Biocemented Sand Research Articles

Thermal Conductivity of Biocemented Graded Sands

This paper includes an investigation of the thermal conductivity of biocemented soils to better understanding the regimes of heat transmission through soils treated by microbially induced calcium carbonate precipitation (MICP). A series of thermal conductivity tests using the transient plane source method (TPS) was performed on biocemented silica sand specimens with different gradations, void ratios, and MICP treatment cycles. The results showed that MICP treatment greatly improved the thermal conductivity of sand specimens. An increase in uniformity coefficient or a decrease in void ratio of the sand resulted in an increase in the thermal conductivity of MICP-treated specimens for a given MICP treatment cycle. The increment of thermal conductivity of MICP-treated specimens with respect to that of untreated specimens was also affected by gradation, void ratio, and content of calcium carbonate. The greatest improvements in thermal conductivity were achieved for sands having an initial degree of saturation between 0.82 and 0.85. An empirical equation was established to predict the thermal conductivity of MICP-treated silica sand with different variables, which may be useful in designing energy piles in biocemented sand layers.

Tensile Strength of Artificially Cemented Sandstone Generated via Microbially Induced Carbonate Precipitation.

Artificially bio-cemented sands treated with microbially induced calcite precipitation are weakly cemented rocks representing intermediate materials between locked and carbonate sands. Variations in cementation significantly affect the strength of sample, particularly tensile stregth. The modes of fracture and the surface characteristics resulting from the indirect tensile strength tests (Brazilian tests) are strongly correlated with the specimen strength and consequently the degree of cementation. This study examines the tensile strength of bio-cemented fine and coarse sands (average particle diameter 0.18 and 1.82 mm, respectively) and investigates failure modes by recording fracture evolution at both sides of specimen and surface characteristics of the reconstructed surfaces. The dimensionless slope parameter provided the best fit with respect to tensile strength while the power spectral density was a good indicator of surface anisotropy. Finally, wavelet decomposition allowed for comparison of fracture surface characteristics of the two sands ignoring the grain size effects.

A framework for predicting abrasion rupture of crusts in wind erosion

AbstractCrusts play a crucial role in the reduction or control of wind erosion. In this regard, the resilience and durability of crusts are of prime importance. Crusts have high resilience and durability against wind flow shear stresses; however, they are prone to abrasion induced by saltating particles. Therefore, estimating crust durability in abrasion rupture has practical importance. In this study, a cyanocrust and a biocemented sand crust were subjected to a controlled flux of saltating particles for different sandblasting periods to provide a framework for predicting crust rupture. The velocity and pre‐ and post‐collision energy of the saltating particles were measured using high‐speed photography. The changes in the strength of the crusts after different periods of sandblasting were determined using a scratch test. The results suggested that the average strength of the cyanocrust and biocemented sand crust became 0.25 and 0.7 of their corresponding initial values after 30 min of sandblasting. Also, the average stiffness of the cyanocrust and biocemented sand crust decreased to 0.5 and 0.9 of their initial values, respectively. Furthermore, the amount of impact energy absorbed by the crusts increased by the deterioration of the crusts. Compiling the results of the wind tunnel experiment and scratch tests yielded an exponential equation which can be used to estimate crust durability in a given condition of saltation. Based on this equation, the cyanocrust and biocemented sand crust will break down entirely after 23 and 449 min, respectively, at a wind velocity of 6.8 m/s and a saltation flux of 1 g/s/m.

Strength and durability of biocemented sands: Wetting-drying cycles, ageing effects, and liquefaction resistance

