Mechanical Characteristics of Light-Weighted Soils Using Dredged Materials

This study investigates the mechanical characteristics of light-weighted soils (LWS) consisting of expanded polystyrene (EPS), dredged clays, and cement through both unconfined and triaxial compression tests. The mechanical characteristics of the compressive strength of LWS are analyzed with varying initial water contents of dredged clays, EPS ratio, cement ratio, and curing pressure. In the triaxial compression test, it is found that the compressive strength of LWS associated with EPS is independent on the effective confining pressure. When both EPS ratio is less than 2% and cement ratio is more than 2%, the compressive strength rapidly decreases after the ultimate value. This signifies that the compressive strength-strain behavior is quite similar to that of the cemented soil. The ground improved by LWS has the compressive strength of 200 kPa associated with the optimized EPS ratio of 3-4% and initial water content of 165-175%. The ultimate compressive strength under both triaxial and unconfined compression tests is almost constant for a cement ratio of up to 2%.     

Mechanical Characteristics of Light-Weighted Soils Using Dredged Materials

This study investigates the mechanical characteristics of light-weighted soils (LWS) consisting of expanded polystyrene (EPS), dredged clays, and cement through both unconfined and triaxial compression tests. The mechanical characteristics of the compressive strength of LWS are analyzed with varying initial water contents of dredged clays, EPS ratio, cement ratio, and curing pressure. In the triaxial compression test, it is found that the compressive strength of LWS associated with EPS is independent on the effective confining pressure. When both EPS ratio is less than 2% and cement ratio is more than 2%, the compressive strength rapidly decreases after the ultimate value. This signifies that the compressive strength-strain behavior is quite similar to that of the cemented soil. The ground improved by LWS has the compressive strength of 200 kPa associated with the optimized EPS ratio of 3–4% and initial water content of 165–175%. The ultimate compressive strength under both triaxial and unconfined compression tests is almost constant for a cement ratio of up to 2%.     

Laboratory study on cement admixed marine silt bricks

For the purpose of efficient utilization of sediments dredged from harbor, a new method was proposed in this study. Marine silt bricks were made by mixing sediments with cement and gypsum, placing it in a cubic mold with 240 mm in length, 115 mm in width, and 53 mm in height, and curing for certain days. To investigate the effects of cement and initial water content of soil on the mechanical behavior of marine silt bricks, unconfined compressive and flexural strength tests were carried out. Given the same curing time and cement content, the higher the initial water content, the lower the compressive and flexural strength. After 60 days of curing, the compressive strength of marine silt bricks with cement content = 20% and water content = LL (liquid limit) reached approximately 5 MPa. The flexural strength was relatively low. The flexural strength of marine silt bricks with 20% cement and water content = LL was around 1.5 MPa. The compressive and flexural strength decreased with the increase of water/cement ratio. As for the curing time, longer curing time had a positive impact on the compressive strength. The ratio of flexural to compressive strength varied slightly in the range of 0.4–0.5.     

Critical State Parameters of Dredged Chennai Marine Clay Treated with Low Cement Content

The present article discusses the stress–strain behavior and critical state parameters of the dredged Chennai marine clay stabilized with low cement content (2.5–10%). A series of one-dimensional consolidation tests and consolidated undrained tri-axial tests are performed on the cement stabilized dredged Chennai marine clay to evaluate the critical state parameters (λ, κ, M, Г, N) for varying cement contents and curing days. The results show that the slope of the critical state line M increases with an increase in the cement content. The parameter λ for the treated marine clay increases up to a cement content of 7.5% followed by a reduction. The parameter κ decreases with the addition of cement content. Finally, empirical formulations are proposed to predict the critical state parameters as the functions of the cement's contents and curing days.     

