Compaction Water Content Research Articles

The crystallization and salt expansion characteristics of a silty clay

To investigate the mechanisms and principle for salt expansion, theoretical analysis, micro-fabric observation and salt expansion tests are conducted to a silty clay containing sodium sulfate. The equations for calculating the crystalized sodium sulfate in soil are derived through theoretical analysis. In the microstructure test, long strip crystal bridges and bulky crystals are found in saline soil. When these crystals grow upon cooling, soil is supposed to expand. In salt expansion tests, the effects of compaction effort, water content, and salt content of soil are studied. The salt expansion data demonstrate that the volumetric content of crystal seems to have a linear relation with the volumetric strain of saline soil. Such relation seems to be unique and is applicable to the salt expansion prediction of sulfate soil with any water content, salt content and dry density. As the migration of salt in this study is negligible, the salt expansion tests can be regarded as element tests and the relation obtained can be used to build constitute models for salt expansion.

Geotechnical properties and microstructure of lime-stabilized silt clay

The geotechnical properties and microstructures of lime-stabilized silt clay from Jilin province, China, were studied in detail. Laboratory tests were conducted to evaluate the effects of lime content and curing time on the overall soil properties, including compaction characteristics, Atterberg limits, particle size distribution, pH, stress–strain behavior, peak strength, shear strength parameters, and California bearing ratio (CBR). The stabilized mechanisms of lime in silt clay were examined, and the observed test results were explained based on the results of scanning electron microscropy (SEM) and X-ray diffraction analyses of the specimens. Lime content and curing duration significantly influenced the geotechnical properties and microstructure of the lime-stabilized silt clay specimens. An increase in lime content resulted in increases in compaction water content, liquid limit, plastic limit, sand size-fractions, pH, peak strength, cohesion, internal friction angle, and the CBR, but led to a reduction in the plasticity index, silt fractions, clay fractions, swelling capacity, and water absorption. Also, the addition of lime to silt clay changed this soil type from a ductile to a brittle material. The optimum lime content of the silt clays from Jilin province was determined to be approximately 5–7%. SEM micrographs showed that a white cementitious gel was formed after the addition of lime and that peaks related to smectite, illite, kaolinite, and quartz appeared to be sharper after stabilization with lime and a 90-day period of curing. These results show that the geotechnical properties of lime-stabilized silt clay are affected by the microstructural organization of the silt clay itself.

Variation of the Hydraulic Conductivity of Clayey Soils in Exposure to Organic Permeants

Clayey soils are the most common material used in waterproofing and play an essential role in waste and contamination control. Permeability is a key parameter in such problems and its determination is needed in ensuring the satisfactory performance of the soil. Research has shown that a permeant fluid with a low dielectric constant can shrink the double layer around the clay particles which will, in turn, increase the permeability of the soil. In this paper, the permeability of two types of clay with different plasticity, exposed to the flow of water and methanol as polar and miscible solvents and gasoline and car oil as non-polar and immiscible solvents is investigated. In addition, the effect of soil properties such as plasticity and compaction water content on permeability of the samples is examined. To this end, soil samples are prepared and compacted at various water contents. Then, permeability tests are conducted according to the modified constant head method and the effects of parameters such as the fluid dielectric constant, water content of the samples and soil plasticity are examined. The results demonstrate that the lower dielectric constant of the organic fluid decreases the thickness of the double layer, providing more space for the flow of the permeant and as a result, the permeability of the clay increases. The reduction of the permeant dielectric constant from 80.4 to 2.28 led to a remarkable increase in soil permeability.

