.819 MPa, the CBR value reaches 17.5, the cohesion measured by triaxial tests is 78 kPa, the internal friction angle is 27°, and it exhibits low compressibility. These findings provide new solutions for environmentally friendly treatment, resource utilization, and road engineering in river and lake sediments.

Optimizing Soil Performance: Using Cement Kiln Dust along with Polymer Integration for Soil Stabilization

The present study explores contaminated soil collected from solid dump yard and its treatment with cement kiln dust in combination with epoxy liquid polymer. The study explores the improvement in mechanical and geotechnical characteristics of stabilized soil’s properties by adding Cement kiln dust and a liquid polymer in different proportions. The comparison for Maximum Dry Density, Unconfined Compressive Strength and California bearing ratio test for untreated and stabilized soil was done. The optimal mixtures of the 10% Cement kiln dust dosage indicate that with usage of cement kiln dust, decreases maximum dry density and optimum moisture content increases. However, Cement kiln dust and epoxy liquid polymer resulted in Unconfined compression test increase from 402.11 kN/m² to 1288 kN/m²and 1005.27 kN/m2 to 3221.825 kN/m2 for a curing time of 14 days and 28days. Moreover, the California bearing ration values also improved 38% with the addition of Cement kiln dust. Over curing periods of 7 and 14 days, Unconfined compression test and California bearing ratio test outcomes show increases due to the of cementitious materials. Additionally, the treated soil exhibits a notable reduction in harmful compounds like Chromium and Lead. The cohesion and frictional properties of stabilized soil showed significant improvement too.

Optimizing Soil Stabilization with Chitosan: Investigating Acid Concentration, Temperature, and Long-Term Strength.

Civil and geotechnical researchers are searching for economical alternatives to replace traditional soil stabilizers such as cement, which have negative impacts on the environment. Chitosan biopolymer has shown its capacity to efficiently minimize soil erosion, reduce hydraulic conductivity, and adsorb heavy metals in soil that is contaminated. This research used unconfined compression strength (UCS) to investigate the impact of chitosan content, long-term strength assessment, acid concentration, and temperature on the improvement of soil strength. Static triaxial testing was employed to evaluate the shear strength of the treated soil. Overall, the goal was to identify the optimum values for the mentioned variables so that the highest potential for chitosan-treated soil can be obtained and applied in future research as well as large-scale applications in geotechnical engineering. The UCS results show that chitosan increased soil strength over time and at high temperatures. Depending on the soil type, a curing temperature between 45 to 65 °C can be considered optimal. Chitosan biopolymer is not soluble in water, and an acid solution is needed to dissolve the biopolymer. Different ranges of acid solution were investigated to find the appropriate amount. The strength of the treated soil increased when the acid concentration reached its optimal level, which is 0.5-1%. A detailed chemical model was developed to express how acid concentration and temperature affect the properties of the biopolymer-treated soil. The SEM examination findings demonstrate that chitosan efficiently covered the soil particles and filled the void spaces. The soil was strengthened by the formation of hydrogen bonds and electrostatic interactions with the soil particles.

A Realistic 3D Grain-Based Modeling Approach for Reproducing the Mechanical and Failure Behavior of Brittle Granites

Exploring cracking behavior from mineral-scale do good help to understand the failure mechanism of rock materials. The present study proposes a realistic three-dimensional grain-based modeling (3D-GBM) method considering the actual distribution, geometry and mesoscopic mechanical properties of different minerals in granite samples. The geometrical characteristic and distribution were captured based on high-precision computed tomography (CT) scanning and polarized microscopy. The mesoscopic mechanical properties were measured using nanoindentation combined with the scanning electron microscope-energy dispersive spectroscopy scanning (SEM-EDS). The results indicate that the established model can realistically reproduce the mechanical and failure behavior of granite subjected to unconfined compression in terms of stress-strain curves, failure mode, crack evolution, and force transmission. Investigating crack propagation at mineral-scale shows that the relative damage degree is greater at weak boundaries (i.e., boundary related to mica) and relatively soft minerals (i.e., mica) than that of strong boundaries (i.e., quartz-quartz and quartz-feldspar) and stiffer minerals (i.e., quartz and feldspar). Grain boundaries and soft mica minerals play an important role in guiding and deflecting the crack propagation path due to the mismatch in elasticity and strength compared with the stiffer and harder minerals (i.e., quartz and feldspar).

Strength damage analysis on cement-and-fly ash-treated organic soils subjected to freeze–thaw cycles

ABSTRACT 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.

