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Microbially induced calcite precipitation (MICP) is currently appraised to improve sandy soils, but only a few studies use it to solidify loess soil. MICP solidification tests and undrained cyclic triaxial tests were conducted to study the liquefaction resistance of MICP-solidified loess soil samples. The results showed that because calcium carbona...
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... functions, and natural loess soil is in high porosity state, thus resulting in worse liquefaction resistance (Juang et al. 2019). With MICP treatment, salts dissolve and loess particles are cemented by precipitated CaCO 3 instead of salt crystals. Moreover, the voids of loess soil will also be filled by bacterial cells and CaCO 3 , as shown in Fig. 2. Therefore, MICP treatment can be used to stabilize the skeleton structure of loess soil and improve the liquefaction resistance. In this study, undrained cyclic triaxial tests were conducted to comparatively study the liquefaction response of untreated loess soil samples and MICP-solidified loess soil samples. Pore pressure ratio (r u ...
Citations
... Compared with microbial reinforcement, plantderived urease is characterized by its nanoscale size, better water solubility, ability to reinforce fine-grained soils, and capacity to avoid the complex steps involved in microbial culturing [17,20,27,35,81]. The application of microbial/ enzyme-induced calcium carbonate precipitation (MICP/ EICP) technologies has expanded over the past decades from initial curing of sandy soil surfaces and gravel borehole reinforcement to foundation reinforcement [18,23,32], repairing of cracks and overlays [13,64,72], treating heavy metal-contaminated soils [26,49], enhancing soil liquefaction resistance [25,62], improving foundation impermeability [15,45], stabilizing slopes [21,63], treating wind erosion resistance [44,65], restoring ancient buildings and site soils [42,73], and protecting against coastal erosion [41,56]. ...
Dispersive soil is a widely distributed problematic soil in arid or semiarid areas of the world and can cause pipe erosion, gully damage and other seepage failures. This study analyzed the effect of environmentally friendly enzyme-induced carbonate precipitation (EICP) on the dispersivity of dispersive soils. This methodology was tested for the stabilization of three dispersive soil types (two high-sodium soils, two low-clay-content soils, and two soils with both high sodium and low clay contents) to examine the impact on dispersivity based on the results of pinhole tests and mud ball tests. Physical, chemical, mechanical, and microscopic tests were also conducted to investigate the effects of the components in the EICP reaction solution on dispersive soil modification. The experiments showed that the concentration of the reaction solution and the curing time required to limit the dispersivity decreased with increasing clay content in the soil. Ca²⁺ limited the dispersivities of dispersive soils via four distinct mechanisms. The first mechanism was ion exchange; Ca²⁺ decreased the percentage of exchangeable sodium ions to less than 7% while reducing the thickness of the diffuse double layer such that the spacings between soil particles were reduced and the chemical dispersivity was limited. Second, Ca²⁺ increased the viscosity of the solution by salting out the organic matter present in the soybean urease. Subsequently, the D1-class physically dispersive soil was converted into an ND2-class nondispersive soil. Third, Ca²⁺ decreased the soil pH by reducing the CO3²⁻ content, which could hydrolyze to increase the soil alkalinity. Finally, the presence of Ca²⁺ led to the generation of cementitious minerals through the precipitation of CaCO3 crystals that continuously generated CO3²⁻, filling and cementing soil particles and thereby limiting their physical dispersivity. These results indicated that a low-concentration EICP reaction solution efficiently controlled the dispersivities of the three dispersive soils.
... The produced carbonate precipitation with cementation property can cement loose soil particles to form a strong unit [1,9]. The MICP and EICP techniques have significant application potential for soil improvement [16,63], soil permeability reduction [13,76], liquefaction resistance improvement [60,62], and sandstorm and dust control [21,44,66]. ...
Enzymatically induced carbonate precipitation (EICP) is widely studied as a promising technique for soil stabilization and cementation. The solidification inhomogeneity resulted from higher urease activities always hampers the wide application of EICP. To date, several methods have been developed to effectively improve the solidification homogeneity at temperatures below 60 °C; however, several practical application fields have a higher environmental temperature over 60, even reaching 75 °C. The higher urease activity and quick decay at these temperatures easily result in solidification inhomogeneity and eventually lower strengths. In this study, the combined addition of garlic extract (GE) and dithiothreitol (DTT) was proposed to solve the problem. The influence of the proposed method on urease activities and production rates for calcium carbonate (CaCO3) was investigated and the sand solidification test was conducted to further study the influence of the method on treatment effects. Results showed that the urease activity significantly decreased with the GE addition, while the urease activity increased after the DTT addition, regardless of temperatures. With a higher content of DTT, both the increasing ranges of urease activities and production rates for CaCO3 were larger. In the sand solidification test, the GE addition decreased the precipitation rate of CaCO3 at high temperatures, which was beneficial to obtain smaller differences in sonic time values and CaCO3 contents at different parts of sand columns. Subsequently, the DTT would recover urease activity to ensure a sufficient produced amount of CaCO3 and to achieve higher strength. The optimum contents of GE and DTT were different for the samples solidified at different temperatures. The proposed method had significant application potential in the fields of geotechnical and materials engineering.
