Pollutants behaviour and temperature effect on chemical piles treated marine clay

Weak marine clay deposits are present in several regions of the world and they are imposing severe problems for structures founded in these deposits. The use of chemicals lime to improve the properties of these soft deposits is not new. In the present investigation, a test programme was carried out to study the influence of temperature on the engineering behaviour of chemical piles treated clays in the presence of sulphate and chloride contaminated marine environment. The formation of various cementation compounds due to soil-lime reactions were identified by X-ray diffraction studies, and the attributed changes occurred in the engineering properties of the soil systems were also brought out. The test results indicated that the increase in temperature has improved the engineering properties of soil significantly.     

Compressibility behaviour of lime-treated marine clay

The necessity to tap natural marine resources from the ocean beds represents a considerable challenge for the construction of offshore structures on weak marine deposits. The use of lime to improve the behaviour of soft clays is not new. The present investigation examines lime-induced changes in the compressibility of marine clay. The test results indicate a reduction of 1/2 to 1/3 in the compressibility of the soil system within 30 to 45 days of treatment. The formation of various cementation compounds due to soil–lime reactions improves the soil characteristics with time. The results encourage the application of lime column and lime injection techniques to improve the engineering behaviour of soft marine clayey deposits. However, one has to be cautious in applying the lime technique to marine clays that contain sodium sulfate.     

Microfabric, chemical and mineralogical study of Indian marine clays

Marine clay deposits are encountered in the coastal regions of the world. They are soft in consistency with low shear strength and are highly compressible. The properties of these deposits are complex and diverse, and they mainly depend on the minerals present and microstructural arrangement of constituent particles. In the present investigation, the physico-chemical properties of the sediment samples obtained from marine deposits of east and west metropolitan coastal cities of India are discussed, and the test results obtained are compared with the synthetic samples such as bentonite and kaolinite. Mineralogical and fabric studies were carried out using scanning electron microscopy and x-ray diffraction techniques. Several consolidation and strength tests were carried out to study the engineering behaviour of these deposits. The strength and compressibility (Cc) values of these deposits varies from 27 to 45 kN/m² and 0.37 to 0.81 respectively. XRD studies confirm the presence of highly compressible clay minerals such as smectite, vermiculite, chlorite and traces of the low swelling mineral, kaolinite. The fabric studies indicate that the constituent particles were arranged in an open network, or flocculated structure resulting in a high void ratio.     

Undrained monotonic shear behavior of marine soft clay after long-term cyclic loading

Abstract

In the coastal area, nearshore and offshore structures have been or will be built in marine soft clay deposits that have experienced long-term cyclic loads. Therefore, the mechanical behavior of marine clay after long-term cyclic loading needs to be investigated. In this research, a series of monotonic and cyclic triaxial tests were carried out to investigate the postcyclic mechanical behavior of the marine soft clay. The postcyclic water pore pressure, shear strength and secant stiffness are discussed by comparing the results with the standard monotonic test (without cyclic loading). It is very interesting that the postcyclic behavior of marine soft clay specimen is similar to the behavior of overconsolidated specimen, that is, the specimen shows apparent overconsolidation behavior after long-term cyclic loading. Then relationship between the overconsolidation ratio and the apparent overconsolidation ratio is established on the basis of the theory of equivalent overconsolidation. Finally, a validation formula is proposed which can predict the postcyclic undrained shear strength of marine soft clay.     

Effect of salt on strength development of marine soft clay stabilized with cement-based composites

Abstract

Marine soft clay with a high salt concentration is widely distributed in coastal areas. In this study, cement-based composites consisting of cement, silica fume, plant ash and NaOH were used as a substitute for ordinary Portland cement, and the effect of salt (sodium chloride) on the strength development of clay was investigated by unconfined compressive strength (UCS) testing and scanning electron microscopy (SEM). With the addition of sodium chloride (NaCl), the amount of cementitious materials decreased, and the salt (sodium chloride) was considered to consume the cement-based composites. The consumption effect could be quantitatively evaluated by the consumption index of salt (CIS) and the clay-water/cement ratio hypothesis. The relationship between the CIS and curing period and an UCS prediction model of clay stabilized with cement-based composites with different salt contents and curing times were established. The CIS gradually decreased with increasing curing time and cement-based composites content. The accuracy of the prediction model was evaluated by a comparative analysis between the measured strengths and predicted strengths; the deviation was mostly within 10%. SEM analyses were employed to describe the changes in the microstructure of the specimens and the influencing mechanism of salt on clay stabilized with cement-based composites.     