Microbially induced calcite precipitation (MICP), an emanating, sustainable and potentially sound technique for biocementation of granular soils. The method is based on the metabolic activity of urease-producing microbes. Bioaugmentation through individual microorganisms has been investigated till now, and synergistic effect of bacteria mixtures (hybrids) for bioaugmentation is under-explored yet. Durability aspect of biocemented soils in terms of wetting–drying resistance and ageing also requires special attention and thorough investigation before adopting in field application. Thus, considering these limitations of MICP, present study has been carried out to aim multiple objectives, including optimization of cementation solution injection strategy. Poorly graded liquefiable sand was treated in polyvinyl chloride (PVC) tubes by augmenting it with Sporosarcina pasteurii, Bacillus sphaericus, and their mixed culture for hybridized activity. The biotreatment was continued by using 0.50 M cementation solution using injection frequency 12 and 24 h, and injection pore volumes (PV) 1, 0.75, and 0.5 up to 18 days. Permeability and calcite content of biocemented specimens were determined after treatment. For durability analysis, biocemented specimens were subjected to 0, 5, 10, 15, and 20 wetting–drying (W-D) cycles and kept in an uncontrolled temperature environment for 0, 1.5, 3, 4.5, and 6 months to investigate ageing effects. After W-D cycles and ageing time, samples were tested for ultrasonic pulse velocity (UPV), shear modulus, unconfined compressive strength (UCS), and split tensile strength (STS). The mass-loss rate of biocemented specimens was also determined after cyclic W-D actions. The liquefaction resistance of biotreated sand was compared with untreated dense sand specimen using dynamic cyclic simple shear (DCSS) tests. The results showed W-D resistance of biocemented sand even after 20 W-D cycles, and ageing effects showed more than two times increase in mechanical properties. The DCSS test results showed that excess pore pressure ratio was not reached to 1 in biocemented sands up to 100 cycles.

Less is more: Optimising the biocementation of coastal sands by reducing influent urea through response surface method

The excessive effluent ammonia produced during the conventional biocementation of coastal sands by ureolytic Microbially Induced Calcite Precipitation (MICP) poses a looming threat to the marine environment. This research mitigates this threat by employing a brute force deployment of the Response Surface Method (RSM) for optimal minimisation of urea, which is the primary contributor of this effluent ammonia, to develop a sustainable MICP treatment model for the biocementation of coastal sand columns. The unconfined compressive strength (UCS) and calcium carbonate content (CCC) results of these columns, measured during their UCS and gravimetric acid washing testing, were used in this developed model for its validation and further optimisation. The biocementation solution resulting from this finally optimised MICP model used 75% lesser influent urea per gram of sand than its predecessor treatment model and still significantly improved the UCS of biocemented sand columns (from 0 kPa to 111.63 kPa). The structural analyses (XRD, FESEM) of these biocemented columns showed the adsorption of calcium carbonate and nesquehonite crystals on sand grains. This reduction in the consumption of urea significantly lowers the production of effluent ammonia during the biocementation of coastal sands. Therefore, it is suggested that this optimised MICP treatment model offers a sustainable method for strengthening coastal sands with little to no effect on the natural mosaic of their subsurface ecosystems.

Unconfined compressive strength of bio-cemented sand: state-of-the-art review and MEP-MC-based model development

As a clean and sustainable method, the microbially induced calcite precipitation (MICP) approach has been widely used for reinforcing weak soils. This study presents a state-of-the-art review on the unconfined compressive strength (UCS) of bio-cemented sand treated by MICP, followed by the high-performance prediction using a machine learning algorithm combined with the Monte-Carlo (MC) method. First, various influencing parameters affecting the UCS of bio-cemented sand are identified, such as initial relative density, angularity of particle shape, bacterial concentration, precipitated calcium carbonate content, temperature and degree of saturation. Besides, the particle size distribution, urea and calcium concentration, and initial pH level also influence the UCS of the bio-cemented sand, but the effects remain contradictory or unclear. Following the state-of-the-art review, a large database covering 351 bio-cemented sand samples is developed, with the UCS as the output and seven influencing parameters (median grain size, coefficient of uniformity, initial void ratio, optical density of bacterial suspension, urea concentration, calcium concentration and precipitated calcium carbonate content) as inputs for the correlation. The multi expression programming (MEP) method combined with the MC method is proposed to develop the prediction models. All data groups randomly generated from the database are with 80% of the samples as the training sets and 20% as the testing sets. Finally, the optimal prediction model is selected with the lowest mean absolute error, further based on the analyses of monotonicity, sensitivity and robustness regarding more general applications.

