Compaction Water Content Research Articles

Evolution of structure and anisotropic shear stiffness of compacted loess during compression

Different compaction conditions (water content and density) may induce various soil structures. The influence of these structures on small strain shear stiffness G seems contradictory and is not understood (e.g., denser specimens may have larger or smaller G than looser specimens after compression). Furthermore, the influence of compaction condition on stiffness anisotropy remains unclear. This study investigated the evolution of structure and anisotropic stiffness of saturated and compacted loess during isotropic compression. Specimens compacted at different water contents and densities were explored. The measured G was normalised by a void ratio function (f(e)) to eliminate density effects. Before yielding, G/f(e) increases with decreasing compaction water content and increasing density. These two trends are reversed at large stresses (2 to 3 times yield stress), implying that an initially softer structure becomes stiffer. Based on MIP, SM and SEM results, the trend reversal is likely because interparticle contacts are more strengthened and pores are more compressed in the initially softer specimens. Furthermore, the stiffness anisotropy becomes more significant with decreasing compaction water content and increasing density because of more orientated fabrics, as evidenced by the particle/aggregate directional distribution results.

Assessing the Potential for Valorisation of a Pulp and Paper Industry Byproduct for the Construction of Unpaved Forest Roads: A Geotechnical Perspective

Integration of sustainability into industry has encouraged practices of circular economy, reusing and recycling resources. This paper studies alternative solutions to materials traditionally used for unpaved roads, with a byproduct of the pulp and paper industry (not pre-treated), and analyses its valorisation potential from a geotechnical perspective. Two approaches were adopted: (1) assessment of geotechnical properties of base materials (aggregate, local soil and byproduct) and mixtures (aggregate/local soil and byproduct, 3% or 6%); (2) design of the base layer (case study), considering different solutions for the material forming that layer, assessing its height and life cycle. The small incorporation percentages studied changed the geotechnical properties of aggregate and local soil, reducing sensitivity to water and increasing the water content for optimum compaction. The CBR of mixtures reduced with the incorporation of the byproduct. For the case study, incorporation of byproduct (6% maximum) in the local soil did not significantly affect the base layer height. Total replacement with the byproduct is mechanically possible. For the fixed height of the base layer, incorporating the byproduct in traditional materials reduced the unpaved road life cycle, reflecting CBR reductions. From a geotechnical perspective, the valorisation of this byproduct is promising, and from an industry point of view, its use (geotechnical valorisation) represents a way to promote circular economy and sustainability.

Impact of Hillslope Agriculture on Soil Compaction and Seasonal Water Dynamics in a Temperate Vineyard

Major losses of agricultural production and soils are caused by erosion, which is especially pronounced on hillslopes due to specific hydrological processes and heterogeneity. Therefore, the aim of this study was to assess the impact of agricultural management on the compaction, infiltration, and seasonal water content dynamics of the hillslope. Measurements were made at the hilltop and footslope, i.e., soil water content and potential were measured using sensors, wick lysimeters were used to quantify water flux, while a mini-disk infiltrometer was used to measure the infiltration rate and calculate the unsaturated hydraulic conductivity (K_unsat). Soil texture showed differences between hillslope positions, i.e., at the hilltop after 50 cm depth, the soil is classified as silty clay loam, and from 75 cm onward, the soil is silty clay, while at the footslope, the soil is silt loam even at the deeper depths. The results show a higher K_unsat at the footslope as well as higher average water volumes collected in wick lysimeters compared to the hilltop. Average water volumes showed a statistically significant difference at p < 0.01 between the hilltop and the footslope. The soil water content and water potential sensors showed higher values at the footslope at all depths, i.e., 8.0% at 15 cm, 8.4% at 30 cm, and 27.3% at 45 cm. The results show that, even though the vineyard is located in a relatively small area, soil heterogeneity is present, affecting the water flow along the hillslope. This suggests the importance of observing water movement in the soil, especially today when facing extreme weather (e.g., short-term high-intensity rainfall events) in order to protect soil and water resources.

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.

