High Plasticity Index Research Articles

Treatments Technology and Mechanisms of East Asia Black Cotton Soil

The East Asia black cotton soil (BCS) cannot be used as embankment filling directly due to its high clay content, liquid limit, plasticity index, and low CBR strength (CBR < 3%). This study evaluates the effects of treating East Asia BCS with lime, volcanic ash, or a combination of both on its engineering properties. Experiments were conducted to analyze the basic physical properties, swelling characteristics, and mechanical properties of the treated soil. Results indicate that lime addition significantly reduces the free swelling rate, improves limit moisture content, increases optimum moisture content, decreases maximum dry density, and enhances CBR value. Although volcanic ash also improves BCS performance, its effects are less pronounced than those of lime. The combined treatment with lime and volcanic ash exhibits superior performance, greatly reducing expansion potential and significantly increasing soil strength. Specifically, a mixture of 3% lime and 15% volcanic ash optimizes the liquid limit, plasticity index, and CBR value to 49.2%, 23.8, and 24.7%, respectively, meeting the JTG D30-2015 requirements and reducing construction costs. The treatment mechanisms involve hydration exothermic reactions, volcanic ash reactions, and semipermeable membrane effects, which collectively enhance the soil’s properties by producing dense, high-strength compounds.

Influence of adding gypsum on the properties of lime-stabilized expansive soil

Abstract Expansive soils present major structural and geotechnical engineering problems. Expansive soil undergoes considerable changes in volume because of variations in water content. These variations in volume can occur as either swelling or shrinking and are commonly referred to as swell-shrink soils. Considering key aspects, such as the characteristics of the soil, is essential when dealing with swelling soils. There are expansive soils in both humid areas, where they pose problems with a high plasticity index, and in semi-arid or arid areas, where even moderately swelling soils can cause considerable damage. In order to solve problems related to expansive soil, it is important to stabilize it using various additives like gypsum, lime, and so on. The effects of adding three percentages of gypsum (2%, 4%, and 8%) to 6% lime-stabilized expansive soil to improve its engineering properties are investigated through several tests. The results of tests displayed that adding gypsum has improved properties of prepared soil with 6% lime. The optimum mixture for (gypsum-lime) that gets the highest improvement in soil properties is (6% lime + 4% gypsum). This mixture shows reducing in the free swell, swelling pressure, and plasticity index (from 8.51% to 2.81%, from 715.68 Kpa to 89.18 Kpa, from 33% to 29% respectively). Also, this mixture shows increasing in CBR (from 13.69% to 16.17%) and unconfined compressive strength (UCS) for the curing time of 0, 7, and 14 days (from 264.318 Kpa to 492.131 Kpa, from 380.584 Kpa to 736.318 Kpa, and from 480.192 Kpa to 828.590 Kpa respectively). The maximum dry density (MDD) and optimum moisture content (OMC) increase with increasing gypsum content, While the specific gravity decreases.

Mineral Identification as an A-7-5 Clay Stability Indicator Using Volcanic Ash

Soil is a building material and the foundation of the structure, it must be considered. There are bumpy roads and collapses on Jalan Elak Lhokseumawe. This study’s primary focus is on road subgrade. Because of its high plasticity index and clay minerals that swell when water is added, the soil cannot be used as a subgrade. Volcanic ash from Burni Telong Bener Meriah was used in this study. The combined volcanic ash content ranges between 7.5% and 15%. The goal is to see if the bearing can be stabilized afterward. Based on XRD analysis, this soil has an illite clay mineral content with a WT value of 0.817%. The Atterberg limit test on soil is classified as A-7-5 by AASHTO and MH by USCS. At a percentage of 12.5% volcanic ash, the CBR test results for soaked and unsoaked conditions yielded optimal values of 5.9% and 9.4%, respectively. The swelling value continued to fall at a percentage of 12.5% volcanic ash. UCS test results in soaked and unsoaked conditions at 12.5% volcanic ash percentage yielded optimum values of 1.46 kg/cm2 and 2.18 kg/cm2, respectively. The soil is found to be usable, but it needs to be stabilized.

