Soil Improvement Techniques Research Articles

Soil Element Assessment in Organic Paddy Fields in the Thung Kula Ronghai Zone, Thailand

Organic rice production (ORP) has been promoted as a means of sustaining both farmers and the ecology of paddy fields, so this research aims to evaluate soil properties and soil elements in the ORP and general rice production (GRP) systems in the Thung Kula Ronghai (TKR) zone in Thailand. Soil samples were collected in Roi-et province from fields classified as ORP (5 fields) or GRP (4 fields), and interviews were also conducted with the field owner about rice yield and rice production. Data from the ORP and GRP groups were compared by t-test, and soil enhancement practices were measured by one-way analysis of variance (ANOVA) for variances. Results indicate there were 14 indicators of soil element control in the TKR. All indicators in the ORP and GRP systems were lower than the rate in soil that is suitable for rice production. The macroelement content in the TKR zone was total nitrogen > total potassium > phosphorus available at a ratio of 338: 3: 1, and the soil organic matter (SOM)/soil organic carbon (SOC) ratio is about 3.45. The soil improvement techniques used in the ORP systems—manure only and manure combined with green manure—have a higher pH value (p < 0.05) than the fertilizer only input but a lower TK value (p < 0.05) than the fertilizer only input. As a result, the ORP yield was higher than that of the GRP systems (p < 0.05), greatly affecting farmers’ practices.

Evaluating the sustainability of soil improvement techniques in foundation substructures

The soil is not always suitable or competent to support a direct shallow foundation in construction. In many cases, to avoid costly deep foundations, it is indicated to replace, improve, or reinforce such soil. This paper focuses on evaluating the contribution to sustainability between different soil improvement techniques and the outcome of their application to the foundation of a single-family house as an alternative to the one built. The life-cycle performance in sustainability is compared between the baseline design (without intervention), backfilling and soil compaction, soil-cement columns, rigid inclusion of micropiles, and nailing of precast joists. To characterize sustainability, a set of 37 indicators is proposed that integrate the economic or environmental aspects of each design alternative and its social impacts. A sustainability ranking is obtained for the different alternatives based on the ELECTRE IS method for multi-criteria decision-making (MCDM). The sensitivity of the obtained results is evaluated against different MCDM methods (TOPSIS, COPRAS) and different criteria weights. The evaluation provides a cross-cutting view, comparing the ability and reliability of each technique to prioritize the ground consolidation solution that best contributes to the sustainability in the design of a building's substructure.

Numerical models for shallow foundation on soft clay reinforced with a group of stone columns

ABSTRACT Stone columns are widely used around the world as cost-effective soil improvement techniques for highways and embankments. They are also used as drainage to expedite the consolidation period, and accordingly to increase the allowable pressure, reduce settlement, and reduce the liquefaction potential for shallow foundations. Currently the design of these columns is based on the unit cell or homogenised material concepts, which neglect the effect of the interaction of the columns. This paper presents a 3-D numerical model using the finite element technique and the commercial software ‘ABAQUS’ to simulate the case of a group of stone columns installed in soft clay. The model is capable of capturing the interaction between columns and the surrounding soil and of establishing the mode of failure of the system. After validating the model with the available experimental results, it was used to predict the allowable pressure and the failure mechanism of groups of stone columns for given geometry/soil conditions. An improvement factor was introduced ‘IF’, which is defined as the ratio of the capacity of the improved to the unimproved soft clay. The results of this investigation are presented in the form of design charts to assist the engineer to determine the level of improvement needed to achieve a given allowable pressure for the foundation.

Laboratory investigation of geogrout inclusion: the influence of the substitution ratio

Laboratory investigations using balloon tests were performed on normally consolidated kaolin samples to investigate their behaviour during and after the balloon expansion. The tests were carried out to simulate a soft soil improvement technique called CPR grouting (acronym for deep radial consolidation). The results allowed estimations of the parameters used in the design method, such as the consolidation potential, and evaluating the generation of pore pressures, injection pressures, post improvement deformation and optimised expanded volume. It was observed that the consolidation potential was extremely dependent on the substitution ratio. The tests satisfactorily reproduced the behaviour of the technique and represent a new device for geotechnical engineers, especially for those concerned with the improvement of soft soils.