A graph-based approach for modeling the soil–water retention curve of granular soils across the entire suction range

This study investigates experimentally the water retention behavior of granular soils from saturation to oven-dry state. The soil–water retention curve (SWRC) tests were conducted on a well-graded sand with clay using tensiometer and chilled-mirror hygrometer techniques. The soil samples were statically compacted at various water contents to different initial densities. The results showed that individual linear segments in the log–log graph could characterize the desorption process of capillary and adsorption water. A novel water retention model in a simple mathematical form was developed by conceptualizing the total water content as the sum of the suction-dependent capillary and adsorption components. The model parameters possess an unambiguous physical meaning. They can be easily calibrated based on the graphical properties of the test data using simple linear regression, which is a significant advantage over conventional SWRC models. The model was validated using the water retention data of the tested soil in this study and the available data of granular soils in the literature. The reproduced curves agree well with the experimental results. This study also analyzed the influence of compaction water content, initial density, and clay content on the capillary and adsorption components of the water retention curve. Additionally, the proposed framework provides a quick approximation method for the adsorption capacity, which plays an essential role in assessing the effective stress and the simulation of liquid film flow in unsaturated granular soils.

Mechanical properties and field test of lime-soda residue stabilized soil for subgrade

To broaden the sources of subgrade filler and the utilization of Soda Residue (SR), SR was employed to modify clay by adding a small amount of lime for further stabilization, forming a Lime-Soda-Residue-Stabilized Soil (LSRSS). A set of intensive research paths was established, from testing of laboratory mechanical property, mechanism disclosure, and field verification to operational effect. Through Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), and Resilient Modulus (MR) experiments, it was concluded that with the increase in SR content, the UCS, CBR, and MR values of LSRSS showed an increasing trend then followed by a decrease, reaching their peak values, respectively of 0.62 MPa, 65.0%, 78.83 MPa, all at 30% SR content. An optimal proportion was determined for LSRSS as 6% lime, 30% SR, and 70% clay. The UCS, CBR, and MR values of optimal proportion all increased with the increase of compaction degree, but increased first and then decreased with the increase of water content. Their maximum values did not correspond to the OWC of 23% but to 27%, called the compaction water content, which was suitable for application in the actual LSRSS subgrade. Field test results showed that the UCS, CBR, and MR values were 0.85 MPa, 86.5%, and 135.7 MPa, which all were higher than the laboratory values, and the long-term road performance was outstanding. The analysis demonstrates that the better strength and road performance of LSRSS are mainly determined by the superior gradation and the reaction of three materials. The laboratory and field test results collectively provide data evidence for excellent performance and lay a solid foundation for the wider application of the LSRSS subgrade.

Effect of Initial Conditions on the Pore Structure and Bimodal Soil–Water Characteristic Curve of Compacted Granite Residual Soil

Granite residual soil typically forms complex pore structures and exhibits high water sensitivity due to physical and chemical weathering processes. Changes in initial compaction conditions significantly affect the mechanical and hydraulic properties of in situ granite residual soil subgrades, with these variations fundamentally related to changes in pore structure and soil–water characteristics. This study investigates the pore structure and bimodal soil–water characteristic curve (SWCC) of a compacted granite residual soil through laboratory tests and mercury intrusion porosimetry tests. Nine initial conditions were selected based on potential in situ compaction conditions of subgrades, and their effects on the pore size distribution (PSD) and SWCC were thoroughly analyzed. The results show strong correlations between bimodal pore structure and SWCC. The size and volume of inter-aggregate pores exhibit noticeable changes with initial conditions, affecting SWCC within the low and middle suction range. Conversely, the intra-aggregate pores, which constitute over 60% of the pore structures, remain nearly intact across different initial conditions, resulting in similar SWCCs within the high suction range. As the compaction energy increases, the inter-aggregate pores are compressed and lead to a higher water retention capacity. In addition, as the compaction water content increases, the SWCC becomes less sensitive to compaction energy after the aggregates in the pore structure are fully saturated. Additionally, a three-dimensional bimodal SWCC equation is proposed and validated using test data with an R2 value above 0.98. These findings offer valuable insights for the design and quality control of granite residual soil subgrades.

Effects of Compaction Water Content on Water Retention and Deformation Behavior of Compacted Loess

Compacted loess is widely used as a construction material in engineering practices. The compaction dry density and compaction water content have significant effects on the hydromechanical behavior of compacted loess, thereby influencing the serviceability and safety of engineering structures. The former was widely studied in previous studies, while the latter is rarely known. In this study, the water retention, compression, and collapse behavior of compacted loess at different compaction water contents are investigated through pressure plate and oedometer tests. Microstructure analysis was carried out for insight analysis of the test results. The air entry value and yield stress of compacted loess decreased by 64% and 50%, respectively, with the compaction water content increasing from 12.4% to 19.0%. This is due to the fact that the number of clods increases with increasing the compaction water content, leading to many large-sized pores (i.e., diameter > 1,000 μm) and weaker soil skeletons. The influence of compaction water content on the water retention and compression behavior of loess is more pronounced at lower compaction dry densities and lower testing water contents, respectively. In addition, the specimen shows smaller collapse indexes at higher compaction water contents, mainly because of the larger deformation induced by the initial compression.

