Biopolymer stabilization of clayey soil

This study investigates the efficacy of sodium alginate(SA),xanthan gum(XG),guar gum(GG)and chitosan(CS)d each applied at five different solid biopolymer-to-water mass ratios(or dosages)and cured for 7 d and 28 d d on the unconfined compressive strength(UCS)performance of a high plasticity clayey soil.Moreover,on identifying the optimum biopolymer-treatment scenarios,their performance was compared against conventional stabilization using hydrated lime.For a given curing time,the UCS for all biopolymers followed a riseefall trend with increasing biopolymer dosage,peaking at an optimum dosage and then subsequently decreasing,such that all biopolymer-stabilized samples mobilized higher UCS values compared to the unamended soil.The optimum dosage was found to be 1.5%for SA,XG and CS,while a notably lower dosage of 0.5%was deemed optimum for GG.Similarly,for a given biopolymer type and dosage,increasing the curing time from 7 d to 28 d further enhanced the UCS,with the achieved improvements being generally more pronounced for XG-and CS-treated cases.None of the investigated biopolymers was able to produce UCS improvements equivalent to those obtained by the 28-d soilelime samples;however,the optimum XG,GG and CS dosages,particularly after 28 d of curing,were easily able to replicate 7-d lime stabilization outcomes achieved with as high as twice the soil’s lime demand.Finally,the fundamental principles of clay chemistry,in conjunction with the soil mechanics framework,were employed to identify and discuss the clayebiopolymer stabilization mechanisms.

Effects of oil contamination and bioremediation on geotechnical properties of highly plastic clayey soil

Leakage of oil and its derivatives into the soil can change the engineering behavior of soil as well as cause environmental disasters.Also,recovering the contaminated sites into their natural condition and making contaminated materials as both environmentally and geotechnically suitable construction materials need the employment of remediation techniques.Bioremediation,as an efficient,low cost and environmentalfriendly approach,was used in the case of highly plastic clayey soils.To better understand the change in geotechnical properties of highly plastic fine-grained soil due to crude oil contamination and bioremediation,Atterberg limits,compaction,unconfined compression,direct shear,and consolidation tests were conducted on natural,contaminated,and bioremediated soil samples to investigate the effects of contamination and remediation on fine-grained soil properties.Oil contamination reduced maximum dry density(MDD),optimum moisture content(OMC),unconfined compressive strength(UCS),shear strength,swelling pressure,and coefficient of consolidation of soil.In addition,contamination increased the compression and swelling indices and compressibility of soil.Bioremediation reduced soil contamination by about 50%.Moreover,in comparison with contaminated soil,bioremediation reduced the MDD,UCS,swelling index,free swelling and swelling pressure of soil,and also increased OMC,shear strength,cohesion,internal friction angle,failure strain,porosity,compression index,and settlement.Microstructural analyses showed that oil contamination does not alter the soil structure in terms of chemical compounds,elements,and constituent minerals.While it decreased the specific surface area of the soil,and the bioremediation significantly increased the mentioned parameters.Bioremediation resulted in the formation of quasi-fibrous textures and porous and agglomerated structures.As a result,oil contamination affected the mechanical properties of soil negatively,but bioremediation improved these properties.

Test study of high liquid limit clay modified by quick lime used as sub-grade material

Through laboratory test, the relationships among change of compactibility, liquid/plastic limit, free swell, swell ratio without load, california bearing ratio (CBR) and soakage (after being soaked in water), and mix-ratio of quick lime and time were studied. The results show that optimum water content, plastic limit and CBR of high liquid limit clay improved by quick lime increase with the increase of mix-ratio of quick lime, while the maximum dry density, liquid limit, plasticity index, soakage (after being immersed in water), free swell, and swell ratio without load decrease with the increase of mix-ratio of quick lime. Plastic limit of high liquid clay improved by quick lime gradually increases with time, while the liquid limit, plasticity index, free swell and swell ratio without load gradually decrease with time. When the mix-ratio of quick lime exceeds 2%, after 14 d, swell ratio without load of the improved clay is zero, its free swell is about 30% of that of untreated soil, and its plasticity index is less than 26 for sub-grade material, satisfying the requirement by 'Specifications for Design of Highway Subgrade'.

Experimental research on unloading properties of clay under high stress

Abstract： Mechanical properties of clay under high stress are quite different from those under low stress. It is necessary to investi- gate unloading properties of clay under high stress for the design and construction of deep underground engineering projects. A series of experiments were conducted to investigate the unloading properties of clay under high confining pressures by using a SKA-1 high pressure consolidation instrument designed by us. The stress versus strain relationship and the way that K0 values of clay change during the loading-unloading process were discovered. The results show that there are clear differences in the state of stress and deformation behavior of the clay along different unloading paths.

Hydrometallurgical Purification of Some Clay Deposits for High Temperature Applications

The characterization of five different Nigerian clay deposits has been carried out by employing three different characterization techniques (X-ray Diffraction, X-ray Fluorescence and Scanning Electron Microscopy/EDX). The clays obtained from the various deposits were carefully prepared for the analyses and the results obtained were compared to confirm the consistency and reliability of the different methods employed. The results revealed the various desirable (SiO2 and Al2O3) and deleterious (Fe3O4, K2O, MgO, MnO and Na2O) elements and compounds contained in the clay samples in the various proportions and the appropriate purification technique required for preparing the clays for high temperature applications. Consequent upon the identification of the deleterious impurities, oxalic acid at different concentrations was used to leach the impurities out of the various clays. However, three out of the five deposits were chosen for purification because they possess the least quantities of the most deleterious (Fe2O3) of the impurities.

