Contribution to the Characterization of Lateritic Soils for the Manufacture of Compressed Stabilized Earth Bricks

The aim of this study is to contribute to the mastery of the physical characteristics of lateritic soils in order to improve their use for the manufacture of Compressed Stabilized Earth Bricks (CSEB) in the province of North Kivu in the Democratic Republic of Congo (DRC). The study of the physical characteristics of lateritic soils was carried out. Samples were subjected to experimental identification tests on the physical characteristics (water content, density characteristics, particle size distribution and consistency). The results of the laboratory analysis of soil samples show that the water content varies between 5.4% and 36.99%. The density of the solid grains has an arithmetic mean of 2.5 g/cm3. The apparent density varies from 0.83 to 1.35 g/cm3. As for the dry density, it is in the range of 0.61 to 1.25 g/cm3. These relatively low densities indicate that the material studied has a significant degree of deformability. From the particle size analysis, it appears that the material studied contains an important fraction of fine particles. According to the consistency study, the soils studied are plastic clay as Ap class according to the Central Laboratory for Roads and Bridges (CLRB) geotechnical classification system. The particle size curves of the studied samples are within the preferential range of good soils for the manufacture of CSEB. The points representing the studied samples are within the preferential plasticity range of good soils for the manufacture of CSEB. From the above parameters, it appears that the studied material is well adapted for the manufacture of the Compressed Stabilized Earth Bricks.

Influence of variables related to soil weathering on the geomechanical performance of tropical soils

This paper presents an experimental and analytical investigation of the influence of variables related to soil weathering on the geomechanical performance of sand-silt mixtures containing lateritic soils,i.e.intensely weathered tropical soils with the influence of interparticle bonding.The sand-silt mixtures containing different relative proportions between uniform sand and lateritic soil were produced,and geomechanical soil characterization tests were performed.Based on the results,a transition from a primarily coarse-to a fine-grained prevailing soil structure was found to cause considerable impact on the geomechanical performance of these soils,as evidenced by design variables related to soil mineralogy and size distribution characteristics.Specifically,fines contents of both individual soil particles and soil aggregations were found to correlate with experimental results,while the relative proportion between sesquioxides(aluminum,and iron oxides),and silica,i.e.sesquioxide-silica ratios(SSR^(-1)),facilitated estimates concerning changes in geomechanical performance.Finally,the application of the sandsilt mixtures containing lateritic soil on soil walls reinforced with polymeric strips was also evaluated,further emphasizing the potential advantages of adopting variables related to soil weathering on design guidelines concerning tropical soils.

Effect of soaking time of dithionite-citrate-bicarbonate solution on strength and deformation characteristics of lateritic soil

This study aimed to reveal the influence of different free-iron-oxides contents on the strength and deformation characteristics of in situ lateritic soil.A test method that combined the selective chemical dissolution method and in situ Ménard pressuremeter test(PMT)was proposed.The soaking time in dithioniteecitrateebicarbonate(DCB)solution was used as a variable to control the free-iron-oxides content in lateritic soil.Then,the in situ lateritic soil boreholes with different soaking time were tested by PMT.The results showed that the in situ horizontal pressure p0,critical edge pressure pf,ultimate pressure prediction pl,pressuremeter modulus Em,shear modulus Gm,and foundation-bearing capacity f0k of lateritic soil decreased rapidly after immersing in DCB solution within 1e4 d.With increasing soaking time,the decrease rate reduced gradually.Moreover,the relationship curve between free-iron-oxides content and soaking time declined rapidly and then stabilized,and the free-iron-oxides content at the inflection point was 30.11 g/kg.When the free-iron-oxides content changed to the inflection point,the free-iron-oxides that played a cementing role was largely removed,indicating that the effective cementing iron-content of Miaoling lateritic soil was about 52.9%.This study demonstrated that the proposed test method can determine the influence of free-iron-oxides content on the strength and deformation characteristics of lateritic soil.