The importance of the microstructure on hydro-mechanical behaviour of compacted granular bentonite

Granular bentonite (GB) with extended grain size distribution, a candidate material to construct engineered barriers, has low water permeability, high swelling potential and self-sealing capacity and is desirable in portability and workability. However, few systematic data combining microstructural descriptions and hydro-mechanical (HM) behavioural features are available. The present work investigates the HM performance of Wyoming (MX80)-type GB samples compacted at different initial water contents and at a fixed dry density of 1550 kg/m3. The samples' microstructure and its evolution along stress paths were studied using X-ray micro-computed tomography and mercury intrusion porosimetry. The results highlighted that the compacted GB presented local density heterogeneity and a multi-porosity network. Compaction at low initial water content increased the proportion of macropores and contributed to the enhancement of the compressibility and collapse on wetting under high stresses. During isochoric saturation, two stages of swelling development were identified. First, the flooding of macropores and matric suction reduction was related to the initial increase in swelling pressure. The secondary swelling was due to the water absorption of clay sheets in micropores and the expansion of micropores within granules and aggregates, during which the density of pore water increased. A decrease in the compaction water content can result in a higher pore water density after isochoric saturation and a lower water permeability. Finally, the water retention behaviour of the compacted sample within drying/wetting cycles was less sensitive to the initial pore size distribution. The current outcomes underline the critical role of the microstructure on the HM behaviour of compacted GB.

Limiting Water Content for Compaction Induced by Mechanized Operations in the Soil with Oil Palm in the Eastern Amazon

Limiting Water Content for Compaction Induced by Mechanized Operations in the Soil with Oil Palm in the Eastern Amazon

Soil Bulk Density and Matric Potential Regulate Soil CO2 Emissions by Altering Pore Characteristics and Water Content

Soil pore structure and soil water content are critical regulators of microbial activity and associated carbon dioxide (CO2) emissions. This study evaluated the impacts of soil bulk density and matric potential on carbon dioxide (CO2) emissions through modifications of total porosity, air-filled porosity, water retention, and gas diffusivity. Soil samples were manipulated into four bulk densities (1.0, 1.1, 1.2, and 1.3 Mg m−3) and ten matric potential levels (−1, −2, −3, −4, −5, −6, −7, −8, −9, and −10 kPa) in controlled soil cores. The results showed that lower bulk densities enhanced while higher densities suppressed CO2 emissions. Similarly, wetter matric potentials decreased fluxes, but emission increased with drying. Correlation and regression analyses revealed that total porosity (r = 0.28), and gravimetric water content (r = 0.29) were strongly positively related to CO2 emissions. In contrast, soil bulk density (r= −0.22) and matric potential (r= −0.30) were negatively correlated with emissions. The results highlight that compaction and excessive water content restrict microbial respiration and gas diffusion, reducing CO2 emissions. Proper management of soil structure and water content is therefore essential to support soil ecological functions and associated ecosystem services.

Effect of compaction water on strength and hydraulic properties of bentonite-based liner

The abundance of pond ash and its resemblance to natural sand encourages its use as a substitute for sand in sand–bentonite (SB) liner material. Compaction water content influences the geoengineering properties of cohesive soil to a great extent. Accordingly, the compaction, strength, permeability and shrinkage characteristics of both pond ash–bentonite (PAB) and SB mixes are investigated at standard and modified Proctor compaction energies at various water contents to support the recommendation of the PAB mixture as an alternative landfill liner. At similar compaction conditions, the PAB mix exhibits higher unconfined compressive strength (UCS) and hydraulic conductivity than the SB mix. The UCS values of mixes compacted on the dry side of optimum are higher than those of mixes compacted on the wet side. Dry-side compacted mixes exhibit a reduction in hydraulic conductivity with permeation time, whereas no substantial reduction in hydraulic conductivity is noticed for wet-side compacted mixes. Furthermore, the volumetric shrinkage of both PAB and SB mixes is within the permissible value of 4%, for a wide range of water variation from the dry to the wet side of optimum. The observed mechanical properties are correlated to the shape of coarse fraction particles and the corresponding microstructural arrangements of the compacted specimens.

