Soil Improvement Techniques Research Articles

Enhancement of Shear Strength Parameters of Clayey Soil by using Polypropylene Fiber

When the foundation soil is not strong enough to hold on with the loads transmitted to it .At such places the structure could be damaged, in order to eliminate this threat the soil properties such as stability, shear strength, durability etc are enhanced by mixing it with different admixtures such as lime, cement etc .At some occasions fibers (obtained from waste materials)are used to enhance the soil properties. In past a large number of studies have shown the effectiveness of such mixing materials at considerable percentages. It has been studied that the outcome of such materials when used in soil improvement techniques is handsome. In this examination the polypropylene fiber ,obtained from waste materials has been used. The different percentages of fiber reinforcement are used and the corresponding changes in the shear strength parameters are examined. The effects of polypropylene fiber reinforcement on the soil samples are examined by carrying out Direct Shear Test and Unconfined Compression Test.

Study the grain size and infiltration method effects for sand soil improvement using the microbial method

Today, with regard to land shortage and ever-increasing growth of the world’s population, construction on loose soil has been inevitable. Therefore, to deal with this issue, it is necessary to improve project site materials. The conventional soil improvement techniques are limited due to high costs and environment unfriendliness. In this regard, microbial-induced calcite precipitation (MICP) is a relatively environment-friendly method that is efficient for soil improvement. In this method, hydrolysis of urea by bacteria containing urease enzyme and in the presence of soluble calcium ions leads to the precipitation and attachment of CaCO3 among the soil grains. In this study, the effects of grain size, a method of infiltration, infiltrated bacteria suspension (BS) volume and infiltrated fixation solution (FS), and cement solution (CS) on Quartz sand shear strength are investigated. The results of the conducted tests showed that among four different infiltration methods, continuous infiltration of BS and CS, have the strongest effect on shear strength. Studying shear strength two different sand sizes based on direct shear test showed that sand with larger effective size and higher permeability has a shear strength 6.2 times compared to non-treated sand. The results showed that soils with less volume of infiltrated bacteria have a higher shear strength. Adding a FS to three different BS volumes showed the one with the lowest amount has the highest shear strength. According to the X-ray diffraction and scanning electron microscopy analyses, the efficient CaCO3 precipitation between the soil particles is confirmed.

Numerical evaluation of square arrangement of charges in explosive compaction

Explosive Compaction (EC) or Blast Densification (BD) is a common deep soil improvement technique where loose, saturated granular soils are compacted with a huge compression force of the explosion. The design of EC is often conducted using empirical equations and/or preliminary explosion tests. The former is based on limited experiments and provides rough estimation, whereas the latter is costly. Recently, the numerical approach has shown advantages in capturing complex condition of such problems and pose itself as a robust alternative. In this study, a numerical method is evaluated as a design tool to optimize EC. A fixed volume of soil is therefore considered to be densified with a specific amount of explosive charges. All charges are located at the same depth and are horizontally placed using square pattern arrangement. An estimation of EC design is achieved using an empirical equation. Subsequently, numerous numerical simulations are performed to achieve the efficient design in terms of the optimum equivalent weight of TNT and arrangement distance. The induced pressure in the soil, as well as the surface displacement, is used as measures of efficiency. Results show that the empirical equations provide a rough or inaccurate design while by use of the numerical approach this range is narrowed. Also, by reaching the optimum distance a more uniform compaction is achieved which reduces the unwanted surface heaving caused by cumulative upward waves. A compaction variation of about 30% was observed due to settlement variation, whereas the compaction variation due to change in explosive weight was approximately 80%. By applying the detonation delay the surface heaving is reduced up to 50%, which improves the EC efficiency.

Comparison between Analytical Method and Numerical Model for Footings on Soft Clay Supported by Stone Columns

The increase in population in many locations and the value of land has increased significantly. This has made the use of all areas including soft problematic soils inevitable. Due to the lack of bearing capacity of these soils, different methods of soil improvement techniques such as stone columns are used. In this study, four different analytical methods published before are briefly motioned. Also, three-dimensional (3D) numerical analyses were carried out on a stone column under footing on the soft clay soil. The main point of the current paper is to make a comparison between a numerical model and different analytical methods to represent a footing on the soft clay soil reinforced by a group of stone columns.

