Dispersive Clay Soils Research Articles

Effects of metakaolin and zeolite on the dispersion properties and shear strength of dispersive clay soil

ABSTRACT The current study used metakaolin and zeolite either separately or in combination at 0%, 2%, 4%, 6% and 8% of the soil weight to improve dispersive clay soil at optimal humidity levels. The samples were tested to determine the extent of change in the dispersion potential, as well as improvements in the shear strength of dispersive clay soil. The dispersive soil was obtained near the city of Ardakan in Iran and the extent of change in its soil dispersion potential was evaluated after 7 days of curing. The results of the pinhole test indicated that the addition of 2% zeolite plus 8% metakaolin to the soil considerably decreased the dispersion potential. Uniaxial testing after 7, 14 and 28 days of curing revealed that the UCS of the samples increased. The greatest increase was observed in samples containing 2% zeolite and 8% metakaolin after 28 days of curing. The direct shear test was carried out after 7, 14 and 28 days of curing on the unmodified soil and soil modified with optimal percentages of metakaolin and zeolite. The combined addition of zeolite and metakaolin was found to increase the shear strength parameters of the samples.

Evaluation of dispersive nature of soil in the piping affected regions of Kerala

The soil piping erosion has been closely related to the soil composition and its dispersive nature. The phenomenon of dispersivity is explained by the property by virtue of which the soil breaks down into their component particles upon exposure to water. Dispersive soils are highly prone to erosion. If the soil at top is hard and soft dispersive clays present at bottom, in presence of seepage water, there are chances for piping erosion to occur. These kinds of process are very common in lateritic terrains. In appearance the normal erosion resistant clays are similar to dispersive clays, they are, in fact, prone to significant erosion and are susceptible to severe damage. Exchangeable sodium present in the soil is the primary cause of dispersivity. Special methods are required to distinguish between dispersive and non-dispersive soils, common soil classification tests are not sufficient. The recommended tests to identify the dispersive clay soils are Crumb test, Double hydrometer test, Pin hole erosion test, and some chemical tests.This paper reports the problems associated with dispersive soils and discuss the results of double hydrometer tests carried out in various piping regions of Kerala along with the stabilization of dispersive soils with lime. Double hydrometer test as per British standards have been used in the present study. Comparative study of the dispersion ratios obtained for various samples shows that the Idukki samples are having more dispersion ratio than other regions. And as the piping was present in those areas the dispersion ratio was expected to be higher than 30%, the lower values obtained can be due to the erosion of dispersive clays in those regions. Effectiveness of stabilization with lime is checked and it was found that the ideal proportion of lime for minimizing dispersion potential is 1%.

Factors influencing the germination, establishment and distribution of

Context Little is known of the ecology of Micromyrtus minutiflora, a threatened plant species endemic to the Cumberland subregion, New South Wales, Australia. Aims To fill ecological knowledge gaps of M. minutiflora, including habitat preferences, population size and structure, survivorship; and responses to fire and disturbance to inform appropriate management practices. Methods Surveys of distribution and abundance, regeneration mode and response to fire, survivorship, size-class analysis, greenhouse germination experiments using soil blocks; and plant tissue and soil analyses. Key results Micromyrtus minutiflora was estimated to have a population of ~4.3 × 106, an extent of occurrence of ~13 000 ha and ~1.5% area of occupancy within study areas. It is strongly associated with low tree canopy cover (few trees), dispersive clay soils and Castlereagh Scribbly Gum Woodland. In the one area studied, survivorship decreased by ~15% per annum across 14 years. However, total population numbers were stable across 3 years, indicating continuous recruitment. Size distributions were unimodal and continuous from small to large plants, consistent with recruitment matching mortality. Plants lack a lignotuber and have a high shoot:root ratio. Seedling emergence was unaffected by mechanical disturbance, but heat and smoke significantly increased germination. Conclusions This species is abundant on dispersive clays but restricted to the northern Cumberland Plain in open woodland areas. It is an obligate seeder; plants are killed by fire and can flower within 2 years of germination. Implications Understanding its soil seedbank dynamics is pertinent in determining an appropriate fire regime to maintain habitat while not directly threatening populations. Populations require regular monitoring.