High-Temperature Clay Anti-Plumping Agent

The NW-3-7 high-temperature clay anti-plumping agent is a new generation of product developed in 1993 by the Binhu Jiufan Group Corporation. According to cation polymer’s function of peridium flocculation, the product uses a small molecular weight of cation organic compound to function as a peridium for a clay surface, thus reducing hydrability, swelling and the dispersion of slurry and stabilizing mineral content of sensitive sandy clay. Such an effect creates a high anti-plumping and anti-sanding

Investigation on reinforcement-sand-clay layer system using direct-shear test

The property of the contact surface between geosynthetics and soil directly affects the whole structure＇s stability. The interface property is one of the most important indices for the reinforced structure. Systematic direct-shear tests with large direct-shear apparatus are carded out for geobelt reinforced clay under different normal stresses and water content. A reinforcement-sand-clay layer system improving the interface behavior greatly is designed. The stress-strain relationship is investigated on the basis of the experimental results. The results show that with the increase of the normal stress, the shear strength between the clay and the reinforcement increases nonlinearly, and with the increase of the water content, the friction coefficient between the clay and the reinforcement decreases dramatically and the cohesion between the clay and the polypropylene geobelt increases initially, then decreases. There is an optimal value for the water content between the clay and the polypropylene geobelt, which is 2% lower than the optimal water content of clay compaction. This reinforcement-sand-clay layer system improves the shear strength of the interface remarkably. Therefore, the clay-sand-reinforcement layer system is a rather good design for practical use in reinforcement engineering.

High temperature and high pressure rheological properties of high-density water-based drilling fluids for deep wells

To maintain tight control over rheological properties of high-density water-based drilling fluids, it is essential to understand the factors influencing the theology of water-based drilling fluids. This paper examines temperature effects on the rheological properties of two types of high-density water-based drilling fluids （fresh water-based and brine-based） under high temperature and high pressure （HTHP） with a Fann 50SL rheometer. On the basis of the water-based drilling fluid systems formulated in laboratory, this paper mainly describes the influences of different types and concentration of clay, the content of a colloid stabilizer named GHJ-1 and fluid density on the rheological parameters such as viscosity and shear stress. In addition, the effects of aging temperature and aging time of the drilling fluid on these parameters were also examined. Clay content and proportions for different densities of brine-based fluids were recommended to effectively regulate the rheological properties. Four theological models, the Bingham, power law, Casson and H-B models, were employed to fit the rheological parameters. It turns out that the H-B model was the best one to describe the rheological properties of the high-density drilling fluid under HTHP conditions and power law model produced the worst fit. In addition, a new mathematical model that describes the apparent viscosity as a function of temperature and pressure was established and has been applied on site.

Methane Adsorption on Montmorillonite, Kaolinite and Illite at High Pressures

Shale gas, which is derived from organic matters in shale and stored in shale deposits, is an important unconventional gas resource and attracts attention due to its significant requirement in the hydrocarbon production. Methane (CH4) is the dominant component of shale gas, and adsorbed gas is an important reservoir form. Many studies have investigated the adsorption capacities and adsorption mechanisms of CH4 in shale. Organic matters and clay minerals have been proposed to be the two major components for CH4 adsorption. Adsorption of CH4 in organic matters, such as the adsorption capacity and effects of characteristics of the organic matters, has been well investigated. However, studies on CH4 adsorption on clay minerals have mainly focused on evaluating the adsorption capacity, and very little information about the adsorption mechanism has been provided. For example, the adsorption sites and factors influencing CH4 adsorption on clay minerals remain unclear. Three main reasons account for this: (1) the co-existence of organic matters in samples affects the evaluation of CH4 adsorption on clay minerals; (2) the pressures used during adsorption are not representative of actual reservoir pressures; and (3) the clay minerals selected have low swelling capacity and a smaller interlayer distances than a CH4 size, resulting in the misunderstanding of the CH4 adsorption sites.

Stress-dependent undrained shear behavior of remolded deep clay in East China

Consolidated-isotropically undrained triaxial compression （CIUC） tests were performed on the reconstituted deep clay from a mine in East China. It was consolidated to maximum stresses in the range of 0.3-2.6 MPa. The test results show that the stress-strain-strength properties of the clay during undrained shear are significantly stress-dependent. In particular, in the case of high consolidation pressure, the post-peak drop in strength on stress-strain curves and shear plane in soil specimens are more evident, the peak stress ratio and the axial strain at which this ratio was reached are smaller, and the relationship between pore pressure and axial strain is also significantly different from that for the case of low consolidation pressure. The environmental scanning electron microscope observations and micro analysis lead to an understanding of the physical mechanisms underlying the above stress-dependent mechanical behavior. In addition, the CIUC behaviors of the studied clay are discussed in the context of critical state soil mechanics.