Reduction of hydraulic conductivity of sand using combination of microbially produced and chemical source of ferrous cations

ABSTRACT Biogeotechnology, is one of the most notable methods of soil improvement techniques. Along with the use of calcium-based biocement, the probability of using an inventive approach through the iron salts precipitation was also investigated. The present study discussed the feasibility of iron-based biocement using the combination of chemically and microbially source of ferrous cations. The method was introduced as an economical and green method using a cheap and accessible source of iron ore. A biocement treatment test via iron-based process was used to investigate the suitability of using three methods to improve geotechnical properties of loose sand and determine their respective hydraulic conductivity. The results of this study demonstrated that 1% of cation salts in sand was sufficient to reduce the hydraulic conductivity to 10−7 m/s as the bioclogging was performed mainly in the channels between sand particles. Moreover, the precipitation of iron salts was also seen between sand grains in the SEM images.

Numerical study on the effect of rigid inclusions on existing railroads

SummaryRailroad track problems have been exacerbated by the continuous increase in freight loads and train traffic. The need to implement soil improvement technique in a relatively short window‐time (ie, to minimize train‐traffic disruption) is a key aspect to be considered when adopting a convenient remedial solution to control settlements in railroads constructed on problematic subgrades. Rigid inclusions are selected in this paper because they are reliable solutions relatively easy to implement. Furthermore, they can be used in different ground conditions and are suitable for short construction times (eg, do not require a curing time, as in grouting methods). Typical (analytical) methods for the design of rigid inclusions are adopted in this paper to define an optimal distribution of piles for the case of existing railroads. The selected layout is then analyzed in detail by means of a 3‐D dynamic finite element simulator using both, elastoplastic and elastic models. The performance of rigid inclusions is studied considering different operational scenarios, with dynamic and static loads, as well as involving subgrades with different plasticity index values. It is found that the predictions from the analytical design methods for rigid inclusion tend to be unconservative when compared against the finite element results. As for the numerical solutions, the most unfavorable stress condition is associated with the dynamic elastoplastic finite element solution. It is estimated that the rigid inclusions will contribute to a reduction in the ground settlements of around 15% to 20%, depending on the subgrade plasticity index.

Bio-remediation of desiccation cracking in clayey soils through microbially induced calcite precipitation (MICP)

Desiccation cracking is a common natural phenomenon in clayey soils, considerably degrading their mechanical and hydraulic properties. Typical remediation methods are associated with high labor costs, high maintenance costs, or the usage of environment-unfriendly chemicals. Microbially induced calcite precipitation (MICP) has emerged as a green and sustainable soil improvement technique. The application of MICP in clayey soils remains poorly investigated due to the presence of microscopic pores among clay soil particles that restrain the free passage of bacteria. In this study, we carry out cyclic wetting-drying tests to characterize the effect of MICP on the desiccation cracking behaviors of clayey soils. We prepare four groups of soil samples sprayed with deionized water, bacteria solution, cementation solution, and both bacteria and cementation solutions, respectively. Soil desiccation cracking behaviors captured by a high-resolution camera are quantified using image processing. We resort to optical microscopy and scanning electron microscopy for microstructural characterizations. Experimental results reveal the effects of fluid type and treatment cycle number on the crack evolution and volumetric deformation of soils. Comparatively, the MICP treatment involving both bacteria and cementation solutions work most effectively in lowering the soil cracking potential. Geometrical parameters featuring the crack pattern such as surface crack ratio, average crack width, total crack length, crack width distribution range and the most probable value of crack width decrease significantly with the increasing treatments. This study is expected to improve the fundamental understanding of desiccation cracking mechanisms in the MICP-treated soils and provide insights into the potential application of MICP for cracking remediation in clayey soils.

Feasibility study for slope soil stabilization by microbial induced carbonate precipitation (MICP) using indigenous bacteria isolated from cold subarctic region

Microbial induced carbonate precipitation (MICP) is relatively an innovative soil improvement technique, learnt from the bio-mediated geochemical reactions that naturally occur in the earth surface. During the MICP, CaCO3 is metabolically precipitated in soil pores, cement the particle contacts and improves the strength and stiffness of soil. Environment temperature is one of the most key factors that determines the efficiency MICP. The purpose of this study is to investigate the feasibility of stabilizing the slope soil of cold subarctic region (Hokkaido, Japan). The implication of MICP in cold subarctic zones remains as a major challenge, as the enzymatic performance of the bacteria typically declines during lower temperatures hence insufficient formation of CaCO3 in soil matrix. Therefore, as a potential approach, this study attempted to investigate the feasibility of using the bacteria which have been adapted to native cold climatic conditions. The objectives of this paper are evaluating (1) the effect of temperature in bacterial response, and (2) the effect of grain size distribution in cementation mechanism. The observations suggest that the enzyme activity of the bacteria is negligible at and above 30 °C, whereas it is significant at relatively lower temperatures. The comparison of treated soils suggests that the fine content in slope soil increased number of particle contacts, facilitated effective packing, and promoted the effectiveness of MICP compared to that of uniformly graded sands. Finally, the technical feasibility in slope soil stabilization was well demonstrated using model solidification test. The limitations in stabilizing the slope are also discussed in detail.

