Optimum Water Content Research Articles

A new simple index for characterizing the labile heavy metal concentration in soil by diffusive gradients in thin films technique

Diffusive gradients in thin films technique (DGT) is recognized as a more reliable method for determining labile heavy metal (HM) concentration in soil than traditional destructive methods. However, the current DGT measurement index, CDGT, theoretically underestimates the true labile concentration (Clabile) of HMs in soil and lacks direct comparability with the conventional soil HM content indices due to unit differences. Here, we proposed CDGT-W, a new simple index which is defined as the HM accumulation in the binding layer, normalized to the weight of soil (optimized water content = 100% of the maximum water holding capacity) filled in the open cavity-type DGT device over a specified deployment time (optimized time = 24 h). The procedure for measuring CDGT-W is analogous to that of CDGT but includes precise determination of water content (water/dry soil) and the mass of soil filled in the cavity. We conducted measurements of Cu, Pb, Cr(Ⅵ) and As(V) as CDGT-W, CDGT, solution concentration (Csoln), and CaCl2 extractable concentration (CCaCl2) on three soils with a diverse range of HM concentrations. CDGT-W showed significant linear correlations with all other tested indexes. The ratios of CDGT-W to CCaCl2 varied between 0.30 and 0.98 for all HM–soil combinations with only one exception, a range much greater than CDGT/Csoln (typically <0.1) but lower than 1. This suggested that CDGT-W may more accurately reflect Clabile than CDGT (theoretically underestimates Cliable) and CCaCl2(likely overestimates Cliable). Additionally, CDGT-W measurements for these four HMs exhibited a broad measure concentration range and a low detection limit (mg/kg level). Consequently, CDGT-W may offer a more reliable alternative to CDGT for characterizing Clabile in unsaturated soils.

Effect of Quarry Dust in Compaction Characteristics of Loose Sandy Soil from a Local Paddy Field

Loose Soils found in locations such as paddy fields deemed as unsuitable for construction works in general. Loose sandy soil is characterized by its granular and non-cohesive structure, which results in a high porosity and low bulk density. In construction, achieving adequate compaction is essential for enhancing the load-bearing capacity and stability of the soil. Therefore, if the geotechnical properties of these soils can be improved using a waste material such as quarry dust, which is a byproduct of the construction aggregate crushing process, it can offer a significant advantage. This study aims to assess the effect of quarry dust in maximum dry density and optimum moisture content of sandy soils from a local paddy field. Quarry dust is mixed with the soil in proportions of 10%, 20%, 30%, 40% &amp; 50% by weight. Laboratory tests such as sieve analysis, specific gravity, Atterberg limit and proctor compaction tests were conducted on soil and soil – quarry dust. The results indicated that maximum dry density continues to increase with the addition of quarry dust while optimum water content reduces up to the addition of 30% quarry dust. The findings support that compaction characteristics can be improved using quarry dust which increases the suitability of the soil for construction purposes.

Influence of desiccation during freeze-thaw cycles on volumetric shrinkage and tensile strength of compacted clayey soils

Tensile strength is a crucial mechanical property that governs the initiation and propagation of soil tensile cracks. With the global prevalence of warming effects and extreme climatic events, the recurrent freeze-thaw (F-T) cycles intensify the complex evolutions of soil pore structure and tensile strength in regions with widespread seasonal freezing or permafrost active layers. This study investigates the combined influence of F-T cycles and desiccation on the tensile strength of clayey soils. Specimens with varying compaction water contents (14.5%, 16.5%, and 18.5%) and dry densities (1.5 Mg/m3, 1.6 Mg/m3, and 1.7 Mg/m3) were prepared and subjected to cyclic F-T actions. A direct tensile test apparatus was utilized to measure tensile strength (σt) along the desiccation path. Additionally, the changes in void ratio (e) and suction (s) during F-T cycles were analyzed to understand the mechanism behind the changes in σt. Experimental results reveal that as the number of F-T cycles (N) increases, water content (w) declines at a decreasing rate and eventually stabilizes. With increasing N, the tensile displacement at failure and σt show a pattern of initially decreasing and subsequently rising, with the inflection point typically around 1.5%–2.0% lower than the compaction water content (w0). Under a few F-T cycles, soils compacted at the optimum water content and on the wet side exhibit higher void ratio and lower suction and σt compared with dry-side compacted soils. However, this trend reverses with further increasing N. In addition, σt increases as compaction dry density (ρd0) rises within all water content ranges, primarily attributed to the significant interparticle cohesion controlled by a dense pore structure. The variation of σt under F-T and associated desiccation is linked with the microstructural evolution characterized by aggregates, interaggregate pores and water-bridges. It is recommended to compact soils both on the dry side of the optimum water content and at the maximum dry density to enhance the freeze-thaw resistance of earth-works in seasonally frozen regions.

