A newly emerging microbiological soil stabilization method, known as microbially induced calcite precipitation (MICP), has been tested for geotechnical engineering applications. MICP is a promising technique that utilizes the metabolic pathways of bacteria to form calcite precipitation throughout the soil matrix, leading to an increase in soil strength and stiffness. This paper investigates the geotechnical properties of sand bio-cemented under different degrees of saturation. A series of laboratory experiments was conducted, including sieve analysis, permeability, unconfined compressive strength, consolidated undrained triaxial, and durability tests. The results indicate that higher soil strength can be obtained at similar CaCO₃ content when the treatment is performed under a low degree of saturation. The experimental results are further explained with a mathematical model, which shows that the crystallization efficiency, i.e., actual volume of crystals forming at the contact point where they contribute the most to strength, can be calculated from the degree of saturation and grain size. Fine sand samples exhibited higher cohesion, but lower friction angle than coarse sand samples with similar CaCO₃ content. The results also confirm the potential of MICP as a viable alternative technique for soil improvement in many geotechnical engineering applications, including liquefiable sand deposits, slope stabilization, and subgrade reinforcement. The freeze–thaw and acid rain resistance of MICP-treated sand has also been tested.

Microbially induced calcite precipitation (MICP) is a sustainable biological ground improvement technique that is capable of altering and improving soil mechanical and geotechnical engineering properties. In this paper, laboratory column studies were used to examine the effects of some key environmental parameters on ureolytic MICP mediated soils, including the impact of urease concentrations, temperature, rainwater flushing, oil contamination, and freeze–thaw cycling. The results indicate that an effective crystal precipitation pattern can be obtained at low urease activity and ambient temperature, resulting in high improvement in soil unconfined compressive strength (UCS). The microstructural images of such crystals showed agglomerated large clusters filling the gaps between the soil grains, leading to effective crystals formation. The rainwater flushing was detrimental to the biocementation process. The results also indicate that traditional MICP treatment by the two-phase injection method did ...

In recent years, artificial neural networks (ANNs) have been applied to many geotechnical engineering problems with some degree of success. In the majority of these applications, data division is carried out on an arbitrary basis. However, the way the data are divided can have a significant effect on model performance. In this paper, the issue of data division and its impact on ANN model performance is investigated for a case study of predicting the settlement of shallow foundations on granular soils. Four data division methods are investigated: (1) random data division; (2) data division to ensure statistical consistency of the subsets needed for ANN model development; (3) data division using self-organizing maps (SOMs); and (4) a new data division method using fuzzy clustering. The results indicate that the statistical properties of the data in the training, testing, and validation sets need to be taken into account to ensure that optimal model performance is achieved. It is also apparent from the resul...

This study proposes and describes a novel approach for cementing sandy soils in marine environments by modifying the promising technique of microbially induced carbonate precipitation (MICP). In contrast to the usual MICP technique described in the literature, the method proposed herein relies on the calcium ions dissolved in seawater as the sole source of calcium for calcite formation. This proposed method involves flushing high-salinity-tolerant, urease-active bacteria followed by a mixture of urea and seawater through a porous sandy soil, leading to bacterial carbonate release from the urease reaction and precipitation of insoluble and semi-soluble carbonate salts including calcium carbonate and magnesium carbonate trihydrate. This precipitation method resulted in a physical stabilisation of sand that reached an unconfined compressive strength of up to 300 kPa, which is about two-fold higher (with same amount of crystals produced) than that of the MICP treatment in which highly concentrated calcium and urea solutions are used. Permeability was retained at about 30% for all MICP-treated samples, suggesting good drainage ability. This new exploration of MICP technology provides a high potential for using bio-cementation in marine environments, for applications such as mitigation of submarine sediment liquefaction and prevention of beach sand erosion and cliffs scouring.