Experimental study on engineering mechanical properties of loess-like backfill under various conditions

Aiming at the loess-like backfill soil in the Lanzhou area, the samples with different compaction coefficients and different moisture content were prepared in the laboratory and tested by a double-line method. In the analysis of compression deformation, the pore ratio change rate is introduced, and the interval with the pore ratio change rate less than 10% is defined as the corresponding insignificant compression area. The corresponding compaction coefficient and water content of this area are summarized. The critical compaction coefficient is introduced in the analysis of collapsible deformation, according to which the subdivision is carried out, and the corresponding compaction coefficient and water content of the non-collapsible area are summarized. According to the variation curves of the subsidence coefficient under different compaction coefficients, the deformation mechanism of backfill soil after flooding is discussed. It is divided into two areas: water-compression area (low-pressure solid area) and water-subsidence area (high-pressure solid area).

Influence of aggregate structure on the compressibility of an unsaturated compacted silty sand

It is well recognised that the compressibility of unsaturated soils is affected by soil structure. However, the effects of soil aggregation and pore structure on the compressibility behaviour of unsaturated soil are still not well understood. In this study, the effects of soil aggregation and pore structure on the compressibility of unsaturated silty sand were investigated. Specimens were purposely prepared at two compaction water contents to similar void ratios. They were saturated after compaction and dried to suction values of 0, 50, 150, or 300 kPa following a similar hydraulic loading path, after which they were subjected to isotropic loading and unloading. Mercury intrusion porosimetry (MIP) and micro-X-ray computed tomography (μ-XCT) were used for microstructural studies. At a given suction, specimens compacted on the dry side are less aggregated (smaller aggregate sizes) showing higher compressibility, whiles specimens compacted on the wet side are highly aggregated (larger aggregate sizes) revealing lower compressibility. The low compressibility of the highly aggregated soil is attributed to the additional drying-induced intra-aggregate strength due to the suction stiffening effects from meniscus water within the aggregates.

Comparing the trend of Vsat similar range of saturated and unsaturated stress state variables

The effect of matric suction on S-wave velocity (Vs) of unsaturated soils has been observed to show different trends from the Vs relationship with effective confining pressure. In some soils, the increase in S-wave velocity per unit stress change in matric suction (ua-uw) is greater than the increase in S-wave velocity per unit stress change in effective confining pressure (σ’3) for saturated and dry soils and vice versa for other soils. In this study, the difference was examined through the stress state variables for unsaturated soils on similar soil samples. Experiments were conducted on sand and kaolin specimens using a triaxial cell modified to include bender elements and a high-air-entry disk for the testing of unsaturated soils. The soil specimens were first fully saturated and Vsat various effective confining pressures were measured. The tests were repeated with similar soil specimens subjected to net confining pressure and matric suction for similar stress range as the previous tests. Data was also collated from the literature. Comparisons were made by plotting on two-dimensional and three-dimensional plots to understand the differences. It was found that soil type and soil fabric play important role in the differences. Soil fabric plays a more important role for compacted soils where soil fabric is affected by the compaction water content.

Evaluation of Soil-Water Characteristic Curve and Pore-Size Distribution of Fine-Grained Soils

A soil’s physical properties, mineral types, and pore structure significantly influence the shape and properties of the soil-water characteristic curve (SWCC). This study investigated the effects of the soil’s physical properties and mineral types on the SWCC and pore-size distribution (PSD). Eight different soils from an alluvial deposit in Istanbul and Adapazarı/Türkiye were used in the study. The test samples were prepared by compaction at optimum water content (OWC) and wet side of optimum water content (wet of OWC). The samples were prepared by consolidation from the slurry. The PSDs of the samples were calculated using the SWCCs and evaluated with scanning electron microscope (SEM) analysis. In addition, the mineral types of all soils were determined by X-ray diffraction analysis. The soil which contains illite-type minerals has higher matric suction than containing kaolin-type. The effect of the clay percentage is more pronounced in silty soils than in plasticity and activity. Soil suction increased with decreasing compaction water content in clayey soils. The air entry water contents rose as the void ratio, liquid limit, clay content, and plasticity increased. The compaction conditions affected the macropore structure more than the micropore structure. In addition, the ratio of macro-micro pore sizes increased with the rise of the compaction water content.