Advances in Enzyme Induced Carbonate Precipitation and Application to Soil Improvement: A Review

Climate change and global warming have prompted a notable shift towards sustainable geotechnics and construction materials within the geotechnical engineer’s community. Earthen construction materials, in particular, are considered sustainable due to their inherent characteristics of having low embodied and operational energies, fire resistance, and ease of recyclability. Despite these attributes, they have not been part of the mainstream construction due to their susceptibility to water-induced deterioration. Conventional soil improvement techniques are generally expensive, energy-intensive, and environmentally harmful. Recently, biostabilization has emerged as a sustainable alternative that can overcome some of the limitations of existing soil improvement methods. Enzyme-induced carbonate precipitation (EICP) is a particularly promising technique due to its ease of application and compatibility with different soil types. EICP exploits the urease enzyme as a catalyst to promote the hydrolysis of urea inside the pore water, which, in the presence of calcium ions, results in the precipitation of calcium carbonate. The purpose of this paper is to provide a state-of-the-art review of EICP stabilization, highlighting the potential application of this technique to field problems and identifying current research gaps. The paper discusses recent progress, focusing on the most important factors that govern the efficiency of the chemical reactions and the precipitation of a spatially homogenous carbonate phase. The paper also discusses other aspects of EICP stabilization, including the degree of ground improvement, the prediction of the pore structure of the treated soil by numerical simulations, and the remediation of potentially toxic EICP by-products.

Numerical Analysis to Study Lateral Behavior of Cement Fly Ash Gravel Piles under the Soft Soil

Cement Fly ash and Gravel Piles are modern soil improvement techniques widely used in China for infrastructure development. It significantly impacts the fundamental characteristics of load-carrying capacities and deformation. The cement fly ash and gravel (CFG) piles are located on highways, railway embankments, essential projects, and problematic soil. These are often subjected to high risk of external load like flooding, seismic, etc. In such a case, foundation design can be governed by a required lateral resistance. The present study is based on the deformation behaviour of a CFG pile subjected to axial, lateral, and combined loading in soft clay. Numerical analysis using Plaxis 3D on a CFG pile with various influencing parameters soil condition, diameters, length, length to diameter ratio, and pile head loading condition to observe its effect. Overall, the pile study found variations in initial stress level, pile type, and pile head constraint. Still, these were minor compared to the impact of soil behaviour and mobility. The soil models varied stiffness and strength properties. The effects originating from the boundary conditions used were responsible for significantly decreasing lateral resistance for inner CFG piles under the active and passive loading.

Optimum Bacteria Suspension Volume for Stabilizing Silty Sand Soils by Sporosarcina pasteurii Bacteria

Recently, the bio-mediated soil improvement techniques have gained an increasing attention. In this method, the bacteria was cultivated aerobically in the laboratory and added to the soil with reactant solutions such as urea and calcium chloride. Most of the existing studies are on sandy soils and a few researches have done on silty sandy soils. However, most soils in nature are compounds of fine-grained and coarse-grained soils. In fine-grained soils, silt does not have very good resistance due to the lack of adhesion between its particles. Hence, in this study Sporosarcina pasteurii bacterium was aerobically cultivated for stabilizing the sand with different percentages of silt to determine the optimum bacteria suspension volume. After some bacterial tests such as measuring bacterial growth, standard plate count, gram staining, pH determination, growth without urea, and urease test, geo-technical tests like soil sieve, compaction, and Atterberg limits were also done. Standard plate count was estimated 2.5*108 through serial dilution plating and culture media pH was determined 8.64 from different samples. Moreover, to achieve the best results, different sampling methods were compared. As the calcium carbonate creates a network of calcified bridges of calcite between sand grains, an electron microscope was used for scanning the surface with a focused beam of electrons. Results of triaxial tests showed that by adding optimum bacteria suspension volume, the maximum strength for samples with 0, 10, 20, 30 and 40% of silt was improved from 700, 900, 750, 600 and550 to 1100, 1400, 1550, 1600, and 1500 kPa, respectively.

