Limestone ash waste as a substitute for lime in soil improvement for engineering construction

 A by-product of the manufacture of cement at Nkalagu, Nigeria, is the waste material comprising 70% CaO and 30% undecomposed CaCO₃, referred to as limestone ash. The potential of this waste as a substitute for lime in the improvement of the engineering properties of laterite soils for construction purposes has been assessed. The geotechnical properties of lateritic soils when untreated and when treated with varying percentages of limestone ash have been established, including particle size analyses, Atterberg limits, Proctor compaction, California bearing ratio (CBR) and shear strength. The results confirmed those obtained by other workers on the use of lime stabilisation and indicate that limestone ash may form a substitute for lime in soil improvement for engineering construction. Received: 14 November 1997 · Accepted: 16 August 1999     

The influence of oil contamination on the geotechnical properties of coastal sediments in the Yellow River Delta,China

The effect of contamination by crude oil has been assessed using samples from hand dug trial pits in the Hai-gang region of the Yellow River Delta. In addition to electrical resistivity and in situ penetration tests, grain size analysis, Atterberg limits, compaction, direct shear test and a micro-structure scan were undertaken. The results show that contamination was in the shape of a plume and non-uniform to a depth of 1 m. The more heavily polluted soil had a higher clay particle content, liquid and plastic limit and compression coefficient. However, no notable correlations were found between oil contamination and shear strength parameters.     

An experimental study on the influence of metakaolin on mechanical properties of a clayey sand

The aim of this research is to investigate the effect of the additive metakaolin on the strength parameters of clayey sand soil. For this purpose, in addition to identification tests, a set of experiments including Atterberg limits and modified Proctor, uniaxial compressive strength, direct shear, permeability, and pH tests have been performed on some samples of the clayey sand soil under non-stabilized and stabilized conditions for different percentages of metakaolin. Furthermore, scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been performed to investigate the microstructure of the non-stabilized and stabilized soil. The results showed that the maximum extent of increase in the strength occurred by metakaolin 25% and after 28 days of curing. Furthermore, elevation of the weight percentage of metakaolin in clayey sand soil causes to increase shear strength, diminish hydraulic conductivity, reduce the maximum specific dry weight of soil, and increase optimal water content, but it has a minor effect on pH value during the curing time. Investigation of the results obtained from XRD of the sample treated with metakaolin indicated the emergence of the cement compound called calcium silicate hydrate (CSH). Furthermore, the results of SEM imaging indicated that with the addition of metakaolin, the dispersed structure of soil changes into a flocculated structure, thereby enhances the soil strength.

     

The role of carbide lime and fly ash blends on the geotechnical properties of clay soils

Carbide lime is a by-product obtained during the manufacturing of acetylene from the reaction of calcium carbide and water. A major portion of carbide lime is dumped in waste deposition areas, creating an environmental problem. Carbide lime and fly ash have possible applications in slope stabilization, subgrade improvement of roads, and soil treatments under shallow foundations. A series of Atterberg limits tests, compaction tests, unconfined compressive strength tests, ultrasonic pulse velocity tests, and wetting–drying tests were performed on carbide lime and fly ash treated clay soils to evaluate the effects of additive content, curing time, strength development, and the effects of wetting and drying. A total of 8% of carbide lime constituted the fixation point, and peak strength was achieved at 12% carbide lime content. A total amount of 25% additive was found as a threshold changing the Atterberg limits. Test results indicated that the strength of the treated soil improved by the existence of carbide lime and fly ash; best performance was observed in 28-day specimens with 10% carbide lime and 20% fly ash content reaching to 8 times larger strength than untreated soil. The failure patterns of the specimens reflected the curing time and wetting–drying effects. Although, the application of wetting–drying cycles deteriorated the treated soil, the presence of carbide lime partially prevented the strength loss. New relationships between normalized strength and curing time depending on carbide lime content were proposed. Furthermore, a linear relationship between the unconfined compressive strength and the ultrasonic pulse velocity of the treated soils was established.

