Soil stabilization using lime precipitation technique

Expansive soil is one among the problematic soils that has a high potential for shrinking when it is dried and swelling due to change of moisture content. Expansive soils (clays) popularly known as black cotton soils in India. Due to alternate swell-shrink behavior of expansive soils causes, distress in the foundation structures such as buildings, pavements of earth retaining walls etc. Understanding the behavior of expansive soil and adopting the appropriate control measures have been great task for the geotechnical engineers. Extensive research is going on to find the solutions for black cotton Soils. In this study, Nylon Fiber has been used in the form of fibers. The effect of the stabilisation was evaluated through carrying out standard laboratory tests. The tests included the standard compaction test, unconfined compressive strength (UCS) test, California Bearing Ratio (CBR) test. The main motive of this research is to investigate the optimal combination of Nano-Silica and Nylon Fiber with clay soil. The engineering properties such as liquid limit, plastic limit, maximum dry density and unconfined compressive Strength (UCS) are analyzed with virgin soil, the soil with Nano-Silica and combination of soil with Nano- Silica and Nylon Fiber. Three different combinations of Nano-Silica at different percentages 2%, 4% & 6% are used in integration with Nylon Fiber is used in different percentages such as 2.0%, 3.0% and 4%. From these experiments, it has been analyzed that with the increase of Nylon Fiber content in addition to Nano-Silica, the UCS increases and maximum value of UCS is obtained at 6% of Nano-Silica with 2.5% of Nylon Fiber. The intermixing of Nylon Fiber with the soil acts as a reinforcing material in binding the soil particles and the ‘bridge effect’ of fiber reinforcement in soil impedes the further development of tension cracks. Key Words: Compaction test, CBR, UCS, Nano Silica, Nylon Fiber

Lime stabilization prevails to be the most widely adopted in situ stabilization method for controlling the swell-shrink potentials of expansive soils despite construction difficulties and its ineffectiveness in certain conditions. In addition to the in situ stabilization methods presently practiced, it is theoretically possible to facilitate in situ precipitation of lime in soil by successive permeation of calcium chloride (CaCl2) and sodium hydroxide (NaOH) solutions into the expansive soil. In this laboratory investigation, an attempt is made to study the precipitation of lime in soil by successive mixing of CaCl2 and NaOH solutions with the expansive soil in two different sequences. Experimental results indicated that in situ precipitation of lime in soil by sequential mixing of CaCl2 and NaOH solutions with expansive soil developed strong lime-modification and soil-lime pozzolanic reactions. The lime-modification reactions together with the poorly developed cementation products controlled the swelling potential, reduced the plasticity index, and increased the unconfined compressive strength of the expansive clay cured for 24 h. Comparatively, both lime-modification reactions and well-developed crystalline cementation products (formed by lime-soil pozzolanic reactions) contributed to the marked increase in the unconfined compressive strength of the expansive soil that was cured for 7–21 days. Results also show that the sequential mixing of expansive soil with CaCl2 solution followed by NaOH solution is more effective than mixing expansive soil with NaOH solution followed by CaCl2 solution.

Utilization of fly ash with and without secondary additives for stabilizing expansive soils: A review

Methods commonly used to evaluate the improvement of lime-treated expansive soil include swelling characteristics and unconfined compressive strength. In the field, lime-treated expansive soils are in compacted unsaturated state. Soil water characteristic curves (SWCCs) represent a key parameter to interpret and describe the behavior of unsaturated expansive soil. This paper investigates the use of SWCC as a technique to evaluate improvements acquired by expansive soil after lime treatment. Three different lime contents were considered 2%, 4% and 6% by dry weight of clay. Series of tests were performed to determine the SWCC for the different lime content under curing periods of 7 and 28 day. Correlations between key features of the soil water characteristic curves of lime treated expansive soils and basic engineering behavior such as swelling characteristics and unconfined compression strength were established. Test results revealed that initial slope (<TEX>$S_1$</TEX>), saturated water content (<TEX>$w_{sat}$</TEX>), and air entry value (AEV) play an important role in reflecting improvement in engineering behavior achieved by lime treatment.

Expansive soils have a high tendency for volume change in case of fluctuations in moisture content, potentially causing significant damage to light structures, particularly road pavements. This paper investigates the influence of waste paper sludge () as an alternative sustainable stabilizer on the volume change behavior of expansive road subgrade soils of different origins. For this purpose, was added to the expansive soils at ratios of 3%, 6%, 9%, 12%, and 15% by dry weight of the soils. A series of Atterberg’s limit, swelling, shrinkage, compaction, and consolidation tests were performed on pure soils and soil specimens with to attain a comprehensive understanding of the role that plays in the volume change behavior of expansive soils. The experimental test results showed that the addition of led to a considerable decrease in the plasticity and swell-shrink potentials of subgrade soils. The consolidation settlement of expansive road subgrades was also reduced to some extent with . Moreover, the statistical analysis of the test data indicated a significant relationship among different swelling-shrinkage parameters. The experimental results presented here suggest that the may be a cost-effective, environmentally friendly, and sustainable stabilizer to reduce the volume change sensitivity of expansive road subgrade soils.