Comparison of Stabilized Shear Strength of Blangjerango Clay and Some Quarry Soils With Tripe Jaya Gayo Lues Limestone Ash

Soil stabilization is a way that is most considered to be cheaper than replacing old, less good soil with better ones with the aim of improving the properties of the original soil which has low bearing capacity, high plasticity index, high swelling and poor gradation, especially for areas that requires soil improvement. One of the stabilizing materials that can be used is lime as an additive which is useful for increasing soil stiffness and strength. The lime used in this research came from Tripe Jaya District, Gayo Lues Regency. This research was carried out by taking soil samples in a quarry which was then added with lime as a stabilizing agent. This soil was tested for physical properties, compaction, and a shear strength test (direct shear). Research was conducted to see the results of soil stabilization with lime on changes in soil strength when receiving the effects of both natural and artificial (remolded) factors. The results of the research can be used to mitigate cases of road or building collapse on the subgrade or infrastructure built on the land. The primary data required in this research was taken from the results of examinations and tests in the laboratory. The tests and inspections carried out are in the form of measuring the physical properties of the soil such as water content, specific gravity, plastic limit, liquid limit, and PSA (Particle Size Analyzer), as well as measuring mechanical properties in the form of soil compaction parameters with a standard proctor on the original soil and soil shear strength using direct shear test to obtain friction angle (ϕ) and cohesion (c). In this research, a comparison of the stabilized shear strength of clay soil with Gayo Lues limestone has been carried out with several other soil sources for landslide analysis. The analysis results show that Gayo Lues limestone has a good ability to increase the strength and stability of clay soil. It is hoped that this research will provide useful information in selecting the right soil stabilization material.

Geosynthetic solutions for road stabilization and railway ballast optimization over frost susceptible and expansive clays: A case study of the Cargill Canola processing facility

The Cargill Canola processing facility, a $350 million project, began construction in July 2022 and is set to be operational in 2025. The site's geology primarily consists of fine-grained glaciolacustrine sediments, mainly silts and clays. A significant geotechnical challenge was the presence of a weak upper silty clay soil layer, approximately 10 metres thick, which was susceptible to frost heave during freezing temperatures and volumetric changes due to water exposure. Spring melt also raised concerns about excess water accumulation weakening the subgrade, leading to structural damage. The high plasticity index of the subgrade increased the potential for swelling in warmer conditions, complicating the design challenges during seasonal transitions. To address these issues, geosynthetics were employed. Three types were used: a moisture management woven geotextile to provide hydraulic and mechanical stabilization in the rail and road structures, an integrated high-modulus woven geotextile to provide ballast reinforcement, and a biaxial geogrid for base reinforcement in the access roads. The integrated high-modulus woven geotextile was also used in staging areas and gravel pavements to reduce the amount of granular base material required. This case study offers valuable insights for geosynthetic solutions in stabilizing roads and optimizing railway ballast over frost-susceptible and expansive clays. It demonstrates the effectiveness of geosynthetics in mitigating challenges posed by weak soils, frost susceptibility, and expansive clays, contributing to more resilient infrastructure designs.

Elastoplastic contact model of pitch-based rough surface and its polishing characteristics

Fused silica glass is widely used in optical systems, including astronomical telescopes, laser systems, optical communications, and the semiconductor industry. At the same time, the surface quality of the fused silica directly determines the performance and precision of the system. In order to analyze the microscopic surface interaction based on the basis of tribology, a roughness contact model of pitch and fused silica glass surfaces was established. Analyze the performance parameters of contact materials, surface roughness, and the relationship between load and contact area. Pitch materials with a higher plasticity index have a larger elastoplastic contact area with the fused silica surface during the polishing process. The experimental results demonstrate that the surface quality of the polished fused silica improves as the plasticity index of the pitch material increases. At the same time, judging from the PSD curve results, the polished surface of the No. 55 pitch on the spatial-frequency band curve (100-101/mm) is significantly lower than the other two brands of pitch. Additionally, the Ra value of the workpiece surface roughness reaches 0.091 nm. The results of this study provide important theoretical guidance for achieving full-diameter, full-frequency ultra-smooth polishing of large-diameter complex curved surfaces.