Effect of a cement-lignin agent on the shear behavior of Shanghai dredged marine soils

With the rapid urbanization in Shanghai, China, suitable fill materials have been reported to be in great shortage in recent years. A prospective solution to these issues is to convert the huge amount of existing dredged marine soils to construction materials via solidification. However, there have been no studies on the shear behavior of solidified dredged materials from Shanghai region so far, while it has been reported by various researchers that the available data obtained from certain types of clay cannot be confidently and readily applied to other types of soils. To address this challenging issue, in this article, samples of Shanghai marine dredged soils were retrieved from the world’s largest reclamation project in Shanghai Lin-gang New City. A series of laboratory tests have been conducted to investigate the shear behavior of Shanghai dredged marine soils solidified using a new composite curing agent made of cement and lignin. The test results and the effect of this cement–lignin agent on the shear behavior of Shanghai marine soils, including the stress–strain behavior, shear strength properties, and failure characteristics are presented and discussed, which can provide valuable reference for the use of dredged soils as construction materials in the Shanghai region.     

Strength evaluation of marine clay stabilized by cementitious binder

Abstract

Evaluation of the strength of cement-treated clay with a broad range of mix ratios and curing periods was conducted using unconfined compression tests (UCTs). The influence of cement content, total water content, and curing period on the unconfined compressive strength of cemented clay are investigated. It is found that, at constant total water content, higher cement content results in higher unconfined compressive strength, while the total water content has an opposite effect. A power function can be used to correlate the unconfined compressive strength with the cement content or the total water content. For a fixed mix ratio, the unconfined compressive strength of cement-stabilized clay increases with the curing period, the effect of which can be characterized by a semi-log formula. Also, a strength-prediction model that considers both mix ratios and curing periods for cement-admixed marine clay is developed and validated; the model can capture the effect of clay type by considering the plastic index of untreated soils. It is also proved that the proposed framework for strength development is also applicable for other cement types.     

Effects of fly ash and slag content on the solidification of river-dredged sludge

Abstract

River-dredged sludge has a high water content and minimal bearing capacity and strength. Adding cement, fly ash, and slag to dredged sludge as a combined curing agent can quickly reduce its water content and improve its strength. This study experimentally investigates the solidification effectiveness of different proportions of curing agents using methods including electron microscopy, particle size analysis, water ratio limit, and water content and direct shear tests. The water content and shear strength of different combined curing agents are obtained at different ages. We find that an optimum curing agent combination exists. With increases in fly ash and slag content, test results indicate that the water content of solidified sludge first decreases and then increases, whereas the shear strength first increases and then decreases, allowing an optimal combination curing agent to be obtained. When using industrial waste residue as curing agent, it is necessary to consider the negative effects of the curing agent to better control the dosage so as to achieve better curing effect.     

Geotechnical properties of dredged marine sediments treated at high water/cement ratio

Cement and lime are widely employed in soil and sediment treatment for an improvement of geotechnical properties, such as an increase in mechanical strength which enables beneficial use in various geotechnical applications. In this study, fine organic-rich dredged harbour sediments of 120% relative water content were treated with dry cement at contents varying between 2% and 10% of bulk sediment wet weight. Tests based on assessments of one-dimensional compression and Atterberg limits were performed on untreated and cement-treated sediments for various curing periods, as well as grain-size, SEM and X-ray diffraction analyses. The results confirm that increasing the cement content improves the geotechnical properties of these harbour sediments. Already in the early phase of curing (first 3 days of curing), particle size increases while sediment plasticity decreases. Changes in the compressibility behaviour include an increase in apparent preconsolidation pressure, in the compression index C _c and in the primary consolidation coefficient C _v, and a decrease in the secondary compression index . This means that the new materials are characterized by a behaviour intermediate between that of fine and that of coarser soils.     

