Assessment of Unconfined Compressive Strength of Cement Stabilized Marine Clay

Two aspects of deep mixing method, the difference relating strength gain in dry jet mixing (DJM, reagent powder introduced into the ground) and cement deep mixing (CDM, reagent slurry introduced into the ground), and prediction of unconfined compressive strength of cement stabilized marine clay, are discussed in this paper. The first part of this paper concentrates on the difference between DJM and CDM on strength gain, and suggests a guideline for DJM and CDM selection. An indicator in terms of water content ratio, which is defined as the ratio of water content to the liquid limit of the soil, is presented by statistical analysis from the laboratory and field test data as a guideline for the selection of DJM or CDM. Based on the laboratory test data, a mathematical model relating strength gain of cement stabilized marine clay to related variables is developed. A new simple index designated as total water-cement ratio, which is defined as the ratio of water weight in the soil-cement to the weight of cement in dry state, is proposed for interpretation of test data of soil-cement. The proposed method is then verified with available test data published by other different researchers.     

Experimental Investigation of Unconfined Compression Strength and Stiffness of Cement Treated Salt-Rich Clay

Soft clay with high sodium chloride salt concentration is a problem encountered by geotechnical and highway engineers. Chemical stabilization using cement is an attractive method to improve the engineering properties of soft soil. However, very limited studies have been conducted to reveal the effect of salt concentration on the engineering properties of cement-stabilized soil and the reported results in literature are not consistent. The impact of sodium chloride salt on the strength and stiffness properties of cement-stabilized Lianyungang marine clay is studied in this study. The clay with various sodium chloride salt concentrations was prepared artificially and stabilized by various contents of Ordinary Portland cement. A series of unconfined compressive strength (UCS) tests of cement stabilized clay specimen after 7, 14, and 28 days curing periods were carried out. The results indicate that a high sodium chloride salt concentration has a detrimental effect on the UCS and stiffness of cement-stabilized clay. The detrimental effect of salt concentration on the strength and stiffness of cement-stabilized clay directly relates to cement content. Soils mixed with high cement content are more resistant to the negative effect of salts than soils mixed with low cement content. The ratio of modulus of elasticity to UCS of cement treated soil does not have an obvious relationship with salt concentration. The findings of this study present a rational basis for the understanding of the impact of salt on the engineering properties of cement-treated soil.     

Effect of Sample Disturbance on Unconfined Compression Strength of Natural Marine Clays

1 .IntroductionCoastalstructuresoftenencountersettlementandstabilityproblemsofsoftmarinefoundation (Liuetal.,1 999;Zhouetal.,2 0 0 0 ;Liuetal.,2 0 0 3) .Manyresearchershaveillustratedthatnaturalmarineclaysaregenerallysubjectedtotheeffectsofsoilstructureduringtheirdepositionalandpost depositionalprocesses (Zhangetal.,1 995;Hongetal.,2 0 0 3a ;2 0 0 3b) .Thesoilstructureofnat uralmarineclaysiseasilydamagedduringsamplingandhandlingbecausenaturalmarineclaysgeneral lyhavehighwatercontentandlowsti…     

Strengthening of Soft Marine Clay Using Bioencapsulation

Dredged or excavated soft marine clay can be improved by mixing it with cement or lime. However, these treatments are usually expensive. It is shown in this paper that soft marine clay can be strengthened through a bioencapsulation method in which the shear strength of clay aggregates can be substantially increased after the aggregates are treated with urease-producing bacteria, calcium chloride, and urea. We found that the bioencapsulation had increased the unconfined compressive strength of marine clay aggregates with a size of 5 mm from almost zero to more than 2 MPa. The strength of the bioencapsulated clay aggregates decreases with the increase in the size of the aggregate when the size is greater than 5 mm.     

Effect of Silica Fume on Compressive Strength of Oil-Polluted Concrete in Different Marine Environments

In the present research, effect of silica fume as an additive and oil polluted sands as aggregates on compressive strength of concrete were investigated experimentally. The amount of oil in the designed mixtures was assumed to be constant and equal to 2% of the sand weight. Silica fume accounting for 10%, 15% and 20% of the weight is added to the designed mixture. After preparation and curing, concrete specimens were placed into the three different conditions: fresh, brackish and saltwater environments (submerged in fresh water, alternation of exposed in air & submerged in sea water and submerged in sea water). The result of compressive strength tests shows that the compressive strength of the specimens consisting of silica fume increases significantly in comparison with the control specimens in all three environments. The compressive strength of the concrete with 15% silica fume content was about 30% to 50% higher than that of control specimens in all tested environments under the condition of using polluted aggregates in the designed mixture.     