Strength and permanent deformation properties of demolition wastes, glass, and plastics stabilized with foamed bitumen for pavement bases

Foamed bitumen (FB) stabilization is an in-place soil improvement technique that has become popular in recent times. Nevertheless, a lack of understanding exists about the strength and deformation responses of FB stabilized recycled demolition wastes in pavements. This paper aims to introduce the application of FB stabilized recycled demolition waste blends with glass and plastic in the pavement base layer. A suite of laboratory tests was undertaken to evaluate the indirect tensile strength, unconfined compressive strength, California bearing ratio, and permanent deformation behavior of FB stabilized blends. Recycled concrete aggregate (RCA) was blended with recycled glass (RG), recycled plastic (RP), and reclaimed asphalt pavement (RAP) in various percentages and the performance of the FB stabilized blends were characterized through extensive experimental testing. A multi-stage repeated load triaxial (RLT) testing procedure was adopted to evaluate the permanent deformation behavior of the unbound and FB stabilized blends under various stress levels. The ITS, UCS, and CBR values exhibited decreasing trends with increasing the RAP, RG, and RP contents. The permanent deformation of the blends was found to be reduced as a result of FB stabilization, most notably for the blends with higher percentages of RAP, RG, and RP. The permanent deformation responses of the blends were ranked using the shakedown concept that indicated the FB stabilized demolition wastes exhibited relatively stable responses under cyclic loads. The deformation response of the blends with 50%RAP and 7%RP changed from incremental collapse to plastic creep as a result of FB stabilization. The results indicated that the FB stabilization of recycled aggregates is a suitable practice for developing more sustainable roads with enhanced ductility and resistance to rutting.

Strength properties of biopolymer treated clay/marble powder mixtures

Depending on their unique layer structures and chemical structures, soil problems such as swelling, settlement and loss of strength can be seen especially on clay soils when exposed to water. Settlement occurring on clay soils on which the structure is built, causes various damages in the building. Additionally, in the clay soil interacting with water, strength loss occurs due to the effect of the building load. Today, when soil improvement techniques are developed and diversified, clay soils can be stabilized by using different additives. A clay soil that has been improved by adding waste marble powder within the scope of this study in certain percentages (5%, 15%, 25%), biopolymer added clay / marble powder samples were obtained by interacting with locust bean gum in certain percentages (0.5%, 1%, 1.5%). There are many studies in the literature on improving clay soils using only marble powder or only biopolymer. In this study, marble powder and biopolymer were used together and thus, the feasibility of a more effective soil improvement has been investigated. The results showed that the unconfined compressive strength of the biopolymer added clay-marble powder mixtures are higher when compared with natural clay. Similarly, shear box test results showed that the unconsolidated-undrained cohesions and internal friction angles of the doped clay samples increased. It was observed that the strength values of marble powder-added clay increased after improving with biopolymer.

Numerical study of soilbag columns and comparison to encased soil columns in loose sand

Wrapping granular soils with geosynthetic to form a “soilbag” results in a significant enhancement in the bearing capacity of foundation elements formed from such bags due to additional confining pressure induced by the confinement. This paper describes the modeling and efficacy in soil improvement of soilbag columns (SBCs) as compared to encased sand columns (ESCs). Compared to ESCs, the mathematical modeling of SBCs is complicated by the three-dimensional nature of soilbags. Three-dimensional finite element models were thus developed for both soil improvement techniques and were validated with experimental data. The results of a series of parametric finite element analyses that highlighted the benefits of SBCs, as compared to ESCs, under different conditions in loose sand, are presented. To conduct such analyses, the encased and surrounding soils’ properties were varied, along with the geosynthetic stiffness and length ratios. The results of these analyses indicate that, compared to ESCs, SBCs perform better in compression. The performance of SBCs is enhanced by using backfill materials with higher friction angles or using stiffer geosynthetic.

