Effect of the combination of lime and natural pozzolana on the compaction and strength of soft clayey soils: a preliminary study

Soft soil stabilization has been practised for quite some time by mixing additives, such as cement, lime and fly ash to the soil to increase its strength. However, there is a lack of investigations on the use of natural pozzolana alone or combined with lime for ground improvement applications. An experimental programme was undertaken to study the effect of using lime, natural pozzolana or a combination of both on the geotechnical characteristics of soft soils. Lime or natural pozzolana was added to soft soils at ranges of 0?C10% and 0?C20%, respectively. In addition, combinations of lime?Cnatural pozzolana were added to soft soils at the same ranges. Test specimens were subjected to compaction tests, shear tests and unconfined compression tests. Specimens were cured for 1, 7, 28 and 90?days, after which they were tested for unconfined compression tests. Based on the favourable results obtained, it can be concluded that the soft soils can be successfully stabilized by the combined action of lime and natural pozzolana. Since natural pozzolana is much cheaper than lime, the addition of natural pozzolana in lime?Csoil mix may particularly become attractive and can result in cost reduction of construction.     

Effect of Lime Stabilized Soil Cushion on Strength Behaviour of Expansive Soil

An experimental investigation was undertaken to study the effects of lime-stabilized soil-cushion on the strength behavior of expansive soil. In the present investigation, a series of laboratory tests (Unconfined compression tests and CBR tests) were conducted on both expansive soil alone and expansive soil cushioned with lime-stabilized non-expansive cohesive soil. Lime contents of 2, 4, 6, 8 and 10% by dry weight of cohesive non-swelling soil was used in the stabilized soil cushion. Both expansive soil and lime stabilized soil cushion were compacted to Standard Proctor’s optimum condition with thickness ratio 2:1. Tests on cushioned expansive soils were conducted at different curing and soaking periods i.e., 7, 14, 28 and 56 days. The test results revealed that maximum increase in strength was achieved after 14 days of curing or soaking period with 8% of lime content.     

Compaction characteristics of granular soils in United Arab Emirates

Most of the topsoils encountered in United Arab Emirates and in the Arabian Peninsula are granular soils with small percentages of silt and clay. Determination of the compaction characteristics of such soils is an essential task in preparing for construction work. The accumulating experience over many years of soil testing in our laboratories suggested that there exists an underlying trend that governs the compaction characteristics of such soils. As such, a study was undertaken to assess the compaction characteristics of such soils and to develop the governing predictive equations. For the purposes of this study, 311 soil samples were collected from various locations in the United Arab Emirates, and tested for various including grain-size distribution, liquid limit, plasticity index, specific gravity of soil solids, maximum dry density of compaction, and optimum moisture content following ASTM D 1557-91 standard procedure C. Following the development of the predictive equations, a new set of 43 soil samples were collected and their compaction results were used to test the validity of predictive model. The range of variables for these soils were as follows: percent retained on US sieve #4 (R#4): 0–68; Percent passing US sieve #200 (P#200): 1–26; Liquid limit: 0–56; Plasticity index: 0–28; Specific gravity of soil solids: 2.55–2.8. Based on the compaction tests results, multiple regression analyses were conducted to develop mathematical models and nomographic solutions to predict the compaction properties of soils. The results indicated that the nomographs could predict well the maximum dry density within ±5% confidence interval and the optimum moisture content within ±3%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Random Inclusion of Polypropylene Fibers on Strength Characteristics of Cohesive Soil

This paper presents the effect of random inclusion of polypropylene fibers on strength characteristics of soil. Locally available cohesive soil (CL) is used as medium and polypropylene fibers with three aspect ratios (l/d = 75, 100 and 125) are used as reinforcement. Soil is compacted with standard Proctor’s maximum density with low percentage of reinforcement (0–1% by weight of oven-dried soil). Direct shear tests, unconfined compression tests and CBR tests were conducted on un-reinforced as well as reinforced soil to investigate the strength characteristics of fiber-reinforced soil. The test results reveal that the inclusion of randomly distributed polypropylene fibers in soil increases peak and residual shear strength, unconfined compressive strength and CBR value of soil. It is noticed that the optimum fiber content for achieving maximum strength is 0.4–0.8% of the weight of oven-dried soil for fiber aspect ratio of 100.     