The Identification of the Existence of Dispersive Soil on the Soft Soil for Dam Filling Material

Dispersive clay soils are highly erodible, even under standing water conditions. Dispersive clay soils are easily eroded both on the surface and in landfills, despite their high plasticity index and ability to be passed by water flows at low velocities. Dispersive soil will cause a variety of problems in dams and water structures, including the potential for seepage patterns in the embankment material, which can trigger piping, compromising the stability of the water structure. Dispersive soils occurring in many parts of the world are easily erodible and deflocculated in water, posing serious problems for stability of the earth and earth-retaining structures. Earth dams constructed on dispersive soils have sustained internal and external soft soil damage. The purpose of the current study was to identify the predetermine of dispersive clay soil as a filling material for the Way Sekampung Dam in Indonesia. Pinhole and Crumb tests were carried out to determine the dispersity of the original soil. This study analysed 17 undisturbed soil samples collected from 17 different locations throughout the study area. The research findings indicate that there is no evidence of dispersive soil distribution in the samples studied. According to the Pinhole and Crumb tests, all soil samples have ND-1 and 1 status, respectively. These findings are supported by laboratory test results which indicate that the soil content with a diameter greater than 0.005 mm is always less than 12% for each sample. In addition, another test revealed that the permeability value of all tested clay samples was not too low (around 10^-2 to 10^-4), indicating that they did not possess the properties of dispersive clay, which had a very low permeability value (around 10^-6 to 10^-7). In general, the clay surrounding the dam site is free from dispersive properties and is therefore safe and suitable for use as a dam filling material. Finally, these findings will be beneficial for dam constructions to understand the possibility of dispersive soil causing significant issues that require attention in geotechnical engineering.

Treatment of dispersive clay soil by ZELIAC

Dispersive clays are prone to erosion and could cause significant problems in geotechnical and geo-environmental projects. In this research, a new additive - the ZELIAC – was investigated for treating a Malaysian dispersive clay soil where an appreciable decrease in dispersivity was achieved due to treatment with 8% ZELIAC. The curing time was found to be significant that after 28days, the initially dispersive samples became non-dispersive. Furthermore, due to the treatment, the samples had increased unconfined compressive strength (UCS), permeability, and optimum moisture content; and decreased fines content, plasticity index, maximum dry density, and compressibility index. The UCS increased nearly 7.3 times for sample treated with 8% ZELIAC and cured for 90days. The X-ray fluorescence (XRF) results showed a cementitious structure with calcium content 10.8 times more in the treated sample than in the untreated one, reflecting the constructive cation exchange reaction taking place during the curing process. The sodium ion was noticeably replaced by calcium ion which resulted in a decreased thickness of the diffused double layer and the subsequent reduction in the dispersivity of the sample. These results were also reflected by the lower peak intensity as measured by the X-ray diffraction test (XRD) for the treated sample, as compared to the higher peak intensity for the un-treated sample. Finally, the SEM images indicate that the flocculated structures of the treated dispersive clay were surrounded by the ZELIAC particles. Thus, the ZELIAC was proven to be effective in improving the studied Malaysian dispersive clay.

Durability, Strength, and Stiffness of Dispersive Clay–Lime Blends

AbstractDispersive clays undergo deflocculation in the presence of relatively pure still water to form colloidal suspensions and as such are highly susceptible to erosion and piping. Lime treatment is one of the most practical methods to improve such undesirable characteristics of dispersive clays, as well as improve their mechanical properties. The present research aims to quantify the influence of amounts of hydrated lime, compacted dry unit weight, and curing time in the assessment of transformation to a nondispersive state by the lime treatment, as well as improving durability, strength, and stiffness properties of clay–lime mixtures. This manuscript advances understanding of the parameters controlling strength and stiffness of compacted lime-treated dispersive clay soil by quantifying the influence of porosity/lime index initial shear modulus (Go) and unconfined compressive (qu) and split tensile (qt) strengths. A single qt/qu relationship equal to 0.136 was found, being independent of the porosity/l...