Contribution of osmotic suction to shear strength of unsaturated high plasticity silty soil

The engineering behaviour of unsaturated soils is affected by suction. It is widely accepted that soil suction consists of two major components: matric and osmotic suctions. Matric suction is associated with the capillary effects whereas osmotic suction is associated with the salt content of the pore water. Soil suction has been incorporated as “effective” stress or suction stress when describing the engineering behaviour of unsaturated soils. Usually, the suction component that is incorporated is matric suction while the contribution of osmotic suction is seldom investigated. In this paper, the contribution of osmotic suction to shear strength of unsaturated soils is investigated through unconfined compression tests on three series of compacted soil prepared using distilled water and sodium chloride solution. Specimens were prepared at three water contents corresponding to dry densities at dry of optimum, optimum and wet of optimum on the standard Proctor compaction curve. Series one and two consist of specimens compacted using distilled water and sodium chloride solution, respectively. In series three, one half of the specimen was compacted using distilled water and the other half compacted using sodium chloride solution. Unconfined compression tests were conducted on the soil specimens at various elapsed times after compaction to allow for ionic equilibrium due to the osmotic gradient in the third series of soil specimens. The test results show soil specimens have similar strength at each compaction water content regardless of elapsed time and type of pore water. No effect of osmotic suction or osmotic suction gradient on shear strength of the compacted soil specimens was found. It was concluded that the salt content of the pore water affects the soil structure of clayey soils and does not act like matric suction. Hence, matric suction should be measured in order to quantify the engineering behaviour of unsaturated soils.

Soil improvement using recycled aggregates from demolition waste

Fine-grained soils with an in situ water content above the optimum compaction water content show poor suitability for installation and compaction. This paper presents the findings of an experimental study on the improvement of such soils by adding recycled aggregates from demolition waste. The study covers nine different base soils with a wide range of plasticity and addition rates of up to 50 mass% of recycled aggregates with a grain size 0/4 mm. A comparative analysis of the results from the laboratory study focused on the following parameters: improvement effect, compaction characteristics, air void content and bearing capacity. Soil-related patterns in the changes of these parameters were identified. For any fine-grained soil under consideration for this method of soil improvement, the findings presented herein can thus be used as a first indicator of the achievable results.

Experimental study on limitation of internal erosion in dams by upstream zones of well-graded soils

The limitation of the progression of internal erosion in zoned dams, potentially caused by an upstream zone built of coarse, well-graded soils with non-plastic fines, is assessed using a new test cell. This device allows two types of tests to be conducted: the flow-limiting erosion test (FLET) and the crack-filling erosion test (CFET), which are designed to study the isolated influence of the flow-limiting action and the crack-filling action, respectively. The specimen is subjected to water flow along a hole drilled in the core and the upstream zone. In the CFET, the specimen additionally includes a downstream filter. Three upstream materials with non-plastic fines, a core and a filter are examined. The results of nine FLETs and nine CFETs are presented and analysed. The FLETs show the clear influence of the compaction water content, fines content and gravel content of the upstream soils in their capability to provide the flow-limiting action. The CFETs show that the specimen using the coarsest upstream soil (with 21% non-plastic fines) compacted on the dry side is capable of stopping the progression of erosion, enabling a partial crack-filling action. In all other test conditions, the filtering mechanism due to erosion of the upstream soil provides an important limitation of the erosion process. Based on the tests, practical recommendations to assess the influence of upstream zones on the limitation of internal erosion are proposed.

Water sensitivity and microstructure of compacted loess

Abstract Loess is abundant around the world, and China has the most extensive and thickest distribution of loess, which is currently widely used as subgrade or subbase of roads after ground improvement by compacting. This paper presents a study to investigate the effects of compaction parameters (compaction energy and water content) on the bearing capacity and microstructure of compacted loess. The bearing ratio, mineralogy, microstructure of loess compacted with different compaction water contents and energies were characterized by California bearing ratio testing, X-ray diffraction, scanning electron microscopy to elucidate the origin of water sensitivity. A total of 72 samples were compacted with different compaction energies and water contents, on the dry side of optimum, at optimum and on the wet side of optimum, using the Proctor procedure for soaked and un-soaked CBR testing. The compacted samples exhibit expansibility and strength loss (decreasing of CBR values) when soaked in water. For a given compaction energy, the samples compacted on dry side of optimum have higher strength and bearing capacity in terms of unsoaked CBR value, but have higher expansion and more strength loss when soaked in water. From the microstructural point of view, the microstructure characteristics like pore size and shape, porosity, particle contact and association change with the compaction water content and energy. The results show that the water sensitivity is strongly related to the mineralogy and microstructure of the compacted loess. For the Engineering implications in transportation construction, compaction at a very low water content should be avoided for the water sensitivity and metastable structure of dry compacted samples.