Experimental study on the interface characteristics of geogrid-reinforced gravelly soil based on pull-out tests

The factors influencing geogrid–soil interface characteristics are critical design parameters in some geotechnical designs. This study describes pull-out tests performed on gravelly soils commonly encountered in the Xinjiang region and reinforced with two types of geogrids. The factors affecting the geogrid–gravelly soil interface properties are investigated with different experimental loading methods (pull-out velocity, normal stress), geogrid types, and soil particle size distributions and water contents. The ultimate pull-out force increases with the normal stress and pull-out velocity. Furthermore, with increasing coarse particle content and water content, the ultimate pull-out force increases and then decreases sharply. Based on these research results, this paper provides reasonable parameters and recommendations for the design and pull-out testing of reinforced soil in engineering structures. In reinforced soil structure design, the grid depth should be increased appropriately, and the coarse particle content of the overlying soil should be between 30 and 40%. During construction, the gravelly soil should be compacted to the maximum compaction at the optimal water content, and the structure should have a reasonable waterproofing system. According to the calculation results of the interface strength parameters, the uniaxial geogrid–gravelly soil interface has a high cohesive force csg, which should not be ignored in reinforced soil structure design.

Laboratory and field measurements of water relations, photosynthetic parameters, and hydration traits in macrolichens in a tropical lower montane rainforest in Thailand.

Ecophysiological studies of lichens in tropical Asia are rare, and additional studies can increase the understanding of lichen life in this region. The main aim of this study was to observe the relationships between water availability and photosynthetic parameters, as well as hydration trait parameters, in macrolichens during the rainy and dry seasons in a tropical forest. A total of 11 lichen species growing in a lower montane rainforest in Thailand were collected and studied. The results clearly showed that the specific thallus mass (STM), net photosynthetic rate (Pn), the potential quantum yield of primary photochemistry (Fv/Fm), chlorophyll content, and carotenoid content of almost all lichens were lower in the dry season than in the rainy season. Field measurements in the dry season revealed that only the foliose chlorolichen Parmotrema tinctorum was metabolically active and exhibited slight carbon assimilation. In the rainy season, all lichens started their photosynthesis in the early morning, reached maximal values, declined, and ceased when the thalli desiccated. The photosynthetically active period of the lichens was approximately 2-3h in the morning, and the activities of the cyanolichens ended approximately 30min after the chlorolichens. The hydration trait parameters, including the STM, maximal water content (WCmax), and water holding capacity (WHC), were greater in the cyanolichens. In addition, the maximal Pn (Pnmax) and optimal water content (WCopt) for Pn were also greater in the cyanolichens, but the maximal Fv/Fm (Fv/Fmmax) was lower. The cyanolichens compensated for their inability to use humid air to restore photosynthesis by having higher water content and storage, higher photosynthetic rates, and longer photosynthetically active periods. This study provides additional insights into lichen ecophysiology in tropical forests that can be useful for lichen conservation.

How to reduce waste using black soldier fly larvae and produce a high-quality product

Abstract With the growing human population the demand for protein is rising and waste production is increasing. Insects can provide a sustainable solution for both problems and produce food (protein and fat) from waste. Our study tested the ability of the black soldier fly (BSF) to reduce agricultural waste and produce a high-value product rich in unsaturated fatty acids. Initially, we tested the diet limitations of the larvae. We tested the composition of the agricultural wastes (brewery and avocado wastes) and the ability of the larvae to grow on them. A mixed diet based on brewery and avocado wastes was composed to increase larval weight and improve their fatty acid composition. The larvae were limited by the protein and water content of the diet (7% and 70%, respectively). The mixed diet that met the requirements of a minimal ratio of protein (7%) and optimal water content (70%), did not improve larval weight but increased the unsaturated fatty acid content. Therefore, using BSF larvae to reduce waste and produce protein is feasible; however, the end product should be considered when composing their diet from a waste mixture.