Sustainable Improvement of the Crack Resistance of Cohesive Soils

Desiccation cracking of cohesive soils is the development of cracks on the soil surface as a result of a reduction in the soil moisture content. The decrease in soil surface area owing to the desiccation of cohesive soils has an undesirable impact on the mechanical, hydrological, thermal, and physico-chemical properties. Many efforts have been made to improve the desiccation crack resistance of cohesive soils, but the current solutions raise a number of environmental issues, increasing the demand for sustainable soil improvement alternatives. Therefore, the main objective of this study is to investigate novel eco-friendly soil improvement techniques, such as recycled carpet fibers and a gelatin-based bioplastic, and their effect on desiccation cracking in cohesive soils. The improvement of soil crack resistance was studied by conducting desiccation cracking tests on plain and improved soils. In addition, image processing was conducted to quantitatively describe the effect of soil improvement type on the geometrical characteristics of crack patterns. Each soil improvement technique enhanced the soil strength and reduced cracking at room temperature, at an elevated temperature, and when subjecting to cyclic wetting and drying. The addition of bioplastics proved to be the most effective solution, thus demonstrating a viable option to advance future sustainable engineering practices.

Strength, stiffness, and microstructure characteristics of biocemented calcareous sand

Calcareous sands are known as problematic soils in nature and challenge geotechnical engineers in many practical projects. Microbially induced calcite precipitation (MICP) is an innovative soil improvement technique that uses biomineralisation processes to induce cementation in-situ. The work described in this paper investigates the strength, deformation, and microstructure characteristics of biocemented calcareous sand under different cementation solution to sample volume ratios. A series of laboratory experiments was conducted, including unconfined compressive strength tests, splitting, tensile (i.e., Brazilian) strength tests, and consolidated drained triaxial tests. The results indicate that an exponential function reasonably describes the unconfined compressive strength and splitting tensile strength with increasing cementation solution to sample volume ratios. The tangent modulus at 50% peak strength increases exponentially with an increase in cementation solution to sample volume ratio, whereas it increases linearly with an increase in strength. The strength parameters for this MICP-improved soil, including the peak cohesion and friction angle, are derived to facilitate engineering design. Microstructure analyses are used to illustrate the physical basis for the increase in strength and stiffness with increases in the calcite content, as demonstrated using the cementation solution to sample volume ratio.

MICROBIAL INDUCED SLOPE SURFACE STABILIZATION USING INDUSTRIAL-GRADE CHEMICALS: A PRELIMINARY LABORATORY STUDY

One of the promising soil improvement techniques that have recently gained increased attention in Geotechnical and Civil Engineering is microbial induced carbonate precipitation (MICP). The MICP is mediated by ureolytic bacteria through a chain of biochemical reactions which lead to the formation of calcium carbonate cement in soil matrix and persuades the substantial bonds between the soil particles. The study presented herein focuses on surficial stabilization of slope soil (Hokkaido, Japan) by mediating industrial-grade chemicals through two different scales of preliminary laboratory investigations: small-scale columns and bench-scale slopes. Locally isolated Psychrobacillus sp. was cultivated in both industrial-grade media (beer yeast) and laboratory-grade media (NH4-YE: tris-buffer, ammonium sulfate and yeast extract), and the urease activities were compared. The results showed that the cultivation of bacteria in beer yeast resulted in higher urease activity (0.9 U/mL) compared to that in conventional laboratory media (0.4 U/mL). Also, UCS of the specimen treated using industrial-grade chemicals (urea fertilizer, beer yeast and snow melting reagent) was about two times higher than the specimen treated using conventional laboratory-grade chemicals (urea, CaCl2 and nutrient broth). The benchtop-scale test revealed that the highest surface strength (UCS of 1.02 MPa) was achieved while treating the soil by 0.5 M cementation solution at 30oC. Sets of colorimeter measurements were undertaken on treated slope models to compare precipitation profile at different locations. These findings suggest that industrial-grade chemicals can contribute as potential candidates in MICP applications from the perspective of cost reduction.