Performance evaluation of laterite soil embankment stabilized with bottom ash,coir fiber,and lime

In tropical regions,heavy rainfall induces erosion and shallow landslides on road embankments.Cement-based stabilization methods,common in these regions,contribute to climate change due to their high carbon footprint.This study explored the potential application of coir fiber-reinforced laterite soil-bottom ash mixtures as embankment materials in the tropics.The objective is to enhance engineered embankment slopes'erosion resistance and stability while offering reuse options for industrial byproducts.This study examined various mix designs for unconfined compressive strength(UCS)and permeability,utilizing 30%bottom ash(BA)and 1%coir fiber(CF)with varying sizes ranging from 10 to 40 mm,6%lime,and laterite soil(LS),followed by microstructural analyses.The results demonstrate that the compressive strength increases as the CF length increases to 25 mm.In contrast,permeability increases continuously with increasing CF length.Lime-treated mixtures exhibit superior short-and long-term strength and reduce permeability owing to the formation of cementitious materials,as confirmed by microstructural analyses.A lab-scale slope box was constructed to evaluate the surface erosion of the stabilized laterite soil embankment.Based on the rainfall simulation results,the LS-BA-CF mixtures show better resistance to erosion and deformation compared to untreated LS,especially when lime is added to the top layer.This study provides insights into a sustainable and cost-effective approach for slope stabilization using BA and CF,offering a promising solution for tropical regions susceptible to surface erosion and landslides.

Study on Liquid Special Fertilizer for Drip Irrigation of Sugarcane and Its Irrigation Mode in Guangxi Lateritic Red Soil Region

[Objective] Liquid special fertilizer for drip irrigation of sugarcane was de- veloped and the fertilizer patterns were explored in the production to provide techni- cal support for fertigation production of modern agriculture. [Method] ROC22 was selected as experimental material, two formulas of liquid special fertilizer for sugar- cane developed by the cooperation between Guangxi Academy of Agricultural Sci- ences and New Orientation （Guangxi） Chemical Industry Co.,Ltd. were selected, namely, balanced 21-21-21 ~ TE of Xinfangxiang and hyperkalemic 13-6-39-TE of Xinfangxiang. Taking conventional fertilization as the control （CK）, two modes of ap- plying base fertilizer at the earlier stage ＋ fertigation in the tillering stage and ferti- gation in the whole growth period were set. [Result] The two modes of fertilization had not significant effects on the emergence of sugarcane, but applying base fertil- izer at the earlier stage ＋ timely applying water soluble fertilizer in the tillering stage was conducive to the tillering of sugarcane. Harvest results showed that the effects of different treatments on plant height and yield were significant, in which the yield of sugarcane under the treatment of hyperkalemic water-soluble fertilizer increased by 13.04% compared with conventional treatment, and the income increased by 4 500 yuan/hm2, [Conclusion] Liquid special fertilizer for drip irrigation of sugarcane signifi- cantly promoted the growth of sugarcane, moreover, under the same condition, the effect of hyperkalemic water-soluble fertilizer was better.

Effects of physical properties on electrical conductivity of compacted lateritic soil

Natural soils of various types have different electrical properties due to the composition,structure,water content,and temperature.In order to investigate the electrical properties of lateritic soil,electrical conductivity experiments have been conducted on a self-developed testing device.Test results show that the electrical conductivity of laterite increases with the increase of water content,degree of saturation and dry density.When the water content is below the optimum water content,the electrical conductivity of soils increases nonlinearly and the variation rate increases dramatically.However,when the water content,degree of saturation,or dry density increases to a certain value,the electrical conductivity tends to be a constant.In addition,soil electrical conductivity increases with the increase of temperature,and it is observed that the electrical conductivity decreases with the increase of the number of wetting–drying cycles.

