Untreated Soil Samples Research Articles

Mechanical Behaviour of Nano-material (Al2O3) Stabilized Soft Soil

Rapid urbanization and requirement of infrastructure, stable construction sites are not available. Therefore, there is a dire need for improvement of marginal soils to be used as a construction material. However, weak soils comprise of saturated clays, fine silts, and loose sand, which are susceptible to failure and pose problems of stability. Therefore, this research aims to study the strength and microstructural behavior of soft soils treated with nano-alumina (Al2O3) additive. In this study, Al2O3 of different percentages (0.5, 1.0, 1.5, and 2.0%) by dry weight of soil was added to a clayey soil and subjected to compaction and unconfined compression strength tests. The compaction tests showed that nano-Al2O3 (< 2.0%) stabilized soils exhibit higher unit weight and lower water content compared to untreated soils. This may be attributed due to the fact that nano-materials possess higher unit weight compared to untreated soils and these materials occupy the pore spaces in-between the soil grains, which reduce soil porosity and increase the shear strength. The unconfined compressive strength test on cured treated soil specimens showed a significant increase in shear strength on the addition of nano-alumina. The scanning electron microscopic analysis on untreated and treated soil specimens showed that untreated soil samples exhibit a compact array of clay grains and nano-material treated soil display closely packed and condensed fine structure, which authenticates an increase in shear strength. Thus, with the addition of Al2O3, there has been a significant improvement in the engineering properties of soft soils.

Investigating the Pull-out Capacity of a Horizontal Plate Anchor Embedded in Sandy Soil

Anchor systems have been widely used recently due to its importance in increasing the stability of structures subjected to uplift forces and overturning moments. Accordingly, it is vital to investigate the parameters that might affect anchor systems’ operational performance and structural behavior. The current study investigates the characteristics and parameters that might affect the uplift capacity of a horizontal anchor plate embedded in cohesionless soil. The sample of soil was brought from Al-Najaf province (Iraq). The parameters included are; plate embedding depth, the soil’s effective dimension above the plate, and soil improvement by compaction. The model setup includes forming a steel container with dimensions (70 x 70 x 70) cm and a circular steel plate of 10 cm diameter. Three embedding depth ratios were chosen; these are 0.1, 0.2, and 0.3 of the total soil sample depth. Three effective soil diameters were chosen as percentages of the plate diameter; these are 1.0%, 1.5%, and 3%. According to the ASTM specification, several physical and chemical tests were carried out on the soil sample to determine its classification and needed engineering characteristics. The laboratory test results revealed that for both treated and untreated soil samples, the ultimate uplift capacity of the anchor plate increases with increasing the embedded depth of the anchor plate; for example, at improvement ratio (D/d=3.0), the ratio (P/Po = 1.05,1.28 and 1.6) for depth ratio (h/T=0.1,0.2, and 0.3) respectively. The values of the pull-out capacity of the anchor plate are increased with increasing the improvement area above the anchor plate; for example, at depth ratio (h/T=0.3), the values P/Po = 1.05,1.28 and 1.6 for D/d=1,1.5 and 3.0) respectively. Finally, the compaction technique can effectively improve the behavior of the anchor plate.

Increasing the biodegradability of epoxy materials by means of vegetable oils and their oxygenated derivatives