Research on Physical and Engineering Properties of Unstabilised Soil

Soil improvement techniques are inevitable due to the severe hazards caused by excessive settlement of foundation, debris flow, destructive landslides and the further softening by means of infiltration of prolonged rainfall. The environmentally sustainable technique that utilizes a biological process for biomineralization is Microbial Induced Calcite Precipitation (MICP). Biomineralization is the process in which living organisms produce minerals. There are different metabolic activities that lead to MICP such as ureolysis, denitrification, ammonification, photosynthesis, sulphate reduction and methane reduction. In this study, the photosynthetic soil-borne bacteria is used to enhance the soil stability. The photosynthetic bacteria is isolated from the soil, the characteristic growth is studied and the most efficient strain is selected to be injected back into the soil. The final properties of the soil are tested and are expected to increase its strength. The initial and final variations in the surface of the soil are studied using SEM analysis and EDAX

Análisis técnico-económico de la erosión del suelo y su impacto en el bienestar de productores

Soil erosion in rural agricultural communities in Mexico and low yields is the subject of the present work, places where production has stopped due to the low profitability and productivity generated by the loss of nutrients as a result of natural phenomena, as well as by the action of man. The objective is to identify the current condition of the soil and its impact on agricultural production, in order to suggest soil improvement and conservation techniques appropriate to regional characteristics, to raise the income level of producers in a rural community of Hidalgo, Mexico. The work is divided into three stages: the first consisted of identifying the predominant agricultural crops; the second, sampling to develop the soil analysis; the third, to evaluate economically the income that currently generates the agricultural activities that are practiced in the community and later to evaluate the changes that could be generated when applying measures of soil conservation; as well as the application of the methodology to identify the profitability and the products.

Influence of Microbe and Enzyme-Induced Treatments on Cemented Sand Shear Response

AbstractMicrobial-induced calcium carbonate precipitation (MICP) and enzyme-induced calcium carbonate precipitation (EICP) are both soil improvement techniques that improve the shear response of sa...

Microbially induced carbonate precipitations to improve residual soil at various temperatures

Microbial induced carbonate precipitation (MICP) has emerged recently as a new approach of green and sustainable soil improvement technique. The main aim of this study was to determine the most suitable temperature for MICP to improve tropical residual soil. The physical and engineering properties of residual soil used in the study were determined through several laboratory experiments. A urease active strain of Sporosarcinapasteurii obtained from American Type Culture Collection (ATCC) was used to trigger the carbonate precipitation. Experimental parameters such as curing temperature, treatment duration and bacteria to cementation reagents ratios were evaluated. The results show that the optimum temperature for MICP treatment of residual soil is 55°C. It was also found that at this optimum temperature, specimens treated with bacteria and cementation reagents in proportion of 2:1 produces the highest strength improvement ratio of 1.27 relative to untreated sample and calcite content of 1.09% after 7-day curing. The shear strength of the treated soil also increases with the increase in treatment durations as the 7 days curing produces higher strength improvement for all the experimental conditions. The specimens cured under the atmospheric temperature recorded the lowest calcite content and hence the lower shear strength improvement ratio. Moreover, the experimental results obtained from this study also can be used as a guide in the future bio-geotechnology researches and lead to further scope in geotechnical applications.

Reliability of Soil and Ground Improvement Techniques on Peaty Clay Soil – A Review

Reliability of Soil and Ground Improvement Techniques on Peaty Clay Soil – A Review

Improved understanding of geogrid response to pullout loading: insights from three-dimensional finite-element analysis

Soil reinforcement has rapidly become one of the most common soil improvement techniques used in geotechnical engineering. Understanding the behavior of a geogrid under pullout loading is essential for the analysis and design of reinforced soil systems. The overall behavior of reinforced soils is generally dependent on the properties of the geogrid material, the backfill soil, and the interface condition. Modeling the three-dimensional aspects of soil–geogrid interaction under pullout loading condition is numerically challenging and requires special consideration of the different modes of resistance that contribute to the pullout capacity of the geogrid reinforcement. This study describes the results of a three-dimensional finite-element analysis that has been developed to investigate the behavior of a biaxial geogrid embedded in granular backfill material and subjected to pullout loading. The modeling approach considers the noncontinuous nature of the geogrid geometry and the elastoplastic response of the geogrid material. Model validation is performed by simulating laboratory-size pullout test and comparing the experimental data with the analytical as well as numerically calculated results. The detailed behavior of the geogrid and the surrounding backfill is investigated using the proposed numerical approach. Conclusions are made to highlight the suitability of this technique for analyzing similar soil–structure interaction problems.