Consolidation and swell characteristics of dispersive soils stabilized with lime and natural zeolite

Abstract Many engineering structures such as dam embankments, road way embankments have suffered serious erosion problems and have failed due to the presence of the dispersive soils. Different additives are used to control the dispersivity properties of these soils. In this study, the effects of lime and natural zeolite on the consolidation and swell characteristics of dispersive clay soils were investigated. For this purpose, identification and compaction tests were carried out on the soil samples. Dispersivity, swell and consolidation tests were performed on the specimens prepared by standard Proctor energy and constant lime content levels (2%, as a percentage of dry weight of the soil), the percentage (0%, 1%, 3%, 6%, 10%, 15% and 20%) of a mixture of natural zeolite additives. As a result of this study, it is shown that the dispersive soils can sufficiently be treated using lime and natural zeolite. From the test results, 2% lime and 3% natural zeolite was the most effective stabilizer in decreasing swell and compressibility potential of dispersive soils.

The effect of magnesium chloride solution on the engineering properties of clay soil with expansive and dispersive characteristics

Because expansive and dispersive soils damage engineering structures, extensive studies on using additives to ameliorate the effects of these soils have been conducted. In this study, the effect of magnesium chloride (MgCl2) solution on the engineering properties of clay soils was evaluated. Previous studies on this subject have shown that MgCl2 is more commonly used as an anti-icing agent on roads than as a soil stabilizer. MgCl2 is also used to control dust and humidity on roads and to reduce the scattering of coarse particles from road surfaces. However, as the use of MgCl2 becomes more common, its potential to improve the geotechnical properties of problematic soils will receive increasing attention.To this end, the variation in the engineering properties of expansive and dispersive clay soil samples as functions of the added MgCl2 content was investigated. First, the physical and chemical properties of the soil sample were determined. Next, the swell percentage, swell pressure, crumb, pinhole and unconsolidated undrained (UU) triaxial compression tests were performed at different curing times on samples with and without the additive by compressing the sample to achieve particular compaction characteristics. Scanning electron microscopy (SEM) analyses were performed to observe the microstructures in the sample without the additive and with the amount of additive that most strongly improved the expansive and dispersive qualities of the clay. The results show that dispersive and expansive clay soils can be effectively improved using an additive MgCl2 solution.

Application of a fuzzy rule-based method for the determination of clay dispersibility

Some clay soils are highly susceptible to erosion and piping because of dispersion or deflocculation in pore water. These soils, called “dispersive clay soil” in geotechnical engineering, are structurally unstable, easily dispersive and, thus, highly erodible. There are many tests to determine dispersibility both physically and chemically. However, these tests can give different results for the same soil sample. Therefore, more than one test should be used to identify dispersive soils more accurately. In previous research, the discriminant method was used to combine these test results. In this study, a fuzzy logic approximation method was developed to combine the different results of the double hydrometer, pinhole, Na(%)–TDS and ESP–CEC methods into a single value. This new method was applied to the dispersibility test results of 29 samples, and it gave more reliable and objective results for identifying the dispersibility of the clay soil.

Crust development in relation to vegetation and agricultural practice on erosion susceptible, dispersive clay soils from central and southern Italy

The propensity for dispersive soils to crust when exposed to rainfall is influenced by vegetation cover and agricultural practice. Crust formation on cambisols developed in dispersive Plio–Pleistocene clays from the Creti Senesi, Tuscany, central Italy and from around Pisticci, Basilicata, southern Italy was investigated in the laboratory using simulated rainfall. No discernable crusts formed on samples of aggregates obtained from beneath woodland or scrub, but those from tilled arable land, from badlands and from former badlands reclaimed for agriculture by modelling the landscape, each developed distinctive crusts. Crust development was inversely related to stability of the soil aggregates which in these soils was most strongly determined by organic matter content and exchangeable sodium percentage. Soil aggregates from reclaimed land used for cereal cultivation remain very vulnerable to the crusting when exposed to rainfall by tillage operations.