Stabilization of Tropical Peat Soil from Sarawak with Different Stabilizing Agents

This paper describes a study on tropical peat soil stabilization to improve its physical properties by using different stabilizing agents. The samples were collected from six different locations of Sarawak, Malaysia, to evaluate their physical or index properties. Out of them, sample having the highest percentage of organic content has been selected for stabilization purposes. In this study, ordinary portland cement (OPC), quick lime (QL), and class F fly ash (FA) were used as stabilizer. The amount of OPC, QL, and FA added to the peat soil sample, as percentage of dry soil mass, were in the range of 5–20%; 5–20% and 2–8%, respectively for the curing periods of 7, 14, and 28 days. The Unconfined Compressive Strength (UCS) test was carried out on treated/stabilized samples with the above mentioned percentages of the stabilizer and the result shows that the UCS value increases significantly with the increase of all stabilizing agent used and also with curing periods. However, in case of FA and QL, the UCS value increases up to 15 and 6%, respectively with a curing period of 28 days but decreases rather steady beyond this percentage. Some UCS tests have been conducted with a mixture of FA and QL to study the combined effect of the stabilizer. In addition, Scanning Electron Microscope (SEM) study was carried out on original peat soil and FA, as well as some treated samples in order to study their microstructures.     

Prediction of copper content in waste dump of Sarcheshmeh copper mine using visible and near-infrared reflectance spectroscopy

The pore structure characteristics of soil are closely related to soil engineering properties. For saline soil distributed in seasonally frozen areas, existing studies have focused on the influence of freeze–thaw cycles on pore structure, while the influence of soluble salt in the soil is not well understood. This study aims to explore the influence of salt content and salt type on the pore structure of freeze-thawed soil. Soil samples with different salt contents (0–2%) and types (bicarbonate salt and sulfate salt) were subjected to 10 freeze–thaw tests, and their pore size distributions (PSDs) were obtained by mercury intrusion porosimetry tests. In addition, the PSDs were quantitatively analyzed by fractal theory. For both salts, the PSDs of the tested soil samples were bimodal after the freeze–thaw cycles, and the porosity of saline soil samples increased with increasing salt content overall. However, the contents of various types of pores in soil samples with two salt types were quite different. The variation in bicarbonate salt content mainly affected the mesopore and macropore contents in the soil samples, and their change trends were opposite to each other. For soil samples with sulfate salt, the porosity and macropore content increased significantly when the salt content exceeded 1%. In addition, the pore structures in saline soil presented fractal characteristics after the freeze–thaw cycles, and the fractal dimension was positively correlated with macropore content. This study may provide references for understanding the engineering properties of saline soil in seasonally frozen areas at the microscale.     

人工制备结构性土力学特性试验研究

通过对结构性土的研究可以掌握天然土受荷过程中的变形破损过程, 从而为考虑土结构性的结构物设计、地基加固等提供依据。本文尝试了一种简单可行的结构性土样的人工制备方法, 通过在原状土料中加入少量水泥和盐粒以形成颗粒间的胶结作用和大孔隙组构以模拟天然黏土的结构性。然后进行了室内压缩试验和不同胶结强度土样在排水和不排水条件下的三轴剪切试验,分析结构性土样的力学特性,以探讨结构性土的破损过程和变形机理。     

Shear Modulus and Damping Ratio of Organic Soils

The paper presents results from a laboratory investigation into the dynamic properties of natural intact and model organic soils by means of resonant-column tests. The natural intact organic soils were sands, cohesive soils and peats with varying content of calcium carbonate. The model organic soils were formed in laboratory by mixing kaolinite and paper pulp. The influence of various soil parameters, such as strain level, confining stress, void ratio, plasticity index, organic content and secondary consolidation time on shear modulus, G, and damping ratio, DT, is presented and discussed. The test results on natural organic soils show that only high organic contents (OC ≥ 25%) have significant influence on G and DT at both small and high shear strains. For the model organic soils, however, a significant influence of even lower values of organic content (5% ≤ OC ≤ 20%) on G at small strains and DT at both small and high strains is observed.     