Mechanical properties soil stabilized with nano calcium carbonate and reinforced with carpet waste fibers

Abstract One of the geotechnical engineering strategies for dealing with weak soils in a construction site is to alter their mechanical properties with the assistance of soil improvement techniques. The present study examined the effect of the addition of nano calcium carbonate (0, 0.4, 0.8 and 1.2% by weight of the soil) as a stabilizing nanoparticle and carpet waste fibers (0, 0.2, 0.4, and 0.6% by weight of the soil) as a reinforcement agent on the soil behavior. A total of 52 unconfined compressive strength tests, 52 ultrasonic pulse velocity tests, 12 unconsolidated undrained (UU) triaxial tests, and 8 Atterberg limit tests were performed to investigate the effect of fiber and nanoparticle contents and treatment time on the geotechnical properties of the clayey soil. The results showed that the addition of nanoparticles to the clayey soil reduces its liquid limit and increases its plastic limit. The best improvement in the soil strength, which was about 100%, was observed in the 42 days old sample with 1.2% nano calcium carbonate content. The combined use of fibers and nanoparticles also led to significant strength improvement. The addition of carpet waste fiber was found to increase the soil stiffness. Increasing the carpet waste fiber content above the 0.2% did not have much impact on the maximum strength, but significantly improved the residual strength. The addition of carpet waste fibers up to 0.2% increased the velocity of ultrasonic waves, but further increase in the fiber content resulted in reduced velocity. The paper provides a number of equations that express the relationship between the unconfined compressive strength and the ultrasonic pulse velocity for the clayey soils with different additive contents. The provided equations can be used to estimate the success of stabilization and strength improvement efforts based on the results of non-destructive ultrasonic pulse velocity test. The results of unconsolidated undrained triaxial tests showed that the used fibers alter the sample behavior in high strains. Also, the use of nano calcium carbonate and carpet waste fibers together almost doubled the undrained cohesion.

Lattice element method for simulations of failure in bio-cemented sands

Microbiologically induced calcite precipitation following the ureases is a bio-geo-chemical soil improvement technique in which the microorganism facilitates to create an environment for the precipitation of carbonates among the grains. It results in binding the loose granular media and prevention against mechanical failure. Although, the bio-cemented processes and media have been studied in the past in qualitative sense with experimental programs, the mathematical and numerical modelling techniques to quantify the strength parameters are rare. In this article, we propose the lattice element methodology which we applied to perform numerical computations of unconfined compression tests on bio-cemented sands. We also provide the experimental results of the unconfined compression tests on bio-cemented sands treated with a different number of cycles that we conducted in our laboratory. The experimental procedure is explained in details. The ultimate goal is to study the macroscopic response and also to quantify the process for engineering applications. The developed model with an embedded discontinuity can capture the macroscopic behaviour from meso-scale element failure, where the diagonal shear cracks which are seldom inherent to compression failure of highly cemented granular media lead the specimens to final failure. The model can capture the complex interaction of the cracks such as initiation and propagation, branching, coalescence and fingering at a nominal computation cost. The numerical and experimental results show good agreement to a large extent. The developed model is suitable to study brittle, and quasi-brittle behaviour of highly cemented granular media.

Enzyme Induced Biocementated Sand with High Strength at Low Carbonate Content

Specimens of silica sand treated via enzyme induced carbonate precipitation (EICP) showed surprisingly high strength at a relatively low carbonate content when non-fat powdered milk was included in the treatment solution. EICP is a biologically-based soil improvement technique that uses free urease enzyme to catalyze the hydrolysis of urea in an aqueous solution, producing carbonate ions and alkalinity that in the presence of calcium cations leads to precipitation of calcium carbonate. The strength achieved at less than 1.4% carbonate content via a single cycle of treatment was unprecedented compared to results reported in the literature from both EICP and microbially induced carbonate precipitation (MICP). Scanning electron microscope images show that in the specimens treated with the solution containing powdered milk the carbonate precipitate was concentrated at interparticle contacts. The impact of these results include reductions in the concentration of substrate and enzyme required to achieve a target compressive strength, reduction in the undesirable ammonium chloride by-product, and, depending on the desired strength, reduction in the number of cycles of EICP treatment. These advantages enhance the potential for development of a sustainable method of soil improvement via hydrolysis of urea.