     

Effect of fly ash and polypropylene fibres content on the soft soils

Fly ash is a waste produced from the burning of coal in thermal power stations. The staggering increase in the production of fly ash and its disposal in an environmentally friendly manner is increasingly becoming a matter of global concern. Efforts are underway to improve the use of fly ash in several ways, with the geotechnical utilization also forming an important aspect of these efforts. An experimental program was undertaken to investigate the effects of multifilament and fibrillated polypropylene fibre on the compaction and strength behavior of CH class soil with fly ash in different proportions. The soil samples were prepared at two different percentages of fibre content (i.e. 0.5 and 1% by weight of soil) and two different percentages of fly ash (i.e. 10 and 15% by weight of soil). A series of tests were prepared including optimum moisture content and laboratory unconfined compression strength tests, compaction tests and Atterberg limits test. The fibre inclusions increased the strength of the fly ash specimens and changed their brittle behavior into ductile behavior.     

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 enviro nmental 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,bio re mediation 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.Micro structural 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 bio re mediation 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.     

Mechanical behavior of lightweight soil reinforced with waste fishing net

Lightweight soil is cement-treated and consists of dredged clayey soil, cement, and air-foam. Reinforced lightweight soil (RLS) contains waste fishing net to increase its shear strength. This paper investigates the strength characteristics and stress–strain behavior of reinforced and unreinforced lightweight soils. Test specimens were prepared with varying admixtures of cement content (8%, 12%, 16%, and 20% by the weight of untreated soil), initial water content (125%, 156%, 187%, 217%, and 250%), air-foam content (1%, 2%, 3%, 4%, and 5%), and waste fishing net (0%, 0.25%, 0.5%, 0.75%, and 1%). Then several series of unconfined compression tests and one-dimensional compression tests were conducted. The experiments with lightweight soil indicated that the unconfined compressive strength increased with an increase in cement content, but decreased with increasing water content and air-foam content. The stress–strain relationship and the unconfined compressive strength were influenced by the percentage of waste fishing net. In addition, the strength of RLS generally increased after adding waste fishing net due to the bond strength and the friction at the interface between waste fishing net and soil mixtures, but the amount of increase in compressive strength was not directly proportional to the percentage of waste fishing net. The results of testing indicated that the maximum increase in compressive strength was obtained for a waste fishing net content of about 0.25%. The bulk unit weight of lightweight soil was strongly dependent on the air-foam content. The compression characteristics of lightweight soil, including the yield stress and compression index, did not depend greatly on whether the samples were cured underwater or in air.     

Application of phosphogypsum in soil stabilization

This paper describes the application of phosphogypsum with cement and fly ash for soil stabilization. Atterberg limits, standard Proctor compaction and unconfined compressive strength tests were carried out on cement, fly ash and phosphogypsum stabilized soil samples. Treatment with cement, fly ash and phosphogypsum generally reduces the plasticity index. The maximum dry unit weights increase as cement and phosphogypsum contents increase, but decrease as fly ash content increases. Generally optimum moisture contents of the stabilized soil samples decrease with addition of cement, fly ash and phosphogypsum. Unconfined compressive strengths of untreated soils were in all cases lower than that for treated soils. The cement content has a significantly higher influence than the fly ash content. The use of two waste by-products, phosphogypsum and fly ash may provide an inexpensive and advantageous construction product.     

Engineering properties and slope stability of road cuttings along the enugu-onitsha express road,Southeastern Nigeria

The new express highway linking Enugu (in Enugu State) and Onitsha (in Anambra State) both in Southeastern Nigeria, is plagued with landslides, a few years after completion. The active landslides are concentrated on the road cuttings between Otuocha junction and Awka, specifically between km 29 and km 40 from the Onitsha end of the road. Three of these slides have been studied. The investigation involved detailed field and laboratory studies of the physical conditions and geotechnical properties of the sites and soils therein. The laboratory tests performed included grainsize distribution analysis, Atterberg limits, specific gravity, natural water content, bulk density, permeability and shear strength. Each site was analysed for stability using the strength parameters obtained from laboratory tests and Bishop's 1955 simplified method of analysis. There is evidence from the analyses results that although the cut slopes are vulnerable to toe undermining and over-steepening by runoff, the generally “loose” nature of the soils as evidenced by the low bulk density (1580–1960 kg/cm³), fairly high void ratio (0.53–0.66) but low permeability (2.15–3.25×10^?3 cm/s) and consequent high saturation and strength reduction during the rains, are the major contributors to instability of the cut slopes.     