Influence of the dry density and compaction water content on the scanning drying curve of a residual soil derived from volcanic ash

Introduccion: Una curva exploratoria de humedecimiento o secado relaciona los resultados de mediciones sucesivas del contenido de agua y la succion de un suelo originalmente en equilibrio que parte de una condicion inicial de saturacion parcial y sigue un proceso de humedecimiento o secado.Objetivo: Estudiar la influencia de la densidad seca y el contenido de agua de compactacion en la curva exploratoria de un suelo residual derivado de ceniza volcanica, el cual se sometio a un proceso de secado expuesto al ambiente.Metodologia: El trabajo experimental inicio con la determinacion de la curva de compactacion del material estudiado. Con base en ello, se seleccionaron seis puntos dentro de la curva que permitieron estudiar la relacion existente entre la densidad seca y el contenido de agua de compactacion con la succion a traves de la compactacion estatica de muestras del suelo estudiado, usando para tal fin curvas exploratorias de secado a traves de la tecnica del papel de filtro.Resultados: La densidad seca inicial del material no influye en las trayectorias que describen las curvas exploratorias para valores similares de succion. El contenido de agua de compactacion influye en la capacidad de almacenamiento del suelo estudiado, encontrandose que, para un mismo valor de densidad, muestras compactadas del lado humedo del contenido de agua optimo presentan mayores valores de succion que muestras compactadas del lado seco.Conclusiones: La capacidad de almacenamiento de agua del suelo estudiado es independiente de la densidad seca inicial del material. La capacidad de almacenamiento de agua del suelo estudiado esta influenciada por el contenido de agua de compactacion, encontrandose que muestras compactadas del lado humedo del contenido de agua optimo presentan mayores valores de succion que muestras compactadas del lado seco.

Effect of Unit Weight on Porosity and Consolidation Characteristics of Expansive Clays

Abstract This study investigated the relationship between pore characteristics and unit weight of clayey soils. This relationship was particularly important in case of expansive soils, as the pore characteristics determine moisture flux boundaries, which in turn represent volume change behavior. Current research tried to evaluate the effect of compaction unit weight on the pore size and pore volume along with consolidation and swell characteristics on two expansive clays from semi-arid environment. The two selected clays represent soils with different degrees of expansion, particle size and mineralogy. Pore size characterization for these two soils was performed using Mercury Intrusion Porosimetry, while swell and consolidation characteristics were determined using a conventional oedometer test. Samples for both tests were compacted at different unit weights including, 100, 95, 90, 80, 75, and 70 % of maximum dry unit weight (MDUW) obtained from standard proctor. The compaction water content was kept constant for all unit weight levels. Both pore volume and pore size distribution was analyzed with varying unit weight characteristics and particle sizes. In addition, swell strains and compression indices were studied with varying unit weight of compacted specimens. It was observed that, in the case of samples compacted at 100 % MDUW, about 50 % of the pores were larger than 0.1μm, and this value increased with reduction in unit weight. Current research is of practical importance, especially in the wake of microbial treatments for clayey soils where the passage of microbes depends on the pore size and more specifically pore throat size.