Experimental investigation to mitigate aeolian erosion via biocementation employed with a novel ureolytic soil isolate

• A novel soil strain of Pseudogracilibacillus family isolated for biocementation. • Soil properties of Thar desert soil tested on various levels of MICP treatment. • Wind erosion traits of Thar desert soil tested on various levels of MICP treatment. Aeolian ecosystems suffer severe land degradation due to wind erosion. This study presents the erosion mitigation via bio-cementation technique for the soil collected from Jaisalmer region of the Thar Desert of India. Most of the previous studies considered conventional microbe Sporosarcina pasteurii for aeolian erosion mitigation. Alternatively, as the soils containing vegetation are rich in microbial diversity, this study presents isolation and characterisation of a novel urease-positive microbial strain from a soil slope, which is later utilised for the aeolian-erosion mitigation. The desert sand was subjected to biocementation treatment using the isolated microbe and various molar concentrations (M) of cementation solution, ranging from 0.25 M to 1 M. The engineering properties of the biocemented sand such as coefficient of permeability (k), unconfined compressive strength (UCS), and erodibility was investigated. The soil erosion test was conducted in a lab-scale wind tunnel to investigate parameters such as soil mass loss and threshold detachment velocity. The investigation revealed a decrease of one order in the magnitude of the permeability coefficient with 1 M biocementation treatment. A high UCS value of around 1 MPa was observed with a low calcium carbonate content of 1.3% precipitated with 0.5 M cementation solution treatment. The erosion resistance is observed to be maximum with 1 M cementation solution treatment withstanding the maximum wind velocity above 55 km/h. With lab-scale investigation, this study confirms drastic improvement in soil erodibility resistance with biocementation using the isolated microbe and encourages field trial for protecting the desert ecosystem from severe erosion.

Effect of stress path on the shear response of bio-cemented sands

Effect of stress path on the shear response of bio-cemented sands

Experimental and Analytical Study on Geomechanical Behavior of Biocemented Sand

Abstract Research on soil biocementation has gained momentum given its advantages over ordinary Portland cement-based techniques that entail a negative environmental impact. Soil biocementation occ...

Durability of biotechnologically induced crusts on sand against wind erosion

Crusts on soil surfaces are well recognized for wind erosion control in arid regions and mine tailings. In the last two decades, the use of microorganisms for crust formation on the soil surface has been developed. The topic here is to examine the durability of a biocrust created by Microcoleus vaginatus cyanobacterium and a biocemented sand crust induced by precipitation of calcium carbonate by Bacillus subtilis against wind erosion. To this aim, the crusts were subjected to three wind velocities and one sandblasting condition for three different periods in wind tunnel simulation. Also, the strength of the crusts was measured after each period of sandblasting by a penetration test. The results suggested that the biocemented sand crust has a comparatively stronger bonding and more coherent structure so that its strength did not change in sandblasting in contrary to that of the cyanocrust. Concerning the crusts' erodibility, the biocemented sand crust was more durable than the cyanocrust, and its erosion was not progressive at any conditions.

Effect of freeze-thaw cycles on engineering properties of biocemented sand under different treatment conditions

The recently developed microbially induced calcite precipitation (MICP) method is a potentially effective and environmentally friendly technique to improve the unfavorable soil conditions. However, the durability of biotreated sand under freeze-thaw cycles has not been investigated. This study investigates the effects of freeze-thaw (FT) cycles on shear strength and shear modulus of Narmada river sand (a poorly graded liquefiable sand) treated with MICP under different conditions. The bacterial growth and biotreatment were conducted under non-sterile and environmentally uncontrolled conditions that are typically encountered in the field conditions. First, the effects of main control variables involved in the MICP treatment, specifically two bacteria strains i.e., Sporosarcina pasteurii ( S. pasteurii ) and Bacillus sphaericus ( B. sphaericus ), two treatment cycles viz. 12 h and 24 h, and different pore volumes (1 PV, 0.75 PV, and 0.5 PV) of cementation solution injection, were investigated. After 18 days of continuous treatment, the biocemented specimens were tested for unconfined compressive strength (UCS), split tensile strength (STS), hydraulic conductivity, ultrasonic pulse velocity (UPV), and shear modulus after 0, 5, 10, 15 and 20 freeze-thaw (FT) cycles. The calcite content distribution in all of the biotreated samples was also analyzed. The results demonstrated that the maximum UCS, STS, UPV, shear modulus, and reduction in hydraulic conductivity were 2333.2 kPa, 437.7 kPa, 2670 m/s, 13 GPa, and 96.6%, respectively, at 12% calcite content using S. pasteurii , 12 h treatment cycle, and injection of 1 PV cementation solution in every cycle up to 18 days. The biocemented specimens maintained almost 90% shear strength and 77% shear modulus after 10 FT cycles in 9–12% calcite precipitated samples augmented with S. pasteurii. The similar biocemented samples resulted in 14–17% and 31–35% decrease in shear strength, and 41–44% and 54–57% decrease in shear modulus after 15 and 20 FT cycles, respectively. • Non-sterile cultivation of bacteria was explored to optimize time, energy, and cost. • Bioaugmentation with two bacteria was investigated in uncontrolled environment. • Strength and shear modulus increase with the increase in calcite content. • Ultrasonic pulse velocity results showed rock-like behavior of biocemented sand. • Biocemented sand was found durable even after 20 freeze-thaw cycles.