Changes in chemical composition and engineering properties of gypseous soils through leaching: an example from Mashhad,Iran

Gypseous soils are considered problematic when used as the foundation in civil engineering structures such as roads, buildings and dams, due to their solubility. These soils are resistant and have good engineering properties in their dry state. However, when saturated by rainwater or a rising groundwater table, the soluble minerals are washed out, resulting in the subsidence of the structures built on them. In the recent decades, buildings constructed in the Southern Mashhad Metropolitan Area, Iran, have been widely faced with this problem. Since the changes in chemical composition and engineering properties of these soils are based on the amount of dissolved gypsum, the focus of this study is to characterize the soluble soils of this area and their changes throughout the leaching process. Thirty-eight samples were taken from different locations in the area. Chemical tests were conducted on the samples and the gypsum and sulfate concentration maps were produced based on these results, combined with the previously available data from 511 boreholes drilled in the area. Seven soil samples with different gypsum concentrations were selected for further analysis in four major groups of tests, including hydraulic tests (permeability and solubility), chemical tests (chemical analysis of soils samples and total dissolved solids, calcium hardness and chlorine of the leachate samples), physical tests (grain size analysis, Atterberg limits and specific gravity) and mechanical tests (consolidation and direct shear). Changes in the mentioned parameters were investigated through a 5-day leaching process. The results indicate that extensive dissolution of gypsum and removal of gypsum bonding between soil particles change soil chemical composition and decrease the soil compressibility and strength parameters. Therefore, the structures built in this area are in high risk of subsidence and foundation failure; proper measures should be taken to improve the soil quality before construction.     

水泥固化锌污染高岭土强度及微观特性研究

采用水泥作为固化剂对锌污染高岭土进行固化稳定处理,对固化后养护7 d和28 d的人工锌污染土的液塑限特性,无侧限抗压强度和变形模量特性,土样pH特性,以及微观机理进行了研究.结果表明,液塑限随锌离子浓度增加而降低.随锌离子浓度增加,固化污染土的无侧限抗压强度值总体均呈下降趋势;随试样pH值升高,无侧限抗压强度值增大;变形模量E₅₀均随锌离子浓度增大而减小;水泥的主要水化产物的数量均随锌离子浓度的增加而减少,且由成熟形态向早期形态退化,并最终消失.随着锌离子浓度的增加,试样中的直径1～10 μm的孔隙数量明显增加,并且伴随着直径0.01～1 μm的孔隙数量的减小.     

Behavior of diatomaceous soil in lacustrine deposits of Bogota,Colombia

This work presents a study on the behaviors of diatomaceous soils. Although studies are rarely reported on these soils, they have been identified in Mexico City, the Sea of Japan, the northeast coast of Australia,the equatorial Pacific, and the lacustrine deposit of Bogota(Colombia), among other locations. Features of this kind of soil include high friction angle, high initial void ratio, high compressibility index, high liquid limit, and low density. Some of these features are counterintuitive from a classical soil mechanics viewpoint. To understand the geotechnical properties of the diatomaceous soil, a comprehensive experimental plan consisting of more than 2400 tests was performed, including physical tests such as grain size distribution, Atterberg limits, density of solid particles, and organic matter content; and mechanical tests such as oedometric compression tests, unconfined compression tests, and triaxial tests.Laboratory tests were complemented with scanning electron microscope(SEM) observations to evaluate the microstructure of the soil. The test results show that there is an increase in liquid limit with increasing diatomaceous content, and the friction angle also increases with increasing diatomaceous content. In addition, several practical correlations were proposed for this soil type for shear strength mobilization and intrinsic compression line. Finally, useful correlations were presented, such as the relationship between the state consistency and the undrained shear strength, the friction angle and the liquid limit, the void ratio at 100 kPa and the liquid limit, the plasticity index and the diatomaceous content, among others.     

Behavior of diatomaceous soil in lacustrine deposits of Bogotá, Colombia

This work presents a study on the behaviors of diatomaceous soils. Although studies are rarely reported on these soils, they have been identified in Mexico City, the Sea of Japan, the northeast coast of Australia, the equatorial Pacific, and the lacustrine deposit of Bogotá (Colombia), among other locations. Features of this kind of soil include high friction angle, high initial void ratio, high compressibility index, high liquid limit, and low density. Some of these features are counterintuitive from a classical soil mechanics viewpoint. To understand the geotechnical properties of the diatomaceous soil, a comprehensive experimental plan consisting of more than 2400 tests was performed, including physical tests such as grain size distribution, Atterberg limits, density of solid particles, and organic matter content; and mechanical tests such as oedometric compression tests, unconfined compression tests, and triaxial tests. Laboratory tests were complemented with scanning electron microscope (SEM) observations to evaluate the microstructure of the soil. The test results show that there is an increase in liquid limit with increasing diatomaceous content, and the friction angle also increases with increasing diatomaceous content. In addition, several practical correlations were proposed for this soil type for shear strength mobilization and intrinsic compression line. Finally, useful correlations were presented, such as the relationship between the state consistency and the undrained shear strength, the friction angle and the liquid limit, the void ratio at 100 kPa and the liquid limit, the plasticity index and the diatomaceous content, among others.     

