Effect of Reagent Concentration on Strength of Lateritic Soil Bio-Treated with Bacillus thuringiensis-Induced Calcite Precipitate Tested with Pocket Penetrometer †
by
and
Ianna Moris Kanyi
1,*, 
Thomas Stephen Ijimdiya
2,
Adrian Oshioname Eberemu
2,3 and
Kolawole Juwonlo Osinubi
2 1
Department of Civil Engineering, Joseph Sarwuan Tarka University, Makurdi 970212, Benue State, Nigeria
2
Department of Civil Engineering, Ahmadu Bello University, Zaria 810107, Kaduna State, Nigeria
3
Africa Center of Excellence on New Pedagogies in Engineering Education (ACENPEE), Ahmadu Bello University, Zaria 810107, Kaduna State, Nigeria
*
Author to whom correspondence should be addressed.
†
Presented at the 4th International Electronic Conference on Applied Sciences, 27 October–10 November 2023; Available online: asec2023.sciforum.net/.
Eng. Proc. 2023, 56(1), 279; https://doi.org/10.3390/ASEC2023-15502
Published: 31 October 2023
(This article belongs to the Proceedings of The 4th International Electronic Conference on Applied Sciences)
Abstract
:The strength of lateritic soil bio-treated with a Bacillus thuringiensis (Bt)-induced calcite precipitate was investigated using a pocket penetrometer (PPT). The effect of bacterial (Bt) and cementation solution concentration (Cs) on the strength of the microbial-induced calcite precipitate (MICP) worked soil was also evaluated. Soil samples were treated with Bt and Cs using three mix ratios (i.e., 25% Bt: 75% Cs, 50% Bt: 50% Cs, and 75% Bt: 25% Cs) based on the natural soil liquid limit (LL = 36.0%). Bt suspension densities of 0, 1.5 × 108, 6.0 × 108, 1.2 × 109, 1.8 × 109, and 2.4 × 109 cells/mL were applied to the soil with four varying Cs concentrations (i.e., 0.25, 0.5, 0.75, and 1 M). The prepared specimens were allowed to homogenise and equilibrate at laboratory conditions. A pocket penetrometer (PPT) was used to test the unconfined compressive strength (UCS) of the prepared specimens at 3, 5, and 7 days after bio-treatment to evaluate the strength of the MICP worked soil at different moisture contents. The results obtained show that the UCS values increased with higher Bt and Cs as well as with a reduction in moisture content as the bio-treated soil equilibrated with the environment. The recorded UCS values for the mix ratios considered were in the order: 50% Bt: 50% Cs > 25% Bt: 75% Cs > 75% Bt: 25% Cs. Therefore, a PPT can be used to determine the approximate unconfined compressive strength of treated soil.
1. Introduction
The success of any construction project is hinged on the comprehensive knowledge of the physico-mechanical dynamics of the bearing soil. The resistance of soil to penetration under the loading condition during construction remains one of the key aspects in evaluating the soil bearing strength [1]. The factors that impact the soil strength include the clay size, moisture content, and the proportion of the clay mineralogy. The soil strength and its water holding ability is therefore a function of the soil texture and mineralogy as well as the distribution and composition of the particle sizes [2].
Conventionally, the triaxial test is used in the laboratory to determine the unconfined compressive strength (UCS) of soils, especially those with a significant amount of clay content. However, the test is time consuming and has a high cost. Additionally, it is very difficult to maintain the desired intactness of the cored samples for the test, hence the variability that exists between laboratory and in situ test results [3]. A fast and easy means of assessing the UCS of soil is the use of a hand pocket penetrometer (PPT), which has a low cost both in the laboratory and in the field [4,5].
Current soil improvement trends suggest a widely utilised technique bordering on the intentional inducement of desirable minerals (calcite) into the soil using different bio-inspired or bio-mediated approaches to improve the soil bearing capabilities [5,6]. Soil microbes have also been used for liquefaction mitigation through a process known as microbial induced desaturation (MID) [7,8,9,10]. However, the commonly used bio-inspired or bio-mediated methods are microbial-induced calcite precipitation (MICP) and enzymatic-induced calcite precipitation (EICP) [11]. The former requires soil microbes to hydrolyse urea for the desired calcite formation while the latter does not require microbes, however, the urease enzyme is extracted from plants and introduced into the soil when other favourable conditions are put in place for calcite precipitation to occur [5,11].