... For the same e before MICP treatment, the authors observed that MICP-treated sand exhibited greater efficiency in improving the cyclic resistance than untreated sand. Sun et al. [74] investigated the liquefaction resistance of MICP-treated loess soil and found that liquefaction resistance increased with the number of treatment cycle (N TC ). That is, the number of cycles required for liquefaction (N L ) and the residual strength exponentially increased and the damping ratio decreased with the increase in N TC , i.e. ...
In the present study, the undrained cyclic behaviour of biotreated sands using microbial and enzyme-induced carbonate precipitation was investigated for a wide range of initial void ratio after consolidation, initial effective normal stress and calcium carbonate content under direct simple shear testing conditions. The critical state soil mechanics framework for untreated sand was first established using a series of drained and undrained (constant volume)tests, which served as a benchmark for evaluating the undrained cyclic liquefaction behaviour of untreated and biotreated sands. The results indicated that the modified initial state parameter in DSS condition showed a good correlation with instability states and phase transformation under monotonic shearing. In undrained cyclic DSS loading condition, samples displayed cyclic mobility indicated by an abrupt accumulation of large strain or initial effective normal stress transiently reaching zero or a sudden build-up of excess pore water pressure. The linkage between static and cyclic liquefaction was established for untreated and biotreated sand specimens based on the equivalence of characteristic soil states. The number of cycles before liquefaction (NL) for the biotreated sand specimens was mainly controlled by the cyclic stress ratio, initial void ratio after consolidation, initial effective normal stress and calcium carbonate content. For a similar initial state prior to undrained cyclic loading, the biotreated specimens required a larger NL compared to the untreated sand. The cyclic resistance ratio at NL = 15 (CRR15) increased with decreasing modified initial state parameter for the untreated sand, while the CRR15 for biotreated sand increased with increasing calcium carbonate content and decreasing initial effective normal stress.
... MICP treatment excited several researchers to examine in various geotechnical applications to solve the engineering challenges in various fields like improvement shear strength [9], soil liquefaction [10], carbon dioxide sequestration [11], erosion control [12], and remediation of contaminated soils [13]. The size of the bacterial cell ranges from 0.3 to 0.5 µm and also has a lesser viscosity compared to the chemical grouting which ease the infiltration of the MICP solution making deeper and thicker cementation. ...
... This improvement was attributed to the influence of calcium carbonate precipitation between the voids, enhancing the overall strength and resistance to cyclic loading rather by densification. Sun et al. [10] adopted MICP treatment to stabilize loess soil and evaluated liquefaction resistance through two different treatment methods: bacterial suspension and cementation solution supplied together (AT) and supplied separately (AS). In MICP-solidified samples, AT treatments with an initial density of 1.4 g/cm 3 exhibited higher liquefaction resistance compared to AS treatment with initial densities of 1.5 and 1.6 g/cm 3 . ...
The enzyme-induced calcite precipitation (EICP) has recently gained popularity as a ground improvement technique. Bio-cementation via EICP increases the strength, stiffness, and soil liquefaction resistance by clogging the voids and binding the soil particles with calcium carbonate. The objectives of the study involve assessing the mechanical behavior of the EICP-treated sand by performing monotonic consolidated drained triaxial and undrained cyclic triaxial tests. This study adopted a one-phase EICP cementation solution consisting of 1 M Urea, 0.67 M Calcium chloride dihydrate, and 3 g/l urease enzyme. The monotonic triaxial tests on pure sand and EICP-treated sand with 3,7, and 14 curing days were carried out at 50, 100, and 200 kPa confining pressures, respectively. A noticeable effective cohesion was observed for EICP-treated sand for all curing durations. Undrained cyclic triaxial tests on the EICP-treated specimens with 7 days of curing were performed at an effective confining pressure of 100 kPa. As expected, the number of cycles to liquefaction was higher in the EICP-treated specimen compared to pure sand due to the cementation effect. Finally, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) mapping confirmed the enhanced liquefaction resistance in EICP-treated sand due to calcium carbonate precipitation, leading to particle-to-particle interlocking. Additionally, X-ray Diffraction (XRD) analysis revealed the presence of calcite crystals resulting from the EICP treatment.