Strength Behavior of Naturally Cemented Marine Clay Due to Change in Ground Water Level

The change in strength and deformation behavior of a typical marine clay deposit formed under shallow water is presented and discussed for the conditions of changing water table. This is a costal marine clay deposit with moderate carbonates along the east coast of India. The soil samples were taken from tidal flats where the sea had receded some time back, and the behavior of this deposit had been studied for the conditions of 1976, with high water table, and for the conditions of 2001, with depleted water table. Undisturbed soil samples were taken from sheeted open test pits. Standard consolidation and triaxial shear tests were conducted. Consolidation tests conducted on the samples taken for 1976 conditions with high water contents indicate that cementation effect are erased out under moderate stresses. Beyond this stress range, it behaves like soft, normally consolidated clay. In contrast, the results obtained from samples taken during 2001, with depleted water table, clearly indicate that the soil behaves like an over-consolidated one, and the improvement in the system is due to the chemical bonding and desiccation.     

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.     

原土环境下水泥土强度衰减过程室内试验研究

在水土耦合的室内原土环境中,通过微型贯入、扫描电镜(SEM)、能谱(EDS)分析、X射线衍射(XRD)、离子含量及pH值测试等多种试验手段,研究滨海相软土场地形成的水泥土强度的分布规律及其衰减过程,并阐明水泥土劣化层和未劣化层的发展规律。结果表明:水泥土劣化深度随养护时间的增长和水泥掺入比的减小不断增大,至360d时最大劣化深度达到11.9mm,明显大于同龄期海水环境中养护的水泥土的劣化深度;与未劣化层相比,劣化层的孔径增大,孔隙增多,水泥水化产物减少;经原土养护相同时间,水泥土中pH值及主要离子含量分布规律与室内海水环境中的水泥土相似,其中pH值和Ca^2+含量随着试样深度的增大而增大,而Mg^2+、SO4^2-、Cl^-含量随试样深度的增大而减小;水泥土中Ca^2+含量沿试样深度方向的分布规律与强度变化规律相似。在原土条件下,水泥土中Ca的溶出更加显著,导致后期水泥土强度衰减加剧。原土中水泥土强度衰减过程与海水中相同。     

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.     

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.     

Field Evaluation of Undrained Shear Strength from Piezocone Penetration Tests in Soft Marine Clay

The use of the piezocone penetration test (CPTU) in a geotechnical site investigation offers direct field measurement on stratigraphy and soil behavior. Compared with some traditional investigation methods, such as drilling, sampling and field inspecting method or laboratory test procedures, CPTU can greatly accelerate the field work and hereby reduce corresponding operation cost. The undrained shear strength is a key parameter in estimation of the stability of natural slopes and deformation of embankments in soft clays. This paper provides the measurements of in situ CPTU, field vane testing and laboratory undrained triaxial testing of Lianyungang marine clay in Jiangsu province of China. Based on the literature review of previous interpretation methods, this paper presents a comparison of field vane testing measurements to CPTU interpretation results. The undrained shear strength values from both the field vane tests and cone penetration resistances are lowest at the mid-depths of the marine clay layers, and the excess pore water pressures are highest at the mid-depths of the marine clay layers, indicating that the marine clay layer is underconsolidated.     

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.     

海相软土场地水泥土劣化机理室内试验研究

将水泥土和周围土体作为研究对象,利用室内化学分析试验得到了离子浓度的时空分布规律,并从腐蚀离子干预水化反应进程和分解水化产物两个过程揭示了海相软土场地水泥土劣化机理。Ca^2+由水泥土向土体中扩散,Mg^2+、SO42^-及Cl^-从土体向水泥土扩散;随着水化反应的进行,Ca^2+不断生成,水泥土中足够多的Ca^2+是保证水化反应进行并维持水化产物稳定的必要条件,Ca^2+不断向土体扩散是水泥土劣化的原因之一;水泥土内部的SO42^-及Cl^-在浓度较低(分别低于9和15 g/L)时有利于水泥土强度的提高,浓度较高时则导致水泥土发生胀裂;水泥土中Mg^2+的存在会阻碍水化产物的生成并分解水化产物,但浓度较低(低于3 g/L)时,影响不明显;土体中Mg^2+、SO42^-及Cl^-浓度高于水泥土中的浓度,在水泥土表层与水化产物反应生成胶结性差及膨胀性高的物质,促使水泥土劣化。     

Long-Term Consolidation and Strength Behavior of Marine Clay Improved with Fly Ash

This paper presents an investigation of the long-term consolidation and strength behavior with fly ash as an additive in improving soft marine clay in Wando, Korea. 0%, 5%, 10%, 20% and 25% of the soil was replaced with fly ash. Consolidation tests were performed as incremental loaded tests. In addition, unconfined compressive strength were determined after 1, 14, 28 and 90 days. A series of forty-two long-term consolidation tests that lasted for 60 days under the constant loading were also conducted. Creep settlements of the blends decreased significantly with an increase in fly ash content. The shear strength properties increased with an increase in fly ash content. Statistical evaluation reveals an excellent correlation between the measured and predicted undrained shear strengths.     