The impact of land use on the credibility of dispersive clay soils in central and southern Italy

Abstract. Tracts of dispersive Plio‐Pleistocene clays in central and southern Italy suffer from severe erosion, which has led to the creation of badlands characterized by ‘calanchi’(unvegetated knife‐edge ridges) and ‘bian‐cane’(cone‐shaped hummocks). In recent decades, large areas of this eroded land have been reclaimed for arable cultivation by remodelling the landscape with heavy earth moving equipment. This exposes the clay to erosive rainfall. Wet aggregate strength was used to assess those physical and chemical properties that govern the erodibility of the clays. Regression analysis demonstrated that the most significant variables in predicting soil erodibility were the % organic matter and the exchangeable sodium percentage (ESP). Threshold values of 1–2% and 3–4% organic matter were obtained, dependent on the method of pre‐wetting. Reclaimed land is on the borderline of these thresholds and therefore at risk of erosion. Nevertheless, the stability of reclaimed land is significantly higher than that of the badland parent material, ascribable to a lower ESP. Careful land management is required to avoid a recurrence of erosion and the reestablishment of badlands.

Reclamation of a failed subsurface drainage system on an unstable clay soil

The soil structure of a dispersive clay soil on which a subsurface drainage system had failed was modified by applying gypsum (5 t/ha) and growing a crop of sunflowers. The sunflower crop and gypsum application increased macroporosity from 8 to 15% and stabilised the clay microstructure. Sunflowers without gypsum produced a similar increase in soil macroporosity but with a potentially more dispersive clay microstructure. Gypsum alone produced a stable clay microstructure and intermediate values (about 11%) of macroporosity. The yield of wheat was similar on both drained and undrained areas (4 t/ha) following the sunflower crop with and without gypsum application, whereas on untreated areas, yields were 2.1 t/ha in the absence of drainage and 3.3 t/ha when drained.

Evaluation of chemical tests for engineering soils using discriminant analysis

In the field of geotechnical, engineering, dispersion refers to a process whereby soil will spontaneously deflocculate when exposed to water having little or no hydraulic velocity. Such soil behavior may lead to catastrophic failure of earthen structures, such as embankment dams, when dispersive clay soils are improperly used in construction. Sherard et al. suggested that chemical data could be used to corroborate results from physical tests on suspected dispersive soils. When application of Sherard's chemical method did not adequately corroborate physical tests performed on soils from an earthen dam project in Oklahoma, discriminant analysis was used to quantitatively evaluate the observed lack of success. Chemical and physical test data from several other geographic locations were also evaluated. Results indicate that the chemical variables suggested by Sherard et al. are not universal indicators of dispersive behavior. Further data exploration with discriminant analysis revealed that other chemical variables could corroborate physical tests for the Oklahoma soils, and substitution of these data into derived discriminant classification functions may be used as a method to classify soils as dispersive or nondispersive.

Application of multivariate statistics and saturation extract data to identify dispersive clay soils : Craft, D Geotech Test J V9, N1, March 1986, P34–37

Application of multivariate statistics and saturation extract data to identify dispersive clay soils : Craft, D Geotech Test J V9, N1, March 1986, P34–37

The Application of Multivariate Statistics and Saturation Extract Data to Identify Dispersive Clay Soils

Abstract Soils from a geotechnical project in Oklahoma may be classified as dispersive or nondispersive with a high degree of confidence by substituting selected pore-water data (weight percent H2O at saturation, saturation extract pH, log base 10 of the pore-water conductivity, and log base 10 of the pore-water sodium concentration) into derived discriminant classification functions. The discriminant functions were derived using discriminant analysis, a multivariate statistical classification technique, performed on a 28-sample data set. This statistical procedure was utilized after problems were noted with the currently accepted porewater chemical test for dispersion, suggested by Sherard et al. Suggestions for using the derived discriminant function as the basis of a simple chemical field test and precautions regarding data interpretation are presented.

Lime Treatment of Dams Constructed with Dispersive Clay Soils

ABSTRACT A description of the existence and performance of dispersed clay soil in earth embankment dams and the construction requirements and experience in the use of lime in the treatment of such clay soil.

Identification and treatment of dispersive clay soils : HALIBURTON, TA PETRY, TM HAYDEN, ML OKLAHOMA STATE UNIV. REPORT, JULY, 1975, 170P. PB-248840

Identification and treatment of dispersive clay soils : HALIBURTON, TA PETRY, TM HAYDEN, ML OKLAHOMA STATE UNIV. REPORT, JULY, 1975, 170P. PB-248840