Expansive soils are responsible for extensive infrastructure damage worldwide, prompting the urgent search for innovative, sustainable stabilization methods. Nanomaterials have emerged as a promising next-generation solution capable of addressing both performance and environmental challenges. This review investigated the use of nanomaterials such as nano-silica, nano-alumina, nano-copper, nano-MgO, and nano-calcined clay and terrasil, and a combination of nanomaterials with lime or cement (hybrid) as sustainable stabilizers. It was found that plasticity index (PI) decreases by 20-60%, optimum moisture content decreases of 10-12%, and maximum dry density increases of 5-10% for ≤1% nonadditive. Swell potential and swell pressure typically reduced by 20-30% or more at dosages ≤1-1.5%, while hybrid mixes achieve even higher reductions. Strength gains were particularly significant: unconfined compressive strength (UCS) commonly doubles in the short term and exceeds 5 times untreated values with long-term curing, reaching up to 6 times with hybrid stabilization. Similarly, soaked CBR values improve by about 2 times with nanomaterials alone and up to 5-6 times with hybrid systems. These mechanical enhancements were supported by microstructural evidence showing pore filling, formation of cementitious gels (CSH, CAH, MSH, CASH), and surface coatings that densify soil, strengthen particle bonding, and reduce water ingress. Performance was strongly dosage- and material-dependent, with excessive amounts sometimes leading to agglomeration and reduced efficiency. Overall, findings confirmed that nanomaterials, especially when combined with lime or cement, provided a reliable, sustainable, and long-term stabilization approach, offering substantial improvements in expansive soil behavior and geotechnical infrastructure performance.

Expansive soils present significant design and maintenance challenges because of their pronounced shrink-swell behaviour under changing moisture regimes. This paper investigates the mechanisms by which fly ash—an industrial by-product—improves the engineering properties of expansive soils. A comprehensive laboratory program was carried out on an expansive clay (CH) stabilised with fly ash at dosages of 0, 5, 10, 15, 20, 25 and 30% by dry weight. Tests included Atterberg limits, standard Proctor, unconfined compressive strength (UCS) at 7 and 28 days, California Bearing Ratio (CBR), and free swell index. Results, supported by microstructural interpretations, demonstrate a multimechanistic improvement in soil behaviour: particle packing and filler effects, cation exchange and flocculation reducing diffuse double-layer thickness, and long-term pozzolanic reactions creating cementitious C–S–H and C–A–H phases. Collectively, these mechanisms reduce plasticity and swelling potential while increasing strength and stiffness, with an optimal fly ash range observed around 15–20% for the synthetic dataset presented. The study also discusses the sustainability benefits of using fly ash in geotechnical practice.

Stabilization of expansive subgrade soil by using fly ash

This study focuses on the advancements of characterization of unsaturated expansive soils which would allow better prediction of its swelling and mechanical behaviours. The paper has been divided into three parts. Firstly, a novel model is developed by considering two micro-soil parameters, soil-specific surface area and internal pore size distribution, to predict the natural swelling in expansive clayey soils. The model was validated by comparing the predictions with experimental results for eight soils. Secondly, the paper deals with the diffused-double-layer (DDL) theory-related electrostatic forces from individual clay minerals of expansive soils and their influence on soil swelling. A DDL-based model was also developed, which was validated for swell prediction for fourteen expansive soils. A good correlation was observed for both models when the results were compared with experimental results. Finally, the paper demonstrated the use of vapour pressure technique to control suction beyond 5 MPa for performing suction-controlled repeated load triaxial (RLT) test at high suction state. This novel technique mitigates the limitation of axis-translation technique for maintaining suction till the air-entry-value (AEV) of the ceramic disk. These new models and unsaturated laboratory testing techniques would aid in better characterization of expansive soils in their unsaturated state. This would also provide accurate prediction of swell and stiffness behaviours of soils, thereby reducing the uncertainties in the design of civil infrastructure built on expansive soils.KeywordsUnsaturated soilsSwellingExpansive soilsResilient modulusHigh-suction state

Expansive soils pose significant geotechnical challenges due to their time-dependent swelling behaviour, which can cause severe infrastructure damage. The ability to predict swell potential accurately is vital for effective designs and risk mitigation. This study combines constitutive modelling with machine learning to enhance the predictive capability of swell behaviour in expansive clays. The constitutive swell model introduced by Liu et al. was evaluated by experimental one-dimensional swell tests, demonstrating its ability to accurately predict time-dependent swelling behaviour under varying surcharge pressures (SPs). A data-driven decision tree (DT) framework was created to relate key swelling parameters of Liu et al. model to fundamental soil index properties such as moisture content, SP, and plasticity index to improve predictive accuracy. Based on these measurable index properties, the model successfully captured the final swell potential of clay samples. Independent validation using literature datasets demonstrated high accuracy, with R2 &amp;gt; 0.97 for predicting final swell potential. The proposed DT framework provides geotechnical engineers with a practical tool to assess final swell potential based on fundamental soil index properties, aiding in better infrastructure design and mitigating the risks associated with shrink-swell behaviour.