Effect of compaction degree and water content on performance of sandy silt

Effect of compaction degree and water content on performance of sandy silt

Pore-size distribution of a compacted silty soil after compaction, saturation, and loading

Soil microstructure is an important feature that controls soil behaviour at the macroscale. This microstructure depends on the sample preparation method and evolves during saturation and loading. This paper investigates the effects of compaction water content, drying techniques adopted prior to performing porosimetry, saturation and loading on the evolution of the microstructure of a silty soil. Mercury intrusion porosimetry is used to obtain the pore-size distribution at different states of soil presenting single and double porosity. It is observed that in presence of aggregates (obtained from a compaction on the dry side of optimum), the bimodal pore-size distribution is not significantly affected by the saturation process at zero stress. This feature of behaviour is quite specific to low plasticity silty soil. Conversely, loading under saturated conditions has a more significant effect on the pore-size distribution. This bimodal distribution converges into a single mode of pore size when the stress is significantly greater than the apparent preconsolidation pressure. The observed experimental results are interpreted in the light of pore-size distribution evolution during saturation and loading.

Experimental investigation of matric suction in compacted fine-grained soils

ABSTRACTThis paper presents the results of laboratory tests performed to study the effect of compaction properties on the development of matric suction in four different soils (three soils were classified as silty clay and one was classified as silty sand). The soils were compacted at the optimum water content (OWC) and wet and dry of optimum according to the standard Proctor procedure (ASTM D698-12). For each sample, matric suction measurements were made using the filter paper technique. When the silty clay soils were compacted at a water content less than the OWC, a significant increase in matric suction was observed. For all the soils tested, matric suction values were very low when the compaction water contents were greater than the OWC. Plots of matric suction vs. compaction water content [ranging from (OWC-2%) to OWC] were developed for the compacted silty clays. The test results indicate that there is a direct relationship between the compaction properties (i.e. compacted dry unit weight and water content) and the matric suction values retained in compacted silty clays. Preliminary relationships were proposed between the matric suction of compacted silty clays and water content based on the data collected in this paper.

Rate effects on the undrained shear strength of compacted clay

Unconsolidated-undrained (UU) triaxial compression tests were performed on low-plasticity clay specimens compacted to the same void ratio but different initial degrees of saturation to evaluate the impact of axial strain rates ranging from 0.1 to 150%/min on the undrained shear strength. Although an effective stress analysis cannot be performed on the results, they are useful to evaluate the relative roles of initial hydraulic conditions (i.e., matric suction and degree of saturation) and compaction effects (i.e., potential changes in soil structure with compaction water content). This evaluation is relevant due to difficulty in measuring shear-induced pore water and air pressures in consolidated-undrained (CU) compression tests on unsaturated clay. In all tests, the undrained shear strength quantified as the maximum principal stress difference increased log-linearly with axial strain rate, with rates of increase ranging from 4.1 to 9.7% per log cycle of axial strain rate for specimens having initial degrees of saturation ranging from 0.99 to 0.59. The undrained shear strength, rate of increase in undrained shear strength with axial strain rate, and secant moduli all increased nonlinearly with decreasing initial degree of saturation, although compaction effects played an important role in these trends. The increase in undrained shear strength with axial strain rate can be attributed to a reduction in the magnitude of excess pore water pressure, with similar reductions in magnitude for all the degrees of saturation considered. A comparison between the measured undrained shear strength values and the drained shear strength values estimated using the suction stress concept was useful in delineating the impacts of initial hydraulic conditions and compaction effects on the trends in measured undrained shear strength.

Factors Limiting the Progression of Internal Erosion in Zoned Dams: Flow Limiting by an Upstream Material

AbstractIn zoned dams, some types of materials, when located upstream of a damaged core, may impose high hydraulic losses capable of limiting the flows converging toward the flaw in the core. In this paper, the factors influencing flow limiting by an upstream material are addressed experimentally, using the flow limitation erosion test (FLET). The results of eighteen FLETs, on five coarse, broadly graded soils as upstream material, are presented. The laboratory testing shows that the flow-limiting action is strongly dependent on the grading and the compaction characteristics of the upstream soil. The critical parameters are the fines and the gravel content, the nature of the fines, and the compaction water content. Practical rules for the preliminary estimation of the likelihood of flow limiting by an upstream coarse material being effective in stopping the progression of erosion in zoned dams are suggested, based on the results of the experimental study.