Recycling of epoxy resin products is an urgent problem due to the microbiological resistance of such polymers. In this work, we aimed to increase the biodegradability of epoxy materials under the action of soil microorganisms and mycelial fungi. The modification of epoxy materials was carried out using soybean oil, rubber tree oil and their oxygenated derivatives, as well as a mixture of soybean oil and oleic acid. According to the obtained results, the introduction of a material based on unmodified epoxy resin into a soil leads to a 2.2-fold decrease in the respiratory activity of the soil microbiocenosis compared to untreated soil samples. This proves that epoxy-diane resins or hardeners (aminophenol) inhibit soil microbiocenosis. In comparison with the action of unmodified epoxy resins, the epoxy resins treated with vegetable oils and their oxygenated derivatives caused an increase in the respiratory activity of soil microbiocenosis, thus indicating the biodegradability of the materials under study. The decrease in the content of carboxylic acids in the composition of rubber tree oil after its epoxidation, which was confirmed by a decrease in the acid value, led to a slight decrease in the respiratory activity of soil microbiocenosis. For the same reason, the carbonation of vegetable oils had a similar effect. An improved biodegradation profile of epoxy materials following their modification was also confirmed by assessing their fungal resistance in terms of the number of the Tricho-derma fungi. It was concluded that vegetable oils and their oxygenated derivatives increase the biodegradability of epoxy materials. Among all the studied compositions, the epoxy materials modified with rubber tree oil and a mixture of soybean oil and oleic acid demonstrated the highest level of biodegradability.

Enzyme induced carbonate precipitation for soil internal erosion control under water seepage

Seepage induced internal erosion in earth dams, dikes, and their underlying soil strata may cause destruction of earthen structures and flooding of lowland regions. In this study, efforts were made to evaluate the use of the enzyme induced carbonate precipitation (EICP) method for the control of internal erosion under water seepage. Gap-graded soils with 15% fine particles were improved by the EICP method for 1 to 5 passes. In each pass of treatment, 1.5 pore volume treatment liquid containing soybean-derived urease and 0.5 mol/L equimolar urea-calcium chloride was applied to the soil sample. After the EICP improvement, the soil samples underwent seepage erosion of stepwise-increased flow rates. In addition to the EICP-treated soil samples, an untreated soil sample and a soil sample treated by the microbially induced carbonate precipitation (MICP) method were also tested for comparison. The results showed that, in terms of the amount and rate of eroded fine particles, the EICP soil samples had stronger resistance against seepage erosion as compared with the MICP sample and the untreated soil sample. The erosion control effects also improved with treatment passes. The EICP improvement was also effective in reducing the axial deformation of soil. The level of axial deformation was roughly consistent with the amount of fine particles eroded. The calcium carbonate distribution was relatively uniform in the EICP samples compared with the MICP sample. The results presented in the paper show that the EICP method is a promising solution for the control of seepage induced internal erosion in soils.

Study of Load & Settlement Behaviour of Expansive Soil Reinforced with Granular Pile Using Natural Aggregates

Expansive soil such as Black Cotton soil is problematic from geotechnical point of view as it is unstable volumetrically with the variation of seasonal moisture making it sensitive to deformation. Its strength decreases, compressibility increases on wetting, it possesses very small shear strength. There are several geotechnical improvement techniques available expansive soil strata, but the use of granular piles is becoming popular in India as it improves the strength parameters, such as increases load bearing capacity, reduces settlement, takes wide spread loads and improves the rate of consolidation. In this study, experimental investigations have been done to judge the load and settlement behaviour of Black Cotton soil when reinforced with geotextile encased granular pile by varying the percentage of natural aggregates, fly ash and lime at varying L/d (length & diameter) ratio of 1.5, 2, 2,5 3 and 3.5. The soil sample was prepared taking a mould of 150mm diameter, 175mm height and granular pile of diameter 50mm. The test results showed significant reduction in settlement on installation of geotextile encased granular pile when compared to untreated soil sample. The ultimate load increased & settlement reduced with increase in percentage of fly ash & lime with each increase of L/d ratio as well.

A laboratory investigation of the compaction properties of road sub-base stabilised with cement and latex copolymer.