The Behavior of Strip Footing Resting on Soil Strengthened with Geogrid

Abstract The soil in Iraq has a low load carrying or bearing capacity and high deflections or settlement because of the applied loads. The use of strip footing as a foundation to support different kinds of heavy structures has become necessary nowadays through solving such problems by using geogrid. This soil improvement technique is widely used all over the world. In this paper, the bearing capacity and settlements were calculated using finite elements and analytical models for strip footing resting on different kinds of soil. The study parameters are footing rigidity, the number of layers in a geogrid, the dimension of geogrid, and spacing of geogrid layers. According to the findings, the geogrid improved the bearing ability of the footing and reduced settlement. The optimum geogrid dimension was three times the footing width, and three geogrid layers were optimum. The changing in footing rigidity also affects the stress and settlement behavior.

Laboratory Study on the Effect of Water-Cement Ratio on Strength Characteristics of Jet Grouting Columns

Jet grouting is one of the most widely applied soil improvement techniques. It is suitable for most geotechnical problems, including improving bearing capacity, decreasing settlement, forming seals, and stabilizing slopes. One of the difficulties faced by designers is determining the strength and geometry of elements created using this method. Jet grouted soil-cement columns in soil are a complicated issue because they are dependent on a number of parameters such as soil type, grout and water flow rate, rotation and lifting speed of monitor, nozzle jetting force, and water to cement ratio of slurry. This paper discusses the effect of the water-cement ratio on the physical and mechanical characteristics of soilcrete. In the laboratory, sandy soil mixed with cement grout with water-cement ratio varies from (0.7:1 to 1.4:1). To evaluate the characteristics of soilcrete, 96 specimens were prepared in the laboratory and tested at different curing times. The results indicate that the Uniaxial Compressive Strength (UCS) of soilcrete decreases with increasing the (W/C) ratio of the grout, where the soilcrete strength of W/C ratio of 0.7 is higher about 237% of W/C ratio of 1.4 at 28-day; the evolution of the (UCS) is proportional to the logarithm of the curing time; the ratio between the modulus of elasticity (Etg50) to the maximum UCS varies from 113 to 175; when the water-cement ratio increases, the dry density of soilcrete decreases, as a result, the (USC) of soilcrete decreases.

Potentially of Soybean as Bio-Catalyst in Calcite Precipitation Methods for Improving the Strength of Sandy Soil

The biocementation-based soil improvement technique that has been recently developed is enzyme-induced calcite precipitation (EICP). Previous studies on the EICP technique used pure commercial urease enzyme as a reaction catalyst to precipitate calcite from urea and calcium chloride. However, pure commercial urease enzyme is inefficient for application on a large scale due to its high price. Therefore, studies reported that soybean is a potential alternative for pure commercial urease enzymes. This study evaluates the strength of sandy soil by treatment using EICP grouting solution with soybean extracts as the bio-catalyst. The extracts used in this study were obtained by filtration and centrifugation treatment. Based on the calcite mass quantification and precipitation ratio, 20 g/L soybean extract concentration in both treatments is used for treating the solution. Then, the unconfined compressive strength (UCS) tests were conducted to evaluate the increase of the strength of sandy soil. The maximum UCS value was obtained at the 28 days of curing time in both treatments. The centrifugation treatment has a higher UCS value with 65.6 kPa than the filtration treatment with 53.6 kPa. Thus, this study elucidated that soybean extract has a great potential to be a bio-catalyst in the calcite precipitation method.