In this study, the MICP bio-treated soil moisture variations and strength development was evaluated using a PPT.
2. Materials and Methods
Soil: The lateritic soil was sourced at Abagana (latitude 6°12′15″ N and longitude 7°0′40″ E) in Anambra State, Nigeria. Samples were taken at depths between 0.5 m and 3 m. The properties of the natural soil determined using British Standard [12] procedures for testing natural soils are summarised in Table 1.
Cementation reagent: The cementation solution (Cs) was composed of an equi-molar of calcium chloride and urea as well as other nutrients such as sodium bicarbonate, ammonium chloride, and nutrient broth. The molar concentrations were varied to produce four different Cs (i.e., 0.25, 0.5, 0.75, and 1 M). The mass concentrations of the various components that make up the Cs are presented in Table 2.
Microorganism: The soil microorganism (Bacillus thuringiensis (Bt)) was isolated and identified from the soil to be treated in the laboratory by using culture and biochemical confirmatory test kits for identifying and characterising Bt.
Preparation of sample: A total of 300 g of soil with a maximum particle size of 425 µm (i.e., soil that passed through BS No. 40 sieve) were treated with bacterial and cementation solutions in three separate mix ratios of 25% Bt: 75% Cs, 50% Bt: 50% Cs and 75% Bt: 25% Cs based on the liquid limit (LL = 36%) of the natural soil. The prepared soil samples were allowed to equilibrate at the prevailing laboratory conditions (i.e., temperature of 25° ± 2 °C and relative humidity of 100%). A pocket penetrometer (PPT) was utilised to test the UCS of the prepared samples at 3, 5, and 7 days after treatment to measure the strength of the MICP treated soil at different moisture contents. Stepped bacterial suspension densities of 0, 1.5 × 108, 6.0 × 108, 1.2 × 109, 1.8 × 109, and 2.4 × 109 cells/mL equivalent to 0, 0.5, 2.0, 4.0, 6.0, and 8.0 McFarland standards, respectively, were used in the study. The varying bacterial suspension densities were applied to the soil with four varying cementation reagent concentrations (i.e., 0.25, 0.5, 0.75, and 1 M) consisting of equal molars of CaCl2 and CO(NH2)2 and other ingredients that make up the cementation solution as described in [14].
Measurement of strength with PPT: A PPT was used as a quick check to estimate the strength development of the bio-treated soil for the three mix ratios stated earlier. The PPT, held perpendicular to the surface of the prepared soil, is gradually pushed into the soil at a constant pressure until the calibrated grove machined at the tip of the piston becomes even with the prepared soil sample surface. The estimated strength (UCS) is read directly on the lower end of the ring closest to the handle, away from the end of the piston. The indicator ring remains in position after releasing the piston (see Figure 1). The average of three similar values were taken as the estimated strength of the bio-treated soil.
3. Results and Discussion
3.1. Effect of Cementation Solution Concentration and Bacterial Population on Strength Development
The strength values of the prepared samples recorded after three days were 98.06 kPa each for the three mix ratios used (i.e., 25% Bt: 75% Cs, 50% Bt: 50% Cs, and 75% Bt: 25% Cs). However, the strength increased from 98.06 kPa recorded for the 0.25 M concentration to 147.1 kPa when treated with the 1.0 M concentration. Similarly, there was an observed increment in the strength values as the Bt population in the mixture increased. The results obtained further revealed that the resistance to penetration (strength) also increased as the exposure period (3–7 days) increased, regardless of the mix ratio considered (see Figure 2 and Figure 3).
The increase in the PPT values at a higher concentration of Cs and Bt population density in mixture may be due to the high urease activity during the hydrolysis process as there were enough microbes in the mixtures to degrade urea, and consequently, calcite was precipitated in the soil matrix, resulting in increased strength [5,6,11,15,16]. Similar reports can be found in the literature including those of [1,4], among others.
3.2. Effect of Cementation Solution Concentration and Bacterial Population on Moisture Content
The variations in the moisture content of lateritic soil with Bacillus thuringiensis suspension density for the different mix ratios (25% Bt: 75% Cs, 50% Bt: 50% Cs, 75% Bt: 25% Cs) are presented in Figure 4 and Figure 5.