The quality of road pavements is an important factor to ensure an acceptable level of service and safety to the road users. When flexible road pavements are to be constructed on weak sub-grade soils, it is often necessary to provide a stabilised sub-base to improve their relevant engineering properties. This paper presents the results and observations from a laboratory investigation evaluating the compaction properties of road sub-base stabilised with Type I cement (ordinary Portland cement) and styrene-butadiene latex copolymer. The proposed polymer contents were 0.5%, 0.75%, 1% and 2% and the proposed cement contents were 2%, 3% and 5%. The 2.5kg rammer compaction test was conducted on the gravelly SAND and sandy GRAVEL samples. It was found that the maximum dry densities (MDD) for the untreated soil samples were higher than the cement-polymer-treated soil samples, indicating that the MDD values decrease when cement and polymer are added. The MDD values for gravelly SAND and sandy GRAVEL treated with cement-polymer lied between 2Mg/m3+0.03Mg/m3 and 2.09Mg/m3+0.04Mg/m3 respectively. The optimum moisture contents for gravelly SAND and sandy GRAVEL treated with cement-polymer were maintained at 9%+0.5%. The air void lines for gravelly SAND and sandy GRAVEL lied between 7%+1% and 3%+1% respectively.

Efficacy of Enzymatically Induced Calcium Carbonate Precipitation in the Retention of Heavy Metal Ions

This study evaluated the efficacy of enzyme induced calcite precipitation (EICP) in restricting the mobility of heavy metals in soils. EICP is an environmentally friendly method that has wide ranging applications in the sustainable development of civil infrastructure. The study examined the desorption of three heavy metals from treated and untreated soils using ethylene diamine tetra-acetic acid (EDTA) and citric acid (C6H8O7) extractants under harsh conditions. Two natural soils spiked with cadmium (Cd), nickel (Ni), and lead (Pb) were studied in this research. The soils were treated with three types of enzyme solutions (ESs) to achieve EICP. A combination of urea of one molarity (M), 0.67 M calcium chloride, and urease enzyme (3 g/L) was mixed in deionized (DI) water to prepare enzyme solution 1 (ES1); non-fat milk powder (4 g/L) was added to ES1 to prepare enzyme solution 2 (ES2); and 0.37 M urea, 0.25 M calcium chloride, 0.85 g/L urease enzyme, and 4 g/L non-fat milk powder were mixed in DI water to prepare enzyme solution 3 (ES3). Ni, Cd, and Pb were added with load ratios of 50 and 100 mg/kg to both untreated and treated soils to study the effect of EICP on desorption rates of the heavy metals from soil. Desorption studies were performed after a curing period of 40 days. The curing period started after the soil samples were spiked with heavy metals. Soils treated with ESs were spiked with heavy metals after a curing period of 21 days and then further cured for 40 days. The amount of CaCO3 precipitated in the soil by the ESs was quantified using a gravimetric acid digestion test, which related the desorption of heavy metals to the amount of precipitated CaCO3. The order of desorption was as follows: Cd &gt; Ni &gt; Pb. It was observed that the average maximum removal efficiency of the untreated soil samples (irrespective of the load ratio and contaminants) was approximately 48% when extracted by EDTA and 46% when extracted by citric acid. The soil samples treated with ES2 exhibited average maximum removal efficiencies of 19% and 10% when extracted by EDTA and citric acid, respectively. It was observed that ES2 precipitated a maximum amount of calcium carbonate (CaCO3) when compared to ES1 and ES3 and retained the maximum amount of heavy metals in the soil by forming a CaCO3 shield on the heavy metals, thus decreasing their mobility. An approximate improvement of 30% in the retention of heavy metal ions was observed in soils treated with ESs when compared to untreated soil samples. Therefore, the study suggests that ESs can be an effective alternative in the remediation of soils contaminated with heavy metal ions.