Saturated anisotropic hydraulic conductivity of a compacted lateritic soil

This study focuses on the saturated anisotropic hydraulic conductivity of a compacted lateritic clayey sandy soil. The effects of the molding water content and the confining stress on the anisotropic hydraulic conductivity are investigated. The hydraulic conductivity is measured with a flexible-wall permeameter. Samples are dynamically compacted into the three compaction states of a standard Proctor compaction curve： the dry branch, optimum water content and wet branch. Depending on the molding water content and confining stress, the hydraulic conductivity may increase or decrease. In addition, the results indicate that, when the samples are compacted to the optimum water content, lower hydraulic conductivity is obtained, except at a confining stress equal to 50 kPa. The increase of the confining stress decreases the hydraulic conductivity for each of the evaluated compaction states. In the wet branch, horizontal hy- draulic conductivity is about 8 times higher than the vertical value. The anisotropic hydraulic conduc- tivities of the dry and wet branches decrease when the confining stress increases, and the opposite is observed in the optimum water content state.

Analysis of Lateritic Soil Reinforced with Palm Kernel Shells for Use as a Sub-Base Layer for Low-Traffic Roads

In tropical areas,palm oil production generates significant amounts of waste,including palm kernel shells.The use of this waste in the civil engineering sector,presents a very challenging task.In the present study,the production of lateritic soil(A-2 in GTR classification and A-7-6(9)in HRB classification)reinforced with palm kernel shells is considered.In order to improve their performances,these materials are mixed using the Fuller’s parabolic law.Moreover,experimental tests are used to characterize the physical and mechanical geotechnical properties of the lateritic soil.After characterizing the matrix(i.e.,lateritic soil)and the inclusions(i.e.,palm kernel shells)in their natural state,it is found that Avrankou’s lateritic soil has a high level of fine particles(56.6%),high plasticity(PI=21%)and low lift(ICBR=17%);which makes it unusable in the pavement layer.Results also prove that the mixture composed of 39%of lateritic soil volume and 61%of PKS with a CBR index equals to 30 and the mixture composed of 45%of lateritic soil,40%PKS and 15%of lagoon sand with a CBR index equals to 41 can be used as sub-base layer for roads for low and medium traffic,respectively.

Comparative Analysis of Curing Methods:Natural and Activated Lateritic Concrete

This work was on non-activated and activated lateritic soil used in proportions of 0%to 30%,to replace fine sand by wt.%,in the production of lateritic concrete.A mix of 1:2:4 was used,and the cube samples were cured in four(4)curing media of water,sand,polythene,and sawdust.The aim was to evaluate the effects of these curing methods on the mechanical strengths,and other properties of lateritic concrete.The sensitivity of the generated data was characterized statistically and developing linear regression models for predictions.For the Non-Activated Laterite soil(NALS,control mix(0%)),the design strength of 20 MPa was achieved by all the curing methods(standard and non-standard).However,for other replacement levels,water curing was adequate for 10%and 30%,sand at 10%,and sawdust for 20%and 30%,respectively.On the other hand,for the Activated Laterite soil(ALS),the 20 MPa design strength was met only at 0%replacement for all curing methods.Sawdust medium at 10%also satisfied the 20 MPa strength.

Preliminary Evaluation of Some Engineering Properties of Laterite as Foundation and Construction Materials in Muglad Basin in Sudan

This paper reports and evaluates the subsurface investigations of lateritic soil in Muglad Basin. Lateritic soil is described as highly weathered and altered residual/transported soil formed by the in-situ weathering and/or decomposition of rocks in the tropical and sub-tropical regions with hot, humid climatic conditions. The field works include excavation of test pits, drilling of boreholes and performing of SRT （standard penetration test）. The engineering properties of soil such as sieve analysis, consistency, compaction test, CBR （California bearing ratio） test are deduced in the laboratory. Lateritic soil is also evaluated to be used as foundation and construction materials. Concretionary lateritic soil is valuable road pavement materials, widely used in the tropics as sub-base, base material and for gravel roads. The term laterite, however, has tended to be indiscriminately applied in tropical highway engineering to any red soil. Lateritic soils in this study area were classified as reddish brown, medium dense to very dense, clayey silty sand with noodles of quartz and gravels. According to laboratory test, the lateritic soil was found to be good as construction materials, and can be used for embankment purposes; on the other hand, blending such materials with gravels can improve the low CBR values.