Expansive soils are inherently known for exhibiting significant volumetric change in response to slight variation in the moisture content. In this study, medical waste material in the form of bottom ash (BA) was investigated as a potential stabilizer for expansive soil. The unique characteristics of BA, such as its cost-effectiveness and availability as a residue, establish it as a potent stabilizer for expansive soils compared to other alternatives. The locally collected expansive soil from Muscat was identified to be of poorly clay type with high plasticity (CH) based on the USCS, and A-6 according to AASHTO classification. The BA was obtained from the medical waste treatment plant of the Be’ah Company in Oman. Samples were prepared by treating the expansive soil with BA in percentages of 6%, 8%, 10%, and 12% by mass. It was found that the pH level of the treated soil continued to reduce with increasing BA content, which was indicative of the reaction between the expansive soil and BA particles. The unconfined compression strength (UCS) test yielded a 57.63% increase over that of untreated expansive soil at 28 days of curing. Similarly, the California Bearing Ratios (CBR) of the treated soils were up to two times higher than the untreated soil, both in its unsoaked and soaked conditions. Based on the results of the UCS, CBR and linear shrinkage tests, the optimum quantity of BA required for treating the expansive soil was determined to 10%, beyond which no further enhancement in the UCS, CBR or shrinkage attributes of the soil was observed. Overall, the outcomes of this research highlight the potential of medical waste material, specifically bottom ash, as a sustainable stabilizer for expansive soil in construction applications.

Expansive soil exhibits remarkable characteristics of water absorption expansion and water loss shrinkage, rendering it susceptible to cracking under the alternating dry–wet environments of nature. The generation and development of cracks in expansive soil can result in catastrophic engineering accidents such as landslides. Vegetation protection is an important approach to stabilizing expansive soil slopes and fulfilling ecological protection requirements. In this study, through indoor experiments and theoretical analysis methods, the effects of Cynodon dactylon roots on the crack development and shear strength of expansive soil subjected to dry–wet cycles were analyzed, and the relationship between the crack development and shear strength decay in root-doped expansive soil was explored. Furthermore, the mechanism of vegetative root system action was elucidated. The results show that the Cynodon dactylon root system exerts a significant inhibitory effect on crack development in expansive soil. The crack indexes of root-doped expansive soil exhibit significant phase characteristics during the process of dry–wet cycles. The crack-blocking and reinforcing effect of the root system becomes pronounced as the root-to-soil mass ratio increases and the root diameter decreased. Moreover, the process of crack development in expansive soil is accompanied by a decrease in soil shear strength. The quantitative relationship between crack development and shear strength decay can serve as a basis for predicting the stability of slope soil. Overall, the results highlight the potential of vegetation-based approaches in protecting slopes with expansive soils and have practical implications for ecological protection and engineering design in areas with expansive soils.

The study involved the utilization of an industrial waste product, Phosphogypsum (PG) as an additive to lime for the stabilization of soil. Three lime dosages, viz. initial consumption of lime (ICL), optimum lime content (OLC) and less than ICL (LICL) were adopted for stabilizing the soil. The study investigated the stress-strain characteristics of soil composites stabilized with these three lime contents modified with optimum dosages of PG. Mineralogical studies were performed on the spent samples used for a series of determinations of unconfined compression strength tests with various combinations of lime and optimum PG content. The addition of an optimum dosage of PG resulted in an early strength gain of 8.8%, 14.1% and 13.9% and a delayed strength gain of 9.9%, 19% and 19.7% for 3%, 5.5% and 7% for the lime-stabilized soil, respectively. It was found that the addition of PG to the lime resulted in enhanced stiffness, residual strength and reduced brittleness due to the PG amendment of the stabilization reactions. However, in terms of the overall improvement of soil properties, the most favorable benefit was obtained by optimal PG modification of ICL rather than OLC. Microanalysis of the X-ray diffraction scatter also supported the results revealed through stress-strain characteristics. ICL with its optimal PG dosage showed a better progression of pozzolanic reactions when compared to the other two in terms of reduction of peaks of soil minerals and increase in peaks of CSH.

Sustainable use of soda lime glass powder (SLGP) in expansive soil stabilization

Freeze-thaw performance of a cement-treated expansive soil