海洋沉积物黏土矿物相对含量不同计算方法对比研究

海洋沉积物黏土矿物相对含量计算存在多种计算方法,并不统一,限制了异源黏土矿物的整合和使用。文章选取了两种较为常见的计算方法,即Biscaye和国标中规定的计算方法,分别对东印度洋109个表层样品黏土矿物的相对百分含量进行计算,分析对比了两种方法计算结果之间的差异。结果显示,两种计算方法结果存在显著正相关,都能显示黏土矿物分布的变化趋势,4种黏土矿物相关系数由高到底分别为:蒙皂石0.986、伊利石0.974、绿泥石0.924、高岭石0.923。相对于Biscaye计算方法,国标计算方法会增加伊利石和高岭石的相对百分含量而降低蒙皂石和绿泥石的相对百分含量。两种计算方法黏土矿物的含量相关性较好,可以建立起相互数学转换关系式。但在不同的海区,由于矿物成因、结晶程度以及混层矿物的出现可能会使衍射峰形态发生改变,从而相关性系数和转换关系也会相应发生改变。     

Non-linear analysis of undrained cyclic strength of soft marine clay

Iwan models are used to simulate the non-linear and hysteretic behaviour of soils under cyclic loading conditions. However, the model in its original form cannot take into account the stiffness degradation which is observed during cyclic loading of soft clays. Studies show that the stiffness reduction (expressed as degradation index) can be represented as a function of the number of cycles and of a degradation parameter depending on the strain amplitude in the case of strain controlled cyclic loading tests. This degradation index has been incorporated into Iwan's series–parallel model as a single fatigue parameter to account for the degradation during cyclic loading. The comparisons made with the existing results of two marine clays tested under undrained cyclic triaxial and simple shear conditions provided an opportunity to understand the capability of the one dimensional model.     

Anisotropic deformation characteristics of soft marine clay involved the change of b-values and stress direction

In actual engineering, soft clay foundations are in drained or partial drained conditions, it would be useful to establish reasonable constitutive relationship and provide guidance for engineering projects. A hollow cylinder apparatus is used to investigate the anisotropic deformation behavior of natural soft marine clay influenced by intermediate principal stress coefficient b and principal stress direction α. Tests were conducted by maintaining a fixed principal stress direction α relative to the vertical direction, while keeping the intermediate principal stress coefficient b constant. It was found that the anisotropic deformation behavior of natural soft clay is merely influenced by major principal stress direction α, but significantly influenced by intermediate principal stress coefficient b.     

Dynamic characteristics of marine soft clay under variable phase difference and initial static shear stress

Abstract

Under seismic loading, the soil layer is subjected to multidirectional cyclic shear stress with different amplitudes and frequencies because of the coupling of multiple shear waves and the soil element within a slope or behind a retaining wall is subjected to initial static shear stress before subjected to cyclic loading. Due to the complexity of seismic loading propagation, a phase difference exists between the initial static shear stress and cyclic shear stress. To investigate the influence of the phase difference and initial static shear stress on cyclic shear strain, cyclic modulus, and cyclic strength, a series of laboratory tests are performed on Wenzhou marine soft clay by multi-directional simple shear system, which can simulate the actual state better by controlling the horizontal cyclic stress in the x and y directions simultaneously. As the phase difference varies from 0° to 90°, the dynamic shear modulus increases and cyclic strain accumulation decreases with an increasing number of cycles. The shear strain increases with the initial shear stress.     

Evaluating the stiffness of chemically stabilized marine clay

Cement-stabilized clay is widely used in soft clay improvement for deep excavation, underground construction, and land reclamation. This paper presents a study on the evaluation of elastic modulus for cement-stabilized marine clay. First, two types of cement-stabilized soils were studied through isotropic compression tests and cylinder split tensile tests. Specimens with different mix ratios and curing periods were used. Stress–strain behavior under isotropic compression was discussed, followed by an introduction and estimation of the stress-free bulk modulus. Empirical correlations between elastic moduli and functions for estimating elastic moduli were then proposed. Further estimation of elastic modulus was conducted with another data set. The results showed that the proposed function for estimating elastic modulus is effective for cement-improved marine clay. Finally, the proposed method and empirical functions were validated with other types of cement-stabilized clay.     

Enhancing the mechanical properties of marine clay using cement solidification

Abstract

The use of soft clay and dredged marine clays as the construction material is challenging. This is because the high water content, high compressibility and low permeability of the clay causing the instability of ground and structure. This detrimental effect of soft clay can be improved by the cement solidification process, which is relatively cheap and efficient. This paper mainly focuses on the study of improvement on the mechanical behavior of cement mixed marine clay. The soil is reconstituted by using ordinary Portland cement of 5%, 10%, 15% and 20% by its mass. The study reveals that cementation of clay significantly improves the peak and residual strength of soil. Similarly, the primary yield stress of the soil is also improved from 16 to 275?kPa as cement content increases from 5% to 20%, respectively. By using statistical tools, the relationships between various parameters are established, which are very important to define the mechanical behavior of the clay. This study reveals that the yield surface of the solidified marine clay is not a smooth elliptical surface. Rather it is composed of two linear surfaces followed by a log-linear surface which can be modeled by using simple parameters obtained from triaxial tests.     

Influence of viscosity on one-dimensional thermal consolidation of marine clay

ABSTRACT

The elastic mechanical response of porous materials under a heat source has many applications in civil engineering and has received considerable attention in the geotechnical literature. In this paper, a Kelvin viscoelastic model is combined with the thermohydromechanical governing equations for marine clay and solved using a numerical inversion of the inverse Laplace transform in the time domain. After validation against existing analytical solutions, numerical parametric studies are conducted to investigate the influence of viscosity on temperature, excess pore pressure, and displacement. It is shown that viscosity has little influence on temperature, a modest influence on displacements, and a quite significant influence on excess pore pressure.     