Experimental Study on Fractal Characteristics of Particle Size Distribution by Repeated Compaction of Road Recycling Crushed Stone

In order to investigate the compaction characteristics of graded crushed stone under repeated utilization, it is necessary to improve the utilization rate of road recycling crushed stone and maintain its strength and stability during recycling. In the present study, repeated compaction characteristic curves of graded crushed stone were developed using repeated compaction and screening of the graded crushed stone. The correlations between the fractal dimension of particle size distribution and repeated compaction times, water content, and dry density were analyzed. The experimental results indicate that both the maximum dry density and the optimal water content increase as the repeated compaction times increase. The fractal dimension of the particle size distribution of the graded crushed stone used in this test is 2.33 to 2.57. The obtained results show that as the fractal dimension increases, the maximum dry density of the graded crushed stone increases. At a constant repeated compaction time, the fractal dimension of the particle size distribution of graded crushed stone increased and then decreased as the water content increased. In summary, the compaction performance of the structural layer of graded crushed stone can be tuned by adjusting the fractal dimension of the particle size distribution of the recycled pavement structural layer in practical applications. Moreover, the optimal graded materials can be prepared under the guidance of the fractal dimension, thereby achieving an optimized working performance of the recycled pavement structural layer.

Investigation of the strength evolution of lime-treated London clay soil

The paper investigates the effect of hydrated lime on shear strength properties and behaviour of London clay, triaxial. Unconsolidated undrained tests were performed to identify the effect of lime dosage, compaction water content and curing time on the shear strength and stress–strain behaviour of the treated soil. The mineralogical and physicochemical transformations occurring during the curing of the soil were also monitored. The results showed that strength gain was strongly influenced by lime content and the curing period, whereas compaction water content was less influential. It was found that the strength evolution is likely to continue over long periods of time and result in very considerable strength gains on the hardening of pozzolanic reaction products. It was also shown that adequate early strength gains can be obtained with reduced material consumption, thus further increasing the sustainability of the treatment processes. The paper also highlighted the importance for engineering design of considering the brittle stress–strain response of the lime-treated soil, and the benefit of using lower amounts of lime to alleviate this undesirable effect. The implications of various aspects of soil brittleness in different situations merit further attention and should be explored by way of modelling in future work.

Saturated hydraulic conductivity of compacted steel slag-bentonite mixtures——A potential hydraulic barrier material of landfill cover

The feasibility of using steel slag and bentonite mixtures to construct the hydraulic barrier of a landfill cover was explored in the present study. Fine-grained steel slag (SS; particle diameter < 1 mm) and sodium-activated calcium bentonite (SACB) were used to prepare compacted specimens, and the saturated hydraulic conductivity (ks) was measured using a flexible-wall permeameter. Influential factors including SACB content (BC), SS gradation, water-washing treatment of SS and compaction water content (ωcomp) were investigated. The hydraulic conductivity results were interpreted in microscopic scale through mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM). It was found that when BC was below 10%, the ks value of the specimens prepared with well graded SS was about one order of magnitude lower than that of the specimens prepared with poorly graded SS. This was due to less macropores caused by better SS gradation. Yet, the effects of SS gradation on ks diminished as BC further increased to 15%, suggesting the dominant role of BC on ks at high BC. Water-washing treatment of SS helped reduce ks significantly to 1.2 × 10−10 m/s at BC of 10%, owing to less multivalent cations and hence lower osmotic swelling reduction caused by cations. Controlling ωcomp 1–2% wetter than the optimum water content (ωopt) also helped reduce ks significantly, owing to the reduction of macropores. Accordingly, it is suggested to use well-graded SS mixed with 10% SACB and then compact at ωcomp slightly wetter than ωopt to the degree of compaction greater than 90% in engineering practice.

Effects of compaction state on desiccation cracking behaviour of a clayey soil subjected to wetting-drying cycles

Desiccation crack is an important factor affecting engineering properties of clayey soils. In this study, the effects of compaction state and wetting-drying cycles on desiccation cracking behaviour of a clayey soil were investigated. Nine samples with various compaction water contents and dry densities were subjected to three wetting-drying cycles and the evolution of desiccation cracks was quantitatively described. The results reveal that both compaction water content and dry density play an important role in the development of desiccation cracks. Specifically, for the samples compacted on the dry side, desiccation cracks develop simultaneously. This phenomenon is also observed in samples compacted on the wet side with low densities. However, for the samples compacted on the wet side with high dry densities, desiccation cracks develop sequentially. Moreover, the higher the compaction water content, the faster development of desiccation cracks, and the smaller surface crack ratio, total crack length and average crack width. The higher the dry density, the slower development of desiccation cracks, and the smaller surface crack ratio and total crack length. Furthermore, the development of desiccation cracks can be divided into two stages according to the evolution of crack propagation velocity: (a) crack length extension, where total crack length increases rapidly with little changes in average crack width, and (b) crack width widening, where total crack length no longer changes and average crack width increases until it stabilizes. In addition, surface crack ratio, total crack length and average crack width all show an upward trend as wetting-drying cycles progresses. This tendency is more pronounced in the soil sample with a higher compaction water content and a larger dry density.