The moisture content of the bio-treated soil decreased with an increase in the exposure period (3–7 days) as well as the Bt population density in the mixture, regardless of the mix ratio used. Higher strength values recorded on the seventh day after treatment recorded the lowest moisture content values. It was observed that the strength of the bio-treated soil reduced with a higher moisture content, most likely due to the cation exchange reaction involving the negatively charged electrons on the surface of the clay particles held together by electrostatic forces. The addition of moisture resulted in the development of a diffused double layer of water surrounding the clay particles, which weakened the electrostatic bonds, resulting in a strength decrease in the soil matrix [1,17,18].
3.3. Effect of Mix Ratio on the Strength of Treated Lateritic Soil
The distributions of the recorded strength and moisture content values against the three mix ratios are shown in Figure 5 and Figure 6. The recorded strength and moisture values indicated a higher dispersion of data at 50% Bt: 50% Cs, suggesting that a higher and wider range of strength values were achieved after bio-treatment of the lateritic soil (see Figure 5). Similarly, a lower range of moisture content values were recorded at 50% Bt: 50% Cs (see Figure 6). The bio-treatment mix ratio performance was in the order of 50% Bt: 50% Cs > 25% Bt: 75% Cs > 75% Bt: 25% Cs (see Figure 6 and Figure 7).
4. Conclusions
The following deductions can be made from the results of this study:
- The PPT measured UCS values increased with higher Cs concentration and Bt suspension density in the soil matrix.
- The moisture content of the bio-treated soil decreased as the soil attained equilibrium with the prevailing conditions of the test environment.
- The 50% Bt: 50% Cs mix ratio recorded the highest strength values, followed by 25% Bt: 75% Cs with intermediate values, and the lowest values were recorded for the 75% Bt: 25% Cs mix ratio.
- A PPT can be used for quick assessment of the strength development of bio-treated lateritic soil.
5. Recommendation
Based on the results of the study, it is recommended that lateritic soil treated with a 50% Bt: 50% Cs mix ratio be further evaluated for use as an embankment material.
Author Contributions
All authors contributed to the study in the aspect of conception, design, analysis and manuscript writing. All the authors: I.M.K., T.S.I., A.O.E. and K.J.O. were involved in the conduct of laboratory experiments and formal analysis of the laboratory outcomes. Materials preparation, laboratory investigations, and data/results analysis were performed by I.M.K., A.O.E., T.S.I. and K.J.O. made significant contributions to the conception of the work and were closely involved in the monitoring of laboratory investigations and analysis of results. The initial manuscript was drafted by I.M.K. The intellectual input in terms of technical writing and vetting at first and second level were provided by A.O.E. and T.S.I. The last level of technical review and vetting was provided by K.J.O. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
All data obtained from the investigation and materials in the study are original and belong to the authors. And will only be made available on request. All other relevant information in the manuscript have been acknowledged and referenced accordingly in line with standard ethics guiding article publication.
Conflicts of Interest
The authors declare no conflict of interest.
References
- Mousavi, F.; Abdi, E.; Ghalandarayeshi, S.; Page-Dumroese, D.S. Modeling unconfined compressive strength of fine-grained soils: Application of pocket penetrometer for predicting soil strength. Catena 2021, 196, 104890. [Google Scholar] [CrossRef]
- Dolinar, B. Undrained shear strength of saturated cohesive soils depending on consolidation pressure and mineralogical properties. Acta Geotech. Slov. 2004, 1, 5–11. [Google Scholar]