... There is a wealth of research on the application of ureolytic carbonate precipitation for various geotechnical applications, such as liquefaction mitigation [22][23][24][25] improvement of problematic soils, namely, dispersive soils [26,27], collapsible soils [28,29] and swelling soils [30,31] as well as increasing soil surface shear strength to withstand wind erosion [32,33], and water erosion [34][35][36][37]. ...
As the world's population grows, there is an increasing need for soil improvement techniques to accommodate construction demands. Current methods, most often, suffer from a high CO2 footprint, leading researchers to resort to biological methods of soil improvement through microbially induced carbonate precipitation (MICP). Commonly used ureolytic microbial carbonate precipitation produces ammonium ions, which can be environmentally concerning. The present study, therefore, addresses the use of non‐ureolytic MICP for soil improvement. The process of non‐ureolytic MICP relies on the use of heterotrophic bacteria to catalyze the oxidation reaction of organic compounds, eventually calcium carbonate precipitation. In this study, heterotrophic bacteria, such as Bacillus subtilis and Bacillus amyloliquefaciens, have been investigated as a solution for soil improvement via an ammonium‐free MICP. Calcium formate and calcium acetate are used as both calcium and carbon sources. This study, furthermore, examines the impact of MICP treatment on sandy soil and the effect of compaction level on treated samples. The findings indicate that the non‐ureolytic MICP method is an effective approach for stabilizing sand. The Calcium Formate‐B.Subtilis composition is shown to be the most effective compound for improving the unconfined compressive strength of sandy soils, while the Calcium Acetate‐B.Amyloliquefaciens composition is the least effective.
... The MICP technique has been reported to reduce soil settlement [16,17], mitigate liquefaction [18][19][20], control internal erosion [13], and improve shear strength and stiffness [21][22][23]. Immersion, grouting, and spraying methods are three methods in the application of the MICP technique. ...
Inordertorespondtothegreenhouseeffectandachievesustainabledevelopment, microbial-
induced carbonate precipitation (MICP) technology based on the spraying method was used as a
substitute for Portland cement to reinforce calcareous sand. In order to simulate the tide and
determine the suitable concentration, the effects of the initial water level and cementing solution
(CS) concentration on the reinforcement were analyzed. The results showed that the distributions
of penetration resistance and equivalent calcium carbonate content mainly include two patterns:
monotonically decreasing, and initially increasing and then decreasing. The fully saturated case
only showed a dense, thin layer of calcium carbonate on the surface, and in the completely dry case,
middle cementation was produced. When the initial water level was 0.5 m, the largest range of
60 cm of effective cementation appeared, and both the equivalent calcium carbonate content and
penetration resistance were the highest because the microorganisms were more likely to migrate
to the particle connection. The calcium carbonate generated by the MICP reaction played a role in
increasing the water retention capacity of the sand. As the degree of cementation increased, the
SWRC gradually moved up and the matrix suction corresponding to the same volume water content
increased sequentially. Increasing the spraying times and the concentration of CS generated more
calcium carbonate. The penetration resistance of higher CS concentrations was larger with the same
calcium carbonate content. There was a linear relationship between the normalized penetration
resistance and the normalized shear wave velocity.
... Microbially induced carbonate precipitation (MICP) is an innovative soil improvement technology [1,17,18] that has several advantages over traditional soil improvement techniques: it is easy to inject and has a limited environmental impact [1,3]. Currently, MICP has been used to solve the geotechnical and geological engineering problems such as liquefaction [19][20][21][22], slope reinforcement [7,8,23,24], crack repair [25][26][27], seepage control [28,29], etc. There are many biological processes that can achieve MICP such as photosynthesis, sulphate reduction, denitrification and urea hydrolysis [30]. ...
... 7 Therefore, it is frequently required to optimise the ingredients to utilise the chemical components fully and maximise the precipitation efficiency. 7,8 Ahenkorah et al. 5 used 20 kU/mol as the ratio of enzyme activity to the urea-calcium chloride ratio. It resulted in maximum precipitation for soil treatment. ...
... Calcium chloride was used because it produces more carbonate than any other calcium source. 8,11 Equimolar solutions of urea and calcium chloride were used to provide a sufficient amount of carbonate anions to bind all of the calcium cations during hydrolysis. ...