Applicability of Filter Design Criteria for Wet Core Embankment Dams in Wet Climates

Abstract In humid and rainy climates, many embankment dams are constructed with core materials, possessing moisture in excess of optimum compaction water content. Since internal erosion and piping are major culprits of embankment dam failures, it would be practically important to understand whether contemporary filter design criteria, which make no reference to moisture content or compaction ratio of soils, are applicable to wet-under compacted cores. In this treatment, 123 no erosion filter (NEF) tests were performed on eleven core materials with varying moisture contents and compaction ratios. Results suggest that proper filter functionality depends on moisture in excess of optimum, soil Plasticity Index, and D15/d85. With increase in excess moisture, a smaller D15/d85 is required for erosion prevention, insomuch as filters designed via recommended criteria, may become inadequate, when the core is excessively wet and under compacted. Generally speaking, D15/d85 ≤ 9 is reliable for cores with limited excess water content and compaction ratios over 95 %; whereas D15/d85 ≤ 7 should be applied for compactions above 90 % and moistures significantly beyond optimum.

Soil-water retention behavior of compacted biochar-amended clay: a novel landfill final cover material

Biochar has long been proposed for amending agricultural soils to increase soil-water retention capacity and therefore promotes crop growth. Recent studies revealed the potential use of biochar-amended soil in landfill final covers to promote methane oxidation and odor reduction. However, the effects of biochar application ratio, compaction water content (CWC), and degree of compaction (DOC) on soil-water retention characteristics of biochar-amended clay (BAC) at high soil suction (dry condition) are not well understood. The present study aims to overcome this knowledge gap. Soil suction was induced using vapor equilibrium technique by a temperature- and humidity-controlled chamber, and the water desorption (drying) and adsorption (wetting) water retention curves (WRCs) of compacted pure kaolin clay and peanut shell BAC with different biochar application ratios (0, 5, and 20 %, w/w), DOCs (80, 90, and 100 %), and CWCs (30 and 35 %) were measured. The correlations between these factors and the gravimetric water content were analyzed by three-way ANOVA followed by the Tukey HSD test. The soil micro-structure was studied by scanning electronic microscope with energy-dispersive X-ray spectroscopy. Measured WRCs of BAC suggest that the soil-water retention capacity at high suction range (48.49–124.56 MPa) was in general increased, upon biochar application. The BAC compacted with CWC of 35 % at low (80 %) and high (100 %) DOCs for the 5 % BAC were increased by 7.30 and 9.77 %, when compared with clay, while the increases of 20 % BAC were 39.89 and 59.20 %, respectively. This is attributed to the embedded effects of clay particles in biochar pores, which reduce the total pore space of BAC. The soil-water retention capacity of BAC was also increased with CWC and decreased with DOC. The results of three-way ANOVA analysis show that the effects of DOC and biochar ratio on soil gravimetric water content was significant (p < 0.05) only at 48.49 MPa on drying path. For other induced suctions, only effects of CWC were significant (p < 0.05). Biochar application increases soil-water retention capacity of the BAC at high soil suction (48.49–124.56 MPa) (dry condition) at both low (80 %) and high DOC (100 %). The soil-water retention capacity of 20 % BAC was much higher than that of 5 % BAC. BAC is a potential alternative landfill final cover soil with a higher soil-water retention capacity to be used in dry areas or regions with a long period of evaporation event.