Comparison Between Shear Behaviors of Overconsolidated Nakdong River Sandy Silt and Silty Sand

From this research, overconsolidated undrained and drained behaviors of specimens with high sand content were highly dilatant. According to the comparison results of laboratory tests, the deviator stresses of silty sand were greater than sandy silt due to high sand content under increasing OCRs, and both silty sand and sandy silt were presented strain softening tendency after failure under undrained loading. The pore water pressure increased with increasing fines content under increasing OCRs. Silty sand exhibited more dilatancy and increasing shear strength than sandy silt because pore water pressures of silty sand were lower than sandy silt under higher OCRs. In overconsolidated drained tests, silty sand is higher strength than sandy silt because silty sand has a lower volumetric strain and higher deviator stress than sandy silt under increasing OCRs. As the degree of overconsolidation increased, similar behaviors of silty sand and sandy silt observed that volumetric strain decreased to negative values due to dilatancy effect and low-cohesion under current effective confining pressures.     

Mechanical properties of calcareous silts in a hydraulic fill island-reef

Abstract

The mechanical characteristics of calcareous silt interlayers play an important role in the stability of island-reef foundations. Direct shear and consolidation tests were performed to study the relationship between the mechanical properties and the physical parameters of calcareous silt. Based on the consolidation test results and analysis of the settling examples, different calculation methods for soil settling were compared. The results show the following. (1) The relationship between the cohesion and water content of calcareous silt can be represented by an M-shaped curve. The water contents corresponding to the two peaks of the M-type curve increase with increasing dry density. (2) When the dry density is less than 1.33?g/cm³, increasing the density significantly improves the internal friction angle of calcareous silts. When the dry density of the calcareous silt is greater than 1.33?g/cm³, the internal friction angle is affected by both the dry density and the water content. (3) The shear strength decreases when the water content exceeds the optimum level. (4) The compressive modulus of calcareous silt is larger than that of terrigenous silt. Specifically, it decreases with decreasing dry density and increasing water content. (5) The stepwise loading method should be used to estimate the soil settling before fill engineering construction.     

A dredged material solidification treatment for fill soils in East China: A case history

Large amounts of sediments are dredged annually from Chinese oceans. Dredged materials (DMs) possess poor geotechnical properties and are normally treated as waste. This paper presents the first large-scale engineering application of DM solidification treatment in China. The technique has been used to treat approximately 1.8?×?10⁶?m³ of DM from Taihu Lake to produce fill soils. Portland cement was chosen as the solidification material, the amount of which is confirmed through indoor unconfined compressive strength (UCS) tests. Special solidification machines process DM at 120?m³/hours. Field-based DM solidification engineering began in September 2006. Curing specimens were examined over 28 days. Results show that both UCS and failure strain of solidified DM could meet fill soil requirements. Bearing capacity was also assessed with a cone penetrometer test. Samples were examined after 2 years (after project completion), and the mean UCS of the specimens was 237.2?kPa, which completely satisfied the engineering request. Wuxi Taihu City Science and Technology Industrial Park has now been established on top of the solidified DM storage yard. The successful engineering of such facilities results in economic and environmental benefits; thus, engineering applications of DM solidification treatment are widely promoted in China.     

Mechanical and Germination Characteristics of Stabilized Organic Soils

High-organic-content dredged soils are known to have inferior mechanical characteristics because they are highly compressible and have low shear strength. To recycle dredged soil with a high organic content as a top soil this study describes an investigation of the mechanical properties and germination characteristics of stabilized organic soils using unconfined compression tests, pH tests, and seed germination tests. Several mixtures with organic contents in the range 0–30% by mass and binder contents in the range 5–15% were prepared to evaluate the effects of the organic content on the mechanical and germination characteristics of the stabilized soils. The results show that an increase in the organic content leads to a decrease in the strength and pH of the stabilized organic soil, which are favorable conditions for germination. The germination rate increased significantly with the increasing organic content, and the plant growth rate also increased. The addition of a binder into the mixtures increased the strength of the soil; however, it also increased the pH and decreased the rate of seed germination and plant growth.     