Enzyme-induced calcium carbonate precipitation (EICP) through the urea hydrolysis pathway has been widely studied for various applications. The EICP solution comprises urea, a calcium source (usually calcium chloride) and the enzyme urease. This study addressed the effect of the chemical concentration of the EICP solution on the morphology of the calcium carbonate product. This was achieved by varying the concentration of urea–calcium chloride and urease activity. The duration of the reaction was the third variable. The precipitation efficiency and the interface shearing resistance were reported. Precipitation efficiency decreased as the concentration of urea–calcium chloride reached beyond 0.75 mol/l. The calcium carbonate polymorph was predominantly calcite. Its crystal size and shape did, however, vary, depending on the precipitation conditions. The findings showed that the urease activity promoted the formation of rhombohedral calcite in the presence of adequate calcium ions and urea. Spherical calcite was formed when the urease activity was further increased. The morphology of calcite evolved from a single, uniform, smooth spherical crystal to a polycrystalline formation with orthorhombic protrusions. The crystals tended to grow as the reaction time increased, resulting in aggregation, when the urease levels crossed 30 kU/l. It was noted that spherical crystals exhibited stronger interface shearing resistance than rhombohedral crystals.
... The permeability of loess decreases with increasing initial water content due to a series of physicochemical reactions that occur in the presence of minerals such as calcite, dolomite, chlorite, and illite, which are abundant in loess. As the initial water content increases, the hydration of carbonate minerals leads to the formation of calcium carbonate cemented particles that fill the pores in the loess, thereby decreasing its permeability [59,60]. Moreover, increasing the soil water content causes more water molecules to come into contact with dry soil particles, thickening the surface-bound water film on each particle. ...
To explore the influence of sample preparation methods on the permeability and microstructure of remolded loess, remolded loess collected from Heifangtai was taken as the research object. A total of 40 sets of falling-head permeability tests were conducted using two commonly used sample preparation methods, and five different dry density and four initial water content conditions. Additionally, the electrical conductivity of the leachate and the microscopic structure of the samples were analyzed. The results demonstrate that compared to the transfer wetting method, the homogeneity of samples prepared using the pre-wetting method is inferior. This difference is particularly evident when the initial water content is high. Due to the long duration of the permeability test, the pore structure is prone to change, resulting in relatively higher permeability coefficients. Moreover, the total dissolved solids (TDS) of the leachate exhibit a significant decrease with increasing seepage time, indicating the loss of soluble salts. Microscopic structural analysis reveals that samples prepared using the pre-wetting method exhibit a greater number of large pores and aggregates, which are intrinsic factors contributing to the observed differences in permeability between the two sample preparation methods. Furthermore, it should be noted that the impact of the sample preparation method on the permeability of remolded loess is more significant when the dry density is relatively low (specifically, less than 1.45 g/cm3). Conversely, when the dry density is higher, the influence becomes less pronounced.
... Over the years, extensive research has shown that the devastating effects caused by liquefaction can be reduced to some extent by employing various chemical or mechanical stabilisation techniques (Phear & Harris, 2008;Stuedlein et al., 2016;Muhammed et al., 2018;Zango et al., 2018;Chao et al., 2021;Sun et al., 2021). However, most of these techniques are expensive, energy intensive and can be detrimental to the environment. ...
Microbial or enzyme-induced calcium carbonate precipitation (MICP/EICP) are relatively new ground improvement technique. In this study, the mechanical behaviour of biotreated (MICP/ EICP) and untreated sands were investigated in light of the critical state soil mechanics framework using a series of direct simple shear (DSS) tests. A wide range of CaCO 3 content (C C ), initial void ratio after consolidation (e 0 ) and effective initial normal stress (σ′ N 0 ) was considered. The biotreated specimens showed improved shear strength and dilative tendency compared to untreated specimens with similar initial states. The ultimate state for the biotreated sand shifted towards a smaller void ratio (e) than e at the critical state of untreated sand at the same σ′ N in e–log σ′ N space. Compared to untreated sand, a significantly larger ultimate state stress ratio was achieved for the biotreated sand, particularly at high C C and low σ′ N 0 . The characteristic features of undrained behaviour, such as instability stress ratio, stress ratio at phase transformation and flow potential showed good relationships with modified initial state parameter, void ratio after biotreatment and C C . Bonding ratio, (τ/σ′ N ) bond was used to quantify the interparticle bonding. The peak value of (τ/σ′ N ) bond for the biotreated sand was significantly larger than zero, particularly at high C C and low σ′ N 0 , while the peak (τ/σ′ N ) bond for the untreated sand was negligible. It is also observed that the mobilisation and degradation of CaCO 3 bonds in biotreated sand during DSS shearing are influenced by both C C and σ′ N 0 .