LAB-SCALE EXPERIMENTS FOR SOIL CEMENTING THROUGH BIO-CHEMICAL PROCESS

Ureolytic bacteria strains of Bacillus show its ability of calcium carbonate precipitation through metabolic activity. Different studies related to self-healing concrete material were reported associated with the generated calcium carbonate of Bacillus subtilis HU58 metabolism in recent communications. In this paper, recent findings of soil cementing with a combination of such precipitated products were presented. The experiments relied on the lab-scale studies with the use of sand-clay mixture as the controlled soil specimens. Bacillus bacteria and nutrients were mixed to introduce in the sand matrix and then curing in high moisture condition. The composition and morphology of soil specimens were characterized after solidifying by FTIR, XRD, and SEM. Water percolation and mechanical stability for the physicomechanical properties were also tested with the unconventional method. Discussing the relevant results can help to figure out the next experiments in the field of geotechnical engineering. From the perspective of this study, the sustainability factor should be considered to apply this promising technique for soil stabilization and improvement and/or for the formulation of bio-brick as an alternative to sintered clay-based brick. From the perspective of this study, this technique for soil stabilization and improvement and/or for the formulation of bio-brick can be considered a promising sustainable alternative to sintered clay-based brick.

Simulation of the time-dependent behaviour of a test embankment on soft soil

The now-abandoned project for a new international airport for Mexico City was located at a site on the former Texcoco Lake, where extremely difficult subsoil conditions prevail. The behaviour of one of the trial embankments built to test foundation solutions for the runways is analysed in this paper. Observational data were gathered over 50 months at the so-called reference embankment, where no special foundation or soil improvement techniques were adopted. The performance of this embankment was investigated through finite-element simulations in which an elasto-viscoplastic constitutive model was implemented in commercial software. The model incorporates key features such as time dependence, long-term deformation and an anisotropic flow surface. The results provide an assessment of the constitutive description adopted as well as the role of anisotropy in the simulation of the case study.

Effects of Fluorogypsum and Quicklime on Unconfined Compressive Strength of Kaolinite

Jang, J.; Jang, J.; Barbato, M.; Gutierrez-Wing, M.T.; Rusch, K.A., and Jung, J., 2021. Effects of fluorogypsum and quicklime on unconfined compressive strength of Kaolinite. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 126–130. Coconut Creek (Florida), ISSN 0749-0208. Coastal areas have environmentally and economically important roles but tend have weak soft ground, which is often vulnerable by waves and unsuitable for coastal construction, such as ports and waterfront areas. Hence, this soft ground, which usually contains large amounts of clays, needs to be ameliorated by using appropriate soil improvement techniques. A common approach to improve soft ground is soil–binder injection techniques to enhance its strength. When avaialbe, binders from industrial wastes can be used instead of commercial products, such as cement and lime, to reduce construction costs and minimize environmental disturbance. Reusing industrial wastes mitigates environmental pollution and reduces the costs of waste management. Construction materials, such as sand and cement, can be partially replaced with industrial wastes if the wastes are granular and induce cementation effects. Fluorogypsum (FG), a by-product obtained during the production of hydrofluoric acid, satisfies these conditions, as it is capable of binding granular materials. Approximately 894,000 metric tons are annually produced in the U.S. However, data on the mechanical strength of clay–FG mixtures are unavailable. In this study, we conducted unconfined compressive strength tests to investigate the mechanical behavior of kaolinite, which represented clay in soft ground, at different FG and quicklime contents. The effects of FG on the compressive strength of kaolinite–FG–quicklime mixtures depend on the curing time and weight ratios of the constituent materials. The composition of the mixture with the highest compressive strength was 30% FG, 5% lime, and 65% kaolinite. We infer that the stoichiometric ratios of mixtures control the chemical reactions for the maximum compressive strength at different quicklime contents based on a series of compressive tests.