Stabilization of Expansive Soil Using Marble Powder and Phosphoric Acid against Physical Properties and SEM-EDS Tests

The Gedebage region faces a myriad of challenges, including road deformations, swelling of roads and bridges, and cracks in drainage foundations, buildings, and asphalt concrete. To address these issues, a comprehensive analysis of soil physical properties was conducted at the POLBAN soil mechanics laboratory, along with chemical tests at the POLMAN laboratory. The primary objective was to understand the physical properties and mineral composition of Gedebage soil and develop effective soil management strategies. Soil stabilization was employed as a method to enhance infrastructure resilience in Gedebage. Marble powder waste (MPW) was utilized in varying concentrations (2.5%, 4%, 5.5%, and 7%) along with 4% phosphoric acid (PA) to optimize the solution. MPW filled soil pores and improved cohesion, while PA reduced moisture content, enhanced particle bonding, increased load-bearing capacity, and minimized soil volume changes. Initial soil tests revealed a high plasticity index (PI) of 54.20%, indicating Gedebage, expansive clay soil nature with significant potential for expansion and plasticity. The AASHTO classified it as "A-7-6", and the USCS classified it as "CH." Stabilization experiments demonstrated that the most effective combination was the original soil + 7% MPW + 4% PA, resulting in a PI of 16.03% and an activity level (Ac) of 0.48. AASHTO classified this combination as "A-2-6," and the USCS as "CL." Furthermore, MPW oxygen, silica, and aluminum content exhibited potential for pozzolanic reactions, while PA reacted with soil mineral cations likes: Ca, Fe, Al dan Phosphor, forming a water-resistant layer. MPW and PA effectively improved the expansive clay soil's ability to withstand moisture-induced changes. This study serves as a foundation for further investigations into the mechanical properties of Gedebage soil, focusing on bearing capacity and stability, using MPW and PA in civil and infrastructure foundation applications.

Research on key technology of cement mixing plie on clay layer with high plasticity index

Cement mixing pile is one of the common methods for road embankment foundation reinforcement, which can improve the bearing capacity, reduce the post-construction settlement caused by embankment loading, and increase the overall stability of embankment. In this paper, through field tests, lab tests and theoretical analysis, the factors affecting the quality of cement mixing piles in deep high plasticity clay soil are analyzed and the results of field tests and lab tests are compared, and finally the key construction parameters and relevant pile strength data in deep marine clay soil area are derived for similar projects.

Wet-Dry Cycles and Microstructural Characteristics of Expansive Subgrade Treated with Sustainable Cementitious Waste Materials.

This work presents an experimental study on the physico-mechanical and microstructural characteristics of stabilised soils and the effect of wetting and drying cycles on their durability as road subgrade materials. The durability of expansive road subgrade with a high plasticity index treated with different ratios of ground granulated blast furnace slag (GGBS) and brick dust waste (BDW) was investigated. Treated and cured samples of the expansive subgrade were subjected to wetting-drying cycles, California bearing ratio (CBR) tests, and microstructural analysis. The results show a gradual reduction in the California bearing ratio (CBR), mass, and the resilient modulus of samples for all subgrade types as the number of cycles increases. The treated subgrades containing 23.5% GGBS recorded the highest CBR value of 230% under dry conditions while the lowest CBR value of 15% (wetting cycle) was recorded for the subgrade treated with 11.75% GGBS and 11.75% BDW at the end of the wetting-drying cycles, both of which find useful application in road pavement construction as calcium silicate hydrate (CSH) gel was formed in all stabilised subgrade materials. However, the increase in alumina and silica content upon the inclusion of BDW initiated the formation of more cementitious products due to the increased availability of Si and Al species as indicated by EDX analysis. This study concluded that subgrade materials treated with a combination of GGBS and BDW are durable, sustainable and suitable for use in road construction.