Roles of corn starch and gellan gum in changing of unconfined compressive strength of Shanghai alluvial clay

Abstract This article aims to study the effects of corn starch and gellan gum (gellan glue) on the unconfined compressive strength of alluvial soft clay in Shanghai. Firstly, starch and gellan gum were evenly mixed into Shanghai cohesive soil in a certain proportion, and soil samples were prepared according to the optimal water content. Secondly, the unconfined compressive strength test was carried out according to the content of corn starch, gellan glue, and curing time. The strength characteristics of Shanghai soft clay under various test conditions were studied. Finally, the software for statistics and drawing was used to perform regression analysis and drawing on the experimental data. The results showed that in the unconfined compressive strength test, when the curing time was 28 days, the starch content was 3% mixed with 0.5% gellan gum, the unconfined compressive strength of the sample was the highest, and generally, it seems that the strength keep increasing with curing time.

The Experimental Analysis Of The Effect Of Geotextile Reinforcement Of Cohesive Soil On The Settlement And Bearing Capacity

The properties of the soils in terms of engineering must be identified for the design of buildings and foundations to be constructed in areas where soft clay or loose sand ground conditions predominate. The engineering properties of different soils diversify in a broad range based on the sort of the ground in addition to the terrain conditions like the degree of compaction, water content, consolidation pressure, loading, and drainage conditions. Grounds may not perpetually hold the desired properties. Thanks to the structures to be built on the grounds, excessive settlements or collapses can happen because of inadequate ground bearing capacity. In order to reinforce the weaknesses of the soils, either the application of a deep foundation should be employed, or a proper improvement method should be applied to the foundation ground.In the study, the effect of the reinforcement of the geotextile, which has become widespread, on the clay ground was examined. Experiments have been conducted to identify the index properties, settlement, and sliding resistance parameters of soils on Süleyman Demirel University Soil Mechanics Laboratory on clay samples from the provinces of İzmir and İstanbul. Following the identification of the settlement and sliding values, the geotextile was added, and its effect on the settlement and bearing strength values was analyzed. Experiments were conducted by placing single-layered and double-layered geotextile in the samples with the values of optimum water content, the water content 10% more than the optimum value, and the water content 10% less than the optimum value.The results achieved after laboratory experiments are displayed with graphics and compared with each other.

Investigation of Cement and Fly Ash on the Improvement of Fine Sand Soil

Soil stabilization problems like liquefaction, bearing capacity, permeability, excessive settlement and swelling can be solved by improving soil’s engineering properties by using various methods. The use of fly ash as a stabilizer has become popular in recent years since it is eco-friendly and effective on soil stabilization, especially for fine-grained soils. This study investigated the reuse of fly ash as a stabilizer (5–25% by weight) and cement (constant 3% by weight) as an activator to enhance the geotechnical properties of poorly graded sand (SP). Standard proctor tests were conducted to determine optimum water content and maximum dry unit weight, followed by direct shear box, falling head permeability and CBR tests at the determined optimum water content. Direct shear box experiments were carried out at two relative densities (30% and 80%) and CBR experiments were performed after 7 and 28 days of curing time. The results demonstrated that the addition of fly ash and cement improved the geotechnical properties, including shear strength, permeability and bearing capacity of the fine sand soil.

Validation of the recycled backfill material for the landslide stabilization at a railway line

In mountain areas landslides many times endanger safety of transport infrastructures, and these must be stabilized with retaining wall structures. In this paper the validation of a new composite as a backfill material for landslide stabilization with a large scale demo retaining wall is presented. The new composite was made from residues of paper industry, which uses for its production deinking process. New composite was validated with the laboratory tests, construction of small demo sites and at the end with a large demo retaining wall structure with a length of 50 m. It was concluded that the paper sludge ash and the paper sludge are in proportion 70:30, compacted on the optimal water content and maximum dry density, reached sufficient uniaxial compressive and shear strength. However, the composite's hydration processes required the definition of an optimal time between the composite mixing and installation. In 2019, the retaining wall structure from the new composite was successfully built. The large demo structure is an example of the knowledge transfer from the laboratory to the construction site, in which composite and installing technology could be verified.

Effect of mixed plant roots on saturated hydraulic conductivity and saturated water content of soil in the loess region

Soil hydraulic properties are essential for understanding soil hydrological and erosion processes. The importance of roots on soil hydraulic parameters has been widely recognized, but current studies have focused mainly on the root effect of a single plant species. However, few studies have been carried out to investigate the effect of mixed plant roots on soil hydraulic parameters. Undisturbed soil samples were collected from three natural sampling sites with single plant types and four sites with mixed plant types. Both soil hydraulic parameters were measured: soil saturated hydraulic conductivity (Ks) and soil saturated water content (SW). Then the root effects on Ks and SW were subsequently evaluated. The results showed that the Ks and SW at the sites with mixed plants were higher than those at the sites with a single plant species. At all the sites, Ks and SW both exhibited a decreasing-increasing-decreasing trend with increasing root density. The critical root density for the above change was quantified. When fibrous roots were mixed with tap roots, Ks was mainly affected by tap roots, while SW was mainly affected by fibrous roots. The influence of roots on Ks and SW was mainly achieved by affecting soil organic matter, not by directly affecting Ks and SW. Based on the root density, the herbaceous coverage with optimal saturated hydraulic conductivity and water content was estimated to be 66.71%.