Performance of Stabilized Earth with Wheat Straw and Slag

ABSTRACTStabilized earth is a very ancient material that has been used in many countries as a low cost, environment friendly construction material. However, its durability under humid environments is low. Stabilization using cement, lime and natural fibres could enhance its durability and lowers the risk of cracking. This paper presents an experimental investigation into the performance of stabilised local soil by either, cement mixed with a proportion of granulated blast furnace slag (GBFS) /or straw naturel fibres. Unconfined compressive strength (UCS), shrinkage, wetting and drying, capillary absorption and thermal conductivity tests were performed on both untreated soil samples and stabilised soil samples. The results show that stabilising the soil with cement and GBFS increased both compressive strength, durability, thermal conductivity and decreased the capillary absorption and the shrinkage. The addition of natural wheat fibres increased the capillary absorption but leads to a decrease in the thermal conductivity and to a further reduction in the shrinkage and hence a better insulating less prone to cracking material.

Shrinkage Mechanism of Laterite Modified by Lime and Metakaolin

In this study, effects of metakaolin and lime on the microstructural characteristics, unconfined compressive strength (UCS), shrinkage, suction, and shear resistance of laterite were investigated. Soil samples treated with 5 wt% of lime (LaL) or 4 wt% metakaolin and 5 wt% of lime (LaLM) were prepared. Samples with an optimal water content of 32% were compacted and cured for 180 days, followed by saturation and dehydration until the desirable water content of the samples was attained. Then, the UCS, shrinkage, and suction and shear resistance of the samples at a normal stress of 200 kPa were determined. In addition, scanning electron microscopy imaging as well as mercury intrusion porosimetry tests were performed to examine the microstructural changes. Results indicate that the shrinkage of treated soil samples is significantly improved in comparison with that of the untreated soil samples. Lime effectively improves the UCS and shearing resistance of laterite. Moreover, metakaolin is composed of amorphous silicon and aluminium oxides and shared edge‐face structures on the microscopic scale; hence, it can considerably capture calcium ions from a lime solution, generating cementitious hydrates in the interaggregates of laterite. Results also revealed that the combination of 5 wt% of lime and 4 wt% of metakaolin can improve the UCS and shearing resistance, but the linear shrinkage is particularly restrained, significantly decreasing by 4 times compared with that of the lime‐treated soil sample and by 8 times compared with that of the untreated soil sample. The study results demonstrate that metakaolin and lime can be effectively used to improve laterite in lieu of the conventional lime treatment for mitigating geotechnical engineering disasters.

Variations in growth behavior, yield and DNA stability of two vegetable crops cultivated in radioactive spiked soils

Radioactive pollution comes on the top of pollution types that affect human life directly through damaging the human genome or indirectly via his food web. The current study focused on the evaluation of radiation effects of Assiut Thermal Power Plant (ATPP) ashes on two crop plants, potato and squash, in terms of morphological and molecular levels. More particularly, the specific activity concentrations were measured in Bq/kg, of the 238U (226Ra) and 232Th series, and 40K-isotope for the untreated soil sample (control) and ATPP ash sample (represents the radioactive source with 100% concentration). Different concentrations of ATPP ash (0, 2, 4, 6 and 8%) were mixed with soil sample to study the effect of radioactively contaminated soil on potato and squash plants. The results of the present investigation revealed that the morphological characteristics of both potato and squash plants were changed, which reflected a steep regression in the values of all vegetative growth and yield traits. The alterations of the characteristic values were directly proportional to the radioactive ash concentration in the soil. In the same context, the molecular evaluation using PCR-based markers, e.g., ISSR and SCoT helps in understanding and explaining experimental observations at morphological level. ISSR/SCoT bands confirmed the toxicity and mutagenicity of radioactive ash samples at their present dose on both potato and squash plants. The present findings clearly explained the morphometric and genetic abnormalities in two of the main consumed crops by a human. Thus, the green area around the ATPP may disappear in the future due to increasing the pollution in terms of the radioactive component that directly attached to plants or indirectly by mixing with soil.