Calibration of Capacitance Sensors for Compacted Silt in Non-Isothermal Applications

Abstract This study investigates how temperature affects the response of capacitance sensors used to measure the dielectric permittivity of unsaturated soils. The dielectric permittivity is strongly correlated with the volumetric water content, an important variable in understanding water flow processes in unsaturated soils. Although capacitance sensors have been used widely in laboratory and field applications, they have only recently been used to characterize thermally induced water flow in unsaturated soils during geothermal heat exchange processes. To date, no studies have characterized the effects of temperature on capacitance sensor output for dense, compacted soils. This paper describes a calibration methodology that was used to isolate the effects of temperature on the response of capacitance probes in compacted soils having different initial conditions (i.e., compaction water content and dry density). It was observed that changes in temperature of 26°C can lead to an increase in the measured dielectric permittivity of up to 24 % with no changes in volumetric water content of the soil. In addition to defining a soil-specific calibration equation to relate volumetric water content and dielectric permittivity under ambient temperature conditions, a correction equation was proposed for temperature effects. The capacitance sensor's response to changing temperatures was observed to be sensitive to both the initial volumetric water content and the initial density of the soil, and parameters were defined for both of these terms in the correction equation.

Experimental Study on the Over-Consolidation Stress History of Subgrade Compacted Clay

To study the over-consolidation stress history of clay in a high-filled embankment during hierarchical compaction, indoor compaction and one-dimensional consolidation tests are performed on roadbed backfill clay. Two homemade compaction devices are used to drill into standard heavy compacted clay to prepare compacted clay samples and subsequently investigate the influence of compaction work, compaction impulse, water content, and compaction degree on over-consolidation stress history. Results provide an experimental basis to determine the parameters of an over-consolidated constitutive model. Experimental results show that compacted clays with the same compaction degree and water content can differ in stress history, and that this stress history increases as the compaction impulse per unit area builds up. Under the conditions of the same compaction work and over-consolidated formation, the compacted clay achieves the maximum compaction degree and stress history if water content is at the optimal level. If the water content deviates from the optimal level, the stress history of the compacted clay decreases, and it is more significantly affected by the compaction degree with increased water content.

Mix design considerations of foamed bitumen mixtures with reclaimed asphalt pavement material

In the present work, a mix design parametric study was carried out with the aim of proposing a practical and consistent mix design procedure for foamed bitumen mixtures (FBMs). The mix design parameters that were adopted in the study are mixing and compaction water content (MWC), compaction effort using a gyratory compactor and aggregate temperature. This parametric study was initially carried out on FBMs with virgin limestone aggregate without reclaimed asphalt pavement (RAP) material and a mix design procedure was proposed. This proposed methodology was also found to apply to FBMs with RAP. A detailed consideration was also given to characterising the RAP material so as to understand its contribution to the mechanical properties of FBMs. Optimum MWC was achieved by optimising mechanical properties such as indirect tensile stiffness modulus and indirect tensile strength (ITS-dry and ITS-wet). A rational range of 75–85% of optimum water content obtained by the modified Proctor test was found to be the optimum range of MWC that gives optimum mechanical properties for FBMs. It was also found that the presence of RAP influenced the design foamed bitumen content, which means that treating RAP as black rock in FBM mix design is not appropriate. To study the influence of bitumen and water during compaction, modified Proctor compaction and gyratory compaction were employed on mixes with varying amounts of water and bitumen. By this, the work also evaluated the validity of the total fluid (water + bitumen) concept that is widely used in bitumen–emulsion-treated mixes, and found it not to be applicable.

Effects of Variation in Compaction Water Content on Geotechnical Properties of Lime-treated Clayey Soil

The note presents the results of an experimental research study on the behaviour of a clayey soil of high plasticity treated with 3% quicklime for the stabilization of the foundation soil of a plant to be constructed along a slope. The aim of the study is to investigate the effect of a wide range of water content and of curing time on the mechanical and hydraulic characteristics of the treated soil. Soil-lime samples were prepared by wet mixing and Standard Proctor compaction. The development of chemical reactions in the compacted soil-lime mixtures were monitored by measuring the pH values of the soaking water with curing time. In the long term, a reduction of three orders of magnitude in permeability values was observed by comparing optimum and 5% wet of optimum conditions. Also compressibility was affected by variations in the compaction water content. The shear strength was not significantly affected by water content varying in the considered range.