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.     

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.     

Lime Stabilization of Soils Underlying a Salt Evaporation Pond: A Laboratory Study

The purpose of this article is to investigate a possible use of lime for the stabilization of base soils underlying salt evaporation ponds in Çamalt? Solar Marine Salt Plant. The plant is located on the old Gediz River Delta, on the north shore of the Izmir Bay-Turkey, where alluvial deltaic soft marine sediments constitute the local soil condition. The low bearing capacity of the pond base soils results in some problems on the mechanical harvest of the solar salt. Therefore, stabilization was taken into consideration for improving the productivity of the salt plant. For this purpose, bench-scale laboratory tests were performed on the specimens that had been sampled from the bases of the salt evaporation pond to investigate the influence of lime on the unconfined compressive strength (UCS) of these marine sediments. By interpreting the pH test results and consistency limits of the lime stabilized soils, optimum lime content was determined as 8%. The verification of the long-term pozzolanic reactions for the optimum lime content was conducted by performing UCS tests with up to six months curing periods, along with the microstructural analysis through X-ray diffraction analysis (XRD) and a scanning electron microscope (SEM). Long-term tests revealed that the optimum lime content successfully sustained the required pozzolanic reactions, and a strength gain of 500% was achieved for a six-month curing period.     

Primary yielding locus of cement-stabilized marine clay and its applications

ABSTRACT

Strength and stiffness properties of materials are widely studied and used in civil engineering practice. However, most studies are based on unconfined conditions, which are different from real status of soil. This study investigated the primary yielding and yield locus for cement-stabilized marine clay. In this study, two types of cement-stabilized soils were studied through isotropic compression, triaxial drained shearing, unconfined compression, and bender element testing. Specimens with 20–50% of cement content and 7–90 days of curing period were used for the tests. Stress–strain behavior and primary yielding were evaluated, followed by construction of the primary yield locus. The characteristics of the primary yield locus and its development with curing time then were studied. The results showed that the properties of the primary yield locus were dependent on the type of stabilized soil, but were independent of the cement content and curing period. Thus, the approach provides a way to estimate the primary yield stress and drained stress path before primary yielding for cement-stabilized soil under confined condition. An empirical function was used to fit the primary yield locus. The primary isotropic yield stress was correlated to unconfined compressive strength or maximum shear modulus. Three indirect methods were proposed to predict the primary yield stress for cement-stabilized marine clay. The results showed that the primary yield stress can be estimated with reasonable accuracy.     

Properties of sediments deposited in a fluid with different pH

Abstract

The effect of pH on the physical and mechanical properties of a sediment was investigated through a set of experimental tests. The sediment was formed from deposition of suspended particles in a fluid. Two different types of clay soil were suspended in fluids with different pH (2, 4, 7, 9 and 11) in cylindrical tubes with volume of 1?liter and also in special cylindrical reservoirs. The height of the sediment was measured in the cylindrical tube until equilibrium was achieved. The sediment deposited in the reservoirs was dried in air and then Atterberg limit, compaction and unconfined compressive strength (UCS) tests were conducted on samples prepared from each sediment. The results showed that the final height of the settled sediment is a function of pH; the height of sediment is increased with increasing the pH. Also, the Atterberg limits increased with increasing the pH. The maximum dry unit weight and optimum water content decreased and increased with increasing the pH. The final strength of the sediment decreased with increasing pH. Based on the SEM analysis, it was found that the values of pH influence the properties of the formed sediments.     

Experimental study on recycling dredged marine sediment and phosphate tailing to produce earth fill

Environmental friendly earth fill was produced by recycling dredged marine sediment and phosphate tailing. The properties of the marine sediment and tailing were tested. Composite soil samples of different mix ratios were prepared. The optimum moisture contents, basic physical properties, compression characteristics, and shear strength characteristics under the optimum moisture contents were tested and analyzed. The results indicated that the optimum moisture content decreases with increasing phosphorus tailing content and that composite soil is preferable over both marine sediment and phosphate tailing because of its higher dry density, lower compressibility, and higher shear strength. When the phosphorus tailing content is in 50–65%, the dry density is maximized and the void ratio is minimized, indicating the best ratio. The coefficient of compressibility is in 0.07–0.12?MPa^?1. When the phosphorus tailing content is 50%, the compression index and coefficient of compressibility are minimized, whereas cohesion is maximized. The internal friction angle increases with increasing phosphorus tailing content. The optimum phosphorus tailing content is 50%; at this phosphorus tailing content, the compacted composite soil can be reutilized as good earth fill. The results demonstrate the properties and optimal conditions of composite soil composed of mud and silty sand.     