Using Reclaimed Asphalt Pavement in Backfilling Works Beneath the Structures

Reclaimed asphalt pavement (RAP) is produced in significant amounts. Nevertheless, the use of RAP is limited due to the absence of laboratory and field performance data. This research addresses laboratory and field tests to evaluate the use of RAP and various adapted mixtures in constructions such as road-bed layers and substitution layers. Modified proctor compaction, California bearing ratio, unconfined compression test, and static plate loading tests have been conducted on RAP, a mixture of RAP and crushed stone aggregates (CSA), and RAP stabilized with cement to satisfy the objective. Results have shown that 100% RAP material is suitable for use as a sub-base material. The ability of RAP material to be utilized as a cement-treated base layer is more pronounced when it is stabilized with cement (100% RAP + 8% and 10% cement). Utilization of 100% RAP stabilized with cement has been demonstrated to be economical in comparison with 100% CSA without cement. Finally, RAP material has shown good performance as a substitution layer.

From Waste to Strength: Applying Wastepaper, Fungi and Bacteria for Soil Stabilization

Biocementation is a promising soil stabilization technology that relies on microbiologically induced calcite precipitation (MICP). The addition of wastepaper was found to enhance the mechanical strength of biocemented soil. This study examined the effects of incorporating wastepaper into biocemented soil, focusing on the use of the ureolytic bacterium Bacillus licheniformis DSMZ 8782 and the yeast-like fungus Scytalidium candidum 3C for soil stabilization. The optimal wastepaper content was determined to be 2%, as it did not disrupt the uniform distribution of CaCO3 and contributed to improved soil strength. The combination of bacteria and fungi significantly increased the unconfined compression strength of samples containing 2% wastepaper (161.1 kPa) compared to untreated soil (61 kPa) and bacteria-only treatments (66.5 kPa), showing improvements of 2.6 and 2.4 times, respectively. Furthermore, we demonstrated that adding fungal biomass without wastepaper significantly improved the compressive strength, achieving a value of 236.6 kPa—nine times higher than untreated soil (26.4 kPa) and four times higher than soil treated with bacteria alone (60.6 kPa). This study identifies the optimal wastepaper content and highlights the potential of combining fungal and bacterial biomass for biocementation in soil stabilization.

Statistical damage model with strain softening for lime-stabilized rammed earth after elevated temperature

Many historical earthen buildings are damaged due to fire exposure in the past. It is important to understand the strength degradation of rammed earth after elevated temperature for guiding the strategy of building protection or rehabilitation. A total of 24 unconfined compression tests are conducted on lime-stabilized rammed earth specimens after elevated temperature up to 700°C. A quasi-linear reduction in strength and stiffness is found for rammed earth with the increase of temperature. At high temperature, the ductility of rammed earth is enhanced, e.g., strain at peak strength of 2.5% and 1.5% at 700°C and 20°C, respectively. Microstructural analyses demonstrate that with the increase of temperature, the specimen becomes more porous with reduced calcium carbonate precipitation, explaining the strength reduction. A new thermal damage model is proposed to describe the behavior of rammed earth after elevated temperature, in which the closure of pores is captured to show unrecoverable deformation, and the skeleton part is simulated using a thermal damage variable in a statistical manner to present the damage evolution (strain softening). By comparing with the measured stress-strain curves, one can confirm that the proposed method can provide effective prediction for the response of rammed earth after elevated temperature.

Enhancing the Geotechnical Properties of Expansive Soils through Coconut Shell Ash Treatment: An Experimental Investigation

Expansive Soils (ES) present a significant challenge to civil engineering projects worldwide due to their propensity to undergo volumetric changes in response to fluctuations in the moisture content. This study examined the potential of Coconut Shell Ash (CSA) as a soil stabilizer to mitigate the adverse effects of ES. The objective was to conduct a systematic evaluation of the impact of CSA on a range of soil properties, including the plasticity index, compressive strength, shear strength, swelling potential, and compaction characteristics, across a diverse array of soil types. This study adopted a comprehensive methodology, which involved the laboratory testing of soil samples with varying proportions of CSA. The tests included the determination of the Atterberg limits, the evaluation of the compaction properties, unconfined compression tests, and swelling tests. The findings revealed significant variations in the soil properties in response to the CSA content. The plasticity index responses exhibited a range of subtle changes, with a downward trend at lower CSA concentrations and more complex behaviors at higher concentrations. The compaction characteristics exhibited alterations in the optimum moisture content and maximum dry unit weight, indicating changes in soil density and stability. Similarly, the compressive and shear strength properties exhibited fluctuations with varying CSA content, underscoring the necessity for a comprehensive assessment of soil stability under CSA-treated conditions. Additionally, swelling tests demonstrated the potential of CSA to mitigate soil expansiveness, with lower swelling percentages observed in treated soils. This study highlights the importance of considering the soil type, CSA content, and engineering requirements to optimize the effectiveness of CSA in soil stabilization applications.