Effects of rock fragments on infiltration and evaporation in hilly purple soils of Sichuan Basin,China

This paper presents the results of laboratory experiments showing the effects of rock fragments contained in three different purple soils of the Sichuan basin of southwest China. The experiments investigated how these rock fragments alter the soil’s physical, chemical, and agronomical characteristics such as infiltration and evaporation. We found that the infiltration rate, whether horizontal or vertical, in the three soils has the following order: gray brown purple soil < reddish brown purple soil < brown purple soil. With increasing rock fragment contents the accumulated infiltration decreases, while the total time decreases first and then increases. The minimum occurs at approximately 10–20% of fragment content by weight. The infiltration rate also changes with the distance. In the 0–5 cm range, the initial infiltration rate increases with increasing rock fragment contents, while in the 5–10 cm range, the slope of infiltration curve increases with increasing rock fragment contents. With increasing distance, the slope gradually decreases and finally reaches a stable value. The presence of rock fragments reduces soil water content, the minimal value appearing when the rock fragments were on top of the soil column (soil + rock sample), decreasing with increasing rock fragments for other samples mixed with fragments. Under the constant 40°C temperature, the accumulated evaporation and evaporation rate are minimal for soils covered by rock fragments, and the accumulated evaporation decreases with increasing rock fragment for other soil samples. However, the evaporation rate increases with increasing rock fragments in the first 4 days and decreases thereafter.     

Effect of sodium sulphate on the shear strength of clayey soils stabilised with additives

The effect of sulphates on the soil stabilisation using mineral additives such as lime, cement and fly ash has been reported by several researchers. The effect of sodium sulphate (Na₂SO₄) (0–6% by dry weight of soil) on the behaviour of the grey clayey soil (GS) and red clayey soil (RS) stabilised with lime (L) (0–8%), natural pozzolana (NP) (0–20%) and with a combination of lime-natural pozzolana (L–NP) was investigated. The soil specimens were subjected to testing of direct shear strength after 7, 30, 60 and 120 days of curing period. In the absence of Na₂SO₄, the results show that both clayey soils can be successfully stabilised with L or with a combination of L–NP, which substantially increases their shear strength and produces high values of shear parameters. However, at short curing period and for any content of Na₂SO₄, a further increase in shear strength and shear parameters is observed. Moreover, after 30 days of curing, the RS specimens stabilised with L or with NP alone are altered when the Na₂SO₄ is greater than 2%, whereas the GS specimens are not altered. However, the alteration of RS specimens is little when the L and NP are combined on curing with a high content of Na₂SO₄. Generally, the effect of Na₂SO₄ on both stabilised clayey soils depends on the curing time, percentage of additives used and their type, mineralogical composition of stabilised soils and Na₂SO₄ content.     

Effect of Cement Type on the Mechanical Behavior of a Gravely Sand

The behavior of a cemented gravely sand was studied using triaxial compression tests. Gypsum, Portland cement and lime were used as the cementing agents in sample preparation. The samples with different cement types were compared in equal cement contents. Three cement contents of 1.5%, 3.0% and 4.5% were selected for sample preparation. Drained and undrained triaxial compression tests were conducted in a range of confining pressures from 25 kPa to 500 kPa. Failure modes, shear strength, stress–strain behavior, volume and pore pressure changes were considered. The gypsum cement induced the highest brittleness in soil among three cement types while the Portland cement was found to be the most ductile cementing agent. In lower cement contents and lower confining pressures the soil cemented with Portland cement showed the highest shear strength. However, in the same range of cement content, the soil cemented with gypsum showed highest shear strength for highest tested confining stress. For higher cement contents the shear strength of soil cemented with Portland cement is higher than that for the two other cement types for the range of confining pressures tested in the present study. The samples cemented with lime had the least peak and ultimate shear strength and the highest pore pressure generation in undrained tests. Contrary to the soil cemented with lime, the brittleness of soil cemented with gypsum and Portland cement reduces in undrained condition. Finally it was found that the effect of cement type on the shear strength of cemented soils is more profound in drained condition compared to undrained state.     