Impact of open dumping of municipal solid waste on soil properties in mountainous region

This paper presents the effect of open dumping of municipal solid waste (MSW) on soil characteristics in the mountainous region of Himachal Pradesh, India. The solid waste of dumpsite contains various complex characteristics with organic fractions of the highest proportions. As leachate percolates into the soil, it migrates contaminants into the soil and affects soil stability and strength. The study includes the geotechnical investigation of dump soil characteristics and its comparison with the natural soil samples taken from outside the proximity of dumpsites. The geochemical analysis of dumpsite soil samples was also carried out by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Visual inspection revealed that the MSW consists of high fraction of organics, followed by paper. The soil samples were collected from five trial pits in the dumpsites at depths of 0.5 m, 1 m and 1.5 m. Then the collected soil samples were subjected to specific gravity test, grain size analysis, Atterberg's limit test, compaction test, direct shear test, California bearing ratio (CBR) test and permeability analysis. The study indicated that the dumpsite soils from four study regions show decreasing trends in the values of maximum dry density (MDD), specific gravity, cohesion and CBR, and increasing permeability as compared to the natural soil. The results show that the geotechnical properties of the soils at all four study locations have been severely hampered due to contamination induced by open dumping of waste.     

Interface shear strength between geosynthetic clay liner and covering soil on the embankment of an irrigation pond and stability evaluation of its widened sections

Geosynthetic clay liners (GCLs) are typically used for widening sections of an embankment. They are also used as low permeability liners to minimize water leakage from reservoirs such as irrigation ponds. However, few investigations have been carried out on the specific properties of GCLs, such as granulated bentonite sandwiched between geotextiles, their internal shear strength, and the shear strength at the interface between a GCL and an embankment body. In this study, a series of direct box shear tests were performed to determine the shear strength properties of bentonite and compacted soils as well as at the interface between a GCL and bentonite or compacted soil. In addition, a series of field-loading tests were conducted to investigate the failure behaviour of an embankment body containing a GCL when changes in the water content of the bentonite of the GCL in a real embankment occur. Furthermore, the stability of widened embankment bodies that incorporated GCLs were evaluated. The main conclusions of this study are as follows: (1) The shear strength of the interface between the covering soil and geotextiles varied according to the soil type, geotextile type, and the submergence period, (2) the maximum safety factor was observed at the interface between decomposed granite soil and the geotextiles, while the minimum safety factor was observed at the interface between the bentonite and the geotextiles, and (3) the influence of GCLs on the instability of a widened embankment was extremely small.     

Three-dimensional geotechnical modeling of the soils in Riyadh city,KSA

A standard penetration test (SPT) was carried out for 700 samples from 143 boreholes in four districts in Riyadh city, Kingdom of Saudi Arabia (KSA). Rock quality designation (RQD) and unconfined compression strength (UCS) tests were also performed for 238 samples from 154 boreholes in 15 districts of the city. Three-dimensional (3D) models of the SPT, RQD, and UCS were produced using the Voxler 3 software package. Further, 333 soil samples collected from 106 boreholes in 11 districts were examined to spatially model the distinctive geotechnical patterns of the alluvial soils in two dimensions. Tests were carried out to determine the soil grain size distribution, natural water content (NWC%), Atterberg’s consistency limits [liquid limit (LL%), plastic limit (PL%), and plasticity index (PI%)], and soil–water chemical components (pH Cl⁻, SO₃²⁻, and CO₃⁻). Spatial maps of the geotechnical parameters were produced by applying the geostatistical ordinary kriging implemented in ArcGIS. Soil samples were classified according to the unified soil classification system (USCS), and a thickness of the silty clay layer was produced. Plasticity charts indicated that the soils are inorganic cohesive clays with low and moderate plasticity (CL). Soil strength parameters showed wide ranges of UCS (average 220, range 21.3–618 kg/cm²), SPT (average 39, 0–100 N), and RQD (average 44, 11–78%). UCS and SPT 3D models clarified a regional southeastward trend of increase. RQD 3D models showed poor to fair engineering quality of rocks (25–75%). The results presented here can help to establish geohazard zonation maps with construction favorability ratings for safe urban expansion.