Study on “buoyancy-viscous force” of slurry-like soils

In newly completed hydraulic-fill dump sites, the water content of dredged slurry is usually more than two times of the liquid limit, objects can be stabilized after penetrating into dredged slurry for a certain depth. This property can be defined as the “buoyancy-viscous force” of slurry-like soils in this study. To investigate the mechanism of specific bearing capacity of slurry-like soils, the interaction between the penetrating objects and the slurry was observed. Based on the boundary layer theory of viscous fluid and the energy conservation principle, a theoretical model was established to calculate the “buoyancy-viscous force” of slurry-like soils, and then validated by load-controlled penetration tests in laboratory. It is indicated that the model prediction agreed with the experimental results very well when the water content is more than two times of the liquid limit.     

Rheological behavior of dredged slurries at high water contents

Each year in the world, there is significant amount of dredged slurries generated during geotechnical jobs. In the slurry storage process, the rheological behavior is a key factor affecting the motion of dredged slurries. To gain better understanding on this behavior, experiments on dredged slurries with different liquid limits are conducted using rotary viscometer. It has been found that, as water content increases, slurry property can change from Bingham plastic fluids to Newtonian fluids. In log–log coordinates, their corresponding yield stress and plastic viscosity are in linear relationship with their water contents and the intersection of these two lines can be treated as the turning point which is 4.7 times the liquid limit. The yield stress and plastic viscosity of different dredged slurries can be normalized efficiently using normalized water content. So, in this paper, a new quantitative prediction method for yield stress and plastic viscosity is proposed, which is effective for use in alkined modes of motion, is proposed.     

Mechanical Behavior of Light-Weight Soil Under Consolidated Drained Shear Condition

To reveal the influence of material composition on mechanical properties of light-weight soil, stress-strain -volumetric strain characteristics and Poisson's ratio of mixed soil were researched by consolidated drained shear tests. The results show that light-weight soil is a kind of structural soil, so its mechanical properties are affected by mixed ratio and confining pressure, and mixed soil possesses structural yield stress. When confining pressure is less than the structural yield stress, strain softening occurs; when confining pressure is more than the structural yield stress, strain hardening is observed. There are two kinds of volume change behavior: shear contraction and shear dilatancy. Shear dilatancy usually leads to strain softening, but there isn't an assured causal relationship between them. Poisson's ratio of mixed soil is a variational state parameter with the change of stress state, it decreases with increased confining pressure, and it increases with increased stress level. When axial strain is near 5%, Poisson’ ratio is gradually close to a steady value. The main range of Poisson's ratio is 0.25～0.50 when confining pressure changes from 50 to 300 kPa. When unconfined compressive strength of mixed soil is less than 328 kPa, its stress-strain-volumetric strain characteristics can be predicted very well by Duncan-Chang model (E-B model). However, when the range of unconfined compressive strength is [328 kPa, 566 kPa], the model can't predict stress-strain characteristics accurately when confining pressure is under 200 kPa, and it also can't predict the strong shear dilatancy phenomenon of mixed soil under low confining pressure.     

Strength Characteristics of the Cement-Stabilized Surface Layer in Dredged and Reclaimed Marine Clay, Korea

A series of tests in both laboratory and field were performed to investigate the engineering and mechanical properties, especially flexural strength, of cement-stabilized soils. The strength of cement-stabilized soils mainly depends on water-to-cement ratio and curing temperature. The higher curing temperature and the longer curing time, the higher strength in cement-stabilized soils generates. The high ratio of water-to-cement results in lower strength. The compressive strength observed in the field is similar to the strength in the laboratory. Field tests on a cement-stabilized soil layer indicate that the strength is significantly affected by the thickness of the improved layer, which is directly related to the moment of inertia. In addition, the failure shape observed in a cement-stabilized layer in the field looks likes a bending failure type, because the flexural tensile strength, rather than the compressive strength, mainly dominates the failure of cement-stabilized layer. The flexural tensile strength is closely related to the moment of inertia. Therefore, the flexural tensile strength should be considered for determining the thickness and strength in improvement of soft clay.     