Effects of Vermicompost and Salinity on Proctor Optimum Water Content, Maximum Dry Bulk Density and Consistency of a Sandy Clay Loam Soil

ABSTRACT Salinity and sodicity greatly influences ongoing physical processes in soils. Organic matter may rehabilitate physical and mechanical properties of soils. Vermicompost as an amendment influences moisture-related parameters including consistency (plastic – PL and liquid limit – LL) and compaction. This study was conducted on soils (sandy-clay-loam) treated with different salinity levels (0.58 (control – irrigation water quality, tap water), 4 and 8 dS m−1) to investigate the effects of different vermicompost doses (0% (control), 2.5% and 5% w/w) on soil consistency limits and compaction. The pot experiment was carried out in a total of 27 pots, i.e. 3 (vermicompost doses) x 3 (salinity levels) x 3 (number of replicates). For Proctor compaction properties, maximum dry bulk density (MDD) reduced and optimum water contents (OWC) increased with increasing vermicompost doses under different salinity levels (p < .01). Increasing vermicompost doses under the lowest salinity level (0.58 dS m−1) yielded increasing optimum water contents for control (LL = 35.93% and PL = 25.85%). Optimum water contents were determined as 42.19% (LL) and 29.93% (PL) for 2.5% vermicompost dose and as 47.33% (LL) and 36.01% (PL) for 5% vermicompost dose under the lowest salinity level. LL, PL, OWC and MDD were significantly affected by vermicompost x salinity interactions. The highest maximum dry bulk density (1.92 g cm3) and the lowest optimum water contents (13.50%) were obtained from 0% vermicompost under the 8 dS m−1 NaCl level. Mean weight diameter (MWD) values ranged from 0.690 mm for 0% VC treatment under high Na salt level (8 dS m−1 NaCl) to 0.821 mm for 5% VC treatment under lowest Na salt level (0.58 dS m−1 NaCl). The correlations between aggregate stability (particle size group 1–2 mm) and optimum water content were 0.647*, 0.587* and 0.598* as compared to correlations of −0.512*, −0.470*, and −0.617** between aggregate stability (particle size group 1–2 mm) and maximum dry bulk density for the 0, 4 and 8 dS m−1 NaCl levels, respectively. MWD was positively correlated with OWC (0.386*) and negatively correlated with MDD (−0.385*). The greatest (2.39%) and the lowest (0.32%) soil organic matter values were respectively observed in 5% VC under the lowest salinity level (0.58 dS m−1) and 0% VC with at high Na salt level (8 dS m−1 NaCl). It was concluded that vermicompost reduced compaction-induced damage in soils.

Effect of zeolite replacement and tyre fibre inclusions on geotechnical properties of cement- or lime-stabilised sand

ABSTRACT In the current study, the effects of cement or lime content, fibre content, partial cement or lime replacement with zeolite and curing time on the Unconfined Compressive Strength (UCS) of sand have been investigated. The results reveal that increasing cement or lime content increases Maximum Dry Density (MDD) and Optimum Water Content (OMC). However, increasing zeolite replacement percentage decreases MDD and OMC. Increasing the fibre content from 0 to 4% reduces the MDD and increases OMC. The optimum combination of the stabiliser and fibre has been derived from an array of tests. Results comparison shows the 0.5% fibre content and 8% stabiliser results in maximum effect. Also, the optimum percentage of 80% replacement of lime and 30% and 40% replacement of the cement with zeolite leads to the maximum UCS. Observing failure patterns demonstrates the influential performance of fibre content such as controlling the crack length and brittle behaviour. Moreover, SEM analysis was conducted to compare the microscale behaviour.