Behavior of Marine Clay Subjected to Cyclic Loading with Sustained Shear Stress

Foundations of offshore structures are designed to withstand a combination of static and cyclic loads due to ocean waves. Wave action on offshore structures can cause a significant amount of cyclic horizontal and vertical forces to be transmitted to the soil through the foundation. In all these cases, these cyclic loads are considered to be superimposed over the initial sustained static stress due to the self-weight of structures. This study considers various factors that influence the development of deformation and pore water pressure in a typical cemented marine clay. These results show that the sustained static shear stress significantly influences the strength and deformation behavior of marine clay under cyclic loading. Up to a certain range of sustained static stress, there is an improvement in strength during cyclic loading and the cyclic strains are greatly reduced.     

Behavior of Marine Clay Subjected to Cyclic Loading with Sustained Shear Stress

Foundations of offshore structures are designed to withstand a combination of static and cyclic loads due to ocean waves. Wave action on offshore structures can cause a significant amount of cyclic horizontal and vertical forces to be transmitted to the soil through the foundation. In all these cases, these cyclic loads are considered to be superimposed over the initial sustained static stress due to the self-weight of structures. This study considers various factors that influence the development of deformation and pore water pressure in a typical cemented marine clay. These results show that the sustained static shear stress significantly influences the strength and deformation behavior of marine clay under cyclic loading. Up to a certain range of sustained static stress, there is an improvement in strength during cyclic loading and the cyclic strains are greatly reduced.     

Laboratory and Field Observations for Golden Horn Marine Clay

Istanbul, the largest city in Turkey and one of the major metropolitan areas in the world, cleaned one of its environmentally polluted areas—Golden Horn—by dredging 5 million m³ of the bottom sediments and pumping the resulting sludge to a storage area behind a dam built at an abandoned rock quarry site in Alibey district. The reclamation of the land that formed over the storage area of Golden Horn dredged material is socially and economically very desirable. In this paper, results from experimental studies that are focused on determining the shear strength behavior of the dredge material and undisturbed soil are presented. Slurry consolidometer test, large model tests and small model tests are used to consolidate the dredged soil samples from Halic to simulate the natural consolidation behavior of these soils. Shear strength parameters are determined by laboratory vane tests; unconfined compression tests; undrained-unconsolidated (UU) and consolidated-undrained (CU) triaxial tests on samples that are obtained through in situ undisturbed samples and laboratory model tank and slurry consolidation. Moreover, the effects of fly ash and lime additives on the undrained shear strength were determined by mixing the materials with the dredged clay from Golden Horn during the model experiments conducted in the laboratory. Based on these findings, equations are proposed that govern the relationships between undrained shear strength and water content value.     

Strength Sensitivity of Marine Ariake Clays

Natural Ariake clays are characterized by high sensitivity. In this study, the mechanism and the factors controlling undrained shear strengths of both undisturbed and remolded Ariake clays are discussed. A series of unconfined compressive tests were performed on undisturbed samples of natural Ariake clays. The remolded undrained shear strength is predicted using a quantitative expression derived from extensive data of remolded undrained shear strength for a number of soils compiled from resources in the literature. The sensitivity of natural Ariake clays derived from the ratio of half of unconfined compressive strength for undisturbed samples to remolded undrained shear strength is found to be affected by both natural water content and normalized water content that is defined as the ratio of natural water content to liquid limit. The smaller the natural water content, the higher the sensitivity is at the same normalized water content. At the same natural water content, the larger the normalized water content, the higher the sensitivity is.     

Strength Sensitivity of Marine Ariake Clays

ABSTRACT

Natural Ariake clays are characterized by high sensitivity. In this study, the mechanism and the factors controlling undrained shear strengths of both undisturbed and remolded Ariake clays are discussed. A series of unconfined compressive tests were performed on undisturbed samples of natural Ariake clays. The remolded undrained shear strength is predicted using a quantitative expression derived from extensive data of remolded undrained shear strength for a number of soils compiled from resources in the literature. The sensitivity of natural Ariake clays derived from the ratio of half of unconfined compressive strength for undisturbed samples to remolded undrained shear strength is found to be affected by both natural water content and normalized water content that is defined as the ratio of natural water content to liquid limit. The smaller the natural water content, the higher the sensitivity is at the same normalized water content. At the same natural water content, the larger the normalized water content, the higher the sensitivity is.     

Secondary Compression Features of Jiangsu Soft Marine Clay

The results of one-dimensional compression tests conducted on undisturbed specimens of Jiangsu soft marine clay is presented. Because of its high in situ void ratios and natural water content, Jiangsu soft marine clay displays high values of both the virgin compression index, C_c, and the secondary compression coefficient, C_α. The laboratory data indicates that the value of the ratio C_α/C_c for Jiangsu soft marine clay is constant. However, neither C_α nor C_c are constant: they both depend upon the natural water content (or void ratio) and thus are also dependent on the deformation (or compression) of Jiangsu soft marine clay. Settlement analyses show that the secondary settlement of Jiangsu soft marine clay is a significant component of the field settlement. The concept of a constant value for C_α/C_c is used to predict the secondary settlement of a surcharged embankment founded upon Jiangsu soft marine clay. The predictions are in agreement with the limited post-construction field measurements of the embankment settlement.