Experimental study on improvement of seawall filler materials composed of sea sand and sea mud

Abstract

The coastal area of Fujian Province in China is rich in both sea sand and sea mud. However, sea sand and sea mud are both unsuitable as direct filler materials for seawalls due to their poor geotechnical properties. To turn waste into a useful product, a mixture composed of sea sand and sea mud is proposed as a filler material for seawalls. The strength, compressibility, moisture sensitivity, and permeability of the mixture are investigated experimentally. The results show that when the mass ratio of sea sand to limed sea mud is 1:2, the mixture exhibits good engineering properties and can serve as a filler material for general engineering purposes in dry environments. To apply the mixture under saturated conditions, both cement and lime are used to improve the engineering properties of the mixture. The improvements in the properties increase with both the binding agent content and the curing time, and the improvement with the addition of cement to the mixture is better than that with the addition of lime. The engineering requirements of seawalls can be satisfied by adding cement, and the cement content can be chosen according to considerations of the construction period and engineering costs.     

Use of Posidonia Oceanica Ash in Stabilization of Expansive Soils

Posidonia oceanica (PO) is the most plentiful seaweed of the Mediterranean Sea, which grows all along the coastal areas, forming widespread meadows. The leaf rejuvenation process of Posidonia oceanica typically occurs in fall when an increase in wave action causes the dead seaweeds to be transported and usually piled up along the coastal areas. This paper investigates the effect of PO ash stabilization on behaviour of an expansive clay. The ash was obtained by combustion of crushed PO pieces in a muffle furnace at 550°C. Atterberg limits, linear shrinkage, particle size distribution, one-dimensional swell, and unconfined compression tests have been carried out on natural soil as well as soil mixtures with 5% and 10% PO ash. There has been no significant improvement in the soil properties with 5% ash inclusion, whereas 10% ash has noticeably reduced the swell amount and increased the compressive strength. It is therefore concluded that there is a potential for the use of PO ash in geotechnical engineering applications.     

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…     

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.     

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.     

Experimental study on the unconfined compressive strength of carbon fiber reinforced clay soil

To study the effect and mechanism of carbon fiber reinforced clay, a series of unconfined compression tests for clay reinforced with carbon fiber have been performed under the conditions of controlled water content and dry density. The carbon fiber is mixed into soil with the quality percentage of 0.01, 0.02, 0.03, 0.05, 0.1, 0.15, 0.25, 0.35, and 0.5%, then a certain quality of water was added in the soil to achieve the optimum soil water content. Ten groups of samples were tested by the unconfined compression experiment. The results showed that the incorporation of carbon fiber elements can effectively improve the unconfined compressive strength and brittle failure mode of soil. The soil is strengthened at the beginning and then weakened with the increased incorporation of carbon fiber, the effect is especially significant when the mix percentage becomes 0.1%. The interaction at the interface between carbon fiber surface and soil matrix is analyzed by using scanning electron microscopy (SEM). It is found that the enhancement mechanisms of carbon fiber reinforced soil are one-dimensional reinforcement of a single carbon fiber thread and three-dimensional reinforcement caused by fiber network respectively.     

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.     

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.     

Engineering behaviour of MICP treated marine clays

Abstract

In the present scenario, with much focus on sustainable development worldwide, Microbially Induced Calcite Precipitation (MICP) is a promising biological soil improvement technology. However, only very limited research is reported on the effectiveness of this technique in marine clays. This paper presents the salient features of an experimental study conducted on two typical marine clays stabilised by MICP. Effectiveness of the technique was evaluated through a series of one-dimensional consolidation tests, unconfined compression tests, and index property determinations. It is found that biostimulation approach is not effective in marine clay; bio-augmentation is needed for soil improvement. Bio-augmentation results in the reduction of liquid limit and plasticity index to about 29% and 47%, respectively for the marine clays. A comparable improvement in volume change behaviour is also observed. There is a marked increase in undrained shear strength, upto about 148%, of MICP treated marine clays at toughness limit water content. Curing is also found to have a significant role in soil improvement. The observed transition in the nature of the tested marine clays from that of fat clay to elastic silt suggests the potential of the proposed approach. An empirical equation is also proposed to predict compression index of MICP treated marine clays.     