BEARING CAPACITY OF RAFT-PILE FOUNDATION USING TIMBER PILE ON SOFT SOIL

Problematic soil (soft soil), generally require a soil improvement techniques. One of the concepts of soil reinforcement is to utilize timber as a material for raft-pile foundation. In this study, a circular containers were used as testing medium for the various model of reinforcement techniques (i.e. pile with different length embedded, raft and raft-pile foundation) including unreinforced model sample. The small-scale model tests were carried out in the laboratory and the numerical analysis conducted by using Plaxis3D. The raft and pile material using a locally available timber.The results show that the raft-pile foundation shows the smallest vertical deformation (settlement) compared to other types of foundations. The highest settlement reduction was observed in the raft-pile foundation which is almost 65% compared to unreinforced soil. Good agreement results were found between small-scale laboratory model test and numerical modelling, thus indicating the potential used of this foundation type by using local timber.

Bio-Cementation for Improving Soil Thermal Conductivity

A promising technology for renewable energy is energy piles used to heat and cool buildings. In this research, the effects of bio-cementation via microbially induced calcite precipitation (MICP) using mixed calcium and magnesium sources and the addition of fibres on the thermal conductivity of soil were investigated. Firstly, silica sand specimens were treated with cementation solutions containing different ratios of calcium chloride and magnesium chloride to achieve maximum thermal conductivity improvement. Three treatment cycles were provided, and the corresponding thermal conductivity was measured after each cycle. It was found that using 100% calcium chloride resulted in the highest thermal conductivity. This cementation solution was then used to treat bio-cemented soil samples containing fibres, including polyethylene, steel and glass fibres. The fibre contents used included 0.5%, 1.0% and 1.5% of the dry sand mass. The results show that the glass fibre samples yielded the highest thermal conductivity after three treatment cycles, and SEM imaging was used to support the findings. This research suggests that using MICP as a soil improvement technique can also improve the thermal conductivity of soil surrounding energy piles, which has high potential to effectively improve the efficiency of energy piles.

BIOREMEDIATION OF COAL CONTAMINATED SOIL AS THE ROAD FOUNDATIONS LAYER

Waste area ex-coal mining land is left without proper management and utilization. After analysis, ex-mining land material can be reused as road construction material by increasing mechanical properties. Microbial-induced calcite precipitation (MICP) is a soil improvement technique using microorganisms capable of altering and enhancing their mechanical and physical properties. In this study, an unconfined compressive test was used to see the effect of calcite precipitation on the behavior of the unconfined compressive strength of sand contaminated with coal. Variations in the concentration of Bacillus subtilis were applied as much as 3%, 4.5%, and 6% on sand contaminated with coal. The bacteria used were 3 days of culture was still in the stationary phase and 6 days of culture in the dead phase. After 28 days of curing, there is a significant increase in the UCS values of the MICP-stabilized soil compared to the untreated soil. The use of 3 days of bacterial culture was more effective in increasing the UCS value than 6 days of culture. At optimum conditions, the UCS value increased up to 15 times after the 28-day curing period. As a conclusion the ex-mining land material after treated with MICP using Bacillus subtilis, it can be reused and qualifies as a road construction material

Improvement of the critical speed in high-speed ballasted railway tracks with stone columns: A numerical study on critical length

The pressure to achieve a higher speed of train operation has increased in the last few years due to the development of high-speed railway lines. In the presence of soft soils, this speed increase is not possible without undertaking soil improvement measures, since the critical speed is lower than the desired speed of train operation. One of the most widely used soil improvement techniques is that of stone columns. In relation to these is the concept of critical length which, up to now, has only been studied for static cases. This research focuses, for the first time, on the enhancement of the critical speed in high-speed railways with stone columns and with special reference to critical length. Moreover, others parameters such as: maximum rail displacement and Dynamic Amplification Factor (DAF) are also studied. Analysing three profiles of ground representative of soft soils, it can be observed how the effect of the stone columns on critical speed is relevant, showing that critical length is different with respect to the three parameters above, the most restrictive one being that which corresponds to the critical speed. The influence of other parameters on the critical length and on the effectiveness of stone columns, such as the area replacement ratio, the dynamic pressure bulb and the existing soil stiffness is analysed and discussed.