Utilisation of Class-F fly ash in xanthan gum–amended neutral or acidic soils

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 hydrolyse, thereby weakening the efficacy of soil improvement. In this study, the feasibility of utilising 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 increasing soil acidities, the beneficial effect of FA on the geotechnical performances of XG-amended soils grew. The improvement in both mechanical strength and compressibility of XG-amended 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, for example, biopolymer-based soil amendment in acidic soils.

Assessment of the Numerical Behavior of Remolded and Undisturbed Clayey Soil

Abstract The simulation of soil behavior using finite element analysis depends mainly on the input parameters considered in analysis, moreover, in the case of clayey soil, most of the experimental studies for small models are performed on remolded samples because of difficulty of providing undisturbed soils. This leads to unreal results for numerical analysis as the validation process of numerical results is performed on remolded sample. It was conducted experimental work on remolded clay including load-settlement tests of model footing at three states on undrained cohesion (cu), and then performed unconfined compression tests at the same undrained cohesion. After that, performing numerical modeling of the model footing from the data of unconfined compression tests. It was observed that the value of the modulus of elasticity in clay from unconfined test considering the initial tangent is low for remolded state compared to the findings of the previous research. Moreover, great care must be taken in selecting the elasticity modulus in performing the numerical analysis of the clayey soil, however, for undisturbed clay it is greater than remolded, the difference in the value is up to two times for stiff clay in the case of large scale footing, while it was reaches about four times.

Bio-cementations: A Review on Enzyme and Microbially Induced Calcite Precipitation Mechanisms and Applications in Geotechnical Engineering

Modern methods to improve soil must deal with sustainable and green building purposes, and precipitated calcite is the most modern bio-cementation method to improve soil sustainably. Enzyme-induced calcite precipitation and microbially-induced calcite precipitation are precipitated calcite's best branches in bio-cemented soil improvement. EICP and MICP contain calcium chloride, urea, water, urease enzyme and other chemical materials (for MICP As nutrients for bacteria) that are mixed together to precipitate calcium carbonate in the soil. The precipitated calcium carbonate was worked as a binder between soil particles, filling the void and improving the soil's properties. By utilizing this technique in the field, several researchers were able to achieve favorable outcomes in the areas of soil improvement and other engineering applications, including concrete repair and other applications, while also taking into consideration the objectives of sustainability. treatment carried out on soils with one or many cycles of the treatment solution. The treatment revealed a significant improvement in the value of unconfined compression strength, compared to untreated soils. During certain experiments, the unconfined compression strength revealed that soils treated with the enzyme approach exhibited higher values compared to soils treated with a mixture containing a certain proportion of regular Portland cement. The encouraging outcomes that were achieved through the utilization of this test in both the laboratory and the field can be utilized in large-scale operations. Till now, this method has been considered under study. In Iraq there are no any research in term of EICP treatment while there are several research about using MICP in soil treatment.

Rheology Assessment of Mortar Materials for Additive Manufacturing

Abstract: This review article discusses the relevant rheological tests to evaluate the properties of compositions applied to the 3D printing of concrete (3DCP). These materials must rapidly develop rigidity and resistance, avoiding the collapse of the printed structure, with suitable buildability and other state properties, such as extrudability. A good balance must be maintained between properties and rheological parameters, such as yield stress and viscosity. Cohesion, Young's modulus, and thixotropy are also among the parameters used in these evaluations. The rheological tests addressed are the rheometer, direct shear test, uniaxial unconfined compression test, and penetration test. Their limitations must be taken into account to obtain accurate values of the rheological parameters. It was found that the most used test is the rheometer, and the test that needs to be further studied is the penetration test. Hence, it is recommended to search for a more expeditious method related to the rheological assessment to facilitate obtaining the associated parameters in a simple way.

Optimization of Strength Factors in Microbial Solidification of Uranium Tailings Using Response Surface Methodology

Once the uranium tailings dam collapses, it will cause great harm to the surrounding ecological environment and people’s safety. This study experimentally investigates microbial grouting reinforcement of uranium tailings to advance microbial reinforcement technology and facilitate its large-scale engineering applications. The study simulated original environmental conditions and used tap water to prepare the culture medium and cement without sterilization or pH adjustment. The response surface method was employed to optimize parameters affecting the immobilization of uranium tailings, and the results were verified. The mechanical strength of the immobilized uranium tailings was determined through unconfined compression tests, while their microstructures were analyzed using X-ray diffraction, scanning electron microscopy and computed tomography. The findings indicate that the response surface method optimizes test parameters accurately, with the concentration of the cementation solution and the grouting amount being two main factors influencing the compressive strength of the solidified uranium tailings. Without pH adjustment, sterilization, or slurry modification using tap water, the bacteria−cementation ratio was set at 1, the concentration of the cementation solution was 1.3 mol/L, and the grouting volume was 70 mL. Notably, the strength of the uranium tailings increased 27-fold after seven rounds of grouting compared to the water-only group, and 6-fold compared to the cementation solution-only group. This study contributes to reducing the complexity associated with the application of microbial grouting technology in soil stabilization and provides valuable references for other engineering practices.