现代黄河三角洲沉积物临界剪切应力研究

为研究现代黄河三角洲沉积物临界剪切应力空间分布特征及其影响要素,本文在现代黄河三角洲不同沉积区域,垂直海岸线布设测线,采用黏结力仪进行沉积物临界剪切应力测试,并在相应测点开展沉积物物理力学性质与粒度成分测量工作。研究结果表明高潮滩沉积物临界剪切应力最高,在1.1~4.02Pa之间,沉积物不易发生侵蚀,含水量低、干容重大、黏粒与粉粒含量高、平均粒径小、不排水剪切强度大是高潮滩沉积物临界剪切应力偏高的重要因素;中潮滩沉积物受生物活动影响显著,临界剪切应力在0.10~1.90Pa之间,生物活动扰动、生物排泄及遗体遗迹的程度与数量是造成不同区域测试差异的重要原因;低潮滩沉积物临界剪切应力很低,在0.08~0.80Pa之间,沉积物极易发生侵蚀,含水量高、干容重偏低、砂砾含量高、平均粒径大、不排水剪切强度小是其典型的沉积物物理力学性质,也是造成低潮滩沉积物临界剪切应力普遍低于高潮滩的重要原因;现代黄河三角洲沉积物临界剪切应力区域特征表现为北部沉积物临界剪切应力水平最低,在0.11~0.4Pa之间,东部最高,在2.8~4.55Pa之间,南部与东北部居中,分别在0.63~0.84Pa与0.83~2.99Pa之间,东北部空间非均匀性分布显著,粒度组分的分异是导致沉积物临界剪切应力区域差异显著的重要因素,黏粒含量高的沉积区域沉积物临界剪切应力普遍高于砂砾含量高的沉积区;与世界其他大型河口三角洲相比,现代黄河三角洲沉积物临界剪切应力水平偏低但非均匀程度较高。     

波浪作用下粉土海床中的孔压响应试验研究

海床在波浪作用下是否稳定对海底工程的安全至关重要,海床的稳定性与土体中的孔压响应密切相关。水槽模拟试验表明:在波浪的作用下,黄河三角洲粉土海床中将产生振荡孔隙水压力和累积孔隙水压力。振荡孔隙水压力大小与土层深度、波高和粘粒含量有关,其振幅(能量)在土层中随深度的增加呈指数衰减,且粘粒含量越高衰减越快;加载波高越大,能量衰减越快。而累积孔压响应模式表现为在波浪作用最初的一段时间内,孔隙水压力快速上升,然后逐渐减小而趋于稳定,其大小和速率也与波高、粘粒含量、土层埋深有关,粘粒含量越高,孔压累积速度越低。     

大洋多金属结核矿区表层沉积物的物理性质

利用大洋多金属结核矿区调查过程中4个航次所得的600多组表层沉积物物性测试资料,将矿区的沉积物分为5种类型,并分析了这些沉积物的物理性质,同时,运用回归分析方法,统计分析了不同类型沉积物的含水量、湿密度、孔隙比与埋藏深度的关系,以及各物性指标之间的相关关系。结果表明:(1)大洋多金属结核矿区表层沉积物均为粉质土,黄棕色粉质土是西部矿区的主要沉积物类型,棕黄色粉质土是东部矿区的主要沉积物类型;(2)除褐色粉质土外,其余4种类型土的含水量、孔隙比均随埋藏深度的增加而减少和降低,湿密度则随深度增加而增大;(3)各类土的物性指标与埋藏深度的相关性甚好,因而可以利用埋藏深度对矿区的沉积物进行物性指标预测;(4)含水量、孔隙比、湿密度等物性指标之间呈线性相关,其中含水量与孔隙比的相关性最为密切,呈明显线性关系。     

南黄海油气资源区粘性土物理力学性质及微结构特征

用土质学的显微结构理论和技术方法,研究了南黄海油气资源区粘性土微结构特征。结合原状样物理力学性质参数,研究颗粒接触、堆垒、孔隙等现象与物理力学性质之间的关系。研究结果表明,沉积物主要为粘质粉土、淤泥质粉质粘土和淤泥等粘性土,其微结构类型有粒状链接微结构、蜂窝状微结构和疏松基质状微结构3种,其中淤泥类土主要为蜂窝状微结构和疏松基质状微结构,结构疏松,孔隙度较大,含水率很高,强度低,压缩性高。粘质粉土为粒状链接微结构．含水率较低,孔隙度相对淤泥类土较小,抗剪强度比淤泥类土略高,压缩性较高。该区粘性土为不理想工程地基土,工程施工时应采取相应措施避开或对其进行改良。     

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.