Burnt-Bricks Production Using Extracted Finer Particles from Soil with Fly Ash Addition

Earthen building materials, including mud, adobe, rammed earth, and bricks, have a long history of use in civil engineering construction all throughout the world. Burnt bricks are one of these materials thatis important. However, the availabilityof raw materials for making bricks is limited. As a result, numerous alternatives have been investigated as raw materials for making bricks. These substitutes include fly ash, rice husk and ash, industrial, and agricultural waste. The current study suggests a novel method for producing burnt bricks using extracted finer and fly ash.Finer particle extraction was done through soil washing. Since the extracted finer is having high plasticity index and high linear shrinkage, extracted finer was mixed with 20%, 25%, 30%, 40% and 50% fly ash. Fly ash is an industrial waste; hence the use of fly ash for this kind of production would give a sustainable solution for waste management. Every finer-fly ash combination underwent an Atterburg test to evaluate its qualities, particularly its plasticity index and linear shrinkage. Standard-type mold (220 x 115 x 75 mm) was used to producethe handmade bricks. Compressive strength, flexural strength, water absorption, density, and dimension variations of burned bricks were all examined. Results were compared with SLS 39: Specification for burnt clay bricks. Further, these properties were compared with the same properties of bricks made with soil taken from the brick-making industry mixed with fly ash and industrial available burnt-bricks.Additionally, wire-cut bricks were produced using extractedfiner and 25% fly ash. The dimensional variationof finer-fly ash mixed burnt bricks is decreasing when the fly ash % is increased relative to the mold size. Compressive strength of the Grade 2 category was demonstrated using bricks manufactured with a 25% fly addition, according to SLS 39. According to the aforementioned findings, burnt bricks composed of extractedfiner and fly ash have higher desirable qualities when 25% more fly ash is added. Additionally, it shows that using fly ash results in lightweight bricks.The wire-cut bricks made with this selected mixture give 10.64 N/mm2 of compressive strength and it satisfies the SLS 39 requirements for wire-cut bricks. Also, its water absorption was nearly 16% which is below the SLS required value (18%).

THE EFFECT OF ADDED NICKEL SLAG TO COMPRESSION AND SHEAR STRENGTH ON LATERITE SOIL SOUTH KALIMANTAN

Laterite soil is an embankment soil that is often used because it is easy to find and is widely found in South Kalimantan. However, this land has many shortcomings to be used as embankment soil. This is because the lateritic soil has a clay content and a high Plasticity Index (PI) value. So the quality is still questionable to be used as landfill. To overcome this, it is necessary to improve or stabilize the lateritic soil. In this study, the lateritic soil was stabilized by the addition of slag nickel This study aims to determine the physical characteristics of laterite soil after being given a mixture of nickel slag addition, this study also aims to determine the effect of the percentage of nickel slag on primary consolidation (Sc) of laterite soil. As well as knowing the effect of the percentage of nickel slag on the parameters of shear strength in the form of cohesion (c) and shear angle (f). Consolidation and shear strength specimens were made with 90% of the optimum moisture content. The variations of the nickel slag mixture used in this study were 0%, 5%, 10%, 15%, and 20% of the weight of the soil used. Based on the results of data analysis, the addition of a mixture of nickel slag in each sample variation can reduce the plasticity index value of the lateritic soil. In addition, the addition of nickel slag also affects the value of the primary consolidation settlement value (Sc) of the laterite soil. The addition of the percentage of nickel slag also affects the parameters of the shear strength of the soil, for the cohesion value (c) of the laterite soil experiences a value that decreases with the increase in the percentage of nickel slag. Meanwhile for the shear angle (φ) of the laterite soil, the value increases with the increase in the percentage of nickel slag.Keywords: laterite soil, nickel slag, plasticity index, consolidation of laterite soil, shear strength of laterite soil

Comparative study of pre-Hispanic and colonial adobes in Mexico. Preliminary inferences on the effects of the granulometric distribution and used recycled materials in the state conservation of earth architecture