Investigating the Effect of Medicago sativa L. and Trifolium pratense L. Root Exudates on PAHs Bioremediation in an Aged-Contaminated Soil

Polycyclic aromatic hydrocarbons (PAH) are persistent organic compounds of major concern that accumulate in the environment, especially soils, and require remediation. Researches to develop bioremediation and phytoremediation (alternative eco-friendly technologies) are being conducted. First, a bioaccessibility measurement protocol was adapted to a brownfield soil using Tenax® beads in order to compare PAHs bioaccessibility in soil samples. PAHs desorption kinetics were established, described by a site distribution model, and a common extraction time was calculated (48 h). Second, the role of two Fabaceae (Medicago sativa L. or Trifolium pratense L.) root exudates in enhancing PAHs bioaccessibility and biodegradation in the studied soil was evaluated during microcosms experiments (28 °C). The CO2 emissions were significantly higher in presence of T. pratense exudates; the dehydrogenase activities showed improvements of the soil microbial activity in presence of two types of root exudates compared to untreated soil samples; the PAHs residual contents decreased more in untreated samples than in the presence of T. pratense exudates; and M. sativa exudates lowered PAHs bioaccessibility but not residual contents.

Improving the Shear Strength of the Soil by using Jute Fabric

Bearing capacity of the soil is based on the shear strength of the soil. By improving the shear strength, bearing capacity of soil increases. Various additives such as lime, fly ash, cement, bitumen, tar etc. and easily available on-site materials such as sands, mining waste, natural stone waste etc were using to improve the shear strength of the soil. The main aim of this project is to improve the shear strength of the soil by adding jute fabric in various proportions. Jute fabric is mainly produced from a plant species called Corchorus olitorius. Soil samples were collected from Mangalapuram, Trivandrum and the identification tests such as specific gravity, liquid limit, plastic limit and sieve analysis of soil were done based on IS2720 recommended procedures. As per IS1498 – 1970 the soil is classified as poorly graded sands (SP). Jute fabric is added to the soil on 3%, 6% and 9% of weight of soil sample. Standard proctor test is conducted as per IS 2720 (part VII) to determine the optimum moisture content value (OMC). Optimum moisture content value of the soil sample is 10%. The shear strength of the soil is determined by direct shear strength test, which is conducted on both treated and untreated soil sample. From the result it is concluded that by adding 6% of jute fabric the shear strength of the soil reaches its maximum value, further addition of jute fabric reduces the shear strength of soil. Hence it is recommended to use 6% of jute fabric in sub-grade soils for pavements to improve the shear strength.

Permanent deformation behaviour of black cotton soil treated with calcium carbide residue

Uncontrolled dumping of huge quantities of calcium carbide residue (CCR) which is an industrial by product of acetylene gas industry is hazardous to environment due to its high alkalinity. Utilization of calcium carbide residue for stabilization of subgrade soils is a cost effective and sustainable practice, which can be adopted in design and construction of flexible pavements. In the present work, the efficacy of treatment with CCR in reducing the accumulation of permanent deformations in black cotton soil (BC soil) subgrade subjected to repeated loading is investigated. Untreated black cotton soil samples and CCR stabilized samples are subjected to repeated load triaxial tests for determining the accumulation of plastic strain with repeated loading cycles. Effect of cyclic deviatoric stress levels and moulding water content on the development of permanent deformation is examined. The accumulation of permanent deformation is quantified using the critical cyclic stress levels based on the shake down theory. The experimental data for the permanent deformation of treated as well as untreated soil samples is found to fit well with two the models (VTT model and power law model) reported in literature. The efficacy of CCR stabilization in reducing the permanent deformations of black cotton soil subjected to repeated loading is confirmed based on the mineralogical and morphological studies carried out on the treated samples.