Comparison of improved shear strength of biotreated sand using different ureolytic strains and sterile conditions

AbstractThe present study aims to improve shear strength of poorly graded sand using microbially induced calcite precipitation (MICP) technique. Two soil‐based bacteria, namely Sporosarcina pasteurii (SP) and Bacillus sphaericus (BS), were bioaugmented in sand. The cementation solutions of 0.50 M concentration were prepared using distilled water (DWCS) and tap water (TWCS), maintaining sterile and non‐sterile conditions, respectively. The biotreatment was carried out in direct shear test (DST) moulds using 12‐hr treatment cycles up to 14 days. The biotreated sand samples were subjected to DST to determine shear strength parameters, and results were statistically explored using analysis of variance (ANOVA). The amount of calcite precipitation, XRD and SEM was used to interpret biocementation. The non‐sterile treatment using TWCS showed significant strength. Additional biotreatment samples were prepared in DST and cylindrical PVC moulds using TWCS for 18 days but adopting different treatment cycles of 12, 24, 48 and 72 hr to explore inexpensive treatment option. All of these biotreated samples were tested for hydraulic conductivity, shear strength (based on DST and triaxial consolidated undrained (CU) tests) and three‐layer calcite contents. In CU tests, stress‐strain response of biocemented sands showed initial brittle behaviour followed by strain‐softening, analogous to rock‐like behaviour similar to sandstone. The maximum increase in strength was achieved with 12‐hr treatment cycle. The 24‐hr treatment cycle showed 1.7–1.8 times lesser strength than 12‐hr treatment cycle specimens. However, a significant amount of calcite precipitation and strength in 24‐hr treatment cycle showed its effectiveness in achieving cost reduction for large‐scale field applications.

Effects of Different Types of Fibers on the Physical and Mechanical Properties of MICP-Treated Calcareous Sand.

Microbial-induced calcite precipitation (MICP) has been a promising method to improve geotechnical engineering properties through the precipitation of calcium carbonate (CaCO3) on the contact and surface of soil particles in recent years. In the present experiment, water absorption and unconfined compressive strength (UCS) tests were carried out to investigate the effects of three different fiber types (glass fiber, polyester fiber, and hemp fiber) on the physical and mechanical properties of MICP-treated calcareous sand. The fibers used were at 0%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, and 0.40% relative to the weight of the sand. The results showed that the failure strain and ductility of the samples could be improved by adding fibers. Compared to biocemented sand (BS), the water absorption of these three fiber-reinforced biocemented sands were, respectively, decreased by 11.60%, 21.18%, and 7.29%. UCS was, respectively, increased by 24.20%, 60.76%, and 6.40%. Polyester fiber produced the best effect, followed by glass fiber and hemp fiber. The optimum contents of glass fiber and polyester fiber were 0.20% and 0.25%, respectively. The optimum content of hemp fiber was within the range of 0.20–0.25%. Light-emitting diode (LED) microscope and scanning electron microscope (SEM) images lead to the conclusion that only a little calcite precipitation had occurred around the hemp fiber, leading to a poor bonding effect compared to the glass and polyester fibers. It was therefore suggested that polyester fiber should be used to improve the properties of biocemented sand.