Physical, Chemical and Compaction Characteristics of Slightly Weathered Tephras of New Zealand

AbstractThe North Island of New Zealand is a region of high volcanic activity, with significant eruptions over the past. Analogous to past events, future volcanic eruptions would produce a considerable volume of ash and granular soils, covering widespread areas and raising concerns for their disposal and storage. Such deposits, primarily airfall tephra, could be potentially used in geotechnical engineering applications such as foundations, roadway embankments and land reclamations. However, before their use as structural fills can be recommended, detailed laboratory investigations of their physical, chemical, compaction, and geotechnical engineering properties (strength, compressibility, collapsibility, liquefaction potential, etc.) must be conducted. Different tephra deposits can be products of different eruptions, so chemical composition analyses can be combined with the physical, compaction, and engineering properties to characterize such deposits. Accordingly, this paper provides useful insights from physical (grain size, specific gravity, and morphology), chemical (elemental and mineralogy using X-ray fluorescence and X-ray diffraction), and compaction tests (maximum dry density, optimum water content, and particle breakage) for eleven selected volcanic tephra samples sourced from the North Island of New Zealand in the Rotorua, Taupo, and Auckland regions.

Kinetics and structure analysis of CO2 mineralization for recycled concrete aggregate (RCA)

CO2 mineralization of solid waste in the construction industry for green concrete production is a promising approach for economically storing CO2 and recycling solid waste. Recent investigations have underscored the significance of CO2 sequestration and the augmentation of RCA performance engendered by the holistic reaction processes. While there is a pronounced interest in the optimization of macroscopic reaction conditions (e.g., temperature, pressure, etc.), the exploration and enhancement of the reaction kinetics stage often remains under explored. This study employed a reaction kinetics model to quantify the reaction rate unveiled two distinct reaction stages within the mineralization reaction. Early evaporation and pore formation established the groundwork for the diffusion mechanism of gas product layers in the middle and later stages, emphasizing the crucial role of water in connecting solid ion leaching and gas dissolution-diffusion in the reaction. The water content of the reaction has an optimal value (4%–6%), smaller particle size correlates with a higher optimal water content. Pre-soaking with a calcium hydroxide (CH) solution or suspension was employed to improve mineralization reaction kinetics, resulting in RCA with improved pore characteristics and strength. The crushing index decreased by 28.8% and 21.8%, the water absorption rate decreased by 11.1% for both coarse and fine RCA, and the cumulative total porosity of fine RCA decreased by 17.6%. This research aims to broaden the applications of waste concrete in the CO2 capture, utilization and storage (CCUS) industry and produce low-cost, extensively processed, and high-strength RCA products while contributing to sustainable CO2 management.

On the Impact of Plastic Fines on the Compaction Characteristics of Sand

AbstractBinary mixtures of plastic fines and a non-cohesive host material are used in geotechnical barriers to obtain high shear strength and low permeability. To achieve such properties, the sand grains must form the force chain and the clay must fill the voids of the host material. However, clays are known to affect the grain to grain contacts by forming cohesive membranes. Since engineered barriers are usually compacted at water contents below saturation (Proctor conditions), it is still unclear whether such membranes will form. The aim of the current research is to shed light on the compaction characteristics of such mixtures. Proctor datasets were analysed in terms of skeleton and fines void ratio and optimal water content. Oedometric compression behaviour and limiting void ratios were studied to outline the characteristics of mixtures in a saturated or dry state, respectively. The results show that depending on the mixing ratio, compaction properties can be divided into three different ranges, where either the properties of one of the input materials dominate the behaviour or a transitional range exists that is characterised by a strong mutual influence of both materials. Furthermore, even a small amount of the highly plastic clay was found to influence the properties of the host sand.

Utilization of Municipal Solid Waste Incineration Bottom Ash in Cement-Bound Mixtures

In order to protect the natural resources, it is beneficial for the environment when materials that are not valuable, such as waste or recycled materials, are used in engineering. This article presents laboratory studies on the use of mixtures of incineration bottom ash (IBA) from municipal waste incinerators with natural, fine grain and uniform aggregate in cement-bound layers. The mechanical and engineering properties of aggregates were studied, their usefulness was assessed and possible applications are indicated. The chemical composition of the material was found to be consistent with typical IBA from other incineration plants, and leachability studies were carried out, confirming lack of any environmental impact. The authors’ own mixtures were prepared based on optimal water content and maximal dry densities of solid particles, and the compressive strength was calculated after 7 and 28 days of hardening. The results indicate that replacing natural aggregates with IBA permits an increase in the compressive values for the specimens using the same amount of CEM I 42.5R while improving the frost resistance of cement–aggregate mixtures.