Influence of Briquette Fertilizer of Levels of Nitrogen and Silica on Paddy

Nitrogen is the major nutrient plays a key role in the production of rice crop and the lateritic soils are low in available nitrogen content.Accordingly,the field study was carried out in lateritic soils of Konkan(Coastal)region during year(2017-2018)to find out the effect of different levels of nitrogen along with silica levels on growth and yield of rice.The major aspect behind taking this kind of research was to see the interaction between the applications of varying levels of nitrogen with the different levels of silica.An experiment was carried out with FRBD design.The nitrogen was given by the Konkan Annapurna Briquettes(KAB)which is the compressed tablet type mixture of the fertilizer which is having major nutrients N,P and K.Silica was applied solely through potassium silicate with the paper packets.There might have been positive response with growth and silica levels also with the rate of application of nitrogen with the increased levels of silica.It was observed that the application of 80 per cent RDN through Konkan Annapurna Briquettes(KAB)with Silica@100 kg ha-1 which was applied between four hills was found promising in enhancing the growth and yield of Ratnagiri-24 Cv.in lateritic during Kharif season.It could be concluded that,the application of nutrients in the form of Konkan Annapurna Briquettes along with the application of silica can reduce the recommended dose of fertilizer to the extent of 20 per cent during Kharif season in Konkan region.

Effects of Soil Compaction in the Fight against Unpaved Roads Degradation Due to Erosion Caused by Heavy Rain: Proposition of a Specific CBR Evaluation Model

Unpailt roads are generally subject to erosion, when they need to be bitumen, civil engineers need to know the geotechnical capabilities of the soil layers to be used as support, among these capabilities, for example, soil characteristics to withstand erosion. CBR has often been used to classify these soils according to their compaction. In this article, we propose a correlation between CBR and eroded soil mass through a simulator. Indeed, in this article we show that using a simulator, soils can be classified according to their ability to withstand water erosion, whether internal or external. Indeed it is shown that the mass of eroded soil is related to the compaction capacity of the soil just as the CBR also has. We study the effects and influence of soil compaction on the ability of an unpaved road to resist erosion caused by falling raindrops. To do this, lateritic soil is submitted to different compaction pressures. The compacted soil is then submitted to CBR test and rain fall through a mini rain simulator. Correlations between eroded soil masse and compaction pressure as well as CBR are derived. The study shows that the compaction reduces the erodibility and increases the bearing capacity of soil. The formula obtained is significant because we have a new way of evaluating soils in the laboratory.

Effect of Water Content and Grains Size Distribution on the Characteristic Resilient Young’s Modulus (<i>E_c</i>) Obtained Using Anisotropic Boyce Model on Gravelly Lateritic Soils from Tropical Africa (Burkina Faso and Senegal)