Rock-like behavior of biocemented sand treated under non-sterile environment and various treatment conditions

Microbially induced calcite precipitation (MICP) is a recently developed technique for microbiological ground improvement that has been applied for mitigating various geotechnical challenges. However, the major challenges, such as calcite precipitation uniformity, presence of different bacteria, cementation solution optimization for cost reduction, and implementation under non-sterile and uncontrolled field environment are still not fully explored and require detailed investigation before field application. This study aims to address these challenges of MICP to improve the geotechnical properties of sandy soils. Several series of experiments were conducted using poorly graded Narmada River (India) sand, which were subjected to various biotreatment schemes and tested for unconfined compressive strength (UCS), split tensile strength (STS), ultrasonic pulse velocity (UPV), hydraulic conductivity (after 6 d, 12 d, and 18 d of treatment), and calcite content. The microstructure of sand was examined through a scanning electron microscope (SEM). Initially, the sand was individually augmented with two non-pathogenic bacterial strains, i.e. Sporosarcina (S.) pasteurii and Bacillus (B.) sphaericus. The stopped-flow injection method was adopted to provide cementation solutions at three different durations (treatment cycle) of 12 h, 24 h, and 48 h and three different pore volumes (PVs) of 1, 0.75, and 0.5. The pore volume here refers to the porosity which is expressed as a ratio, i.e. a porosity of 50% was used as 0.5. The results showed rock-like behaviors of biocemented sand with the UCS, STS, and UPV enhancement up to 2333 kPa, 437 kPa, and 2670 m/s, respectively. The hydraulic conductivity reduction of 96.6% was achieved by 12% of calcite formation after 18 d of treatment using Sporosarcina pasteurii, 12-h treatment cycle, and one pore volume of cementation media in each cycle. Overall, a 24-h treatment cycle and 0.5-pore volume cementation solution were found to be the optimal treatment which was effective and economical to achieve heavily cemented, rock-type biocemented sand using both bacteria.

Sandy Soil Improvement Using MICP‐Based Urease Enzymatic Acceleration Method Monitored by Real‐Time System

This paper aims at monitoring the improvement of sandy soil properties with biocementation through the microbially induced calcite precipitation (MICP) method with reaction accelerations by self‐developed soybean urease enzymes. In this study, the concentration of calcium ions (Ca2+ ions as CaCl2) is varied at 50, 100, 250, and 500 mM to determine an optimum shear strength. The self‐developed soybean urease enzymes of 20% by volume (v/v) are used to accelerate the MICP reaction to finish within 7 days. Based on real‐time monitoring bender element system and direct shear tests, the optimum Ca2+ concentration is found as 250 mM. However, a detrimental effect occurs in case of high concentration of Ca2+ as CaCl2 (500 mM) because of solution acidification from high Cl− concentration. This condition lowers CaCO3 precipitation causing the reduction of biocementation process. At equivalent shear modulus, the biocementation time of MICP‐based sand with acceleration by urease enzymes is about 10 times faster than that without. Using spectrophotometer and pH meter, the ammonification rate and the solution pH of biocemented sand with acceleration by urease enzymes for 3 days are found relatively higher than those without urease enzymes for 40 days. The analyses by scanning electron microscopy (SEM) and X‐ray diffraction (XRD) confirm not only the occurrence of CaCO3 binding sand particles together but also the improvement of physical strengths of sandy soil samples with the MICP‐based urease enzymatic acceleration method. These results introduce an option to accelerate biocemented sandy soil improvement.

Stress-Dilatancy Behavior of MICP-Treated Sand

Abstract Biocementation of soil using microbial-induced carbonate precipitation has become a new approach for soil treatment. The biocemented sand behaves differently from uncemented sand. One of t...

Effect of Jute Fibres on the Process of MICP and Properties of Biocemented Sand.