长江漫滩相软土结构性特征及其工程效应分析

采用自由活塞薄壁取土器从地表至深度30 m取得不扰动原状土样,通过室内的固结压缩试验,并结合现场CPTU原位测试,利用重塑土的压缩与强度特性作为描述天然沉积土相应特性的基准框架,探讨了长江漫滩相天然沉积软土的物理力学性质。结果表明,长江漫滩相天然沉积软土具有高位结构性,固结系数Cv在土体屈服后急剧降低,屈服前后有明显的分段特征。同时指出,在静荷载水平相对较低的低路堤结构下,软弱土层沉积过程中形成的固结屈服压力和结构强度对其工程特性的影响相对更加显著。减小对天然沉积土的施工扰动作用、充分利用土结构力学效应、尽可能使地基工作于力学性质良好的屈服前阶段,在实际工程应用中具有重要的现实意义。     

Copper contamination of soils and vegetables in the vicinity of Jiuhuashan copper mine,China

Copper contamination in soils and vegetables in the vicinity of an abandoned copper mine in China was investigated. The Cu concentrations of 93 soil samples ranged from 30.4 to 3,191 mg kg⁻¹ soil for a mean of 816.8 mg kg⁻¹ soil. Among 15 samples from a 0 to 20-cm soil layer used for the toxicity characteristic leaching procedure (TCLP) test, the highest value of Cu-TCLP was 133.8 mg kg⁻¹ soil and the TCLP values were positively correlated with the total Cu content of the soils. The sequential extraction of soils in the 0–20-, 20–40-, and 40–60-cm soil layers showed that Cu existed mainly in the Fe–Mn oxide fraction, sulfide/organic fraction, and residual fraction. The copper contamination of 21 species of vegetables from in situ sampling was also examined. Cu concentrations in the edible portions of Brassica chinensis and Solanum melongena were higher than the FAO/WHO standard (40 mg kg⁻¹ DW). The health risk of copper for local inhabitants from consuming these vegetables was assessed on the basis of the target hazard quotient. Enriched concentrations of copper were also found in situ in eight cultivars of B. chinensis planted in the fields, with two levels of Cu concentration. The results showed that there is severe copper contamination in this mine area, and the pollutant in soils show a high risk of leaching into the groundwater and diffusing through the food chain.     

天津滨海地区深部黏土层弹塑性变形特征与地面沉降关系研究

利用在滨海新区施工的2眼全取芯钻孔（G2和G3）,通过原状土样工程特性指标测试、固结压力试验、0-P0反复加、卸荷试验及地面沉降分层标监测数据分析等,系统阐述了滨海地区深部黏性土层弹塑性变形特征与地面沉降的关系。结果表明：天津滨海地区100 m以浅主要为欠固结土层;100～400 m土层处于超固结和微超固结状态,主要是由过去地下水超量开采造成的;400 m以下土层以正常固结为主。G2和G3孔不同层位黏性土层在反复加、卸荷试验过程中表现出塑性变形量逐渐减小,而弹性变形量几乎不变,与反复加、卸荷次数无关,表明黏性土层在水位反复升降条件下,逐渐变为以弹性变形为主。黏性土层这种特性显示,在地下水位反复升降多次后,黏性土层将会逐渐变成弹性体,在水位恢复时,将产生同步回弹,对防治地面沉降具有重要意义。分析弹塑性变形与黏性土层深度、天然含水率和黏粒含量的相关性发现：弹性变形量与黏性土层深度、天然含水率及黏粒含量呈正相关性;塑性变形量与深度相关性不明显,与天然含水率和黏粒含量呈负相关性。     