Investigating Soil Water Retention and Water Content in Retrogressive Thaw Slumps in the Qinghai-Tibet Plateau, China

Retrogressive thaw slumps (RTSs) are becoming more common on the Qinghai-Tibet Plateau as permafrost thaws, but the hydraulic properties of thaw slumps have not been extensively studied. To fill this knowledge gap, we used the “space-for-time substitution method” to differentiate three stages of RTSs: original grassland, collapsing, and collapsed. Our study included on-site investigations, measurements in the laboratory, and measured and simulated analyses of soil water retention curves and estimated hydrological properties. Our findings show that the measurements and simulated analyses of soil water retention were highly consistent across RTSs, indicating the accuracy of the Van Genuchten model in reproducing soil hydraulic parameters for different stages of RTSs. The original grassland stage had the highest soil water retention and content due to its high soil organic carbon (SOC) content and fine-textured micropores. In contrast, the collapsed stage had higher soil water retention and content compared to the collapsing stage, primarily due to increased proportions of soil micropores, SOC content, and lower bulk density (BD). From original grassland stage to collapsed stage, there were significant changes on the structure of each RTS site, which resulted in a decrease in SOC content and an increase in BD in general. However, the absence of soil structure and compaction led to the subsequent accumulation of organic matter, increasing SOC content. Changes in field capacity, permanent wilting point, and soil micropore distribution aligned with variations in SOC content and water content. These findings highlight the importance of managing SOC content and water content to mitigate the adverse effects of freeze-thaw cycles on soil structure and stability at different thaw collapse stages of RTSs. Effective management strategies may include incorporating organic matter, reducing soil compaction, and maintaining optimal water content. Further research is needed to determine the most suitable management practices for different soil types and environmental conditions.

Using Repeated Light-Weight Deflectometer Test Data to Predict Flexible Pavement Responses Based on the Mechanistic–Empirical Design Method

This study investigated the potential of lightweight deflectometer (LWD) data in predicting layer moduli and response measurements within the Mechanistic–Empirical Pavement Design Guide. To achieve this goal, field repeated LWD tests and laboratory repeated load triaxial tests were carried out on granular base material compacted at 3% and 6% water content, sandy subgrade soil compacted at 3%, 4% and 9% water content and silty sand subgrade soil compacted at 8% and 10% water content. The results revealed that substituting traditional repeated load triaxial (RLT) data with LWD data for predicting these parameters was notably effective for cohesionless materials, especially for unbound granular materials (UGMs) compacted at optimum water content. The accuracy and reliability of predictions were remarkably high, showcasing the potential of LWD to enhance efficiency and precision in pavement design within this context. Conversely, for cohesive road materials, the study emphasized the importance of considering specific material properties and water content when integrating LWD into the Mechanistic–Empirical Pavement Design Guide. The distinctive characteristics and behaviors of cohesive materials necessitate a nuanced approach. This understanding is critical to ensuring the accuracy and reliability of pavement design and assessment across diverse conditions. In summary, the study presents a promising avenue for utilizing LWD data in cohesionless road materials, offering potential cost and time-saving advantages. Additionally, it underscores the necessity of tailored approaches when considering material properties and moisture content for cohesive materials, thereby advancing the field of pavement engineering by providing insights for improved practices and adaptable frameworks.

Micro-scale investigations on the mechanical properties of expansive soil subjected to freeze-thaw cycles

Freeze-thaw (FT) cycle is one of the most important factors contributing to the deterioration of expansive soil properties in seasonal frozen regions. In this study, a multiscale approach was used to investigate the impact of FT cycles on the volume deformation, mechanical properties and microstructure of expansive soil with different initial compaction states. FT cycle, unconfined compression, scanning electron microscopy and mercury intrusion porosimetry tests were carried out. The test results indicated that the volume deformation of the frozen expansive soil showed a completely opposite trend and varied in magnitude with different initial compaction states. The failure strength and elastic modulus of the expansive soil sample decreased significantly with increasing number of FT cycles. Under the impact of FT cycles, the porosity of the expansive soil increased significantly and the proportion of macropores grew. The growth of macropores and the generation of microcracks in the expansive soil were the main causes of FT damage. Besides, the FT damage variable was defined by the failure strength and had a good linear relationship with the soil porosity. In addition, the strength of loose and dense soil samples decreased significantly after FT cycles. It is found that an optimal compaction state may exist at around 95% compaction and the water content can be controlled on the dry side of the optimum water content, where FT cycles have minimal effect on the soil strength and microstructure. The study can provide guidelines for selecting the appropriate initial compaction and water content for the expansive soil projects in seasonal frozen regions.