- Salgado, R.; Yoon, S. Dynamic cone penetration test (DCPT) for subgrade assessment. Jt. Transp. Res. Progr. 2003. [Google Scholar] [CrossRef]
- Yasun, A.S. Capability of pocket penetrometer to evaluate unconfined compressive strength of baghdad clayey soil. Al-Nahrain J. Eng. Sci. 2018, 21, 66. [Google Scholar] [CrossRef]
- Maryam, N.; Chu, J.; Khosroshahi, M.; Zenouzi, L. Soil stabilization for dunes fixation using microbially induced calcium carbonate precipitation. Geoderma 2023, 429, 116183. [Google Scholar] [CrossRef]
- Martinez, A.; Frost, D. Bio-inspired Anchors and Deep Foundations. Geostrata Mag. 2023, 27, 30–39. [Google Scholar] [CrossRef]
- Flora, A.; Chiaradonna, A.; Bilotta, E.; Fasano, G.; Mele, L.; Lirer, S.; Fanti, F. Field tests to assess the effectiveness of ground improvement for liquefaction mitigation. In Earthquake Geotechnical Engineering for Protection and Development of Environment and Constructions; CRC Press: Boca Raton, FL, USA, 2019; pp. 740–752. [Google Scholar]
- Mele, L.; Lirer, S.; Flora, A. An energetic interpretation of liquefaction laboratory tests on partially saturated soils. J. Geotech. Geoenviron. Eng. 2022, 148, 04022082. [Google Scholar] [CrossRef]
- Molina-Gómez, F.; da Fonseca, A.V.; Ferreira, C.; Caicedo, B. Improvement of cyclic liquefaction resistance induced by partial saturation: An interpretation using wave-based approaches. Soil Dyn. Earthq. Eng. 2023, 167, 107819. [Google Scholar] [CrossRef]
- Khosravifar, A.; Moug, D. Microbial Desaturation for Liquefaction Mitigation. Geostrata Mag. 2023, 27, 22–29. [Google Scholar] [CrossRef]
- Alessia, C.; Gallipoli, D.; Bruno, A.W.; Augarde, C.; Hughes, P.; La Borderie, C. Soil Stabilization against Water Erosion via Calcite Precipitation by Plant-Derived Urease; CNRIG 2019, LNCE 40; Calvetti, F., Cotecchia, F., Galli, A., Jommi, C., Eds.; Springer International Publishing: Cham, Switzerland, 2020; pp. 753–762. [Google Scholar] [CrossRef]
- BS 1377; Method of Testing Soils for Civil Engineering Purpose. British Standard Institute (BSI): London, UK, 1990.
- AASHTO. Standard Specification for Transportation, Material and Methods of Sampling and Testing, 14th ed.; American Association of State Highway and Transportation Official: Washington, DC, USA, 1986. [Google Scholar]
- Stocks-Fischer, S.; Galinat, J.K.; Bang, S.S. Microbiological precipitation of CaCO3. Soil Biol. Biochem. 1999, 31, 1563–1571. [Google Scholar] [CrossRef]
- Osinubi, K.J.; Sani, J.E.; Eberemu, A.O.; Ijimdiya, T.S.; Yakubu, S.E. Unconfined Compressive Strength of Bacillus Pumilus Treated Lateritic Soil. In Proceedings of the 8th International Congress on Environmental Geotechnics Volume 3; Springer: Singapore, 2019; pp. 410–418. [Google Scholar]
- Osinubi, K.J.; Gadzama, E.W.; Eberemu, A.O.; Ijimdiya, T.S. Comparative evaluation of strength of compacted lateritic soil improved with microbial-induced calcite precipitate. In Geo-Congress 2020—Geo-Systems, Sustanability, Geoenvironmental Engineering, and Unsaturated Soil Mechanics; Hambleton, J.P., Makhnenko, R., Budge, A.S., Eds.; GSP No 319; American Society of Civil Engineers: Reston, VA, USA, 2020; pp. 240–248. [Google Scholar]
- Murtala, U.; Khairul, A.K.; Kenny, T.P.C. Biological process of soil improvement in civil engineering: A review. J. Rock Mech. Geotech. Eng. 2016, 8, 767–774. [Google Scholar] [CrossRef]
- Ning-Jun, J.; Soga, K.; Kuo, M. Microbially induced carbonate precipitation for seepage-induced internal erosion control in sand-clay mixtures. J. Geotech. Geoenvironmental Eng.-ASCE 2017, 143, 100–114. [Google Scholar] [CrossRef]
Figure 1.
(A,B) Pocket penetrometer testing. (C) Pocket penetrometer.
Figure 2.
Variation in PPT strength (3 days) of lateritic soil with Bacillus thuringiensis suspension density for different mix ratios: (A) 25% Bt: 75% Cs; (B) 50% Bt: 50% Cs; (C) 75% Bt: 25% Cs.
Figure 2.
Variation in PPT strength (3 days) of lateritic soil with Bacillus thuringiensis suspension density for different mix ratios: (A) 25% Bt: 75% Cs; (B) 50% Bt: 50% Cs; (C) 75% Bt: 25% Cs.
Figure 3.