     

含盐量对极细颗粒黏土强度影响的试验研究

 为深入研究滨海盐渍土等极细颗粒黏土的不良工程特性产生的物理化学机制,探讨在水的作用下由可溶盐离子引起土颗粒表面微电场的变化对极细颗粒黏土抗剪强度的影响,首先对一系列含盐量即不同孔隙液离子浓度下的人工土(膨润土、高岭土与膨润土的混合土、石英)进行常规直剪与液塑限试验,同时测试人工土的阳离子交换量与比表面积等微细观参数用于计算颗粒的表面电位,建立抗剪强度与表面电位之间的关系。测试结果表明,可溶盐离子通过扩散的双电层改变土颗粒表面电位,引起结合水膜厚度的变化致使土颗粒之间的变形阻力发生改变,在宏观上表现为土体强度的变化。结合科威特Bubiyan岛的海港盐渍土软基加固工程,研究可溶盐含量对当地滨海盐渍土的强度与液塑限的影响,证实孔隙液离子浓度对人工土的强度的影响机制与变化规律同样适用于天然极细颗粒黏土,为从微细观角度揭示盐渍土的不良工程特性提供理论解释与试验基础。     

Some contributions to mechanical behaviors of lacustrine deposit in Bogotá, Colombia

This paper presents the mechanical behaviors of the lacustrine deposit, a representative soil in Bogotá, Colombia. Initially, the physical characterization of the deposit is performed via laboratory tests (grain size distribution, scanning electron microscopy, Atterberg limits and water content). This characterization intends to explain the special characteristics of the mechanical behaviors of this soil. Then, various triaxial tests are carried out with controlled loading path, strain rate change, relaxation, extensile stress, and cyclic loading. The test results reveal the shape of the yield curve for Bogotá soil (in a natural state), and also show that an increasing effect of the strain rate depends on the liquid limit. This effect is also preserved with extensile stresses (which are poorly studied in soil mechanics). Finally, other effects, such as the loss of structure in the reconstituted samples and the effect of shear modulus at low strains, are studied for Bogotá soil.     

Geotechnical properties and microstructure of lime-stabilized silt clay

The geotechnical properties and microstructures of lime-stabilized silt clay from Jilin province, China, were studied in detail. Laboratory tests were conducted to evaluate the effects of lime content and curing time on the overall soil properties, including compaction characteristics, Atterberg limits, particle size distribution, pH, stress–strain behavior, peak strength, shear strength parameters, and California bearing ratio (CBR). The stabilized mechanisms of lime in silt clay were examined, and the observed test results were explained based on the results of scanning electron microscropy (SEM) and X-ray diffraction analyses of the specimens. Lime content and curing duration significantly influenced the geotechnical properties and microstructure of the lime-stabilized silt clay specimens. An increase in lime content resulted in increases in compaction water content, liquid limit, plastic limit, sand size-fractions, pH, peak strength, cohesion, internal friction angle, and the CBR, but led to a reduction in the plasticity index, silt fractions, clay fractions, swelling capacity, and water absorption. Also, the addition of lime to silt clay changed this soil type from a ductile to a brittle material. The optimum lime content of the silt clays from Jilin province was determined to be approximately 5–7%. SEM micrographs showed that a white cementitious gel was formed after the addition of lime and that peaks related to smectite, illite, kaolinite, and quartz appeared to be sharper after stabilization with lime and a 90-day period of curing. These results show that the geotechnical properties of lime-stabilized silt clay are affected by the microstructural organization of the silt clay itself.

     

Some contributions to mechanical behaviors of lacustrine deposit in Bogota,Colombia

This paper presents the mechanical behaviors of the lacustrine deposit,a representative soil in Bogota,Colombia.Initially,the physical characterization of the deposit is performed via laboratory tests(grain size distribution,scanning electron microscopy,Atterberg limits and water content).This characterization intends to explain the special characteristics of the mechanical behaviors of this soil.Then,various triaxial tests are carried out with controlled loading path,strain rate change,relaxation,extensile stress,and cyclic loading.The test results reveal the shape of the yield curve for Bogota soil(in a natural state),and also show that an increasing effect of the strain rate depends on the liquid limit.This effect is also preserved with extensile stresses(which are poorly studied in soil mechanics).Finally,other effects,such as the loss of structure in the reconstituted samples and the effect of shear modulus at low strains,are studied for Bogota soil.