The characterization of the pre-Hispanic and colonial adobes used in the construction of buildings in Mexico was carried out to know the differences between their processes and manufactures. The eight samples obtained correspond to adobe blocks 0.45 m long x 0.35 m wide and 0.12 m thick, which were part of the interiors of houses, the structure of fences, and hacienda galleys. These samples were investigated using X-ray Diffraction, X-ray Fluorescence, and Scanning Electron Microscopy techniques to determine the morphometry of the material and its chemical and mineralogical composition. Likewise, some analyzes were performed to determine their mechanical properties (simple compressive strength), physical properties (granulometry, solid density, cohesion, plasticity index, porosity, and moisture content), and biological (organic matter content). The results obtained in terms of the granulometric distribution indicate that pre-Hispanic adobe has a higher content of sand than silt-clay and gravel, while the colonial adobes present a low or null content of gravel with a higher content of silt-clays. Regarding the organic matter content, the colonial adobe presents the highest percentages compared to those of the pre-Hispanic adobes. Taking into account the above the pre-Hispanic adobes have better resistance and durability than colonial adobes due to their granulometric distribution, low organic matter content, good cohesion, high plasticity index, and the use of materials found in their natural environment, while the colonial used recycled materials, coming from the economic activity to which the hacienda was dedicated, for example, agriculture, mining, livestock, this has given rise to different manufacturing techniques and construction styles that reflect the state of conservation of buildings throughout the pre-Hispanic and colonial times. The granulometric distribution that pre-Hispanic adobe provides favorable physical and mechanical qualities for any construction technique, so it is recommended to use this formula to manufacture resistant and durable adobe.

Performance of Sustainable Road Pavements Founded on Clay Subgrades Treated with Eco-Friendly Cementitious Materials

Clays encountered during road construction are mostly weak and result in major pavement failures due to their low California bearing ratio (CBR) and high swelling potential. In this study, sustainable and eco-friendly waste materials including brick dust waste (BDW), ground granulated blastfurnance slag (GGBS), recycled plastic (RP) and recycled glass (RG) at varying proportions of 11.75% and 23.5% were used as partial replacement for cement and lime in clay treatment. After determining the water content by conducting Atterberg limit and compaction test, A CBR and swell characteristics of treated and untreated clay were also conducted. A road pavement design was conducted using the Design Manual for Road and Bridges (DMRB) as a guide to determine the performance of treated clay with varying CBR values. A road pavement failure analysis was also conducted to understand the defect formation within pavement structures supported by eco-friendly treated clay. The embodied carbon of treated clay was calculated and a life cycle cost analysis (LCCA) of flexible pavement with treated clay and road with imported materials was conducted. The results show a liquid limit of 131.26 and plastic limit of 28.74 for high plasticity index (clay 1) and liquid limit of 274.07 and a plastic limit of 45.38 for extremely high plasticity index (clay 2). An increase in CBR values from 8% and 9% to 57% and 97% with a reduction in swell values from 4.11% and 5.03% to 0.38% and 0.56% were recorded. This resulted in a reduction in pavement thickness and stresses within the road pavement leading to reduced susceptibility of the pavement to fatigue, rutting and permanent deformation. Very low embodied carbon was recorded for eco-friendly treated clay and a high life cycle cost (LCC) with clay removed and replaced with imported materials compared with clay treated using eco-friendly waste materials. The study concluded that carbon and overall construction costs can be reduced using waste materials in road construction. Owners and operators can save money when clay is treated and used in road construction instead of removing clay and replacing it with imported materials.

The Performance of Ca(OH)2 to Reduce the Plasticity Index and Increase the Shear Strength Parameter for Expansive Soil

The design on expansive soils can easily change in volume due to the influence of water content. This makes it necessary to consider soil improvement methods in the planning process to maintain the variation in the water content. One of these methods includes chemical stabilization, which is carried out by adding materials such as cement or lime. In expansive soils, stabilization efforts aim to reduce the plasticity index and increase the shear strength parameters. Therefore, this study focused on the addition of slaked lime (Ca(OH)2) to expansive soil in Lakarsantri, Surabaya. The stabilizing materials used contain calcium to form pozzolan in the clay and increase the bearing capacity parameter, which is variation in shear strength. The soil was taken at 2 points A and B with a different moisture content of 48.57% and 35.12%, as well as a high plasticity index value > 50% using a percentage (Ca(OH)2) of 6%-24% at a certain curing time. Based on the results, the plasticity index in the soil changed from very high to moderate with an optimum percentage value of 6% at 30 days of curing time. The optimum value of soil shear strength is (Ca(OH)2) 6% at 30 days of age in soil A, the cohesion value is 0.02 kg/cm2, and an internal shear angle of 36°. In soil B, the optimum shear strength obtained (Ca(OH)2) was 6% at the age of 10 days with a cohesion value of 0.14 kg/cm2 and an internal shear angle of 23.80°. Therefore, the results of this study show that the parameter of shear strength of the soil from the cohesion value showed that the cohesion value decreased with the addition of Ca(OH)2, while the internal shear angle increased.