Variation in PPT strength (7 days) of lateritic soil with Bacillus thuringiensis suspension density for different mix ratios: (A) 25% Bt: 75% Cs; (B) 50% Bt: 50% Cs; (C) 75% Bt: 25% Cs.
Figure 3.
Variation in PPT strength (7 days) of lateritic soil with Bacillus thuringiensis suspension density for different mix ratios: (A) 25% Bt: 75% Cs; (B) 50% Bt: 50% Cs; (C) 75% Bt: 25% Cs.
Figure 4.
Variation in the moisture content (5 days) of lateritic soil with Bacillus thuringiensis suspension density for different mix ratios: (A) 25% Bt: 75% Cs; (B) 50% Bt: 50% Cs; (C) 75% Bt: 25% Cs.
Figure 4.
Variation in the moisture content (5 days) of lateritic soil with Bacillus thuringiensis suspension density for different mix ratios: (A) 25% Bt: 75% Cs; (B) 50% Bt: 50% Cs; (C) 75% Bt: 25% Cs.
Figure 5.
Variation in moisture content (7 days) of lateritic soil with Bacillus thuringiensis suspension density for different mix ratios: (A) 25% Bt: 75% Cs; (B) 50% Bt: 50% Cs; (C) 75% Bt: 25% Cs.
Figure 5.
Variation in moisture content (7 days) of lateritic soil with Bacillus thuringiensis suspension density for different mix ratios: (A) 25% Bt: 75% Cs; (B) 50% Bt: 50% Cs; (C) 75% Bt: 25% Cs.
Figure 6.
Distribution of pocket penetrometer data for the three mix ratios (after 7 days).
Figure 7.
Distribution of moisture content data for the three mix ratios (after 7 days).
Table 1.
Parameters of the natural lateritic soil.
| Property | Quantity |
|---|---|
| Natural moisture content (%) | 19.6 |
| Percentage passing no. 200 sieve | 33.2 |
| AASHTO [13] classification | A–2–6 (2) |
| USCS | SC |
| Specific gravity | 2.67 |
| Liquid limit (%) | 36 |
| Plastic limit (%) | 17.1 |
| Plasticity index (%) | 18.9 |
| Linear shrinkage (%) | 7.7 |
| Dominant clay mineral | Kaolinite |
| Colour | Reddish-brown |
Table 2.
Mass per litre of cementation reagents.
| Concentrations (M) | 0.25 | 0.5 | 0.75 | 1.0 |
|---|---|---|---|---|
| Calcium chloride (CaCl2) (g/L) | 27.75 | 55.49 | 83.24 | 110.98 |
| Nutrient broth (g/L) | 3 | 3 | 3 | 3 |
| Sodium bicarbonate (NaHCO3) (g/L) | 2.12 | 2.12 | 2.12 | 2.12 |
| Ammonium chloride (NH4Cl) (g/L) | 10 | 10 | 10 | 10 |
| Urea (CO(NH2)2) (g/L) | 15.05 | 30.03 | 45.05 | 60.06 |
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |
© 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Share and Cite
MDPI and ACS Style
Kanyi, I.M.; Ijimdiya, T.S.; Eberemu, A.O.; Osinubi, K.J. Effect of Reagent Concentration on Strength of Lateritic Soil Bio-Treated with Bacillus thuringiensis-Induced Calcite Precipitate Tested with Pocket Penetrometer. Eng. Proc. 2023, 56, 279. https://doi.org/10.3390/ASEC2023-15502
AMA Style
Kanyi IM, Ijimdiya TS, Eberemu AO, Osinubi KJ. Effect of Reagent Concentration on Strength of Lateritic Soil Bio-Treated with Bacillus thuringiensis-Induced Calcite Precipitate Tested with Pocket Penetrometer. Engineering Proceedings. 2023; 56(1):279. https://doi.org/10.3390/ASEC2023-15502
Chicago/Turabian StyleKanyi, Ianna Moris, Thomas Stephen Ijimdiya, Adrian Oshioname Eberemu, and Kolawole Juwonlo Osinubi. 2023. "Effect of Reagent Concentration on Strength of Lateritic Soil Bio-Treated with Bacillus thuringiensis-Induced Calcite Precipitate Tested with Pocket Penetrometer" Engineering Proceedings 56, no. 1: 279. https://doi.org/10.3390/ASEC2023-15502