There has been increasing interest, in the past decade, in bio-mediated approaches to soil improvement for geotechnical applications. Microbially induced calcium carbonate precipitation (MICP) has been investigated as a potentially sustainable method for the strengthening and stabilisation of soil structures. This paper presents the results of a study on the effect of jute fibres on both the MICP process and properties of biocemented sand. Ureolytic Sporosarcina pasteurii has been used to produce biocemented soil columns via MICP in the laboratory. Results showed that columns containing 0.75% (by weight of sand) untreated jute fibres had unconfined compressive strengths approximately six times greater on average compared to biocemented sand columns without jute fibres. Furthermore, efficiency of chemical conversion was found to be higher in columns containing jute fibres, as measured using ion chromatography. Columns containing jute had calcimeter measured CaCO3 contents at least three times those containing sand only. The results showed that incorporation of jute fibres into the biocemented sand material had a beneficial effect, resulting in stimulation of bacterial activity, thus sustaining the MICP process during the twelve-day treatment process. This study also explores the potential of jute fibres in self-healing MICP systems.

Soil bio-cementation using an improved 2-step injection method

To improve the uniformity of calcium carbonate distribution in soil treated by microbially induced carbonate precipitation (MICP), an improved biological injection method, namely “2-step method”, was proposed. This method was achieved by first injecting a certain volume of pure bacterial suspension into soil, followed by injecting the remaining pore volume with the mixed bacterial suspension, which was prepared by mixing pure bacterial suspension and fixation solution containing CaCl2. The method was validated through various physical and mechanical properties of the bio-cemented sand, including the bacterial adsorption efficiency, calcium carbonate content and distribution, and unconfined compressive strength. The results showed that the proposed 2-step method could effectively improve the bacterial adsorption, calcium carbonate content, and strength of bio-cemented sand. The prepared bio-cemented sand had relatively uniform distribution of calcium carbonate and higher strength. The optimal volume ratio between the mixed bacterial suspension and pure bacterial suspension for the 2-step method was 0.6:0.4.

Assessment of erosion resistance of biocemented sandy slope subjected to wave actions

The microbial induced carbonate precipitation (MICP) technique has been increasingly employed for ground improvement and fracture sealing, as well as for erosion mitigation and stabilization of sandy slopes. However, there is a lack of an effective assessment method to estimate the erosion resistance of biocemented sandy slope under wave actions. In this study, a series of bench-scale flume erosion tests was conducted on sandy slopes with and without MICP treatment under waves to quantitatively investigate the erosion resistance. Variables, including the MICP treatment cycle(0 ~ 4 cycles) and the slope angle (10°, 20°, and 35°), were explicitly considered. Penetration tests were conducted to measure the strength of biocemented sand at the slope surface. The calcite mass was calculated using theacid washing method to evaluate the level of cementation. Results show that the erosion resistance follows a nonlinear relationship with the penetration resistance. A fitting calculation was therefore carried out to evaluate the erosion process of MICP-treated sandy slope based on the results oferosion and penetration tests for use to assess the slope stability. A microstructure study also shows that there was interlocking cementation produced between sand particles in the sandy slope after MICP treatment,whichcontributed to the increase in erosion resistance ofsand.

Effect of fiber reinforcement on the mechanical behavior of bio-cemented sand

To explore the possibility of providing additional reinforcement to bio-cemented sand through fiber inclusions, a series of sand-fiber mixtures were prepared by mixing sand with three types of fibers (polypropylene fiber, basalt fiber and carbon fiber) at different fiber contents (0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.8% by volume of sand). Each mixture was subjected to two cycles of controlled microbial-induced calcite precipitation (MICP) treatments. Unconfined compression tests and calcium carbonate content tests were performed to characterize their mechanical properties and calcite amounts, respectively. Stress-strain results indicate that fiber inclusions change the bio-cemented soil from brittle to ductile failure modes. Basalt fibers with the highest tensile strength were most effective to increase the unconfined compressive strength (UCS) of the mixture. Due to higher elongation at breakage, polypropylene fiber is superior to the other two fiber types for energy absorption during the softening phase, resulting in higher residual strength. Scanning electron microscopy (SEM) photographs reveal the spatial distribution of calcite precipitations at the inter-particle contacts, on sand grain surfaces, and on the fiber surfaces, which primarily contributes to the roughening of the surface texture of particles and fibers and increases the internal friction and inter-particle bonding.