Mechanical Behavior, Compressibility, and Microstructural Analysis of Problematic Soil Through a Green Soil Stabilization Approach.

Researchers have explored various materials and methods to improve the strength and stabilization of peat soil for construction. Deep peat soil's significant compressibility, low bearing capacity, and high creep potential present major challenges in geotechnical engineering. In this paper, the unconfined compression strength (UCS) and oedometer testing were conducted to determine peat strength and compressibility behavior after being stabilized with a bio-cement called vege-grout, derived from fermented vegetable waste. Soil stabilized with 5%, 10%, 15%, 20%, and 25% vege grout was cured for up to 8 weeks before undergoing UCS testing. The finding showed that, in between 4 to 6 weeks of the curing period, the UCS of the peat stabilized with vege-grout exhibiting substantial mechanical strength at all vege-grout inclusion levels. The results showed optimum strength improvements, with a 449% increase in UCS at 15% vege-grout after 8 weeks. At the optimal percentage, vege grout's cementitious properties bind peat particles, densify the matrix, and enhance soil strength and load-bearing capacity. The coefficient of consolidation (Cv) also improved, reducing settlement from 23.34 ± 7.8 m2/year to 7.13 ± 3.5m2 per year over increasing effective stress. The significant improvement in strength and compressibility of peat after treatment with 15% vege grout demonstrates the effectiveness of vege grout as a peat stabilizer and highlights its potential as an alternative to chemical stabilizers for foundation applications.

Porosity and cement controlling the response of artificially cemented tailings under hydrostatic loading to high pressures

Cemented tailings find various applications in mining, such as open-pit and underground backfill, dam decommissioning and filtered tailings stacking. This research investigates the compression behaviour of iron ore tailings (IOT) mixed with distinct amounts of Portland cement and compacted in different conditions through isotropic compression, pulse velocity, and unconfined compression tests. The results show the adequacy of the porosity/cement index (η/Civ) in predicting elastic and plastic characteristics of compacted filtered IOT - Portland cement blends, an original correlation that has not been reported by previous work. This index is useful in selecting the cement content and target density for essential parameters required to design cemented IOT stacks. Besides, both cement addition and compaction have promoted the tailings isotropisation (conversion of an anisotropic system to an isotropic one). The evolution of the Post-Yield Compression Line (PYCL) with cementation is shown. Finally, it is demonstrated that distinct initial (after compaction) porosities of uncemented specimens reach a unique PYCL after isotropic pressures above 100 MPa, and cemented specimens do not reach a unique PYCL even at 120 MPa of isotropic pressures. The results underscore the requirement of rigorous compaction control in the field and offer a methodology for the dosage and technological control of artificially cemented tailings.

Unconfined compression tests of cement-treated soil with carbon dioxide containment

Unconfined compression tests of cement-treated soil with carbon dioxide containment

Optimal Utilization of Biochar, Polyacrylamide, and Straw Fiber for Subgrade Stabilization of Forest Roads

Subgrade stabilization is crucial for forest road construction, especially in Northeast China and the Russian Far East, with great economic growth potential. This study explored a novel and green solution of integrating biochar (BC), polyacrylamide (PAM), and straw fiber (SF) in the form of a ternary composite for stabilizing forest subgrade soil in cold regions. Using central composite design-based response surface methodology, the optimal mix ratio design was obtained, and the composite stabilizer was designated as BPS. Afterward, the stabilizing performance of BPS was studied by conducting an unconfined compression strength (UCS) test. The results showed that the optimum composition of BC:PAM:SF stood at 81:9:10. The UCS and deformation modulus with 3% BPS at 28 days reached 565.42 kPa and 17.24 MPa, respectively, which were 3.36 and 6.05 times higher than those of the untreated samples. The BPS-treated soil also possessed better resistance to freeze–thaw cycles. The freezing–thawing-induced loss ratio of strength was 49.3% lower than that of natural soil. Moreover, empirical models for the UCS of BPS-stabilized soil, as well as its relationships with the modulus, were established and validated by data in the literature. Finally, the “filling, cementing, and reinforcing” stabilization mechanism of BPS was elucidated by scanning electron microscopy analysis.