Stabilisation of Urmia Lake peat using natural and artificial pozzolans

Peat generally found in thick layers in limited areas such as Urmia Lake, Iran has low shear strength and high compressive deformation. Therefore, an appropriate soil improvement method is required. This paper presents an experimental study of the stabilisation of Urmia Lake peat on the Urmia–Tabriz highway, 7·8 km to the east of Urmia city in Iran. A type of fly ash (artificial pozzolan) and two types of volcanic ashes (natural pozzolans) were used in this investigation. Unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were conducted on stabilised mixtures and untreated soil samples after 3 and 7 d of curing. According to the obtained results, the UCS of peat can be increased by using both the fly ash and the volcanic ash, but the amount of strength increase depends on the organic content, water content, stabiliser content and its particle size. Furthermore, the CBR test showed that the filling property of the stabiliser is as useful as its pozzolanic activity in increasing the bearing capacity of peat in road constructions.

Compaction characteristics of lime-treated tropical soil

Like soils of other regions in the world, some tropical soils are also associated with problems of low strength. To improve engineering characteristics of soils, several methods have been employed worldwide which are categorized as mechanical, chemical, thermal and electrical. The aim of this research is to compare the compaction characteristics of untreated and lime-treated soils. Soil samples obtained from three different points within a project site in Klang, Selangor were utilized in this study. Each sample was subjected to Eades and Grimm’s test in accordance with ASTM D6276-99a to determine the appropriate lime dosage for soil stabilization. The required lime dosage was found between 1.3% and 3.4%. Then each untreated soil and soil sample mixed with 5% lime, higher than that obtained from Eades and Grimm’s tests were compacted in accordance with BS 1377:1990. Generally, each soil sample achieved lower values of maximum dry density after treated with 5% lime than those of the untreated soils. Such observations were in good agreement with those obtained by previous researchers working on lime-treated soils. Nonetheless, the optimum moisture content of the lime-treated sample from Points 1 was slightly higher than that of the untreated sample. This finding was different from those obtained by previous researchers. Such contradicting observation might be due to the type and quantity of mineralogical contents of the soils studied.

Residual effects of neem Azadirachta indica A. Juss. (Sapindales: Meliaceae) seed-based fertilizer and NPK on the performance of Basella alba L. (Caryophyllales: Basellaceae) plant

Organomineral formulations are low input technology fertilizers, which combine the attributes of both organic and inorganic fertilizers. A completely randomized design (CRD) pot experiment was conducted in the screen house of the Department of Crop, Soil and Pest Management, of the Federal University of Technology, Akure, to evaluate the residual effects of neem Azadirachta indica A. Juss. (Sapindales: Meliaceae) seed based fertilizer and NPK 20:10:10 on the growth, yield and nutritional quality of Basella alba L. (Caryophyllales: Basellaceae). Results showed that the plots previously treated with neem seed-based fertilizer especially at 150-300 kg/ha enhanced the growth, yield and nutritional quality of B. alba, and increased these parameter significantly (P &lt; 0.05) compared to the NPK treated and the untreated soil samples. It was therefore concluded that the Neem seed based fertilizer can serve as a viable alternative to NPK chemical fertilizers especially in rotational cropping systems owing to its prolonged soil action.

The Effect of Glyphosate Harbicide on Soil Fungi

Glyphosate herbicide is one of the herbicide used throughout the world and they are very important to agriculture. Despite the role of glyphosate herbicide to agriculture, they also posed direct or indirect threats to the health of humans and also to the nature and survival of soil microorganisms. This study was carried out to determine the effect of glyphosate herbicide on soil fungi. Enumeration of fungal population in the soil samples before and after treatment was carried out. The fungal count was found to be 2.8x103cfu/g before the treatment with glyphosate herbicide and the number continue to decrease up to 0.4x103cfu/g in the 15day of glyphosate herbicide treatment. The fungal population decreased upon treatment with glyphosate herbicide when compared to the control i.e. the untreated soil sample. Glyphosate herbicide causes greater reduction in fungal count because the fungal populations decreased gradually and complete disappearance of some species after 6 days of treatment and continue to decrease up to 15 days after treatment. Soil fungi were isolated from the soil before the application of glyphosate herbicide; they include A. niger, A. flavus, Penicillium spp., Microsporium spp. Trychophyton spp. upon application of glyphosate herbicide, not all the fungi isolated before treatment survive the effect of glyphosate herbicide. The most frequently isolated fungi that survive up to 15 days of treatment is Aspergillus species (A. flavus and A. niger) while Microsporium spp., Trychophyton spp. and Penicillium spp. disappeared completely after 9 days of treatment.&#x0D;