The potentials of lime stabilization of lateritic soils

The paper reviews lime stabilization of lateritic soils and shows that all Nigerian lateritic soils from A-1-a soil to A-7-6 soil used in the investigation, improved their engineering characteristics substantially by the addition of lime. The plasticity indices of the soils were reduced whereas the plastic limits increased; the liquid limits increased slightly, the maximum dry density decreased and the optimum moisture content increased. From the results of Durability and CBR tests, only the A-1 soil and A-2 soil have any potential as competent base materials and consequently only these require any further field tests. 6% lime is recommended for these field tests. The other soils that do not qualify for bases may be utilized as sub-base materials.     

不同排水条件下砂-黄土界面的剪切力学特性

为了研究异质土在不同排水条件下的力学机理,进行了一系列环剪试验,对单一黄土、单一砂、砂-黄土组成的异质土在剪切力学特性上的差异及其产生机理进行了比较分析。结果表明：在不同排水条件下,砂-黄土组成的异质土在相互接触剪切的过程中,剪切应力变化形态和抗剪强度与单一黄土、单一砂之间存在显著差异,即砂-黄土组成的异质土在其剪切过程中呈现出了黏性土的剪切力学特征;在相同剪切速率条件下,砂-黄土组成的异质土在不同排水条件下的抗剪强度比单一黄土和单一砂的抗剪强度至少降低了71%和51%。不同排水条件下砂-黄土的剪切力学性质出现了差异,其主要原因与剪切面处砂与黄土之间的相互作用以及剪切面处土体内孔隙水状态有关。     

Environment impact of heavy metals on urban soil in the vicinity of industrial area of Baoji city,P.R. China

Heavy metals in soils are of great environmental concern, in order to evaluate heavy metal contents and their relationships in the surface soil of industrial area of Baoji city, and also to investigate their influence on the soils. Soil samples were collected from 50 sites, and the concentration of Pb, Zn, Cu, Cr, Ni heavy metals and the contents of characteristics in soil from industrial area of Baoji city were determined with X-ray fluorescence method. The concentrations of Pb, Zn, Cu, Cr and Ni in the investigated soils reached the amount of 2,682.00–76,979.42, 169.30–8,288.58, 62.24–242.36, 91.96–110.54 and 36.14–179.28 mg kg⁻¹, respectively. The major element Pb contents of the topsoils were determined. to highlight the influence of ‘anthropic’ features on the heavy metal concentrations and their distributions. To compare, all values of elements were much higher than those of unpolluted soils in the middle of Shaanxi province that average 16.0–26.5, 67.1–120.0, 17.8–57.0, 46.9–65.6 and 24.7–34.6 mg kg⁻¹ for Pb, Zn, Cu, Cr and Ni, respectively. An ensemble of basic and relativity analysis was performed to reduce the precipitate of Pb in soil was extremely high and greatly relativity with other elements. Meanwhile, Pb, Zn, Cu, Cr, Ni heavy metals were typical elements of anthropic activities sources, so it was easy to infer to the tracers of anthropic pollutions from the factorial analysis, which was coming from the storage battery manufactory pollutions. The pollutant distributions were constructed for the urban area which identified storage battery manufactory soot precipitate as the main source of diffuse pollution and also showed the contribution of the topsoils of industrial area of Baoji city as the source point of pollution. Consequently, the impact of heavy metals on soil was proposed and discussed. These results highlight the need for instituting a systematic and continuous monitoring of heavy metals and other forms of pollutants in Baoji city to ensure that pollution does not become a serious problem in the future.     