THE EFFECT OF ADDED COARSE SAND FRACTION ON LATERITE SOIL SHEAR STRENGTH

Laterite soil is the most common type of embankment soil used for road construction in Kalimantan. This is because laterite soils are easy to find and widely available in several locations in South Kalimantan. However, this soil has many drawbacks, one of which is that it has a high plasticity index to be used as embankment, both for ordinary embankments and selected embankments. Therefore, it is necessary to improve or stabilize the soil so that the laterite soil can meet the requirements or specifications as embankment soil. In previous studies, the addition of a mixture of sand to laterite soils tends to decrease the value of the plasticity index.This study aims to determine the characteristics of laterite soils and the effect of adding a mixture of sand and plasticity to the shear strength of laterite soils by using a direct shear test apparatus. The specimens were made by testing the standard type of compaction and the value of 90% of the maximum density. The variation of the Sand mixture used is 0%; 7%; 14%; 21%; and 28%.Based on the USCS classification system, the soil for the three preliminary test locations is classified as CH (clay-high) group, while according to the AASHTO classification system, Landasan Ulin and Mandiangin location are classified as group A-7-5 and Sungai Ulin location is classified as group A-7-6 (clayey soils). There was a decrease in the value for the shear strength parameter of the laterite soil from the peak condition to the residual condition. The addition of a mixture of sand in each variation of the sample can reduce the PI value along with the addition of sand. In addition, the addition of sand also changes the parameters of the shear strength of the laterite soil. All samples of laterite and sand mixture variations have a value liquidity index < 0 which indicates that the soil is in a solid or semi-solid condition, while a value consistency index > 0 indicates that the soil is in a solid or semi-solid condition. The higher the value of the plasticity index of a soil, the higher the cohesion value of the soil and the lower the value of the internal shear angle. The more addition of a mixture of sand can reduce the plasticity index and soil cohesion and can increase the value of the internal shear angle. It can be said that the addition of a mixture of sand can reduce the plasticity index of the soil and affect the parameters of the shear strength of the soil in both peak and residual conditions.Keywords: shear strength, residual shear strength, laterite soil, sand, plasticity index

Physicochemical and Mineralogical Characterization of Clay Materials in the Douala Coastal Sedimentary Sub-basin (Cameroon, Central Africa)

This study is focused on the physicochemical and mineralogical characterization of five different clay materials of Eastern part of Douala sub-basin. It aims to know the nature and geotechnological properties of the clay raw materials in order to raise the idea of their potentialities in industrial applications. The samples were subjected to several analyses such as geotechnical tests notably the particle size distribution, the Atterberg limits, the swelling index, the chemical (cation exchange capacity, pH-H2O and pH-KCl, X-ray fluorescence) and mineralogical (X-ray diffraction) analyses. These clay materials showed high fine fractions (up to 99%) and high plasticity index (15 to 63%). The swelling index is medium (16 to 20) and the CEC moderate (30 - 40), indicating the presence of a small proportion of swelling 2:1 type clays. The clay materials are predominantly constituted by kaolinite (32 – 72%), quartz (20.2 - 50.7%) and illite (4.6 – 10%), which are characteristic of the sedimentary environment and morphoclimatic conditions of the Douala coastal sedimentary sub-basin. The predominant oxides in clay materials are SiO2 (34.05 - 51.18%) and Al2O3 (16.05 - 23.98%). Iron oxide Fe2O3 is moderate (1.55 - 11.22%) and alkali and alkaline earth oxides are weak less than 2%. The physicochemical parameters associated with mineralogical and geochemical data make them suitable for ceramic applications and also serve as backfilling materials in building constructions when improved by adding sand.