This research was carried out to determine the rheological parameters of lateritic soils in order to contribute to the improvement of the technical documents used for pavement design in tropical Africa. The study is based on the loading repeated of cyclic triaxial tests (LRT) performed at University Gustave Eiffel (formerly Institut Français des Sciences et Technologies des Transports de l’Aménagement et des Réseaux (IFSTTAR)) in Nantes with the application of the European standard EN 13286-7: 2004 [1]. The tests were performed at constant confinement stress and using the stepwise method to determine the resilient axial () and radial () deformation as a function of the axial and radial stresses. Four gravel lateritic soils from different sites selected in Burkina Faso and Senegal were the subject of this research for the triaxial tests. These materials have a maximum diameter of 20 mm and a percentage of fines less than 20%. The LRT tests were carried out on samples compacted at three moisture contents (wopm - 2%, wopm and wopm + 2%) and at 95% and 100% of optimal dry density (γdopm). Test results showed that the characteristic resilient Young’s modulus (Ec) of gravelly laterites soils depends on the compacted water content and the variation of the grains size distribution (sand (ø < 2 mm), motor (ø < 0.5 mm) and fines content (ø < 0.063 mm) obtained after (LRT). Materials with a high percent of fines (>20%), mortar and sand (Sindia and Lam-Lam) are more sensitive to variations in water content. The presence of water combined with the excess of fines leads to a decrease in modulus around 25% for Lam-Lam and 20.2% for Sindia. Materials containing a low percent of fines, mortar and sand (Badnogo and Dedougou) behave differently. And the resilient modulus increases about 225.67% for Badnogo and 312.24% for Dedougou with the rise of the water content for approximately unchanged the percentage of fines, mortar and sand. Granularity therefore has an indirect influence on the resilient modulus of the lateritic soils by controlling the effects of water on the entire system. Results of statistical analysis and coefficients of correlation (0.659 to 0.865) showed that the anisotropic Boyce’s model is suitable to predict the volumetric () and deviatoric strain () with stress path (Δq/Δp) of the lateritic soils. The predicted Er resilient Young’s modulus from anisotropic Boyce’s model varies according to the evolution of the bulk stress (). A correlation around 0.9 is obtained from the power law model.

Effect of pH on transport of Pb^(2+),Mn^(2+),Zn^(2+) and Ni^(2+) through lateritic soil: Column experiments and transport modeling

This study investigated the effects of pH on the transport of Pb 2＋ , Mn 2＋ , Zn 2＋ and Ni 2＋ through lateritic soil columns. Model results by fitting the symmetric breakthrough curves （BTCs） of bromide （Br ） with CXTFIT model suggested that physical non-equilibrium processes were absent in the columns. The heavy metal BTCs were, however, asymmetrical and exhibited a tailing phenomenon, indicating the presence of chemical non-equilibrium processes in the columns. The retardation factors of Pb 2＋ were the largest of the four metal ions at both pH 4.0 （33.3） and pH 5.0 （35.4）. The use of Langmuir isotherm parameters from batch studies with HYDRUS-1D did not predict the BTCs well. Rather the two-site model （TSM） described the heavy metal BTCs better than the equilibrium linear/nonlinear Langmuir model. The fraction of instantaneous sorption sites （ f ） of all four metal ions on the lateritic soil was consistently about 30%–44% of the total sorption sites.

Effects of Ionic Strength and Sesquioxides on Adsorption of Toxin of Bacillus thuringiensis subsp.kurstaki on Soils

Chemical reactions and fate of the toxins of Bacillus thuringiensis （Bt） in the soil environment are causing increasing concerns due to the large-scale cultivation of transgenic Bt plants. In this study, the effect of ionic strength （0-1 000 mmol kg-1） adjusted by NaCl or CaCl2 on adsorption of Bt toxin by a lateritic red soil, a paddy soil and these soils after chemical removal of organic-bound or free Fe and Al oxides, as well as by pure minerals （goethite, hematite and gibbsite） which are widespread in these soils, were studied. The results indicated that when the supporting electrolyte was NaCl, the adsorption of Bt toxin by the lateritic red soil and paddy soil increased rapidly until the ionic strength reached 250 mmol kg-1 and then gradually slowed down with the increase of ionic strength; while in ease the supporting electrolyte was CaCl2, the adsorption of Bt toxin enhanced significantly at low ionic strength （〈 10 mmol kg-1） and then decreased as the ionic strength increased. The adsorption of Bt toxin by the tested minerals and soils after the removal of organic-bound or free Fe and Al oxides also increased with increasing ionic strength controlled by NaCl. Removing organic-bound Fe and Al oxides obviously increased the adsorption of Bt toxin in the tested soils. Differently, removing free Fe and Al oxides increased the Bt adsorption by the paddy soil, but decreased the adsorption by the lateritic red soil. The study indicated that the varieties of ionic strength and the presence of Ve and Al oxides affected the adsorption of Bt toxin by the soils, which would contribute to the further understanding of the fate of Bt toxin in the soil environment and provide references for the ecological risk assessment of transgenic Bt plants.