Cement-Stabilization of Sabkha Soils from Al-Auzayba,Sultanate of Oman

Sabkha soils are salt-bearing formations that are formed in arid regions. In their in situ states the sabkha soils have high compressibility and low shear strength. These soils are also heterogeneous and their properties depend on the type and amount of salt present. Thus, these soils are not suitable for support of infrastructures without the risk of high settlement and/or bearing capacity failure. This paper investigates the possibility of using cement to improve the shear strength of sabkha soils for possible use as a foundation-bearing soil. The sabkha soil used in this study is a sandy sabkha obtained from the coastal plains at Al-Auzayba, Sultanate of Oman. Cement was added in percentages of 2.5, 5, 7.5 and 10%, by dry weight of soil. The soil-stabilizer mixers were allowed to cure for 7, 14 and 28 days. Laboratory tests such as compaction, unconfined compression, consolidated undrained triaxial and durability tests were performed to measure the engineering characteristics of the stabilized material. The results showed substantial improvements in the shear strength of the sabkha–cement mixtures and the mixtures are also durable with small weight loss after 12 wetting/drying cycles. Thus, cement can be used to improve the shear strength of sabkha soils. Furthermore, the effective stress path and the tress-strain relation of the sabkha–cement mixtures follow trends similar to those of cemented calcareous soils.     

Cation Exchange Capacity of Phosphoric Acid and Lime Stabilized Montmorillonitic and Kaolinitic Soils

Studies on the chemically stabilized soils have shown that the effectiveness of treatment is largely dependent on soil??s natural environment. In this research, the time-dependent changes induced in permanent cation exchange capacity of lime and phosphoric acid treated soils, comprised mainly of montmorillonite and kaolinite minerals, were investigated. Also, in order to study the relationship between the exchange capacity and acidity/alkalinity of pore water, pH measurements were performed on cured samples. Based on the collected data, it was found that the pH of stabilized soils showed a tendency for reaching soil??s natural pH with increasing curing time. In addition, the increase in number of broken bonds around the edges of soil particles and also the formation of cementitious compounds that acquired negative charges contributed to achieving higher CEC_p values at longer curing periods. Nevertheless, the kaolinite mineral with pH-dependent structural properties, showed a rather limited behavior in the acidic medium. From engineering point of view, the lime treated samples revealed the highest degree of improvement with an approximately ten-fold strength increase in comparison to the natural soil over an 8?months curing period.     

Assessment of heavy metal contamination in soils around Balanagar industrial area,Hyderabad, India

The concentration of heavy metals such as Ba, Co, Cr, Cu, Ni, Pb, Rb, Sr, V, Y, Zn, Zr were studied in soils of Balanagar industrial area, Hyderabad to understand heavy metal contamination due to industrialization and urbanization. This area is affected by the industrial activities like steel, petrochemicals, automobiles, refineries, and battery manufacturing generating hazardous wastes. The assessment of the contamination of the soils was based on the geoaccumulation index, enrichment factor (EF), contamination factor, and degree of contamination. Soil samples were collected from Balanagar industrial area from top 10–50 cm layer of soil. The samples were analyzed using X-ray fluorescence spectrometer for heavy metals. The data revealed that the soils in the study area are significantly contaminated, showing high level of toxic elements than normal distribution. The ranges of concentration of Cr (82.2–2,264 mg/kg), Cu (31.3–1,040 mg/kg), Ni (34.3–289.4 mg/kg), Pb (57.5–1,274 mg/kg), Zn (67.5–5819.5 mg/kg), Co (8.6–54.8 mg/kg), and V (66.6–297 mg/kg). The concentration of above-mentioned other elements was similar to the levels in the earth’s crust pointed to metal depletion in the soil as the EF was <1. Some heavy metals showed high EF in the soil samples indicating that there is a considerable heavy metal pollution, which could be correlated with the industries in the area. A contamination site poses significant environmental hazards for terrestrial and aquatic ecosystems. They are important sources of pollution and may results in ecotoxicological effects on terrestrial, groundwater and aquatic ecosystems.