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.     

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.     

海洋含黏粒砂土共振柱试验研究

本文利用英国GDS公司生产的RCA共振柱系统测试海洋含黏粒砂土动剪切模量,同时对比纯砂样的动剪切模量,系统研究固结应力、初始密实度、黏粒含量等因素对砂土最大动剪切模量的影响。试验结果表明:最大动剪切模量随有效固结应力增大而增大;随初始密实度增大而增大;随黏粒含量的增加而降低。     

Adsorption and desorption of proteins and polyamino acids by clay minerals and marine sediments

The adsorption and desorption of proteins and polyamino acids on illite, montmorillonite, goethite, and marine sediments was investigated. Three ¹⁴C-labeled hydrophilic proteins, Rubisco from C. reinhardtii, and GroEL and GroES from genetically modified Escherichia coli, were synthesized and purified for this study. The proteins were strongly and rapidly adsorbed by the clay minerals and marine sediments, and much of the adsorbed protein was not readily desorbed. Sodium dodecyl sulfate (SDS) extraction and separation by SDS-polyacrylamide gel electrophoresis (PAGE) and sucrose density gradients showed that Rubisco and GroEL were adsorbed on illite and sediments in their original forms. The apparent adsorption partition coefficients of the proteins were on the order of 10² l/kg on illite, 10³–10⁴ l/kg on goethite and montmorillonite, and 200 and 75 l/kg on Skan Bay and Resurrection Bay (Alaska) sediments, respectively. These partition coefficients are sufficiently large to permit sedimentary protein preservation via an adsorptive mechanism. Generally, basic polyamino acids had greater adsorption partition coefficients than acidic polyamino acids. Molecular size did not affect the electrostatic interaction between polyamino acids and mineral surfaces. Adsorption of bovine serum albumin (BSA) and negatively charged polyamino acids inhibited Rubisco adsorption, while positively charged cytochrome c and polyamino acids increased Rubisco adsorption. These results indicate that electrostatic interactions dominated in protein adsorption.     

Evaluation of the uplift behavior of plate anchor in structured marine clay

The uplift behavior of a plate anchor in a structured clay (soft Ariake clay) is investigated through a series of laboratory tests and method of finite element analysis. The tests are adopted to identify the factors influencing the behavior of the anchor, including the thixotropic nature of Ariake clay, consolidation time, and embedment ratio of the anchor. A finite element method (FEM) is used to analyze and predict the uplift behavior of the anchor plate well in the elastic region and the yield load. The results from both the laboratory tests and the FEM analysis suggest that the embedment ratio for a deep anchor in Ariake clay is close to 4. Further increase in embedment ratio improves the capacity to a lesser extent. FEM overestimates the failure load of the uplift anchor in soft Ariake clay by about 20%. This may be ascribed to the hypothesis in the FEM analysis that there is continuous contact between the clay and the anchor until failure. Vesic’s theory for deep anchors, which may be used to predict the ultimate pullout resistance of the plate anchor in reconstituted Ariake clay, is verified to be applicable. In this paper, the plastic flow zone around the anchor is discussed using FEM which makes the behavior of anchor more understandable during the design stage.     

Immersed tunnel foundation on marine clay improved by sand compaction piles

The sand compaction pile (SCP) method can be applied to soft marine clay ground that is a reinforcement of composite ground consisting of compacted sand piles and surrounding clay. The application of SCP method in the immersed tunnel of Hong Kong–Zhuhai–Macao Bridge verify SCP method is a robust solution to limit the total settlement and differential longitudinal settlement and to promote smooth transition from immersed tunnel to artificial island. The SCP method has significant settlement reduction effect on marine clay. The SCPs can also function as a drainage path to accelerate the consolidation process in marine clay. It is also found that the consolidation rate of SCP-improved ground is delayed compared with that predicted program which is most probably because of the soil disturbance effect during the installation of SCPs.     

Influence and countermeasure of specimen misalignment to small-strain behavior of soft marine clay

Triaxial test with local displacement transducers is an effective technique to obtain the small-strain stiffness of soils. Many previous studies provided feasible solutions for reducing or avoiding potential sources of error in conventional triaxial tests. However, little literature gave out detailed explanations on how to identify those potential errors from the measured testing data and corresponding solutions. Therefore, nowadays, it is still not easy for a new user to gain proficiency in such kind of advanced tests. In this article, by conducting triaxial tests featured with Hall effect transducer on Shanghai soft marine clay, it is found that the influence of the specimen misalignment to the measured small-strain stiffness cannot be neglected. The typical symptom of specimen misalignment, namely the tilting of specimen, was described carefully. An improved connection between top cap and load cell was applied to overcome the problem. The new connection can reduce the disturbance to specimen in terms of both force and displacement. It can be applied to both isotropic and anisotropic consolidated triaxial tests.     

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.