Improvement of Strength Characteristics of a Highly Plastic Expansive Soil with Fly Ash

Highly plastic expansive clays swell or shrink due to change in moisture content and they often have very low bearing capacity. Construction of engineering structures particularly pavements and lightweight buildings on problematic soils such as highly plastic expansive clays may create severe structural problems due to poor engineering properties of that kind of soil. This study focused on the influence of fly ash on strength properties of highly expansive clays which are problematic soils due to their undesirable engineering characteristics such as high plasticity index, liquid limit, swelling and shrinkage characteristics, and low bearing capacity. Atterberg’s limit tests and hydrometer tests were conducted to obtain consistency limits and grain-size distribution of the highly plastic expansive clay. Standard proctor tests for clay samples with different fly ash contents such as 10%, 15%, and 20% were performed to determine maximum dry densities and optimum water contents of the mixtures of clay and fly ash. The clay and fly ash mixtures were prepared at optimum water content and maximum dry density for unconfined compression strength (UCS) and California Bearing Ratio (CBR) tests. Effects of fly0ash content on the strength characteristics of a highly plastic expansive clay were investigated through unconfined compression and CBR tests. The experiment results showed that fly0ash is a promising additive to enhance strength characteristics of highly plastic expansive clays. An approximately 66% increase in UCS and CBR values was observed with the addition of 20% fly ash into the clay mixture in weight.

Thermal properties of soft clayey soils from the former Lake Texcoco in Mexico

Thermal properties of soils are essential for the design of many engineering projects, such as underground cable systems, thermal ground improvement techniques, and energy geostructures. Although the thermal properties of typical soils have been widely studied, little research has focused on the thermal characterization of soils with unusual properties, such as the soft clays from the former Lake Texcoco in Mexico. These sediments are known for their exceptionally high water content, plasticity index, and porosities. The present study describes a systematic evaluation of the thermal conductivity, specific heat capacity, and thermal diffusivity of Texcoco clays and their inherent variability. Forty laboratory samples from eleven different locations were studied using the dual-probe heat pulse method, X-ray diffractometry, Scanning Electron Microscopy, and standard soil classification tests. The results showed that the studied samples have lower thermal conductivities and higher specific heat capacities than those previously reported for saturated clays. These differences were mainly attributed to the high porosities of the peculiar clays from the former Lake Texcoco. The thermal conductivity did not show a specific trend with depth. From statistical analyses, it was established that the shifted lognormal distribution and the normal distribution accurately describe the natural variability of the thermal conductivity and specific heat capacity, respectively. Finally, the efficacy of eight selected prediction models for the thermal conductivity of saturated clays was assessed. The geometric mean and the weighted series-parallel heat flow (WSP) models delivered the best fit to the experimental data. This study deepens our understanding of ground thermal properties by providing information about soil with unusual characteristics. Furthermore, it gives an initial database for the thermal properties of Mexican soils that can serve as a reference for the development and design of some of the geotechnical applications previously described.

Microstructure, Mechanical and Tribological Properties of Advanced Layered WN/MeN (Me = Zr, Cr, Mo, Nb) Nanocomposite Coatings.

Due to the increased demands for drilling and cutting tools working at extreme machining conditions, protective coatings are extensively utilized to prolong the tool life and eliminate the need for lubricants. The present work reports on the effect of a second MeN (Me = Zr, Cr, Mo, Nb) layer in WN-based nanocomposite multilayers on microstructure, phase composition, and mechanical and tribological properties. The WN/MoN multilayers have not been studied yet, and cathodic-arc physical vapor deposition (CA-PVD) has been used to fabricate studied coating systems for the first time. Moreover, first-principles calculations were performed to gain more insight into the properties of deposited multilayers. Two types of coating microstructure with different kinds of lattices were observed: (i) face-centered cubic (fcc) on fcc-W2N (WN/CrN and WN/ZrN) and (ii) a combination of hexagonal and fcc on fcc-W2N (WN/MoN and WN/NbN). Among the four studied systems, the WN/NbN had superior properties: the lowest specific wear rate (1.7 × 10−6 mm3/Nm) and high hardness (36 GPa) and plasticity index H/E (0.93). Low surface roughness, high elastic strain to failure, Nb2O5 and WO3 tribofilms forming during sliding, ductile behavior of NbN, and nanocomposite structure contributed to high tribological performance. The results indicated the suitability of WN/NbN as a protective coating operating in challenging conditions.

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.