Volume Change and Cracks Behavior of Lime Treated Expansive Soils

This research work study the influence of cyclic wetting and drying on free swell potential of untreated and lime treated expansive clayey soils. Such a study is required to understand the behavior of these soils during wet-dry cycles. Two expansive soils (a polwhite bentonite and a kaolinite) with different plasticity indexes were used in this study. The soil samples were treated with different lime content in the order of (3, 5 and 7% by the dry weight of soil). The lime treated soil samples were cured at 20ºC for 28 and 180 days. The untreated and lime treated soil samples were subjected to four wet-dry cycles. Free swell potential and cracks propagation were studied during lime addition and wet-dry cycles. Results showed that, the free swell potential of untreated soil samples; in general; decreased with increasing wet-dry cycles, and all of the soil samples reached equilibrium after the second cycle. While the cracks propagation increased with these cycles, especially of bentonite soil samples. Larger cracks propagation has been observed in the bentonite soil samples. Lime addition enhanced the free swell potential values of the two expansive soils and there was a drastic decrease in free swelling potential and cracks propagation of these soils. The beneficial effect of lime treatment to control the swelling values was partly lost by the first wet–dry cycles, and the free swell potential increased at the subsequent cycles.

Volume Change and Cracks Behavior of Lime Treated Expansive Soils

This research work study the influence of cyclic wetting and drying on free swell potential of untreated and lime treated expansive clayey soils. Such a study is required to understand the behavior of these soils during wet-dry cycles. Two expansive soils (a polwhite bentonite and a kaolinite) with different plasticity indexes were used in this study. The soil samples were treated with different lime content in the order of (3, 5 and 7% by the dry weight of soil). The lime treated soil samples were cured at 20ºC for 28 and 180 days. The untreated and lime treated soil samples were subjected to four wet-dry cycles. Free swell potential and cracks propagation were studied during lime addition and wet-dry cycles. Results showed that, the free swell potential of untreated soil samples; in general; decreased with increasing wet-dry cycles, and all of the soil samples reached equilibrium after the second cycle. While the cracks propagation increased with these cycles, especially of bentonite soil samples. Larger cracks propagation has been observed in the bentonite soil samples. Lime addition enhanced the free swell potential values of&nbsp; the two expansive soils and there was a drastic decrease in free swelling potential and cracks propagation of these soils. The beneficial effect of lime treatment to control the swelling values was partly lost by the first wet–dry cycles, and the free swell potential increased at the subsequent cycles.

Effect of carbon fiber and nanosilica on shear properties of silty soil and the mechanisms

In this study, the effects of carbon fiber and nanosilica on properties of silty soil including physical, microstructural characteristics and shear resistance were investigated. Soil samples treated with different contents of carbon fiber and nanosilica were prepared and studied. The samples were tested by direct shear method under different normal pressure levels. Besides, SEM (scanning electron microscopy) tests were performed to examine the microstructural changes. The test results indicated that the shear strength of treated soil samples was significantly improved compared with the untreated soil samples. Carbon fiber was found effective in improving internal friction angle and cohesion thanked to the interface friction between fiber and soil. On the other hand, nanosilica could improve cohesion effectively due to full filling of the pores between soil particles. The results also showed that the combination of 2 wt% carbon fiber and 3 wt% nanosilica could improve the shear stiffness and particularly the residual shear strength, which was increased significantly by 128.3% compared with the untreated soil sample at a normal stress of 100 kPa. The results demonstrated that the use of carbon fibers and nanosilica can be an effective method to improve silty soil in lieu of traditional cement grouting in mitigating geotechnical engineering disasters.