Strength Characterization of Sand-Bentonite Mixtures and the Effect of Cement Additives

This article studies the strength properties of compacted sand-bentonite landfill barrier material with and without cement addition at different periods of aging. Test results indicated that strength values, both in compression and tension, increased up to threefold in cement added samples, as well as enhancing the ductile behavior. Cubic modulus, described as the slope of the elastic portion of the cubic compressive stress versus strain curves, is determined along with initial and flexural moduli, and all the strength and moduli values were correlated with each other. Finally, it is concluded that there is a marked improvement in strength properties and moduli with cement inclusion and that the effect of aging has been very effective.     

Engineering Characteristics of the Lightweight Air-Mixed Soil (LWS) Containing Silty Marine Sediment

This study was conducted to find out the characteristics of the lightweight air-mixed soil (LWS) used for a road embankment. Compressive strength, permeability, and capillary height of the LWS were studied, and to support these studies, its inside structure was analyzed in detail. Various size air pores exist in the LWS, and their distribution with a location is almost constant. Numerous tiny cracks formed by different grain sizes between in-situ soil (silty marine sediment) and solidificator exist inside the air pores so that the LWS can be affected by water. Peak strength of the LWS is found to be less dependent on the water, but the behavior of strength-strain was affected by water. Permeability is a little bit higher than clay's permeability. Capillary rise is rapid in the beginning of the test, and then slows down. The capillary rise can increase the density of the LWS, and thus requires special attention during design and maintenance of the structures, which were constructed with the LWS.     

Strength Characteristics of the Cement-Stabilized Surface Layer in Dredged and Reclaimed Marine Clay,Korea

ABSTRACT

A series of tests in both laboratory and field were performed to investigate the engineering and mechanical properties, especially flexural strength, of cement-stabilized soils. The strength of cement-stabilized soils mainly depends on water-to-cement ratio and curing temperature. The higher curing temperature and the longer curing time, the higher strength in cement-stabilized soils generates. The high ratio of water-to-cement results in lower strength. The compressive strength observed in the field is similar to the strength in the laboratory. Field tests on a cement-stabilized soil layer indicate that the strength is significantly affected by the thickness of the improved layer, which is directly related to the moment of inertia. In addition, the failure shape observed in a cement-stabilized layer in the field looks likes a bending failure type, because the flexural tensile strength, rather than the compressive strength, mainly dominates the failure of cement-stabilized layer. The flexural tensile strength is closely related to the moment of inertia. Therefore, the flexural tensile strength should be considered for determining the thickness and strength in improvement of soft clay.     

Behavior of Loose Silty Sand of Chlef River: Effect of Low Plastic Fine Contents and Other Parameters

This article presents a laboratory study of static behavior of silty-sand soils. The objective of this laboratory investigation is to study the effect of initial confining pressures and fines content on the undrained shear strength (known as liquefaction resistance) response, pore pressure, and hydraulic conductivity of sand–silt mixtures. The triaxial tests were conducted on reconstituted saturated silty-sand samples at initial relative density D_r = 15% with fines content ranging from 0 to 50%. All the samples were subjected to a range of initial confining pressures (50, 100, and 200 kPa). The obtained results indicate that the presence of low plastic fines in sand–silt mixture leads to a more compressible soil fabric, and consequently to a significant loss in the soil resistance to liquefaction. The evaluation of the data indicates that the undrained shear strength can be correlated to fines content (F_c), inter-granular void ratio (e_g), and excess of pore pressure (Δu). The undrained shear strength decreases with the decrease of saturated hydraulic conductivity and the increase of fines content for all confining pressures under consideration. There is a relatively high degree of correlation between the peak shear strength (q_peak) and the logarithm of the saturated hydraulic conductivity (k_sat) for all confining pressures.